﻿ 微肋管管内沸腾换热特性的数值分析
 舰船科学技术  2019, Vol. 41 Issue (2): 85-88 PDF

Numerical analysis of boiling heat transfer characters in micro-fin tube
JIANG Guo-bao, ZHOU Ai-min, SHEN Xu-dong
Wuhan Second Ship Design and Research Institute, Wuhan 430064, China
Abstract: Improvements in heat transfer enhancement and refrigerant replacement is significant to ship air conditioning which is an important part of the ship guarantee system. In this paper a forced boiling heat transfer characters of refrigerant R22 and R410A in a 5 mm micro-fin tube has been numerically simulated with the application of thermal phase change RPI model in Ansys CFX. The simulation results agree well with experimental results. It is found that the heat transfer coefficient with R410A is about 1.3 to 1.4 times of that with R22.
Key words: micro-fin tube     boiling     heat transfer coefficient, refrigerant replacement
0 引　言

 图 1 微肋管的结构示意图 Fig. 1 Diagram of micro-fin tube

1 物理模型

 图 2 直肋管数值计算区域的物理模型图 Fig. 2 Diagram of micro-fin tube
2 数值方法及沸腾换热模型 2.1 数值方法

1）连续性方程

 $\nabla \cdot \left( {{\gamma _\alpha }{\rho _\alpha }{U_\alpha }} \right) = \varGamma _{\alpha \beta }^ + - \varGamma _{\beta \alpha }^ + \text{。}$ (1)

2）动量守恒方程

 $\begin{split} & \nabla \cdot \left( {{\gamma _\alpha }\left( {{\rho _\alpha }{U_\alpha } \otimes {U_\alpha }} \right)} \right) + {\gamma _\alpha }\nabla p= \\ & \nabla \cdot \left( {{\gamma _\alpha }{\eta _\alpha }} \right)\left( {\nabla {U_\alpha } + {{\left( {\nabla {U_\alpha }} \right)}^{\rm T}}} \right) + {\gamma _\alpha }{\rho _\alpha }g + {M_\alpha }\text{。} \end{split}$ (2)

 ${\eta _{ld}} = {\eta _l} + {\eta _{lt}} + {\eta _{lv}}\text{，}$ (3)
 ${\eta _{vd}} = {\eta _v} + {\eta _{vt}}\text{。}$ (4)

3）能量守恒方程

 $\begin{split} & \nabla \cdot \left( {{\gamma _\alpha }\left( {{\rho _\alpha }{U_\alpha }{h_\alpha }} \right)} \right) =\\ & \quad \nabla \cdot \left( {{\gamma _\alpha }{\lambda _\alpha }\left( {\nabla {T_\alpha }} \right)} \right) + \left( {\varGamma _{\alpha \beta }^ + {h_{\beta {\rm{s}}}} - \varGamma _{\beta \alpha }^ + {h_{\alpha {\rm{s}}}}} \right) + {q_\alpha }\text{。} \end{split}$ (5)

4）体积守恒方程

 ${\gamma _\alpha } + {\gamma _\beta } = 1\text{。}$ (6)

2.2 沸腾换热模型

 ${q_w} = {q_c} + {q_q} + {q_e}\text{。}$ (7)

 图 3 壁面热流密度分配示意图 Fig. 3 The distribution of heat flux on wall

 ${q_c} = {A_1}{h_c}\left( {{t_w} - {t_l}} \right)\text{，}$ (8)
 ${q_q} = {A_2}{h_q}\left( {{t_w} - {t_l}} \right)\text{，}$ (9)
 ${q_e} = \dot m\left( {{h_v} - {h_l}} \right)\text{。}$ (10)

3 计算结果 3.1 网格独立性考核

 图 4 直肋管横截面网格划分区域示意图 Fig. 4 Diagram of micro-fin tube cross-section grid

 图 5 直肋管管内沸腾换热系数随网格数量的变化 Fig. 5 The heat transfer coefficient of micro-fin tube with grid number variation
3.2 数值计算换热结果

R410A在不同干度条件下的换热系数随干度变化的数值模拟结果与相同工况下实验结果[14]进行比较并列于图6中。从图中可以看出，换热系数数值模拟结果均要比实验结果小一些。负偏差产生的原因可能与模型本身有关，因为现有的RPI模型的参数主要是从平表面的实验结果中提取的，对于带微肋表面的微肋管由于汽化核心区域的增加，换热系数会得到一定程度的提高从而减少模型误差。实验过程中换热系数的数值模拟结果与实验结果的平均偏差为–18%而最大偏差为–26%。考虑到沸腾换热实验数据本身的不确定性，总体上采用Euler多相流模型和RPI沸腾模型的计算结果基本能够反映直肋管管内沸腾过程中的换热特性。从图中可以看出，不同干度条件下R410A的换热系数要比R22小，大约要高30%～40%，在进行制冷剂替换过程应考虑两种制冷工质的换热特性。

 图 6 直肋管管内沸腾过程中换热系数与实验结果的比较 Fig. 6 Comparison between computational and experimental results
4 结　语

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