最新刊期
卷 36 ， 期 5 ， 2015
- 摘要：To overcome the disadvantage of high discharge temperature in R32 compressor, two-phase refrigerant injection was proposed to decrease discharge temperature as well as improve system performance in severe conditions, and an improved injection system with economizer was proposed to realize two-phase injection. Based on the validated dynamic distributed parameter model of R32 scroll compressor, the optimization of heat transfer capability of internal heat exchanger and intermediate pressure according to system performance and discharge temperature were discussed. Through the optimized design and control of the two-phase injection system, the cooling capacity was enhanced by 7.1%-11.4% and COP was improved by 2.6%-6.2%.关键词：two-phase injection;R32;scroll compressor;intermediate pressure;injection quality2388|2866|2发布时间：2024-07-18
- 摘要：In order to analyze the relationship between the suction injection and the performance of the scroll compressor, the suction injection circuit was set up. And the mathematic model, containing the loss of leakage and heat exchange, was established at the same time. The discharge temperature and the refrigerating capacity and the COP of the system were investigated when the injection flow rate and the pressure ratio were varied. The result of the simulation was in reasonable agreement with the experimental data. The error was 2.5% at the low injection flow, and 10% at the high flow. It was also found that the discharge temperature decreased and the COP slightly increased then went down, when the injection flow increased. The COP of the system increased by 0.6%, while the discharge temperature decreased by 14 ℃ at the condition of the low injection flow. When the discharge temperature decreased by 42 ℃, the decline in the COP was less than 5%. Additionally, there existed an optimal value of the COP in the suction injection circuit when the injection flow varied at the high pressure ratio. Furthermore, the higher the pressure ratio was, the lower the COP decreased. As a result, the suction injection could put into use to decrease the discharge temperature.2511|2974|4发布时间：2024-07-18
- 摘要：A comprehensive physics-based model for a semi-hermetic CO2 reciprocating compressor is presented. The model is composed of two major sub modules, the thermal module and the mechanical module. The thermal module is used to simulate the vapor compression process inside the cylinder, while the mechanical module is to simulate the frictional loss happened in the bearing connected to the cylinder. Extensive experimental validation of the compressor model were carried out for a CO2 prototype compressor under different operating conditions. The maximum deviations of mass flow rate and power consumption are within 3% and 8%, respectively. Furthermore, parametric study was conducted to investigate the compressor performance as a function of the stroke-to-bore ratio and the gap between cylinder and piston under different operating conditions. The results indicated that there is an optimal stroke-to-bore ratio under different operating conditions. Both volumetric efficiency and isentropic efficiency fall with the increasing compressor speed. There are optimal diameters for suction and discharge valves. On the volumetric efficiency, the gap between suction valve and valve seat has heavier impact than the gap between discharge valve and valve seat, while the gap between piston and cylinder has greater impact than the gap between cylinder and cylinder ring. The analysis would help further improvement on the compressor design.关键词：trans-critical CO2;reciprocating compressor;model;simulation;analysis2283|2775|1发布时间：2024-07-18
- 摘要：The condensation heat transfer characteristics of R290 and R22 were investigated experimentally in a horizontal circular minitube with 1.085 mm diameter. The mass flow rate of R22 is 200-1200 kg/(m2?s), and that of R290 is 200-650 kg/(m2?s). The saturation temperature is 40 ℃ and 50 ℃ respectively during the experiment. The experimental results show that at the higher mass flow rate of R22, the condensation heat transfer coefficient increases slowly or even decreases little with the vapor quality increasing, for the R290 at a less mass flow rate, the heat transfer coefficient will decreases slightly at a low vapor quality. The condensation heat transfer coefficient of R290 is higher than that of the R22 at the same experimental conditions. The experimental results are also compared with some of the existing correlations, which shows that the Wang et al.(2002) correlation predicts the experimental data of R290 very well ,with an overall mean absolute error of 17.5%, while Kim et al. (2013) correlation makes the best prediction to the R22’s data, with an overall mean absolute error of 18.4%.关键词：minichannel;flow condensation;convective heat transfer;R2902490|2521|4发布时间：2024-07-18
- 摘要：Liquid-vapor separation microchannel condenser (LSMC) is a novel microchannel condenser. This paper calculated heat transfer coefficient and pressure drop theoretically, and the theoretical results have been verified by experiments. Penalty factor (PF) was employed to evaluate the thermodynamic performance of the LSMC. The results showed number of pass (NP) and tube number per pass (TNPP) have obvious effect on the thermodynamic performance. Under the condition of completely liquid-vapor separation, the 4-tube-pass and 5-tube-pass LSMC showed 5.7% and 13.8% higher heat transfer coefficient than 3-tube-pass LSMC separately. In addition, the pressure drop of 4-tube-pass and 5-tube-pass LSMC is also 23.5% and 138.7% more than 3-tube-pass LSMC separately. In contrast, the TNPP showed a less effect on the heat transfer coefficient and pressure drop. It showed that the NP had a larger effect on simplex performance than the TNPP within the research scope. The thermodynamic performance for the LSMC with completely liquid-vapor separation was better than that with incompletely liquid-vapor separation. Compared with the experimental results, the theoretical heat transfer coefficient showed a maximum deviation of 25.6% and the theoretical pressure drop showed a maximum deviation of 20.8%.关键词：liquid-vapor separation microchannel condenser;tube pass scheme;heat transfer coefficient;penalty factor2511|2581|3发布时间：2024-07-18
- 摘要：The effects of different storage temperature (0, 5, 10, 15, 20, 25 and 30 ℃) on respiration rate and storage quality of strawberry in terms of quality attributes such as sensory evaluation, weight loss, firmness, relative conductivity, sugar-acid ratio, Vitamin C content and color difference were studied. The results showed that the higher the storage temperature was, the higher the respiration rate and the shorter the shelf life of strawberry. Respiration rate of strawberry stored at 30 ℃ was about 13.97 times as high as that of strawberry stored at 0 ℃. The shelf life of strawberry were 9 d, 7 d, 5 d, 4 d, 3 d, 2 d and 8 h at 0, 5, 10, 15, 20, 25 and 30 ℃, respectively. With the storage temperature increasing, the sensory evaluation, firmness, sugar-acid ratio, Vitamin C content, L* and hue value of strawberry decreased gradually, while the weight loss, relative conductivity and respiration rate of strawberry increased. Compared with the quality of strawberry stored at other temperatures, the quality of strawberry stored at 0 ℃ was the best. After 9 days storage, its sensory evaluation, weight loss, firmness, relative conductivity, sugar-acid ratio, Vitamin C content, L* and hue value were 5.4, 3.18%, 11.13N, 39.05%, 12.48, 22.01mg/100g, 37.84, 32.81, respectively.关键词：storage and processing of fruits and vegetables;strawberry;storage temperature;respiration rate;quality2283|2672|3发布时间：2024-07-18
- 摘要：The real-time model which is widely used in the detection of long pipeline leakage is applied to detect ammonia leakage in the pipeline of refrigeration systems in cold stores. The pipeline of refrigeration system with R22 is used to simulate the ammonia system. The real-time model of leak detection and positioning is set up through the dynamic characteristics of refrigerant and testing results of leakage. The model is verified by experiments and the result shows that the accuracy of leak detection can reach 3.0%, and the positioning precision and stability is related to the position of leakage, which indicates that it can efficiently and rapidly achieve leak detection and determine position of leakage. This research provides effective methods and theoretical basis for the safe operation of refrigeration system in cold stores.关键词：refrigeration system;cold store;refrigerant;pipeline leakage;real-time model2276|2364|1发布时间：2024-07-18
- 摘要：Based on the solar photovoltaic-thermal integrated system, we designed a dual-source, i.e., solar photovoltaic-thermal and air source, heat pump unit. The unit becomes solar assisted heat pump system when combined with solar photovoltaic thermal unit, which produces domestic hot water by air source and circulating water in the solar photovoltaic solar-thermal components (PV/T) and reduces circulating water temperature and solar photovoltaic panel temperature. We drew the conclusion by experiment that when the inflow water temperature is 20 ℃ on the evaporation side and the outflow hot water temperature is 50 ℃ under the rated conditions, the unit capacity is 2.855 kW for refrigeration and 3.594 kW for heating, and the COP is 3.6. When the unit operates in the water-water condition and water-air condition, the experiment result shows the dual-source heat pump unit has remarkable energy-saving compared with single air source heat pump when the photovoltaic-thermal solar heat is used for domestic hot water.关键词：solar photovoltaic;air-source heat pump;refrigerating capacity;coefficient of performance2459|2776|6发布时间：2024-07-18
- 摘要：With the base of traditional air conditioning system, the grid-connected photovoltaic household air conditioning system based on the solar photovoltaic power generation technology is designed in this paper. The power with the solar photovoltaic power generation technology is transformed into the household power of 220 V and 50 Hz by inverter. The household air conditioning system is then driven by the transformed power and national grid. The performance of the photovoltaic grid-connected household air conditioning system was tested by Enthalpy Difference Lab under the different power (100 W, 135 W and 185 W) of solar panels. The experimental results show that under normal cooling conditions, the average power consumption of the air conditioning system with the different power (100 W, 135 W and 185 W) of solar panels are 52 W, 78 W and 104 W lower than that of the traditional air conditioning system respectively. Similarly, energy efficiency ratios of the air conditioning system with the different power (100 W, 135 W and 185 W) of solar panels are 4.2%, 5.5% and 10.2% lower than that of the traditional air conditioning system respectively. Under heating mode, the average power consumption of the air conditioning system with the different power (100 W, 135 W and 185 W) of solar panels are 68 W, 84 W and 116 W lower than that of the traditional air conditioning system, and the coefficients of performances are 6.4%, 8% and 11% lower than that of the traditional air conditioning system. It can be concluded that the photovoltaic grid-connected household air conditioning system is feasible.关键词：air conditioning system;grid-connected photovoltaic generation;solar panels;energy efficiency ratio (EER);coefficient of performance (COP)2340|2566|2发布时间：2024-07-18
- 摘要：An improved multi-functional air-conditioning water heater is devised to solve the problem of frequent starts and stops of fan, which always occurs while a traditional one produces hot water in summer. The improved multi-functional air-conditioning water heater can be highly efficient and stable operation in the various modes of different seasons owing to the change of input voltage and speed of fan, and improvement of the outdoor air-cooled heat exchanger. The critical output voltage for the stable operation of compressor and fan is found out, and the relationship between COP and the opening degrees of throttling valve is investigated. Compared with the system improved before, the system's stability has a great enhancement after adding a transformer in the multi-functional air-conditioning water heater. When the outdoor environment temperature is 32 ℃, the opening degree of of throttling valve is 0.4, and the output voltage of transformer is 160 V. The improved system can reach an optimum COP of 4.68 under the hot water only mode in summer.关键词：air- conditioning hot water heater;variable-air-volume system;throttling valve;energy efficiency ratio2234|2650|1发布时间：2024-07-18
- 摘要：A physical and mathematical model to describe the melting process in foam-filled ice cold-plate was developed. The natural convection of liquid water was taken into account. The melting processes of ice cold-plates filled with open-cell polyurethane foams and copper foams were simulated. The principles of the melting rates, temperature distributions, interface movements were analyzed. Comparisons were made between the model predictions and experimental data. The influences of foams pore parameters to ice melting rates were confirmed. The results indicate that foams with low thermal conductivity efficiently extends the melting time. The time increases obviously with the decrease of pore density and increases slowly with the increase of porosity. In contrast, the foams with high thermal conductivity effectively improve the temperature distribution and accelerate the melting rate. The rate increases obviously with the decrease of porosity and increases slightly with the decrease of pore density.关键词：ice cold-hold;porous material;simulation;polyurethane foam;pore parameter2392|2544|2发布时间：2024-07-18
- 摘要：It was found that the introduction of enhanced vapor injection(EVI)technology can significantly improve the performance of air-source heat pump products under low-temperature condition. This technology is based on quasi two-stage compression cycle. The present paper expounded quasi two-stage compression cycle model and different EVI principles. A comparison among EVI system and other systems was made to find their advantages and disadvantages. The paper provides a literature review on heat pump systems with EVI technology from three aspects: mathematical model, experimental study and optimization. The review summarized the research and application achievement of EVI system in improving heating performance, reducing exhaust temperature and other aspects. The results show that even at -15 ℃ low temperature, EVI systems can increase COP 7.7%-25.0%, and decrease exhaust temperature 6.37 ℃-20.36 ℃. It also prospects the future research direction of EVI system.关键词：air-source heat pump;enhanced vapor injection;quasi two-stage compression;economizer2864|3754|9发布时间：2024-07-18
- 摘要：Heat regenerator formed by capillary and suction pipe has an important influence on the performance of small refrigeration equipment. At present, there are four main types of regenerator: capillary wear type, aluminum foil cover type, copper and tin welding type, capillary inside pipe type. Combining with theoretical analysis, the refrigeration performance of regenerator was experimentally studied by capillary inlet and outlet temperature, suction pipe inlet and outlet temperature, evaporator temperature and discharge temperature of compressor suction. The results show that, wear inside the capillary regenerator and copper tin welding type regenerator have the same performance in heat transfer performance. However, the refrigerating capacity per unit of swept volume of capillary inside pipe type regenerator was 17.4% higher than that of capillary wear type and aluminum foil cover type regenerator under the same conditions. The performance of refrigerator can be improved by using capillary inside pipe type regenerator.关键词：heat regenerator;performance test;capillary;small refrigeration device2296|2693|0发布时间：2024-07-18
- 摘要：Since the difficulty of building mechanism model and the structure of COP model of chiller is complex, greatly affected by operating parameter, a COP prediction model of chiller is proposed based on Support Vector Regression, and the parameters are optimized by Particle Swarm Optimization algorithm. In this paper, 396 sets of operating data of chiller of a shopping mall are randomly selected to train and test this model. The results shows that the prediction accuracy of SVR model based on PSO optimization algorithm is higher than that of BP neural network and the relative error is within 3%. At last, operating data of two days in summer and transition season are randomly selected to verify the model. The relative error is within 5%. So this model can provide theoretical basis for the chiller energy efficiency analysis, fault detection and diagnosis and optimizing control.关键词：chiller;COP;prediction model;support vector regression;particle swarm optimization2289|2684|3发布时间：2024-07-18
- 摘要：In order to improve the performance of chilled radiant panel(CRP) containing air layer, we firstly established a mathematical heat conduction model of CRP with air layer and evaluated its reliability. The deviation of model and experimental results about CRP cooling capacity and surface temperature was 9.20% and 4.00%, which indicated that the model had high reliability. Then we change the contact form of CRP’s chilled water brass and thermal plate by two ways and used the verified model to analyze the performance of the transformed CRPs. The results showed that two CRPs’ cooling capacity increased 36.92 W/m2 and 33.19 W/m2 when the air layer thickness was reduced to 1mm under the optimal parameters; the cooling capacity averagely increased 7.46 W/m2 and 7.54 W/m2 as chilled water temperature decreased per 1 ℃ and indoor temperature increased per 1 ℃; the CRP’s surface maximum temperature difference was constant. In conclusion, CRP containing thin layer has better performance on the cooling and anti-condensation, and it has the potential to be widely used.关键词：chilled radiant panel containing air layer;cooling capacity;anti-condensation;heat conduction model2374|2696|3发布时间：2024-07-18
- 摘要：In order to verify thermoelectric refrigerator’s capability to be used as domestic dehumidifier, a typical single-stage thermoelectric dehumidification system was built by using a thermoelectric refrigerator. The moist air flowed through the cold side and the hot side in turn which condensed in the cold side and the heat dissipation was recycled in the hot side. The factors (voltage, temperature, mass flow rate etc.) which affect the thermoelectric dehumidification capacity and efficiency are analyzed. In addition, by conducting the experiment, the performance of this thermoelectric dehumidifier was optimally improved. For example, a test was carried out at atmospheric conditions of 26 ℃ and 65% humidity，the maximum amount of dehumidification of this device can reach 150 g/h, dehumidification efficiency can reach 0.37.关键词：semiconductor refrigeration;dehumidification;optimal operation;experimental investigation3308|4678|10发布时间：2024-07-18
- 摘要：Thermal expansion valve’s flow characteristic under different conditions is one of the most important factors affecting refrigeration system performance. So it is necessary to detect the actual refrigerant flow of thermal expansion valve. A thermal expansion valve test-bench was developed and its range of refrigerating capacity was 1.7~10 kW. In the system, in order to avoid the influence of flow resistance difference of the high pressure part on the measured results, inlet pressure of expansion was treated as the testing condition. The uncertainty of flow measurement is 0.5% and temperature control accuracy is ±0.5 ℃. Performance of a 7 kW capacity H-type thermal expansion valve was tested in the standard condition, and the property of flow-opening, temperature-opening, flow-temperature was acquired and analyzed. In the thermal expansion valve’s work range, the flow increases linearly with the increase of temperature. Through the quantitative analysis of thermal expansion valve's gain and hysteresis, the performance of thermal expansion valve is judged.关键词：automobile air-conditioning;thermal expansion valve;opening;flow13254|10688|0发布时间：2024-07-18
- 摘要：In order to determine optimal freezing methods for vegetable soybean, effect of three freezing rates of ﹣35 ℃ with 8 m/s wind, ﹣35 ℃ and ﹣18 ℃ on freezing temperature curve and the quality index changes of frozen vegetable soybean stored at ﹣18 ℃were investigated. The results showed that freezing at ﹣35 ℃ with 8 m/s wind had best freezing speed. Under the condition, the zone of maximum ice crystal formation in vegetable soybeans took the shortest time of 40 s, while freezing at ﹣35 ℃ and ﹣18 ℃ took about 6 minutes and 1 h, respectively. Freezing methods had significantly influence on the texture, drip loss rate, membrane permeability, MDA content, chlorophyll content, Vc content. In general, the lower temperature and faster freezing speed during freezing, the obviously lower speed of quality deterioration during storage. Quality of soybean frozen at ﹣35 ℃ with 8 m/s wind was significantly better than that frozen at ﹣18 ℃, so freezing at ﹣35 ℃ with 8 m/s is suitable for the rapid freezing of vegetable soybean.关键词：vegetable soybean;quick freezing;freezing rate;frozen storage3170|3707|2发布时间：2024-07-18
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