Calculation and analysis of thermal performance of horizontal circular tube falling film evaporative condenser

doi:10.11949/0438-1157.20240941

Abstract

Abstract:

The thermal process calculation software of the evaporative condenser was compiled on the MATLAB platform. The thermal performance of the horizontal circular tube falling film evaporative condenser was calculated and analyzed. This study thoroughly explored the impact of various factors, such as the wind speed outside the tube bundle and the water spray density, on crucial parameters including heat transfer, external heat transfer coefficient, and mass transfer coefficient. The results of the calculations indicate that an increase in the head-on wind speed significantly enhances the heat transfer efficiency. This improvement is largely attributed to the disturbances that the wind creates on the liquid film outside the tubes, which, in turn, has a profound impact on the mass transfer processes as well. Notably, when the wind speed reaches approximately 4.21 m·s⁻¹, a critical threshold is observed where the trends of the outlet air temperature and humidity reverse, further intensifying the evaporation of the liquid film. Additionally, the study found that increasing the water spray density can lead to a slight improvement in heat transfer, it also results in a rise in the temperature of the water film on the tube surfaces. This temperature increase, coupled with a reduction in the outlet air humidity, can actually impede both heat and mass transfer processes. Consequently, it was determined that there exists an optimal spray density, which is approximately 0.068 kg·m⁻¹·s⁻¹, where the benefits of increased spray do not offset the drawbacks of higher water film temperatures.

Key words: falling film evaporation, evaporative condenser, mass transfer, heat transfer, horizontal circular tube, phase change

摘要：

在MATLAB平台上编制了蒸发式冷凝器热力过程计算软件，对水平圆管降膜蒸发式冷凝器的热力性能进行了计算分析，探讨了换热管束外迎面风速和水的喷淋密度对蒸发式冷凝器的换热量、管外传热系数和传质系数的影响规律。计算结果表明，迎面风速增大会提高换热量，且迎面风速对管外液膜产生的扰动会对传质产生较大的影响，风速达到4.21 m·s^-1后，空气出口温度和湿度的变化趋势发生反转，更加促进液膜蒸发；增大喷淋密度虽会小幅增加换热量，但管外水膜温度会升高，出口空气湿度下降，阻碍传热和传质的进行，故最佳喷淋密度约为0.068 kg·m^-1·s^-1。

关键词: 降膜蒸发, 蒸发式冷凝器, 传质, 传热, 水平圆管, 相变

CLC Number:

TK 124

Xiankai ZHANG, Boyu WANG, Yali GUO, Shengqiang SHEN. Calculation and analysis of thermal performance of horizontal circular tube falling film evaporative condenser[J]. CIESC Journal, 2025, 76(3): 995-1005.

张先开, 王博宇, 郭亚丽, 沈胜强. 水平圆管降膜蒸发式冷凝器热力性能计算分析[J]. 化工学报, 2025, 76(3): 995-1005.

Figures/Tables 17

Fig.1 Schematic diagram of evaporative condenser

Fig.2 Schematic diagram of heat transfer process of evaporative condenser

Table 1 Structural parameters

管轴向长度/m	迎风面长度/m	迎风面宽度/m	管间距	管列数	管程数
0.288	0.3	0.18	1.6D	5	6

Table 2 Operating parameters

冷凝温度/℃	进口空气干球温度/℃	进口空气湿度/%	喷淋水温度/℃
26	20	60	25

Fig.3 Comparison of experimental and calculated heat transfer

Table 3 Operating conditions

冷凝温度/℃	进口空气干球温度/℃	进口空气湿球温度/℃	喷淋水温度/℃
36	31	25	25

Fig.4 The change curve of heat transfer with head-on wind speed under different spray density

Fig.5 The variation curve of heat transfer coefficient and mass transfer coefficient of outer tube wall and water film with head-on wind speed at different spray densities

Fig.6 The change curve of mass transfer heat ratio with head-on wind speed at different spray densities

Fig.7 The change curve of circulating water temperature with head-on wind speed at different spray densities

Fig.8 Change curve of outlet air temperature and humidity with opposite wind speed under different spray density

Fig.9 The variation curve of water temperature in external circulation with spray density under different head-on wind speed

Fig.10 The variation curve of heat transfer coefficient and mass transfer coefficient with spray density under different head-on wind speed

Fig.11 The change curve of heat transfer with spray density under different head-on wind speed

Fig.12 The change curve of outlet air temperature and humidity with spray density under different head-on wind speed

Fig.13 The change curve of the heat transfer and mass transfer heat ratio with the relative humidity of the environment at different dry bulb temperatures

Fig.14 Variation curve of circulating water temperature with ambient relative humidity at different dry bulb temperatures

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