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。     

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。     

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。     

低温流体在竖直通道中降膜蒸发研究进展

降膜蒸发作为一种高效传热传质技术,已经在空分领域得到了应用。本文介绍了空分膜式主冷凝蒸发器的原理和特点,从波状特性和破断特性方面阐述了下降液膜的动态特性,总结了入口流量、壁面结构、工质组分和热流密度因素对传热传质的影响,重点介绍了低温液氮在大空间平板上降膜过程的临界热流密度规律和过热壁面再湿润动态特性,并对现有竖直通道内降膜蒸发过程换热关联式进行了归纳。由于低温工质物性和通道结构的特殊性,已有的常温工质换热关联式应用于空分膜式主冷凝蒸发器的传热设计还存在较大差距。最后指出小传热温差条件下,复杂狭窄通道内低温流体降膜蒸发过程需要进一步研究。     

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。     

抢占节能技术制高点 美的超高效降膜式离心机组通过鉴定

3月21日,对于美的中央空调来说,又是一个值得铭记的日子,美的研发的超高效双级压缩降膜式离心机组通过了专家组鉴定,被认定为：“美的超高效双级压缩降膜式离心机组整体技术达到了国际领先水平,预期将带来良好的社会效益。”据美的相关负责人介绍,该机组采用行业领先的航天气动技术以及全球首创的全降膜蒸发技术,使系列机组的能效最高可达到行业最高水平的7．11（国标工况）。     

溴化锂降膜式发生器的传热传质研究

对于使用低温热源的溴化锂吸收式制冷机，可以采用降膜式发生器改善传热传质，提高机组的性能。本文提出了一个水平管束构成的降膜式发生器的数学模型，求得了传热传质特性的数值解，并以热水为热源对一个由８排水平管构成的发生器模型进行了试验研究，数值解和试验结果吻合程度较好，通过分析得出了有益于降膜式发生器传热传质的一些结论。     

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。     

12000m3／h制氧机预防氧化亚氮危害的改造

介绍了膜式冷凝蒸发制氧机增加氧化亚氮循环吸附器防爆的改造,N2O循环吸附器系统的一些特点进行了描述。     

降膜式冷水机组在工程中的应用价值刍议

针对目前行业内普遍存在的对降膜式冷水机组在工程中应用价值的质疑,笔者根据近几年从事降膜式冷水机组市场推广技术支持工作中的体会,结合实际应用案例,对降膜式冷水机组、干式冷水机组、满液式冷水机组和双板换冷水机组在工程应用中的技术特点进行比较分析,得出结论:降膜式冷水机组只要性价比做到一定水平,在很多工程领域都有比较大的应用价值,尤其在0～3℃冰水、15℃以上高温冷水工程应用中优势明显。     

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.     

制冷空调系统水平管降膜蒸发研究

在制冷剂面临严峻的环境保护控制要求的背景下,研究表明,降膜蒸发由于其较低的制冷剂充注量在制冷空调行业具有重大的应用潜力。本文主要从降膜蒸发管外液膜的流动模式和强化传热2个方面,对水平管降膜蒸发的国内外研究现状进行研究分析。分析表明,管外液膜存在滴状流、射（柱状）流和片状流等模式,而且强化传热须区分高低热流密度情况。为了进一步探究降膜蒸发的机制,从换热和可视化的角度开展强化管外降膜蒸发的特性实验研究。     

Effects of nonuniform heating and thermocapillarity in evaporating films falling down an inclined plate

Summary. The dynamics of a thin evaporating liquid film falling down an inclined plate is studied in the cases of both uniformly and nonuniformly heated plates. The film flow is influenced by gravity, mean surface tension, thermocapillary force and mass loss. The dynamics of the two-dimensional evaporating film is studied by the use of long-wavelength theory. Numerical solution of the evolution equation indicates that the evaporation has a strong stabilizing effect on the film instability and that a sequence of instability, stability and then instability of the falling film during its evaporation exists. The effect of nonuniform heating is dominant prior to film disappearance and it enforces film rupture. Due to the joint action of thermocapillarity and evaporating mass loss, the film evolution exhibits the formation of multi-hump structures, the downstream propagation of which is suppressed. When the nonuniformities in the imposed temperature differences are increased, large deformations of the liquid-vapor interface occur that lead to an enhancement of the heat transfer processes.     

Experimental investigations of R134a and R123 falling film evaporation on enhanced horizontal tubes

Falling film evaporation is an efficient heat transfer mode in refrigeration and air conditioning industries. In this paper, the falling film evaporation performances of R134a and R123 outside four enhanced tubes and a smooth tube are tested. The results reveal that: with the decrease of film flow rate the falling film heat transfer coefficients of both R134a and R123 on the five tubes exhibit two general stages (a plateau stage and a sharp drop stage); for R134a the plateau is quite uniform while for R123 a mild decrease occurs with the decrease in film flow rate. The four enhanced tubes behave differently in heat transfer performances for R134a and R123. R134a provides around 2–3 times of heat transfer coefficients of R123 for all tubes.     

水平管式降膜蒸发器布液器的方案比较

介绍降膜蒸发器原理及其核心部件一一布液器,并通过流场模拟与理论分析,总结3种布液器方案的优缺点,为研发及生产提供参考。     

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。     

Heat transfer and wave characteristics of a binary freon film flowing over a three-dimensional textured surface

The results of the study of heat transfer, crisis phenomena, and wave characteristics of laminar-wavy liquid films falling over a vertical three-dimensional texture surface have been considered. The R21/R114 freon mixture is served as a working fluid. Some peculiarities of heat transfer, hydrodynamics, and development of crisis phenomena in a binary liquid film falling over heat-releasing surfaces of different geometry have been revealed. The dependence of the heat-transfer coefficient on the flow rate for a three-dimensional texture surface in the regime of evaporation is shown to be similar to the dependence for a smooth surface with slightly intensified heat transfer in the region of inlet film Reynolds numbers of 100–500. The heat transfer coefficients of nucleate boiling on the studied types of structured surfaces are much lower than for a smooth tube. In the regime of undeveloped nucleate boiling, the critical heat flux for all surface types is deter-mined by the dependence obtained by considering the appearance of the heat transfer crisis in an evaporating wave liquid film.     

高阻隔透明陶瓷膜蒸镀技术

对高阻隔透明陶瓷膜的发展概况及应用进行了综述,介绍了陶瓷膜的真空蒸镀技术、PECVD蒸镀技术的原理、特点和应用,并对陶瓷膜蒸镀技术的发展趋势进行了展望.     

Mathematical modeling of falling liquid film evaporation process

A mathematical model of evaporation process from a laminar falling liquid film on a vertical plate of constant temperature is presented. The model is developed with and without interfacial shear stress due to the vapor flow at the liquid film surface. The vapor pressure drop, vapor exit velocity and cooling rate are calculated for different liquid mass flow values. It is shown that lower liquid mass flow produces higher cooling rate. The results also show that the interfacial shear stress has a considerable negative effect on the cooling rate. It is proved that there exists an optimum distance between the plates, which gives the maximum volumetric cooling rate.