共查询到17条相似文献,搜索用时 140 毫秒
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基于换热器几何结构参数以及流路布置等相同的3HP商用空调,在空调工况下,研究了相对湿度对R22替代制冷剂R407C、R410A、R32以及R290在蒸发器内的流动和传热性能的影响规律。研究表明:在一定的条件下,增加环境相对湿度,这五种制冷剂对应蒸发器换热量、压降和质量流量均增加,其中R407C蒸发器换热量最大,R290和R32蒸发器压降和制冷剂质量流量均小于R22蒸发器。在低湿度环境下(约20—30%相对湿度),显热换热占主导因素。随着相对湿度的增加,显然换热减少,潜热换热增强且起主导因素。在满足换热量的要求下,R290在协调压降与质量流量具有一定的优势且满足现行工质替代理念,可以作为现有商用空调的环保型替代工质。 相似文献
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理论研究了翅片管式蒸发器不同的结构参数,如管排数、翅片间距对风冷热泵室外侧蒸发器结霜特性的影响,获得了蒸发器结构参数对蒸发器结霜厚度和空气侧压降的变化规律。研究发现蒸发器结构参数对蒸发器结霜有很大的影响。计算结果和实验测试的结果吻合较好,研究结论为翅片管式蒸发器除霜以及优化设计提供了可靠的依据。 相似文献
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风速分布形状对空调中翅片管蒸发器性能的影响 总被引:1,自引:0,他引:1
通过建立空调蒸发器分布参数模型,并对模型进行了验证,进而研究了四种不同风速场对R22和R290翅片管蒸发器流动和换热性能的影响规律。研究表明:在上三角型、下三角型和三角型风速场分布下,蒸发器单位面积换热量、质量流量以及压降均较均匀风速场降低;上三角型较均匀型单位面积换热量下降达7%左右,下三角型和三角型较均匀型下降4%左右;在不同风速场下,各换热温差基本持平,总传热系数起主导作用;R290质量流量均较R22小40%左右,且压降均较R22小24%左右。在满足换热量的要求下,R290在协调压降与质量流量具有一定的优势,可以作为现有空调制冷剂R22的环保型替代工质。 相似文献
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以R600A为工质的分离式热管的实验研究 总被引:1,自引:0,他引:1
对分离式热管的整体热量传递特性进行了实验研究。以蛇形翅片管作为冷凝段和蒸发段进行热管实验,探讨了蒸发器进风面风温及分离式热管蒸发器与冷凝器之间高度差、工质充注量对分离式热管的影响。实验表明,随着蒸发器进风温度的升高,蒸发器与冷凝器换热系数都是呈现先增大后减小的趋势。在冷凝端进风温度恒定为16.55℃、蒸发端进风温度低于60℃时,以R600A为工质的分离式热管的传热量曲线近似于二次曲线,蒸发端进风温度高于60℃时,其传热量曲线近似于一条直线。加大充液率及增加蒸发器与冷凝器的高度差,分离式热管的传热能力均会得到提高。 相似文献
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建立了一种应用于CO_2热泵热水机的内螺旋管式气体冷却器(逆流型)的换热特性稳态仿真模型,且与实验数据吻合较好。在仿真模型基础上,分析气体冷却器内部流体温度沿管长分布情况,研究结构参数和水侧进口温度对气体冷却器换热性能的影响,研究结果表明:由于CO_2侧出口温度不会低于水侧进口温度,因此换热量受水侧进口温度限制,当气体冷却器换热面积增加到一定程度时,换热量增加幅度放缓并逐渐接近其上限值;随着水侧进口温度的增加,水侧与CO_2侧的对数平均温差和换热量降低,水侧出口温度增加幅度越来越小。 相似文献
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《Heat Recovery Systems and CHP》1988,8(4):299-308
This paper presents an experimental study of waste heat recovery shell-and-tube heat exchangers. The exchanger heat duty, overall heat transfer coefficient, effectiveness and tubeside friction factor are investigated as functions of the tube surface geometry (plain or dimpled), the flow type (counter or parallel), the tube Reynolds number and the shellside heat capacity rate. Water and the exhaust gases of a Diesel engine are passed inside the tube and the shell, respectively.The heat transfer characteristics increase with an increase in tube Reynolds number and the shellside heat capacity rate, for all the flow types and the surface geometries examined. The counter-flow, shell-and-dimpled-tube heat exchanger, compared with that exchanger having a plain tube, increases the heat duty and the overall heat transfer coefficient by 80%, and the heat exchanger -effectiveness increases by 35%. For the parallel-flow, shell-and-dimpled-tube heat exchanger, the heat duty, the overall heat transfer coefficient and the effectiveness increase by 30, 55, and 25%, respectively. At the same time the dimpled tube increases the tubeside friction factor by 600% over that of the plain tube. The rate of waste heat recovered from the exhaust gases of the Diesel engine by the counter-flow, shell-and-dimpled-tube heat exchanger is equal to 10% of the maximum brake power of the engine running at 1500 rpm, and the tube Reynolds number equal to 8875. 相似文献
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The aim of this research was to investigate the flow patterns and heat transfer of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV). In this study, the heat pipe was made of a high-quality glass capillary tube with an inner diameter of 2.4 mm bent into 10 meandering turns. The number of check valves was 2 and the tube was filled with R141b at a filling ratio of 50% of internal volume of the tube. The combined lengths of the evaporator, adiabatic and condenser sections were equal to 50 mm. The pipe was operated at the top heat mode, and the angles of inclination were 20°, 40°, 60°, 80°, and 90°. The heat applied at the evaporator section was controlled at 85°Cto 105°C, and 125°C. The results show that in the evaporator section, bubbles are produced and grow as a result of the continuous nucleate boiling. They coalesced and their volume expanded. Similarly, in the condenser section the vapor plug condensate caused the bubbles to collapse and accumulate as a liquid mass at the lower section of the U-bend tube. A new slug then developed and the bubbles coalesced in an upward flow. Heat flux increased when the evaporator temperature and inclination angle increased causing the average length of the vapor plug to decrease and the average velocity of vapor plug to increase. The maximum heat flux occurred at an evaporator temperature of 125°C and an inclination angle of minus 90°. 相似文献
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The effect of thermal environment on boiling heat transfer performance in a section of a horizontal tube bundle was investigated using R-113 as the working fluid. The in-line tube bundle has five columns and 27 rows with a pitch-to-diameter ratio of 1.3. Heal transfer coefficients obtained from the instrumented tube in the tube bundle with only one tube heated while the other tubes remained unhealed and with all the lubes in the bundle heated are reported for a range of heat flux, pressure, mass flow rate, and quality. The results showed that heat transfer coefficient of a tube in a heated bundle is slightly higher than that in an unhealed bundle, with the variation of heat transfer coefficient decreasing as heat flux, mass flow rate, or pressure increased. It was also found that higher quality would tend to improve the heat transfer. However, the effect of quality disappeared as heat flux, mass flow rate, and pressure increased. Based on the experimental data, the mechanism of the heat transfer augment due to thermal environment was analyzed. It was proposed that fluid agitation and thin liquid film formation are two main factors for a heated bundle to have better transfer performance than an unhealed bundle, 相似文献
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水平管降膜蒸发器传热优化研究 总被引:1,自引:0,他引:1
基于分布参数方法,对大型制冷系统中的水平管外降膜蒸发进行了传热优化数值模拟计算.在计算中,分析了饱和的液态制冷剂R134a在水平的铜管束外流动蒸发的换热特性.模型考虑了不同的管子类型和2流程不同管程布置对蒸发器换热特性的影响,结果表明,蒸发器采用Turbo-EHP管的性能高于其它管;不同管程布置对蒸发器性能的影响比较大,其中,下进上出管程布置的换热性能优于其它管程布置.同时,本文考虑了传热管外"干斑"对换热的影响.本文结论对于大型制冷系统中的降膜蒸发器传热优化设计具有指导性意义. 相似文献
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《Revue Generale de Thermique》1996,35(411):197-207
Experimental terrestrial study of an ammonia two-phase loop for thermal control in spatial environment. This paper presents the terrestrial test results of a mechanically pumped two-phase fluid loop, using ammonia as the working fluid. The 600 W experimental set-up (main components, instrumentation) is described. The two-phase flow patterns observed are compared with several flow regime maps. The experimental results are in good agreement with the predictions of Taitel and Dukler. The condensation lengths and the mean heat transfer coefficients of the condenser are given. The friction pressure gradients of adiabatic two-phase flow increases with mass flow rate and quality. The wall temperatures and heat transfer coefficients of the evaporator show the influence of the liquid distribution on the heat transfer : it is better at the top than at the bottom of the tube and at the ends than in the center part of the evaporator. The best evaporation coefficients are obtained with high mass flow rates and low qualities. The results obtained show the good operation of the system. 相似文献
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本文利用传热传质之间的比拟关系研究了错排环布圆管换热板芯的平均传热特性及阻力特性。实验中我们采用了三种翅片间距(Tp)、三种管排数(Nrow)以及三种管数(Ntube)组成的27种板芯结构,传质实验采用萘升华的方法来进行。然后通过三种限制条件对不同翅片间距、不同管排数和不同管数下的换热板芯的传热性能进行了比较。最后利用最小二乘法得出了具有工程指导意义的准则关联式。 相似文献