制冷用水平降膜式蒸发器研究进展

降膜式蒸发器目前在牛奶、制药、化工、海水淡化等行业取得了较为广泛的商业应用,它从上世纪90年代以后开始应用于制冷空调系统。目前针对制冷用水平降膜式蒸发器的研究目的主要是明确各个参数对蒸发器传热性能的影响以及他们之间的联系,由于降膜式蒸发器的独特结构和内部传热传质的复杂性,这些研究尚处于初步阶段。在介绍其工作原理的基础上,针对水平降膜式蒸发器,着重讨论了布液器的结构与高度、管束(包括管径、管排数、管道表面形状)、制冷剂(流型、流量)等参数对其性能的影响。由于经验关联式在实际应用中的巨大优势,还总结了前人提出的关联式及其适用的范围,文章将为制冷用降膜式蒸发器的进一步研究和应用提供参考。     

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。     

冷水机组用降膜式蒸发器研究进展综述

降膜式蒸发器以其高效的换热性能、有效减少制冷剂充注量等优点,被逐步应用于冷水机组。与其相关的研究受到行业越来越多的关注,成为相关领域的一个研究热点。本文分析当前降膜式蒸发器应用于空调冷水机组面临的技术挑战,包括制冷剂分配和换热性能影响因素,并给出改进降膜式蒸发器性能的研究方向。     

水平管降膜式蒸发器的研究进展及新技术

降膜式蒸发器以其高换热性能、低制冷剂充注量,以及紧凑的结构等优点,被广泛应用于工业过程的各个领域。本文以大型冷水机组中降膜式蒸发器的应用为例,从换热效率、制冷剂充注量、结构成本等几个方面与满液式蒸发器进行对比,探讨降膜蒸发技术在实际应用方面的优势、局限性和解决之道,并介绍大型冷水机组中蒸发器发展趋势以及一些新技术的应用,以期为未来设计方向和实际生产提供参考依据。     

制冷剂充注量及布管方式对降膜式蒸发器性能影响的试验研究

水平管降膜蒸发器由于其较少的冷媒充注量和较高的换热性能在制冷空调领域得到广泛的应用。本文以R134a为工质,对冷媒充注量和两流程下管程布置方式对采用降膜式蒸发器性能的影响进行了试验研究,并与满液式蒸发器进行对比。结果表明:随着冷媒充注量的增加降膜式蒸发器换热性能逐渐提升,但提升趋势逐渐缓慢;冷冻水进出水管采用下进上出的方式机组性能优于上进下出;同等能力下,采用降膜式蒸发器机组的冷媒充注量比满液式蒸发器可减少34%。     

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。     

降膜式蒸发器中改善吸气带液现象的隔板研究

降膜式蒸发器由于其高的换热性能、低的制冷剂充注量、极为紧凑的结构,是目前商用制冷空调领域的研究热点。然而由于许多设计准则缺失,产品实际经验匮乏,降膜式蒸发器设计还不完善,吸气带液现象就是其中一个显著问题。本文以某款降膜式蒸发器的制冷剂通道为研究对象,通过CFD模拟分析,指出流速过大可能存在的风险区域。通过增加隔板,从而降低流速以达到减少吸气带液风险目的,并最终经过CFD验证分析。     

空气源螺杆式热泵机组制冷剂迁移特性的试验研究

对使用降膜式蒸发器的空气源螺杆式热泵机组在制热运行模式下的各种制冷剂迁移现象进行试验研究,包括停机过程、开机准备工况以及除霜切换工况。试验结果表明,使用降膜式蒸发器后,上述过程存在明显的制冷剂迁移现象。针对此类特性,提出可能的改进建议,以达到机组可靠运行的目的。     

不同冷却方式制冷系统的热点问题分析

针对水冷系统和蒸发冷系统适用的蒸发器和螺杆式压缩机类型及2种系统的总体效率对比等相关热点问题进行分析,得出如下结论:降膜式或满液式蒸发器和半封闭螺杆式压缩机不适用于蒸发冷系统而更适用于水冷系统,干式蒸发器和开启式螺杆压缩机更适用于蒸发冷系统;在大多数工程应用中,配置降膜式或满液式蒸发器+半封闭螺杆式压缩机+水冷式冷凝器+开式冷却塔+冷凝器在线清洗装置的水冷系统,总体效率高于配置干式蒸发器+开启式螺杆压缩机的蒸发冷系统;蒸发冷系统更适合严苛工况及特殊工程应用,水冷系统更适合常规工艺冷却应用。     

降膜式蒸发器出气口液滴夹带风险预测及优化设计研究

为解决降膜式蒸发器出气口液滴夹带和压缩机吸气带液问题,本文采用计算流体动力学(CFD)进行流动-传热-相变过程中蒸发器液滴夹带空间分布和流体动力学参数研究,并结合K1、K2典型样机实际测试结果验证数值方法的准确性,构建了以蒸发器出气口液滴夹带率(φ≤0.37％)、水平气流通道平均速度(vH≤0.24 m/s)、出气挡板...     

Investigation on the effect of ejector liquid recirculation system on the performance of falling-film water chiller with R134a

To analyze the influence of liquid spraying flow rate on the performance of a falling-film evaporator with R134a, the finite difference model of the horizontal-tube falling-film evaporator is established, and a falling-film air-cooled water chiller with ejector liquid recirculation system (LRS) is presented; then the comparison between numerical simulation and experimental tests are performed. The analysis results show that the experimental and numerical evaporating capacities increase 9.5% and 6.7%, respectively, when the liquid recirculating ratio R_l increases from 1.0 to 1.21; and the deviation between the experimental and numerical capacities of the evaporator is about 3.3%. And that the evaporated liquid flow rate rises quickly at first and then increases slightly as R_l increases. Moreover, the results show that the optimum value of R_l is about 1.2, the corresponding value of integrated falling-film factor φ with about 0.85. This suggests that attempting to eliminate completely the dryout patch outside of tubes is unadvisable.     

Study on the effect of refrigerant distributing nonuniformity on the performance of falling-film evaporator with liquid recirculation system

To investigate the effect of liquid distributing nonuniformity on the heat transfer of horizontal-tube falling film, a horizontal-tube falling-film air-cooled water chiller with an ejector liquid recirculation system (LRS) is presented, and then the finite difference model of the horizontal-tube falling-film evaporator is given. Also a new method of dividing the liquid refrigerant distributor into several subzones is proposed as well as the model of liquid refrigerant distributing nonuniformity is established. The analysis results show that increasing the liquid spraying flowrate in a certain range is obviously valid for enhancing the evaporator capacity, and the suitable R_l is about 1.2, the corresponding value of φ is about 0.85. The analysis results also suggest that the higher the liquid recirculating ratio, the more the turning point of nonuniformity coefficient, and the turning point of nonuniformity coefficient is 0.1483 when the liquid recirculating ratio is equal to 1.21. The performance of falling-film heat transfer is more sensitive to the number of subzones under the condition of higher nonuniformity coefficient, and a suggested optimal number of partitioned subzones is 4.     

基于分布参数的房间空调蒸发器的数学模型及其仿真研究

本文从制冷系统热动力学的观点出发,在分布参数的基础上建立了蒸发器的实用性数学模型.通过数值分析,对其进行了仿真运算.结果证明,该模型能有效的预测蒸发器内的运行指标,也可作为部件及系统优化设计的依据.     

Performance study of a falling-film absorber with a film-inverting configuration

This paper describes the development of a novel film-inverting design concept for falling-film absorbers. The solid surface of the absorber is segmented so that both surfaces of the falling-film are alternatively cooled in a periodic manner. A conventional tubular absorber is modified by introducing film-guiding fins between tubes to produce a film-inverting arrangement. A maximum increase in vapour absorption rate of about 100% is obtained with the film-inverting design compared to the tubular absorber. The numerical simulation indicates that the vapour absorption rate can be increased by using a large number of film-inverting segments in the absorber.     

Experimental evaluation of an ejector as liquid re-circulator in a falling-film water chiller

To experimentally evaluate the performance of an ejector working as a liquid re-circulator in a horizontal-tube falling-film evaporator with R134a, experimental tests are performed using a horizontal-tube falling-film water chiller prototype. Experimental observations on intertube liquid flow pattern of tube bundle validate the feasibility of the liquid re-circulation system using a liquid–liquid ejector. The analysis results show that the influence of the motive flow rate on the entrainment ratio of the ejector is small, and the average entrainment ratio of the ejector is about 2.03. With the increase of the valve opening of the regulating valve, the evaporating capacity of the falling-film water chiller rises 4.8%, from 940.2 kW with the re-circulation ratio of one, to 985.5 kW with the re-circulation ratio of 1.135. The COP of the falling-film water chiller reaches a maximum and then drops down with the increase of the re-circulation ratio, and the optimal re-circulation ratio is 1.135.     

The impact of geometric structure and flow arrangement on the performance of CO2 evaporators in multi-deck medium temperature display cabinets

The CO₂ refrigerant is widely applied in retail refrigeration systems to replace HFC fluids such as R404A, but its system performance requires further improvement. One feasible method would be to pinpoint the matching components of the system, in particular its evaporator coils. This paper focuses on the potential optimization of the CO₂ evaporator design in an existing multi-deck medium temperature display cabinet charged previously with R404A refrigerant. To achieve this target, a display cabinet model with an integrated CFD and detailed evaporator sub models was utilized. This model could readily imitate the actual cabinet performance under varied operating conditions and component designs. Various design options of the CO₂ cabinet evaporator were considered and their impacts on the cabinet performances were predicted by the integrated model. Ultimately, the optimized designs of CO₂ cabinet evaporator coil geometries and refrigerant side operating parameters have been attained.     

人字形波纹板式蒸发器数值模拟

本文根据两相流动换热理论,提出了一个板式换热器的稳态分布参数模型.在此模型基础上,利用分布参数法求解各控制方程,得出了制冷剂的温度、压力、气液相速度以及冷冻水温度、压力沿通道方向上的分布情况.此模型可用于分析换热器的整体性能,为板式换热器的优化设计、制冷系统的匹配提供依据.