最新刊期
卷 43 ， 期 5 ， 2022
- 摘要：CO2 is considered to have great application potential in cold storage due to its low global warming potential and zero ozone depletion potential. In this study, a mathematical model was established for a CO2 transcritical two-stage compression refrigeration cycle with complete inter-cooling and double-stage throttling (DTCC cycle) used in cold storage applications. The effects of evaporation temperature, compressor efficiency, gas cooler outlet temperature, discharge pressure, and heat recuperative cycle on the refrigeration coefficient of performance (COP) of the cycle were analyzed atdifferent working conditions. The correlation of optimum discharge pressure and intermediate pressure under a maximum COP was given. When the evaporation temperature te = -30–10 ℃ and the gas cooler outlet temperature tgs = 30–45 ℃, the optimal discharge pressure of the two-stage cycle is approximately 0.3 MPa less than that of the single-stage transcritical refrigeration cycle under the same working conditions. Further analysis showed that the refrigeration coefficient of the DTCC cycle was improved by using anadditional gas cooler for low-pressure discharge gas and by setting arecuperatorat the outlet of the high-pressure gas cooler.关键词：CO2;complete inter-cooling and double-stage throttling;optimal discharge pressure;optimal intermediate pressure;recuperative cycle1292|1361|0发布时间：2024-07-18
- 摘要：The low-grade waste heat resources of industrial buildings are abundant but difficult to utilize, especially when the waste heat is below 80 ℃. The effective recovery and utilization of such waste heat are of great importance for energy conservation and environmental protection. In this study, a low-grade heat-driven dehumidification and cooling air-conditioning system for industrial buildings is proposed. The hot water drives the chiller first and then drives the liquid desiccant dehumidification unit for fresh air, which realizes the cascade utilization of low-grade heat. The system features separate sensible and latent cooling technology, which is manifested by using the liquid desiccant dehumidification fresh air unit forthe latent load and the chiller for the sensible load. The results of this application show that when operating at an average temperature of 77.2 ℃ under a periodically fluctuating heat source temperature, the average coefficient of performance of the chiller is 0.69, which can provide high-temperature chilled water at 15.1–16.3 ℃ and effectively control the thermal environment of the building. The liquid desiccant dehumidification fresh air unit can reduce the humidity ratio of the fresh air from 19.4 to 11.9 g/kg at an average dehumidification efficiency of 61.2%.关键词：utilization of waste heat;air-conditioning;absorption refrigeration;liquid desiccant dehumidification1060|1057|1发布时间：2024-07-18
- 摘要：In this study, an air-refrigeration system for data center cooling is proposed. The effects of pressure ratio, ambient temperature, indoor temperature, and rotating component efficiencies (compressor and expander) on cycle performance were studied by numerical simulation. Approaches to improve the system performance are proposed, and the performance of the composite system comprising the air-refrigeration system and the free cooling system in typical climate cities is analyzed. The results show that the optimal pressure ratio is 1.5–2.0 in the actual air-refrigeration cycle. The unit refrigerationcapacity and refrigeration coefficient of performance (COP) increase with a decrease in ambient temperature or an increase in indoor temperature. The efficiency of the expander is more critical than that of the compressor for improving the performance of the air-refrigeration system. Under the optimal pressure ratio of the actual cycle (both rotating component efficiencies = 0.8), the refrigeration COP can be increased by 22% by implementingthe recuperator. The annual energy efficiency ratio (AEER) of the composite system in Hohhot can reach 14.61, indicating that it has more advantages in areas with a long freecooling period throughout the year.关键词：data center;air-refrigeration;coefficient of performance;recuperative cycle1133|1091|0发布时间：2024-07-18
- 摘要：Frosting (especially severe frosting) in air-source heat pump (ASHP) units leads to a substantial decrease in operating performance. The development of frost-suppression ASHPs (FSASHPs) is key to ensuring their efficient application and healthy development. In this study, a field test study was conducted using a residential demonstration project in Kangding City, Sichuan Province. The study compared an FSASHP and a conventional ASHP unit to explore the frosting suppression and operating performances and analyze the economy of the FSASHP unit. The results showed that the effects of frosting suppression and the improvement of heating performances were substantial for the FSASHP unit. The coefficients of performance of the FSASHP unit were 21%–37.3% higher, with annual costs 13% lower compared to those of the conventional ASHP unit. The payback period of the FSASHP unit was approximately 1 year, and the FSASHP unit had better technical and economic efficiency. This study was helpful for the efficient application of ASHP units in severe frosting regions.关键词：air-source heat pump;frosting-suppression;operating performance;technological economy;field test1066|970|0发布时间：2024-07-18
- 摘要：Precise temperature control is needed for developing and applying microfluidic technology in biochemical analysis and medical diagnosis. A temperature control system based on a thermoelectric cooler with a specially shaped structure was designed to realize the temperature control of the target area of microfluidic chips. The heat transfer and temperature response characteristics of the temperature control system were analyzed based on numerical simulation and experimental tests. The results showed that the thermoelectric cooler reduced the temperature of the sample cell of the microfluidic chip to -24 ℃. However, the pull-downrate of the sample cell was much lower than that of the thermoelectric cooler, which exhibited temperature response hysteresis. To address this challenge, a T-shaped concentrated cooling structure was proposed. The results showed that the concentrated cooling structure substantially improved the response rate of the temperature control system and effectively reduced the response time, at the cost of consuminga small amount of cooling. For the concentrated cooling structure with a lower diameter of 14 mm and 10 mm, the temperature response time was reduced by 30% and 40.7%, respectively.关键词：thermoelectric cooling;microfluidics;pull-down rate;concentrated cooling structure;temperature control996|1024|1发布时间：2024-07-18
- 摘要：Thermoelectric generators (TEG) are one way to utilize the cold energy of LNG. Inadequate research on the Seebeck coefficient (α) of thermoelectric materials at cryogenic temperatures has hindered the design of TEG at cryogenic temperatures. Consequently, this paper proposes a method to measure α of the thermoelectric material, Bi2Te3, at cryogenic temperatures using a TEG module experiment, which measures α of thermoelectric materials in the temperature range of 90 K to 180 K. The results showed that α of Bi2Te3 decreased with decreasing temperature. When the temperature decreased from 180 K to 90 K, α decreased from 124.6 μV/K to 49.3 μV/K, which is a quadratic function of temperature.关键词：Seebeck coefficient;cryogenic temperature;thermoelectric module;thermal resistance network919|876|0发布时间：2024-07-18
- 摘要：In this study, the problem of heat dissipation of non-uniformly distributed hot spots in high-power chips used in cell phones was investigated. A cell phone chip was used as a heat source, and software was used to accelerate the operation speed and monitor the frequency usage rate that replicates the realistic operating condition. A thermally conductive layer with anisotropic thermal conductivity and a heat sink for a cooling system was designed to increase the cooling efficiency of the thermoelectric cooler. A thermal management system based on the simulation results was built with a variable cooling efficiency. Furthermore, for long-term stability, a periodic power supply controller was designed to reduce heat accumulation on the hot side of the thermoelectric cooler and reduce power consumption. As a result, chip temperature was reduced from 48 to 34 ℃, and the utilization of a full load chip was improved by approximately 20%, whichserves as a solution to the problem of cooling heat sources with non-uniform distribution.关键词：thermoelectric cooler;chip;thermal management system;thermal conductivity992|873|2发布时间：2024-07-18
- 摘要：In this study, the characteristics of a linear compressor with vapor injection (VI) were investigated. A model of a linear compressor with VI validated by the experiment was proposed to explore the effects of VI pressure, piston stroke, and driving frequency on the operating parameters. The results showed that the VI caused delayed opening and early closing of the suction valve. Under the rating condition, when the injection pressure was 200 kPa and 400 kPa, the mass flow rate of suction decreased by 61% and 100% (to zero), and that of discharge increased by 50% and 60%, respectively. Under constant electrical parameters, the stroke, offset, clearance, and resonant frequency of the free-piston increased with increasing injection pressure. Both the equivalent gas spring stiffness and gas stiffness increased with increasing injection pressure at constant clearance volume. For an increasing piston stroke, the mass flow rate of suction increased, while that of injection increased and then remained constant. When the compressor operates close to the resonant frequency, both the suction and injection mass flow rates reached their respective maxima, weakening the effect of injection on the decline of suction flow rate at high operating frequencies.关键词：linear compressor;vapor injection;simulation;variable parameters;pumping parameters950|947|0发布时间：2024-07-18
- 摘要：An experimental investigation was conducted into the heat transfer performance of the fin-and-tube heat exchanger in an air handling unit (AHU), and calculation models were used to analyze the experimental data. The tube-by-tube and row-division methods were extended to process the experimental data under the heating conditions, and the fin-and-tube heat exchanger was analyzed in terms of the heat transfer performance of the air side. Compared with the traditional logarithmic mean temperature differenceand number of transfer units methods, the deviations of the j factorand heat transfer coefficient h calculated by the four methods were all within 10%. The effect of the j factor under different fin spacing, tube diameters, and the number of tube banks was studied. The results showed that the jfactor gradually decreased by 25.6% when increasing Re from 3 000 to 6 020. The j factor of a louver fin was larger than that of a wavy fin at the same Re, and the maximum deviation decreased from 26.3% to 8.3% with increasing Re. The j factor increased with increasing fin spacing and tube diameter and decreased with the number of tube banks. When there were eight tube banks, the j factor decreased sharply to approximately 0.008. The research provides a theoretical basis for the design optimization and operation of heat exchangers for AHUs.关键词：fin-and-tube heat exchanger;heat transfer characteristics;tube by tube method;row-division discrete method;air handling unit1054|1049|0发布时间：2024-07-18
- 摘要：A main factor restricting the performance of dry-expansion evaporators is the imbalance of refrigerant distribution between each tube. In this study, two improvementschemes for setting a distribution pipe and an orifice plate have been proposed to address this problem. The computational fluid dynamics simulation and heat transfer calculation were used to analyze the changes in the uniformity of the refrigerant distribution, pressure drop, and heat transfer performance of the evaporator. The results showed that although they lead to greater pressure loss, the optimal distribution pipe and orifice plate improved the distribution uniformity by 56.60% and 60.80%, and the evaporator heat transfer of the two schemes improved by 19.69% and 23.83%, respectively, compared to the baseline.关键词：discharge distribution;refrigerant;distributor;coefficient of heat transfer;dry-expansion evaporator1026|943|0发布时间：2024-07-18
- 摘要：The uneven distribution of refrigerant flow in a micro-channel evaporator leads to the dry-out phenomenon that deterioratesthe heat transfer performance. In this study, a dual-circuitrymicro-channel evaporator performance test platform was established to investigate the influence of a gas diversion device on the heat transfer performance of the evaporator and the uniformity of refrigerant distribution in a flat tube. The results showed that the maximum latent heat of the phase change was the same as that of the liquid phase refrigerant evaporation, giving rise to the small differences in heat transfer and heat transfer coefficient between the two structures. The maximum difference was only 0.5% and 6.9%, respectively. However, the length of the two-phase section increased by 87.3%, and the superheat of the two structures decreased considerably. When the wind speed was 3 m/s, the superheat difference between the two structures was 44.4%. The distribution of refrigerant between the flat tubes tends to be consistent; the uniformity is improved; the dry steaming phenomenon is relieved.关键词：microchannel evaporator;coefficient of heat transfer;flow distribution;superheat degree1064|877|0发布时间：2024-07-18
- 摘要：A steady-state heat transfer model of a micro-channel parallel flow loop heat pipe was established based on the distributed parameter model. Model feasibility was verified experimentally, with a maximum relative error of 10.5%. The simulation study analyzed the influences of the filling ratios and the height difference between the evaporator and the condenser on the heat transfer performance of the loop heat pipe. The results showed that the optimal filling ratios of the loop heat pipe were 80%–105.4%, and the heat transfer capacity was 1.27–1.36 kW; when the height difference between the evaporator and condenser increased from 0.4 m to 1.0 m, the heat transfer capacity increased by approximately 8.7%. The model predicted the unevenness of the evaporator flow distribution and the two-phase state inside the flat tube, improving the accuracy of the simulation results. This study can be used as a reference for the structural design of micro-channel parallel flow loop heat pipes.关键词：loop heat pipe;distributed parameter model;micro-channel;heat transfer;experimental validation1265|832|0发布时间：2024-07-18
- 摘要：In this study, an L-shaped pulsating heat pipe was proposed to address the thermal management problem of lithium-ion batteries in electric vehicles. A pulsating heat pipe has a long heating section, a short cooling section, and a short insulation section. The parametric effects on the start-up and heat transfer characteristics of an L-shaped pulsating heat pipe were studied, includingthe heating capacity of 10–30 W, cooling water temperature of 20–30 ℃, and methanol filling ratio of 7.1%–21.2%. The results showed that as the filling ratio increased, the start-up temperature increased, and the thermal resistance first decreased and then increased. As the heating power increased, the start-up temperature, start-up time, and thermal resistance decreased. The maximum temperature of the heater was 54.7 ℃ for a 14.1% filling ratio and 10–20 W heating power, indicating that the L-shaped pulsating heat pipe can effectively maintainthe temperature required for the normal operation of batteries in an electric vehicle.关键词：oscillating heat pipe;heat transfer performance;operating conditions;lithium-ion battery thermal management982|950|1发布时间：2024-07-18
- 摘要：A sharp whistling noise may occur during the refrigerant throttling process in the electronic expansion valve of air conditioning systems, which may lead touncomfortable experiences. To reduce the whistling noise, the mechanism for the whistling noise and the noise generation rules as the refrigerant flows through the electronic expansion valve must be understood. In this study, an experimental rig was designed to adjust the refrigerant state before and after the electronic expansion valve and measure the generated whistling noise. The influences on the whistling noise of the refrigerant operation conditions and the valve opening width were measured. The results showed that the whistling noise came from the periodic oscillation of the fluid caused by the high-frequency pressure pulsation inside the valve. Its acoustic characteristics are the result of the selective amplification of the noise source signal near the resonance frequency of the Helmholtz resonance cavity structure comprising the annular conical throttle channel and the valve cavity. The sound pressure level of the whistle is mainly related to the refrigerant flow rate inside the valve and the valve opening width. The noise pressure level increased by 21% when the refrigerant velocity increased from 2.5 m/s to 3 m/s at a valve opening of 700 pls. The refrigerant flow rate inside the valve determined the fluid oscillation frequency, and the valve opening degree determined the resonance frequency of the acoustic cavity inside the valve. By changing the valve cavity structure to increase the resonance frequency, the oscillation frequency caused by the refrigerant impact inside the valve under common air conditioning conditions was lower than the resonance frequency, which can effectively avoid the generation of whistling noise.关键词：electronic expansion valve;whistling noise;self-oscillation1428|1340|1发布时间：2024-07-18
- 摘要：In this study, an experiment was conducted to compare and analyze the concentration diffusion law of R32 gas in different planes ofthe testedroom following leakage from different positions of 3.6 kg R32 refrigerant. The safety impact in the room when the lower flammable limit (LFL) was reached for the first time in typical planes was analyzed along with the flammable risk time. The results showed that when the height of the leak position increased, the concentration diffusion rate of refrigerant gradually converged along the height direction. The concentration increase and decrease rates remained at approximately 0.5%/min and 0.06%/min, respectively. When the refrigerant gas leaked horizontally from the upper part of the room, the maximum concentration and concentration diffusion rate at the plane near the leak was reduced by approximately 50%, with the flammable risk time reduced by approximately 78%. The flammable risk time at the lower part of the room increased gradually with the height of the leak location. When the leak was in the upper part of the room, the LFL value was reached first at the bottom of the room and then in the planesthat are close to the leaking position.关键词：leakage of combustible refrigerant;concentration distribution;flammable risk time;safety evaluation957|1121|2发布时间：2024-07-18
- 摘要：Blizzards seriously affect the safe operation of trains. To prevent traffic accidents, the international standard CEN-TR 16251 proposes that snow drift tests should be conducted in an artificial climate room before trains go online. The artificial climate chamber is affected by the multi-air coupling of its air supply and snow drifting equipment. In this study, a numerical simulation for the train’s artificial climate chamber was conducted to investigate the motion characteristics of ice and snow particles. The results showed that when the diameterof ice and snow increased from 1.6 mm to 3.2 mm, the trajectory inclination angle was increased by 82.9%; the snowfall area was reduced by 73.1%; the snowfall distance was shortened by 54.7%. When the initial wind speed increased from 4.67 m/s to 7.82 m/s, the trajectory inclination angle was increased by 5%; the snowfall area was decreased by 63.3%;the snowfall distance was decreased by 6.41%. When the climate chamber wind speed increased from 1.98 m/s to 6 m/s, the trajectory inclination angle was reduced by 67.3%; the snowfall area was increased by approximately 500%; the snowfall distance was extended by approximately 460%. In addition, based on the simulation results, a prediction model for the trajectory of ice and snow particles under multi-parameter coupling was established. This model can accurately predict the trajectory of ice and snow particles, thereby providing technical support for implementing the snow drift experiment in the artificial climate chamber of trains.关键词：train;artificial climate chamber;ice and snow particles;motion characteristics998|799|1发布时间：2024-07-18
- 摘要：Considering the problem of frequent cleaning and replacement of filter elements for household water purifiers, a new household pure water production system based on the semiconductor Peltier effect and the principle of air humidification and dehumidification was proposed and established. The effects of circulating air flow rateon the system operation conditions, power consumption, water production rate, and water production per unit power consumptionwere experimentally studied. The results showed that with the increase incirculating air flow rate, the temperatures at the hot and cold sides of the semiconductors all decreased, the temperature difference between the hot and cold sides decreased slightly, and the cooling capacity of the system, semiconductor power consumption, and coefficient of performance all increased. When the circulating air flow ratewas 100 m3/h, the water production rate and water production per unit power consumption reached maximum values of 345 g/h and 459 g/(kW?h), respectively. The total dissolved solids (TDS) hygienic indicator was <3 mg/L and the daily water production of the system was >7.2 L/d, thus meeting the drinking water needs of general households.关键词：humidification and dehumidification;Peltier effect;purified water system;system performance;circulating air flow rate1111|915|0发布时间：2024-07-18
- 摘要：During the fermentation and drying of Fu Brick Tea, the stability of temperature and humidity in the oven and the low energy consumption of the energy system are important factors for ensuring the quality and cost of the tea. In this study, the Transient System Simulation Tool (TRNSYS) and experimental research were combined to studythe air-source heat pump system used in a Fu Brick Tea factory in Xianyang. By studying the changes in temperature and humidity in the typical monthly drying room in each season, the operating state of the air-source heat pump system during the whole year was assessed to determine whether it met the technological requirements. On this basis, the simulation results of the energy consumption of the system in the representative month and the gas boiler system used in the early stage of the production plant were compared, and the energy-saving and environmental protection characteristics of the air-source heat pump system were studied. The results showed that in January, April, and October, the average standard coal consumption of the heat pump system was 44.42% of the boiler system, and the average emissions of CO2, SO2, and NOx were 34.13%, 44.1%, and 40.6% of the boiler system, respectively. In the fermentation and drying process of the tea, the air-source heat pump system had better energy saving and environmental protection characteristics than the gas boiler system.关键词：energy conservation and environmental protection;TRNSYS;Fu Brick Tea;air-source heat pump944|954|0发布时间：2024-07-18
- 摘要：System performances with different packings (wire mesh corrugated, metal hole plate, ceramic corrugated, paper wet curtain, and plastic S-type) were examined to study the effect of packing on the performance of ice slurry wet pre-cooling systems. Key indicators are the temperature and humidity in the pre-cooling room, the pre-cooling process duration, the temperature variation coefficient, and the weight loss rate. The results showed that the final temperature of the circulating air in the precooling room could reach -1 ℃ with all types of packing, and the relative humidity of the air could be stabilized above 90%, meeting the precooling process requirements of pleurotuseryngii. When the ceramic corrugated and paper wet curtain packings were used in the pre-cooling room, the temperature variation coefficients were 0.26% and 0.28%, respectively, which are significantly less than the other packings (P<0.05), indicating that the pre-cooling of pleurotuseryngii was more uniform. When the wire mesh corrugated packing was used in the pre-cooling room, the pre-cooling process duration was significantly less than the other four packings (P<0.05), which was 70.2 min. When the wire mesh corrugated packing and metal hole plate were used in the precooling room, their weight losses were significantly lower than the other three packings (P<0.05), which were 2.65% and 2.85%, respectively, indicating that the weight loss of pleurotuseryngii was smaller than the others.关键词：fruits and vegetables precooling;humid cool heat exchanger;ice slurry;packing;cold storage1042|834|0发布时间：2024-07-18
- 摘要：The performance and feasibility of the air refrigeration system applied to vaccine cold storage were explored and compared with a cascade refrigeration system based on characteristics of safety and environmental protection, local availability of the refrigerant, and no temperature fluctuation caused by evaporator defrosting. The accuracy of the thermodynamic model was verified by comparison with the literature. The research results showed that when the ambient temperature was 35 ℃, the coefficient of performance (COP) of the air refrigeration system using three-stage compression (total pressure ratio of 8) and a regenerator (pinch point temperature difference of 5 ℃) was 0.23–0.38 and varied linearly within the storage temperature range of -70–10 ℃. This COP is 25.8% less than the COP of the cascade refrigeration system at -70 ℃. When the ambient temperature increased by 10 ℃, the COP and cooling capacity of the air refrigeration system were reduced by 5% and 3%, respectively. This difference was considerably less than that of the cascade refrigeration system (reduced by 15% and 8%, respectively); thus, the impact of ambient temperature on the storage temperature was less sensitive. The air refrigeration system can change the air supply pressure difference to a uniform supply of air in the vaccine cold storage by adjusting the air outlet state. Compared with the cascade refrigeration system, the cost and power consumption of the fan equipment in air refrigeration systems are less, and the adjustment is more convenient. Therefore, the air refrigeration system applied in the low-temperature storage of vaccines in the temperature range below -70 ℃ shows advantages of high reliability and stability. It is especially suitable for cold-chain logistics equipment for the low-temperature transportation of vaccines.关键词：air refrigeration;low-temperature cold storage;thermodynamic analysis;vaccine storage1033|1066|1发布时间：2024-07-18
- 摘要：In this study, the efficient preservation of fresh frozen plasma was investigated. Improving the quick freezing efficiency was achieved by adding a magnetic field to assist the freezing process. The changes in plasma ice crystal structure and size in the quick-freezing experiment under a magnetic field of 0–100 Gs were analyzed. Considering magnetic field-assisted quick-freezing accelerates the mass and heat transfer rate, the growth rate of ice crystals is faster than the speed of water migration, resulting in changes in the shape and distribution of the ice crystals. Therefore, small, round, and uniform ice crystals were formed in the plasma, which reduced the damage to the structure of the plasma by the ice crystals and thus improved the quality. The plasma coagulation factor Ⅷ content in the quick-freezing experiment under 0–100 Gs magnetic field intensity was reduced by different amounts depending on the magnetic field intensity when compared with that for fresh frozen plasma. The maximum reduction of 3.56% occurred at a magnetic field of 20 Gs. The active concentration under magnetic fields of 60 Gs and 80 Gs were higher than those atother field strengths, and the plasma quality effect after quick-freezing storage was better.关键词：plasma;magnetic field intensity;freeze;coagulation factor Ⅷ824|909|0发布时间：2024-07-18
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