共查询到19条相似文献,搜索用时 156 毫秒
1.
2.
流速对混合蒸汽Marangoni凝结换热影响的实验研究 总被引:1,自引:0,他引:1
本文在蒸汽压力为47.36 kPa的条件下,通过实验研究了不同蒸汽流速(u=2、4、5 m/s)下纯水和不同酒精浓度水-酒精混合蒸汽沿重力方向流过竖直紫铜平板表面上的凝结换热特性,并实现了实验的可视化,同时分析了不同蒸汽流速下造成Marangoni凝结换热特性差异的原因.实验及分析结果表明,在相同蒸汽浓度、蒸汽压力和表面过冷度条件下,高流速下的凝结换热系数比低流速的大.且蒸汽流速对凝结换热的影响因混合蒸汽酒精浓度的不同而不同,低浓度0.5%和高浓度50%时流速的增加对凝结换热特性的影响较小,而在中间浓度2%时凝结换热强度随流速的增加明显. 相似文献
3.
水和酒精Marangoni凝结换热特性研究 总被引:7,自引:2,他引:5
本文首先构造了一个在常温水冷却时,纯水蒸汽凝结时表面温度差可以达到11℃的黄铜试件。利用该试件在蒸汽流速为0.3m/s时,进行了不同浓度水-酒精混合蒸汽以及纯水蒸汽的凝结换热特性和凝结状态的实验研究。实验结果表明:由于凝结表面存在温度差,水-酒精混合蒸汽出现珠状凝结,凝结换热系数最大可以达到纯水蒸汽凝结的2.8倍;混合蒸汽凝结换热系数随表面过冷度减小而增加,并在较小过冷度时出现陡增;凝结换热量随表面过冷度增加存在最大值;观察得出了不同表面过冷度下不同酒精浓度时的凝结状态。 相似文献
4.
蒸汽压力对Marangoni凝结换热特性的影响 总被引:4,自引:3,他引:1
本文研究了蒸汽压力对水-酒精混合蒸汽竖直平板表面凝结换热特性的影响.搭建了具有高气密性的Marangoni凝结换热实验台,分别针对不同压力(31.16 kPa,47.36 kPa,84.53 kPa)、不同表面过冷度(表面过冷度范围2-32℃)的纯水、水-酒精混合液(气相酒精质量百分比浓度为2.28%,5.1%,51%)和酒精进行了换热特性的实验研究,实验结果表明混合蒸汽在相同流速和浓度下凝结表面传热系数随压力的升高而升高,分析认为这是因为相平衡压力的提高会导致凝结液量增加和凝结液平均温度提高,而使凝结汽液界面的表面张力提高,进一步增强了Marangoni效应的影响,从而使凝结表面传热得到加强. 相似文献
5.
6.
7.
8.
9.
超音速蒸汽浸没射流凝结换热的实验研究 总被引:1,自引:0,他引:1
针对入口压力为0.20~0.50 MPa的饱和蒸汽在20~70℃过冷水中超音速浸没射流凝结换热进行了实验研究.结果表明入口蒸汽压力和过冷水温度是影响汽羽形状的主要因素.分子动力学理论得到的凝结换热系数在0.16~1.91 MW/(m2·℃)之间,随着过冷水温度的增加而增加;湍流强度理论得到的凝结换热系数在0.68~1.68 MW/(m2·℃)之间,随着过冷水温度的增加基本不变;对流换热理论得到的凝结换热系数在1.47~2.11 MW/(m2·℃)之间,随着过冷水温度的增加先增大后减小. 相似文献
10.
本文对水和酒精混合蒸气在表面具有不均匀温度场的竖直平板上的凝结换热进行了实验研究,分别从凝结换热特性和凝结形态两个方面与具有均匀温度场的竖直平板凝结换热实验结果展开了比较.实验结果表明,本实验凝结面上的液珠明显要比均匀温度场的密集细小,液珠的冲刷速度也明显较快;在相同的工况下,本实验中的凝结换热系数在任何浓度下都比均匀温度场壁面的高.初步的理论分析也表明,本实验中凝结表面浓度梯度和温度梯度共同作用引起表面张力梯度增大,导致的Marangoni对流加强,凝结换热得到强化. 相似文献
11.
12.
13.
蒸气凝结相关问题探讨 总被引:3,自引:1,他引:2
讨论了几个与蒸气凝结相关的问题,指出壁面上球冠形液滴的内外压差和临界半径同样遵循经典的Laplace公式和Kalvin公式;蒸气在冷壁上的冷凝形态主要由后退接触角决定;空气中的水蒸气在换热器表面呈膜状冷凝时换热器的性能优于呈滴状冷凝时换热器的性能。 相似文献
14.
1前言前文山提出了计算环状流和波状分层流型下非共沸混合工质在水平管内凝结的换热系数的折算方法。租界面温度Ti的取值对计算结果影响很大。现在常用的方法是根据液膜和气相区传热传质的经验公式确定问,不仅计算工作量大,且无公认的计算方式。这给工程计算带来许多不便。本文取Ti二(Tv十几w,即气相温度Tv和壁面温度见的算术平均值,以计算相界面上的平衡参数,并将前文中的折算因子计算式改为如下形式:对环状流将由于相界面温度的取法所引起的误差归于用实验数据确定的经验系数A、B与经验指数p、q。式中Ja为雅各布数,无量纲温度0… 相似文献
15.
16.
Heat transfer with vapor condensation inside a longitudinally finned tube is numerically studied. The proposed model considers vapor condensation on two initial flow areas, namely, annular and rivulet. The model allows prediction of pressure difference along the tube length, vapor velocity profiles in the central channel and an interfin groove, and also a velocity profile in the condensate rivulet at the bottom of the interfin channel, local heat transfer coefficients at different fin points, and average heat transfer coefficients over tube section and length. The calculations showed that in the case of vapor condensation in longitudinally finned tubes of a small diameter it is of fundamental importance to divide the flow tube section into a central channel and interfin channels. The governing vapor velocities in these channels may differ by more than an order of magnitude. The reduced vapor velocity, used in engineering calculations, does not reflect the character of dynamic vapor impact on a condensate film on the most part of the heat transfer surface. For tubes with relatively large fins the proposed model describes vapor condensation almost completely,meanwhile, the mass vapor quality by the time of filling of the grooves reaches 0.01–0.05. The highest heat transfer intensification was obtained for “sharp fins” with a high value of the fin head curvature. Comparison of results of calculation by the model with results of the known experiments on water vapor condensation yields a good qualitative and quantitative agreement for low vapor velocities at the channel inlet (under 30 m/s). The wall thermal conductivity coefficient value affects significantly the condensation efficiency. 相似文献
17.
18.
19.
This article directly investigates the effect of a cooling medium's coolant temperature on the condensation of the refrigerant R-134a. The study presents an experimental investigation into condensation heat transfer, vapor quality, and pressure drop of R-134a flowing through a commercial annular helicoidal pipe under the severe climatic conditions of a Kuwait summer. The quality of the refrigerant is calculated using the temperature and pressure obtained from the experiment. Measurements were performed for refrigerant mass fluxes ranging from 50 to 650 kg/m2s, with a cooling water flow Reynolds number range of 950 to 15,000 at a fixed gas saturation temperature of 42°C and cooling wall temperatures of 5°C, 10°C, and 20°C. The data shows that with an increase of refrigerant mass flux, the overall condensation heat transfer coefficients of R-134a increased, and the pressure drops also increased. However, with the increase of mass flux of cooling water, the refrigerant-side heat transfer coefficients decreased. Using low mass flux in a helicoidal tube improves the heat transfer coefficient. Furthermore, selecting low wall temperature for the cooling medium gives a higher refrigerant-side heat transfer coefficient. 相似文献