最新刊期
卷 45 ， 期 3 ， 2024
- 摘要：With the continued miniaturization and high integration of electronic devices, the challenge of heat dissipation caused by the excessive power consumption of electronic devices needs to be resolved urgently. An effective thermal management solution is proposed for heat dissipation in high-power electronic devices using flat heat pipes with excellent temperature uniformity and high heat dissipation efficiency. However, with the increasingly diverse heat dissipation requirements, the creation of an efficient flat heat pipe to suit the heat dissipation demands of emerging electronic equipment remains an important research topic. Therefore, based on expounding the working principle and structural characteristics of the flat heat pipes, the heat transfer performance of the flat heat pipe, the factors that affect the heat transfer performance (capillary wick structure, cavity thickness, working medium, liquid filling rate, inclination angle, and heat source), the measures to strengthen the heat transfer performance of the flat heat pipe (different wettability surfaces and support column structure, etc.), and its application in miniature electronic equipment (IGBT, LED and battery pack) are systematically reviewed. By evaluating the internal flow and heat transfer characteristics of flat heat pipes under different capillary wick structures and cavity thicknesses, the mechanism and comprehensive optimization method of heat dissipation performance, and the design of a flat heat pipe with strong space adaptability and high heat dissipation performance compatible to different electronic device heat management requirements are still key technologies to be further developed. A valuable reference is provided for further research and optimization of flat heat pipes in cooling electronic devices.关键词：flat heat pipe;critical heat flux;surface wettability;enhanced heat transfer;heat dissipation of electronic devices592|624|0发布时间：2024-12-03
- 摘要：A refrigerant is an essential working fluid in a vapor-compression refrigeration cycle. Hydrofluorocarbons are currently used as refrigerants in refrigeration, air-conditioning, and heat pump systems and are potent greenhouse gases. Thus, replacement refrigerants with high thermal performances and low environmental impacts must be identified. This paper presents a comprehensive review of the refrigerants in different vapor-compression cycle applications covering the temperature range from ?100 to 200 °C. The most promising low-GWP alternative is proposed. Moreover, five refrigerants, including HFO-1234yf, HFO-1234ze(E), HFO-1234ze(Z), HCFO-1233zd(E), and HFO-1336mzz(Z), for application in vapor compression equipment, are summarized.关键词：refrigerant;air conditioning;heat pump;organic Rankine cycle;GWP490|622|0发布时间：2024-12-03
- 摘要：Immersion battery cooling involves immersing the battery directly in a coolant and has the advantages of a simple structure, rapid cooling, and better temperature uniformity than conventional indirect liquid cooling, air cooling, and two-phase cooling. This study summarizes the relevant technologies for immersion battery cooling, including screening of immersion liquid, cooling system structure design, and thermal safety, and then analyzes the technical applications of the immersion battery cooling system based on this work. The results show that immersion cooling can rapidly reduce the battery temperature and effectively improve the temperature uniformity of the battery pack. However, this technology requires a high sealing performance of battery modules, and challenges such as leakage and corrosion need to be addressed.关键词：new energy vehicles;immersion battery cooling;battery thermal management;immersion fluids535|766|0发布时间：2024-12-03
- 摘要：Cooling towers dissipate waste heat generated in industrial or domestic processes, thereby reducing the temperature of circulating water. Compared to other cooling methods, it has the advantages of effective cooling, corrosion resistance, and low cost. This paper discusses the application and performance optimization of cooling towers based on a literature review of recent domestic and international studies. It summarizes and analyzes the applications and related research on cooling towers for industrial cooling and building cooling. It also extends and analyzes cooling tower’s application in carbon capture and waste heat recovery. Various methods have been reviewed for performance optimization, including model, structural, and operational optimization. This paper highlights the challenges that still exist in the state-of-the-art and discusses its future development directions, which will facilitate efficient, green, and stable operation for future cooling tower systems.关键词：cooling tower;evaporative cooling;thermodynamic characteristics;performance optimization495|692|0发布时间：2024-12-03
- 摘要：Air-source heat pumps, as a new, energy-saving, and environmentally friendly technology, are widely applied in various heating applications, yet their reliable operational efficiency at low ambient temperatures is a concern. In this study, a simple, low-cost, and reliable heat pump system is constructed using safety and environmentally friendly binary refrigerant CO2/R1233zd(E), and the system performances such as the coefficient of performance (COP), volumetric heating capacity, suction pressure, and exhaust pressure are obtained through optimization analyses at ambient temperatures from -30 to -10 ℃. By comparing the vapor-injection heat pump system and cascade heat pump system, it was deduced that a recuperative heat pump system using a binary refrigerant can maintain high efficiency at low ambient temperatures. At ambient temperatures ranging from -30 to -10 ℃, the COP of the recuperative heat pump system decreases by 9.8% to 20.6%, whereas the volumetric heating capacity increases by 3.5% to 56.1% compared to the R410A vapor-injection heat pump system. Moreover, the compressor pressure ratio and its variation with ambient temperature are lower than other heat pump systems. Owing to the simple structure of the recuperative system and the adoption of the safe and environmentally friendly binary refrigerant CO2/R1233zd(E), the solution proposed in this study has unique advantages in heat pump applications in regions with low ambient temperatures.关键词：air source heat pump;heat regenerative cycle;mixed refrigerant;optimization analyses389|522|0发布时间：2024-12-03
- 摘要：The motive flow state in a transcritical CO2 ejector significantly affects its performance. The heat transfer on the wall of the motive nozzle can change the motive flow state, and its effect on the performance of the ejector should be studied. A CFD model of the transcritical CO2 two-phase ejector is constructed based on the homogeneous equilibrium model. The influence of heat transfer in the nozzle divergence section on the performance and flow field structure of the transcritical CO2 two-phase ejector is simulated. The effect of heat transfer on the system performance of using a split ejector at the condenser outlet is analyzed. The results show that the entrainment ratio of the ejector increases with an increase in the heat flux at the nozzle divergence section and the length of the nozzle divergence section. The effect is not obvious and can be ignored under a moderate heat flux, i.e. less than 120 kW/m2 since the entrainment ratio changes within 1%. In addition, the heat transfer in the nozzle divergence section has a slight effect on the internal flow field of the ejector. The temperature of the internal flow in the nozzle divergence section increases slightly, the vapor quality at the ejector outlet rises slightly, and the Mach numbers of the mixed flow at the nozzle outlet and in the mixing chamber increase. In the condenser outlet split ejector expansion refrigeration system, the fluid is subcooled using the ejector, and the coefficient of performance (COP) of the system is significantly improved, with a maximum COP increase ratio of 8.89%. In general, heating the divergence section of the motive nozzle of the ejector exerts minimal effect on its performance. However, it significantly improves the performance of the condenser outlet split-ejector expansion refrigeration system.关键词：two-phase ejector;homogeneous equilibrium model;heat transfer;refrigeration system;carbon dioxide377|438|0发布时间：2024-12-03
- 摘要：The electronic expansion valve (EEV) used in multisplit heat pump air conditioners has the structural characteristics of import and export tubes perpendicular to each other, such that the refrigerant has two forms of flow into the EEV, that is, in the direction perpendicular to the valve needle axis and the direction parallel to the valve needle axis. The sound pressure level of the throttling noise exhibits evident differences in these two directions, and it is necessary to clarify the impact of the flow direction on the throttling noise. The purpose of this study is to design and build an experimental rig that can regulate the refrigerant state flowing into and out of the valve, observe the refrigerant flow pattern, and measure the sound pressure level of the throttling noise, thus obtaining the effects of the refrigerant flow directions on the throttling noise under different refrigerant flow rates and vapor qualities. The results show that when the refrigerant flows from the inlet pipe parallel to the direction of the valve needle axis, the throttling noise is mainly the collapse noise of vapor bubbles generated by the refrigerant throttling cavitation, and the overall noise sound pressure level is low. When the refrigerant flows from the inlet pipe perpendicular to the direction of the valve needle axis, the throttling noise is a combination of the noise due to bubble collapse and the noise due to vibrations of the valve needle, and the overall noise sound pressure level is high. In this experiment, the sound pressure levels of the throttling noise in these two flow directions range from 47.1 to 57.1 dB and 61.9 to 67.7 dB, respectively. The throttling noise in the air-conditioning system can be effectively reduced by optimizing the design of the refrigerant flow direction of the air-conditioning system and ensuring that the refrigerant always flows into the EEV from the inlet pipe parallel to the direction of the valve needle axis.关键词：variable refrigerant flow;electronic expansion valve;throttling noise;refrigerant flow direction;experimental research414|471|0发布时间：2024-12-03
- 摘要：In response to the issue of heat exchanger design in a dual evaporating temperature air conditioning system, in this study, a simulation model is established for a dual evaporating temperature air conditioning system to evaluate the impact of the heat exchanger area on the system performance. A dual evaporating temperature air-conditioning system experimental platform is built, and the compressor frequency (30–120 Hz) and supply air volumetric flow rate (400–1000 m3/h) under experimental conditions are used to obtain the cooling capacity Qc, sensible heat cooling capacity Qs, and sensible heat ratio (SHR) of the air-conditioning unit. These performance metrics are used to verify the accuracy of the established model. The range of the system operation adjustment is studied by changing the heat exchanger area (48, 60, and 72 coils) in the model. The results show that with an increase in the heat exchanger area, the adjustment ranges of systems Qc, Qs, and SHR expand generally, with maximum increases of 5.0%, 13.8%, and 11.8%, respectively. When the heat exchange area increased from 48 to 60 coils and 72 coils, at an air supply volumetric flow rate of 1000 m3/h and the compressor frequency of 30 Hz, the increase in Qs was 9.8% and 13.8%, respectively, indicating that when the heat exchange area increased to 60 coils, the increase in Qs was obvious. When the heat exchange area was further increased, although Qs increased, the growth rate decreased. Finally, a method was proposed to design the heat exchanger area according to the ambient temperature and humidity adjustment range, with the required cooling capacity as the target.关键词：dual evaporating temperature;sensible heat ratio;refrigeration capacity;independent temperature and humidity control404|461|0发布时间：2024-12-03
- 摘要：A new heat pipe-type natural convective heat dissipation terminal with a thermal energy storage material is proposed. A sleeve is added to the heat exchange tube at the end of the heat pipe, and the thermal energy storage material is placed between the tubes. Through condensation heat exchange, the steam in the tube transfers heat to the thermal energy storage material and then to the outer sleeve, which features natural convective heat exchange and radiative heat exchange against indoor air, thereby constructing a new household air source heat pump system. A heat transfer model of the heat pipe heat dissipation terminal with the solid-state thermal energy storage material is established, and the start-stop process of the heat pump system and the influence of the type and thickness of the thermal energy storage material on the temperature distribution and its variation with time are studied. The variation laws of the macro-performance metrics, such as the heating capacity and compressor power of the heat pump system, are analyzed. The results show that magnesium brick as the solid-state thermal energy storage material is the best. The operating time of the heat pump and the external surface temperature of the thermal energy storage material are affected by the thickness of the thermal energy storage material, and a critical thickness exists. When a magnesium brick with a thickness of 12 mm is selected as a thermal energy storage material, the domestic air source heat pump with the thermal energy storage terminal runs for 12 minutes, leading to 26 minutes of heating time, while the surface temperature changes within the range of 35–50 ℃.关键词：heat dissipation terminal;solid-state thermal energy storage;tube-in-tube;discontinuous operation386|449|0发布时间：2024-12-03
- 摘要：This study proposes a method for determining summer outdoor design parameters and design days using the current code. Based on the method from the current code in China, four typical cities are selected according to the adaptation zone of evaporative cooling technology, forming outdoor design parameters for evaporative cooling air conditioning with wet bulb temperature as the primary factor and dry bulb temperature as the secondary factor. Based on the historical long-term meteorological data, a new method for determining the design days is proposed. The characteristics and trends of outdoor climate change in typical cities in summer are extracted, and the data of the summer design days are obtained using the hourly coefficient method. The results show that the new method reduces the temperature difference between dry and wet bulbs and the evaporative cooling potential. Guiding the design according to the method in the current code results in an insufficient design. The design days in the current code cannot accurately reflect the variation trend of the outdoor climate in summer in different regions. However, the design days obtained by the hourly coefficient method proposed in this study are more consistent with the measured data of typical cities.关键词：evaporative cooling;outdoor design parameters;design day;hourly coefficient method378|402|0发布时间：2024-12-03
- 摘要：To deliver comfortable conditioned air by reducing humidity levels while enhancing comfort levels in an air-conditioned space under variable load conditions, an improved design for fully modulating dehumidification with a hot gas reheat system was developed. By managing the charge balance between the cooling and reheat modes, the modulation valve operating range for the reheat mode was expanded. Different microchannel heat exchanger (MCHE) reheat coil patterns were analyzed. The test results showed that an air-cooled unitary unit equipped with this novel MCHE reheat system improved the refrigerant charge balance between the cooling and reheat modes. Under rating conditions, the energy efficiency ratio (EER) in the reheat mode increased by 17%, and water condensate removal through dehumidification was enhanced by 6%. The modulating valve opening range for the reheat mode could be increased from a baseline of 20%–70% to 15%–85%. For the rated reheat dehumidification condition, the modulating range of the reheat temperature rise increased from 8.3–14.4 ℃ to 6.1–19.4 ℃. This innovative solution was proven to achieve a wider operating range that improved dehumidification capacity and achieved energy conservation.关键词：dehumidification with hot gas reheat;refrigerant management;unitary air conditioner;modulating reheat;microchannel reheat coil360|419|0发布时间：2024-12-03
- 摘要：In this study, the leakage diffusion and concentration distribution characteristics of R32 refrigerants from a wall-mounted split air-conditioner indoor unit are analyzed by combining experiments and simulations under different leak locations, refrigerant leak rates, and operating conditions. Safety is compared and evaluated based on whether the R32 mass fraction reaches the R32 refrigerant detector alarm concentration (4% LFL), the positions of the responsive detectors, and the lower flammability limit (LFL) area. The results show that the response time of the detectors inside the indoor unit is approximately 40 s and 50% faster than that located in the room. The experimental and numerical results show a high consistency. The diffusion law of R32 is different at different leak locations. The leak rate of R32 slightly influences the concentration distribution in the indoor unit. The area where the 4% LFL is reached when the air conditioning is ventilated is four times smaller than when the air conditioning is turned off. The best position to install the R32 refrigerant detector is the lower area between the electrical box and the front heat exchanger. When R32 leaks at the fin of the heat exchanger, the R32 refrigerant detector fails to respond, and the refrigerant continues to leak into the room, posing a safety hazard. The LFL volume is approximately 3×10-6 m3. The LFL region is a small area around the R32 leak port, and its safety risk is low.关键词：refrigerant leakage;safety evaluation;diffusion law;concentration distribution;flammable area357|395|0发布时间：2024-12-03
- 摘要：Data center computer room air-conditioning equipment operates for prolonged periods, and its performance must be tested and evaluated annually to ensure safe and efficient operation. This study conducts field measurements on the server layout, blind plate structure, and working condition adaptability in the rack. The thermal environment of a data center using the closed cold aisle underfloor air distribution system is studied, and the thermal environment safety and energy efficiency throughout the year are evaluated through thermal performance indicators and energy efficiency indicators. The results show that it is recommended to install a rack with a power of more than 2 kW in the middle area of the cold aisle. Installing a blind plate in the gap between the racks can promote the circulation of cold air inside the server, reduce the backflow interference of hot air, and reduce the maximum outlet temperature by 3.32 °C. The average supply air speed was reduced by approximately 24%. Under summer operating conditions, the PUE, WUE, and CUE of the data center were approximately 1.2, 3.5, and 0.84, respectively, and the WUE exhibited strong seasonality. Under winter operating conditions, free cooling can effectively reduce the energy consumption of data centers. In addition, the overheating problem of the racks at the end of the cold aisle of the data center is significant. The cabinet cooling index of the 16 racks was less than 90%, and the heat loss was high.关键词：data center;air supply scheme;server room air conditioning;thermal performance evaluation index;energy efficiency318|400|0发布时间：2024-12-03
- 摘要：To meet the need for energy efficiency improvement and substitution of traditional refrigerants in the field of supermarket refrigeration, a supermarket booster refrigeration system using the eco-friendly zeotropic refrigerant CO2/R1234yf is proposed in this study. A thermodynamic model is established and compared with that of a pure CO2 booster refrigeration system. The results show that the maximum COP (1.40) of the system using CO2/R1234yf was obtained under the optimal CO2 mass fraction (0.94) and discharge pressure (8.81 MPa). The COP of the CO2/R1234yf booster refrigeration system was significantly improved compared with the pure CO2 system, which increased by 7.25% when the ambient temperature was 35 ℃. The APF improvement of the CO2/R1234yf booster system was 2.68%–4.72%. The APF increased with an increase in the latitude of typical cities. The exergy efficiency of the CO2/R1234yf booster system first increased and then decreased with increasing CO2 mass fraction. The CO2/R1234yf booster refrigeration system exhibited the highest exergy efficiency (0.18) when the CO2 mass fraction was 0.95, which was 4.62% higher than that of the CO2 system.关键词：supermarket booster refrigeration system;zeotropic working fluid;CO2/R1234yf;annual performance factor;exergy analysis;energy efficiency improvement367|467|0发布时间：2024-12-03
- 摘要：The rapid development of fresh food distribution is facing significant pressure to reduce global carbon emissions. Reducing carbon emissions from last-mile distribution is important for energy conservation, environmental protection, and economic benefits. In this study, six typical cities in China are selected to analyze and evaluate the carbon emissions from ice storage and photovoltaic refrigeration in fresh food distribution using the entire life cycle method. When the design temperature in the delivery box is -5 °C, the results show that the carbon emission of six cities in the production stage for the photovoltaic refrigeration mode is higher than that of the ice storage mode. In the case of a 20-year life cycle, the total carbon emissions of the photovoltaic refrigeration mode in each city were reduced by 97.95%–98.78% compared with the total carbon emissions of the ice storage mode, and the emission reduction effect was significant. Among them, the carbon emissions from the use stage of the ice storage distribution mode contribute the most, and the carbon emissions from the production stage of the photovoltaic refrigeration distribution mode account for the most. Emission reduction benefits can be obtained in the decommissioning stage. When the design temperature in the distribution box increases from -5 °C to 0 °C, the carbon emissions of each city in the photovoltaic refrigeration mode are reduced by 17.74%–19.31%, whereas the carbon emissions in the ice storage mode are reduced by 13.21–18.79%. When the design temperature in the distribution box is increased from 0 °C to 5 °C, the carbon emissions of each city in the photovoltaic refrigeration mode are reduced by 17.03%–18.24%, whereas the carbon emissions in the ice storage mode are reduced by 15.22%–19.71%.关键词：carbon emission;refrigerated transport;fresh food distribution;cold storage;photovoltaic324|403|0发布时间：2024-12-03
- 摘要：Rainbow trout (Oncorhynchus mykiss) is a popular commercial fish in China owing to its delicious and nutritious meat. However, it is extremely prone to spoilage and deterioration during storage, transportation, and sale, which affects its edible value. To study the efficient preservation proposal for rainbow trout during storage and extend its shelf life, this study uses 4 ℃-cold storage as control and studies the effects of the ice temperature (0 ℃) storage combined with composite bio-preservatives (the mass concentration of chitosan, tea polyphenols, and lemon juice are 1.75%, 0.25%, and 4.98%, respectively) on the quality of rainbow trout by measuring the drip loss, pH, and total volatile base nitrogen (TVB-N) of meat samples under different experimental conditions. The results show that the various indicators and their increasing amplitudes over time of the 0 ℃ ice temperature storage group are better than those of the 4 ℃ storage group, which can effectively slow down the spoilage process of rainbow trout meat. On the 12th day, the pH and TVB-N values of the 4 ℃ and 0 ℃ groups are 6.86 and 51.89 mg/100g, and 6.56 and 31.82 mg/100g, respectively, whereas those of the 0 ℃ with bio-preservative group are only 6.32 and 16.96 mg/100g, respectively. This scheme has a better preservation effect on rainbow trout meat and can effectively extend its shelf life.关键词：ice temperature storage;preservation effect;bio-preservative;rainbow trout365|498|0发布时间：2024-12-03
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