【作者】 刘巍；

【导师】 朱春玲；

【作者基本信息】 南京航空航天大学 ， 人机与环境工程， 2013， 博士

【摘要】 微通道蒸发器以其造价低、重量轻、结构紧凑、换热效果好等诸多优点，在民用和军用制冷领域均有广阔的应用前景。微通道蒸发器的特点是制冷剂同时流入平行排列的多根扁管，也叫平行流蒸发器，涉及到各扁管内的流量分配均匀性问题。目前微通道蒸发器内制冷剂的流量分配研究需要深入，蒸发器的内部结构设计还需进一步优化。基于上述问题，本文对微通道蒸发器进行了流动、换热性能的研究和结构优化设计工作。采用数值模拟方法，基于连续介质假设，研究了微通道的换热机理，对已有的试验方法进行了分析，对实验结果进行了修正，证明了微通道内的换热规律与常规通道内是一致的。采用数值模拟方法，针对24通道两流程的微通道蒸发器内的流量分配问题，对分流板进行了结构优化，提出了12孔分流板的结构，找出了分流板的最佳开孔面积。对27通道两流程的微通道蒸发器的分流板进行了结构优化，提出了新的分流板结构，找出了最佳开孔面积。针对24通道两流程的微通道蒸发器，建立了分流板的流量分配试验系统，以水为工质，研究了不同结构的分流板的流量分配均匀性。结果表明：12孔分流板的流量分配均匀性和稳定性均是最好的，流量分配的均匀性随着雷诺数增大而略有提高。采用试验方法，对比研究了入口分流板的结构对蒸发器的流动和换热性能的影响。试验结果表明：分流板的开孔数量和位置对蒸发器的流动和换热性能影响很大。分流板上的总开孔面积一定时，开孔数量和位置的变化对蒸发器的内部阻力系数没有明显影响。证明了蒸发器采用12孔分流板时流动和换热性能优于其它分流板结构。对24通道的微通道蒸发器内部结构进行了优化，并以R134a为工质，进行性能对比试验，以期通过改变制冷剂的流向和流动阻力来提高蒸发器的性能。试验结果表明：在保证制冷剂的流量分配均匀性不降低的前提下，增大流通面积可以减小蒸发器内的流动阻力，提高制冷能力。以水为工质，保持分流板的结构不变，试验研究了12孔分流板在不同开孔面积时的流量分配特性，得出如下结论：分流板的开孔面积存在一个最佳值，为150.7mm2，此时的流量分配稳定性最好，几乎不受入口雷诺数变化的影响，安装12孔分流板后的流量分配均匀度比无分流板时提高一倍以上。试验研究了分流板的开孔面积变化对微通道蒸发器性能的影响，得出如下结论：随着开孔面积的增加，蒸发器的内部阻力系数减小，但制冷量是先增加后减少。当分流板的开孔面积为150.7mm2时，蒸发器的内部流动阻力系数和流量分配均匀性达到最佳匹配，制冷量最大。更多还原

【Abstract】 Micro-channel evaporator with parallel flow with its low cost, light weight, compact structure,good performance of heat transfer and many other advantages, had a very broad applicationprospected in the field of civil and military refrigeration. The characteristic of the micro-channelevaporator was that refrigerant flow arranged in many parallel flat tubes, also called parallel flow typeevaporator, and related to the flow distribution. The flow of the micro-channel evaporator withparallel flow and heat transfer performance of work needed to be further improved. Based on theabove issues, flow and heat transfer performance of micro-channel evaporator was studied andstructure optimization work was done.Based on the hypothesis of continuum, the mechanism of micro-channel heat exchanger wasdiscussed. Using numerical simulation method, combined with the existing experimental setup anddata, the influence of wall thickness on the micro-channel heat transfer was studied. The heat transferlaw in the micro-channel was proved to be the same as the conventional channel.The numerical simulation method was used to study the structure of deflectors and flowdistribution in micro-channel evaporator with24flat tubes: a deflector structure with12holes wasdevised; the flow distribution uniformity and pressure drop rule of a variety with structures and openarea of deflectors in different position were studied, and the optimum opening area of deflectors werefounded. The micro-channel evaporator with27flat tubes also was studied by the same method.The next experiments were processed on the micro-channel evaporator with24flat tubes. Inorder to verify the structure and clarify the flow distribution law of deflector, flow distribution testplatform was built; as water as the working fluid, flow distribution characteristics of deflectors wasstudied. The results show that the flow distribution uniformity and stability of the deflector with12holes are always the best, and as the entrance Reynolds number increased, the flow distributionuniformity is improved slightly. The deflector with reasonable structure can improve the fluid flowdistribution uniformity in micro-channel evaporator.Effects of deflectors with different structures on the flow and heat transfer performances of theevaporator were experimental investigated and compared. The results show that the structure ofdeflector affects the flow and heat transfer performances of the evaporator remarkably. With the sameopen area in the deflector, the number and location of holes in deflectors produce no evident effect onthe resistance coefficient of the evaporator. The performance of deflector with12holes is proved to bethe best.Structure optimized design and performance tests of micro-channel evaporator were done: in the condition of flow distribution of refrigerant being not decreased, the increase of circulation area candecrease the pressure drop and improve cooling capacity.Flow distribution characteristics of the three deflectors with same structure but different openingarea (45.6mm2，150.7mm2，339mm2) were experimentally studied with water as the working fluid.The results show that the flow distribution stability of deflector with the opening area of150.7mm2isthe best. Compared with the condition of without deflector, the flow distribution uniformity of thedeflector with12holes is improved more than doubled.Then effects of the deflector opening area on the performance of evaporator were investigatedwith above three deflectors. R134a was the working fluid. The results show that with the samedeflector structure, increasing the open area of holes in the deflector can reduce the resistancecoefficient of the evaporator, but the cooling capacity of evaporator is first increased and thendecreased. There is an optimum open area of holes in deflector of the micro-channel evaporator, withwhich the negative impact of pressure drop and mal-distribution of refrigerant on the cooling capacityof evaporator is the minimum, so the cooling capacity can get to the maximum. For the evaporator, theoptimum open area of holes in the first deflector is about150.7mm2.更多还原