制冷系统水平管降膜蒸发特性的理论分析和实验研究

发布时间：2018-03-10 05:17

  本文选题：[降膜蒸发]　切入点：[液膜厚度]　出处：《天津大学》2014年硕士论文　论文类型：学位论文

【摘要】：本文基于国内外节能减排和环境保护的大背景下,在制冷剂减量技术的思想上,进行制冷系统水平管降膜蒸发研究。以降膜蒸发为研究对象,对降膜蒸发流动及换热理论进行了归纳与总结,为实验现象的分析奠定理论基础。水平管外液膜厚度的大小对降膜过程非常重要。因此,本文建立二维物理模型,在忽略相变传热的前提下,以R134a为工质,对降膜过程中水平管外液膜厚度的分布情况进行了研究。模拟结果表明:管外液膜厚度并非均匀分布,其厚度先由厚变薄,再由薄变厚,在管表面角度为150°左右时,液膜厚度为最薄;管外薄膜厚度随着制冷剂入口速度的增加而增加;在相同的入口速度下,液膜的厚度在本文模拟条件下基本不受管型的影响。在实际中,压缩机出口的工质是含有润滑油的,润滑油随着工质的流动进入蒸发器,势必对蒸发器的换热性能造成影响。针对这一问题,通过改造实验台,以R134a为工质并对3种不同管型进行研究,并分析润滑油对水平管降膜蒸发传热特性的影响。实验中蒸发温度为6℃,含油率分别为0.5%、1.2%、5.1%。工质喷淋密度分别为0.13、0.17和0.21kg?s~(-1)?m~(-1)。对测试结果进行分析与对比发现,在喷淋密度一定时,对于光滑管和02号强化管,整体上表现出管外换热系数随着含油率的增加而增大。而对于01号强化管,在低喷淋密度下,管外换热系数随着含油率的增加而增大,一直到某一最佳含油率,然后随着含油率增加而降低;在大喷淋密度下,含油率的变化对管外换热系数影响不是特别明显。出现这种情况的原因可能是由于管表面结构不同所导致的。在较高含油率时,对于光滑管,存在某一个合适的喷淋密度使管外换热系数达到最大值;对于01号强化管与02号强化管,管外换热系数的变化受喷淋密度的影响较小。在较低含油率时,对于光滑管管外换热系数受喷淋密度的影响不明显;对于01号强化管,管外换热系数随着喷淋密度的增加而增大,直到某一值,然后随着喷淋密度的增加而减小;对于02号强化管,在实验范围内,管外换热系数随着喷淋密度的增大而增大。
[Abstract]:In this paper, based on the background of energy saving and environmental protection at home and abroad, based on the idea of refrigerant reduction technology, the study of falling film evaporation in horizontal tube of refrigeration system is carried out. The theory of falling film evaporation flow and heat transfer is summarized and summarized, which lays a theoretical foundation for the analysis of experimental phenomena. The thickness of liquid film outside the horizontal tube is very important for the falling film process. Therefore, a two-dimensional physical model is established in this paper. On the premise of neglecting phase change heat transfer, the distribution of outer liquid film thickness in horizontal tube is studied with R134a as working medium. The simulation results show that the thickness of liquid film outside the tube is not uniformly distributed, and its thickness first changes from thickness to thinning. When the surface angle of the tube is about 150 掳, the thickness of the liquid film is the thinnest; the thickness of the outer film increases with the increase of the inlet velocity of the refrigerant; at the same inlet velocity, the thickness of the liquid film increases with the increase of the inlet velocity of the refrigerant. The thickness of the liquid film is not affected by the pipe type under the simulated conditions in this paper. In practice, the working fluid at the outlet of the compressor contains lubricating oil, and the lubricating oil enters the evaporator with the flow of the working fluid. The heat transfer performance of evaporator is bound to be affected. In order to solve this problem, three different tube types are studied by modifying the test bench, taking R134a as the working fluid, and using R134a as the working medium. The effect of lubricating oil on the heat transfer characteristics of falling film evaporation in horizontal tube was analyzed. The evaporation temperature was 6 鈩，

本文编号：1591926