Abstract

Printed circuit heat exchanger has been recognized as a perspective mini-channel heat exchanger. Semi-circular cross-section is designed here due to the special manufacture technology. However, there is a lack of related investigations on condensation process in mini-channels with semi-circular cross-section. In this paper, corresponding three-dimensional numerical simulations are presented. The horizontal straight channels with radius of 1 mm and 1.222 mm, and length of 250 mm are considered as the geometric models. Constant mass flux (317 kg/m² s) and wall temperature (310 K) are applied as the boundary conditions. Heat transfer and flow characteristics are conducted by comparing to that in common circular channel with identical wetted perimeter. The effect of placing direction and surface wettability are present as well. The results show that the liquid film in the semi-circular channel is more uneven compared to that in the circular channel. The liquid is accumulated in corners because of surface tension, and this brings worse heat transfer to the semi-circular channel further. Besides, the placing direction has little influence on heat transfer with the variation range of heat transfer coefficient within 4% in the present conditions. The influence of surface wettability can be neglected for the larger tube.

摘要

印刷电路换热器已被公认为具有远景的微型通道换热器。由于特殊的制造技术，这里设计了半圆形横截面。然而，对于截面为半圆形的微通道内的冷凝过程还缺乏相关的研究。在本文中，提出了相应的三维数值模拟。以半径为1 mm和1.222 mm、长度为250 mm的水平直通道作为几何模型。恒定质量通量 (317 kg/m ²s）和壁温（310 K）用作边界条件。通过与具有相同湿周长的普通圆形通道的比较来进行传热和流动特性。放置方向和表面润湿性的影响也存在。结果表明，与圆形通道相比，半圆形通道中的液膜更加不均匀。由于表面张力，液体在角落处积聚，这给半圆形通道带来了更差的热传递。此外，布置方向对传热影响不大，目前条件下传热系数的变化范围在4%以内。对于较大的管，表面润湿性的影响可以忽略不计。