间冷式冰箱蒸发器结霜模拟

针对间冷式冰箱蒸发器的结霜工况进行了模拟。在改进现有的计算霜表面水蒸气过饱和度公式的基础上,建立了适用于间冷式冰箱蒸发器的霜层生长模型,并模拟出结霜过程中的结霜量,空气侧压降,霜的密度和厚度随时间的变化。通过与实验数据的比较,结霜量的误差在10％以内,空气侧压降在25％以内,该模型能够有效的模拟间冷式冰箱蒸发器的结霜过程。     

空气源热泵结霜/除霜特性的数值模拟

为研究空气源热泵的结霜与除霜特性,建立了热泵系统结霜动态模型和显热除霜模型,求解模型获得了结霜与除霜过程中各系统参数变化规律。结果表明,初期霜层对系统性能影响较小;当结霜工况运行70 min时,系统性能系数(COP)、制热量和蒸发压力降幅分别为6.9%、10.9%和12.3%;随着霜层继续生长,系统性能衰减加剧;除霜工况下,管壁温度迅速升高,霜层预热后进入融霜阶段,从蒸发器入口微元到出口微元,融霜时间从7 s增加到52 s;进入融霜水蒸发阶段后,管壁温度增速减慢,沿制冷剂流动方向融霜水蒸发时间逐渐增加;当换热器散热与得热达到平衡时,管壁温度维持恒定。     

空气源热泵蒸发器并联轮换除霜理论研究

针对大中型空气源热泵系统除霜,提出一种空气源热泵蒸发器并联轮换除霜系统,该系统能够实现除霜时不停止制热。为分析系统的结霜/除霜特性,建立空气源热泵蒸发器并联轮换除霜系统理论模型。通过模拟研究蒸发器并联轮换除霜系统结霜/除霜过程中霜层和系统制热性能随运行时间的变化情况。结果表明,在环境温度-5℃,相对湿度80%时,系统运行60 min时,室外机霜层厚度已影响机组正常运行;在运行40 min时开始运行除霜,除霜周期为15.76 min,获得的最大制热量为7.94 kW,最大制热COP为2.77。     

医用冷藏箱热气旁通化霜性能的试验研究

结霜现象普遍存在于冷冻冷藏装置中,并会降低系统传热性能、增加能耗。为了代替传统的电加热除霜,本文利用一台医用冷藏箱研究了热气旁通化霜的效果,它的原理是利用压缩机排出的高温气态制冷剂融化蒸发器表面的霜层。通过结霜、化霜试验分析得到热气旁通的化霜效率可以达到80%以上;并进一步分析了结霜时间和微调阀开度对化霜性能的影响,得到结论:1)结霜时间越长,化霜效率越高,但霜层较厚时,系统制冷性能严重下降;2)阀门开度越大,旁通流量越大,化霜效率越高。此外,综合考虑系统性能和化霜效率,本文提出了适用于医药冷藏箱的除霜控制策略。     

结霜工况下不同结构微通道蒸发器换热性能实验研究

针对微通道蒸发器结霜问题,设计了具有相同换热面积的单层和双层微通道蒸发器。基于制冷剂分布平定参数(RDP)分析了不同结构微通道蒸发器制冷剂分布对结霜的影响,并对比分析了单、双层微通道蒸发器在结霜工况下的换热性能。研究表明:单层蒸发器RDP高于双层蒸发器,结霜30min时,双层蒸发器结霜量高于单层蒸发器1.1倍,随着结霜时间的增长,蒸发器制冷剂压损逐渐降低,空气侧阻力逐渐升高。单层蒸发器和双层蒸发器的换热量分别减少56.4%、72%,制冷剂压损分别下降26.5%、53.05%,空气阻力分别增大30.08%、51.55%,结霜对双层蒸发器出风温度均匀性影响更大。单层结构的微通道蒸发器比双层结构更适用于结霜工况。     

风冷无霜家用电冰箱热泵式除霜系统

一、概述现有风冷无霜家用电冰箱,在其运行一定时间后,蒸发器就会凝结上一层霜,为了及时清除凝结在蒸发器上的霜层,以保证蒸发器正常运行。传统的方法是采用电加热,以产生辐射热,来溶化霜层,使霜溶化成水,然后让水排出冰箱外,从而实现除霜。这种方法的缺点,是除霜系统消耗的功率较大;新用的电加热系统元件多;系统的结构复杂;由此造成产品的可靠性,安全性降低。本文提出的新除霜加热系统,是利用压缩机排出的高温     

空气源热泵除霜性能测试系统设计

为实现空气源热泵产品除霜性能测试工况的低温高湿环境，设计一种长期低温运行设备及其温度耦合控制系统，通过2套制冷系统的除霜模式与制冷模式的交替循环，解决因蒸发器结霜而导致制冷量下降问题。基于实际测试系统和研究，提出切入除霜、除霜结束的判定依据：电加热输出为零且环境测试间内干球温度高于设定值0.1℃作为切入除霜判定依据；在除霜过程中，蒸发器制冷剂出口温度高于环境测试间干球温度10℃,且蒸发器空气侧阻力小于150 Pa作为除霜结束判定依据。该方案能够解决环境测试间内因空气处理机组蒸发器除霜需求而造成的干球温度和相对湿度的剧烈波动问题，保证环境测试间内低温高湿环境工况的长期稳定，提高除霜工况的测试准确性。     

流态化速冻器空气除霜机理的研讨

制冷设备蒸发器的除霜,是制冷设备设计与操作中的重要课题之一,这是因为霜的导热性比金属差,因此,蒸发排管外的霜层增大了导热热阻,其厚度达到一定值时会大大影响传热效果。翅片管蒸发器表面结霜时,不但增大了导热热阻,减小了外表面的传热系数,而且增大了翅片间的空气流动阻     

空气源热泵结霜机理及除霜/抑霜技术研究进展

结霜导致蒸发器的热阻增加,传热系数降低,系统COP减小,制约了空气源热泵的推广应用。本文在表面结霜机理研究现状的基础上,总结了影响结霜的各种因素相应除霜/抑霜技术,综述了逆循环、热气旁通和电加热三种常用除霜方法的研究进展,概括了改变空气参数、表面温度和换热器结构的抑霜效果,以及表面改性抑霜技术的研究现状。指出霜导热系数模型的局限性及除霜/抑霜技术存在的问题,提出今后应结合多种措施着重探索对水蒸气凝结、冷凝水冻结、霜层回融和塌陷等阶段均有较强抑制作用的抑霜技术。     

低温冷库热氟融霜的探讨与设计

低温冷库在运行过程中,伴随着结霜现象,导致制冷效率下降,常规的除霜方法不尽人意,本文通过制冷系统的优化设计,依靠阀件开闭状态的切换,改变制冷剂的流向,使高温高压的制冷剂进入蒸发器内部,利用制冷剂的显热和潜热,对蒸发器表面的霜层进行加热,从而达到除霜的目的。实现了制冷与融霜工况可以同步进行、库温波动小、效率高的热氟融霜系统。     

Improving defrosting performance by controlling frost distribution to match defrosting heat distribution in frost-free household refrigerators

In the defrosting process of most of existing frost-free refrigerators, major part of the heat generated by electric heater cannot be absorbed by the frost, resulting in the raise of the energy consumption. The objective of this study is to present a new method to improve the energy efficiency in the defrosting process. Based on the idea of making the frost absorb most of the heat generated by electric heater, a new method of defrosting is proposed, and its principle is to make the defrosting process at different locations complete simultaneously by optimizing the frost mass distribution on the evaporator. In this method, the defrosting heat distribution on evaporator surface, the required frost mass distribution, the required air flow distribution and the structure of return air duct are determined, respectively. Application of this method in an actual household refrigerator shows that the defrosting efficiency is improved by 29.8%.     

间冷冰箱风道系统流量分配特性的模块化计算方法

本文提出了一种用于计算间冷冰箱风道系统流量分配特性的模块化计算方法。首先将整体风道根据风道串并联位置划分成若干个模块,单独得出每个模块的流量阻力特性公式,其次将各模块按照冰箱实际串并联关系连接成网络,根据网络图构建模块的流量阻力方程并联立求解,最终获得整个风道系统的流量分配特性。通过实验对模型进行了验证,结果表明应用模块化计算方法得出的系统风量值与实验测量值误差在5%以内。风道系统流量分配特性的模块化计算方法具有计算准确、方便建模与求解、通用性强等优点,可应用在间冷冰箱的实际设计中。     

In-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerating appliances

The present paper advances an in-situ study of frosting and defrosting processes in tube-fin evaporators of household refrigerators and freezers. Frost growth experiments were carried out using a purpose-built test facility comprised of a refrigerated cabinet placed inside a climatized chamber, and a vapor compression refrigeration loop that controls both the evaporating temperature and the evaporator superheating. A first-principles two-dimensional simulation model was put forward to predict the evaporator blocking over time, and also the heat and mass transfer rates. The model validation exercise has shown that the model follows well the experimental trends of pressure drop, frost mass, cooling capacity and air flow rate, with all predictions falling inside ±10% error bounds. The model was then used to assess the impact of several design parameters on both the evaporator blockage and defrost efficiency. It was found that a nearly ideal defrost efficiency is achieved when the defrosting process is performed by two simultaneous heaters.     

Refrigerant flow instability as a means to predict the need for defrosting the evaporator in a retail display freezer cabinet

For refrigerated display cabinets to perform their function of keeping food cold, there must be free movement of air through the evaporator. The moisture in the ambient air entrained in the cabinet forms frost on the evaporator. It is traditional for heat to be applied to the evaporator at regular intervals to melt this frost. The frequency, typically 3–4 times per day, is enough to avoid the frost becoming excessive even in extreme conditions. For much of the time defrosting is not always necessary. A large portion of the energy used during a defrost is an overhead – heating and then cooling the metal and the food rather than melting the frost. The effect of this is examined in the paper along with the results from testing an algorithm that detects the need for a defrost from the pattern of refrigerant flow (or evaporator exit superheat). The algorithm allows the number of defrosts to be reduced without excessively raising the temperature of food stored in the cabinet. The reduction in energy and carbon dioxide emission were examined and were shown to be substantial.     

Experimental study of warm-air defrosting of heat-pump evaporators

The defrosting of a heat-pump evaporator with warm air has been investigated experimentally under controlled conditions in an air-conditioned wind tunnel. The work was initiated to explore the possibility of defrosting an evaporator under conditions where a heat pump continues to perform heating duty. A four-row straight-fin heat exchanger was used, supported from below by a load transducer to measure its weight variation during both frost accumulation and removal. The rate of melting was determined as a function of air temperature, relative humidity and velocity. The removal from the evaporator surfaces of water produced by defrosting was found to be dependent on air velocity. Proposals are advanced for further experimental studies.     

空气源热泵热水器冬季性能实验研究

空气源热泵热水器是一种新型的热水器，具有安全、节能、环保等特点，但是它也存在着许多缺点：受环境温度影响较大，尤其是在冬季环境温度很低的北方，系统效率不是很高，表现不够稳定，针对这些情况，本文对其冬季性能作了研究，分别在环境温度为0℃、-5℃、-20℃，三种工况下做了开机时间与水温的变化、开机时间与系统COP的变化，和融霜等实验，通过实验找到了影响空气源热泵热水器冬季性能的因素，为其系统优化和空气侧换热器的除霜提供了依据。     

恒温恒湿系统最佳除霜时刻控制的研究

针对于恒温恒湿系统的除霜最佳时刻的研究,本文提出了在户外温湿度恒定,室内温湿度变化状况下,当蒸发器表面上所结的霜的面积达到蒸发器总换热面积的75%时,利用此时的冷凝压力与蒸发压力的比值作为对机组除霜指令发出的基准.经实验的验证此方法还是可行的,能够运用于实际的工业恒温恒湿机组的最佳除霜时刻控制.     

不均匀风速分布下翅片管换热器的优化分析与实验

风速分布对翅片管换热器性能影响较大。本文在换热器结构尺寸、空气进口状态一定的条件下,对三种典型风速分布时翅片管换热器的流程布置形式进行了仿真优化与实验研究。结果表明:在上三角和中三角两种风速分布形式下,优化后制冷量分别提高了10.3%、3%;对于上三角优化形式,高风速区是改善换热效果的重点区域;在制冷量相同的情况下,上三角优化形式使系统COP提高8%左右。搭建实验台对仿真结果进行了验证,表明模拟值和实验值相对误差均控制在5%以内。     

以R407C为工质的翅片式蒸发器结霜过程模拟

翅片式蒸发器的结霜特性对于空气热源热泵的冬季运行十分关键。随着 对HCFCs替代的展开,一些非共沸制冷剂被建议为替代品。同现在使用的纯工质相比,这些非共沸制冷剂的温度滑移使和沿流动方向制冷剂的温度分布更加不均匀。在本文中,作者建立了翅片式蒸发器的分布参数模型,用以模拟结霜过程。传热与流动被认为是准稳态的。文中探讨了数值算法,并以某蒸发器为例进行了模拟。计算表明,结霜过程中空气量的改变明显,整个结霜过程存在一转折点,经过这点后流量急剧下降。R407C在蒸发过程中的温度滑移对霜层在蒸发器上的分布有重要影响。