Experimental study on condensation heat transfer characteristics of low mass flow rate steam in a vacuum horizontal tube

doi:10.11949/0438-1157.20211180

Abstract

Abstract:

The heat transfer characteristics of steam condensation flow in a vacuum horizontal tube with the length of 3.4 m and inner diameter of 38 mm were studied experimentally. The steam mass flow rate is less than 9 kg/(m²·s), steam saturation temperatures are 50, 60 and 70℃, and steam inlet saturation temperature and cooling water inlet temperature difference is from 3 to 7℃. By analyzing the condensation heat transfer mechanism of stratified flow, the calculation model of thermal partition angle was established. The results of experiments indicate that the thermal partition angle increases with the increase of mass flow rate and heat transfer temperature difference. The saturation temperature has little effect on the local heat transfer coefficient and the thermal partition angle. The empirical correlation of local heat transfer coefficient is established by taking the thermal partition angle as the zone boundary. Under the experimental conditions, the predicted results in filmwise condensation area at the top of the tube are within ±25% and the predicted results in convective heat transfer zone of condensate at the bottom of the tube are from +25% to -35%.

Key words: condensation, heat transfer coefficient, horizontal tube

摘要：

对换热长度为3.4 m、内径为38 mm的真空水平管内的蒸汽凝结流动换热特性进行了实验研究。分析了蒸汽质量流率小于9 kg/(m²·s)，蒸汽饱和温度为50、60和70℃，换热温差为3~7℃时对凝结过程的影响。通过对分层流动冷凝换热机理分析，建立了热分区角计算模型。实验结果表明，热分区角随着质量流率的增加而增加，随着传热温差的增大而增大；饱和温度对管内凝结的局部传热系数和热分区角影响较小。通过以热分区角为分区界限，建立了局部传热系数经验关联式，在预测实验工况下，对于管顶部膜状冷凝区，预测精度在±25%以内；对于管底部冷凝液对流换热区，预测精度在+25%~-35%。

关键词: 冷凝, 传热系数, 水平管

CLC Number:

TK 01⁺9

Yu GU, Luyuan GONG, Yali GUO, Shengqiang SHEN. Experimental study on condensation heat transfer characteristics of low mass flow rate steam in a vacuum horizontal tube[J]. CIESC Journal, 2022, 73(2): 595-603.

谷雨, 龚路远, 郭亚丽, 沈胜强. 低质量流率蒸汽真空水平管内凝结传热特性的实验研究[J]. 化工学报, 2022, 73(2): 595-603.

Figures/Tables 12

Fig.1 Schematic of experimental system

Fig.2 Distribution of the thermocouples

Table 1 The direct and indirect uncertainty of the experiment

参数	不确定度
实验管内径D	±0.05 mm
实验管有效换热长度L	±2 mm
蒸汽入口饱和温度T_sat	±0.046℃
冷却水总传热温差ΔT_s,c	±0.14℃
冷却水流量m_c	±1.3%
管内凝结段传热量Q	±14.1%
传热系数h	±15.7%
蒸汽质量流率G	±2.5%
质量含气率x	±14.1%

Fig.3 Local heat transfer coefficients at different mass flow rates

Fig.4 Local heat transfer coefficient at different total temperature differences

Fig.5 Local heat transfer coefficient at different inlet saturation temperatures

Fig.6 Schematic diagram of thermal partition angle

Fig.7 Thermal partition angle at different total temperature differences

Fig.8 Thermal partition angle at different mass flow rates

Fig.9 Thermal partition angle at different inlet saturation temperatures

Fig.10 Comparison between the predicted value and the experimental value of the local heat transfer coefficient in the condensation heat transfer zone at the top of the tube

Fig.11 Comparison between the predicted value and the experimental value of the local heat transfer coefficient in the condensation convective heat transfer zone at the bottom of the tube

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