翅片管式蒸发器的计算机辅助设计

拟合了制冷剂(R22、R134a和R407C)热力性质的公式,并以这三种制冷剂为工质,选择平直翅片、波纹翅片、开缝翅片和百叶窗翅片,采用稳态集中参数模型,用VB语言编制翅片管式蒸发器的计算机设计程序。在程序的编制过程中,还采用了模块化开发技术,避免公式的反复使用和繁琐的迭代计算而造成的错误,以提高计算效率和准确性。软件主要的计算结果包括热流密度、换热系数、压降等基本量,还包括蒸发器尺寸以及蒸发器的耗材。本软件的界面可视化较好,功能比较齐全,精确度满足空冷式蒸发器工程设计的要求。最后算例验证了程序的可靠性。     

蒸发器建模仿真与试验的比较

采用稳态分布参数模型对R134a单元机的蒸发器进行仿真。使用改进的Kattan模型对R134a在光滑管内的流动形式进行划分,从而得出流型图。根据流型图,应用不同表达形式的关联式计算管内局部沸腾换热系数。CCWang的模型用于计算百叶窗形翅片管式蒸发器的表面换热系数及压降。析湿系数通过试验数据建立的数据库确定。在仿真过程中,应用隐式三次多项式拟合模型计算R134a的物性。将仿真结果与试验数据对比发现,仿真值能够较为真实的反映机组的运行状态。通过误差分析得出制冷量的平均相对误差为1．12％,出风干球温度的平均相对误差为1．25％,出风焓的最大相对误差为0．88％,R134a出口温度的平均相对误差为4．0％。     

R134a单元式风冷冷风机组冷凝器设计

单元式风冷冷风空调机组普遍采用波纹翅片管冷凝器。对冷凝器进行设计的关键是确定制冷工质在铜管内的冷凝换热系数及空气在翅片侧的表面换热系数，同时也需要考虑空气流过冷凝器的压降，以便选择风机。采用数学模型及换热关联式计算相关参数，在此基础上对R134a单元式风冷冷风空调机组的冷凝器进行设计。     

冷藏车层叠式蒸发器应用R404A与R22和R134a的比较

采用分布参数法对层叠式蒸发器建立数学模型，并对蒸发器采用R404A，R22和R134a时的换热和流动性能进行模拟比较。结果表明，在空调工况范围内，新型中低温混合制冷剂R404A具有R134a换热性能好和R22压降小的特点，能够很好地适用于冷藏车系统空调侧层叠式蒸发器。     

板式蒸发器换热性能的数值模拟1：数学模型

采用分布参数法对波纹型多通道单流程板式蒸发器建立数学模型，通过计算局部蒸发换热系数和摩擦压降可以简化板式蒸发器内复杂三维流动的换热关系。总结了文献已有的各种换热和压降关联式，并添加到模型控制方程组中。基于此模型，可对目前应用较广的R134a和R410A制冷剂的板式蒸发器在小换热温差下的换热性能进行研究。     

空调用翅片管式蒸发器的模拟与分析

建立R410A翅片管式蒸发器的稳态分布参数模型,分析制冷剂侧换热、压降、温度和干度沿流程的分布情况,并讨论风量、制冷剂流量及翅片管结构形式对蒸发器换热和流动性能的影响,为翅片管式蒸发器的设计和性能优化提供理论依据。     

纯工质及混合工质管外沸腾换热特性研究

对水平管外纯工质R22、R134a,R125浓度分别为6%,12%,18%的R134a/R125混合工质以及三元混合工质R417A(R134a/R125/R600浓度分别为50%/46.6%/3.4%)池沸腾换热性能进行了试验研究。通过对不同工质在光管和强化管外的沸腾换热性能进行比较与分析表明:强化管外沸腾换热系数明显高于光管,在热流密度为60k W/m2时,纯工质R22在强化管外沸腾换热系数是光管的3.10倍;纯工质R134a在强化管外沸腾换热系数是光管的2.85倍;在分别含6%、12%、18%R125的R134a/R125混合工质中,强化管外的沸腾传热系数是相对于同条件下光管的2.49、2.42、2.28倍;在R417A中,强化管外沸腾换热系数是光管的2.10倍。不同质量浓度的R125对光管沸腾换热系数影响相对较小,而对强化管外沸腾换热系数影响较大。     

基于NSGA-III算法的小管径翅片管式蒸发器高维多目标优化

以稳态分布参数法和NSGA-III算法为基础，提出一种翅片管式蒸发器结构参数与流路参数混合寻优的方法，并依此展开小管径蒸发器结构和流路参数的影响分析与流路的高维多目标设计优化。建立的小管径翅片管式蒸发器模型与实测数据的误差在4%以内，可以较好地用于小管径翅片管式蒸发器的计算。基于该模型进一步建立以结构参数与流路参数为自变量，换热量、制冷剂侧压降、空气侧压降以及成本为因变量的神经网络模型，并利用NSGA-III算法对模型进行优化求解，得到小管径翅片管式蒸发器在一定的结构参数变化范围内的最优结构参数及最佳流路。研究结果显示：管外径对小管径翅片管式蒸发器的换热量、制冷剂侧压降以及成本的影响程度最大；翅片间距对小管径翅片管式蒸发器的空气侧压降影响程度最大；翅片厚度对换热量、制冷剂侧压降、空气侧压降以及成本的影响程度均最小；流路主要影响蒸发器的换热量及制冷剂侧压降；制冷剂流路为二支路、三支路和四支路时，模型可输出综合性能最优的结构及流路特征。     

整体型内螺旋翅片管氟利昂12干式蒸发器传热强化试验研究

本文是一篇关于利用整体型内螺旋翅片管强化沸利昂12干式蒸发器传热的试验报告。文章报道了试验研究的结果。试验结果表明,整体型内螺旋翅片管用于氟利昂干式蒸发器的流动沸腾传热是非常有效的。在相同操作工况下,它的总传热系数比光滑管提高60％左右,即可节约换热面积37％。管束试验结果为中央空调机干式蒸发器提供了设计依据。     

板式蒸发器换热性能的数值模拟Ⅰ:数学模型

采用分布参数法对波纹型多通道单流程板式蒸发器建立数学模型,通过计算局部蒸发换热系数和摩擦压降可以简化板式蒸发器内复杂三维流动的换热关系.总结了文献已有的各种换热和压降关联式,并添加到模型控制方程组中.基于此模型,可对目前应用较广的R134a和R410A制冷荆的板式蒸发器在小换热温差下的换热性能进行研究.     

Development and validation of a micro-fin tubes evaporator model using R134a and R1234yf as working fluids

This paper presents a model of shell and tube evaporator with micro-fin tubes using R1234yf and R134a. The model developed for this evaporator uses the ε-NTU method to predict the evaporating pressure, the refrigerant outlet enthalpy and the outlet temperature of the secondary fluid. The model accuracy is evaluated using different two-phase flow boiling correlations for micro-fin tubes and comparing predicted and experimental data. The experimental tests were carried out for a wide range of operating conditions using R134a and R1234yf as working fluids. The predicted parameter with maximum deviations, between the predicted and experimental data, is the evaporating pressure. The correlation of Akhavan– Behabadi et al. was used to predict flow boiling heat transfer, with an error on cooling capacity prediction below 5%. Simulations, carried out with this validated model, show that the overall heat transfer coefficient of R1234yf has a maximum decrease of 10% compared with R134a.     

客车空调系统用管片式蒸发器流程的优化设计

对客车空调系统中的管片式蒸发器的流程进行优化设计,即通过焊接一个三通管来改变制冷剂在管片式蒸发器中的流程,降低制冷剂在蒸发器内的流阻,使客车空调系统的功耗降低3％～5％,蒸发器的换热能力提高4%,系统的能效比提高5％～8％。     

板式蒸发器换热性能的数值模拟Ⅱ:结果及分析

在已建立的数学模型的基础上,对板式蒸发器换热能力进行了数值模拟.针对应用较广的R134a和R410A制冷剂来比较和分析板式蒸发器在小的温差下的换热性能.在三种不同的计算工况下简要分析了各种热力参数的变化对蒸发器整体换热性能的影响.不同的制冷剂,其换热系数和压降差别较大,相同工况下采用R410A替代R22,板式蒸发器的换热性能可提高8.5%～10.0%,且压降可大幅降低.     

Boiling hysteresis at low temperature on enhanced tubes

The boiling hysteresis phenomenon is studied for a real scale enhanced evaporator tube (2 m long Turbo-B type) with R134a refrigerant used in the flooded evaporator of a centrifugal brine chiller for the ice-making facility. Unlike previous studies of the boiling heat transfer with uniform heat flux and uniform wall temperature, the wall temperature varies along the tube in the present experiment. To see if the similar hysteresis occurs as in the case of uniform wall temperature, a careful control of refrigerant temperature and heat flux is made. We have found hysteresis of the temperature overshoot (TOS) at the onset of nucleate boiling initially at the inlet section of the tube, before it gradually moved downstream section of the tube until the nucleate boiling occupied the whole section of the tube as the inlet temperature increased. The hysteresis became stronger at low refrigerant temperatures. The decreasing trend of heat flux after the contents of the whole tube boiled was different from the increasing trend. This paper provides a guideline how to design the evaporator in order to avoid the abnormal operation of the chillers.     

R134a臣卧式螺旋管内流动沸腾换热特性实验研究

对R134a在水平直管和螺旋管内的沸腾换热特性进行了实验研究.在三个不同的蒸发温度(5℃、10℃和20℃),工质R134a的质量流量范围为100～400kg/(m~2·s)和干度范围为0.1～0.8的条件下,实验得到了R134a在水平直管和螺旋管内的沸腾换热系数随其质量流量和干度的变化关系,将水平直管和螺旋管内的沸腾换热特性数据进行了比较,结果显示,在实验条件下,卧式螺旋管的传热系数比直管的平均增加13.7%.     

The effect of lubricant concentration, miscibility, and viscosity on R134a pool boiling

This paper presents pool boiling heat transfer data for 12 different R134a/lubricant mixtures and pure R134a on a Turbo-BII™-HP surface. The mixtures were designed to examine the effects of lubricant mass fraction, viscosity, and miscibility on the heat transfer performance of R134a. The magnitude of the effect of each parameter on the heat transfer was quantified with a regression analysis. The mechanistic cause of each effect was given based on new theoretical interpretation and/or one from the literature. The model illustrates that large improvements over pure R134a heat transfer can be obtained for R134a/lubricant mixtures with small lubricant mass fraction, high lubricant viscosity, and a large critical solution temperature (CST). The ratio of the heat flux of the R134a/lubricant mixture to that of the pure R134a for fixed wall superheat was given as a function of pure R134a heat flux for all 12 mixtures. The lubricant that had the largest CST with R134a exhibited the greatest heat transfer: 100%±20% greater than that of pure R134a. By contrast, the heat transfer of the mixture with the lubricant that had the smallest viscosity and the smallest CST with R134a was 55%±9% less than that of pure R134a. High-speed films of the pure and mixture pool boiling were taken to observe the effect of the lubricant on the nucleate boiling.