最新刊期
卷 45 ， 期 2 ， 2024
- 摘要：Lubricating oil is a key factor affecting the performance and reliability of transcritical CO2 heat pump air conditioners dealing with complicated application environments and the requirements of new energy vehicles. The type of oil products and the amount of charged oil play an important role in maintaining high performance and ensuring the safe and stable operation of the system. This study discusses the function and influence of lubricating oil in transcritical CO2 automotive heat-pump air conditioners. Several common lubricating oils used in CO2 automobile heat-pump air conditioners are summarized, and the performance of each lubricating oil is compared. The effects of adding lubricating oil on the performance of each component and the overall performance of the transcritical CO2 heat-pump air-conditioning system are analyzed. Lubricating oil reduces the abrasion and working noise of moving parts and prevents refrigerant leakage and excessive discharge temperature in the compressor. However, excessive oil accumulation in the compression chamber leads to reduced volumetric efficiency and increases power consumption. In the heat exchanger and pipeline, the oil slick that forms on the heat exchanger wall increases the flow resistance and thermal resistance. Simultaneously, oil has an effect of restraining nuclear boiling and bubble disturbance in the evaporator, which deteriorates two-phase heat transfer. Finally, the existing research results, conclusions, and key research directions in related fields are discussed.关键词：lubricating oil;CO2;automotive air conditioning;oil circulation rate866|699|0发布时间：2024-07-18
- 摘要：Vapor-injection heat pump (VIHP) technology has become a research hotspot in the field of energy in recent years owing to its advantages of high efficiency, energy saving, and environmental protection under low-temperature conditions. The current research status of VIHP technology is stated based on the existing literature. The application type, compressor type, implementation method, and optimization research are discussed in depth. The advantages and disadvantages of improving the performance of VIHP systems are compared and analyzed. Finally, in combination with existing research problems, the development trend of VIHP is envisioned, thereby providing a reference for future research applications of VIHP technology.关键词：vapor injection;heat pump;application type;compressors;performance optimization839|1221|0发布时间：2024-07-18
- 摘要：Driven by the compliance of the Kigali Amendment to the Montreal Protocol on substances that deplete the Ozone Layer and the "carbon peak and carbon neutrality" strategy, refrigerant substitution has become one of the most important hot spots in the R&AC(refrigeration and air conditioning) field. Using low-GWP HFO refrigerants, which have similar thermal properties to natural refrigerants, as alternatives to achieve phase-down of HFCs, represents an appropriate replacement technology. However, with the announcement of the EU’s PFAS restriction proposal in February 2023, some concerns regarding the future of HFOs have emerged, which could affect global refrigerant substitution development. Therefore, this study introduces PFASs and analyzes their relationship with fluorinated refrigerants. We then interpret the formation and key contents of the proposed PFAS law. Finally, this paper summarizes the views of different fields on this issue to provide discernment and reference values for the formulation of future refrigerant substitution programs.关键词：refrigerant substitution;EU PFAS restriction;PFASs;HFOs;Kigali Amendment734|1203|0发布时间：2024-07-18
- 摘要：As the main energy-consuming equipment of the centralized air-conditioning system, the improvement of the energy efficiency of water chiller (heat pump) units has a significant role in promoting the realization of the "dual carbon" target. GB/T 18430, as a basic standard for plumbing units, is nearing the end of its revision, and the accompanying energy efficiency standards GB19577–2015 need to be revised and upgraded accordingly. In this study, the assessment method of comfort-type water chiller (heat pump) units in GB/T 18430 is analyzed and compared with those of the corresponding U.S. and European standards. A theoretical model of water-cooled water chiller (heat pump) units is constructed such that the limited value levels specified in the energy efficiency standards of China, the U.S., and Europe are converted into the same index for comparison. The IPLV entry limit values of China's water-cooled units, after increases of 5.4% and 25.2%, can match the energy efficiency levels of Path A and Path B of the American standard, respectively, and align with the European standards after a 13.4% increase; the energy efficiency limit values of air-cooled units can be basically on par with the European energy efficiency standards after increasing by 25.4%. This work provides a reference for the subsequent revision of the energy efficiency standard GB19577—2015.关键词：chiller(heat pump);integrated part load value;comparison of test methods;energy efficiency limit value807|994|0发布时间：2024-07-18
- 摘要：This study introduces an annular elliptical finned-tube evaporative condenser. The heat and mass transfer performance and operation characteristics of the evaporative condenser under different circulating water ratios, different regional environments, and four different operating modes are determined by the experimental system of the evaporative condenser, in which the air-cooled, water-cooled, evaporative-cooled, and full working modes are studied. The results show that the heat flux of the "full working" mode is higher than that of the "air-cooled" and "evaporative-cooled" modes under the same conditions; the "water-cooled" mode has the highest heat flux because its heat transfer area is much smaller than that of other modes. Under the "full working" mode with a fixed air volumetric flow rate and the total amount of circulating water, the heat flux increases first and then decreases with the increase in the water circulating ratio, where the best flow rate ratio between spray water and cooling water is 2:5. The total heat flux of the "full working" mode in dry cold areas, cold areas, and hot summer and warm winter areas is 5 879.64 W/m2, 3 964.28 W/m2, and 2 933.05 W/m2, respectively. Hence, the heat transfer performance of the "full working" mode varies significantly in different regions, and the "full working" mode of the condenser has better heat transfer performance when the spray and cooling water temperature ranges from 13 to 18 ℃. Under the same conditions, the mass transfer coefficient of the water film in the "evaporative-cooled" mode is higher than that in the "full working" mode, which of both modes increases and then decreases with the increase of the spray density.关键词：evaporative condenser;annular elliptic finned tube heat exchanger;heat and mass transfer performance;operating characteristic;experimental analysis504|673|0发布时间：2024-07-18
- 摘要：Tunnel ground-source heat pumps are effective in solving the thermal pollution problem in subway tunnels. A capillary-tube heat exchanger (CHE) is used as the front-end heat exchanger of the tunnel ground-source heat pump system because of its corrosion resistance, easy bending, good heat transfer performance, and compactness. In this study, a CHE fluid-thermal coupling heat transfer model is established based on a demonstration project, and a CHE simulation system is built on the TRNSYS platform to analyze the heat transfer performance of the CHE in tunnel linings under continuous and intermittent operation. When the run-time ratio increases from 1/3 to 1, the average daily heat flux of CHE in the cooling and heating seasons decreases from 100.59 W/m2 and 87.42 W/m2 to 78.14 W/m2 and 68.62 W/m2 after 7 days, respectively, whereas the inner surface temperature of the surrounding rock increases and decreases in the cooling and heating seasons, respectively. The results show that intermittent operation can significantly improve the heat transfer performance of the heat exchanger and help alleviate the problem of cold and heat accumulation in the rock surrounding the tunnel.关键词：renewable energy;heat pump;capillary tube;intermittent operation;heat transfer performance485|547|0发布时间：2024-07-18
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Effect of Carbon Nanotube Diameter on Phase Change Thermal Energy Storage Properties of Paraffin Wax
摘要：To solve the problems of poor thermal conductivity and low thermal energy storage efficiency of paraffin wax, carbon-containing materials with high thermal conductivity are used to improve its thermal energy storage performance. Three carbon nanotube powders with different diameters, 8–12 nm, 10–20 nm, and 20–40 nm, are added to paraffin wax at a mass fraction of 5% to evaluate the influence of the carbon nanotube diameter on the thermal energy storage properties and the anisotropic thermal conductivity of carbon nanotube/paraffin wax composite phase change material (CPCM). The experimental results show that the specific heat capacity and latent heat value of CPCM decreases as the diameter of the carbon nanotubes decreases. The phase change temperature decreases by approximately 1 ℃; the latent heat value decreases by 0.5%–3.8%, and the specific heat capacity decreases by 16.2%–16.5% compared with those of pure paraffin wax. The improved thermal conductivity and thermal diffusivity shorten the paraffin wax melting time, and the melting time of 8–12 nm composites is reduced by 18.2%–46.7%. Temperature uniformity in the vertical direction was also effectively improved. At the external measurement points, the temperature fluctuation of 8–12 nm composites was 47.7% compared with pure paraffin, whereas at the internal measurement points, the temperature fluctuation of 10–20 nm was 32.9% of pure paraffin. The diameter of the carbon nanotubes significantly improved the thermal energy storage properties of the CPCM.关键词：phase change thermal energy storage;carbon nanotubes;thermal conductivity;thermal energy storage properties490|511|0发布时间：2024-07-18 - 摘要：To promote the development of hydrogen fuel cells, this paper designs a new diaphragm compressor that features diaphragm head wrap-around cooling. A plurality of the first cooling flow channels are provided inside the upper diaphragm head of the diaphragm compressor, which are arranged vertically to each other in the plane with the air inlet pipe and exhaust pipe. The air inlet pipe and exhaust pipe are located between the first cooling flow channels, wherein the first cooling flow channels include a plurality of cooling pipelines, and the cooling pipeline is arranged in an asterisk pattern. The second cooling channel is provided at the end of the lower diaphragm head near the oil chamber side with a cooling line arrangement similar to that of the first cooling line; thus, the diaphragm compressor can be fully cooled inside the diaphragm head. By building a new diaphragm head wrap-around cooling diaphragm compressor test bench, its performance is tested, and the effects of the pressure ratio, inlet gas temperature, and cooling effect of the wrap-around cooling line with the cooling medium temperature change law are analyzed. The test results show that the isentropic and volumetric efficiencies of the diaphragm compressor decrease with the increase in the pressure ratio, and the highest isentropic and volumetric efficiencies can reach 65% and 64%; under the condition of a certain pressure ratio, the exhaust temperature increases with the increase in the inlet gas temperature, and in the case of a similar inlet gas temperature, the higher the pressure ratio the higher the exhaust temperature. The cooling effect of the wrap-around cooling line is more significant under the condition of a large pressure ratio, and the highest can be reduced by 184.5 ℃.关键词：hydrogen station;diaphragm compressor;membrane head wrap-around cooling;pressure ratio442|490|0发布时间：2024-07-18
- 摘要：The effects of an expansion valve opening on the robustness and system performance of an R32 heat pump system under variable heat source inlet temperatures and hot-water inlet temperatures are studied. The results show that the system has different superheat oscillation ranges under different operating conditions, and the heat source inlet temperature has a significant effect on the initial oscillation superheat, whereas the hot water inlet temperature has no obvious effect on it. Under the variable heat source inlet temperature (15–25 ℃) conditions, the heating capacities show different variation trends with the superheat, whereas the COP shows the same changing trends, and the maximum COP of the system is obtained within the superheat oscillation range. Under the variable hot water inlet temperature (30–40 ℃) conditions, the heating capacities and COP show the same trends with the superheat, and both of them reach the maximum values in the superheat oscillation range. Both the increase in the heat source inlet temperature and the decrease in the hot water inlet temperature can increase the maximum heating capacity and the maximum COP, which are 9.287 kW and 4.646, respectively when the heat source inlet temperature is 25 ℃, and 9.148 kW and 5.665, respectively, when the hot water inlet temperature is 30 ℃.关键词：system robustness;superheat oscillation;heat pump system;off-design performances;R32540|642|0发布时间：2024-07-18
- 摘要：In this study, physical models of six-row and four-row arrays of a low-ambient-temperature air-source heat pump with and without wall obstruction are established. A three-dimensional numerical simulation of the ambient flow field of the low-ambient-temperature air-source heat pump under nominal working conditions at 261.15 K is carried out. In this study, the inlet air temperature of the evaporator surface and the heat transfer rate of the low-ambient-temperature air-source heat pump under different horizontal wind speeds are investigated. The location of the unit under the worst conditions is determined, and the influence of cold air backflow on the heat transfer performance is analyzed. The ambient wind hindered the diffusion of cold air at the fan outlet and increased the deflection angle of the fan outlet, resulting in the accumulation of cold air in the upper part of the fan, and the cold air reflux phenomenon in the unit was more obvious inside and on the lee side the array. The results showed that when the horizontal distance between the units was 0.6 m, the horizontal wind speed increased from 0 to 5 m/s. The lowest inlet air temperature of the array unit is 2.44–3.69 K lower than the ambient temperature; the average heat transfer decreases by 1%–6.2%, and the average inlet air temperature is 0.78–1.57 K lower than the ambient temperature. When the distance between the unit and wall is 0.6 m, the horizontal wind speed increases from 0 m/s to 5 m/s, respectively; the lowest inlet air temperature of the array unit is 3.51–4.14 K lower than the ambient temperature; the average heat transfer rate decreases by 5.9%–11.5%, and the average inlet air temperature is 1.29–1.98 K lower than the ambient temperature. On this basis, an array air-source heat pump was simulated under different lateral spacings and distances from the wall. The results showed that increasing the lateral spacing or distance from the wall enhanced the heat transfer of the array low-ambient-temperature air-source heat pump unit. When the lateral spacing increases to 1.8 m, the average heat transfer rate of the array unit can reach more than 96.5% of the baseline heat transfer rate of the array unit. When the distance from the wall is increased to 1.8 m, the average heat transfer rate of the array unit can be more than 91.3% that of the baseline unit. A horizontal spacing or a spacing from the wall of 1.2 m is a better installation spacing, which provides a theoretical basis for on-site installation.关键词：low ambient temperature air-source heat pump array;numerical simulation;cold air backflow;ambient wind fields469|535|0发布时间：2024-07-18
- 摘要：A critical research topic is the improvement of the system performance by efficiently cooling carbon dioxide in transcritical vapor compression cycles. In this study, a distributed compression cycle system (DCCS) is proposed. For the DCCS, the transcritical CO2 from the gas cooler outlet is not further subcooled but boosted. It is then cooled by conventional heat sink conditions. The DCCS performance under different operating conditions with variations in the second boost ratio is calculated by a thermodynamical cycle model. It is shown that the DCCS can effectively improve the system performance compared with the baseline system, with the maximum refrigeration COP increase ranging from 8.2% to 10.76% at a constant gas cooler outlet temperature. The refrigeration capacity is increased up to approximately 26%. The maximum refrigeration COP increase ranges from 8.57% to 13.51% at a constant evaporating temperature. The ideal second boost ratio requirements in DCCS are not high, and the additional system power consumption for the second boost is not more than 20% compared with the baseline system. The DCCS still has advantages in terms of the system COP compared with current systems that only adopt a single subcooling technology. The proposed DCCS provides a new path for improving and refining the performance of the carbon dioxide transcritical vapor compression cycle systems.关键词：distributed compression;carbon dioxide;transcritical;equivalent subcooling;refrigeration cycle485|601|0发布时间：2024-07-18
- 摘要：In contrast with the conventional drying technology, a novel air cycle heat pump drying (ACHPD) system, which uses air as its working medium, is proposed to solve the problems of low energy efficiency and eliminate the use of HCFCs/HFCs. A simulation model is established, and its verification via experimental results from a constructed test bench indicates errors of the drying rate within ±0.01% and the system power within ±7%. Compared with a conventional electric heater drying (EHD) system, the energy-saving rate of the ACHPD system reaches 15%–27% when the water evaporation rate increases from 0.75 kg/h to 3.45 kg/h. The increase of the inlet air temperature is 10–40 ℃ and the relative humidity is 30%–80%, which reduces the moisture extraction ratio (MER) by approximately 7% and 21%, respectively. The efficiency improvements of the expander and compressor are 0.55–0.8 and 0.4–0.9, respectively, which can deteriorate the energy efficiency of the system by 17% and 36%, respectively. The research results provide new technical references for the application of heat pump technology in the drying field.关键词：open loop;air cycle;heat pump;drying system465|569|0发布时间：2024-07-18
- 摘要：To improve the comprehensive utilization of regional energy and promote low-carbon development, this study constructs an integrated energy system for typical areas, such as parks, including a new energy power generation system driven by photovoltaic and wind power, heating and cooling energy supply systems for ground-source/air-source heat pumps, water chillers, and energy storage equipment. TRNSYS? software is used to simulate and study the dynamic characteristics of the system under six climate conditions in Beijing, and the game theory is used for intelligent operation, which is then compared with the logic control method. The results show that the logic control method can meet the load demand but cannot realize the efficient operation of the heat pump unit and the charge and discharge balance of the energy storage device. The integrated energy system after optimization via game theory can not only realize flexible energy scheduling and distribution through electric-thermal coordination, but also save the entire energy consumption of the heat pump unit and achieve the goal of regional energy economic benefits. The research presented in this paper provides an important theoretical basis for the intelligent operation of heat pump systems in integrated electric-thermal cooperative grids.关键词：electric-thermal coordination;heat pump;intelligent operation;dynamic characteristics;TRNSYS;game theory based optimization474|475|0发布时间：2024-07-18
- 摘要：In this study, a 294 L high-low temperature test chamber with two power batteries in the test area is investigated. The temperature rise and heat dissipation of the batteries in the chamber at a constant temperature of 45 ℃ are simulated through CFD, and the flow field of the high-low temperature test chamber is analyzed and optimized. The results show that for the air distribution pattern on the same side as the upper air supply and lower air return, the perforated plate in the upper part of the test area is helpful in improving the uniformity of the flow field. A vortex phenomenon occurs between the two power batteries. Increasing the distance between the shelf and bottom of the test chamber and appropriately increasing the return air grille area can reduce or even eliminate this phenomenon and thereby improve the flow field uniformity. When the distance between the shelf and bottom of the inner chamber increases to 0.2 m and the height of the return air grille increases to 0.15 m, the overall inhomogeneity of the flow field in the test chamber decreases from 1.73 to 0.4, and the vortex phenomenon between the batteries disappears.关键词：power battery;high-low temperature test chamber;flow field;vortex428|517|0发布时间：2024-07-18
- 摘要：To evaluate the thermal-hydraulic characteristics and mechanism of the bubble absorption process inside a solution in a vacuum environment, we design an experimental device for measuring the bubble absorption and transport characteristics of solutions in a pressurized vertical tube and introduce the structure and work of the device. Its reliability is verified by system vacuum pressure experiments, and its accuracy is verified by bubble flow and energy conservation experiments. The results show that pressurization technology achieves bubble absorption in a vacuum environment. The vacuum increase rate of the system is only 2.33% after 12 h of idling, corresponding to a gas leakage rate of 2.4 mL/h. The device exhibited good reliability. The behavior of bubble generation, rising, collision, coalescence, and rupture during the experiment was consistent with the bubble flow behavior reported in the literature. The maximum relative deviations in the outlet temperature and outlet concentration of the solution and cooling water were 0.08%, 0.02%, and 0.01%, respectively. The maximum errors of the energy calibration experiment of the different solution inlet temperatures and solution flow rates are 10.4 J and 12.5 J, respectively, and thereby the device has good accuracy. The experimental device provides a good experimental foundation for evaluating the transport characteristics of bubble absorption and the heat transfer characteristics of bubble absorption in a vacuum environment and revealing its transfer mechanism.关键词：pressurized;bubble absorption;flow;heat transfer;experimental device407|562|0发布时间：2024-07-18
- 摘要：The problem of inconsistency between the measurement results of the cooling capacity of room air conditioners between environmental chambers still plagues China's air-conditioning industry and is a meteorological problem that easily leads to conflicts in international trade. A standard cold-source device that can calibrate laboratory measurement results of the enthalpy difference needs to be urgently studied. In this study, a standard cold-source device based on ice slurry refrigeration is proposed, including an ice slurry preparation system and a heat exchange system, based on a study of several mainstream cooling capacity measurement methods for room air conditioners and the research status of standard cold sources at home and abroad, combined with an in-depth understanding of the physical process of ice slurry refrigeration. Experimental research and refrigeration capacity uncertainty analysis are conducted to verify whether the standard cold-source device could calibrate the enthalpy difference laboratory. The experimental results show that the relative uncertainty of the measured cooling capacity of the standard cold-source device in the enthalpy difference chamber can reach 1.2% when setting 0 ℃ on the ambient side and setting the standard cooling condition on the room side with mass flow rate of 70 g/s, which is approximately 1/3 of the air enthalpy method and can be used as a standard cold source to calibrate the cooling capacity measurement results of the enthalpy difference chamber, which can help improve the international competitiveness of the refrigeration industry.关键词：ice slurry refrigeration;standard cold source;enthalpy difference chamber;air-enthalpy test method;calibration;relative uncertainty425|520|0发布时间：2024-07-18
- 摘要：To address the problem of high-efficient heat dissipation in the insulated gate bipolar transistor (IGBT) modules used in high-speed trains, a pin-fin heat sink was designed and applied to dry ice particle spray cooling. Three sets of different pin-fin parameter models are established, and the influence of the pin-fin number, diameter, and height on the heat dissipation effect is analyzed by numerical simulation. The optimal pin-fin heat sink has 64 pin-fins, a diameter of 12 mm, and a height of 45 mm. Compared with the baseline heat sink without fins, the surface temperature of the heat transfer substrate is reduced by 10.57 °C, and the sublimation rate of dry ice inside the radiator is increased by 17.2%. The flow state of the dry ice particle cooling fluid in the pipeline and the disturbance and collision processes of the dry ice particles inside the heat sink are observed experimentally, and the simulation results are verified. The dry ice particle spray cooling keeps the IGBT module with a heat source power of 1.6 kW at approximately 25 °C to meet its heat dissipation requirements. Therefore, it is necessary to provide guidance for in-depth research on dry ice particle spray cooling technology.关键词：dry ice sublimation;heat sink;phase change;IGBT module433|526|0发布时间：2024-07-18
- 摘要：Air-cooled garments are designed and the cooling capacity, state parameters, and flow rates of the air inlet and outlet are determined. The refrigeration capacity required by the cooling device matching that of the garment is calculated. Experimental and numerical simulations of a thermoelectric refrigeration device are conducted. The accuracy of the simulation results is verified by comparing the experimental data with the simulation results. An optimization scheme for refrigeration devices is proposed. The thermoelectric refrigeration device is optimized by validated numerical simulation calculation models, which can provide 6.283×10-3 m3/s of cold air at 29 ℃ for a garment under the dry bulb temperature of 34.4 ℃ and wet bulb temperature of 27.9 ℃, and the device can meet the design requirements of the air-cooled garment.关键词：cooling garment;thermoelectric refrigeration;Peltier effect;air cooling470|601|0发布时间：2024-07-18
- 摘要：By comparing the cooling characteristics of four types of cryoprobes under different inlet pressures, the effects of the inlet pressure, J-T slot inner diameter, and backflow channel size on the cooling of cryoprobes are analyzed, and the size of ice hockey balls formed in gelatin are tested. The results show that the temperatures of 1.8–0.42 mm, 1.8–0.30 mm, 1.8–0.12 mm, and 1.1 mm cryoprobes are the fastest under the inlet pressure of 4.5 MPa, 4.0 MPa, 5.5 MPa, and 5.5 MPa, respectively. When the pressure is low, the cooling rate is positively correlated with the inlet pressure. When the inlet pressure is greater than the optimal pressure, the ice blockage increases with increasing pressure. Among the cryoprobes, a smaller inner diameter of the J-T slot improves the cooling rate of the cryoprobes and lowers the temperature of the tip, and a larger backflow channel can reduce ice blockage in the pipe and improve the cooling rate; 1.8–0.42, 1.8–0.30, 1.8–0.12 mm, and 1.1 mm cryoprobes have the largest ice hockey ball diameters under air supply pressures of 4.5, 4.5, 6.0, and 6.0 MPa, respectively. When the inner diameter of the J-T slot decreases, its optimal air supply pressure increases.关键词：transbronchial lung cryobiopsy;Joule-Thomson effect;cooling rate;cryoprobe411|530|0发布时间：2024-07-18
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