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Cement industry is both energy and emission intensive. This paper examines energy and environmental performance of cement plants in Ethiopia and Sweden. Energy intensity (thermal and electrical), alternative fuel (AF) share, CO 2 emission intensity and clinker substitute rate are applied to compare Ethiopia and Sweden cement industries. In most of the parameters, the Ethiopian cement industry ranks lower than the Sweden cement industry. The average thermal and electrical energy intensities for the Ethiopian cement industry is 3.76 gigajoules per tonne of clinker (GJ/t clinker) and 138.6 kilowatt hours per tonne of cement (KWh/t cement), respectively. Whereas, in Sweden cement industry, the average intensity is about 3.6 GJ/t clinker for thermal and 131 KWh/t cement for electricity. The emission intensity is 0.853 tonne CO 2 /tonne clinker (0.853t CO 2 /t clinker) in Ethiopia and 0.701t CO 2 /t clinker in Sweden. The alternative fuel (AF) share reaches 62% in Sweden cement industry, while in Ethiopia the share is almost insignificant (less than 1%). Adoption of specific energy efficiency measures, such as waste heat recovery power plant (WHRPP) and thermal fuel switch, significantly improved both the energy and environmental performances of Sweden cement industry. Therefore, this study suggests deployment of WHRPP and raise of AF share in Ethiopian cement industry, but the technical and economic viability of these measures should be investigated in the context of Ethiopian cement plants.

The integration of latent heat thermal energy storage (LHTES) units with heating systems in buildings is regarded as a promising technology for heating load management; however, so far a limited number of experimental studies have been reported that focus on space heating applications on a representative scale. In this study, we develop and test a 0.38 m3 LHTES unit containing cylindrically macro-encapsulated phase change materials (PCMs) with a melting temperature range of 44–53 °C and with gross mass of 154 kg. The unit has been tested with two tank orientations, horizontal and vertical. In the horizontal orientation tests, parametric studies show that increasing the difference between heat transfer fluid (HTF) supply temperatures and phase-change temperatures of PCMs, as well as increasing HTF flowrates, can both reduce the complete melting/solidification and complete charging/discharging time. Non-linear charging/discharging rates in PCMs are observed. The vertical orientation enables the forming of either a stratified or mixed flow regime in the tank. For charging, the stratified flow provides higher charging rates in PCMs compared to the mixed flow. When discharging the unit with a stratified HTF flow at 35 °C, lower HTF flowrates prolong the discharging time during which the released heat sustains an outlet temperature above 45 °C. Finally, comparisons between horizontal and vertical orientation tests reveal that although the vertical orientation can shorten the charging/discharging time by up to 20% for the entire unit to reach an energy density of 30 kWh/m3, it leads to decrease in PCM thermal capacity by at most 8.2%. The speculated cause of this loss is phase segregation suggested by observed fluid motions in PCM cylinders. This study comprehensively characterizes an LHTES unit providing insights to optimizing its operating strategies considering its coupling with space heating systems.

Fast urbanization process and promotion of life standard in China requires a great amount of energy input in building heating sector. North China now faces challenges of upgrading existing fossil fuel based high emission district heating systems into more environmental friendly heating systems. South China is discussing to choose proper building heating solutions for new and existing buildings which lack proper heating facilities. Renewable heating technologies such as ground source heat pump and air source heat pump are candidates to upgrade traditional heating solutions such as fossil fuel boilers and electric heaters. In order to find the most feasible building heating solution for different geolocations of China, this paper proposes a spatial data based techno-economic and environmental analysis methodology to fulfill such research gap. Case studies are carried out in two selected cities by using proposed methodology. Evaluation model shows that, heat pumps is quite competitive in south China compared with electric heaters, whereas in north China heat pumps have to reach several preconditions to be competitive with coal boiler district heating system under current techno-economic and environmental situations. In north China, a heat pump should reach a minimum seasonal coefficient of performance of 2.5–3.7 (for ground source heat pump) or 2.7–3.0 (for air source heat pump) to become CO2 and PM2.5 emission neutral as well as economically competitive compared with coal boiler district heating system. The advantage of proposed methodology is its simplicity in execution and could be repeated to other areas as the data required are available.

With continuing of urbanization, improving of life quality as well as combating against air pollution, China is facing comprehensive challenges to supply modem clean heating to a majority of its ci ...

Recently the interest in solar thermal cooling has been growing for Air Conditioning (AC) applications. This paper presents an applied experimental and numerical evaluation of a novel triple-state sorption solar cooling module. The performance of a LiCl-H2O based sorption module (SM) for cooling/heating system with integration of an external energy storage has been evaluated. The dynamic behavior of the SM, which can be driven by solar energy, is presented. Two PCM assisted configurations of the SM have been studied herein; (i) PCM assisted sorption module for cooling applications (ii) PCM assisted sorption module for heating applications. Initially, an experimental investigation was carried out to evaluate the charging/discharging process of the SM without external energy storage. Secondly, the initial experimental configuration was modeled with a PCM integrated storage compartment. The PCM storage compartment was connected to the Condenser/Evaporator (C/E) of the SM. The temporal history of the sorption module's C/E and PCM storage, the cyclic and average performance in terms of cooling/heating capacity, cooling/heating COP, and the total efficiency were experimentally and numerically investigated. Furthermore, PCM charging/discharging power rate and solidification/melting process of the PCM in the integrated storage compartment to the SM were predicted by the model.

Fossil fuel based building space heating and cooling contribute to more than 10% total final energy consumption in China. Consequent carbon dioxide and air pollutants emissions bring about atmospheric pressure and associated respiratory diseases. Seawater heat pumps as a candidate sustainable building space heating and cooling solution can alleviate such environmental pressure since China has a long coastline and many coastal cities have the possibility for seawater heat pump implementation. However, stakeholders are still suffering from insufficient understanding of seawater heat pumps feasibility in different coastal cities of China from techno-economic, environmental and geographical perspectives. This paper proposes a systematic method to evaluate seawater heat pump potential in different locations of China considering various local spatial parameters in the source and sink side of the energy system. A key performance indicator system is introduced to quantitatively analyze the relative advantages and disadvantages of applying seawater heat pumps compared with status-quo systems. Quantitative evaluation results show that seawater heat pumps have a higher potential in north Chinese coastal cities from techno-economic point of view when compared with existing heating and cooling systems. Environmentally, seawater heat pumps have to reach a critical seasonal coefficient of performance value to guarantee its potential in carbon emissions saving. In south Chinese coastal cities, seawater heat pumps have to reach a more satisfactory system efficiency and a more competitive system cost in order to exploit its full advantages over status-quo systems from techno-economic perspectives. Environmentally, seawater heat pumps are more attractive than competing technologies in south cities. Also, north Chinese cities are geographically more feasible for seawater heat pumps applications compared with south cities. QC 20200103 STINT - NSFC

This experimental study investigated the application of fluid flow pulsations for in-tube flow boiling heat transfer enhancement in an 8 mm smooth round tube made of copper. The fluid flow pulsations were introduced by a flow modulating expansion device and were compared with continuous flow generated by a stepper-motor expansion valve in terms of the time-averaged heat transfer coefficient. The cycle time ranged from 1 s to 7 s for the pulsations, the time-averaged refrigerant mass flux ranged from 50 kg m−2 s−1 to 194 kg m−2 s−1 and the time-averaged heat flux ranged from 1.1 kW m−2 to 30.6 kW m−2. The time-averaged heat transfer coefficients were reduced from transient measurements immediately downstream of the expansion valves with 2 K and 20 K subcooling upstream, resulting in inlet vapor qualities at 0.05 and 0.18, respectively, and covered the saturated flow boiling range up to the dry-out inception. Averaged results of the considered range of vapor qualities, refrigerant mass flux and heat flux showed that the pulsations at low cycle time (1 s) improved the time-averaged heat transfer coefficients by 5.6% and 2.2% for the low and high subcooling, respectively. However, the pulsations at high cycle time (7 s) reduced the time-averaged heat transfer coefficients by 1.8% and 2.3% for the low and high subcooling, respectively, due to significant dry-out when the flow-modulating expansion valve was closed. Furthermore, the flow pulsations were visualized by high-speed camera to assist in understanding the time-periodic flow regimes and the effect they had on the heat transfer performance.

The majority of Aquifer Thermal Energy Storage (ATES) systems studies have been conducted in aquifer systems located in large sand aquifers. Esker formation present a more challenging geometrical complexity compared to typical sand aquifers. This study aims to conduct comprehensive and long term performance evaluation of doublet type ATES system in esker geological formation in Stockholm, Sweden. The total heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. The licensed total amount of water extraction and injection is 50 liters per second with undisturbed groundwater temperature of 9.5°C. Over the first three storage cycles, the average injection and extraction temperatures for the warm side are 13.3°C and 12.1°C, and for the cold side 7.6°C and 10.5°C. The average temperature differences across the main heat exchanger from the ATES side are 4.5 K during winter and 2.8 K during summer which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. This was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is the oversizing of the heat pumps which were designed to be coupled to larger thermal loads as compared to the ones in the final system implementation. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the paper discusses the limitations of currently used energy and thermal key performance indicators (KPI) for ATES and propose an additional thermal KPI named heat exchanger efficiency balance ( β HEX ) that connects and evaluate the optimum operational point of temperature differences from both the building and ATES prospective. In addition to ATES energy and hydraulic KPIs, β HEX can contribute in providing more complete picture on the ATES-building interaction performance as well as highlights if the losses in energy recovery from ATES are due to the subsurface processes or building energy system operation which has been proven to be critical for the optimum ATES performance.

The dynamics and heat transfer characteristics of flow boiling bubble train moving in a micro channel is studied numerically. The coupled level set and volume of fluid (CLSVOF) is utilized to track interface and a non-equilibrium phase change model is applied to calculate the interface temperature as well as heat flux jump. The working fluid is R134a and the wall material is aluminum. The fluid enters the channel with a constant mass flux (335 kg/m2 ∗ s), and the boundary wall is heated with constant heat flux (14 kW/m2). The growth of bubbles and the transition of flow regime are compared to an experimental visualization. Moreover, the bubble evaporation rate and wall heat transfer coefficient have been examined, respectively. Local heat transfer is significantly enhanced by evaporation occurring vicinity of interface of the bubbles. The local wall temperature is found to be dependent on the thickness of the liquid film between the bubble train and the wall.

This experimental study investigates an active method for flow boiling heat transfer enhancement by means of fluid flow pulsation. The hypothesis is that pulsations increase the flow boiling heat transfer by means of better bulk fluid mixing, increased wall wetting, and flow-regime destabilization. The fluid pulsations are introduced by a flow modulating expansion device and are compared with continuous flow by a stepper-motor expansion valve in terms of time-averaged heat transfer coefficient. The cycle time ranges from 1 to 9 s for the pulsations. The time-averaged heat transfer coefficients are reduced from transient measurements immediately downstream of the expansion valves at low vapor qualities. The results show that the pulsations improve the time-averaged heat transfer coefficient by 3.2% on average at low cycle time (1 to 2 s), whereas the pulsations may reduce the time-averaged heat transfer coefficient by as much as 8% at high heat flux (q ⩾ 35 kW/m2) and cycle time (8 s). The latter reduction is attributed to a significant dry-out that occurs when the flow modulating expansion valve is closed. Additionally, the effect of fluid flow pulsations is found to be statistically significant, disregarding the lowest heat flux measurements.

Multi bubbles interaction and merger in a micro-channel flow boiling has been numerically studied. Effects of mass flux (56, 112, 200, and 335 kg/m2 ∗ s), wall heat flux (5, 10, and 15 kW/m2) and s ...

A numerical study on the transition from slug flow (or elongated flow) to annular flow of convective boiling under high heat flux in a micro-channel with diameter of 0.4 mm is conducted. A constant ...

The EU innovation effort to address grand societal challenges is facing an increasing divide. The C-Extended Erasmus+ Strategic Partnership project has the vision to help join this divide by extend ...

This study investigates the thermal performance of laminar single-phase flow in an additively manufactured minichannel heat exchanger both experimentally and numerically. Distilled water was employed as the working fluid, and the minichannel heat exchanger was made from aluminum alloy (AlSi10Mg) through direct metal laser sintering (DMLS). The minichannel was designed with a hydraulic diameter of 2.86 mm. The Reynolds number ranged from 175 to 1360, and the heat exchanger was tested under two different heat fluxes of 1.5 kWm−2 and 3 kWm−2. A detailed experiment was conducted to obtain the thermal properties of AlSi10Mg. Furthermore, the heat transfer characteristics of the minichannel heat exchanger was analyzed numerically by solving a three-dimensional conjugate heat transfer using the COMSOL Multiphysics® to verify the experimental results. The experimental results were also compared to widely accepted correlations in literature. It is found that 95% and 79% of the experimental data are within ±10% range of both the simulation results and the values from the existing correlations, respectively. Hence, the good agreement found between the experimental and simulation results highlights the possibility of the DMLS technique as a promising method for manufacturing future multiport minichannel heat exchangers.

Heat exchangers with mini- and micro-channel components are capable of high energy exchange due to their incumbent large surface area to volume ratio. Concurrently, recent advances in additive manufacturing simplify the creation of metallic minichannels that incorporate turbulators for heat transfer enhancement. As part of the development of a minichannel heat exchanger with turbulators, this study analyzes the three-dimensional conjugate heat transfer and laminar flow in a minichannel heat exchanger equipped with rectangular winglet vortex generators (VGs) through numerical simulation. The minichannels have a hydraulic diameter of 2.86 mm and are assumed to be made from aluminum alloy AlSi10Mg. This material is one of the popular alloys in the additive manufacturing industry (three-dimensional (3D) printing) because of its light weight and beneficial mechanical and thermal properties. The working fluid is distilled water with temperature-dependent thermal properties. The minichannel is heated by a constant heat flux of 5 W cm−2 and the Reynolds number is varied from 230 to 950. The simulations are performed using the COMSOL® platform, which solves the governing mass, momentum, and energy equations based on the finite element method. The effect of the VG design parameters, which include VG angle of attack, height, length, thickness, longitudinal pitch, and distance from the sidewalls, is investigated. It is found that the generation of three-dimensional vortices caused by the presence of the vortex generators can notably boost the convective heat transfer, at the cost of increased pressure drop, potentially reducing the heat exchanger size for a given heat duty. A sensitivity analysis indicates that the angle of attack, VG height, VG length, and longitudinal pitch have the most significant effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and distance from the sidewalls only had minor influences on the heat exchanger performance over the studied range of design parameters.

Decarbonizing the district heating sector is a key measure to achieve the 2040 net-zero emissions target for Stockholm City. One significant question to answer is to find out the locations of all the clean non-fossil fuel heat sources that could be used for district heating within the city’s administrative boundary, and to evaluate how much heat could be extracted from these heat sources. This paper maps out both the geolocations and the technical potentials of the clean non-fossil fuel heat sources for densely populated Stockholm City region, using Geographical Information System based integrative-analysis method. The mapping achieves 1-meter high-resolution and provides integrated open datasets to overcome the data availability issue. The mapping results show that a great number of clean and non-fossil fuel heat sources are available for district heating in Stockholm City. By fully unlocking the potentials of these heat sources, around 7054 GWh heat energy is estimated to be possibly exploited per year, which could cover 100% of the existing district heating energy requirement in Stockholm City. The potential share of each mapped heat source is: water bodies 48.3%, data centers 45.4%, supermarkets 4.5%, underground subway stations 0.8%, sewage plants 0.5%, shallow geothermal 0.3% and ice rinks 0.2%. A total of 9 heat sources clusters are identified, which could be prioritized for clean heating energy exploitation. By using the high-resolution mapping, the district heating utilities could plan the capacity in a forward looking way according to the local heat source availability. The method pipeline developed in this study could be recommended to other cities with district heating needs and assist their clean district heating transition roadmap design.

This study aims to characterize experimentally the heat transfer in micro-milled multi-microchannels copper heat sinks operating with flow boiling, in the attempt to contribute to the development of novel and high heat flux thermal management systems for power electronics. The working fluid was R-134a and the investigation was conducted for a nominal outlet saturation temperature of 30 ∘C. The microchannels were 1 cm long and covered a square footprint area of 1 cm2. Boiling curves starting at low vapor quality and average heat transfer coefficients were obtained for nominal channel mass fluxes from 250 kg/m2s to 1100 kg/m2s. The measurements were conducted by gradually increasing the power dissipation over a serpentine heater soldered at the bottom of the multi-microchannels, until a maximum heater temperature of 150 ∘C was reached. Infrared thermography was used for the heater temperature measurements, while high-speed imaging through a transparent top cover provided visual access over the entire length of the channels. The average heat transfer coefficient increased with the dissipated heat flux until a decrease dependent on hydrodynamic effects occurred, possibly due to incomplete wall wetting. Depending on the channel geometry, a peak value of 200 kW/m2K for the footprint heat transfer coefficient and a maximum dissipation of 620 W/cm2 at the footprint with a limit temperature of 150 ∘C could be obtained, showing the suitability of the investigated geometries in high heat flux cooling of power electronics. The experimental dataset was used to assess the prediction capability of selected literature correlations. The prediction method by Bertsch et al. gave the best agreement with a mean absolute percent error of 24.5%, resulting to be a good design tool for flow boiling in high aspect ratio multi-microchannels as considered in this study.

A three dimensional numerical study on bubble growth and merger in a micro-channel with diameter of 0.64 mm has been conducted. The working fluid is R134a and the wall material is steel. The inlet Reynolds number is set at 549 in order to keep the flow in laminar regime. Two different heat fluxes ( 14 and 28 kW m 2 ) are supplied to the wall to heat up the fluid. The coupled level set and volume of fluid (CLSVOF) method is used to capture the distorted two-phase interface. An evaporation model is also implemented through UDF (User defined function). The combination of these two methods has successfully eliminated spurious velocities which is a common problem in two phase flow simulation. The boiling and merger processes are well-predicted by the simulation. It is found that the whole process can be divided into three sub-stages: sliding, merger, and post-merger. The dynamics and heat transfer are found to be different in these stages. The evaporation rate is much higher in the first two stages due to the thermal boundary layer effects.

Three-dimensional (3D) printing, known as additive manufacturing, provides new opportunities for the design and fabrication of highly efficient industrial components. Given the widespread use of this technique by industries, 3D printing is no longer limited to building prototypes. Instead, small-to-medium scale production units focus on reducing the cost associated with each part. Among the various industrial components that can be developed with this manufacturing technology are heat transfer components such as heat exchangers. To this end, this study investigated the heat transfer characteristics of minichannel-based heat exchangers embedded with longitudinal vortex generators, both experimentally and numerically. Three enhanced prototypes with different vortex generator design parameters and a smooth channel as a reference case were printed with an aluminum alloy (AlSi10Mg) using direct metal laser sintering (DMLS). The rectangular minichannel had a hydraulic diameter of 2.86 mm. Distilled water was used as the test fluid, and the Reynolds number varied from 170 to 1380 (i.e., laminar flow). Prototypes were tested under two different constant heat fluxes of 15 kW m−2 and 30 kW m−2. The experimental results were verified with a commercial simulation tool, Comsol Multiphysics®, using the 3D conjugate heat transfer model. In the case of the smooth channel, the experimental results were also compared with well-known correlations in the field. The results showed that 95% and 79% of the experimental data were within 10% of the numerical simulation results and the values from the existing correlations, respectively. For the channel enhanced with the vortex generators, the numerical predictions agreed well with the experimental results. It was determined that the vortex generators can enhance the convective heat transfer up to three times with the designed parameter. The findings from this research underline the potential of additive manufacturing in the development of more sophisticated minichannel heat exchangers.

This paper presents a methodology for designing Laboratory Borehole Storages (LABS) intended to generate reference Thermal Response Functions (TRFs) for model validation. The design method is based ...

Latent heat thermal energy storage (LHTES) has been receiving increasing attention from researchers and engineers. A practical LHTES installation requires a deep understanding of phase change material’s (PCM’s) thermal behavior under thermal property testing and realistic operating conditions. To enrich this understanding, an experimental study on a commercial sodium acetate trihydrate-based PCM (Climsel C58) is presented in this article. C58 was characterized with two test methods: T-history tests and full-scale LHTES tests. The results are presented and discussed to exhibit the thermal behavior of C58 with these two test methods and the variations between them. With T-history tests, the thermal properties of C58 such as melting/solidification temperature range (57–61 °C/55–50 °C) and latent heat of fusion (216 kJ/kg) were determined. In full-scale LHTES tests, a parametric study was conducted to investigate the effects of heat transfer fluid flowrate and operating temperature range on the thermal performance of a 0.38 m3 storage prototype containing cylindrically macro-encapsulated C58. Moreover, longitudinal and radial PCM temperature distributions in full-scale tests were analyzed, suggesting the presence of phase separation. In general, C58 behaved differently between the two test methods regarding phase separation (negligible in T-history tests), supercooling effects (within 3 K in full-scale but up to 10 K in T-history tests), and thermal energy storage capacity (10% lower in full-scale tests). When using C58 or other salt hydrate-based PCMs for large-scale heat storage, these thermal behavior differences between the property-measurement and the application-oriented environments should be properly addressed in the design stage to ensure performance.

The present deliverable defines the boundary conditions for the performance assessment of the proposed solar heating technology based on the novel Seasonal Thermal Energy Storage (STES) system. The first aim is to characterize the concerned climate zones, Cold or Temperate, that correspond to South/Central/North Europe, with different uses, habits, and constraints as concerns energy consumption. Also, Nearly Zero-Energy Building (NZEB) standards are considered. All available data will be used for this purpose, such as other European projects (e.g. ZERO-PLUS [1], TABULA [2], EPISCOPE [3]), international projects (e.g. IEA-EBC Annex 66), current European standards (e.g. EN12309:1-7; 2014 for gas-driven sorption heat pump), policy papers, and EC Communications and Recommendations. The second aim is to characterize and classify the typologies of residential buildings, with specific focus to solar active houses, in the selected climate zones, in order to identify potential adopters of the developed system. The classification will be carried out in terms of construction age, energy efficiency, and country-related characteristics, including architectural configuration, residential unit size and key geometry indicators, type of management system, etc.

Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs. QC 20181106 Deep Boreholes for Ground-Source Heat Pumps

A primary motivation underlying the research on room-temperature magnetic refrigeration is reaching energy efficiency levels beyond what is achievable with vapor-compression technology. However, the goal of building commercially viable magnetic refrigeration systems with high performance and competitive price has not been achieved yet. One of the obstacles to reach this goal is the inadequate properties of the currently existing magnetocaloric materials. In this article, the needed improvements in the properties of the magnetocaloric materials are investigated. Two existing vapor-compression refrigerators are used as reference for the required performance, and magnetic refrigerators are simulated using a numerical model. Apart from the requirements such as uniformity of transition temperature for each layer, small increment in transition temperature in adjacent layers, and mechanical strength of the materials, the study shows that for the investigated cases materials with adiabatic entropy change 2.35 times larger than the existing materials are needed to outperform vapor-compression systems. QC 20181008

Nowadays, China faces challenges of further implementing heat pump technology for meeting building heating and cooling demand. The utilization of heat pumps, especially ground source heat pump (GSHP) is associated with a number of geological, hydrological as well as meteorological criteria. Thus it is essential to systematically address the feasibility of ground source heat pumps application using quantitative evaluation. Spatial data analysis is a method widely used in energy field to investigate renewable energy potential. Therefore, this study strives to provide an estimation of electricity driven GSHP’s potential in north China using spatial data assisted tools. Followed by a case study using the methodology recommended, a spatial data assisted GSHP potential evaluation model is built for Qingdao city in north China. The evaluation model is constructed and analyzed through spatial data processing software visualized by ground source heat pump potential maps. The result maps show that, places with most potential of GSHP application locate in south Qingdao close to the sea. Such places have a higher ground extractable heat and relatively low drilling cost. QC 20200103 STINT - NSFC

The advantages of using Al 2 O 3 , TiO 2 , SiO 2 and CeO 2 nanofluids as coolants have been investigated by analysing the combined effect of nanoparticles on thermophysical properties and heat transfer coefficient. The thermal conductivity and viscosity of these nanofluids were measured at two leading European universities to ensure the accuracy of the results. The relative thermal conductivity of nanofluids agreed with the prediction of the Maxwell model within +/− 10% even at elevated temperature of 50 °C indicating that the Brownian motion of nanoparticles does not affect thermal conductivity of nanofluids. The viscosity of nanofluids is well correlated by the modified Krieger–Dougherty model providing that the effect of nanoparticle aggregation is taken into account. It was found that at the same Reynolds number the advantage of using a nanofluid increases with increasing nanofluid viscosity which is counterintuitive. At the same pumping power nanofluids do not offer any advantage in terms of cooling efficiency over base fluids since the increase in viscosity outweighs the enhancement of thermal conductivity.

Experimental results on dryout of seven refrigerants (R134a, R1234yf, R152a, R22, R245fa, R290 and R600a) in small, single vertical tubes under upward flow conditions are reported in this study. The experiments were conducted under a wide range of operating conditions in stainless steel tubes (0.64–1.70 mm and 213–245 mm heated length). The effects of operating parameters like mass flux, vapor quality, saturation pressure and channel size are discussed in detail. In general, dryout heat flux increased with increasing mass flux, and with increasing tube diameter. No effect of varying saturation temperature was observed. The experimental findings were compared with well-known macro and micro-scale correlations from the literature and it was found that Wu’s correlation (in modified form) quite satisfactorily predicted the whole database. A new correlation for prediction of heat flux at dryout conditions is also proposed.

Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf in a vertical stainless steel test section (1.60 mm inside diameter and 245 mm heated length) under upward flow conditions are reported in this article. The experiments were carried out at 27 and 32 °C saturation temperatures with five mass fluxes in the range of 100–500 kg/m 2 s while the applied heat flux was in the range of 5–130 kW/m 2 . The experiments were carried out with gradual increase of the applied heat flux til completion of dryout. Under similar conditions, tests were repeated with R134a in the same test setup to compare thermal performance of these two refrigerants. The results showed that boiling heat transfer was strongly controlled by the applied heat flux and operating pressure with insignificant dependence on mass flux and vapor quality. The frictional pressure drop increased with mass flux and vapor quality and decreased with increasing saturation temperature as expected. Signs of dryout first appeared at vapor qualities of 85%, with the values generally increasing with increasing mass flux. The effect of varying system pressure was insignificant. The experimental results (boiling heat transfer, pressure drop and dryout heat flux) were compared with the predictions from well-known correlations (for macro and micro-scale channels) from the literature.

This paper presents a useful knowledge of ejector working principles and the versatility and diversity of its applications in refrigeration technologies. Various ejector refrigeration systems are described with the associated studies, and categorized as conventional ejector refrigeration system, advanced ejector refrigeration systems, combined refrigeration systems and ejector enhanced vapor compression systems. This paper also presents the important elements that affect the optimum performance of the ejector system, and the results of studies that have generally confirmed their energy saving, great potential for large refrigerating temperature scales and performance enhancement.

Refrigerant-related environmental concerns forced legislative bodies to phase out some types of refrigerants, namely, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and in the near ...

This paper presents a comprehensive investigation of an ejector refrigeration system using conventional and advanced exergy analysis. Splitting the exergy destruction within each system component into endogenous/exogenous and avoidable/unavoidable parts provides additional useful information and improves the quality of the exergy analysis. Detailed calculations of the exergy destruction parts are schematically illustrated. Conventional exergy analysis indicates that about half of the total exergy destruction is caused by the ejector and about one quarter occurs in the generator. The advanced exergy analysis reflects the strong interactions between system components. The ejector has the highest priority to be improved, followed by the condenser and then the generator. The temperature difference in the condenser has the largest influence on the exergy destruction compared to that in the generator and the evaporator, and the ejector efficiencies are also very crucial for the exergy destruction. The system performance can be largely enhanced through improvements of the ejector and the condenser as well as the generator.

This article investigates the influence of temperature, concentration, and size of nanoparticles, and addition of surfactants on dynamic viscosity of water-based nanofluids containing alumina (Al2O ...

In this study a methodology is applied to quantify the effect of evaporator maldistribution on operating costs of air–water heat pumps. The approach is used to investigate the cost-effectiveness of two technologies enabling to counteract maldistribution: a flash gas bypass setup and the individual superheat control in parallel evaporator channels. In the total cost of ownership analysis, different scenarios for climatic conditions, severity of maldistribution, and economic framework are considered. Results show that the flash gas bypass system is cost-effective only in a few conditions, namely severe maldistribution, high electricity prices, and colder climate. Investment in the individual superheat control technology, however, can be quickly amortized in many scenarios. For the warmer climate zone with a small number of operating hours counteracting of maldistribution does not pay off under the used economic assumptions.