水平管外R404A降膜蒸发传热的实验研究

搭建了降膜蒸发实验台,研究了水平单管外的降膜蒸发传热特性。测试管为外径19mm、有效实验长度为2500mm的光滑管和强化管。实验采用R404A作为管外降膜蒸发工质,与管内热水进行换热。布液采用喷嘴喷淋的方式,通过21个喷口当量直径为2mm的喷嘴完成。分别在变饱和温度(0、5、10、15℃)、变热流密度(从8到30kW/m2)和变喷淋量(从0.07到0.11kg/(m·s)时进行实验,研究了降膜蒸发换热性能相应的变化情况,得到R404A的管外降膜蒸发换热的一些规律,这对降膜蒸发器的设计及应用具有一定的参考作用。     

内螺纹铜管齿形参数对传热性能的影响

利用R22单管传热试验台,对相同工况下不同结构参数的内螺纹强化管进行蒸发冷凝换热试验。通过对比分析试验数据,发现改变齿形参数对内螺纹管换热系数影响较大,且Tube-NEW换热性能优于其他管型。     

涟漪纹管换热性能试验研究

为了研究涟漪纹管换热性能搭建测试台。采用外径为12.7 mm,内径为11.5 mm的涟漪纹管,以及外径为12 mm的光管,统一采用外径为17 mm的套管进行试验研究。制冷剂进、出口干度分别为0.8和0.2,制冷剂质量流速为90~260 kg/(m~2·s),冷凝饱和温度为318 K。测试结果表明,单相热平衡损失在±3%以内,光管冷凝换热系数的3个关联式计算结果与试验结果的偏差范围都在±20%以内。随着制冷剂质量流速的增大,涟漪纹管的冷凝换热系数和压降增大,涟漪纹管相对于光管的换热强化倍率为1.05~1.24,涟漪纹管多凹坑表面使得其强化冷凝换热效果明显。     

R1233zd(E)与R123的管内外换热性能的对比研究

对R1233zd(E)和R123的换热性能进行对比研究。管束测试台用于测试管外制冷剂侧换热系数,套管式换热台用来测试管内水侧换热系数。试验中蒸发管选用B5管,蒸发试验的饱和温度为6.7℃;冷凝管选用Gewa C+LW管,冷凝试验的饱和温度为36.7℃。管内侧换热系数采用Wilson Plot方法分离,管外侧换热系数通过总换热系数和分离出的管内换热系数求得。试验结果表明,应用在上述2种管型上时,R1233zd(E)的换热系数在测试的热流密度范围内均稍高于R123。认为R1233zd(E)是一种能够满足环境要求的、具有很好的换热性能的R123的替代物。     

降膜式蒸发器用高效传热管换热性能试验研究

通过试验对降膜式蒸发器用高效传热管的换热性能进行研究,并将其与之相对应的池沸腾换热性能进行比较.由比较数据可知:样管池沸腾换热性能均随热流密度的增大而增强,降膜蒸发性能在一定热流密度下随喷淋流量的增大而增强;在恒定热流密度和恒定喷淋流量下,光管降膜燕发性能低于池沸腾性能,强化管降膜蒸发性能高于池沸腾性能;池沸腾性能高的强化管降膜蒸发性能也强.     

R1233zd(E)和R123的水平管外冷凝换热性能研究

针对制冷剂R1233zd(E)和R123,在饱和温度36. 1℃,冷凝水流速2. 12 m/s,2. 59 m/s和2. 90 m/s工况下,分别对水平光管和强化冷凝管GDHT-GDⅢ的管外冷凝换热系数进行测试。结果表明:R1233zd(E)的光管管外冷凝换热系数高于R123的6%～16%,R1233zd(E)的强化冷凝管GDHT-GDⅢ管外冷凝换热系数高于R123的19%～21%;采用强化冷凝管GDHT-GDⅢ时R1233zd(E)的管外冷凝换热系数是采用光管时的10. 8倍。指出R1233zd(E)可作为R123的替代物,强化冷凝管GDHT-GDⅢ能够很好地发挥R1233zd(E)的换热性能。     

R134a在水平强化管外凝结换热的实验研究

对氟利昂R134a在水平单管外的凝结换热性能进行了试验研究,试验管为光管和三根强化管,采用热阻分离法得到蒸气侧凝结换热系数。试验结果表明:光管管外Nusselt理论值与实验数据偏差小于10%。强化管No.1-3的传热性能均好于光管,当Re=40000时,No.1-4管的总传热系数分别为:5295,5818,5904,1502W/m2.K。在相同热流密度条件下,No.1-3管的管外换热系数分别是光管的7.0-8.8倍,9.0-10.8倍,9.9-12.0倍。管外强化后,管内外的换热系数已比较接近。     

强化冷凝管外侧制冷剂冷凝换热试验分析与新计算方法研究

对外径分别为1″和0.75″的强化冷凝管进行管外冷凝换热性能测试,引入冷凝管管外传热强化因子(h_(o-multiplier)),将其在常用热流密度范围内的平均值作为不同管型冷凝管管外换热系数的评价指标,并对该评价指标进行理论和试验对比分析。结果表明,该评价指标在常规工况条件下与测试值的偏差在±10%以内,满足工程设计要求。     

R410A在7 mm水平强化管内冷凝传热性能的实验研究

为了研究R410A制冷剂在1根光管和5根水平管内强化管冷凝换热特性,搭建一套集蒸发/冷凝于一体的水平单管换热实验台,研究变质量流速、变管型、变冷凝温度等参数对管内冷凝换热特性的影响.结果表明:保持环状流状态有利于强化传热;较大的螺旋角能够增大铜管内表面积和增加湍流效应,有利于强化传热;降低冷凝温度可以提高液相导热性能及...     

管式间接蒸发空气冷却器传热传质模型的建立及验证

回顾和分析现有间接蒸发冷却器的热工性能和数学模型,并在分析管式间接蒸发空气冷却器传热、传质过程及特点的基础上,建立针对管式间接蒸发空气冷却器热工计算模型。基于模型中管外二次空气侧空气与水膜之间的传热、传质系数是影响模型精度的重要因素,对管外二次空气侧空气与水膜之间的传热、传质系数进行深入分析,将模型用于水平单管外蒸发传热、传质系数的计算,并将计算结果与文献中的实验数据进行对比,证明所选模型的正确性,为下一步对管式间接蒸发空气冷却器整体热工性能的数值模拟奠定坚实的基础。     

有关降膜蒸发技术的几个热点问题浅析

从理论和应用实践的角度对有关降膜蒸发技术的几个热点问题进行论述,包括降膜蒸发技术对机组能效比提升的贡献、降膜式蒸发器轴向换热量的差异和降膜式机组的系统优化策略等。     

车载LNG储罐蒸发率的理论与试验

为研究车载LNG低温绝热气瓶内液体的蒸发规律,以200 L高真空多层绝热气瓶为例,采用液氮(LN2)为工质,进行了一系列LN2日蒸发率试验。列出根据实验系统结构参数得到的相关传热学计算结果,包括试验系统分别贮存LN2和LNG各项漏热及理论蒸发率。对理论计算与实验结果进行比较,通过理论计算结果与LN2蒸发率实验结果对LNG试验蒸发率作了预测。根据大气压力下进行的各种充满率的LN2蒸发率实验,拟合出了系统蒸发率与充满率的关系曲线,并分析了系统中环境温度和压力对蒸发率的影响规律。     

Effect of tube diameter on boiling heat transfer and flow characteristic of refrigerant R32 in horizontal small-diameter tubes

This study investigated the effect of tube diameter on flow boiling characteristics of refrigerant R32 in horizontal small-diameter tubes with 1.0, 2.2, and 3.5 mm inner diameters. The boiling heat transfer coefficient and pressure drop were measured at 15 °C saturation temperature. The effects of mass velocity, heat flux, quality, and tube diameter were clarified. The flow pattern of R32 for adiabatic two-phase flow in a horizontal glass tube with an inner diameter of 3.5 mm at saturation temperature of 15 °C was investigated. Flow patterns such as plug, wavy, churn, and annular flows were observed. The heat transfer mechanisms of forced convection and nucleate boiling were similar to those in conventional-diameter tubes. In addition, evaporation heat transfer through a thin liquid film in the plug flow region for low quality, mass velocity, and heat flux was observed. The heat transfer coefficient increased with decreasing tube diameter under the same experimental condition. The fictional pressure drop increased with increasing mass velocity and quality and decreasing tube diameter. The experimental values of the heat transfer coefficient and frictional pressure drop were compared with the values calculated by the empirical correlations in the open literature.     

Effect of pressure and concentration on performance of a vertical falling-film type of absorber and generator using lithium bromide aqueous solutions

Experiments on an absorber and generator in an absorption refrigerating machine were made using a vertical falling-film type of stainless steel column. Three lithium bromid e aqueous solutions (40, 55 and 60wt% LiBr) were used as working fluid. The experimental apparatus was operated at 1.3 kPa (the pressure for a practical absorber) and 5.3 kPa (the intermediate pressure between absorber and generator). The measured absorption (evaporation) rate decreased with reducing pressure an d increasing concentration of LiBr in the falling liquid. The rate agreed with the values obtained from the analysis of heat and mass transfer in a falling film. Therefore, a falling-film type of absorber and generator can be designed and operated by a consistent method.     

Assessment of boiling heat transfer correlations in the modelling of fin and tube heat exchangers

A new way to assess the performance of refrigeration system models is presented in this paper, based on the estimation of cycle parameters, such as the evaporation temperature which will determine the validity of the method. This paper is the first of a series which will also study the influence of the heat transfer coefficient models on the estimation of the refrigeration cycle parameters. It focuses on fin and tube evaporators and includes the dehumidification process of humid air. The flow through the heat exchanger is considered to be steady and the refrigerant flow inside the tubes is considered one-dimensional. The evaporator model is discretised in cells where 1D mass, momentum and energy conservation equations are solved by using an iterative procedure called SEWTLE. This procedure is based on decoupling the calculation of the fluid flows from each other assuming that the tube temperature field is known at each fluid iteration. Special attention is paid to the correlations utilised for the evaluation of heat transfer coefficients as well as the friction factor on the air and on the refrigerant side. A comparison between calculated values and measured results is made on the basis of the evaporation temperature. The experimental results used in this work correspond to an air-to-water heat pump and have been obtained by using R-22 and R-290 as refrigerants.     

40英尺液化天然气铁路及其联运罐式集装箱静态蒸发率计算及测试研究

针对铁路及其多式联运液化天然气罐式集装箱,对其静态蒸发率进行了理论计算,在理论计算中引入了温度修正系数kt来考虑装载LNG介质时对液氮温区下绝热层比热流的影响,同时引入了结构修正系数ks来考虑结构和深冷下罐体收缩对支撑部位热传导的影响,采用液化天然气作为介质开展了静态蒸发率试验测试,综合测试结果对理论计算模型进行了验证,在此基础上开展了相关关键参数对LNG罐式集装箱静态蒸发率的影响分析研究。     

水平管降膜式蒸发器的优化设计模型

对降膜式蒸发器进行热力分析建模,提供一种性能优化的数值计算方法,在模型中引入成本估算算法,用于对降膜式蒸发器的优化设计提供指导。并用样机试验结果验证该计算模型的准确性,为工程设计提供参考。     

全降膜蒸发器应用于冷水机组的研究

在分析蒸发器性能对冷水机组性能影响的基础上,探讨降膜式蒸发器的关键技术,并通过试验研究降膜式蒸发器的换热系数和回油浓度,同时与满液式蒸发器的换热性能进行对比。结果表明,在分配器供液充足时,降膜管束蒸发性能优势显著,表现在换热系数高、回油浓度高等方面。