Analysis of heat transfer characteristics in vertical tube of seepage falling film evaporative condenser

doi:10.16085/j.issn.1000-6613.2022-0838

Abstract

Abstract:

In order to study the vertical pipe seepage falling film evaporative condenser, the heat transfer characteristics of the single condenser tube under different external temperature, air Reynolds number and liquid Reynolds number were explored by using the combination of simulation and experiment method. Combined with the problems in previous research, the physical model and boundary conditions were selected reasonably, the axial distribution of temperature and heat flux density of the falling film process were obtained, and the radial position was analyzed in time series. The results showed that the heat transfer effect of reverse ventilation was better than that of co-directional ventilation, but it was easy to aggravate the instability of the liquid film in the lower part of the pipe section and even cause dry wall. It was found that the dry wall area would be covered by the liquid film immediately through time series analysis. Therefore, the effect of short-term dry wall on the overall heat transfer would not very obvious. It was still necessary to pay attention to the great influence of the high reverse ventilation intensity on the stability of the lower liquid film. It was recommended that the single-pipe air Reynolds number should not exceed 3500 under the working conditions of this paper. In addition, the test results showed that the heat transfer of a single tube in this paper was about 2200W, which was 6.7% different from the simulation results, and the comprehensive heat transfer coefficient of the single tube was about 1400W/(m²·K).

Key words: falling film evaporation, condenser, vertical tube, heat transfer characteristics

摘要：

为研究竖管渗流降膜蒸发式冷凝器，通过仿真和实验相结合的手段，探究了冷凝器单管在不同管外温度、空气雷诺数与液体雷诺数等多工况下的传热特性。结合此前研究中存在的问题，合理选择了物理模型与边界条件，获得了降膜过程的轴向温度、热通量分布等并对径向位置进行了时间序列分析。结果表明逆向通风传热效果优于顺向通风，但易加剧管段下部液膜不稳定甚至出现干壁。通过时间序列分析发现干壁区域会被液膜快速覆盖，因此短暂干壁对整体传热影响并不十分明显，仍需注意逆向通风强度过高会对管子下部液膜的稳定性造成显著影响，本文工况下推荐单管空气雷诺数不宜超过3500。此外，测试结果显示本文单管传热量约为2200W，与模拟结果相差6.7%，单管综合传热系数为1400W/(m²·K)左右。

关键词: 降膜蒸发, 冷凝器, 竖直管, 传热特性

CLC Number:

TK172

XIE Yingchun, MA Hongting, XU Chang, MA Shuo, CHEN Mo, LIU Jun, SUN Guoqiang. Analysis of heat transfer characteristics in vertical tube of seepage falling film evaporative condenser[J]. Chemical Industry and Engineering Progress, 2023, 42(3): 1187-1194.

谢迎春, 马洪亭, 徐畅, 马硕, 陈默, 刘军, 孙国强. 竖管渗流降膜蒸发式冷凝器传热特性分析[J]. 化工进展, 2023, 42(3): 1187-1194.

Figures/Tables 15

References 19

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被测参数名称	相对不确定度/%
流量/kg·s^-1	2.236
风速/m·s^-1	9.177
温度/℃	0.530
相对湿度/%	2.108
换热量/W	8.009
综合传热系数/W·m^-2·K^-1	8.014

被测参数名称	相对不确定度/%
流量/kg·s^-1	2.236
风速/m·s^-1	9.177
温度/℃	0.530
相对湿度/%	2.108
换热量/W	8.009
综合传热系数/W·m^-2·K^-1	8.014

空气流速 /m·s^-1	Re_g	冷水入口流量 /L·h^-1	质量流量 /kg·s^-1	喷淋密度 /kg·s^-1·m^-1	Re_l
0.5	1156	40	0.011	0.111	440
1.0	2312	60	0.017	0.166	661
1.5	3467	80	0.022	0.221	881
2.0	4623	100	0.028	0.276	1 101
2.5	5779
3.0	6935

空气流速 /m·s^-1	Re_g	冷水入口流量 /L·h^-1	质量流量 /kg·s^-1	喷淋密度 /kg·s^-1·m^-1	Re_l
0.5	1156	40	0.011	0.111	440
1.0	2312	60	0.017	0.166	661
1.5	3467	80	0.022	0.221	881
2.0	4623	100	0.028	0.276	1 101
2.5	5779
3.0	6935

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