最新刊期
卷 36 ， 期 6 ， 2015
- 摘要：To investigate the characteristics of flow boiling and heat transfer in microchannels, experiments was carried in rectangular microchannels using refrigerant R22 as working fluid, and visualization experiment was performed using high speed camera. The results show that: heat transfer coefficient is barely influenced by the mass flow rate, but it increases rapidly along with the increment of the heat flux. The smaller the size of microchannels, the better heat transfer effects. Under the same condition of heat flux and mass flow rate, the values of heat transfer coefficient in 0.92 mm and 1.33 mm microchannels increase by 25% and 12% respectively compared to that of 2 mm. A new correlation based on the models of Oh H K et al [15] and Yun R et al [7] is shown to provide very good predictions, evidenced by an overall MAE of 8.8%. Wavy vapor layer was observed under the critical heat flux in visualization experiment.关键词：flow boiling;rectangular microchannels;empiric correlation;visual13504|13504|7发布时间：2024-07-18
- 摘要：The influences of temperature, relative humidity and fire-retardant on the explosion range of new alternative refrigerants HFC-32 were investigated through an experiment bed for the explosion range of flammable gases. The results indicated that the enhancement of temperature can improve the upper explosion range of HFC-32 and decrease its lower explosion range, then enlarges the explosion range of HFC-32 under the temperature of﹣5~55 ℃. The improvement of relative humidity makes the lower explosion range of HFC-32 slightly increase, and the upper explosion range slightly decrease at the relative humidity range of less than 60% for HFC-32. When the relative humidity increases from 60% to 87%, the upper explosion range of HFC-32 decreases rapidly to make the explosive range of HFC-32 disappear. The addition of CF3I or HFC-134a fire-retardant can lead the explosion range of HFC-32 to reduce, and the effect of CF3I on the inflaming retarding of HFC-32 is superior to HFC-134a. When the volume ratio of CF3I/HFC-32 increases from 0 to 1 or HFC-134a/HFC-32 increases from 0 to 10, their explosion ranges disappear. This provides an important theoretical basis for inhibiting the combustion of HFC-32.关键词：alternative refrigerant;explosion range;experimental study;HFC-323098|2640|1发布时间：2024-07-18
- 摘要：R32 is a potential alternative refrigerant for its environmental protection capability and thermal performance. But the slight flammability limits its application. Therefore, safety analysis is needed. This paper studied the influence of different leakage locations and rates on the indoor R32 distribution with air conditioner operating, and obtained the R32 leakage and diffusion characteristics. It showed that the leakage at the evaporator of indoor unit can be divided into two processes, fast leakage stage and slow. Outlet leakage of the evaporator is more dangerous than the inlet. And only large leakage flow in evaporator outlet can cause high R32 concentration near the indoor unit ,reaching 16.79%, which exceeds the lower flammable limit (14.4%) 16.6%. If flammable concentration exists for 22 s, the fire probability exists but it's low. Air exhausting can decrease the concentration of indoor R32 effectively.关键词：refrigerant;leakage;split-type air-conditioner;evaporator;R3213489|11663|4发布时间：2024-07-18
- 摘要：The development of absorption refrigeration has attracted people’s attention under the theme of energy conservation and environmental protection. As one of the core techniques, the development of absorption refrigeration working pairs plays an important role. Some hot topics in the field of absorption refrigeration were enumerated and the gap between theoretical research and practical application problems were pointed out. According to the differences of refrigeration, there are five groups of working pairs, such as ammonia, water, alcohol, fluoride, etc. Historical and current situation of the five-group working pairs were reviewed and defects of the traditional ones were analyzed. This paper explored the relevant optimization measures, new working pairs and compared their performance with that of the traditional ones. In addition, the current research situation of NH3-NaSCN and NH3- LiNO3 was emphasized and a comparison between their advantages and disadvantages in different conditions was made. Moreover, different kinds of salt combinations were introduced to replace LiBr and weaken the corrosivity of LiBr-H2O. On the basis of current researches, more works should be done on the improvement of existing working pairs’ performance and exploration of new ones.关键词：absorption refrigeration working pairs;review;refrigerant;absorbent13549|12972|9发布时间：2024-07-18
- 摘要：The process of ice slurry preparation is observed with the ice slurry preparation equipment based on vacuum stirring method, and the effects of ethylene glycol additive, solution volume and stirring speed on the supercooling degree of ice slurry preparation are investigated experimentally. The results indicate that the procedure of ice slurry preparation under vacuum can be divided into four stages, including solution evaporation, boiling, supercooling, and ice crystal generation. The system pressure increases at the instant of ice crystal generation and the pressure variation which is defined as supercooling crystallization pressure difference can characterize the supercooling degree. The higher the concentration of ethylene glycol additive, the smaller the average supercooling crystallization pressure difference, which is down to 49.4 Pa from 58.9 Pa when the concentration of ethylene glycol additive is varied from 3% to 6%. Furthermore, the increase of solution volume can also reduce the average differential pressure which is dropped by 12.9% when the solution volume is varied from 20 mL to 40 mL. The stirring speed has little influence on supercooling crystallization pressure difference.关键词：vacuum ice;experimental study;ice slurry;supercooling crystallization pressure difference3009|2450|2发布时间：2024-07-18
- 摘要：The overall detection rate using conventional neural networks to detect and diagnose the chillers’ fault is low, even this method can’t detect the fault completely. In order to improve the fault detection and diagnostic accuracy of chiller, an improved neural network fault detection strategy based on Bayesian regularization is proposed. Due to the defects of poor generalization ability of BP neural network, the neural network based on Bayesian regularization can improve the detection efficiency of the model. Bayesian algorithm by limiting the weights of the neural network makes the network more smooth, which make the model more precise. Validation of FDD (fault detection and diagnosis) strategy through using ASHRAE Project data shows that the detection rate is improved obviously.关键词：chiller;fault detection and diagnosis;BP neural network;bayesian regularization2369|2258|11发布时间：2024-07-18
- 摘要：A model of heat pump clothes dryer was developed in this paper, which includes the steady-state heat pump system model and the dynamic fabric drying process model. The simulation results reached a good agreement with the test data of a household heat pump clothes dryer. The drying time error is within 3 minutes and the electricity consumption error is -2.3%. Based on the model, the impact of component size and key system parameters (such as circulation air flow rate, ratio of circulating air, and refrigerant charge) on SMER (Specific Moisture Extraction Rate) and drying time were analyzed. The results indicated that maximum SMER would be achieved at 180 m3/h circulation air flow rate and 9%-10% fresh air to circulating air. Within condensing temperature limit, more refrigerant charge would favor SMER. The results are useful for the system design of heat pump clothes dryer.关键词：heat pump;clothes dryer;drying;simulation;optimization2341|2265|2发布时间：2024-07-18
- 摘要：The existing open heat-source tower has high moisture absorption rate in winter, which affects the safety of system. So a new-type heat-source tower structure with pre-condensation function was designed. The operation process of new-type tower was analyzed. The operation characteristic of new-type tower and ordinary tower were comparatively studied under different inlet solution temperature, mass flow of air and solution. The experiment results showed that the new-type tower had higher heat exchange performance and lower moisture absorption rate. Compared with ordinary tower, when inlet solution temperature rise from 1 ℃to 3 ℃, the new-type tower’s heat exchange rate increased 0.62 - 0.24 kW, and moisture absorption rate dropped 0.13 g/s in average; When air flow increased from 1.41 kg/s to 2.17 kg/s, the new-type tower’s heat exchange rate increased 0.79 - 0.84 kW, and moisture absorption rate dropped 0.1 g/s in average; When solution flow rate increased from 0.36 kg/s to 0.68 kg/s, the new-type tower’s heat exchange rate increased f 0.57 - 0.63 kW , and moisture absorption rate dropped 0.11 g/s in average.关键词：heat-source tower;heat and mass transfer;operating conditions;pre-condensation function2392|2161|4发布时间：2024-07-18
- 摘要：The vapor pressure of desiccant solution is one of the most important parameter of liquid desiccant cooling system. It dominates the performance of this system. This paper selects two typical models—NRTL equation and simple mixed model—to analyze the formation mechanism of the vapor pressure and the role it plays in dehumidification process. The vapor pressure of mixed LiCl-CaCl2 solution is calculated according to these two models. Then the models are verified through measuring the vapor pressure of various mixture ratios and various mass concentrations of the mixed solution under different temperatures. Finally the research considers the mixed solution of 50% LiCl and 50% CaCl2 as the best mixture ratio. Simple mixed model can be adopted when the solution is at low mass concentration while the models should be amended to conform to the actual situations when the solution is at high mass concentration. The modified model is able to make an estimation or prediction on vapor pressure under different conditions which offers a theoretical basis to determine the mixed liquid desiccants in the design of liquid desiccant cooling system.关键词：liquid desiccant;vapor pressure;binary mixed solution;NRTL equation2377|2404|1发布时间：2024-07-18
- 摘要：A combined method of experimental and numerical simulation was used in this paper to study the surface temperature variations of radiant panel in the start-up stage of radiant ceiling system, and the condensation characteristics of radiant panels were analyzed under different moisture strengths and locations of human being in the stable stage of radiant ceiling system. The results show that in the start-up stage when the radiant cooling system is operated independently, the condensation occurs on the radiant panel after the system starts 6 minutes, and the decreasing of radiant panel surface temperature has more significant impact on the condensation time than the increasing of moisture strength. So it is necessary to take effective measures to prevent condensation in time in the start-up stage. In the stable stage, the radiant panel condenses about 12 minutes earlier when the moisture strength equivalent to an adult man body is additionally added. And the radiant panel which is exactly above the moisture source condenses earlier than others. So the surface temperatures of radiant panels above the moisture source should be monitored to prevent condensation.关键词：radiant ceiling;dew point temperature;radiant panel surface temperature;condensation time2227|2456|4发布时间：2024-07-18
- 摘要：Gasket is an important connection structure between refrigerator door and body, and heat transfer through gasket is an important component of refrigerator thermal load. Both CFD simulations and experimental test were carried out to analyze the heat transfer characteristics near gasket region. This paper primarily focuses on heat transfer paths and the proportions, which lays the foundation for the optimal design of gasket. The result shows that total thermal load of gasket is 2.2W, accounting for 5.5% of the total heat loss of a refrigerator, and thermal loads from gasket to refrigerating body and from gasket to refrigerating cabinet account for 41.56% and 45.07% of the total thermal load near the gasket region, respectively. Besides, the magnetic stripe is a key factor of the total thermal load of gasket. To reduce the width of gasket from 9.6mm to 8.4mm could effectively reduce the gasket thermal load from gasket to refrigerating body by 51.7%, resulting in a 21.1% reduction of total thermal load near gasket．关键词：refrigerator;gasket;thermal load;heat transfer characteristics2335|2197|2发布时间：2024-07-18
- 摘要：As the key component of the pulse tuber cryocooler, the regenerator plays a vital role on the thermal performance. In order to analyze the effect of the filled metal meshes on the thermal performance of regenerator, the real single-stage pulse tube cryocooler was designed and manufactured, according to the results of calculation and simulation by REGEN3.3. Four typical multi-metal-mesh filled regenerators were built with stainless screens #300SS, #400SS and #500SS. The comparison experiments were carried out. The thermal property of the refrigerator was collected and the conclusion was obtained. The thermal performance of the pulse tube refrigerator with small metal mesh screen filled regenerator is superior to that of the one with lager metal mesh screen filled regenerator. And filling the lager mesh screen at the hot end of the regenerator and the small mesh screen at the cold end can improve the gas compression ratio and the thermal performance. The method proposed in this paper is really helpful for the optimization of the regenerator.关键词：pulse tube cryogenic cryocooler;regenerator;metal twilled screen;experimental study2561|2341|3发布时间：2024-07-18
- 摘要：This paper proposes a type of ejector throttling refrigeration system (Mode III), and compares it with traditional thermal expansion valve (Mode I) and liquid pump for liquid (Mode II) through experiments. The effects of these three liquid supply modes on freezing time of food, freezing temperature difference and total energy consumption of freezer are studied experimentally. The results show that under the experimental conditions, the freezing time of Mode II & III is shorter by about 14% than Mode I, the falling of food’s temperature is more evenly, and it is good for enhancing the quality of food freezed. On the aspect of energy consumption, Mode III saves 6.3% than Mode I, and saves 9.6% than Mode II. Therefore, the advantages of liquid supply with ejector throttling are obvious.关键词：liquid supply;ejector;freezing time;freezing temperature difference;energy consumption2203|2259|3发布时间：2024-07-18
- 摘要：To study the effect of variable chilled water flow rates and temperature on double temperature chiller with large temperature glide zeotropic refrigerant, the chiller’s performance under different conditions was investigated experimentally, including mass concentration ratio of R32/R236fa (0.4~0.6, 0.5~0.5, 0.6~0.4), chilled water flow rates change from 0.25 m3/h to 0.45 m3/h and temperature change of the high temperature chilling water. The experimental results show that the maximum and minimum COP of the unit under different flow rates is 4.17 and 3.27 respectively, this moment, the inlet and outlet water temperature of condenser are 32 ℃ and 37℃, the high-low temperature chilling water are 7 ℃ and 16 ℃. In addition, the temperature change of high temperature chilled water have obvious effect on the performance of the unit. At last, the results of this paper provide database for the application of double temperature chiller.关键词：zeotropic;variable flow rate;COP;large temperature glide2334|2347|3发布时间：2024-07-18
- 摘要：Transcritical CO2 system has become a hot topic in the field of heat pumps and air conditioning. In this paper, the CO2 gas cooler was taken as a research subject. The system entransy dissipation was produced by the temperature difference of heat transfer and flow resistance of inside and outside fluid. A steady state distributed parameter model for the transcritical region of CO2 gas cooler was established to solve entransy dissipation number . The main reason of entransy dissipation number generation and its distribution were analyzed. Meanwhile, the effects of CO2 and entrance parameters of water on the system entransy dissipation number were discussed. Results from the mathematic model showed that system entransy dissipation was mainly caused by temperature difference of heat transfer. The more the temperature difference, the bigger the entransy dissipation number. In each infinitesimal segment, the entransy dissipation number and the magnitude of CO2 temperature drop were in an inverse relationship. At the critical point, reached a maximum value. With the increase of mass flow rate and inlet pressure of CO2, the system entransy dissipation number became lager. While with the increase of water mass flow rate, the system entransy dissipation number decreased. Meanwhile, the higher the pressure, the smaller the decreased magnitude of entransy dissipation number. With the increasing of CO2 inlet temperature, the entransy dissipation number decreased. The decreased degree of entransy dissipation number goes down with the increase of CO2 inlet temperature. In addition, the inlet temperature of water has little impact on system entransy dissipation number.关键词：gas cooler;transcritical cycle;entransy dissipation number;numerical simulation;carbon dioxide2361|2498|2发布时间：2024-07-18
- 摘要：The best treatment design of fresh-cut spinach was established by using orthogonal test. Spinaches were firstly immersed in two solutions (75 mg/LClO2 and 0.5% NaCl) for 10 minutes successively, and then packed with PVDC cling film. Subsequently, they were evenly distributed and stored in different cold rooms at 0 ℃, 4 ℃, 7 ℃ and 10 ℃. The relationship between the quality change of samples and storage time and temperature was studied by measuring the indexes of the weight loss, the chlorophyll content and the total plate count (TPC). The experimental results show that the chlorophyll content of the spinach is reduced with the increase of storage temperature and time, while the weight loss and TPC are increased. All results indicate that ice temperature (0 ℃) is the best storage temperature of fresh-cut spinach. Based on experimental data, the dynamic models of weight loss, chlorophyll content and total plate count (TPC) were established, and the parameter of the activity energy in the model were obtained, which provides the theoretical foundation for the shelf-life prediction of the fresh-cut spinach.关键词：cold storage;dynamic model;temperature gradient;fresh-cut spinach2419|2284|5发布时间：2024-07-18
- 摘要：The experiments were conducted on 5 mm and 7 mm finned tube heat exchangers with same refrigerating capacity based on enthalpy method. The evaporator simulation model was established to analysis the influence of tube diameter on the heat transfer performance. The results show: 1) the heat transfer coefficient on the air side of the 5 mm tube heat exchanger is 17% higher. 2) With same refrigerating capacity, the refrigerant mass flow rate of 5 mm diameter tubes has a 4.6% reduction and its mass velocity increases by 89.4%, which arises the dry out point in advance. 3) At same vapor quality points, its local heat transfer coefficient increases to 1.43 ~ 1.86 times as that of 7 mm diameter tubes. Meanwhile friction pressure drops, acceleration pressure drops and local pressure drops in 5 mm diameter tubes increase to more than 3 times as those in 7 mm diameter tubes, arising 1.1 ℃ increasing in evaporating temperature.关键词：room air-conditioner;heat exchanger;tube diameter;heat transfer coefficient;pressure drops3214|2580|6发布时间：2024-07-18
- 摘要：IPLV evaluation status of water chilling packages in China and USA standards is introduced. The IPLV evaluation system of the two countries is compared in detail from the aspects of IPLV's principle and weight coefficient, test conditions, test method, test tolerance, interpolation calculation method and so on. The conclusion indicates that current IPLV evaluation system in China is not adapted to the current development of China's construction industry and HVAC industry. This analysis is helpful to distinguish the differences between the two standards and improve the standard IPLV evaluation system of water chilling packages in our country.关键词：water chilling packages;integrated part load value;weight coefficient;test tolerance;interpolation calculation method13347|10835|0发布时间：2024-07-18
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