最新刊期
卷 40 ， 期 2 ， 2019
- 摘要：Liquid nitrogen quick-freezing technology enables food to pass quickly through the ice crystal area, and results in total or partial vitrification, which improves the quality of food and has been widely used in the food cold chain. In this study, the basic principles and classic heat transfer model of the liquid nitrogen quick-freezing technology are briefly introduced, and the characteristics of quick-freezing methods such as liquid nitrogen immersion freezing, cold-air circulation freezing, and spray freezing are compared. A thorough quality evaluation of quick-freezing food and research progress on applications of the quick-freezing technology are conducted. Finally, future research directions for the liquid nitrogen quick-freezing technology are considered.关键词：food quick-freezing;glassy preserved;liquid nitrogen frozen2276|2903|5发布时间：2024-07-18
- 摘要：Based on thermal management systems of pure electric vehicles, a thermal management scheme for a whole vehicle is proposed in this study under summer conditions. In this scheme, a parallel cooling system using refrigerant is developed for the batteries and cabin, and the heat transfer performance of the heat pipe is considered for heat exchange between the batteries and refrigerant. A liquid cooling system is used for the motor. The proposed thermal management system was tested using a system simulation under the New European Driving Cycle at 35 ℃. The results demonstrated that the temperature of the cabin reached 24 ℃ after 64 s. The cabin temperature then maintained a dynamic stability near the setting temperature. Moreover, the temperature of the batteries reached 25 ℃ after 68 s then maintained a stable temperature under the vehicle control strategy. An increase in motor temperature occurred at a low rate under an urban cycle and exhibited a rapid increase under an suburb cycle. However, the temperature of the motor was maintained within 80 ℃关键词：electric vehicle;thermal management system;numerical simulation;refrigerant;heat pipe2155|2621|2发布时间：2024-07-18
- 摘要：The performance of the battery cooling unit is critical to the safe, efficient, and reliable operation of the power battery in a vehicle. Based on the process of refrigerant direct cooling, an 8-kW power battery cooling unit for use in a pure electric truck was designed and developed. The performance of this unit was tested in both a lab and the truck itself. The results showed that if the temperature of the cooling plate located at the bottom of the battery was between 5 and 10 ℃, the highest temperature in the battery core could be reduced to 35 ℃. In addition, the refrigeration capacity could reach 7.8 kW with dual compressor cooling system. The temperature difference between the inlets and outlets of 15 cooling plates was less than 5 ℃ when the distributor and capillary were combined. In a high-temperature environment, the vehicle battery cooling unit used in the truck could maintain an average battery-core temperature of less than 28 ℃. Different inlet temperatures of cooling plates could be controlled within a range of 7–10 ℃, whereas the outlet temperature could be controlled within 9–13 ℃, which is very effective for the cooling of battery. In addition, the influence of refrigerant charge and the opening degree of the H-type thermal expansion valve on the performance of the unit were analyzed, and the control strategy of the unit was formulated and evaluated.关键词：battery cooling;direct cooling system;cooling plate;control strategy;experimental research2139|2406|2发布时间：2024-07-18
- 摘要：A performance simulation model of a cylindrical fin-and-tube heat exchanger is established based on a sub-row-parameter model. The model can calculate the heat transfer performance of a heat exchanger based on thermodynamics equations and heat transfer theory. The calculated results of the model, which were verified by experimental data, show that the mean relative deviations of the heat exchange and outlet dry-bulb temperature were 6.31% and 0.61%, respectively, which represent the largest and lowest mean relative deviations. The calculated results agreed well with the experimental data. The performance simulation model was adopted to calculate the performance of the heat exchanger under different cooling conditions. The effects of air volume, water mass flow rate, air inlet dry-bulb temperature, and water inlet temperature on heat transfer performance were investigated. The results of the analysis under variable conditions not only predicted heat transfer performance in off-design conditions but also provided a basis for adjusting the operating conditions of the heat exchanger.关键词：cylindrical fin-and-tube heat exchanger;performance simulation;variable conditions1990|2055|4发布时间：2024-07-18
- 摘要：How to enhance the heat dissipation performance of water-cooled radiator to maintain the normal operating temperature of computer chips become the research focus of data center server cooling. In this paper, the comprehensive coefficient F and chip temperature of water-cooled radiator are taken as the target parameters. The orthogonal test method is used to optimize the thickness of the radiator's substrate, the location of the channel (located on the substrate), the number of channels and the width of the channel. The optimal combination of F index and F index radiator is obtained according to different needs. The results showed that the maximum heat flux of the T and F index radiators was 78 and 65 W/cm2, respectively, under a cooling water volume flow rate of 0.4 L/min and an inlet temperature of 20 ℃. The heat dissipation performance was analyzed from two aspects, i.e., temperature distribution of the radiator basement and the total thermal resistance. It showed that the temperature gradient and total thermal resistance of the T index radiator were lower than that of the F index radiator, indicating that the T index radiator is superior to the F index radiator. However, the pressure drop of the F index radiator was lower than that of the T index radiator under different flow rates. When the chip heat flux was less than 65W/cm2, the flow performance of fluids in the channel of F index radiator was better and could meet the heat dissipation requirements of the data center server. Moreover, the higher heat flux should be cooled by the T index radiator.关键词：computer server;CPU chip;chip cooling;water cooling radiator;orthogonal design2264|3019|4发布时间：2024-07-18
- 摘要：A refrigerant distribution parameter (RDP) evaluation method is proposed to investigate the influence of frost formation on the distribution of refrigerant in micro-channel evaporators. The distribution of refrigerant under frosting conditions was measured by infrared thermal imaging and digital image processing. Experimental results showed that with an increase in thickness of the surface frost layer of the evaporator, the overheating zone in the evaporator decreased gradually and the distribution of the refrigerant in the two-phase zone was more uniform. In a 180 min experiment conducted in this study, the refrigerant overheat area decreased by 22.7%, the RDP increased by 17.2%, and the heat exchange rate decreased by 2.34%. These results provide a quantitative method to examine the distribution characteristics of micro-channel evaporator refrigerant under frosting conditions.关键词：micro-channel evaporators;frost formation;refrigerant distribution;infrared thermal imaging2188|2076|3发布时间：2024-07-18
- 摘要：In this study, the surface heat transfer coefficient was selected as the evaluation index and the two-phase flow condensation heat transfer characteristics of R134a inside a horizontal micro-fin tube with 6.35 mm outer diameter were studied. The effects of the test conditions and structural parameters of the micro-fin tube on the surface heat transfer coefficient were analyzed. Correlations of Cavallini et al., Miyara et al., and Oliver et al. were also applied to predict the surface heat transfer coefficient inside the micro-fin tube. We found that the correlation of Cavallini et al. was the most effective at predicting the heat transfer characteristics, where the average and mean deviations of predicted and experimental values were ﹣21.47% and 21.94%, respectively. Although the average and mean deviations of the predicted and experimental values of the correlation of Miyara et al. were 16.21% and 30.65%, respectively, the margin of deviation was ﹣47.12% to 82.32%, which indicates that a greater deviation still exists between the predicted and experimental values under certain conditions for the correlation of Miyara et al.. The predictive ability of the correlation of Oliver et al. was the worst of the three correlations, where the average deviation of the predicted and experimental values was ﹣54.93%. The correlation of Oliver et al. was thus modified based on the experimental data, and its predictive ability was improved greatly, where the average and mean deviations of the predicted and experimental values were ﹣2.37% and 10.77%, respectively.关键词：micro-fin tube;R134a;flow condensation heat transfer;surface heat transfer coefficient;pressure drop;modified correlation1962|2127|0发布时间：2024-07-18
- 摘要：This study investigates the flow resistance and surface coefficient of the heat transfer of four types of refrigerant with different tube diameters for a finned-tube heat exchanger. The optimum tube diameter for each refrigerant was studied using a developed simulation model. The simulation results show that the flow resistance characteristics of the four refrigerants followed the order of R22 > R290 > R410A > R32, and the comparison of the surface coefficient of the heat transfer followed the opposite trend. For an air conditioner, the system coefficient is known to increase with the decrease in the condenser inlet pressure (compressor exhaust pressure) under a fixed cooling capacity. According to the simulation results, the condenser inlet pressure first decreased and then increased with the increase in the tube diameter of the heat exchanger when the heat transfer capacity was set to 2 000 W. The optimum diameters of the heat exchanger for R22, R410A, R32, and R290 followed the sequences of 7–7.5 mm, 6–6.5 mm, 6–6.5 mm, and 6.5–7 mm.关键词：matching characteristic;refrigerant species;heat exchanger tube diameter;finned tube heat exchanger2223|2511|0发布时间：2024-07-18
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Study on Key Technology of Refrigerant Cooling to the Frequency Conversion Board in Air Conditioning
摘要：This study focuses on the key technology of refrigerant cooling to the frequency conversion board in air conditioning. Specifically, the design, manufacture and performance test method of a refrigerant cooling board are studied, and a practical prototype of the technology is then developed. In addition, how to choose a suitable thermal pad to enhance the heat transfer between the dissipation plate and heating element is studied. An experiment was conducted to select the best size for the expanding head and copper tube. A reasonable experiment was also developed to test the heat dissipation performance of the heat dissipation plate. The results revealed whether the processing methods of the refrigerant cooling board work or not. This study’s methods and results provide strong support for the practical application of this technology.关键词：frequency conversion board of air conditioning;refrigerant cooling;tube expansion processing;interface thermal material1759|2068|1发布时间：2024-07-18 - 摘要：The heating performance of a heat pump can be improved by using a natural cold source. In this study, two types of sub-cooling systems with natural cold source were proposed: main loop and by-pass loop. A theoretical analysis was conducted and an integrated test bench for an R32 vapor compression heat pump was built. Running parameters such as the discharge temperature, heating capacity and heating coefficient of performance (COP) were investigated in the test bench based on three operation modes: main loop sub-cooling, by-pass loop sub-cooling, and a single-stage system. The results showed that for the main loop and by-pass loop sub-cooling systems, when the sub-cooling volume flow rate increased to 0.02 m3/h, the discharge temperature was reduced to 6.8 ℃ and 8.2 ℃, respectively. In addition, the heating capacity was reduced by 6.4% and 10%, and the heating COP was reduced by 2.5% and 5%, respectively.关键词：natural sub-cooling;heat pump;R32;COP1867|2080|1发布时间：2024-07-18
- 摘要：Automotive heating, ventilating, and air-conditioning (HVAC) noise is the primary noise source in an automotive air-conditioning system and mainly manifests as aerodynamic noise. In this study, the mechanism of aerodynamic noise generation in HVAC was assessed and the aerodynamic noise performance of a vehicle HVAC assembly was improved. The flow field of an HVAC system was simulated and optimized by modifying the molded lines of the air handling unit and the blower volute, and by adjusting the position of the damper. Results showed that the optimized HVAC assembly presents better noise performance than the baseline. Specifically, the noise sound pressure level was severely reduced by 2.3 and 3.3 dB(A) respectively in the vent and defrost modes , which are the typically used ones in the vehicle.关键词：automotive air-conditioner;HVAC assembly;aerodynamic noise;simulation model2237|2100|0发布时间：2024-07-18
- 摘要：Air-source heat pumps have been widely used for room heating and air conditioning because of their stable performance and easy installation. The greatest performance limitation is the frosting and defrosting problem of the outdoor heat exchanger during winter. This study presents a review of the frosting conditions, frost-free method, and different defrosting methods for air-source heat pump systems. In particular, the system and principles of the application of heat storage technology for heat pump defrosting are summarized. The applied phase change material (PCM) and structures of heat storage exchangers based on different studies are also presented in this work. Finally, future research directions for realizing frost-free or effective defrosting and continuous heating of air-source heat pump products are discussed. These include the development of reliable adsorption materials and regeneration methods to overcome problems posed by frost. Methods of high-voltage field and ultrasonic defrosting must be further considered to improve stability and economy. The application of PCM for defrosting has good market prospects, but the design of heat pump systems and the structure of PCM exchangers must be optimized, and PCM should be further studied.关键词：air-source heat pump;frosting;defrost;phase change material;heat storage1869|2214|4发布时间：2024-07-18
- 摘要：In this study, to understand the relationship between compressor frequency and the performance of the R410A/R410A cascade refrigeration system, changes in system performance under different frequency of high and low temperature grade compressors are conducted experimentally and analyzed. The results showed that under the same working conditions, a) the intermediate temperature of the system increased by 2.36 ℃, and the difference between the high and low temperature grade compression ratios was reduced by 44.6% when the frequency of a low pressure compressor increased from 50 to 62 Hz; b) the intermediate temperature of the system decreased by 3.7 ℃, and the high and low temperature grade compression ratios increased by 58.5% when the frequency of the high temperature compressor increased from 50 to 62 Hz. The system cascade temperature difference was smaller when the frequency of high temperature compressor changed, and the system coefficient of performance (COP) was higher than that of the system under the frequency change of low-temperature compressor. When the frequency of both the high and low temperature compressors was 53 Hz, the system cascade temperature difference was the least and the system COP was the optimal.关键词：compressor frequency;cascade system;R410A;COP1901|1986|4发布时间：2024-07-18
- 摘要：To explore the thermal performance and optimization direction of a large natural draft cooling tower, the thermal performance of a large natural draft cooling tower with a watering area of 12 000 m2 was tested for a 1 000 MW coal-fired unit. The gas-water ratio and cooling number were used to fit the results, and thermal performance equation and correction coefficient of the cooling test tower were obtained. The distribution of the measured wind temperature in the tower was given. The water temperature of the tower was calculated using different resistance coefficient formulas. The results showed that the correction coefficient of industrial towers with equal heights of packing and those with unequal packings was 1.047–1.081. The root mean square error of the air temperature in the industrial towers with unequal heights of packings was 0.56–0.67 ℃, which was less than the corresponding cooling tower with equal heights of packing. Thus, the cooling performance of the cooling tower could be enhanced by the unequal arrangement of the packing. The water temperature of the tower could be quickly calculated by using the empirical formula of resistance under the condition that the amount of water entering the tower was large, which provides a reference for the design and modification of large natural draft cooling towers.关键词：thermal performance;field test;natural draft cooling tower;air temperature distribution;outlet water temperature1904|2116|1发布时间：2024-07-18
- 摘要：The heat storage tank is an indispensable component in a solar thermal utilization system. To improve the efficiency of a solar water heating system, phase change material Ba(OH)2?8H2O was added to a heat storage tank. The thermal properties of the heat storage tank were then studied through experiments when the initial water temperature was 80 ℃ and the inlet temperature was 5 ℃. Results showed that the heat storage of the water tank increased from 18.81 to 19.07 MJ when adding the phase change material. With the increase in the inlet volume flow rate, the MIX number of the water tank initially decreased and then increased, whereas the effective heat release efficiency first increased and then decreased. The maximum efficiency of 92.2% occurred at a flow rate of 3 L/min. The addition of the phase change material could increase the heat release efficiency and heat stratification characteristics of the heat storage tank, and the closer the position of phase change material is to the inlet, the better the improvement is.关键词：heat storage tank;phase change material;solar energy;thermal stratification;heat discharging efficiency2129|1988|8发布时间：2024-07-18
- 摘要：To improve the accuracy of fault diagnosis for chillers, a fault diagnosis strategy based on an exponentially weighted moving average (EWMA) and Bayesian network (BN) is proposed in this study. The EWMA-BN method used an EWMA control chart to detect faults, and its control limits classified the fault data into the three states of higher, lower, and normal. The conditional probability table was obtained through probability statistics, and the prior probabilities were obtained from expert knowledge. The conditional probabilities were input to BN for fault diagnosis. With respect to number, input order, and completeness of evidence nodes, experimental data were used to analyze the characteristics of the method for fault diagnosis. The results showed that the EWMA-BN method had a significant effect on fault diagnosis for chillers, and the posterior probability values (fault diagnosis results) were all higher than 85%. The results also showed that the increase of evidence nodes could improve the accuracy of fault diagnosis results, but the order of the input nodes had no effect on the final results. The use of uncertain and incomplete information further improved the fault diagnosis capability of the method. The EWMA-BN method was validated using the data provided by the ASHRAE Project, which revealed that this strategy is robust and effective.关键词：Bayesian network;fault diagnosis;EWMA control chart;conditional probability table;chiller2152|2228|1发布时间：2024-07-18
- 摘要：In this study, a flow structural model in a rectangular channel with an axial flow fan is established and analyzed through numerical simulation and experiments to get the influence of two design parameters, i.e., axial length of the deflector and tip clearance, on the performance of axial flow fan. The mapping relationship between the design parameters and internal and outlet flow characteristics of the rectangular channel with an axial flow fan is also presented based on the simulation model. The experimental data revealed that the outlet static pressure, volume flow rate, and efficiency of the fan were inversely proportional to the clearance factor and directly proportional to the length factor. The comparison between the simulation results and experimental data validated the simulation model. Based on the mapping relationship, the optimal clearance factor and length factor of the fan design parameter factor were 0.8% and 12.5%, respectively, which could guide the design and optimization of a refrigerator duct structure.关键词：clearance factor;length factor;axial flow fan;flow field characteristics;aerodynamic performance1916|2046|3发布时间：2024-07-18
- 摘要：In this study, a three-dimensional mathematical model was established to simulate the pre-cooling process for blueberries in boxes containing three holes. The pre-cooling time and non-uniformity of blueberries with variable wind speeds were analyzed in three types of pre-cooling boxes. Considering the capacity of blueberries in different boxes, a density pre-cooling factor was proposed to evaluate comprehensively the quality of blueberries and the pre-cooling time of the pre-cooling process. The numerical results showed that the pre-cooling time of blueberries decreased with increasing wind speed. At the same pre-cooling wind speed, more than 1/3 of the blueberries could be carried in the No. 3 box, and the 7/8 pre-cooling time increased by less than 5 min. In addition, the unevenness increased by 0.2–0.4, and the density pre-cooling coefficient increased by as much as 3.09 kg/(m3.min). Based on the factors considered, the optimal pre-cooling speed of blueberries was 1.5 m/s. Although the unevenness of cooling increased in the No. 3 box, the utilization rate of pre-cooling storage could be enlarged effectively.关键词：differential pressure pre-cooling;three-dimensional pre-cooling model;vent-hole type;pre-cooling uniformity;density pre-cooling factor2181|1978|2发布时间：2024-07-18
- 摘要：One of the major factors in the annual loss of vaccine products is the failure of cold-chain transportation, where the most common piece of equipment used during transport is the cold storage box. The main factors that influence the performance of a cold storage box include the heat-insulating property of the thermal insulation material, the cooling capacity of the storage material, and the design of the thermal insulation packaging. This study reviews the research progress on cold storage boxes in the vaccine cold chain. The selection and application of common insulation materials and phase-change cold storage materials for vaccines were analyzed, and calculations related to the thermal resistance of the box and the monitoring of the temperature were studied. The research direction for integrated packing and development of phase-change cold storage materials were also proposed.关键词：cold storage box;phase change cold storage;thermal insulation packaging;vaccine cold chain;review2442|2136|6发布时间：2024-07-18
- 摘要：In this study, a swing absorption refrigeration system with 2,2,2-trifluoroethanol/tetraethylene glycol dimethyl ether (TFE-TEGDME) solution as the refrigerant pair was built to observe the vertical tube falling film absorber. Experiments in the stationary state showed that when the mass flow rate was 0.1–0.2 kg/min, the liquid film was in a laminar and monochromatic wave state; when the mass flow rate was 0.5 kg/min and 0.8 kg/min, the liquid film appeared to be a quasi-sine wave and merging wave flow, respectively; when the mass flow rate was 1.2 kg/min, the liquid film partly fell off. The absorption effect depends heavily on the surface wave type. The experimental results in the swing state showed that the perturbation on the liquid film will increase with increasing swing amplitude or a decreasing swing period. When the swing amplitude is 15° or the period is 4 s, the liquid film appears to be a merging wave or falls off from the wall of the tube. Under a fixed swing amplitude and period, the perturbation on the film is greater at the edge of the swing, whereas the flow is smoother at the middle of the swing. When the mass flow rate is 0.28 kg/min, the coefficient of performance (COP) of the system reaches the maximum at the swing amplitude of 8° or a period of 10 s. However, the COP will reach the maximum at a swing amplitude of 10° or a period of 8 s when the mass flow rate is 0.14 kg/min. The results also showed that when the flow rate is higher, the perturbation of the swing is greater.关键词：absorption refrigeration;swing state;falling film wave patterns;visualization2037|1992|0发布时间：2024-07-18
- 摘要：To reduce the production cost and running energy consumption of a solution dehumidification system, experiments were conducted in this study on dehumidification equipment based on a mixed salt solution consisting of LiBr and CaCl2. The temperature and humidity of inlet and outlet air as well as the energy consumption of the dehumidification device were measured. The dehumidification capacity, refrigeration capacity, and dehumidification performance coefficient of the system were analyzed. Based on the initial investment and working performance of the mixed salt solution, a comprehensive performance and cost ratio of the solution was weighed by considering the life cycle cost of the solution dehumidification system. The results showed that the mixed LiBr and CaCl2 solution at a ratio of 3:1 can obtain a higher dehumidification efficiency and lower cost compared to other combination, and the total cost can be reduced by 14.5%.关键词：mixed liquid desiccant;refrigerating capacity;dehumidification capacity;life cycle1765|1930|3发布时间：2024-07-18
- 摘要：Solar liquid desiccant air-conditioning represents a new, environmentally friendly, and energy-saving air-conditioning system. Solar-energy solution regeneration is one of the most important aspects of the system. In this study, a comprehensive review of the latest regeneration technologies for solar liquid desiccant air-conditioning systems is presented. The following three regeneration methods were simulated and compared: photothermal, photovoltaic, and PV/T. The results showed that under ideal conditions, the PV/T-ED regeneration was 40.5% greater than PV-ED regeneration in terms of energy-saving, whereas PV-ED regeneration was 51.6% better than PT regeneration. When the PV/T-ED regeneration was operated for LiCl-H2O, LiBr-H2O, and CaCl2-H2O under ideal conditions, it was found that the LiBr-H2O had the largest concentration difference between the inlet and outlet, whereas the LiCl-H2O had the strongest dehumidification capability after regeneration.关键词：solar energy;liquid regeneration;electrodialysis;energy analysis1761|1949|7发布时间：2024-07-18
- 摘要：A free cooling/vapor compression integrated air-conditioning system, which combines vapor compression refrigeration and a separate heat pipe, was proposed in this study. A first coolant and liquid-pump-driven second coolant are circulated throughout the system. The integrated system can operate on three modes: vapor compression refrigeration, dual refrigeration, and free cooling. In hot seasons, the refrigerating capacity is entirely provided by the vapor compression refrigeration unit, whereas in cold seasons, the refrigerating capacity is fully provided by the heat pipe unit. In transition seasons, the free cold source is used as much as possible by the heat pipe unit, and inadequate refrigeration capacity is supplemented by the vapor compression refrigeration unit. Moreover, a prototype of the HKF-200FH refrigeration unit is designed and tested. The compression and heat-pipe units are paralleled by a shell-tube type evaporative condenser whose tube side is used as an evaporator of the compression unit to supply refrigeration capacity to the shell-side second coolant when operating in compression refrigeration mode or dual refrigeration mode. The test results show that the refrigeration capacity of the integrated system changed little with an increasing energy efficiency ratio (EER) when the ambient temperature decreased. The refrigeration capacity in the compression refrigeration mode (ambient temperature is 35 ℃) and heat-pipe mode (ambient temperature is 10 ℃) were 197.38 and 196.89 kW with EER of 3.5 and 17.26, respectively. Since May 2014, the prototype of the HKF-200FH has been safely and reliably operated at an EB-level cloud storage laboratory in Beijing. The long-term operation results have shown an energy-saving rate of 45% compared with traditional vapor-compression-type computer room air conditioners.关键词：data center air-conditioning;free cooling;integrated refrigeration;energy-saving;heat pipe1959|1981|2发布时间：2024-07-18
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