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1.
水平三维内微肋管在局部蒸干区的沸腾换热及其关联式   总被引:3,自引:1,他引:2  
为了得到不同流型下的换热性能 ,以 R1 3 4a为实验工质在一种水平三维内微肋管内进行了流动沸腾换热实验研究 ,通过可视化等措施对得到的主要流型及其转换曲线表示在 G-x图上。对局部蒸干区的沸腾换热特点进行了讨论 ,并根据此区域换热的特点 ,沿周向管壁分成两个部分 ,即 :蒸干部分和非蒸干部分。对于非蒸干部分又分为淹没微肋的底部液体 ,且认为同环状流换热机理相同 ,而另一部分认为液休带领在沟槽中 ,从而得到了此区域的换热实验关联式 ,此换热关联式与实验值的最大偏差在± 1 6%以内  相似文献
2.
一种新型热风干燥系统的节能分析   总被引:2,自引:0,他引:2  
杨宏军  樊栓狮  李静 《节能技术》2009,27(6):488-491
本文提出了一种新型热风干燥系统-热泵/转轮联合热风干燥系统(HDSHR),介绍了它的系统组成和工作原理.通过热力学分析得出,在某些工况下,HDSHR比热泵干燥系统(HPDS)和转轮热风干燥系统(HDSR)都节能.以干燥系统的单位能耗除湿量(SMER)为性能指标,制冷系统采用环保工质R134a、最高冷凝温度为80℃、采用氯化锂除湿转轮,再生温度70℃时,确定了HD-SHR最佳工况:制冷剂的蒸发温度是20℃、干燥温度范围是55~70℃.在此工况范围内进行了计算,得出HDSHR的SMER值在1.545-2.168之间,HPDS的SMER值在0.813-1.125之间.可见,在最佳干燥温度范围内HDSHR具有显著的节能效果.  相似文献
3.
微型螺旋管蒸发器的沸腾换热与阻力特性实验研究   总被引:1,自引:0,他引:1  
王林  崔廷  孙翠霞  汪洪伟  俞坚  马重芳 《节能》2006,25(6):4-6,10
设计、制造并测试了一种微型螺旋管蒸发器。对微型螺旋管蒸发器的沸腾换热与阻力特性进行了实验研究。根据实验数据获得雷诺数在1460~10000范围内流阻系数与雷诺数的计算关系式。实验结果表明,这种微型蒸发器换热量超过300W。  相似文献
4.
This paper presents an experimental study of R152a and R32, environment-friendly refrigerants with zero ozone depletion potential (ODP) and low global warming potential (GWP), to replace R134a in domestic refrigerator. A refrigerator designed and developed to work with R134a was tested, and its performance using R152a and R32 was evaluated and compared with its performance when R134a was used. The results obtained showed that the design temperature and pull-down time set by International Standard Organisation (ISO) for small refrigerator were achieved earlier using refrigerant R152a and R134a than using R32. The average coefficient of performance (COP) obtained using R152a is 4.7% higher than that of R134a while average COP of R32 is 8.5% lower than that of R134a. The system consumed less energy when R152a was used. The performance of R152a in the domestic refrigerator was constantly better than those of R134a and R32 throughout all the operating conditions, which shows that R152a can be used as replacement for R134a in domestic refrigerator.  相似文献
5.
A comprehensive experimental investigation is conducted on the augmentation of heat transfer coefficients and pressure drop during condensation of HFC-134a in a horizontal tube at the presence of different twisted tape inserts. The test section is a 1.04 m long double-tube counter-flow heat exchanger. The refrigerant flows in the inner copper and the cooling water flows in annulus. The experiments are performed for a plain tube and four tubes with twisted tapes inserts of 6, 9, 12 and 15 twist ratios. The pressure drop is directly measured by a differential pressure transducer. It is found that the twisted tape with twist ratio of 6 gives the highest enhancement in the heat transfer coefficient and the maximum pressure drop compared to the plain tube on a nominal area basis. For this case the enhancement in heat transfer and the pressure drop are increased by 40 and 240% in comparison with to the plain tube. It is observed that the twisted tape with the twist ratio of 9 has the best performance enhancing the heat transfer with the minimum pressure drop. Also empirical correlations are developed to predict smooth tube and swirl flow pressure drop. Predicted results are compared to experimental data and it is found that these correlations are reliable for pressure drop estimation.  相似文献
6.
M. Fatouh  E. Elgendy   《Energy》2011,36(5):2788-2795
The present work aims at evaluating the performance characteristics of a vapor compression heat pump (VCHP) for simultaneous space cooling (summer air conditioning) and hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of evaporator water inlet temperature (14:26 °C) and condenser water inlet temperature (22:34 °C). R134a was used as a primary working fluid whereas water was adopted as a secondary heat transfer fluid at both heat source (evaporator) and heat sink (condenser) of the heat pump. Performance characteristics of the considered heat pump were characterized by outlet water temperatures, water side capacities and coefficient of performance (COP) for various operating modes namely: cooling, heating and simultaneous cooling and heating. Results showed that COP increases with the evaporator water inlet temperature while decreases as the condenser water inlet temperature increases. However, the evaporator water inlet temperature has more effect on the performance characteristics of the heat pump than that of condenser water inlet temperature. Actual COP of cooling mode between 1.9 to 3.1 and that of heating mode from 2.9 to 3.3 were obtained. Actual simultaneous COP between 3.7 and 4.9 was achieved.  相似文献
7.
The paper gives a progress report on a theoretical study of film condensation in microchannels. The model takes account of surface tension, vapor shear stress and gravity. The effect of channel shape is investigated for condensation of R134a in channels with cross sections: square, triangle, inverted triangle, rectangle with longer side vertical, rectangle with longer side horizontal and circle. The case considered here is where the channel wall temperature is uniform and the vapor is saturated at inlet. For a given mass flux, the local condensate film profile around the cross section is calculated together with the mean heat-transfer coefficient at different distances along the channel. Results are presented here for one vapor mass flux, one vapor temperature and one wall temperature.  相似文献
8.
Two-phase flow analysis for the evaporation and condensation of refrigerants within the minichannel plate heat exchangers is an area of ongoing research, as reported in the literatures reviewed in this article. The previous studies mostly correlated the two-phase heat transfer and pressure drop in these minichannel heat exchangers using theories and empirical correlations that had previously been established for two-phase flows in conventional macrochannels. However, the two-phase flow characteristics within micro/minichannels may be more sophisticated than conventional macrochannels, and the empirical correlations for one scale may not work for the other one. The objective of this study is to investigate the parameters that affect the two-phase heat transfer within the minichannel plate heat exchangers, and to utilize the dimensional analysis technique to develop appropriate correlations. For this purpose, thermo-hydrodynamic performance of three minichannel brazed-type plate heat exchangers was analyzed experimentally in this study. These heat exchangers were used as the evaporator and condenser of an automotive refrigeration system where the refrigerant R-134a flowed on one side and a 50% glycol–water mixture on the other side in a counter-flow configuration. The heat transfer coefficient for the single-phase flow of the glycol–water mixture was first obtained using a modified Wilson plot technique. The results from the single-phase flow analysis were then used in the two-phase flow analysis, and correlations for the refrigerant evaporation and condensation heat transfer were developed. Correlations for the single-phase and two-phase Fanning friction factors were also obtained based on a homogenous model. The results of this study showed that the two-phase theories and correlations that were established for conventional macrochannel heat exchangers may not hold for the minichannel heat exchangers used in this study.  相似文献
9.
This paper describes the performance of an ejector cooling system driven by solar energy and R134a as working fluid. The system operating in conjunction with intermediate temperature solar collector in Athens, is predicted along the 5 months (May–September). The operation of the system and the related thermodynamics are simulated by suitable computer codes and the required local climatologically data are determined by statistical processing over a considerable number of years. It was fount that the COP of ejector cooling system varied from 0.035 to 0.199 when the operation conditions were: generator temperature (82–92 °C), condenser temperature (32–40 °C) and evaporator temperature (−10–0 °C). For solar cooling application the COP of overall system varied from 0.014 to 0.101 with the same operation conditions and total solar radiation (536–838 W/m2) in July.  相似文献
10.
Heat pipes are low cost and efficient heat exchange equipment. They are suitable for low temperature heat or cold recovery systems. The latter could be employed to cool incoming warm fresh air in air-conditioned ventilation systems. R-134a is an environmentally friendly refrigerant and has been generally accepted as a substitute for R-12 and R-22. The thermal performance of a thermosyphon filled with R-134a was investigated. The effects of temperature difference between bath and condenser section, fill ratio and coolant mass flow rates on the performance of the thermosyphon were determined. The experimental results indicate that the heat flux transferred increased with increasing coolant mass flow rate, fill ratio and temperature difference between bath and condenser section.  相似文献
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