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Abstract: The success of any process improvement study depends on the quality of the available data and the way in which the plant-specific characteristics are incorporated in the applied conceptual models; in the context of process integration studies these issues are directly related to the rules followed during the data extraction stage. Improving energy efficiency in a pulp and paper Kraft mill requires the identification of the most promising heat recovery network retrofit projects. In a retrofit analysis using pinch technology/process integration methods, only the process streams associated to the existing heat exchangers and some outlet streams (such as wastewater/effluent streams and vents) with high potential for heat recovery are usually included, while the energy exchanged through non-isothermal stream mixing (NIM) or direct heat transfer (DHT) is often assumed fixed and is not considered in the analysis. Relaxing this assumption requires extracting more data to represent the DHT design configuration that exists in the plant. However, different data extraction options can be considered to represent the DHT configuration depending on the associated process/operation constraints. This work describes a systematic procedure to extract and analyse the impacts of DHT on the overall energy efficiency of a Kraft process with a specific focus on mixing along the pulp line and in water tanks. [Copyright &y& Elsevier]

In hot and dry climatic zones, direct evaporative cooling (DEC) system is used as an economical and efficient alternative to traditional air conditioning systems. The present paper concerns comprehensive experimental investigations and analysis of heat and mass transfer characteristics and thermal performance parameters of a bee-hive construction of corrugated-cellulose papers as a new cooling pad material. The performance parameters used to evaluate the effectiveness of the cooling pad materials are the outlet air temperature and relative humidity, pressure drop, humidifier effectiveness, rate of the evaporated water, sensible cooling capacity, specific cooling capacity (SCC), coefficient of performance (COP), specific water consumption (SWC), and Nusselt and Sherwood numbers. The cooling pad performance was investigated for a wide range of air and water temperatures and flow rates and pad thicknesses. The results show the enhancements of heat and mass transfer coefficients and the performance parameters with rising air temperature and water flow rate to humidifier. High values of the performance parameters (h c = 45 W/m2oC and h m = 0.23 m/s, ε h u m = 0.85 and COP = 170) are obtained compared to the traditional pad materials. Experimental correlations for the evaporative cooler performance parameters in terms of air and water temperatures and flow rates pad thicknesses are presented. • Cellulose paper, bee-hive structure has efficient thermal to be used as evaporator cooling pads. • Good thermal-hydraulic characteristics at a wide range of operating and design conditions are obtained. • Presented empirical correlations predict the performance parameters very well. • High values of the performance parameters of the proposed cooling pad were obtained. • The highest saturation efficiency is 84% with associated temperature and pressure drops 18 °C and 8 Pa. [ABSTRACT FROM AUTHOR]

Amidst the various design approaches available for the design of plate-fin heat exchangers for multi-fluid applications, are those based on the segmentation of the exchanger length into blocks that correspond to the enthalpy intervals in the Composite Curves. Such methods are characterized by three main features: identification of exchanger sections, surface selection from among the available types, and reconciliation of dimensions by pressure drop relaxation. The work presented in this paper introduces new concepts and removes some limitations in earlier approaches. In the first place, it reduces the number of block sections when the space between them is too short to fit intermediate headers along the length of the exchanger. Additionally, it introduces the concept of surface design as an aid to fulfil the heat transfer duties. Finally, it allows the design to meet fixed dimensions as design objective together with the heat duty within the limitations imposed by the pressure drop. The approach is demonstrated using a case study solved by different authors in the open literature. It is shown that the number of block sections is reduced from 3 to 2. • Extended design methodology for multi-stream heat exchangers. • Surface design to achieve a specific heat transfer performance. • Surface design to achieve a fixed pressure drop. • Design of heat exchangers to meet fixed dimensions. • Reduction of complexity through enthalpy interval merging. [ABSTRACT FROM AUTHOR]

Porous surfaces are a common modified surface used to enhance boiling heat transfer. In this paper, a method for preparing gradient porous surfaces is presented, that is, magnetic stirring is added to the electrolyte and the cathode surface to be deposited is placed vertically downward. Within the Cl ion concentration range of 30–140 mg/L, increasing the Cl ion concentration results in lager pore sizes. When the Cl concentration was greater than 120 mg/L, the average pore size of the surface gradually increased from the center to the edge, and the number of pores gradually decreased from the center to the edge. All surfaces showed superhydrophilicity. The critical heat flux of Sample#3 is 158.72 W/cm2, which is 67% higher than the smooth surface. The wall superheat of Sample#3 was only 15 °C in the critical state. This porous surface has plenty of nucleation sites. These nucleation sites are gradually activated when the heat flux increases. At low heat fluxes, heat transfer on these porous surfaces presents a disadvantage because the nucleation sites are not fully activated. At high heat fluxes, these porous surfaces show a decrease in wall temperature. Consequently, the porous surface prepared in this paper has good boiling heat transfer at high heat flux. [Display omitted] • An inverted deposition method was designed to prepare gradient porous surfaces. • The gradient porous surface is superhydrophilic and provides a large number of nucleation sites. • An appropriate increase in Cl-ion concentration increases the pore size and pore wall thickness. [ABSTRACT FROM AUTHOR]

New materials and designs have been developed and proposed to enhance the thermal and electrical performance of photovoltaic-thermal (PV/T) systems in recent years. Despite the significant attention received by PV/T technology, the available PV/T modules are scarce due to complex system designs, environmentally unfriendly working fluids, and low thermal efficiency. In this paper, a highly efficient water-based PV/T system is proposed by combining an innovatively designed cooling system with a PV module. An experimental evaluation of the designed PV/T system was carried out in laboratory conditions. The test results of the PV/T system showed that when the inlet mass flow rate and temperature were 0.0458 kg/s and 11.90 °C, the PV/T system reached the maximum thermal efficiency of 96.47 ± 1.40 %. The increase in mass flow rate from 0.0042 kg/s to 0.0375 kg/s and the decrease in inlet temperature from 17.70 °C to 11.40 °C led to a 12 % improvement in thermal efficiency of the PV/T system showing that the inlet mass flow rate and temperature have a significant influence on thermal efficiency. The developed 3-D numerical model accurately estimated the outlet temperature of the PV/T system. A maximum of 3.43 % error occurred between the experimental results and model output. • The paper proposes a novel, highly efficient, state-of-the-art PV/T system. • The designed PV/T system achieves a maximum thermal efficiency of 96.47 ± 1.40 %. • The designed cooling system reduces the PV module temperature by 40.72 °C. • The electrical conversion efficiency of the PV module is enhanced by 18.32 %. [ABSTRACT FROM AUTHOR]

A new absorber surface is designed for solar air heaters to make them compact and enhance heat transfer parameters. The current paper presents the novel absorber design using a tubular surface having three-pass in counter-flow. The absorber tubes are constructed from thin sheets of aluminium; 15 tubes are closely spaced in line with each other to establish three-pass, i.e. five tubes per pass. The research paper investigates numerically and experimentally the thermo-hydraulic performance of a Tubular Three-pass Solar Air Heater (TTPSAH). The numerical model was developed using MATLAB to predict the performance and outlet air temperature. The error in numerical and experimental evaluation is approximately 5%, showing promising results. It was found that the TTPSAH accelerates heat transfer in a compact surface area. The maximum thermal efficiency was evaluated as 60.04%, 41% and 33.3% for an airflow rate of 0.006 kg/s, 0.004 kg/s, and 0.002 kg/s respectively. Thermal enhancement with a maximum outlet air temperature of 110.6 °C, 91.4 °C and 80.2 °C was recorded at a mass flow rate of 0.002 kg/s, 0.004 kg/s and 0.006 kg/s in glazed conditions. Furthermore, the research includes an estimation of the energy cost per kilowatt-hour (kWh), which amounts to $0.017, $0.025, and $0.0311 for mass flow rates of 0.006 kg/s, 0.004 kg/s, and 0.002 kg/s, respectively. • To increase the applicability of solar energy a novel tubular three-pass solar air heaters was designed. • The mathematical model and experimental results are in good agreement. • The maximum outlet air temperature of 110.6 °C attained for a flow rate of 0.002 kg/s. • The thermohydraulic performance parameters of TTPSAH was also studied. [ABSTRACT FROM AUTHOR]

The current Virtual Special Issue of the Energy Journal contains cutting-edge developments in energy research that were presented at the 21st Conference on Process Integration for Energy Saving and Pollution Reduction, held in Prague, Czech Republic, on 25–29 August 2018. Conference PRES hosted more than 234 oral and 221 poster presentations. Out of these papers, the 34 contributions in this VSI represent a selection of the most significant developments in the area of energy research, and each article includes extensions and additional results beyond the conference paper. Conference PRES is an annual symposium that aims to attract thought-leaders and academics to facilitate an ongoing discussion around energy, the impact on the environment, and the way forward. This paper provides an overview of each contribution, the context of their development, and groups them into four research themes: (1) Heat Exchangers and Heat Exchanger Networks, (2) System Optimisation, (3) System Design and Analysis, and (4) Process and System Synthesis. [ABSTRACT FROM AUTHOR]

This paper presents the determination of the heat losses of the pre-insulated pipe and twin pipe in the heating network. The paper compares the heat losses calculated by using the analytical solution (1D model) and numerical model (2D model) based on the Finite Element Method. The developed numerical model considered undisturbed ground temperature at various depths. Therefore, it allowed to study the effect of temperature distribution at various ground depths on heat losses in heating network. Various variants of insulation are considered including standard, plus and plus-plus types for pre-insulated tubes. The remaining heat loss calculation is based merely on temperature levels and thermal resistance factors (in the ground), determined by the pipe dimensions and materials. The differences in calculated heat losses by analytical and numerical model do not exceed 10%. [ABSTRACT FROM AUTHOR]

The development of coalbed methane (CBM) resources by injection thermal fluids is a development method proposed in recent years. Laboratory research and field preliminary practice have proved that the technology has broad application prospects. In this paper, a superheated steam pipe flow model is established on the basis of the characteristics of superheated steam pipe flow and the features of CBM reservoirs. The Effects of strong heat loss and strong friction loss on superheated steam status are studied, and the Joule-Thompson effect on temperature and pressure is revealed. The main findings are: (a) The status of superheated steam are relatively independent. However, the status of superheated steam are influenced by Joule-Thompson effect; (b) The injection speed has a critical value. When injection speed is lower than critical value, fluid temperature increases rapidly with injection speed; when injection speed is lower than critical value, fluid temperature decreases with injection speed. The critical value in this paper is 1.6 kg/s; (c) The critical value of the injection rate is only valid for temperature; (d) When heat loss as well as frictional force loss are large, Joule-Thompson effect becomes weak and negligible. • Research on the development of CBM reservoirs by injection of superheated steam. • A model for superheated steam flow in surface pipelines and vertical wellbore is proposed. • Weak Joule-Thompson effect and strong heat loss-friction loss effect were found. [ABSTRACT FROM AUTHOR]

The existing Chinese solar greenhouse (CSG) had different spatial structure types, which spatial structure can make the greenhouse fully utilize solar energy and obtain the best thermal performance effect is worthy of further research. This paper took the CSG in the Shenyang area as the research object. A mathematical model was established to simulate the three-dimensional dynamic thermal environment of CSG at the crop level by combining experimental and computational fluid dynamics (CFD) numerical simulation. The model can well describe the heat transfer process in the greenhouse. Based on this model, the effects of variation of multiple structural parameters on the temperature distribution, solar energy interception, heat storage and release performance of CSG were quantitatively specified. The simulation results demonstrated that for the CSG with a span of 10 m in the Shenyang area, the optimal ridge height was 6.2 m, the optimal north wall height was 4.4 m and the optimal horizontal projection length of the north roof was 2.0 m. Furthermore, the spatial structure parameters of CSG with an 8 m–12 m span were obtained for the Shenyang area. This paper can provide theoretical guidance for the design and optimization of spatial structure parameters of CSG in the Shenyang area. • A CFD model was established to simulate the thermal environment of crop level in CSG. • The CFD model can accurately depict the dynamic heat and mass exchange process in CSG. • The effect of structural parameters on the thermal environment of CSG was expounded. • The structural parameters of CSG with 8 m–12 m span were obtained for the Shenyang area. [ABSTRACT FROM AUTHOR]

In the process of biomass gasification syngas waste heat recovery, water and organic compounds in the syngas will condense at the same time, resulting in immiscible condensates adhering to the wall, which can reduce the heat exchanger heat transfer efficiency and working life. Changing the wettability of the wall surface can affect the condensate flow state on the wall surface, thus affecting the condensation heat transfer performance. Water and organic cyclohexane were used as immiscible working fluids in this paper, the condensation flow and heat transfer characteristics of the mixed vapors on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces were experimentally investigated. The results showed that cyclohexane in immiscible condensates existed as a liquid film on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces, while the water existed in droplets on the hydrophilic and super-hydrophobic wall surfaces, and there were two forms of channels and droplets on the super-hydrophilic wall surface. The condensation heat transfer coefficient on the super-hydrophobic wall surface was higher than that on the hydrophilic wall surface and the super-hydrophilic wall surface, with a maximum of 34% higher than hydrophilic and 45% higher than super-hydrophilic, which was related to the smaller droplet departure diameter on the super-hydrophobic surface. In addition, the super-hydrophilic wall surface had better heat transfer performance than the hydrophilic wall surface only when the immiscible condensate was a "film-channel" flow pattern. The results can provide guidance for enhancing the condensation heat transfer of the water and organic compounds binary mixed vapors. • Wall wettability can change the immiscible condensates flow behavior and thus affect condensation heat transfer. • The smaller the condensate droplets departure diameter on the wall, the greater the condensation heat transfer performance. • The condensation heat transfer coefficient on the super-hydrophobic wall surface was the highest. [ABSTRACT FROM AUTHOR]

The heat transfer and pressure drop (Δ P) of supercritical fluid are crucial for the safety of advanced power cycles. Here, experiments were performed for sCO 2 in a horizontal tube with inner diameter (d in) of 10 mm, covering in the ranges of (G): 496.7–1346.2 kg/m2, heat flux (q w): 97.4～400.3 kW/m2 and pressure (P): 7.53–23.51 MPa. Inspired by the similarity of the outer wall temperature (T ow) distributions between the sCO 2 flow and those of stratified-wavy-flow in subcritical pressures, the multiphase flow theory is introduced in subcritical pressures to deal with the sCO 2 heat transfer. In the two-phase-like (TPL) regime, heat transfer coefficients (HTC) and friction factors (f) of sCO 2 are found to significantly deviate from the correlations based on the single-phase flow theory. Further, the vapor-like Froude number Fr VL is proposed to develop new correlations for both the heat transfer and the flow resistance covering the whole data range. The present paper establishes a connection between the flow resistance and heat transfer in supercritical pressures, which is important for the design and operation of sCO 2 power cycles. • Supercritical heat transfer and flow characteristics of CO 2 is investigated in a horizontal tube. • Thick vapor-like film can reduce the frequency of negative temperature differences occurring. • Flow resistance and heat transfer in the two-phase-like regime both strongly deviates from the single-phase convection. • Fr VL was proposed to be the similarity criterion number to connect flow resistance and heat transfer for horizontal flow. • The new correlations with Fr VL number for heat transfer and friction factor are established. [ABSTRACT FROM AUTHOR]

Fouling is an important factor affecting the heat transfer performance of condensers in nuclear power plants. In response to the lack of experience in the current cleaning of condensers in nuclear power plants, this paper proposes a particle swarm optimization based LSTM method for predicting fouling thermal resistance and a dynamic optimization theory for condenser cleaning cycles. On the basis of LSTM and the PSO algorithm, compared with the prediction results of LSTM, the MAE, RMSE and MAPE values of PSO-LSTM decreased by 43.3%, 47.3% and 42.1%, respectively, while R2 increased by 26.4%. Considering the load loss and maintenance loss of the unit, as well as the economic loss caused by condenser scaling, the optimal cleaning time of the condenser glue ball system under different fouling rate and circulating water temperature was analyzed, and a calculation theory based on the unit output, the running loss cost of the glue ball and the minimum optimal cleaning cycle of the condenser was proposed. Results show that at rated flow, optimizing the cleaning cycle, with an annual operating time of 300 days, can save $0.45 million in operating costs per year. • Particle swarm optimization based LSTM method for predicting fouling thermal resistance of condenser of nuclear power plant are proposed. • Condenser health index of nuclear power plant based on dynamic power loss is established. • Condenser cleaning cycles of a practical power unit is optimized to show the trade-off. [ABSTRACT FROM AUTHOR]

Many industrial processes belong to complex thermal system coupled by multiple heat sources, in which the energy distribution and transmission for each heat source is closely related to its adjacent neighbors, and the thermal dynamics have obvious nonlinear time-series characteristics, these factors limit the modeling and predict accuracy for this type of systems in actual practice. In this paper, a convolution and memory network-based spatiotemporal modeling approach is proposed to model the nonlinear spatial features and temporal dynamics of these heating systems. First, a deformation convolutional neural network (D-CNN) strategy is developed to extract the spatial features, it designs a deformable kernel matrix for convolution layer to obtain the spatial multi-scale context information of the DPS, and the feature order is reduced by pooling operation. Then, a cascade long-short time memory network (LSTM) model is constructed to model the temporal dynamics of the time-series data. In this model, the sliding window method is used to obtain the sequential dataset for several sampling time, which is taken as the input of each LSTM unit to reconstruct the nonlinear temporal dynamics in this type of systems. The effect of the proposed model for spatiotemporal dynamics is verified by the experiment of serial-connected lithium batteries (S-LIBs), and the result shows that the proposed model has smaller modeling errors for spatiotemporal dynamics than the other two methods. • A convolution and memory network-based modeling approach is proposed to model the spatiotemporal dynamics in thermal processes. • A deformation convolutional neural network strategy is developed to extract the spatial features using a deformable kernel matrix. • A cascade long-short time memory network model is constructed for the temporal dynamics of the time-series data. • The effect of the modeling approach is verified by the experiment of serial-connected lithium batteries (S-LIBs). [ABSTRACT FROM AUTHOR]

Optimizing conjugate heat transfer in laminated configurations is pivotal for efficiently cooling turbine blades. The traditional approaches have limitations in achieving rapid optimization when design conditions change. The emergence of reinforcement learning offers an opportunity to address this issue. However, there is currently a notable scarcity of research on the application of reinforcement learning in the optimization of laminated cooling configurations. This paper presents a novel method using the Deep Q-Network (DQN) model for real-time optimization of laminated cooling configurations. A dataset comprising 246 sets of historical design data was generated through conjugate simulations and augmented with the incorporation of physical information. After undergoing off-policy reinforcement learning, the intelligent model was employed to address optimization problems associated with temperature levels and coolant usage. Results indicate that the intelligent model achieves accurate and real-time optimization for laminated cooling configuration, with an average time of 3 ms. The ability to identify the correct optimization direction is attributed to the formulation of reward and penalty mechanisms in reinforcement learning. Real-time optimization is enabled by establishing a forward computational path from design conditions to optimization results. The findings of this study are easily transferrable and contribute to cost savings in design. • The model learns optimization insights from raw data through reinforcement learning. • Optimization objectives and constraints are achieved through a reward mechanism. • The forward computational path of decision-making facilitates real-time optimization. • Integrating physical information enhances optimization process stability. [ABSTRACT FROM AUTHOR]

In the processes of modeling, optimization, heat transfer analysis, and thermal power conversion analysis in large-scale complex systems, challenges are encountered regarding intricate design and optimization. In this paper, a global heat flow topology is proposed that reveals the synergistic effect of heat transfer and thermal power conversion in large-scale systems. The approach involves the construction of a heat flow topology, mathematical model development, analysis of specific parameters, and multi-objective optimization. It integrates various methods and tools, including heat flow topology, numerical simulation tool, entransy transfer analysis, global thermal resistances visualization, genetic algorithm (GA), and technique for order preference by similarity to ideal solution (TOPSIS). By using the LNG cold energy recovery and regasification process in floating storage and regasification units (FSRU) as a case study, the methodology provides a comprehensive understanding of the interactions and conversions between heat transfer and thermal power within the system. The results demonstrate that the optimal configuration achieves a maximum thermal efficiency of 21.73 % and a maximum cold recovery efficiency of 58.48 %. Additionally, the interaction between LNG pressure and seawater temperature exhibits limited synergistic impact on both LNG cold exergy efficiency and entransy transfer efficiency. Similarly, the combined influence of LNG pressure and evaporator temperature shows weak synergistic effects on parameters such as supply/demand ratio, thermal efficiency, and entransy transfer efficiency. The analysis of the global thermal resistance bubble chart reveals the significant impact of evaporator temperature and seawater temperature on the evaporator resistance, as well as the notable impact of LNG pressure on the condenser resistance. [Display omitted] • Proposed a global modeling and optimization method for large-scale system. • Constructed heat flow topology to describe heat transfer and heat-work conversion. • Energy, exergy, entransy analysis and multi-objective optimization are carried out. • The global overall thermal resistances change is visualized by bubble diagram. [ABSTRACT FROM AUTHOR]

This paper presents experimental and theoretical research on ceiling jet, burn-through, and flame spread behaviors of the combustible ceiling with the impingement of an incipient fire source. Medium-density fiberboard was utilized as the combustible ceiling in experiments, and the ceiling height above the fire source was varied. The flame radial length (r f), ceiling surface temperature, flame shape and spread rate after burn-through, and radiative heat flux were measured. Results showed that r f beneath the combustible ceiling was significantly longer than that of the non-combustible ceiling. Theoretical analysis was conducted for r f based on energy distribution, and an expression of r f beneath combustible ceiling was proposed. The burn-through behavior of the combustible ceiling was explored by combining the ceiling temperature, small-sized experiment and Fourier law. The advancement of char front along the ceiling thickness was calculated, which was the key point during burn-through. Upper surface flame spread in a circular shape after burn-through, and an expression of spread rate was obtained. A three-dimensional radiation model was adopted to calculate the radiative heat flux received by the unburned ceiling surface during the dynamic flame spread process, the calculated results agreed well with the experimental data. • Ceiling jet, burn-through, flame spread behaviors of timber ceiling are researched. • The mechanism of the flame extension beneath the combustible ceiling is revealed. • Burn-through process and char front advancement are explored. • The flame spread behavior and heat radiation after burn-through are clarified. • Expressions of the flame radial length and flame spread rate are proposed. [ABSTRACT FROM AUTHOR]

Abstract Without an intervening wall, the direct contact evaporator (DCE) has been already technically proven to improve the overall thermal efficiency of organic Rankine cycle (ORC) used to recover low-grade heat sources and transform them into power. In the estimation of volumetric heat transfer coefficient (VHTC) which is assumed to vary with flow rate, noises signals caused by various unstable factors (e.g., measurement errors) often corrupt the time series of VHTC. For forecasting the heat transfer performance of DCE in ORC more accurately, this paper proposes a novel approach (refers as EMD-RBF-NN), which combines multi-input radial basis function (RBF) neural network (NN) and empirical mode decomposition (EMD) method. Specifically, the original VHTC time series is firstly decomposed by EMD method that is fully data-driven. Then, the proposed method models the resultant decomposition series with flow rates of two fluids (dispersed and continuous phases) and VHTC by using RBF neural network. This simple technique was illustrated by using the ORC direct contact evaporator (ORC-DCE) and data processing system. Via using the experimental datasets of ORC-DCE, this paper demonstrates that the proposed EMD-RBF-NN model that associates flow rates of two phases with VHTC improves the forecasting accuracy of VHTC noticeably comparing with existing models. Highlights • This paper proposes a novel approach for forecasting the heat transfer performance. • This technique is illustrated using direct-contact evaporator and data processing system. • The proposed EMD-RBF-NN model that associates flow rates of two phases and VHTC. [ABSTRACT FROM AUTHOR]

Abstract Neighbourhood form imposes complex effects on the local microclimate. The overlook of neighbourhood microclimate will lead to miscalculation of building energy performance. In this paper, a neighbourhood-scale building simulation coupled between building energy simulation and CFD is proposed to assess the impact of external convective heat transfer coefficient (CHTC) to the building thermal performance. The co-simulation is run for different types of buildings inside the neighbourhood with different combinations of neighbourhood form parameters. The developed simulation scheme allows the iterations of neighbourhood design parameters and simulation model generation in CFD and EnergyPlus. Five empirical methods are used to predict CHTC, and the results of CHTC values, heating and cooling load intensity are compared in detail with the proposed CFD coupled method. The results suggest that the orientation and multiplier are crucial to the building load intensity in Chicago and the neighbourhood form can affect the thermal load of residential building up to about +27.1% and −18.6%, and +17.2% and −7.7% for office buildings. The proposed method and framework in this paper is capable of generating design guidelines for the optimal energy performance of the buildings in the neighbourhood. Highlights • Neighbourhood-scale building block energy simulation coupled with CFD. • Iterated various neighbourhood design parameters and building model generation. • Empirical methods in evaluating CHTCs are evaluated and compared with CFD method. • Neighbourhood form can affect certain type of building's energy use up to ± 20%. • Neighbourhood design guideline for optimal building thermal load is suggested. [ABSTRACT FROM AUTHOR]

Abstract The absorption refrigeration system driven by low grade heat sources, especially the waste heat sources, becomes more and more attractive in recent decades. However, most traditional absorption systems cannot achieve a high utilization rate of the waste heat with limited heat capacity. These systems are usually designed to obtain heat in the generator, which means that the waste heat sources cannot be utilized to the temperature lower than the generator temperature. This paper proposed a new structure heated by heat conduction oil in the generator and electric heating rings around the stripping section. This structure can simulate the temperature-distributed heat sources when the electric heating rings work. It can also simulate a traditional generator when the electric heating rings do not work. Influences of different heat distributions are analyzed in detail in this paper. The results show that the heat sources utilization rate will increase with the increase of the heat in the stripping section, while the coefficient of performance will be negatively affected by the increasing heat in the stripping section. By optimizing the heating structure, the coefficient of performance can be similar to that of a traditional system when the heat is just added in the middle and lower part of stripping section. The optimum utilization rate of heat sources in this test model can reach 1.8 times to that of a traditional system. Under this heating model, the lowest temperature required in the heating section is 82 °C when the heat conduction oil inlet temperature is 169 °C. It is much lower than the temperature inside the generator, which is 137.3 °C. Highlights • This paper proposed a new structure and both distributed heat sources and basic generator operation conditions can be tested. • Influences of different heat distributions are analyzed in detail. • The optimum utilization rate of heat sources can reach 1.8 times to that of a traditional system. [ABSTRACT FROM AUTHOR]

Abstract Solar aided (coal-fired) power generation (SAPG) system has been proved to be an efficient way to utilize the solar energy for power generation. Due to the instability of the solar radiation, a SAPG system generally operates under transient working conditions. In this paper, performance simulation sub-models of main components in a SAPG plant are established based on the lumped parameter assumption. A 330 MW SAPG power plant as a case study is simulated. The variations of the performances, main parameters of the plant with the solar field heat output and the dynamic responses under a typical day are analyzed. The results show that when the heat output of the solar field changes from 0 kJ/h to 2.13 × 108 kJ/h, the coal saving rate will increase to 6.4%, and the solar power generation share (the proportion of the power from the solar energy to the total power from the SAPG plant) will increase to 7.74%. During the analysis process, in order to optimize the solar field, the concept of the solar field equivalent efficiency (SFEE) is proposed and the optimal velocity of heat transfer fluid (HTF) in absorber tube is obtained. Highlights • The transient model of a solar aided power generation (SAPG) system is developed. • The concept of solar field equivalent efficiency (SFEE) is proposed in this paper. • The optimal velocity of heat transfer fluid in the absorb tube is obtained. • Performances of SAPG system with different solar field heat output are revealed. • The dynamic responses of the SAPG system under a typical day are analyzed. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a new model for the prediction of scaling formation in tubular heat exchangers. In design, the effect of fouling upon the heat transfer performance is accounted for by using fixed values of the fouling factor. In real operation, however, fouling strongly depends upon the prevailing operating conditions and they change over time. Under some conditions, the growth of fouling with time can be linear or it can show an asymptotic behaviour. Fouling factors reported in the open literature are not accompanied with specific information regarding the conditions at which they were obtained such as velocity, temperature, concentration and pH. Therefore, the designer must exercise caution when choosing fouling factors since this choice has an impact upon the size of the unit and upon capital expenditure. In view of the above, the purpose of this paper is to present a new fouling model for the prediction of scaling to assist in the design of heat exchangers and in the assessment of their thermal-hydraulic performance. The new model is validated against experimental data published in the open literature and its performance compared to other published theoretical models. The new model shows improved results. [ABSTRACT FROM AUTHOR]

Spray cooling is believed to be a promising candidate for the cooling of the next-generation high heat-flux electronics. Different from the traditional spray cooling (SC), a modified version of SC – immersed spray cooling (ISC) – is firstly proposed in this paper. Experimental set-up upon which thermal tests of SC, ISC and pool boiling can be conducted was established. In order to realize the multifunction of the experimental system, an ejector, which plays an important role to control the liquid level in the cooling chamber, is integrated in the experimental system. Based on the novel theory of suction according to the need, modelling, design, and fabrication of the ejector was conducted, which proves to be a success in the practical operation. We experimentally demonstrated that the ISC performs the best in terms of cooling performance in all the operating conditions. Comparative study between thermal performances between SC and ISC is the focus in this paper. A maximum 65.6% enhancement in heat flux was observed for the ISC when the surface temperature was 205.6 °C. The enhanced heat transfer of the ISC can be attained due to the vapor layer elimination and chaotic effect around the target surface. [ABSTRACT FROM AUTHOR]

This paper proposes a general superstructure and a Mixed-Integer Nonlinear Programming (MINLP) model for the synthesis and simultaneous optimisation and Heat Integration (HI) of Single- and Multiple-Effect Evaporation (SEE/MEE) systems including Mechanical Vapour Recompression (MVR) and the background process. The proposed superstructure also includes different flow patterns (forward feed, backward feed, parallel feed and mixed feed), Flashing of Condensates (FCs), single- and multi-stage MVR systems and various HI opportunities for preheating of feed stream (e.g. with condensates, bled vapours, and hot streams from the background process). The newly proposed SEE/MEE-FC-MVR superstructure is combined with a Heat Exchanger Network (HEN) superstructure for performing simultaneous optimisation and HI. On the basis of this combined superstructure, an MINLP model with tight bounds on the variables is developed and implemented for its solution in the General Algebraic Modeling System (GAMS). The model is solved using a two-step solution strategy. The proposed model enables to explore simultaneously all interconnections within the proposed superstructure in order to find the configuration with the optimal trade-offs between capital and energy costs as demonstrated in this paper for different cases of a milk concentration process. [ABSTRACT FROM AUTHOR]

Wraparound heat pipes have been used for many years and have found a niche application in outside air handling units in hot and humid climates. They are used in conjunction with primary, chilled water cooling coils to enhance the efficiency of moisture removal and ensure that the process consumes minimal energy. The type of heat pipe employed is a gravity assisted thermosyphon which is formed into a loop and ‘wrapped’ around the main cooling coil. The traditional working fluid for HVAC heat pipes has been a refrigerant and a replacement fluid is desirable as a short and long-term option. From an environmental standpoint, water is an ideal candidate and many of its thermal transport properties suggest that it should be viable. There are manufacturing issues associated with using water which are not the concern of this paper; the paper's intention is to prove the viability of water and compare its performance with that of traditional refrigerants. At the conditions used for the experimentation, the results suggest that the use of water in a loop heat pipe can enhance the effectiveness of the arrangement by up to 18% when compared with a conventional refrigerant filled pipe. The type of thermosyphon, or gravity-assisted heat pipe, that is under consideration has a performance which can be quantified using an effectiveness model. This model has been used in the investigation to compare the performance of identical pipes filled with different working fluids. The effectiveness of the heat pipe is determined by many variables and a good proportion of these are related simply to tube orientation, size and flow path. The application of wraparound heat pipes that is under consideration relies upon specific sizes and orientations of tubes and the conclusions of the report give pointers towards further research which needs to be undertaken, or is currently underway, in order to determine the extents of applicability of water as a working fluid. [ABSTRACT FROM AUTHOR]

Maisotsenko cycle (M-cycle) is a promising air cooling technique which can reduce the temperature of air flow until dew point which was not possible either in direct contact techniques or former indirect evaporative methods. M-cycle systems have been employed previously on gas turbines, air conditioning systems, cooling towers, electronic cooling etc. Simultaneous consideration of all of them prevents detailed presentation. For that reason and because of the wide application of air conditioning systems, this paper focuses only on the use of M-cycle on air conditioning systems. Moreover, former types of indirect evaporative air coolers which do not work based on Maisotsenko cycle are not considered in the present study. Researchers have evaluated the M-cycle characteristics via different methods including analytical solution, numerical simulation, statistical design methods and experimental-techniques all of which is divided into several categories as well. All said methods are organizedly discussed and compared in this paper. It has been tried to provide an evolutionary viewpoint for analytical solutions of M-cycle. Thus, analytical solutions were reorganized with unique abbreviations in order to become more understandable and comparable with each other. All M-cycle parameters (which have been analyzed via numerical or experimental ways) are coherently systematized and then a comprehensive-compact view of obtained results is presented. Finally, the current status of M-cycle industry is summarized and the future research direction on M-cycle is proposed. [ABSTRACT FROM AUTHOR]

After Fukushima accident, more and more attention has been paid on severe accident analysis. As an important severe accident mitigation strategy applied to advanced light water reactor for in-vessel retention (IVR), an important method is external reactor vessel cooling (ERVC). Extensive work has been done on the effectiveness of IVR-ERVC, however simplified assumptions have been applied for lower head in most of these work. Seldom study has been done for the fundamental research work related to IVR-ERVC. This paper will introduce the model development study for the IVR-ERVC process at Shanghai Jiao Tong University. The main points of the paper can be summarized as followed: (1) Based on two-dimensional spherical coordinate, a two-dimensional approach with the aim to investigate transient heat transfer behaviour in the lower head has been developed; (2) A theoretical critical heat flux (CHF) model has been developed based on Weisman-Pei’s bubble crowding model to study the CHF phenomenon on the special condition during the implement of IVR-ERVC; (3) In- and ex-vessel coupled analysis has been performed with a modified heat transfer method considering the heat transfer inside and outside reactor pressure vessel (RPV), and also in the vessel wall. The present work shows that the new developed models can be used to assess the external reactor vessel cooling phenomenon and the effectiveness of IVR-ERVC, which is significant and necessary for the design of large scale advance passive nuclear power plants in the future. [ABSTRACT FROM AUTHOR]

Ocean thermal energy is clean and renewable. In recent years, many scholars have focused on improving the generation efficiency of the ocean thermal energy conversion system. To the best of our knowledge, the majority of the scholars focus on equipment improvement and working fluid optimization, and few study how to reduce the outlet temperature of cold-water pipes. This paper establishes a numerical model, which is solved by the finite volume method, to analyze the temperature distribution and heat transfer characteristics of cold-water pipes during pumping. The influence of cold-water pipe materials, wall thicknesses, flow rates, and insulation layer thicknesses on outlet temperature is explored. In addition, this paper qualitatively gives performance optimization recommendations based on technical and economic indicators. This study will be useful for the OTEC community. • A transient temperature model of CWPs in the OTEC system is created. • This model is applicable to CWPS of all sizes with any working parameters. • Heat transfer mechanism between CWPs and seawater has been explored. • Influence factors on the CWP outlet temperature are investigated. [ABSTRACT FROM AUTHOR]

Highly dense and integrated data centers face key challenges of realizing efficient cooling and improved energy efficiency. To overcome these challenges, this study experimentally investigated the flow and heat transfer characteristics of single-phase immersion liquid cooling (SPILC) systems. The influence of two opposite coolant flow directions on the SPILC performance was examined. Furthermore, a correlation mechanism between coolant thermal properties and SPILC performance was established, along with a control chart for regulating the working conditions of SPILC systems. The results indicate that compared to a pro-gravity flow, an anti-gravity flow scheme reduces the chip case temperature and thermal resistance by 33.8% and 55.6%, respectively, while decreasing the power usage effectiveness (PUE) by 1.4%. Using coolant with the lowest viscosity reduces the chip case temperature and thermal resistance by 9.3% and 10.5%, respectively, while decreasing the PUE by 0.4%. Moreover, the cooling water temperature has a greater impact on the performance of SPILC systems than the volume flow rate of coolants. Additionally, this paper provides control charts for the cooling water temperature and coolant flow rate to improve the PUE while ensuring the safe operation of SPILC systems, with the highest chip temperature and total electricity consumption as indicators. • Immersion cooling performance of system-level data center servers is experimentally studied. • PUE of the anti-gravity flow decreases by 1.4% compared to the pro-gravity flow. • Correlation between coolant properties and immersion cooling performance is established. • Energy-efficient control charts for cooling water and immersion coolant are provided. [ABSTRACT FROM AUTHOR]

Grate boilers are widely applied in biomass combustion for heat and energy generation. However, grate-firing systems often suffer from low efficiency and high emission. Computational fluid dynamic (CFD) becomes increasingly popular as a flexible method to obtain the detailed combustion behaviors in the furnace, and to optimize the performance of existing grate boilers. This paper presents efforts toward a reliable baseline CFD model for an industrial biomass-fired grate boiler, where the structure of the fuel-bed was sufficiently considered. The combustion performances in the furnace were investigated experimentally and numerically by coupling the fuel bed and freeboard, to clarify the impact of bed structure on the simulation accuracy. Results show that when the bed structure has been taken into account, the predictions are in better agreement with the various measurements, as the deviations between them are all within 10 %. Moreover, the flame center drops, the total heat transferred to the water-cooled walls increases, and the residence time of flue gas is greatly prolonged from 2.76 s to 3.90 s, resulting in a distinct difference of the temperature and species patterns in the freeboard. The simulations will provide valuable theoretical guidance for the accurate modeling of grate-fired boiler. [Display omitted] • A baseline model is proposed for accurate modeling of biomass-fired grate boiler. • Effect of fuel-bed structure on the simulation of grate boiler is clarified in detail. • Bed structure greatly affects the predicted temperature and species patterns. • Flue gas residence time and heat transfer are also highly impacted by bed structure. [ABSTRACT FROM AUTHOR]

Natural cooling energy and high-efficient radiant cooling techniques are essential to mitigate energy resources shortage crisis, breakthrough on traditional convective air-conditioning systems in isolation between indoor and outdoor environment with high indoor air quality. In this paper, a polyethylene aerogel (PEA) and phase change material (PCM) integrated novel Trombe wall was proposed, involving natural cooling energy harvesting, cooling energy storage, indoor ventilation and radiant cooling. A two-dimensional unsteady numerical model based on surface-to surface (S2S) radiation model and effective specific heat capacity method was developed in the commercial software Ansys Fluent to evaluate the cooling performance and dynamic heat-transfer mechanism of the novel Trombe wall. Subsequently, climate-responsive operation strategies on ventilation modes were proposed to maximize natural cooling energy utilization and fresh air supply. Parametrical and comparative studies were conducted on optimal structural design and robust operation. Our results showed that, with the novel design and advanced operation strategies, passive cooling capacity of 0.64 kWh/m2·day can be provided, together with fresh air supply of 2705.2 kg/day (1.4 m2 Trombe wall), corresponding to air change rate per hour (ACH) of 1.15. In terms of active cooling system, the integration of PEA and PCM can effectively prevent moisture condensation and shift peak cooling load. Hence, radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 % can be achieved by the novel Trombe wall, with electricity consumption only at valley period. Moreover, economic saving of 55.0 CNY/day and decarbonization potential of 23.8 kg CO 2,e /day can be achieved when the novel Trombe wall is integrated into a typical office building in subtropical climate Guangzhou. This study provides a novel structural design and optimal operation strategies on a Trombe wall, together with guidelines on techno-economic-environmental performance improvement, promoting effective natural cooling energy utilization and energy-flexible/efficient radiant cooling for decarbonization of buildings in cooling-dominant regions. • A novel Trombe wall for natural cooling energy harvesting and radiant cooling. • An unsteady numerical model for thermodynamic analysis. • Passive cooling capacity of 0.64 kWh/m2.day and fresh air supply of 2705.2 kg/day. • Radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 %. • Daily CO 2 reduction of 23.8 kg and economic saving of 55.0 CNY in a typical office building. [ABSTRACT FROM AUTHOR]

A multitude of uncertainties intertwined within the manufacturing and functioning of gas turbines has often been overlooked in numerous prior investigations regarding the aerothermal performance of blade tips. Consequently, the actual lifespan of the blades falls considerably short of the initially anticipated duration. This study proposes an efficient parallel turbo robustness analysis framework and aims to delve into the uncertain characteristics exhibited by various multi-cavity squealer tips during real-world gas turbine operations. The findings of this research reveal that the inclusion of ribs has an adverse impact on the flow field, leading to heightened chaotic tendencies and a considerable reduction in the expected aerodynamic efficiency of the multi-cavity squealer tip. The leakage flow experiences a notable increase, reaching values of 22.30%, 17.88%, and 24.51% for the three distinct multi-cavity configurations, surpassing the corresponding value of 13.63% observed for the conventional squealer tip. However, integrating the flow field uncertainty into the thermal field uncertainty proves challenging due to the disruption of the cavity vortex system caused by the pressure side ribs. Thus, the heat transfer performance of the multi-cavity squealer tip exhibits superior robustness compared to that of the conventional squealer tip. Furthermore, this paper introduces a novel evaluation index, based on comprehensive uncertainty flow and thermal analyses, to assess the robustness of the aerothermal performance. The present work makes a valuable contribution to the development of digital twins for turbomachinery systems. • The robustness of the aerothermal performance of squealer tips with and without ribs is investigated and compared comprehensively. • The presence of the ribs makes it difficult to transfer the uncertainty of the flow field to the heat exchange field. • The existence of large heat flux gradients and sharp fluctuations in the region around the ribs is distinguished. • The shortcomings of conventional sensitivity measures are analyzed and one with engineering relevance is derived. [ABSTRACT FROM AUTHOR]

The application of phase change materials (PCMs) in renewable energy storage and building temperature regulation is considered an effective method to reduce the use of fossil fuels and carbon emissions. However, issues concerning the utilization of PCMs in high-humidity environments remain to be addressed to fill the gap in real-world applications. This paper establishes a simplified novel two-zone model, comprehensively considering the natural convection on the surface of the PCP in high-humidity environments, as well as the formation, movement, and evaporation of water films on the surface. Subsequently, numerical solutions and experimental validation are conducted, and the influence of high-humidity environments on the heat and moisture transfer is elucidated. The results indicate that a high-humidity environment can significantly suppress the sensible heat transfer with a ratio range of latent heat to sensible heat typically around 1–4. Furthermore, the increase in the height of PCP leads to an increase in the proportion of sensible heat transfer. On the contrary, increasing the thermal conductivity of the PCM can amplify the latent heat transfer. The results can help further study the thermal storage and the dehumidification potential of phase change units in application on a large scale under high humidity conditions. [Display omitted] • A simplified model for PCM thermal storage prediction in high humidity environments is established. • The variation of water film on the PCP surface is considered. • Sensitivity analysis for PCM thermal storage in high humidity environments is investigated. • A high-humidity environment can lead to a ratio range of latent heat to sensible heat typically around 1–4. [ABSTRACT FROM AUTHOR]

Flat thermosyphon (FTS) has gained wide attention in solving heat dissipation problems of data centers. The miniaturization of densely packed electronics has led to a demand for compact heat sinks. In this paper, a confined FTS consisting of an evaporator, condenser and customized quartz-glass chamber was developed. Bubble behaviors were investigated by the visualization approach under vacuum conditions. Effects of the space height, nominal heating power, and liquid filling ratio on the thermal characteristics were involved. Experimental results found that the bubble behaviors with 10 mm height are different from others. For 10 mm height, bubble contacts the condensation surface and then bounces back to the evaporator. The quantitative analysis shows that the boiling heat transfer coefficient with 10 mm height is 65.5 % of that with 25 mm height , and a condensation heat transfer coefficient with 10 mm height is 58.9 % of that with 20 mm height. Increasing heating power deteriorates the condensation heat transfer via forming a bubble film on the condensation surface. A small filling ratio (30 %) with 10 mm height is beneficial for the phase change heat transfer. It is hoped that these results can offer guidance for designing effective cooling devices. [Display omitted] • Bubble behaviors of confined flat thermosyphon (FTS) is explored. • Effects of space height, heat power, and filling ratio are involved in analysis. • The bubble directly bounces back to the evaporator of FTS with 10 mm height. • Small filling ratio (30 %) is beneficial for phase change of FTS with 10 mm height. • Reduced space height attenuates the thermal performance of confined FTS. [ABSTRACT FROM AUTHOR]

Cost-effective retrofit of heat exchanger networks (HENs) remains a significant challenge. This paper explores different methods for achieving cost-effective retrofit. The first part of this article presents a novel methodology for the application of heat transfer enhancement in HEN retrofit with a fixed network structure considering pressure drop constraints. Heat transfer enhancement is a low-cost option. However, heat transfer enhancement on its own without changes to the network structure provides a limited scope for energy reduction. The second part of this paper presents a new pinch retrofit method that identifies network structural changes sequentially to meet the retrofit target. However, the high capital cost associated with installing new heat exchangers, relocating existing exchangers, and augmenting the heat transfer area of existing heat exchangers most often leads to uneconomic retrofits. Low-cost retrofit requires few modifications. Therefore, the third part of this paper combines the new pinch retrofit method with the use of heat transfer enhancement to provide low-cost retrofit by combining the merits of both approaches. A case study highlights the benefits of the new approach. [ABSTRACT FROM AUTHOR]

Numerous metrics and indices have been proposed for the assessment of thermal perception and comfort. Commonly used indices based on the estimate of the heat flow between the human and its environment includes the well-known Fanger's method, also known as the PMV-PPD thermal comfort model. Recently this thermodynamic approach has been expanded with the application of the second law of thermodynamics. In this paper, an exergy-based analysis of the relation between the human and its environment is presented. Heat and mass flow rate due to convection, radiation, evaporation and respiration are calculated and expressed in terms of exergy loss. This value is used in the modified Fanger's thermal comfort model, where the heat balance equation is replaced by the exergy loss. The paper builds upon prior studies on determination of internal and external exergy losses by revised and newly defined formulas taking into account clothing and indoor conditions. The results quantitatively show that thermal energy load in the original Fanger's PMV model could be substituted by exergy loss and it corresponds to a certain level of subjective assessed thermal comfort level. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) reservoirs have the characteristics of low porosity, low permeability, strong heterogeneity and high content of adsorbed gas. A large number of studies have shown that the adsorption performance of coalbed methane reservoirs on methane is significantly affected by temperature. Therefore, heat injection development of coalbed methane reservoirs has received extensive attention. This paper takes the superheated steam (SS) flow in the wellbore after fracturing the coalbed methane reservoir as the research object, and establishes a mathematical model of the SS flow. The model consists of momentum conservation equation and energy conservation equation as the main control equation, combined with auxiliary models to form a complete mathematical model. In this paper, the discrete method is used to obtain the numerical solution of the model, and then the influence of the injection parameters on the SS flow is analyzed. The research conclusions of this paper have reference significance for the development of coalbed methane reservoirs with SS injection. This study found that: (a) When the injection rate is low enough (0.2 kg/s in this paper), the effect of gravity on SS pressure is stronger than that of pressurized gas; (b) When the steam injection speed is within a certain range (0.5 kg/s in this example), the pressure of the SS first decreases and then increases, forming a U shape; (c) The SS temperature increases with increasing of injection rate. During this period, the Joule-Thompson effect replaces the heat loss effect as the main factor controlling the temperature drop of the SS; (d) In order to maintain the development advantages of SS, the SS should still have a certain degree of superheat at the bottom of the well. Therefore, the steam injection speed should not be too high (eg 0.2 kg/s in this article); (e) Therefore, with the increase of SS pressure inside the wellbore, the temperature value decreases due to the influence of Joule Thompson effect, resulting in the continuous decrease of superheat degree. • A model of heat carrier-wellbore coupling based on Joule-Thompson effect is established. • The independence and linkage of pressure and temperature is revealed. • This paper provides a basic basis for the development of coalbed methane heat injection. [ABSTRACT FROM AUTHOR]

Maximum power performance of an endoreversible non-isothermal chemical engine (NICE) with simultaneous heat and mass transfer is investigated in this paper. The heat and mass transfer processes are assumed to obey Onsager equations in linear irreversible thermodynamics. The power output of the endoreversible NICE as well as the corresponding vector efficiency [See Eq. (13) in this paper for its definition] are obtained analytically. Special cases for an endoreversible Carnot heat engine with the linear phenomenological heat transfer law [ q ∝ Δ (T − 1) ] and an endoreversible isothermal chemical engine with the linear mass transfer law [ g ∝ Δ (μ) ] are further derived based on the general optimization results. Some numerical examples are provided, and the effects of changes of absorbed energy flux rate, mass flux rate, and heat and mass transfer phenomenological coefficients on the optimization results are analyzed. The results show that there are optimal absorbed energy flux rate and optimal mass flux rate for the power output of the endoreversible NICE to approach to its maximum; the relationship between the power output of the endoreversible NICE and its vector efficiency is paraboloid. [Display omitted] • Performance of endoreversible non-isothermal chemical engine is investigated. • Heat and mass transfer losses are considered simultaneously. • Finite time thermodynamics and Onsager equations in linear irreversible thermodynamics are applied. • Power output and the corresponding vector efficiency are obtained analytically. • There are optimal absorbed energy flux rate and mass flux rate for maximum power output. [ABSTRACT FROM AUTHOR]

The heat transfer from the combustion gases to the cylinder walls inside a spark ignition engine is a key factor in an engine's design, due to its influence on the engine's efficiency, power and emissions. Therefore a lot of research has been conducted in order to accurately model the heat transfer, for engine design and optimization purposes. These models have been found to provide inaccurate predictions for fuels which have significantly different gas properties compared to traditional fossil fuels. This indicates that the models either do not properly include gas properties, or are missing some important properties in their formulation. In order to construct a general (“fuel-independent”) heat transfer model, new measurements need to be executed, with multiple fuels that have different properties. Designing such an experiment requires a thorough understanding of the factors influencing the heat transfer and their interactions. In this paper a literature review is presented of heat transfer measurements in spark ignition engines in order to investigate the effect of the engine factors on the heat transfer. Based on this review, a root cause analysis is conducted to identify the independent factors that affect heat transfer. These factors are then used to set up two experiments according to a Design of Experiments methodology that allows the investigation of the effect of different gas properties and engine settings on the heat transfer in a consistent way. The results of these measurements for motored operation are discussed in [1] and for fired operation in a companion paper [2]. [ABSTRACT FROM AUTHOR]

In the last few years, the effect of diabatic test conditions on compressor performance maps has been widely investigated leading some Authors to propose different correction models. The aim of the paper is to investigate the effect of heat transfer phenomena on the experimental definition of turbocharger maps, focusing on compressor performance. This work was developed within a collaboration between the Polytechnic School of the University of Genoa (Italy) and the testing center CRITT M2A (France). In particular, an original model for the correction of compressor steady flow maps is presented and discussed. The major benefit of this method is represented by the easiness of data post-processing, the data base economy, the reduced number of geometrical and physical input parameters required and the accuracy of the solution. Besides, this model does not need an out-of-standard test bench to obtain the compressor maps. In the paper, experimental tests under quasi-adiabatic conditions developed to validate the proposed model are reported. A satisfactory agreement between measured and calculated compressor maps is highlighted. [ABSTRACT FROM AUTHOR]

M-TES (Mobile Thermal Energy Storage) technology is explored in this paper for transportation of industrial surplus heat for use in LTDH (low temperature district heating network). LTDH has promising potential in utilizing low grade heat, on the other hand, 20%–50% of industry generated surplus heat is often released to the ambient environment. M-TES is used to match thermal energy supply and demand that occur at different locations and that are shifted in time. In this paper, design of M-TES is conducted, optimization in operating strategies is performed, sensitivity analysis on levelized cost is studied, and environmental impact of CO 2 emissions due to transportation is evaluated. The results of the study show an array of transportation means and storage operating strategies under which M-TES is technically, economically and environmentally sound for transportation of industrial surplus heat for use in LTDH network. [ABSTRACT FROM AUTHOR]

To optimize the uneven distribution of flow field in the mechanical draft cooling towers, four cases for deflector plates are proposed. Based on the analysis of the velocity and temperature fields in the tower, the effect of the deflector plates to strengthen the local heat transfer is investigated. In addition, the thermal and ventilation performance is investigated with different fan speed and circulating water flow rate. The results show that the arrangement of the deflector plates can guide the ambient air into the inefficient heat transfer region. Of the four cases studied, Case 4 has the optimal performance. Compared with the original tower, the outlet water temperature reduces by 0.22 °C, the cooling efficiency increases by 1.53%, and the Merkel number increases by 6.35%, while the ventilation rate keeps at 699 m3/s. The thermal performance of Case 4 is better than that of the original tower when only the fan speed or the circulating water flow rate are changed, and it is improved with the increase of the fan speed and the decrease of the circulating water flow rate. This paper can guide the optimization of enhanced local heat transfer in mechanical draft cooling towers. • A numerical model of a mechanical draft cooling tower is developed. • The model can be used for local heat transfer enhancement studies. • Deflector channels are created by the action of the deflector plates. • Regions with lower heat transfer efficiency are optimized. • Utilizing deflector plates exhibits the capacity to enhance the thermal efficiency. [ABSTRACT FROM AUTHOR]

Supercritical water gasification (SCWG) is a potential clean technology for utilizing solid fuel or waste without producing gaseous pollution. Efficient energy integration and recovery strategies play an essential role in the endothermal gasification process. Previous approaches have only focused on the heat source or heat transfer with very little attention to the utilization of the abundant supercritical water in the product gas. This paper proposes an innovative series design for heat integration in the SCWG system while taking the gasification process into account. Notably, the first-stage oxidized hot fluid containing abundant water is directly utilized as the gasification agent for the second-stage gasification reactor. The thermodynamic analysis shows that the cold gas and exergy efficiency in the two-stage series system is 17.4% and 15.0% higher than in the previous single-stage gasification reactor. The sensitivity analysis illustrates that increasing series stages and feedstock concentration while decreasing oxidation proportion and the agent-slurry ratio can improve the overall system efficiency by decreasing the demand for oxygen, power consumption, and heat transfer rate. The series design should offer an innovative and practical approach for the heat supply in the industrial SCWG plant. • Series design for supercritical water gasification of coal-water slurry was simulated. • The optimized cold gas and exergy efficiency is improved by 17.4% and 15.0%. • The Sankey diagram shows that the series design reduces reaction and heat recovery exergy loss. • Higher series stages facilitate methane production, less oxygen demand, and higher efficiency. • The critical parameters were studied by sensitivity analysis for optimization. [ABSTRACT FROM AUTHOR]

The thermal conductivity of rock is an essential thermophysical parameter in geothermal engineering. Experiments have shown that when rock changes from an unsaturated to a saturated state, thermal conductivity can be increased by 50% at most. In this paper, the variation of thermal conductivity with saturation of 101 samples of six different rock types from Songliao Basin, Gonghe Basin, and Ordos Basin in China was measured in the laboratory. Correlations between saturation, porosity, internal structural characteristics of rocks and thermal conductivity were investigated. The results show that the effect of saturation on the thermal conductivity of rock increases exponentially with porosity. Based on three classical models and the relationship between porosity, saturation, and thermal conductivity, improved models and a fitted model of thermal conductivity are proposed. By comparing the improved models to the fitted model, the applicable scope of each model is obtained. The errors of each model are analyzed in detail. The average MAE value of the improved models is 0.405 and the average RMSE value is 1.207 over the applicable model scopes. The R 2 of the fitted model is 0.94. Compared with experimental data from literature, MAE values of the improved models and the fitted model are 0.040 and 0.003 respectively. Unsaturated rock with a single fracture heat transfer model is established by simulation. A thermal-Hydrological coupling model is used to simulate seepage heat transfer through fracture. The effect of variable thermal conductivity simulation is the best with the experimental value, and the MAPE value was 8.3%. This study fills a gap in available models of unsaturated thermal conductivity of rock, and provide theoretical support for the accurate calculation of heat transfer efficiencies in related geothermal engineering applications. • Theoretical saturation coefficient equation on thermal conductivity was proposed. • Three unsaturated thermal conductivity models were improved and verified. • Propose an empirical unsaturated model based on laboratory data. • The relationship between unsaturated model and rocks structure was revealed. [ABSTRACT FROM AUTHOR]

Thermal energy storage material is always filled in the packed bed system in a random accumulation manner, and there is an interrelationship between the tank-to-particle diameter ratio (TPDR) and the porosity. Therefore, in this paper, the packed bed latent heat storage system is constructed based on spherical macro-encapsulated phase change materials (PCM). To study the influence of TPDR on the thermal performance of a randomly packed bed, a transient two-dimensional axisymmetric symmetry continuous solid phase model is developed. The experimental and numerical results are compared to verify the accuracy of the model. The heat transfer and pressure drop characteristics between air and PCM capsules are analyzed in detail. The results indicate that the average porosity reaches the maximum at around TPDR≈1.7 position, which is about 0.7. In the same packed bed, when the TPDR is larger, the pressure drop is more affected. The diameter of the heat storage ball changes from 25 mm to 75 mm, the TPDR is reduced by 66.7%, the heat storage of the PCM is almost unchanged, and the heat storage capacity of the stainless-steel spherical shell is reduced by 72%, and the heat storage capacity of the entire heat storage ball is reduced by 12%. • A high-temperature packed bed latent heat storage system is constructed. • Experimental and numerical results are compared to verify the accuracy. • The influence relationship between tank-to-particle diameter ratio and porosity is given. • The maximum porosity of the packed bed filled with spherical PCM is about 0.7. • Influences of tank-to-particle diameter ratio on thermal performance are analyzed. [ABSTRACT FROM AUTHOR]

Absorption energy storage (AES) has attracted worldwide attention due to the high energy storage density and environmental friendliness. To optimize the performance of the AES system, a finite time thermodynamic (FTT) model considering some influencing factors such as time, heat transfer area, heat transfer temperature difference, internal friction and dissipation has been developed in this paper. A new concept of ratio of charging and discharging time is proposed. The general relation of the energy storage efficiency, energy storage rate and energy release rate are induced based on FTT analysis. The distribution of the total thermal conductivity was optimized under the condition of a certain total thermal conductivity and the optimized maximum cooldown release rate has been increased by 14%. The optimal operating conditions of the AES system are obtained. Furthermore, the influences of the internal irreversibility, ratio of charging and discharging time and heat source temperatures on the performance of the AES system are analyzed. The research results can provide theoretical basis and guidance for the AES system design and optimization. • Finite time thermodynamic model for absorption energy storage system is developed. • The concept of ratio of charging and discharging time is proposed. • Storage efficiency can double by raising ratio of charging and discharging time. • The influence of variables on energy storage efficiency is analyzed. • There is an interaction between the parameters on the energy storage efficiency. [ABSTRACT FROM AUTHOR]

This paper presents a new thermo-hydraulic model for district heating systems simulations, which aims at being a fast and accurate tool to simulate highly renewable networks characterized by fluctuating energy profiles. The main novel aspect of the tool lies in the heat transmission modelling over long pipes based on a Lagrangian numerical approach. In comparison to other existing models, this approach significantly reduces computational time and it increases results' accuracy. The elaborated method avoids numerical diffusion in the results and consequently allows proper prediction of temperature propagation, especially in case of fast changes of fluctuating profiles. The tool is built following a modular procedural programming approach in order to facilitate the simulation of multicomponent system. Thanks to its modular structure, every components of the system is built with the same structure that is differently declined according to each component's requirements. In this way, new additional elements' models easily fit the existing ones. The model is validated under real operating conditions with hourly monitoring data of an Italian district heating network. The results show good correspondence also in the most peripheral nodes of the network, where the largest deviations are normally encountered, thus making the model a reliable and fast simulation tool for district heating network design and operational control. • A model for fast and realistic simulation of district heating network is presented. • The heat-transmission pipe is modelled with the method of characteristics with a Lagrangian approach. • An entire big scale district heating model is validated with yearly monitoring data, proving the model usability. • Simulation results agree with temperatures at distant user's substations and peak demand at generation plant. [ABSTRACT FROM AUTHOR]

A combination of hydraulic fracturing and horizontal wells is now being used to tap geothermal energy from naturally fractured reservoirs. Fully grid-based numerical models are currently used to simulate heat recovery from enhanced geothermal systems (EGS). Such models require a fine unstructured mesh and are computationally expensive. In this paper we present a computationally efficient model that allows us to accurately simulate fracture propagation, fluid flow, and heat transfer in networks of natural fractures that may be created in naturally fractured geothermal reservoirs. The integrated simulator is developed by combining the displacement discontinuity method (DDM) for fracture propagation in naturally fractured reservoirs with a general Green's function solution for fluid and heat flow from the matrix to the fracture. This eliminates the need to discretize the matrix domain resulting in a very computationally efficient solution. A discrete fracture network (DFN) approach is used to represent the pre-existing natural fractures. The model is first validated against an analytical solution for fluid flow and heat transfer in a rock matrix with a single fracture. The computation time with and without discretizing the rock matrix shows a 100-fold reduction in computation cost with very little loss in accuracy. Parametric studies are conducted to investigate the effect of the distribution of natural fracture density, length, and orientation. The results show that the efficiency of tapping geothermal energy is impacted by geometrical and topological complexities of the fracture network and in particular the connectivity of backbone fractures. It is, therefore, important to optimize (not maximize) the connectivity and complexity of the backbone fracture network. The computationally efficient model presented here provides a practical tool for optimizing operational parameters for efficient geothermal production. • Eliminating the discretization of the rock matrix for fracturing-geothermal production is proposed for the first time. • An algorithm is developed to capture the connectivity of fractures automatically. • A new Green's function solution is proposed for fractures oriented at any angle. • The importance of fracture connectivity on heat extraction rate from an EGS is defined and quantified. [ABSTRACT FROM AUTHOR]

The thermal load heterogeneity will lead to inhomogeneous local heat flux and thermal stress, extremely detrimental to the operational stability of heat exchangers with multi-assembly structure. In this paper, a full-scale analysis method for the helical coil steam generator in industry was developed and implemented. The validation was performed against flow boiling heat transfer experiment of helical tube. The simulation of single assembly and full-scale helical coil steam generator in high temperature gas-cooled reactor was performed, and the distributions of thermal-hydraulic parameters in heat exchange region were obtained. The results show that the nonuniform helium flow distribution with the inhomogeneous factor D m value of 34.83% has a significant influence on the heat transfer characteristics. The peak heat transfer power of central assembly increases by 33.76% against design condition, introducing large thermal load heterogeneity with the inhomogeneous factor D p value of 30.45%, even threating the structural integrity of helical tube in long-term operation circumstances. The structural elements design in the superior compartment should be optimized to increase the helium mass flow rate of the assemblies below the nozzle and behind the helium baffle, improving flow distribution uniformity and reducing the peak value of local heat flux and thermal stress. • A full-scale analysis method of helical coil steam generator in HTGR was developed. • The flow distribution in multiple heat exchange assemblies was obtained. • The thermal load heterogeneity was quantificationally investigated. • The optimization suggestion of superior compartment elements was provided. [ABSTRACT FROM AUTHOR]

Reciprocating liquid hydrogen pump operates under alternating pressure, temperature, and flowrate with dramatic changes in the thermodynamic states of liquid hydrogen. The thermodynamic state in the pump is influenced by the dynamic interactions between fluid flow, heat transfer, piston motion, and valve dynamics. This paper presents a numerical study for reciprocating liquid hydrogen pumps based on a coupled simulation of the dynamic processes between the alternating flow, unsteady heat transfer, and valve dynamics with a given piston motion as the input. A pump for hydrogen refueling stations with a nominal flowrate and delivery pressure of 50 kg/h and 87.6 MPa is selected as the research object. The appropriate design parameters of the pump and its valves are determined to avoid cavitation in the cylinder and oscillation of the valves. The effects of the frequency and delivery pressure on the valve motion and pump performance are further analyzed. Finally, the in-cylinder heat transfer leads to an extra evaporation loss of 0.012 kg/day, and the isentropic and volumetric efficiencies of the liquid hydrogen pump are 97.30% and 90.76% respectively. The work presented here would be beneficial for the design and optimization of reciprocating liquid hydrogen pumps. [Display omitted] • A numerical study for dynamic process of reciprocating LH 2 pumps are presented. • Valve parameters and supercooling are optimized for a better pump performance. • Low frequency condition result in valve oscillations and reduction of efficiency. • Heat transfer in-cylinder result in an extra evaporation loss of 0.012 kg/day. • The isentropic efficiency is 97.30%, and the volumetric efficiency is 90.76%. [ABSTRACT FROM AUTHOR]