负压状态窄缝通道乙二醇水溶液传热特性

doi:10.16085/j.issn.1000-6613.2023-1153

摘要/Abstract

摘要：

高效、紧凑的换热方式需求日益增大，具有高度方向速度梯度大的窄缝通道成为最有前景的方式之一。本文以质量分数为55%的乙二醇水溶液为工质，针对钛窄缝通道在负压工况进行流动沸腾换热实验。实验在质量流率750~2000kg/(m²·s)、饱和温度为80~90℃、入口温度60~70℃的条件下进行。结果表明，钛需要更高的热流密度激活大量成核点，从而其过冷沸腾起始点（ONB）前后平均换热系数h基本不变；质量流量对于ONB和沸腾充分发展阶段的平均换热系数影响很大；在高过冷度时，沸腾充分发展阶段，钛窄缝通道换热性能对于入口温度不敏感；提高进口温度降低过冷度可以极大提高平均换热系数，70℃条件下平均换热系数在沸腾充分发展阶段可以提高65%；背压对于换热性能的影响主要在沸腾充分发展阶段，背压越低平均换热系数越大。

关键词: 微通道, 乙二醇水溶液, 负压, 气液两相流, 流动沸腾, 传热

Abstract:

The increasing demand for efficient and compact methods of heat transfer has generated interest in the utilization of a narrow channel with a significant velocity gradient along its height, thus presenting substantial potential. This research study focused on investigating the heat transfer phenomena in a flow boiling system that employs a narrow slot channel made of titanium under negative pressure conditions. The experimental analysis employed a designated working fluid, namely an ethylene glycol aqueous solution with a mass concentration of 55%. The experimentation was conducted under specific operational parameters, encompassing a mass flow rate spanning from 750kg/(m²·s) to 2000kg/(m²·s), a saturation temperature within the range of 80℃ to 90℃, and an inlet temperature ranging from 60℃ to 70℃. The findings of the study revealed that the activation of a substantial quantity of nucleation sites in titanium necessitated an elevated heat flux. Consequently, this phenomenon maintained the average heat transfer coefficient (h) in a state of relative constancy both prior to and subsequent to the onset of nucleate boiling (ONB). The heat flux required to start of ONB and the mean heat transfer coefficient during the phase of fully developed boiling were subject to influence from alterations in the mass flow rate. Notably, in instances where a considerable degree of subcooling was present, the thermal performance within the confines of a titanium narrow-slit channel displayed reduced sensitivity to variations in inlet temperature during the fully developed boiling stage. Elevating the inlet temperature while concurrently reducing the subcooling degree markedly enhanced the average heat transfer coefficient by as much as 65%. The perturbation of back pressure on heat transfer performance manifested primarily during the fully developed boiling stage, wherein diminished back pressure corresponds to augmented average heat transfer coefficients.

Key words: microchannels, ethylene glycol aqueous solution, negative pressure, gas-liquid flow, flow boiling, heat transfer

中图分类号:

TK124

赵晨, 苗天泽, 张朝阳, 洪芳军, 汪大海. 负压状态窄缝通道乙二醇水溶液传热特性[J]. 化工进展, 2023, 42(S1): 148-157.

ZHAO Chen, MIAO Tianze, ZHANG Chaoyang, HONG Fangjun, WANG Dahai. Heat transfer characteristics of ethylene glycol aqueous solution in slit channel under negative pressure[J]. Chemical Industry and Engineering Progress, 2023, 42(S1): 148-157.

图/表 13

图1 泵驱动两相流体回路系统

图2 测试段示意图

表1 质量分数为55%的乙二醇水溶液热物性

温度/℃	黏度/mPa·s	比热容/kJ·kg^-1·K^-1	密度/kg·m^-3	热导率/W·m^-1·K^-1
60	1.5002	3.3872	1055.186	0.3946
65	1.3494	3.4070	1051.932	0.3966
70	1.2186	3.4275	1048.223	0.3983
75	1.1105	3.4474	1045.059	0.4003
80	1.0124	3.4669	1041.435	0.4013
85	0.9197	3.4875	1037.702	0.4030
90	0.8470	3.5073	1033.839	0.4040

图3 流道加热面积示意图

图4 预热段示意图

表2 TC4热导率

温度/℃	热扩散系数 α/mm²·s^-1	定压比热容 c_p /J·g^-1·K^-1	热导率 K_TC4/W·m^-1·K^-1
25.2	2.869	2.444	7.014
100	3.072	2.564	7.878
200	3.349	2.589	8.699
300	3.622	2.746	10.057
400	3.954	2.842	11.235
500	4.237	3.071	13.012

图5 实验段集热铜块示意图

表3 实验设置的实验不确定性概述

物理量	不确定度
质量流量 $m ˙$	±1%
出口压力P_背	±0.5kPa
饱和温度T_sat	±0.35℃
入口温度T_in	±0.5℃
壁面温度T_surf	±1.86%~7.82%
热流密度q	±1.84~7.20W/cm² ±1.40%~13.74%
平均换热系数h	±1959.74~4918W/(m²·K) ±11.17%~23.93%

表3 实验设置的实验不确定性概述

物理量	不确定度
质量流量 $m ˙$	±1%
出口压力P_背	±0.5kPa
饱和温度T_sat	±0.35℃
入口温度T_in	±0.5℃
壁面温度T_surf	±1.86%~7.82%
热流密度q	±1.84~7.20W/cm² ±1.40%~13.74%
平均换热系数h	±1959.74~4918W/(m²·K) ±11.17%~23.93%

图6 不同质量流率下的换热特性（Tsub=25℃、Tsat=90℃）

图7 不同入口温度下的换热特性[G=750kg/(m2·s)、Tsat=90℃]

图8 不同入口温度下的基底温度[G=750 kg/(m2·s)、Tsat=90℃]

图9 不同背压下的换热特性[G=750kg/(m2·s)、Tin=60℃]

表4 乙二醇水溶液在不同背压下的饱和温度

背压/kPa	饱和温度T_sat/℃
35.2±0.5	80±0.35
42.9±0.5	85±0.3
51.9±0.5	90±0.3

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