最新刊期
卷 43 ， 期 1 ， 2022
- 摘要：The finned tube heat exchanger used in air conditioners becomes corroded after long-term use. This affects the heat exchange performance of the heat exchanger and reduces the energy efficiency of the entire air conditioning system. In this review, three main corrosion mechanisms of finned tube heat exchangers were introduced: ant-nest corrosion, pitting corrosion, and gap corrosion. The influence of corrosion on the performance of the finned tube heat exchanger was analyzed from three aspects: morphology, pressure drop, and heat transfer characteristics. The results show that the heat transfer coefficient and heat transfer of the finned tube heat exchanger decreased after corrosion. The air-side pressure drop was less affected (< 5 Pa). The research status of corrosion resistance of finned tube heat exchangers is summarized. It was found that research on improving the corrosion resistance of heat exchangers focused on the preparation of better corrosion-resistant coatings. Finally, future research directions for corrosion protection of refrigeration and air conditioning heat exchangers are summarized and discussed.关键词：finned tube heat exchanger;heat transfer coefficient;anticorrosive coating;corrosion1596|2607|0发布时间：2024-07-18
- 摘要：Thermoelastic refrigeration is a solid-state technology that produces a refrigeration effect by driving the phase change of thermoelastic materials with a stress field. Natural rubber has attracted much attention because of its price and low elastic modulus. In this study, vulcanized natural rubber was subjected to a stretching-twisting-untwisting-retraction cycle at an ambient temperature above 0 °C to eliminate the Mullins effect. Natural rubber with the Mullins effect was subjected to cyclic loading in the ambient temperature range of -30–40 ℃. The temperature change of natural rubber during the cycle was recorded using an infrared thermal imager to explore the influence of temperature on the torsional tensile thermal effect. It was found that the temperature change of natural rubber during the twisting-untwisting process is greater than that in the simple stretching-retraction process. The temperature change is the highest due to the low-temperature crystallization characteristics of rubber at an ambient temperature of -20 ℃. The temperature during unloading reaches -41.3 ℃.关键词：solid refrigeration;natural rubber;thermal effect;crystal1144|1013|1发布时间：2024-07-18
- 摘要：A thermodynamic analysis was conducted on an NH3/CO2 cascade refrigeration system to optimize the operating parameters. An NH3/CO2 cascade refrigeration system test platform was built, and the experimental data at some working points were obtained. Comparative and error analyses were performed using the thermodynamic analysis results of empirical formulas for different compressor isentropic efficiency. The formula that is consistent with the experimental data was used to analyze the maximum coefficient of performance (COPmax), the optimal intermediate temperature (TLC,opt), and the optimal inter-stage capacity ratio (nV,opt) of the system under variable temperature conditions. The temperature conditions included the evaporating temperature (Te), condensing temperature (Tc), cascade heat exchange temperature difference, and subcooling and superheating in the high-and low-temperature loops. The results show that Te has the greatest influence on COPmax and TLC,opt. When Te increased by 5 °C, the COPmax of the system increased by approximately 18.5%, and the TLC,opt increased by approximately 2.23 °C. Tc had the greatest influence on nV,opt, and the low-temperature loop superheat had the least influence on nV,opt. For every 5 °C increase in Tc, the nV,opt increased by approximately 6.34%. A correlation fitting formula between the performance parameters and working conditions is proposed, which can provide a reference for the optimization of operations in a cascade refrigeration system.关键词：compressor isentropic efficiency;cascade refrigeration system;thermodynamic analysis;optimum inter-stage capacity ratio;optimum intermediate temperature1479|1118|1发布时间：2024-07-18
- 摘要：In this study a refrigerant pump-driven heat pipe and vapor compression composite cooling system with an evaporative condenser was proposed to solve the problems of high energy consumption and low cooling efficiency of traditional data center cooling systems. Through experimental research, the operating performance of this system under different outdoor temperatures and air velocities of condenser was analyzed. The results show that in the heat pipe mode, when the outdoor temperature is lower than 0 °C, reducing the air velocity of condenser can increase the system coefficient of performance (COP) and effectively prevent condensation in the evaporator. The evaporation temperature increases by 1.8 ℃ on average for every 1 m/s decrease in the air velocity of condenser. When the outdoor temperature is higher than 0 °C, increasing the air velocity of the outdoor unit can improve the energy-saving performance of the system. Compared with air cooling, when the outdoor temperature is 5–10 °C, the COP is increased by 15.5% on average after the evaporative-cooled mode is turned on. At the same time, evaporative cooling also enhances the cooling capacity of the system, increasing the upper limit of the outdoor temperature in the heat pipe mode from 10 °C to 15 °C. In the vapor compression mode, evaporative cooling can effectively improve the energy efficiency ratio of the system. When the outdoor temperature is 30 ℃, after the system is switched to the evaporative-cooled mode, the COP is increased by 17.5%, 16.2%, and 14.3%, respectively under the three air velocity of low (1.5 m/s), medium (2.5 m/s) and high (3.5 m/s).关键词：data center cooling system;experimental research;air velocity of condenser;evaporative cooling;COP1467|1510|1发布时间：2024-07-18
- 摘要：The aim of this study is to present an optimal method for load allocation in a multi-chiller system. By using the processed data from the historical operation data of the system, the Apriori frequent item set algorithm is used to mine the association rules among the operation variables and minimum energy consumption of each chiller under different operation conditions in stages. An optimal load allocation strategy combining a particle swarm optimization algorithm and association rules is proposed to minimize the total operation energy consumption of the chillers. The simulation results show that the optimal load allocation strategy can effectively reduce the total energy consumption of the chillers by optimizing the on-off and load ratio of the chiller. Compared with the original operation strategy, the total operation energy consumption of the system can be reduced by approximately 12.5%, and it is confirmed that the optimal load allocation strategy can save energy effectively.关键词：load allocation;association rules;chiller system;operating data;data mining1145|1165|0发布时间：2024-07-18
- 摘要：In this study a novel frost-free air-source heat pump (FASHP) system, which uses the waste heat of a screw compressor for auxiliary desorption, was proposed. A mathematical model of FASHP with waste heat desorption was developed, and the accuracy of this model was verified experimentally. A theoretical analysis was conducted concerning the influence of ambient temperature, relative humidity, air temperature, and flow rate on the desorption of the system. The results show that the ratio of the waste heat that the system can use for desorption to the total energy required for desorption could reach 0.61. The coefficient of performance (COP) was affected by the air temperature and humidity, but less affected by the temperature and mass flow of the desorption air. As the ambient temperature increased and the relative humidity decreased to the working condition at 7 °C/70%, the COP reached 2.52. The COP of the novel FASHP system increased by 10% compared to the original system. It was proved that this system can run efficiently and continuously under low-temperature and high-humidity environmental conditions关键词：air source heat pump;frost-free;waste heat;desiccant coated heat exchanger;screw compressor heat pump1278|1302|1发布时间：2024-07-18
- 摘要：In this study an air conditioning system with an ejector is proposed for electric vehicles. The indoor evaporator is designed as a separate front and rear evaporator. An ejector is added between the front and rear evaporators to increase the suction pressure of the compressor, and to form a stepped evaporation in the front and rear evaporators to optimize the performance of the system. The performance of the air conditioning system with an ejector for an electric vehicle was studied experimentally under different evaporation and condensation temperatures, and was compared with that of the traditional air conditioning system for electric vehicles. The experimental results indicated that the performance of the air conditioning system with an ejector for an electric vehicle is always better than that of a traditional air conditioning system under different refrigeration conditions. The performance improvement of the air conditioning system with an ejector gradually increases with an increase in the evaporation temperature or a decrease in the condensation temperature. In the range of the experimental conditions, the refrigeration capacity of the air conditioning system with an ejector increased by approximately 11.10%–14.57%, and the coefficient of performance (COP) increased by approximately 13.09%–16.61% compared with the traditional air conditioning system for electric vehicles. It was found in experiments that the heat transfer of the rear evaporator only accounts for 10.93%–13.51% of the system refrigeration capacity, and its heat transfer potential is not fully released. The flow rate of the refrigerant in the rear evaporator can be increased by adjusting the length of the capillary tube and improving the entrainment ratio of the ejector to further improve the COP of the system.1162|1034|1发布时间：2024-07-18
- 摘要：The thermal management system of electric vehicles is different from that of traditional passenger vehicles. For electric vehicles with a heat pump system and liquid cooling battery, the refrigerant charge is increased by 400–800 g compared with traditional air conditioning. If a combustible refrigerant is used, any leakage will spread to the passenger compartment, and the risk of combustion will increase. In this study, the concentration change process and maximum concentration of R1234yf refrigerant after evaporator damage and leakage with the air supply into the passenger compartment were dynamically monitored by numerical simulation. The results show that the refrigerant in the rear row accumulates more easily than that in the front row. After the refrigerant was completely leaked, the highest average R1234yf volume concentration at the four air outlets was 1.58%. The highest average R1234yf volume concentration at the breathing point of the four passengers was 0.99%. The highest average R1234yf volume concentration at the feet of the four passengers was 0.95%. The highest volume concentration in the passenger compartment was lower than the lower flammability limit of R1234yf. Compared with the test data of different vehicle models, it was found that different vehicle models had the greatest influence on the refrigerant volume concentration, which was 1.2% for different vehicle model.关键词：automotive air conditioning;leakage model;refrigerant;flammability1168|1167|2发布时间：2024-07-18
- 摘要：The compressor is the core equipment of a vapor compression system, which significantly affects the energy consumption and stability of the system. An experimental system was built for the vapor compression system driven by the roots compressor, in which the evaporation temperature, evaporation pressure, compressor pressure, and evaporation capacity were 80–100 °C, 46.60–101.64 kPa, 17.86–36.03 kPa and 125.72–424.85 kg/h, respecitvely. The suction flow rate, compression specific power, volumetric efficiency, and isentropic efficiency of the root water vapor compressor with varying evaporation temperatures were studied experimentally. The results show that the suction flow rate (7.10–11.74 m3/min) gradually increased, and the compression specific power (310.69–158.54 kJ/kg) gradually decreased with the increase in evaporation temperature. Both the volumetric efficiency (52.21%–71.54%) and isentropic efficiency (16.48%–36.15%) increased with the increase in evaporation temperature. Increasing the frequency can enhance the efficiency of the compressor, and the measured volumetric efficiency and compression specific power were consistent with the data in previous studies. There was a difference between the experimental and theoretical values of the volumetric efficiency and the isentropic efficiency of the compressor, but this difference decreased with an increase in the evaporation temperature, and the root water vapor compressor was more stable and highly efficient in the range of evaporation temperature of 90–100 °C.关键词：roots compressor;water vapor compression;volumetric efficiency;isentropic efficiency;experimental study1139|1496|1发布时间：2024-07-18
- 摘要：Many electronic devices can benefit from operating at low temperatures. However, the widespread use of cryogenic electronic devices is limited by the miniaturization of cryocoolers. In this study, a closed Joule-Thomson (JT) cooling system based on a multicomponent mixture was investigated. The system comprised a Hampson-JT microcooler and a linear compressor. The working fluid was a ternary mixture with a molar concentration of 39% methane, 20% ethane, and 41% isobutane. The cooling performance of a refrigerator under different conditions was studied experimentally. The results show that the microcooler can achieve a cold-end temperature of 165 K under 0.10–1.77 MPa and 0.14–1.90 MPa pressure, and 198 K under 0.36–1.73 MPa and 0.18–1.36 MPa pressure. The compact structure of the cooling system promotes the application of cryogenic electronic devices in the fields of military, space science, and biomedicine.关键词：cooler;Joule-Thomson effect;mixed-refrigerant;linear compressor1176|1080|1发布时间：2024-07-18
- 摘要：Fin optimization of tube-fin heat exchangers is a research hotspot, and there are few studies on tube types. A design method for a special-shaped tube with the same hydraulic radius as a circular tube is proposed. A numerical calculation model of the air-side heat transfer of the special-shaped tube-and-fin heat exchanger was established. The effects of tube shape, windward direction, and fin spacing on the performance of special-shaped tube-and-tube-fin heat exchangers were investigated. The results showed that for the double-row special-shaped tube heat exchanger, when the first row of tubes exposed to the air is larger than the second row, the air flow is the most uniform and the pressure drop is the smallest, delivering the best overall performance in the upwind direction. When the round tube, elliptical tube, special-shaped tube, and flat tube-fin heat exchangers are compared, the best resistance characteristic and comprehensive performance is the special-shaped tube at a air velocity of 4 m/s. The pressure drop is lower than that of the round tube by 31.86%, the value of performance enhancement evaluation index (Nu/Nu0)/(f/f0) is 1.456, mainly due to the large net flow area of the air between the tubes, and there is less disturbance when flowing through the heat exchanger. In addition, the larger the fin spacing, the greater the influence of the tube type on the air-side flow and heat transfer. The large fin spacing has better improvement effects on the resistance performance and overall performance of the heat exchanger than the small fin spacing.关键词：heat exchanger;numerical simulation;combination property;special-shaped tube1195|967|0发布时间：2024-07-18
- 摘要：In this study, a heat pump air conditioning system with waste heat recovery was developed based on vapor injection, and the performance was investigated experimentally. The study aimed to address the problem of heating capacity attenuation of heat pump air conditioning systems at low temperatures in winter, through the optimization of heat exchanger design. The experimental results show that the quasi two-stage compression heat pump air conditioner for electric buses exhibits good heating performance at low temperatures. Compared with the same working conditions without waste heat recovery, the heating capacity and coefficient of performance (COP) of the system are improved by 33.15% and 9.94%, respectively, where the ambient temperature is -20 °C, the interior temperature is 20 °C, and the residual heat is 1.8 kW. Compared with the single-stage compression system without battery cooling, the cooling capacity and COP of the optimized electric bus heat pump air conditioning system are increased by 4.58% and 3.72%, respectively, where the ambient temperature is 35 °C, the interior temperature is 27 °C, and the cooling capacity of the battery is 2.0 kW.关键词：heat pump air conditioning;waste heat recovery;vapor injection;heat exchanger1263|1278|1发布时间：2024-07-18
- 摘要：The degradation of the long-term performance of different types of vaporizers is caused by frosting. An experimental platform was built to study the effect of a double-wall heat transfer tube on heat transfer enhancement and frosting. In the experiment a tube was added to the inner side of the ordinary heat transfer tube and liquid nitrogen was used as the working medium. Twelve working conditions were designed based on different inner diameters (Φ6 mm, Φ8 mm, Φ10 mm) of double-wall heat transfer tubes and inlet flow. The temperature at different measuring points on the surface of the finned tube, the frost thickness, and the fluid temperature at the outlet of the finned tube were tested. The results show that when the inlet flow is 2.5 g/s, the outlet temperatures of the ordinary heat transfer tube, and double-wall heat transfer tube with inner diameters of Φ6 mm, Φ8 mm, and Φ10 mm are 193 K, 205 K, 200 K, and 199 K, respectively. This means that compared with the ordinary heat transfer tube, the double-wall heat transfer tube effectively delays the frost growth. Among the three tube specifications, the double-wall heat transfer tube with an inner diameter of Φ6 mm has a better effect on delaying the growth of frosting. When the inlet flow is 2.5 g/s, 3.5 g/s and 4.5 g/s, using a double-wall heat transfer tube with an inner diameter of Φ6 mm, the lower inlet flow can delay frosting on the fin surface.关键词：finned-tube vaporizer;frosting characteristic;double-wall heat transfer tube;heat transfer enhancement1090|902|1发布时间：2024-07-18
- 摘要：To explore the effect of the open structure on the boiling heat transfer of a micro-ribbed rectangular channel, a visual experimental study was conducted on the flow boiling heat transfer performance of open drop-shaped micro-rib channels and compared with the flow boiling heat transfer performance of a water droplet microchannel. At the same time, the flow and growth processes of bubbles under different flow rates in the channel were recorded and analyzed using a high-speed camera. Using deionized water as the working fluid, the inlet temperature was set at 30 °C, with a flow rate of 0.2–7.2 kg/h, heating voltage of 60 V, and shooting frequency of 500 fps. The experimental results show that the opening structure of the micro-fin array affects the flow characteristics. The open structure increases the heat transfer area, which is beneficial for the formation of the vaporization core and heat transfer. At lower and higher Re, the convection heat transfer of the unclosed droplet-shaped micro-fin array is better than that of the water-droplet-shaped micro-fin array. The waiting time and growth time of bubbles in microchannels II and III increase with an increase in Re, and the bubble growth time is greater than the waiting time. In addition, the waiting and growth times of region II were shorter than those of region III.关键词：micro-ribbed rectangular channel;flow boiling;unclosed drop shape;bubble waiting time;bubble growth time1139|908|3发布时间：2024-07-18
- 摘要：In this study, the heat balance method stipulated in the ASHRAE 75–77 standard is adopted to solve the problems of low heat exchange efficiency and high consumption of pipes in traditional tube evaporators used in food cold chain systems. The fin efficiency, heat transfer coefficient, and cooling capacity of a single-tube double-row finned tube evaporator and single-tube eight-row finned tube evaporator used in cold storage were studied experimentally. The results show that the average fin efficiency of the single-tube eight-row finned tube evaporator is 96.03%, which is 5.3% higher than that of the single-tube double-row finned tube evaporator. The cooling capacity per tube length of a single-tube eight-row fin-tube evaporator is 2.5–3 times that of a single-tube double-row fin-tube evaporator, and its unit mass aluminum cooling capacity is 11%–36% higher. Compared with the single-tube double-row finned tube evaporator, the single-tube eight-row finned tube evaporator consumes 10%–30% less at the same cooling capacity.关键词：single-tube multi-row fin-tube evaporator;fin efficiency;cooling capacity;heat transfer coefficient1293|1039|1发布时间：2024-07-18
- 摘要：In order to study the relationship between air velocity and heat transfer performance of CO2 finned-tube evaporator, a distributed parameter model was established in this paper. The changes of refrigerant pressure drop, heat transfer, temperature distribution and heat transfer coefficient of five kinds of flow-number were analyzed under conditions of evaporation temperature of -25 ℃ and air velocity of 0.5~4 m/s, and the reliability of the model was experimentally verified. Compared with the experimental values under the same working conditions, the relative error of the simulation model for predicting the heat transfer, refrigerant pressure drop and air side pressure drop was less than ±4%. Simulations demonstrated the heat transfer, refrigerant pressure drop and heat transfer coefficient of the evaporator with the same flow number all increase with the increase of air velocity, while the increase range decreases with the increase of air velocity. The optimal air velocity range is 2.5~3.5 m/s, reflecting the heat transfer effect and energy consumption. Choosing more flow numbers in a reasonable range can effectively improve the heat transfer performance and enhance the heat transfer uniformity in evaporator design. In this experiment, the 24 flow number evaporator is the best design scheme.关键词：evaporator;air velocity;process layout;natural refrigerant1137|1011|2发布时间：2024-07-18
- 摘要：3D pulsating heat pipes and phase change materials (PCMs) can be used for energy-efficient data centers. In this study an experimental bench of a 3D pulsating heat pipe/PCM module was built to study the heat transfer and energy saving characteristics of the coupled system. The 3D pulsating heat pipe with two liquid-filling rates of 34% and 44% was studied using three working materials, methanol, ethanol, and acetone. The thermal resistance model of the coupling module was established, and the thermal resistance variation rate of the coupling module was defined. The thermal resistance variation and energy-saving characteristics of the coupling module were studied under conditions of variable air temperature (20–26 °C) and velocity (3–9 m/s). In addition, the thermal resistance and energy-saving characteristics of the coupling module were studied. The results show that the thermal resistance change rate of the coupling module with 34% liquid filling rate is higher than that of the liquid filling rate of 44%, in which the thermal resistance change rates using methanol at 80 W and 120 W heating power are 48.2% and 48.7%, respectively. These are higher than those using ethanol and acetone under the same conditions. Compared with the traditional cooling method of data centers, the fans and chips can save 143.61 kWh and 176.82 kWh per year under 80 W heating power, respectively.关键词：data center cooling;3D pulsating heat pipe;phase change material;thermal resistance1115|988|1发布时间：2024-07-18
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Research on Heat Transfer Characteristics of Vapor Chamber Integrated Heat Spreader for Chip Package
摘要：The high heat flux and the development of miniaturized chips have restricted the thermal diffusion ability of traditional metal materials. In this study, a vapor chamber with a micro-pin was designed and used in an integrated heat spreader (IHS). The liquid filling rate, die size, and heat sink operating parameters (water flow rate and water temperature) affect the heat transfer performance of the vapor chamber (VC) IHS compared with a Cu IHS under the same working conditions. The experimental results show that the filling rate of the VC IHS, die size, and operating parameters of the heat sink will affect the heat transfer performance. Under the conditions of high heat flux and the same working conditions, the optimal filling rate of the VC IHS was 90%. The thermal resistance decreased with an increase in the heat sink parameters and die size. When the heat flux was 200 W/cm2, the VC IHS had a shorter start-up time and better temperature uniformity. Its thermal resistance and junction temperature are both lower than those of a Cu IHS, and the thermal resistance is reduced by 20%. In the field of high heat flux and miniaturized chip packaging, the VC has better application prospects in terms of efficient heat dissipation and temperature uniformity. The corresponding relationship between the thermal resistance ratio and the heat flux under different area ratios provides references for the chip packaging VC IHS thermal design.关键词：high heat flux density;chip packaging;vapor chamber;junction temperature;temperature uniformity1280|1234|0发布时间：2024-07-18 - 摘要：Distillation is the separation of components in a gas-liquid mixture using the difference in volatility. The distillation-type oil separator developed in this study combines the principles of traditional oil separation and distillation. The feed conditions of a constant pressure of 1 000 kPa in the tower, inlet temperature of 62 °C, and mass ratio of R134a and PAG of 7:3 were simulated using Aspen simulation software. The results show that the lubricating oil in the binary mixture can be removed by the distillation process. In this study an experimental setup was built to test the efficiency of the oil separator to verify its practical feasibility. The effects of the refrigerant circulation flow rate and the top cooling volume on the separation efficiency of the oil separator were investigated separately. The results showed that the oil separation efficiency was as high as 99.967% at a refrigerant mass flow rate of 7.5 g/s and a maximum cooling capacity of 200 W. From the experimental and simulation results, it was determined that introducing the distillation principle into the oil separator for the separation of the refrigerant-lubricant mixture can improve its separation efficiency. The separation efficiency of the distillation-type oil separator was 9.17 % higher than that of a conventional oil separator.关键词：oil separator;distillation;refrigeration cycle;refrigerant1140|1102|0发布时间：2024-07-18
- 摘要：Air conditioning systems commonly adopt multipath heat exchangers, which require distributors to guide the two-phase refrigerant to each flow path of heat exchangers uniformly. The gas-liquid two phase refrigerant may separate when it flows through the connecting tubes of distributors with bends, resulting in the deterioration of distribution uniformity. In this study, an optimization method was proposed for changing the traditional single-bending of tubes to the multi-bending of tubes to reduce the degree of separation of the gas-liquid two phase refrigerant. First, the influence of the bending structure factors of the connecting tubes on the distribution uniformity was investigated, including the bending angle, bending radius, and tube diameter. Second, the optimized structural parameters of the bending angle, bending radius, and tube diameter were combined to design an optimized connecting tube for the distributor. Finally, the distribution unevenness was compared between the optimized and original connecting tubes of the distributor. The results from the case studies in this study show that the bending angle is the main influencing factor, and the proposed optimization connecting tube of the distributor with three bends can reduce the distribution unevenness by 64.4% compared with the original one with a single bend.关键词：distributor;connecting tubes;distribution uniformity;structure optimization1336|1287|2发布时间：2024-07-18
- 摘要：The implementation of vapor-liquid separation during condensation enhances heat transfer and reduces the pressure drop simultaneously. The vapor-liquid separator is vital for the performance improvement of such liquid-separation condensers. This study focuses on a header baffle with a small hole as the vapor-liquid separator. A 3D numerical model for the separator was established to investigate the vapor-liquid separation characteristics. The model was validated by experimental data first, and then it was used to analyze the effects of hole diameter (0.5–2 mm) and hole position (centered or not) on the flow features of the working fluid in the header. The results showed that when the inlet mass flow rate was 3 g/s and the inlet vapor quality was 0.5, the liquid-separation efficiency and vapor drainage ratio increased with increasing hole diameter. The best performance is achieved when the hole diameter is 1.6 mm and centered. In this case, the liquid-separation efficiency was up to 70.23%, and the vapor drainage ratio was 0.14%. The hole position mainly affects the velocity and pressure distributions. It was found that the vapor-liquid inertial force ratio can reach up to 1.51×10-2 as the hole diameter is 2 mm and its position is not centered. Hence, the unreasonable arrangement of hole diameter and position could lead to “fluid impact” at the liquid-separation hole.关键词：liquid-vapor separation;condenser;liquid-separation hole;liquid-separation efficiency1035|1004|1发布时间：2024-07-18
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