最新刊期
卷 34 ， 期 3 ， 2013
- 摘要：This paper has briefly summarized the development of refrigerant compressor; and accounted the statistic of the electrical efficiency for positive displacement refrigerant compressor. After comparing and analyzing the above data, it is shown that the electrical efficiency of scroll compressors basically varies from 0.5 to 0.75, with a focus on section 0.6 - 0.7; efficiency of piston compressors is basically between 0.4 and 0.7, with a focus on section 0.5-0.65; efficiency of screw compressors is basically between 0.5 and 0.75, with a focus on section 0.65 - 0.75. Besides, the results show that the efficiency of compressors reaches its best when its compression ratio is between 2 and 4, which provides foundation and basis for designing, checking and calculation of refrigeration compressor, and guides the performance improvements for refrigeration system.关键词：electrical efficiency;scroll compressor;piston compressor;screw compressor;evaporative temperature;compression ratio1717|1851|0发布时间：2024-07-18
- 摘要：Flow boiling heat transfer is an important heat transfer method, and many prediction correlations for flow boiling heat transfer have been proposed for a variety of substances. But as the correlations are all empirical or semi-empirical, the accuracy of predicted results would be very different when applying them on different substances or in different working condition. To evaluate the applicability of the present flow boiling prediction correlations for pure substances, eight general predictive correlations are chosen and the prediction results of them are compared with the experimental data from some open literatures for R134a, CO2, liquid nitrogen. The results show that Lazarck(1982) correlation、Kew and Cornwell(1997) correlation have good prediction accuracy for the three substances, and Gungor and Winterton(1987) correlation may be more applicable for CO2，Liu and Winterton(1991) correlation has good prediction accuracy for R134a. But the others all fail to predict heat transfer coefficient（HTC）accurately for the three substances. In addition, the eight correlations have not enough accuracy to predict HTC of flow boiling for liquid nitrogen.关键词：flow boiling;refrigerant;prediction correlation;applicability1633|1778|0发布时间：2024-07-18
- 摘要：A novel VM cycle refrigerator for air-conditioning temperature zone (>16℃) is introduced. It’s driven by pressure wave converted from heat which can be obtained by solar energy, industrial waste heat or fossil fuels. It has the advantages of compactness, low vibration and high reliability. The influences of volume ratio, void volume and phase difference of hot and cold displacers on theoretical cooling capacity had been studied. Also, five kinds of thermal losses were analyzed. Parameters of one VM cycle refrigerator were designed and the influences of charged pressure and frequency on actual cooling capacity and COP had been calculated. Moreover, the prospect of applications was discussed. The results show that a COP of 2.5～3 at 10 Hz can be obtained with a cooling capacity of 2000W. As to thermal losses, the losses in regenerators are dominant.关键词：VM-type refrigerator;thermodynamic calculations;COP1697|1972|0发布时间：2024-07-18
- 摘要：Microchannel heat exchanger as a new substitution heat exchanger has been used in the field of home appliances, but the frost, dust, drain and distribution are the problems which need to be solved. The temperature distribution of microchannel heat exchanger and its influence on the air-conditioning system with refrigerant R22 in which three microchannel heat exchangers with different processes are used as condenser and evaporator respectively, is tested in the performance test bench of air-conditioning system. It is shown that the effect of temperature distribution on the system performance is up to 7.3% and 3.5%, respectively for condenser and evaporator. And the number of processes has different impact on the temperature distribution when microchannel heat exchanger is used for condenser and evaporator.关键词：engineering thermophysics;microchannel heat exchanger;distribution of temperature;the number of processes;performance of system2034|1921|0发布时间：2024-07-18
- 摘要：The ionic liquids have offered a new way for improving working substance of absorption refrigeration cycle. However, the performance of the absorption refrigeration cycle with ionic liquids and water as working pairs is strongly dependent on the hygroscopy of ionic liquids. Two ionic liquids: 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) and 1-hexyl-3-methylimidazolium chloride([HMIm]Cl),which have super water-absorption capability, were selected as the working pairs for absorption refrigeration cycles. First, we studied the thermodynamic properties (vapor pressure, specific heat, enthalpy, etc.) of the two ionic liquid aqueous solutions. Then we analyzed their coefficient of performance for the absorption refrigeration cycle. The study shows the two ionic liquid-water pairs can work in a higher temperature condition for single-stage absorption refrigeration cycles and have better coefficients of performance (COP) comparing to those of the ionic liquid working pairs studied by the existed works of other domestic and foreign scholars. The performance of [EMIm]Ac aqueous solution is superior to that of [HMIm]Cl. Comparing to the performance of the ordinary lithium bromide-water working pair, the COP of the single-stage absorption cycle of [EMIm]Ac aqueous solution is almost the same when the generation temperature reach 100℃, and for higher temperature range, the performance of [EMIm]Ac-water pair is a little superior to that of the ordinary lithium bromide-water working pair. Since the superiority of the ionic liquid is only in higher generation temperature, further breakthrough should be had for good properties of vapor pressure of ionic liquid in the low temperature.关键词：absorption refrigeration cycle;ionic liquid;coefficient of performance2182|1936|0发布时间：2024-07-18
- 摘要：Composite adsorbents of CaCl2/ activated carbon were prepared by charring and activating at high temperature from CaCl2 and fir crumbs. Thermal conductivity was improved by adding expanded graphite into composite adsorbent. The proportion of expanded graphite in composite adsorbents was changed from 0% to 50%. The effect of the proportion of expanded graphite in composite adsorbents on the uptake and the adsorption rate was observed from ammonia adsorption experiment. It is found that the adsorption capacity of composite absorbent is decreasing all the time while the adsorption rate increasing at first but then decreasing with the increase of the proportion of expanded graphite. It is also found that thermal conductivity of the composite adsorbent is improving with the increase of the proportion of expanded graphite. When the proportion of expanded graphite in composite adsorbent is 30%, the composite adsorbent has the optimum performance for adsorption refrigeration—its thermal conductivity of the composite adsorbent is 0.193 W/(m?K) and its uptake is 0.431 g/g in first 15min of the adsorption time.关键词：carbonization and activation;adsorption refrigeration;composite adsorbent;thermal conductivity;expanded graphite1849|1957|0发布时间：2024-07-18
- 摘要：Strontium chloride as one chemical adsorbent is characterized by swelling and agglomeration phenomena in adsorption/desorption process, which will further affect the thermal conductivity and permeability of the adsorbent. In order to determine the rules of thermal conductivity and permeability of strontium chloride under such conditions, expanded natural graphite is selected to enhance the heat and mass transfer of strontium chloride. Three kinds of different proportions as well as two kinds of different densities of strontium chloride compact adsorbents are selected to be tested for thermal conductivity and permeability by steady-heat method and Ergun model respectively. Results show that the thermal conductivity of compact adsorbents increases with the increasing ammonia contents, and the values of strontium chloride increase from 0.88W/(m?K) to 1.61W/(m?K). Permeability of compact adsorbent of strontium chloride decreases with the rise of the refrigerant content.关键词：adsorbent;thermal conductivity;permeability;strontium chloride2102|1946|0发布时间：2024-07-18
- 摘要：The adsorption dehumidification performance of Silica gel, zeolite 4A and 13X molecular sieve as a solid desiccant material in a given fixed bed is experimentally studied for different combinations and filling. The fixed bed temperature and productivity change with time is analyzed during the adsorption dehumidification phase. The energy saving effect of the different combination of solid adsorbent and means of filling is analyzed with the adsorption efficiency evaluation index in adsorption process. The results show thatthe solid desiccant combination and filling method with silicone + 13X molecular sieve is more suitable for the fixed bed of solid adsorbent in the parameters condition of experiment.关键词：temperature and humidity independent control;desiccant dehumidification;experimental analysis2148|1953|0发布时间：2024-07-18
- 摘要：The advantages and disadvantages of the spiral plate adsorption bed are analyzed. The heat transfer process and the demand of cold and heat sources in a spiral plate adsorption bed, which is designed with counter-flow heat transfer and based on 15kW refrigerating output, are theoretically analyzed and optimized. The result shows that the heat-transfer capability of the spiral plate adsorption bed is better and its volume is smaller than other adsorption beds. If the processing difficulties and settings of mass transfer channel can be solved effectively, the spiral plate adsorption bed can be widely used, which will benefit the commercialization of the technology.关键词：the spiral plate adsorption bed;structural style;heat transfer performance;energy requirement;optimal design1959|1937|0发布时间：2024-07-18
- 摘要：A series of experiments are carried out to find approach which can enhance absorption efficiency for transversally grooved tube (TGT) with different sizes, and to choose an optimal tube type. The experiment results show that aqua ammonia can absorb more ammonia gas and the mass transfer coefficient becomes larger with the increase of pressure difference and velocity of cooling water inside tube. When sprinkle density of aqua ammonia outside tube increases, mass transfer coefficient increases firstly and then decreases, so an optimum exists. The group experiments results indicate that transversally grooved tube have better mass transfer ability than smooth tube. For example, when sprinkle density of solution is 479.6kg/(m?h), mass transfer coefficient of transversally grooved tube rise by 97.8% compared to smooth tube. A common law is discovered during three groups of experiment. Different sizes of TGT have different ability to absorb ammonia gas, and No. 2 tube is the best tube considering absorption efficiency. The ratio of groove width to diameter of this tube is 0.0814. Flow patterns of blend and vortex flow are compared among three transversally grooved tubes with solutions flowing through grooves, and the reason why TGT with different sizes have different absorption efficiency is obtained.关键词：aqua ammonia;falling film;absorption;transversally grooved tube;mass transfer coefficient1790|1952|0发布时间：2024-07-18
- 摘要：Boiling regeneration of liquid desiccant solution, which can reduce desiccant air-conditioning’s dependence on the state of regenerator air, is different from spraying-type regeneration. Research on solution’s boiling characteristics is significant for the design of boiling regenerators. Experiments on the pool nucleate boiling characteristics of the aqueous LiBr solution were conducted in the paper. The results show that the heat transfer coefficient of the aqueous LiBr solution is lower than water’s and decreases with the increase of concentration；its boiling temperature is increased with the increase of concentration. Boiling heat transfer mechanism of solution is more complex than that of pure liquid. Pool nucleate boiling heat transfer of aqueous salt solutions remains to be further studied.关键词：aqueous LiBr solution;pool nucleate boiling;boiling temperature;heat transfer coefficient;surface tension1964|1863|0发布时间：2024-07-18
- 摘要：A cooling and heating dual-mode heat pump air-conditioning system has been developed for pure electric vehicles and a test bench has been built. The performances of heating mode at different circumstances temperature was tested and analyzed. The results showed that the heat pump air-conditioning system was feasible and could meet the temperature requirements of the vehicle cabin in a short time. The performance of the heat pump air conditioning system was affected by the ambient temperature. When the ambient temperature was lower, the pressure in the pipeline and the discharge temperature of the compressor was lower, so the heating capacity per unit time is less.关键词：heat pump air-conditioning;electric vehicle;experimental research2055|1988|0发布时间：2024-07-18
- 摘要：In the condensation heat transfer process of steam-gas mixed fluid, the liquid film formed by the condensation has a great effect to heat transfer; so the discussion of the changes of the liquid film thickness along the wall was conducive to the enhancement of heat transfer. The mechanism of steam condensation of mixed fluid, the distribution of liquid film along the wall and the heat transfer performance were analyzed, and appropriate physical and mathematical models were established. With the given initial conditions, the results of the calculation indicate that the thickness of the liquid film was gradually increased along the wall flowing down and the heat transfer performance gradually reduces; meanwhile the effects of tube wall temperature, vapor-gas mixed fluid velocity and tube diameter on the liquid film formation and the heat transfer performance were analyzed, which provided a theoretical basis for the enhancement of condensation heat transfer process.关键词：steam-gas mixed fluid;condensation;liquid film thickness;heat transfer1756|1831|0发布时间：2024-07-18
- 摘要：General exergy models on conventional district cooling system (DCS), natural water-cooled DCS and air-cooled DCS were presented based on the first and the second law of thermodynamics. A commercial building district in Shanghai was discussed as a case study. Dynamic energy and exergy analysis models of three kinds of DCS using the TRNSYS software were developed. And, exergy loss，exergetic efficiency and COP on an hourly basis of three kinds of DCS were analyzed. Furthermore, a method to determine the longest pipeline length from natural water source to chillers of natural water-cooled DCS was presented when natural water-cooled DCS is better than the other two kinds of DCS based on COP and exergetic efficiency. The results of the case study show that the exergetic efficiency of natural water-cooled DCS is the highest, air-cooled DCS the second, and conventional DCS the lowest. The exergetic efficiency for the three kinds of DCS is 16.52%,15.05% and 12.12% respectively, and the exergy loss per unit of cold energy is 0.289, 0.323 and 0.414 respectively. In addition, the COP of natural water-cooled DCS is the highest, conventional DCS the second, and air-cooled DCS the lowest, with the values of 2.52, 2.32 and 2.2 respectively.关键词：DCS;natural water-cooled DCS;air-cooled DCS;exergy analysis;energy analysis1887|1911|0发布时间：2024-07-18
- 摘要：Simulations of the dynamic performance of a ground heat pump system are important to the system design. Based on a one-dimensional numerical transient heat transfer model, a coupling simulation algorithm was developed for the U-tube ground source heat pump system. Given hourly building loads, ground properties and heat pump performance data, this method can compute the ground temperature, the water temperature and energy consumptions, which are the basis of system assessment. Comparisons between this numerical method and an analytical method show that this numerical method is accurate and fast. A one-year-period case study is hourly carried out and recommendations are given regarding to quantity and distance of boreholes based on simulated results.关键词：ground source heat pump system;dynamic performance;numerical simulation1922|1988|0发布时间：2024-07-18
- 摘要：Single and double row parallel-flow condensers had been used in the refrigerated display cabinet. This system was compared to the refrigerator system which used fin-and-tube condenser. This study show that the compressor average power consumption in a cycle was minimum when refrigerant was charged 550g, 650g and 800g respectively in the refrigerator systems which used single, double row parallel-flow and fin-and-tube condensers. The system with double row parallel-flow condenser consumed the least power among the three systems, and the system with single row parallel-flow condenser was almost the same with the system with fin-and-tube condenser. In the air side, parallel-flow condensers’ performance was better than the fin-and-tube condenser. The single and double row parallel-flow condensers only have a quarter and a half volume of the fin-and-tube condenser in the experiment, which indicates that parallel-flow condenser will be a good solution for the insufficient heat exchange capacity in the harsh environment and reduction of the cost when applied in refrigerator.关键词：parallel flow condenser;refrigerator;heat exchange capacity;refrigerant charge;experiment1967|1903|0发布时间：2024-07-18
- 摘要：Hot liquid defrosting is a new method of defrosting. This paper introduces experimental facilities on hot liquid defrosting.The influence of hot liquid defrosting on cold storage was analysed through the aspects of cold storage temperature, defrosting -time and the working condition of refrigeration system. The results show that hot liquid defrosting can recover cold energy by heat transfer between high-pressure liquid refrigerant and frost. After the defrosting process, temperature in cold storage increases considerably. The temperature still reduces during the defrosting process under no-load experimental conditions when the temperature is higher than -5 degree at the beginning of the experiment, which implies that the hot liquid defrosting program can be applied to the quick-freezing device.关键词：cold storage;defrosting;the hot liquid refrigerant defrosting;energy conservation1751|1890|0发布时间：2024-07-18
- 摘要：The platform piston wind is defined firstly. Then, the wall jet theory of the platform piston wind is put forward. Through the mathematical modeling, the initial segment and main section theoretical model of the platform piston wind is built up. The initial segment is divided into boundary layer area, potential flow core area and free shear zone. The main section is composed of boundary layer area and free shear zone. The typical point velocity dynamic characteristics and the typical section velocity distribution in the vertical wall direction both in the initial segment and main section are obtained based on the theoretical expression solution and numerical simulation. The results of the above two methods coincide each other. The theoretical results are verified by the field measurement.关键词：platform piston wind;the initial segment of wall jet;the main section of wall jet;theory modeling;numerical simulation2026|1979|0发布时间：2024-07-18
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