Search

In this paper, heat transfer performance is investigated for plain and nanoparticle coated tube-in-tube heat exchangers. Four types of tubes, i.e. bare copper tube, bare aluminium tube, Cu-Al2O3 nanoparticle coated tube and anodized aluminium tubes are used for performing the experimental investigation. The coating thickness of Cu-Al2O3 nanocomposite surface and anodized aluminium tube varies from 10, 25 and 30 micrometres to 15, 20 and 30 micrometres respectively. The surface is found to be hydrophilic in nature as the contact angle changes from 79.82° to 55.47°. The prepared surfaces are characterized by FESEM, EDS and FTIR. By adjusting the hot and cold fluids relative mass flow rates, one may calculate not only the overall heat transfer coefficient but also the efficiency of the tube-in-tube heat exchanger. The Cu-Al2O3 nanocomposite coated surface has the highest overall heat transfer coefficient and efficiency, followed by an anodized aluminium surface, bare copper surface and bare aluminium surface. The aluminium anodic oxide (AAO) surface also exhibits an increased heat transfer coefficient, but to a lesser extent than the nanocomposite coating. [ABSTRACT FROM AUTHOR]

The rising use of fossil fuels has had major environmental impacts, including global warming, pollution, and higher heating system costs. This emphasizes the need of increasing the efficiency of equipments such as heat exchangers used in heating and air conditioning systems. In the present study, heat transfer augmentation in a double pipe heat exchanger is numerically studied by the use of truncated conical turbulators. Truncated conical structures with a base diameter of 12 mm height, 7 mm, and pitch values ranging from 25 mm to 100 mm with an increment of 25 mm, have been considered in the study. The air flow rate varied from a Reynolds number of 3000 to 15,000 in increments of 3000. Results have been compared with the bare pipe without any turbulators. The heat exchanger with the turbulator showed better performance than the bare heat exchanger in terms of higher Nu, but at the cost of higher pressure drop. Increased Nu was observed up to pitch 50 mm and reduced afterward. Results indicated a highest Nu of 77.7 for Pitch 50 mm at Re 15,000. Maximum Thermohydraulic efficiency of 1.13 was observed for pitch 50 mm at a Re of 11,000. Hence, it is concluded that truncated conical structures can be used as a heat augmentation device in a double pipe heat exchanger to increase the heat transfer rate and thermohydraulic efficiency. [ABSTRACT FROM AUTHOR]

With the application of microdevices in the building engineering, aerospace industry, electronic devices, nuclear energy, and so on, the dissipation of high heat flux has become an urgent problem to be solved. Microchannel heat sinks have become an effective means of thermal management for microdevices and enhancements for equipment due to their higher heat transfer and small scale. However, because of the increasing requirements of microdevices for thermal load and temperature control and energy savings, high efficiency heat exchangers, especially microchannels are receiving more and more attention. To further improve the performance of microchannels, optimizing the channel geometry has become a very important passive technology to effectively enhance the heat transfer of the microchannel heat sink. Therefore, in this paper, the microchannel geometry characteristics of previous studies are reviewed, classified and summarized. The review is mainly focused on microchannel geometry features and structural design to strengthen the effect of heat transfer and pressure drop. In addition, the correlation between boiling heat transfer and geometric characteristics of microchannel flow is also presented, and the future research direction of microchannel geometry design is discussed. [ABSTRACT FROM AUTHOR]

The fouling factor is a complex non-linear function of several feature variables. Accurate estimation of this measurable factor is applicable for controlling the heat transfer efficiency of heat exchangers. Artificial neural network (ANN) and adaptive neural-based fuzzy inference system (ANFIS) techniques are accurate approaches for the understanding treatment of the most complicated systems. The cascade-feedforward (CFF), multi-layer perceptron (MLP), radial basis function (RBF), and generalized regression (GR) neural networks and ANFIS were applied for predicting the fouling factor of the hot wire probe from some measured variables using a huge databank, including 1870 empirical dataset. Pearson's and Spearman's techniques confirmed the highest relation between considered features and the first order of fouling factor. The results demonstrate that the cascade feed-forward neural network containing eight hidden neurons was the best artificial intelligence (AI) model with excellent overall AARE = 3.44 %, MSD = 0.0000315, RMSD = 0.0056, and R2 = 0.9982. This work's significance lies in presenting an applicable and accurate tool for estimating fouling factors on hot wire probes to the research community and industry. This model can be considered a reliable replacement for empirical analyses that are often expensive and time-consuming. [Display omitted] • Hot wire probe has used in academic studies of fouling in heat transfer surfaces. • Five powerful artificial intelligence models are used for fouling factor estimation. • The Levenberg-Marquardt is found as the best training algorithm. • An accurate CFF neural network with eight neurons in one hidden layer developed. • Effects of less studied and various independent variables on fouling is simulated. [ABSTRACT FROM AUTHOR]

With the depletion of shallow metal mineral resources, deep mining has become more common. In the process of deep mining, heat hazards in mines seriously threaten the health of personnel and the safety of mining operations. According to the flow and low-temperature characteristics of abundant water in Maoping Lead Zinc Mine, this paper proposes the direct use of the low-temperature water inflow of the mine as the cold source by which to conduct the heat exchange with a single spiral-tube heat exchanger for mine cooling. An experimental platform was built for the cooling system to allow us to explore the mechanism of the influence of the inlet air volume and air temperature and the inlet water temperature and flow on the cooling effect of the single spiral-tube heat exchanger. It was found that with the increase in the inlet air volume and inlet water temperature, the cooling efficiency of the heat exchanger decreased, while with the increase in the inlet air temperature, the cooling efficiency of the heat exchanger increased. Within the experimental range, 127.2 m3/h was found to be the optimum inlet air volume, and 33.0 °C was the most appropriate inlet air temperature; the water temperature of Maoping Coal Mine is about 20 °C throughout the year, and the industrial test site can reduce the wind temperature of 31.5 °C to 23.9 °C. The inlet water flow is positively related to the cooling effect. With the increase in the water flow, the outlet temperature of the air flow at each working point was continuously reduced, and the cooling effect of the heat exchanger was improved. The moisture content of the inlet air flow can be reduced by increasing the low-temperature inlet water flow. Through experiments, the feasibility of the cooling system that directly uses the mine's low-temperature water as the cold source was verified. A multiple linear regression analysis equation for the cooling system model is proposed, which provides a reference for formulating effective measures to prevent and control heat hazards in mines. [ABSTRACT FROM AUTHOR]

The improvement of the efficiency of heat exchangers has always been one of the most critical concerns of industry. Pulsating heat pipes are a new and high-efficiency technology in the field of heat transfer. Pulsating heat pipes are widely used in solar water heaters, solar water desalination systems, etc. In this study, the effect of different nanofluids on the performance of heat pipes was investigated. ZrO2/SiO2 nanocomposites were tested under functionalized and non-functionalized states in a pulsating heat pipe. For this purpose, the heat pipe was charged with each nanofluid at concentrations of 0.25, 0.5, and 1 g L−1, and the thermal resistance of the pipe was compared as an output parameter. The thermal resistance for different nanofluids was defined and compared at different input powers of the evaporator and a constant filling ratio of 50%. The obtained results showed that nanofluids as a working fluid could improve the heat transfer of pulsating heat pipe compared to the working fluid of water and reduce the thermal resistance. The nanofluid with a concentration of 0.25 g L−1 exhibited the best performance. In this case, the resistance of pulsating heat pipe at some fluxes was decreased up to 48%. [ABSTRACT FROM AUTHOR]

The technique of air sterilization by thermal effect was revisited in this work. The impact of incorporating a high efficiency heat recovery exchanger to a sterilizing cell was especially assessed. A mathematical model was developed to study the dynamics and the steady state of the sterilizer. Computer simulation and reported data of thermal inactivation of pathogens permitted obtaining results for a proof-of-concept. The simulation results confirmed that the incorporation of a heat recovery exchanger permits saving more than 90% of the energy needed to heat the air to the temperature necessary for sterilization, i.e., sterilization without heat recovery consumes 10–20 times the energy of the same sterilization device with heat recovery. Sanitization temperature is the main process variable for sanitization, a fact related to the activated nature of the thermal inactivation of viruses and bacteria. Heat recovery efficiency was a strong function of the heat transfer parameters but also rather insensitive to the cell temperature. The heat transfer area determined the maximum capacity of the sterilizer (maximum air flowrate) given the restrictions of minimum sanitization efficiency and maximum power consumption. The proposed thermal sterilization device has important advantages of robustness and simplicity over other commercial sterilization devices, needing practically no maintenance and eliminating a big variety of microorganisms to any desired degree. For most pathogens, the inactivation can be total. This result is not affected by the uncertainties in thermal inactivation data, due to the Arrhenius-like dependence of inactivation. Temperature can be adjusted to achieve any removal degree. [ABSTRACT FROM AUTHOR]

• Introduces ultra-compact TPMS heat exchangers with record efficiency up to 16.5 W/(cm³·K). • Successfully 3D prints complex TPMS structures, enabling new design possibilities. • Develops experimental correlations in heat transfer and pressure drop. • Achieves up to 200 % improvement in PEC over traditional heat exchangers. With the rapid growth in energy efficiency demands, compact heat exchangers are gaining increasing attention. This study proposes a novel heat exchanger design based on Triply Periodic Minimal Surface (TPMS) structures, leveraging their unique three-dimensional porous structure to enhance heat transfer efficiency and compactness. This study employs computational fluid dynamics (CFD) simulations to analyze the thermal performance of three TPMS structures (Gyroid, Diamond, and Fischer-Koch S) heat exchangers. Two optimized structures are selected for additive manufacturing based on the simulation results. The manufactured heat exchangers are inspected using CT scans, and a dual-fluid experimental performance testing system is constructed to assess the potential application of the two heat exchangers in thermal management systems. Using the least squares method, correlations for heat transfer and pressure drop are separately fitted for the two TPMS heat exchangers. Dimensionless Performance Evaluation Coefficient (PEC) values are utilized to analyze the comprehensive performance of the two TPMS heat exchangers. The heat transfer rate per unit volume has increased by approximately 50 times compared to traditional heat exchangers reported in the literature, which reaches an impressive 717.7 W/cm3 and 16.5 W/(cm³·K). This study will provide design guidance for enhancing the compactness and efficiency of TPMS heat exchangers. [ABSTRACT FROM AUTHOR]

The performance and thermal efficiency of a heat exchanger are critical in various industrial applications, necessitating the continuous improvement of the thermal management system. In the present study, a novel heat exchanger which comprises of delta-nabla-trapezoidal (DNT) configurations of flow channels, is investigated and compared with commercially available concentric tube heat exchangers (CTHEs), to address the limitations of conventional design in terms of thermal efficiency and pressure drop. The current study is the first of its kind to explore the thermal energy exchange potential of the delta-nabla-trapezoidal heat exchangers (DNTHEs) with numerical simulations and experimentally validated them using an in-house designed experimental setup. The proposed heat exchanger comprises of triangular and trapezoidal cross-section channels that are arranged such that the hot fluid flows through the delta and nabla channels while cold fluid flows through the trapezoidal channels. The energy exchange between the two fluid streams is experimentally measured, and Nusselt number correlations are developed for various inlet mass flow rates. The numerical simulations are then used to predict local fluid and heat flow patterns with velocity and temperature profiles. Experimental results indicate a reasonable energy balance, revealing a maximum loss of 15% across all sets of experiments. Furthermore, the cold-side temperature increased to its maximum of 22 K, while the hot-side temperature decreased by 25 K across all tested conditions. The simulation results demonstrated an enhanced energy balance, characterized by a maximum loss of 10%. The thermal efficiency of the proposed DNTHE was experimentally assessed and compared to that of a CTHE in parallel and counter flow configurations. Under similar operating conditions, the maximum heat flux in DNTHE and CTHE was 18.35 and 14.26 kW/m2, respectively. Furthermore, the largest difference in temperature drops and gains between DNTHE and CTHE are 15 and 9 K, respectively. These findings confirmed the efficient thermal energy exchange potential of DNTHE in comparison to CTHE, establishing a new industrial standard for heat exchangers. [ABSTRACT FROM AUTHOR]

• The mechanism of heat conduction of printed circuit heat exchanger with anisotropic thermal conductivity was numerically investigated. • The synergistic effect of thermal resistance in three directions of the solid region on the performance of the heat exchanger was revealed. • A solid region thermal resistance ratio optimization method was proposed. • The efficiency of the heat exchanger is improved by approximately 23% through solid region thermal resistance ratio manipulation. Printed Circuit Heat Exchangers are compact and efficient heat exchangers, widely used in nuclear engineering, very high-temperature reactors, and aerospace systems. This study investigates the heat transfer performance of a heat exchanger with anisotropic thermal conductivity, such as fiber reinforced composites. Numerical simulations were conducted to examine the synergistic effect of three-dimensional thermal resistance on heat exchanger performance. The most significant impact on performance is the z-direction thermal resistance, followed by the y-direction, while the x-direction has the least impact. Contrary to traditional design thinking, increasing the overall heat exchanger thermal resistance under the same thermal resistance ratio improves heat transfer efficiency at the studied conditions. The results suggest that it is necessary to design the lowest thermal conductivity direction as the z-direction and increase the y-direction thermal conductivity to enhance heat exchanger performance. In the numerical investigation presented in this study, the efficiency of the heat exchanger was improved by approximately 23 % under specific operating conditions by adjusting the thermal conductivity of anisotropic materials to control the thermal resistance in the x, y and z directions. It is evident that the manipulation of anisotropic material properties has a substantial influence on the performance of heat exchangers. [ABSTRACT FROM AUTHOR]

The pursuit of sustainable district heating solutions has driven a growing interest in ultra-low temperature district heating (ULTDH) systems, where booster heat pumps (BHPs) play a pivotal role despite challenges posed by their efficiency limitations under large temperature glide conditions. This paper investigates the potential of drop-in R-1234yf/R-32 zeotropic mixtures in BHPs compared to a baseline R-134a system, within the context of a ULTDH framework. This study focused on the viability of the mixtures of R-1234yf/R-32 with the composition ratio of 80 %/20 % and 90 %/10 %. The investigation reveals disparities in compressor efficiency and heat exchanger pressure drop at the component level. Device-level analysis unveils increased COP for R-1234yf/R-32 mixtures, alongside with maximum second-law efficiencies reaching 0.32. A remarkable enhancement in heating capacity up to 58 % was found. System-level analysis demonstrated exergetic efficiencies and identified preferable district heating temperatures. Exergetic efficiencies of 0.47, 0.55, and 0.59 were achieved for domestic hot water preparation at district heating supply temperatures of 30 °C, 35 °C, and 40 °C, with a subsequent shift in optimal district heating temperatures as central heating station efficiency decreased. Temperature profile analysis underscored challenges stemming from excessive subcooling, highlighting the need for configuration refinements. [Display omitted] • Drop-in application of zeotropic mixtures in booster heat pumps are studied. • Coupling effects between district heating and heat pump parameters are analyzed. • Heating capacity and COP improvements with mixture refrigerants are demonstrated. • Temperature profile analysis identified the challenges for efficiency improvement. [ABSTRACT FROM AUTHOR]

Airfoil-finned printed circuit heat exchanger (PCHE) is a new type of microchannel heat exchanger with high efficiency and stable compact features for high temperature and high pressure supercritical carbon dioxide Brayton cycle system. Usually, only one kind of fin structure is used in the microchannel heat exchangers, and little research has been done on flow heat transfer of hybrid fins structure. In this work, a new model of heat exchanger with hybrid fins structure is developed with supercritical carbon dioxide (S–CO 2) as the flow medium. Specifically, three-dimensional numerical simulations of PCHE are performed to study the flow heat transfer characteristics of hybrid fins. Besides, the effect of the different spacing of the airfoils on the flow heat transfer performance is studied. The results show that when the left and right adjacent spacing of the fins L b increases, the heat transfer performance of the heat exchanger improves while the pressure drop decreases. With the same pressure drop, the heat transfer of microchannel heat exchanger increases with the increase of the upper and lower adjacent spacing of the fins L c. Besides, the heat transfer performance of the new hybrid microchannel heat exchanger is much better than that of the conventional zigzag microchannel heat exchanger. The new hybrid fin microchannel heat exchanger shows better heat transfer performance at high Reynolds number, compared with that of the swordfish fin, airfoil fin and rhombic fin microchannel heat exchangers. [ABSTRACT FROM AUTHOR]

Here, to resolve the open problem of the second-law efficiency evaluation for heat exchangers, an efficiency-effectiveness method is developed from pure convection theory, where the entropy transfer efficiency defined as the outlet temperature ratio of cold and hot fluids exchanging entropy and local entropy generation number can measure the global and local irreversibilities of heat transfer. The efficiency and effectiveness are related by the inlet temperature ratio τ and capacity rate ratio φ , and their maxima subject to the local entropy generation number are determined for different flow arrangements. When τ = φ 2, the effectiveness maxima are 0.5/(1 + φ) and 1/(1 + φ) while the highest efficiencies are φ and unity for parallelflow and counterflow arrangements, respectively. The optimum operating points of counterflow exchangers, at which the equal outlet temperature τ T 1 ∞ (T 1∞ represents the hot inlet temperature) of two fluids with a critical capacity rate ratio τ induces uniform irreversibility, the effectiveness limit of 1 / (1 + τ) , and the efficiency limit of unity, are obtained. A linear temperature difference method is also developed based on the redefined convective and overall heat transfer coefficients, invariably yielding an effectiveness equal to the number of heat transfer units. This method has potentials to be extended to wet heat exchangers with phase-change flows. • The open question of second-law efficiency evaluation of a heat exchanger is resolved. • The heat transfer effectiveness and entropy transfer efficiency limits are presented. • The global and local irreversibilities of exchangers are measured by N S and N S,l. • Two optimum design criteria of exchangers are obtained subject to N S,l. [ABSTRACT FROM AUTHOR]

• Chemical equilibrium was introduced and a novel two-stage in-cylinder steam thermodynamic model was proposed. • A theoretical thermodynamic model considering in-cylinder steam assist and exhaust gases waste heat recovery was established. • The effects of the different working fluids on the in-cylinder steam assist cycle were revealed. • The effects of in-cylinder steam assist on thermal efficiency optimization under different working fluids were evaluated. Improving efficiency and reducing emissions are essential to achieving carbon peaking and carbon neutrality in transportation sector. As a carbon neutral fuel, hydrogen is widely considered the most promising fuel for future zero-carbon internal combustion power, while iso -octane, represented by gasoline, symbolizes the current hydrocarbon fuel utilized in modern internal combustion engines. In this study, the maximum indicated thermal efficiency of both hydrogen and iso -octane utilizing air (blending O 2 and N 2), oxy-fuel (blending O 2 and CO 2) and argon power cycle (blending O 2 and Ar) were investigated theoretically based on in-cylinder steam assist cycle. A theoretical thermodynamic model combining in-cylinder steam assist and exhaust gases waste heat recovery was established to explore the thermodynamic process of in-cylinder steam assist and systematically analyze the effects of different working fluids. Results show that the utilization of in-cylinder steam assist improves thermal efficiency under O 2 , N 2, and CO 2 working fluids, but limits the improvement of thermal efficiency under Ar. In addition, the maximum achievable steam temperature and mass are limited by the exhaust gases temperature and heat exchanger efficiency. When running with H 2 under 400 K steam temperature, the optimized water-to-gas ratios were 1.58, 1.13, 1.62, and 1.13 for O 2 , Ar, N 2 , and CO 2 , respectively, the maximum thermal efficiencies increased by 35.80 %, 0.28 %, 28.21 %, and 62.79 % compared with baseline condition. Meanwhile, the competition of overall specific heat ratio and working fluid mass under different working fluids leads to different thermal efficiency enhancement, such as Ar, the decrement of overall specific heat ratio under limited steam mass leads to thermal efficiency deterioration, which can be further improved as steam mass increased. [ABSTRACT FROM AUTHOR]

To address the issue of low efficiency in cooling heat exchangers at the deeper ends of mine fans, we propose a micro-unit approach for arranging the cooling water flow path within the heat exchanger. This method involves subdividing the heat exchanger into micro heat transfer units and determining the heat transfer characteristics of each individual unit through theoretical calculations and software simulations. Utilizing a computer program, these micro units are systematically arranged and combined to exhaust all possible cooling water flow paths. The ultimate objective is to derive the optimal structural arrangement of the cooling water flow path within the heat exchanger, with the goal of achieving the most efficient heat transfer effect. The findings reveal that the optimized structure, obtained through the micro-unit optimization method, achieves an average air outlet temperature of 311.65 K. This temperature is lower than that of the typical current-flow structure (311.88 K) and the typical counter-flow structure (311.68 K), indicating a superior heat transfer effect. Further examination demonstrates that the average air outlet temperature across all counter-flow structures is 311.68 K, which is notably lower than the average air outlet temperature of 311.90 K observed in the current-flow structure. This highlights the enhanced heat transfer effectiveness of the counter-flow structure. This novel method for optimizing the heat exchanger flow path applies the concept of finite element analysis to the optimization process, reducing computational and experimental costs. This approach is significant for improving the efficiency of heat exchangers. [ABSTRACT FROM AUTHOR]

However, while the heat stability of UK bovine milk is good, this can easily change in the newly formulated milk products. Essentially, Siemens has modelled the physical processes involved in spray-drying milk and milk-based products. Mike Lewis used his extensive experience to give a comprehensive overview of the heat stability of milk, paying particular attention to factors affecting heat stability and how this can be measured. [Extracted from the article]

The purpose of the present work was to determine the thermal performance of borehole heat exchangers, considering the influences of their geometric configurations and the thermophysical properties of the soil, grout and pipe wall material. A three-dimensional model was developed for the heat and mass transfer in soil (a porous medium) and grout, together with one-dimensional conductive heat transfer through the pipe walls and one-dimensional convective heat transfer of the heat transfer fluid circulating in the pipes. An algorithm was developed to solve the mathematical equations of the model. The COMSOL Multiphysics software was used to implement the algorithm and perform the numerical simulations. An apparatus was designed, installed and tested to implement the thermal response test (TRT) method. Two wells of depth 50 m were drilled in the Almaty region in Kazakhstan. Gravel and till/loam were mainly found, which are in accordance with the stratigraphic map of the local geological data. In each well, two borehole heat exchangers were installed, which were an integral part of the ground source heat pump. The TRT measurements were conducted using one borehole heat exchanger in one well and the data were obtained. The present TRT data were found to be in good agreement with those available in literature. The numerical results of the model agreed well with the present TRT data, with the root-mean-square-deviation within 0.184 °C. The TRT data, together with the predictions of the line-source analytical model, were utilized to determine the soil thermal conductivity ( λ g = 2.35 W/m K) and the thermal resistance of the borehole heat exchanger from the heat transfer fluid to the soil ( R b = 0.20 m K/W). The model was then used to predict the efficiencies of the borehole heat exchangers with various geometric configurations and dimensions. The simulation results show that the spiral borehole heat exchanger extracts the highest amount of heat, followed by the multi-tube, double U-type parallel, double U-type cross and single U-type. It is also found that the spiral configuration can save 34.6% drilling depth compared with the conventional single U-type one, suggesting that the spiral configuration is the best one in terms of the depth and the maximum heat extracted. The simulation results showed that (i) more heat was extracted with a higher thermal conductivity of grout material, in the range of 0.5–3.3 W/m K; (ii) the extracted heat remained unchanged for a thermal conductivity of pipe material higher than 2.0 W/m K (experiments in the range of 0.24–0.42 W/m K); (iii) the extracted heat remained unchanged for a volumetric flow rate of water higher than 1.0 m3/h (experimental flow rate 0.6 m3/h); and (iv) the heat extracted by the borehole heat exchanger increased with an increase in the thermal conductivity of the soil (experiments in the range of 0.4–6.0 W/m K). The numerical tool developed, the TRT data and simulation results obtained from the present work are of great value for design and optimization of borehole heat exchangers as well as studying other important factors such as the heat transfer performance during charging/discharging, freezing factor and thermal interference. [ABSTRACT FROM AUTHOR]

The scaling of high pressure heat exchanger between feedstock and reaction effluent in residue hydrogenation unit of J Petrochemical Company caused the decrease of heat exchange efficiency, which directly affected the stable operation and benefits of the unit. Through comparison with similar domestic units, it was found that the selection of medium in the shell and tube side of high pressure heat exchanger and the flow rate of fluid had a great impact on the scaling of high pressure heat exchanger. Based on the operation experience of similar units, the proposed measures to improve the scaling of high pressure heat exchanger were put forward. On the one hand, the feedstock properties and hydrogen-to-oil ratio during the operation of the unit were well controlled to slow down the scaling tendency of high pressure heat exchanger. On the other hand, by adding a high pressure heat exchanger, exchanging the medium of the shell and tube side, and optimizing the design of the heat exchanger, the heat exchange efficiency of the heat exchanger was fundamentally improved. [ABSTRACT FROM AUTHOR]

The present work focuses on a numerical investigation of nanofilms' (water/copper and water/aluminium) evaporation inside a heat exchanger by mixed convection flowing down on one channel plate. The channel was composed of two parallel vertical plates. The wetted plate was heated while the other plate was maintained isothermal and dry. The impact of the dispersion of different types of nanoparticles in the liquid film and their volume fraction in mass and heat exchange and the evaporation process has been analysed in this work. The results show that an increase of the nanoparticle inlet volume fraction enhances the efficiency of evaporation in heat exchangers. It is shown that an enhancement of 22% in evaporation rate has been recorded when the inlet nanoparticle volume fraction is elevated by 5%. The results show that the water–copper nanofluid had higher evaporation rate compared to water–aluminium nanofluid. [ABSTRACT FROM AUTHOR]

• A novel open-loop air cycle heat pump drying system is proposed. • The mathematical model built is verified to be both accurate and feasible. • Compared with electric heating drying system, the energy-saving rate of air cycle heat pump water heater system is 15∼27%. • The impact of different working conditions on system performance was determined. Different from conventional drying technology, the novel technology of an air cycle heat pump drying (ACHPD) system, using air as its working medium, is proposed to solve the problems of low energy efficiency, HCFC refrigerant use, and so on. A mathematical simulation model is constructed to evaluate system performance under various working conditions, and its verification via experimental results from a constructed test bench produced errors of temperature within ±1.6%, of drying rate within ±0.01%, and of system power within ±7%. Compared with a conventional electric heater drying (EHD) system, the energy-saving rate of the ACHPD system reaches about 15–27% when the mass evaporation rate increases from 0.75 kg h −1 to 3.45 kg h −1. Under set working conditions, an increase of inlet air flow rate (150–400 kg h −1) improved the dehumidification energy efficiency ratio (MER) by about 1%. However, the increase of inlet air temperature (10–40 °C) and relative humidity (30–80%) reduced MER by about 7% and 21% respectively. The efficiency improvements of heat exchanger (0.3–0.8) can improve the energy efficiency of system by 20%; however, the efficiency improvements of expander (0.55–0.8) and compressor (0.4–0.9) can deteriorate the energy efficiency of system by 17% and 36% respectively. These results would provide new technical references for the application of heat pump technology in drying field from a different perspective. [ABSTRACT FROM AUTHOR]

It has been reported that about 50% of the total amount of fuel in an oil refinery plant is consumed in crude oil and vacuum distillations. Thus, the heat exchanger networks of crude oil distillation units significantly affect the overall energy efficiency and CO2 emissions of refinery plants. Crude oil fouling in heat exchanger networks is one of the most troublesome problems in crude oil refineries. It reduces heat transfer amount or blocks the flows in tubes, leading to requiring additional fuel for the furnace following heat exchanger networks. Therefore, many cleaning methods have been developed. Mechanical cleaning of heat exchangers is the most effective method to mitigate the fouling in heat exchangers. However, it is necessary to open heat exchangers for cleaning. So, the timing of mechanical cleaning is limited because the normal refinery operation must be stopped. Therefore, to keep the good energy and economic performance of the refinery, it is necessary to predict the appropriate maintenance timing and to conduct a suitable cleaning. To find a suitable cleaning schedule or timing, the authors proposed a method for predicting fouling resistance in near future for crude oil fouling from actual online plant data in this research. The prediction results are in good agreement with the measured results, which demonstrate that the proposed method is effective for predicting the cleaning timing for the industry in the future. [ABSTRACT FROM AUTHOR]

Batch heat integration is a critical aspect of process integration. Also, designing heat exchanger networks (HEN) is an important step in heat integration. This article presents a segmented strategy for concurrently targeting and constructing the HEN for the batch process. This method is built on the framework of segregated targeting of utilities in order to design HEN. The main objective is to provide a holistic picture of segregated targeting and build the HEN in a batch process. This method clearly captures the role of individual streams, which may be helpful in exploring reuse and recycling options within the streams. The concept of a segregated time-level grand composite curve was created in order to design a segregated heat distribution network (SeHDN). In a batch process, heat transfer can occur in two ways: direct and indirect. The developed method is capable of incorporating both types of heat transfer, which is further demonstrated through an example. SeHDN depicts the distribution of heat at different time intervals. [ABSTRACT FROM AUTHOR]

The recuperative heat exchangers are an important part of the industrial plants. There are a number of such heat exchangers that differ in the arrangement of the streams. The knowledge of the flow arrangement of the streams is very important from a point of view of the heat exchangers calculations. There are various calculation methods, but only one takes into account the flow arrangement of the streams directly. The quantity that takes this into account is called the countercurrent index. The article deals with the determination of this quantity for a given recuperative heat exchanger.

The aim of this study was to develop a mathematical model with lumped parameters to investigate the energetic parameters of the heat pump with an internal heat exchanger (IHX). The developed mathematical model is validated with 25 tests using R134a as a working fluid. The results show that the maximum prediction error between the modeled and experimental results for the COP is 7.06%. The main objective of this paper was to investigate the COP value of a heat pump as a function of the efficiency of the internal heat exchanger and present a new equation to calculate the COP value. When the efficiency of IHX was increased from 0.65 to 0.95, the COP value increased by 5.41% under the conditions of minimum evaporation − 20 °C and maximum condensation temperature 90 °C. [ABSTRACT FROM AUTHOR]

In this study, the heat transfer and flow characteristics of TiO2‐H2O nanofluids with TiO2 mass fractions of 0.0, 0.1, 0.3, and 0.5 wt.% in corrugated and smooth double‐pipe heat exchangers were compared using numerical simulations. The results demonstrated that TiO2‐H2O nanofluids effectively enhanced the heat transfer compared to deionized water, and that the heat exchange capacity gradually increased with the TiO2 mass fraction. The corrugated pipe heat exchanger disturbed the fluid flow on both the shell side and pipe side, breaking the boundary layer and creating vortices in the corrugated zone. This provided a higher heat transfer capability than the smooth double‐pipe heat exchanger, but also increased the fluid flow resistance in the pipe. In general, the use of nanofluids and corrugated pipes was found to significantly improve the heat transfer efficiency of the double‐pipe heat exchanger. [ABSTRACT FROM AUTHOR]

Improving the energy efficiency in heat exchanger networks (HENs) remains a significant industrial problem, specifically in energy-intensive operations. A particular method for such an objective is the modification of HENs at the equipment-use level, where structural changes take place and units within the network are moved, replaced and/or removed. This practice is usually known as retrofit. The objective of a retrofit is to maximize the heat recovery using the minimum modifications possible and minimum retrofit cost. Traditional retrofit techniques would normally consider one type of heat exchanger (based on the original network) with no additional design features (i.e., heat transfer enhancement technologies). The expansion of such alternatives is limited by practical use and availability of theoretical methods. In this context, the inclusion of high-performance heat exchangers such as plate heat exchangers (PHEs) has not been widely explored, even when their design and operational advantages are known. In this work, a new step-by-step automated HENs retrofit approach based on Pinch Analysis is proposed. The approach is possible to identify the best modification, its location within the network, and its cost simultaneously. Moreover, to increase energy savings, this work presents a strategy that seeks to utilize high efficiency heat exchangers such as plate heat exchangers for retrofit. A distinctive feature of this new method is the ability to handle different minimum approach temperatures, given the different types of exchangers, within the optimization of HENs. Three cases are studied using this methodology to quantify the potential benefits of including PHEs in HEN retrofits, via the analysis of the retrofit cost. Results are compared with a baseline consisting in the same network, where only Shell-and-Tube-Heat-Exchangers (STHXs) are used. In addition, the results demonstrate that this methodology is flexible enough to be applied in a wide range of retrofit problems. [ABSTRACT FROM AUTHOR]

Open cell aluminum foam having high porosity has the potential to increase the efficiency of a heat exchanger and also to be used for diverse other functions. However, being prone to fail easily under tensile mechanical load, their thermal forming using a laser has been proposed in the literature. This work investigates the effect of laser parameters, orientation-position-curvature of scan path, the number of scans, and foam thickness on the bending angle achieved while forming 95% porous pure aluminum (99.7% aluminum) open cell foam plates using a diode laser. Furthermore, the capability of laser forming to produce developable and nondevelopable surfaces out of this foam has been demonstrated. Higher line energy gave a higher bending angle. Under the same line energy, the combination of higher power-higher scan speed produced a higher bending angle. In contradiction to laser forming of the sheet metal, no saturation or reduction in bending angle per scan pass was observed with an increase in scan pass number. This observation could be explained with the help of cell densification by previous scan passes leading to an increase in the coupling of more thermal energy for subsequent scan passes. Scan paths with increased curvature (or less radius) also produced higher bending due to a higher amount of cell collapse in the irradiated region. [ABSTRACT FROM AUTHOR]

A novel efficiency reduction model to tubular heat exchanger based on heat transfer losses by biofilm adhesion is proposed, which included a modified equation based on the real data-dependent time, seawater, hydrodynamics and heat transfer resistance using computational fluid dynamics (CFD). The biofilm growth model based on Verhulst model and experimental data has been obtained and simulated in a CFD software tool to analyze the tubular heat exchanger performance prediction cooled by seawater. The biofilm CFD model with appropriate fit, and the correlation coefficient (R2) values are between 0.97 and 0.99, was validated by experimental data obtained at different flow velocity. The final results of in/outlet difference temperatures were from 3.9 °C to 2.2 °C for different flow velocity with R2 > 0.97. The simulation results demonstrate that the novel CFD model is capable of predicting the efficiency losses during the development period of biofilm growth in in open-loop cooling seawater systems. [ABSTRACT FROM AUTHOR]

This paper designed a platelet heat exchanger in the solar thermal thruster and analyzed the unsteady-state conjugate heat transfer characteristics between heat exchanger and propellant. The conjugate heat transfer (CHT) computational fluid dynamics (CFD) simulation of the 3D model of the platelet under steady-state conditions was carried out with different mass flow rates to find the empirical correlation between the average Nusselt number and the average Reynolds number. The unsteady-state 1D simplified model of the heat exchanger was established using a loose coupling algorithm based on quasi-steady flow domain and finally verified by experiments. The results show that the platelet structure could heat the working medium to more than 2380 K with the heat transfer efficiency of 87% and produce a peak thrust of 0.57 N and specific impulse of 2200 m/s; in steady state, the outlet temperature and heat transfer efficiency of the heat exchanger were stable at 1950 K and 69%. Moreover, 1D model could accurately reflect the real heat exchange situation to a certain extent, the simulation error was less than 5% compared with the 3D model, and the calculation time was greatly shortened, making it more convenient to adjust the heat exchange strategy. The experimental results were consistent with the simulation results at the initial stage of heat exchange, and the difference was mainly reflected in the steady-state stage, which might be caused by the lack of precision of the experimental equipment. [ABSTRACT FROM AUTHOR]

Wastewater has significant potential as a source of clean energy. This energy can be used both within external sewer networks and on the scale of individual residential buildings, and the use of shower heat exchangers appears to be the most reasonable solution. However, in the case of Poland, the problem is still the unwillingness of society to use this type of solution, caused mainly by the lack of space for the installation of vertical drain water heat recovery (DWHR) units and the low efficiency of horizontal units. In response to this issue, the efficiency of a new compact shower heat exchanger designed to be mounted below the shower tray, as well as its linear counterpart, was investigated under various operating conditions. In addition, the financial efficiency of using the compact DWHR unit with average water consumption for showering was evaluated. For this purpose, discount methods were used to estimate the financial efficiency of investments. The study showed that the compact shower heat exchanger has higher efficiency than its linear counterpart. Depending on the temperature of cold water and the flow rate of both media through the heat exchanger, it achieves efficiencies ranging from 22.43% to 31.82%, while the efficiency of the linear DWHR unit did not exceed 23.03% in the study. The financial analysis showed that its use is particularly beneficial when the building uses an electric hot water heater. The investment's sensitivity to changes in the independent variables is small in this case, even with low water consumption per shower. The only exceptions are investment outlays. Therefore, the compact DWHR unit is a clean energy device, which in many cases is financially viable. [ABSTRACT FROM AUTHOR]

Thailand is an agricultural country with several agro-industrial by-products that can be processed into fuels. Although producing ethanol from agro-industrial by-products is an interesting option, the process of distilling ethanol from fermented agricultural products requires a high temperature to increase the ethanol concentration from 10% to 95%. In this research, solar ethanol distillation equipment incorporating a solar parabolic collector with a vacuum heat absorber tube to increase efficiency by reducing heat loss was designed and developed. An electronic device was used to control the distillation process, maintain the required temperature, and make suitable adjustments to the solar radiation acceptance angles of the parabolic solar collector. Ethanol dilution at concentrations of 10%, 15%, and 20%, and Sato (Thai Rice Wine) were used as the reactant in the distillation process. The result of distilling ethanol distillation with a semi-automatic control using a vacuum-tube parabolic solar collector showed that the thermal efficiency of the receiver was 12.61%, 13.93%, 18.58%, and 17.40%, respectively. The thermal efficiency of the heat exchanger was 11.27%, 10.76%, 13.35%, and 12.35%, respectively. The final concentration of ethanol was 67%, 76%, 82%, and 80%, respectively, and the amount of the distilled ethanol was 330 mL, 352 mL, 398 mL, and 360 mL, respectively. [ABSTRACT FROM AUTHOR]

In this research, the effect of using GO/ water nanofluid as a coolant fluid in an isothermal heat transfer system was studied. At first, to evaluate the atomic bond, chemical, and surface structure of the nanoparticles, XRD-FTIR and FESEM tests were used. Two-step method was used to prepared nanofluid then DLS test was utilized to examine the stability of the nanofluid. Thermal conductivity and the dynamic viscosity were measured experimentally from 25 to 75 ℃ and volume fractions of 0–0.15%. The maximum improvement in thermal conductivity is 11.2% at 0.15% and 75 ℃. Also The dynamic viscosity increased. The validity and uncertainty of the test results were examined. The heat transfer and turbulent flow of the nanofluid under a constant temperature boundary condition were investigated between 6000 and 18,700 Reynolds numbers. Various parameters such as the pressure drop, friction factor, convection heat transfer coefficient, and Nusselt number of the turbulent flow were evaluated. According to the results, the greatest increase in the convection heat transfer coefficient of the nanofluid was 34.7% compared to that of the base fluid. Also, the greatest enhancement in the friction factor was 9.64%. It can be stated that the improvement of the convection heat transfer coefficient dominantly affects the pressure drop so this nanofluid can be used as a coolant fluid in industrial systems. [ABSTRACT FROM AUTHOR]

In industry, the thermal flow reverse reactor (TFRR) is considered to be an effective means to reduce ventilation air methane (VAM) from fossil fuel operations. The purpose of VAM combustion is either to reduce the emission of greenhouse gas, to recover energy, or both these subjects. The heat exchanger tubes have been embedded on both sides of high-temperature zone of the regenerative oxidizer for heat recovery in this study to improve economy. The mathematical model is established, as well as the effects of inlet methane concentration and air flow rate on dynamic heat extraction characteristics of heat exchanger tubes under periodic conditions are investigated. The results show that sustainable and stable heat recovery can be achieved when the concentration is greater than 0.6 vol.% and the air flow rate is less than 596 m3/h. Heat extraction mainly depends on downstream heat exchange tubes. The asymmetry of heat transfer process between upstream and downstream heat exchanger tubes is analyzed. It is worth noting that the asymmetry is improved at high inlet methane concentration and low air flow rate. The heat recovery efficiency by the bilateral heat exchanger tubes is 61.72% at most, which provides a reliable theoretical basis for the heat extraction mechanism of the heat exchanger embedded in TFRR. [ABSTRACT FROM AUTHOR]

The present research utilizes an inverse 3D CFD technique, coupled with the least squares approach and laboratory temperature readings, to predict the suitable turbulence flow model and unknown heat transfer rates within a cubic hot box. This enclosure features four cylindrical horizontal tubes arranged in a diamond configuration, functioning as heaters to generate heat within the space. Furthermore, the heat dissipation from each tube, flow field and temperature contours are also established. The energy equation for tubes and the governing equations for air are solved by coupling. The present estimates are obtained assuming a constant heat transfer rate. The range of the Rayleigh number is from 60,294 to 76,824. Testing various turbulence models revealed that the zero-equation turbulence model reduces the root mean square discrepancy between the simulated thermal behavior and laboratory outcomes compared to other methodologies. To verify the chosen flow model’s accuracy, the Nusselt numbers and flow field distributions aress compared with existing correlations and interferometer photographs. The maximum errors between the estimates of heat loss and heat transfer rate and the corresponding values from previous studies are 44 and 28% for St = 0.036, 34 and 3% for St = 0.045, and 37 and 18% for St = 0.054. To assess the impact of tube surface and spacing on the flow field model, calculation results are compared with those from four square-arranged tubes, revealing a lack of existing studies on this specific investigation. [ABSTRACT FROM AUTHOR]

• First and second law analyses of newly oval-CGHEs are introduced. • Oval CGHEs exhibit superior heat transfer with a trading-off in irreversibility. • The irreversibility distribution pinpoints the irreversibility of the studied CGHEs. • The results show reduced irreversibility at the oval-CGHEs sidewalls. • Sensitivity analysis highlights key factors influencing the CGHE's irreversibility. Optimizing the heat transfer and thermodynamic efficiency of Ground Heat Exchangers (GHE) is crucial for maximizing the energy efficiency of Ground-coupled Heat Pump (GCHP) systems utilized in building heating and cooling applications. This study pioneers an effective approach of both the first and second laws of thermodynamics of the newly oval-shaped coaxial GHEs (oval-CGHEs), assessing heat transfer, thermohydraulic performance, and local entropy generation rate to explore the optimum design and operational conditions for heat exchange maximization and entropy generation minimization. Utilizing a three-dimensional numerical model validated by experimental results, this study examines the trade-offs between heat transfer improvements and entropy generation rate intensification of the oval-CGHEs in comparison to the typical circular-shaped CGHE (circle-CGHE) further than exploring the effect of key operational and design parameters and performing sensitivity analysis. The results reveal that oval-CGHEs exhibit higher irreversibility as a penalty for their superior heat transfer capabilities compared to traditional circular-shaped CGHEs (circle-CGHE), which can be mitigated by optimizing the position of the inner tube. Moreover, the study underscores the criticality of maintaining a balance between enhanced heat transfer and the associated rise in irreversibility, particularly concerning the factors of mass flow rates and installation depths. [ABSTRACT FROM AUTHOR]

• A thermo-hydraulic modeling of the plate-fin heat exchanger was performed. • Variations of physical properties for streams were considered in the model. • Investigation of longitudinal conduction heat transfer through walls was performed. • Phase change for natural gas occurs in the last segment of the heat exchanger. • Geometrical parameters mainly affect the high-pressure mixed refrigerant stream. Accurate modeling of a multi-stream plate-fin heat exchanger as a vital component in various industries is crucial in dominating its design. This study considered the main heat exchanger of a single mixed refrigerant process for modeling and simulation. First, the process was simulated with an efficient specific energy consumption. Then, a robust model was developed for the thermo-hydraulic performance of the heat exchanger. The model accuracy is enhanced by considering essential features such as multiple streams, multi-component flows, variation in physical properties, phase change phenomena, and longitudinal heat conduction. The temperature and pressure drop distribution for all streams in the multi-component two-phase parallel flow heat exchanger length are evaluated. The effect of geometrical parameters of fins is investigated on the heat exchanger thermal performance. Phase change occurs at the end of the heat exchanger due to the maximum temperature driving force between hot and cold streams. The results show a good agreement between the results of the proposed model and the commercial software, as well as numerical and experimental case studies. Then, the process simulation was linked to the PFHE model to simultaneously consider the effect of PFHE geometrical parameters on the simulation results. Also, the sensitivity analysis was performed to investigate the effect of operating conditions on Specific Energy Consumption. It can be seen that methane mole% has the most significant impact on the thermal efficiency of the heat exchanger. [Display omitted] [ABSTRACT FROM AUTHOR]

The article offers a preview of the TubePro 6 from Eddyfi Technologies, a cutting-edge tubing inspection and reporting software that enhances efficiency and accuracy in heat exchanger inspections with its redesigned interface, streamlined processes, and advanced reporting features.

Enhancing heat transfer rates while concurrently reducing pressure drop will significantly enhance the energy efficiency of industrial heat exchangers, thereby contributing to a cleaner and more sustainable environment in the future. This study explores the fluid flow of a novel combination solution in a helical heat exchanger under a constant heat flux across various Reynolds numbers (5000–17000) aiming to uncover synergies that enhance heat transfer efficiency while reducing drag for the first time. Two key performance metrics, namely Drag Reduction (DR) and Heat Transfer Enhancement (HTE), along with the thermal effective index, are introduced to evaluate both hydrodynamic and thermal characteristics. Under turbulent conditions, an aqueous solution containing Anionic PAM (100–500 ppm) obtains a noteworthy 43% DR at 500 ppm. Simultaneously, a colloidal solution of nano-SiO2 (500–3000 ppm) in deionized water demonstrates an impressive 47% HTE at 2000 ppm. Furthermore, this study introduces two novel terms, “heat transfer enhancement synergy” and “drag reduction synergy,” marking their debut in the literature. The investigation extends to exploring four Nano-SiO2_PAM combinations which is the novelty of the study, revealing an outstanding 93.3% synergy in HTE. Precisely, at Reynolds 14,000, the synergy between 100 ppm PAM and 2000 ppm SiO2 (named comb.20 as the best combination) attains a remarkable 73.76% in DR, showcasing a noteworthy thermal effectiveness reaching approximately 200%. Even for comb.20, at Reynolds 5000, the synergy achieves a notable 133.33% in DR and 76.22% in HTE, which is quite significant. This result is attributed to a complex formation that elongates the polymer chain due to the presence of nanoparticles around the polymer chain, effectively damping eddies. Furthermore, a novel set of correlations is proposed for the prediction of the Nusselt number of the aforementioned solutions, demonstrating a remarkable agreement with experimental data with a maximum error of 24%.Graphical Abstract: Enhancing heat transfer rates while concurrently reducing pressure drop will significantly enhance the energy efficiency of industrial heat exchangers, thereby contributing to a cleaner and more sustainable environment in the future. This study explores the fluid flow of a novel combination solution in a helical heat exchanger under a constant heat flux across various Reynolds numbers (5000–17000) aiming to uncover synergies that enhance heat transfer efficiency while reducing drag for the first time. Two key performance metrics, namely Drag Reduction (DR) and Heat Transfer Enhancement (HTE), along with the thermal effective index, are introduced to evaluate both hydrodynamic and thermal characteristics. Under turbulent conditions, an aqueous solution containing Anionic PAM (100–500 ppm) obtains a noteworthy 43% DR at 500 ppm. Simultaneously, a colloidal solution of nano-SiO2 (500–3000 ppm) in deionized water demonstrates an impressive 47% HTE at 2000 ppm. Furthermore, this study introduces two novel terms, “heat transfer enhancement synergy” and “drag reduction synergy,” marking their debut in the literature. The investigation extends to exploring four Nano-SiO2_PAM combinations which is the novelty of the study, revealing an outstanding 93.3% synergy in HTE. Precisely, at Reynolds 14,000, the synergy between 100 ppm PAM and 2000 ppm SiO2 (named comb.20 as the best combination) attains a remarkable 73.76% in DR, showcasing a noteworthy thermal effectiveness reaching approximately 200%. Even for comb.20, at Reynolds 5000, the synergy achieves a notable 133.33% in DR and 76.22% in HTE, which is quite significant. This result is attributed to a complex formation that elongates the polymer chain due to the presence of nanoparticles around the polymer chain, effectively damping eddies. Furthermore, a novel set of correlations is proposed for the prediction of the Nusselt number of the aforementioned solutions, demonstrating a remarkable agreement with experimental data with a maximum error of 24%. [ABSTRACT FROM AUTHOR]

Circular pipe heat exchangers, widely used in process industries, rely on passive heat transfer augmentation techniques like twisted tape inserts to enhance thermal performance. The challenge lies in identifying the optimal insert design. This study applies hybrid multi-criteria decision-making (MCDM) techniques to address this challenge, aiming to identify the best twisted tape insert configuration for maximizing heat exchanger efficiency. For developing the method, twenty-one passive enhancement techniques have been identified. This study employs a holistic approach, considering eight parameters (surface–volume ratio, Nusselt number, friction factor, thermal performance factor, total investment cost, cost per efficiency and CO2 emissions) across four criteria (geometric, thermo-hydraulic, economic and environmental criteria) to optimize resource utilization while reducing environmental impact and minimizing costs. The Entropy-CRITIC (Criteria importance through inter-criteria correlation) weighing method (ECWM) was employed to find the weights of all parameters, and ranking of alternatives was done by TOPSIS (Technique of order preference similarity to ideal solution), COPRAS (Complex proportional assessment) and CoCoSo (Combined compromise solution) MCDM methods. These hybrid approaches, combining objective weighting with MCDM ranking, facilitated the identification of ideal twisted tape inserts. To ensure the robustness of the MCDM methods, sensitivity analysis, Spearman rank correlation and rank reversal techniques were employed for validation. COPRAS emerged as the most robust MCDM method, indicating cross-cut twisted tape as the optimal solution for heat transfer augmentation. This research demonstrates the effectiveness of MCDM techniques in selecting optimal sustainable passive inserts for enhancing the thermal performance of circular pipe heat exchangers. [ABSTRACT FROM AUTHOR]

Heat exchanger studies have been conducted for several decades since the beginning of the development of heat transfer theories due to their widespread use in various industries. The ongoing research topics include heat exchanger efficiency, design parameter optimization, material development, and heat transfer technology exploration. Research has been continued to evolve nanofluid compositions, concentrations, and operating conditions that affect heat exchanger efficiency. They have used hybrid nanofluids in heat exchangers, which contain multiple types of nanoparticles or nanoparticles with additional additives, as hybrid nanofluids improve thermal performance. As a result, the development and optimization of hybrid nanofluids as a working medium in heat exchangers are gaining popularity, and the use of hybrid nanofluids in heat exchangers has already drawn a lot of interest as a viable strategy in industrial sectors. Therefore, such a surge of interest in using hybrid nanofluids in heat exchangers has resulted in a significant body of literature on this. In this review paper, the authors aim to incorporate the findings of these studies and offer a thorough evaluation of the state-of-the-art research on the application of hybrid nanofluids in various types of heat exchangers. This review provides a synopsis of the published literature on the efficacy of heat exchangers utilizing hybrid nanofluid. The researchers have also encountered and documented several challenges, including stability and aggregation, improving thermal conductivity, fluid flow characteristics, corrosion and material compatibility, cost and scalability, and determining the ideal size and shape of nanoparticles while considering environmental and health concerns. In addition, this review identifies research gaps in preventing agglomeration, ensuring nanoparticle dispersion, optimizing fluid composition to minimize flow effects, exploring and identifying materials compatible with hybrid nanofluids, investigating cost-effective methods for hybrid nanofluid production, and addressing scalability issues for widespread implementation in industrial heat exchangers. This review paper will be a valuable resource for researchers and practitioners seeking to overcome these challenges and advance the field of hybrid nanofluids for heat exchanger applications. [ABSTRACT FROM AUTHOR]

• The steady-state operation of high-temperature water flow boiling was investigated within 100–250 °C for space heat dissipation. • Four parameters of heat exchanger efficiency (HEE), heat transfer power (HTP), liquid-side outlet quality (LSOQ), and two-phase heat transfer coefficient (HTC) were analyzed under different operating pressures and mass flow rates. • The parameter values were calculated and variation rules were summarized. With the development of space nuclear reactors, the transmission and emission of a large amount of waste heat in space are inevitable. Because of its large heat transfer, clean nature, and safe working medium, flow boiling of high-temperature water is ideal for space applications. This study focuses on high-temperature heat dissipation and experiments on the flow boiling heat transfer of high-temperature water. The steady-state operation characteristics of high-temperature water flow boiling heat transfer in the operating temperature range of 100–250 °C are studied with an emphasis on the variations in heat exchanger efficiency (HEE), heat transfer power (HTP), liquid-side outlet quality (LSOQ) of the high-temperature heat exchanger, and two-phase heat transfer coefficient (HTC). The HTP can be improved to a peak of 16 kW under a moderate air mass flow rate, and the LSOQ can be increased to approximately 0.95. The maximum HTC in this system could reach approximately 2100 W/(m2*K), which offers significant design guidance for the high-temperature water flow boiling system. [ABSTRACT FROM AUTHOR]

• To investigate the accuracy of 3D borehole thermal resistance (R b,3D) and total internal thermal resistance (R a,3D). • To establish the 3D computational model incorporated with a four-resistance model technique to calculate R b,3D and R a,3D for 130 cases. • To Develop two prediction models: Response Surface Methodology (RSM) and the hybrid Deep Feedforward Neural Network-Genetic Algorithm (DFNN-GA). • To rigorously evaluate the performance of the prediction models using statistical metrics, such as R2, RMSE, MAE, and AARE. • The outcomes derived through the implementation of diverse statistical approaches showcase the proficiency of both the RSM and DFNN-GA predictive models in precisely predicting the values of R b,3D and R a,3D. The thermal efficiency of ground heat exchanger (GHEs) relies on optimizing borehole thermal resistance and total internal thermal resistance for cost-effective and efficient design. This study aims to establish a robust correlation among various parameters, including thermal conductivity of pipe, grout, and ground, borehole depth, borehole and pipe diameter, pipe-pipe distance, fluid velocity, and heat transfer rate of the ground, with the 3D borehole thermal resistance (R b,3D) and total internal thermal resistance (R a,3D). This exploration of eight influential factors results in an l-130 design matrix with 130 data points. A 3D computational model, utilizing a four-resistance method, accurately calculates R b,3D and R a,3D , while analyzing heat transfer in both solids and fluids. Two prediction models, Response Surface Methodology (RSM) and a hybrid Deep Feedforward Neural Network-Genetic Algorithm (DFNN-GA), establish the correlation between R b,3D and R a,3D and the eight variables. The results highlight the efficacy of the prediction models, achieving R2 values of 79.87% and 87.90% for RSM and 94.00% and 99.15% for DFNN-GA, corresponding to the predictive accuracy of R b,3D and R a,3D , respectively. Furthermore, lower RSME, MAE, and AARE values are observed. A rigorous comparative analysis assesses the relative effectiveness of these methodologies in achieving the research goals. [ABSTRACT FROM AUTHOR]