基于扁管的蒸发式冷凝器管外传热传质特性研究

doi:10.11949/j.issn.0438-1157.20190033

摘要/Abstract

摘要：

强化蒸发式冷凝器管外传热传质可有效降低系统能耗，利用Fluent软件，结合自编译程序及组分输运模型对扁管蒸发式冷凝器管外传热传质过程建模，选取了等周长圆管模型进行比较，研究了二者传热传质性能的差异。通过研究管外液膜厚度及速度，以及管外温度分布和含湿量的变化规律，对比了扁管和圆管的平均表面传热系数，结果表明扁管的平均表面传热系数于圆管提升了9.04%。模拟了风速从1.5 m·s^-1变化至3 m·s^-1以及喷淋密度从0.15 kg·m^-1·s^-1增加至0.3 kg·m^-1·s^-1时对扁管式蒸发式冷凝器换热的影响，得到随着风速及喷淋密度的增加其平均表面传热系数分别增加了5.68%和30.26%。对扁管式蒸发式冷凝器管外的传热传质特性的研究为其应用提供了理论指导。

关键词: 蒸发式冷凝器, 扁管, 蒸发, 传热, 传质

Abstract:

Enhancement of the heat and mass transfer outside the tube of evaporative condensers can effectively reduce the energy consumption in a refrigeration system. The improving characteristics of heat and mass transfer outside a flat tube for evaporative condensers were investigated. Numerical simulation of the heat and mass transfer on the flat tube was carried out in Fluent using user define functions and component transport models. The heat transfer performance of a circular tube with the same perimeter was compared with that of the flat tube. The thickness and velocity of the liquid film outside the tube, the temperature distribution and the variation of moisture content outside the tube are studied, and the average heat transfer coefficients of the flat tube and the circular tube are compared. The results show that the average heat transfer coefficient of the flat tube is 9.04% higher than that of the circular tube. In addition, the influence of wind speed and spray density on the heat transfer of flat tube evaporative condenser is calculated. The wind speed varies from 1.5 m·s^-1 to 3 m·s^-1 and the spray density varies from 0.15 kg·m^-1·s^-1 to 0.3 kg·m^-1·s^-1. The results show that the average heat transfer coefficient increases by 5.68% and 30.26% respectively. Investigating the heat and mass transfer characteristics outside a flat tube for evaporative condensers provides theoretical guidance for the application of the flat tube in evaporative condensers.

Key words: evaporative condensers, flat tube, evaporation, heat transfer, mass transfer

中图分类号:

TK 172

单思宇, 谭宏博. 基于扁管的蒸发式冷凝器管外传热传质特性研究[J]. 化工学报, 2019, 70(S1): 69-78.

Siyu SHAN, Hongbo TAN. Study on heat and mass transfer characteristics outside flat tube for evaporative condensers[J]. CIESC Journal, 2019, 70(S1): 69-78.

图/表 22

图1 扁管模型尺寸

Fig.1 Flat tube model

图2 物理模型

Fig.2 Physical model

图3 扁管结构示意图

Fig.3 Schematic diagram of flat tube

表1 模拟的基本工况

Table 1 Basic operating conditions for simulation

设置参数	数值
喷淋水入口喷淋密度/(kg·m^-1·s^-1)	0.15～0.30
喷淋水入口温度/K	303.15
壁面温度/K	308.15
空气入口流速/(m·s^-1)	3
空气入口温度/K	298.15
空气入口含湿量/(kg·(kg干空气)^-1)	0.015
喷淋高度/ mm	5
喷淋水入口宽度 /mm	1

图4 模拟值与实验关联式预测值比较

Fig.4 Comparisons between simulated and experimental correlation predictions

图5 气液相分布云图

Fig.5 Gas-liquid phase distribution nephogram

图6 圆管与扁管不同位置速度矢量分布比较

Fig.6 Comparison of velocity vector distribution in different positions of circular and flat tubes

图7 圆管与扁管液膜速度比较

Fig.7 Comparison of liquid film velocity between circular and flat tubes

图8 圆管与扁管不同周向无量纲位置的液膜厚度比较

Fig.8 Comparison of liquid film thickness between circular and flat tubes at different circumferential dimensionless positions

图9 圆管与扁管不同周向无量纲位置的局部传热系数比较

Fig.9 Comparison of local heat transfer coefficients of circular and flat tubes at different circumferential dimensionless positions

图10 温度分布云图

Fig.10 Temperature distribution nephogram

图11 不同周向无量纲位置的温度沿水平方向变化曲线

Fig.11 Temperature curves of dimensionless positions in different circumferential dimensions along horizontal directions

图12 含湿量分布云图

Fig.12 Moisture content distribution nephogram

图13 不同周向无量纲位置的含湿量沿水平方向变化曲线

Fig.13 Variation curve of moisture content in different circumferential dimensionless positions along horizontal direction

图14 不同风速下周向90°位置处温度沿水平方向变化曲线

Fig.14 Temperature curve along horizontal direction at circumferential 90° position under different wind speed

图15 不同风速下周向90°位置处含湿量沿水平方向变化曲线

Fig.15 Moisture content curve along horizontal direction at circumferential 90° position under different wind speed

图16 不同风速下水膜平均表面传热系数变化曲线

Fig.16 Variation curve of average surface heat transfer coefficient of water film under different wind speed

图17 不同喷淋密度下液膜厚度沿周向变化曲线

Fig.17 Circumferential variation curve of liquid film thickness under different spray density

图18 不同喷淋密度下周向90°位置处温度沿水平方向变化曲线

Fig.18 Circumferential variation curves of liquid film thickness under different spray density

图19 不同喷淋密度下周向90°位置处含湿量沿水平方向变化曲线

Fig.19 Variation curves of moisture content along horizontal direction at 90° circumferential position under different spray densities

图20 不同喷淋密度下液膜平均速度

Fig.20 Average velocity of liquid film at different spray densities

图21 不同喷淋密度下液膜平均表面传热系数变化曲线

Fig.21 Variation curves of average surface heat transfer coefficient of water film under different spray density

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