单流程蒸发器表面温度场均匀性的影响因素研究

改善蒸发器表面温度场的均匀性对提高其换热效率具有决定性作用。设计出一种类似平行流蒸发器的圆管单流程蒸发器,改变其集液管和蒸发管衔接处的孔径大小以及制冷剂入口流速,并进行了蒸发器管路的水力计算和相应的实验研究,得出管路中间截面的温度分布。模拟结果表明:在结构一定的条件下,集液管内的制冷剂来流速度具有决定性作用。当集液管内的来流速度在0.04m/s时,蒸发器各支管的温度分布最为均匀;同时在制冷剂流量一定时,支管数及各蒸发管与集液管衔接处的孔径大小也影响着温度分布。试验结果证明了此结论:在一定的液态制冷剂集管入口流速下,最小孔径为0.4mm时,具有8根支管的单流程蒸发器比10根支管的单流程蒸发器具有均匀的温度场。研究结果为研发高效率的平行流蒸发器提供了一定的理论和试验基础。     

双D形管高效换热平行流蒸发器设计

为提升集液管封堵的可靠性,使其更加适用于高压力工况,进一步提高换热效率,设计了一种双D形管平行流冷凝器。设计的双D形管平行流冷凝器主要包括两层芯体、第一双D形管A、第二双D形管B。其长度方向的剖面为D形第一管体、D形板的第一插板、第一插槽、第二插槽等。通过设置第四插板,有效地均匀输送流体,延长了流体路径,提高了平行流蒸发器的热交换效率。第一插板插入第一插槽内实现了双D形管端部,并通过焊接的方式实现封堵,可承受更大的流体压力,封堵可靠性高。双D形管平行流冷凝器在减轻重量、提高集液管封堵的可靠性以及换热效率等方面具有突出优势,是我国汽车空调行业推广应用平行流冷凝器向轻量化、节能、环保方向发展的必然趋势,具有广阔的市场应用前景。     

基于分布参数模型的水平管式降膜蒸发器模拟

建立水平管式降膜蒸发器蒸发换热的分布参数模型,考虑换热性能沿管子轴向、管排方向的变化,以及传热管发生干斑现象时对降膜蒸发的影响。对一降膜蒸发器的性能进行模拟分析,并考察管束布置、制冷剂液膜质量流量、管程布置以及满液位置对降膜蒸发器性能的影响。结果表明,计算结果和试验结果吻合良好,通过合理的设计管排方式和满液位置,可以减少或避免干斑现象的发生,提高降膜蒸发器性能。     

电加热叠板式微通道蒸发器实验研究

提出一款电加叠板式微通道蒸发器,主要由两块端板和两片紫铜薄板叠合而成.紫铜薄板表面加工有2个分布腔和微通道阵列.通过对蒸发器内水的升温响应和出口平衡温度的实验研究,对加热温度、供给流量、流道方式和分布腔形状等因素对蒸发器性能的影响进行了评价.实验结果表明,在供给流量低于6ml/min时,四种蒸发器的升温响应性能非常接近.在供给流量高于6ml/min时,并联式流道与钝角形分布腔之间的组合以及串联式流道与直角形分布腔之间的组合更加有利于提高蒸发器的升温响应性能和出口平衡温度.总体上,串联直角式蒸发器平均的升温响应性能最优,并联钝角式蒸发器平均的出口平衡温度最高.     

异型排列管束蒸发器壳程流场数值模拟

制冷装置蒸发器应用广泛,其壳程内流体的流体力学行为对蒸发器蒸发性能影响显著.利用Gambit软件建立了5种管束排列方式下蒸发器壳程流体流动的二维模型,采用Fluent软件对流体在壳程通道内的流动进行数值模拟.模拟结果表明,相比管束正方形排列和转角正三角形排列,异型排列方式更有利于壳程流体与管换热面接触,流体绕流异型排列管束的压力损失小于正三角形排列.研究结果为蒸发器设计及生能优化提供参考依据.     

分流板开孔面积对微通道换热器流量分配的影响

以水为工质,试验研究了3个结构相同但开孔面积不同的分流板的流量分配性能。结果表明:当雷诺数小于2500时,开孔面积对分流板的流量分配均匀性有明显影响,流量分配均匀性最好的是分流板B(开孔面积为150.7mm2),最差的是分流板C(339mm2)。随着雷诺数的增加,分流板A(45.6mm2)和C的均匀性会提高,而B的均匀性几乎不变化。当雷诺数大于2500时,开孔面积和雷诺数的变化对分流效果的影响很小,3个分流板的流量分配均匀性很接近。分流板B的流量分配稳定性最好,安装分流板后试验件的流量分配均匀度比无分流板时提高1倍以上。     

空气源热泵蒸发器结霜及换热性能的研究

研究了入口空气相对湿度、温度以及风速对风冷热泵蒸发器结霜的影响,获得了各个入口空气参数对蒸发器结霜厚度和换热量的影响规律.研究发现空气入口相对湿度等参数对蒸发器结霜以及换热性能有很大的影响,结霜严重地影响了蒸发器换热性能.计算结果和实验测试的结果吻合良好.     

蒸发器中环形管板的设计

通过对一台蒸发器中环形管板的设计，运用类比的方法对其进行分析，从而验证环形管板设计的可靠性、合理性。     

新型蒸发器对中药大黄溶液浓缩性能的研究

介绍导形竖板降膜蒸发器的结构、工作原理和优点等。采用中药大黄溶液为实验介质，研究了传热性、结垢性和起泡性。阐述了该蒸发器在浓缩中药大黄方面良好的传热和防除垢性能。     

薄膜蒸发器转子系统固有频率及稳态不平衡响应分析

薄膜蒸发器转子系统中的不平衡力易导致转子振幅加大,从而加剧刮板磨损,导致刮板失效.采用VB对ANSYS进行二次开发,对薄膜蒸发器转子系统进行模态分析,并对转子某些位置上的不平衡量进行了稳态不平衡响应分析,初步实现了薄膜蒸发器转子动力学分析,为薄膜蒸发器设计及安全运行提供依据.     

A study on performance analysis of the helically coiled evaporator with circular minichannels

In order to develop a compact evaporator, experiments that show characteristics of evaporating heat transfer and pressure drop in the helically coiled minichannel were performed in our previous research. This study was focused on the performance analysis of helically coiled heat exchangers with circular minichannels with an inner diameter=1.0 mm. The working fluid was R-22, and the properties of R-22 were estimated using the REFPROP program. Numerical simulation was performed to compare results with the experimental results of the helically coiled heat exchanger. As the heat transfer rate and pressure drop were calculated at the micro segment of the branch channels, the performance of the evaporator was evaluated. The following conclusions were obtained through the numerical simulations of the helically coiled heat exchanger. It showed good performance when the flow rate of each branch channels was suitable to heat load of air-side. The numerical simulation value agreed with experimental results within ± 15%. In this study, a numerical simulation program was developed to estimate the performance of a helically coiled evaporator. And, an optimum helically coiled minichannels evaporator was designed.     

新型微小型平板CPL蒸发器流动与传热分析

提出一种新型微小型平板毛细抽吸两相流体回路(Capillary pumped loop,CPL)的蒸发器结构,使其能够适应高热流密度散热的要求。分析蒸发器由于微型化后侧壁导热对系统传热能力的影响。建立新型蒸发器毛细多孔芯内的传热传质数学模型和液体补偿腔的流动与传热模型以及蒸汽槽道和金属外壁区域的导热模型,并用SIMPLE算法对蒸发器进行整场耦合求解。数值结果表明,工质蒸发发生在多孔芯上表面以及侧壁附近,采用热导率较大的铝外壁时,蒸发器加热表面的温度水平较低且温度均匀性较好,但侧壁导热的影响导致CPL的传热能力不高。外壁采用热导率较小的不锈钢可以明显提高CPL的传热极限能力,但同时却较大地增加了加热表面的温度水平以及不均匀性。采用组合结构的蒸发器一方面可以提高系统的传热能力,同时降低了加热表面的温度水平和温度梯度。     

汽车空调蒸发器芯进出水管结构强度分析

针对某一车型汽车空调蒸发器芯进水管在行驶2万公里时蒸发器芯进水管根部出现断裂现象,利用有限元分析软件Hypermesh,建立蒸发器芯的CAD模型并进行有限元网格划分,以ABAQUS为求解器,对蒸发器芯进出水管进行强度校核。分析结果与实际断裂位置吻合,为蒸发器芯进出水管的前期设计提供一种方法。     

EXPERIMENTAL RESEARCH AND DESIGN ON HEAT TRANSFER OF EVAPORATOR USED IN THE LARGE QUICK FREEZE PLANT

The evaporator is the main part of a quick-freeze equipment. There are many factors influencing the heat transfer coefficient of an evaporator. The most important factors among them are the fin shape, tube diameter, distance of fin space, frost, and velocity of air flow etc. They mainly influence the thermal efficiency of an evaporator, and therefore its thermal efficiency has direct relationship with the whole efficiency of the quick freeze plant. Evaporators with different structural types have different heat transfer efficiency. In order to obtain high efficiency structure of evaporator, 8 evaporator models with different fin shape, tube diameter and tube arrangement are analyzed and compared. The calculation results show that the integral waved fins, equilateral-triangle arranged small diameter tubes and varying fin-spacing has the highest heat transfer coefficient. The experimental result also shows that the evaporator with this type of structure has better thermal efficiency. The experimental result is in good agreement with the calculation result. It can instruct engineering design for usual designer. A real quick-freeze equipment is designed and put into production. The result shows that, compared with traditional domestic quick-freeze equipments, this equipment decreases by 40% in size and by 20% in energy consumption.     

基于温度补偿的汽车蒸发器结冰控制及验证

以某款汽车平台为对象,对空调蒸发器表面结冰的原因进行了综合分析。温度传感器的位置定位,传感器反馈到控制器的温度值和控制器的读取精度是影响结冰的主要因素。就此提出改进蒸发器温度传感器R/T曲线的方案,通过汽车环境模拟试验和实车道路测试结果表明,改进的措施能有效防止蒸发器表面结冰,提高了车内环境的舒适性和空调系统的可靠性。     

Dynamic analysis of evaporator characteristics

An analysis of the dynamic characteristics in an evaporator was numerically performed for control and design of the refrigeration and air conditioning systems. The important factors, such as refrigerant flow rate, inlet enthalpy, inlet air velocity and air temperature, are incorporated with this analysis. An evaporator is modeled for the dynamic characteristics analysis separated into three regions which are the two-phase region, the saturated vapor region and the superheated vapor region. The basic equations of each region were derived in the continuity, heat energy equilibrium and heat transfer equations. The transfer functions of the dynamic characteristics were obtained by the linearization and Laplace transformation. The dynamic response characteristics were evaluated on the Bode diagram with the frequecy response method. These results may be used for the analysis of the dynamic characteristics and design in the total system.     

Parametric study on flow and heat transfer characteristics of porous wick evaporator based on AMTEC

By establishing an axial symmetric invariable temperature phase change interface model of porous wick evaporator based on alkali metal thermal-to-electric converter (AMTEC), a parametric study has been implemented to explore the impact of effective thermal conductivity model, working fluid, wick material, porosity and particle size of porous wick on the flow and heat transfer characteristics. The results indicate that the inner surface temperature profile of wick is closely dependent on effective thermal conductivity models; it is the minimum for series model while the highest for parallel model. The inner surface temperature of wick with Na-K alloy as working fluid is obviously lower than that with sodium or potassium as working fluid. The wick made of refractory ceramics makes the minimum of inner surface temperature, while the one with nickel appears the highest temperature. Increasing the porosity can reduce the pressure drop in the wick, but also increases the temperature of evaporator.     

Performance comparison of microchannel evaporators with refrigerant R-22

An experimental study on the performance comparison of microchannel evaporators with refrigerant R-22 was conducted. Six microchannel evaporators were designed and manufactured for a residential air-conditioner. They were tested with psychrometric calorimeter test facilities. The experiment was performed with both vapor compression system and refrigerant circulation system. Each evaporator was made up of two parallel flow heat exchangers connected with several return pipes. The parallel flow heat exchanger had 41 microchannel tubes inserted between inlet and outlet headers. The microchannel tube had 8 rectangular ports with the hydraulic diameter of 1.3 mm. For the vapor compression system, the flow area ratio and the number of return pipes had a great effect on the cooling capacity. Type 3 with a flow area ratio of 73% and 58% showed the best cooling capacity. It had 12 return pipes and 3 circuits. There is a merging manifold in it. The effect of the number of circuits and merging manifold on the cooling capacity was relatively small. For the refrigerant circulation system, the effect of the mass flow rate on the cooling capacity was slightly superior to that of inlet quality. The effect of the number of circuits on the cooling capacity was different from the result of the vapor compression system. The effect of merging manifold was negligible, which was consistent with the result of the vapor compression system. The cooling capacity proportionally increased as the vertical inclination angle of the evaporator increased due to gravity force.