Abstract

This article presents the results of experimental studies of the efficiency of heat transfer on a flat rectangular (\(16\times 24\) mm²) heat transfer surface ( HTS) modified via additive manufacturing. Comparative experimental studies were carried out on an unmodified HTS and two modified HTSeswith different geometric parameters of the modifying coating. A porous sinusoidal coating consisting of spherical bronze granules with an average diameter of 35 \(\mu\)m was 3D printed on the brass base of the heat transfer unit. The coating thickness is 150 \(\mu\)m in the deepenings and 300 \(\mu\)m and 700 \(\mu\)m on the ridges. The heat transfer was studied during free-convection boiling of liquid freon R21 at heat flux densities of 200–\(5\cdot 10^5\) W/m² at a reduced pressure of 0.03. The experiments have shown that for the modified surfaces, activation of nucleation sites begins at a significantly lower heat flux density compared with the case of the smooth unmodified surface. Under conditions of activated nucleation sites on a modified surface, the heat transfer coefficient increases 4–5 times. Activation of nucleation sites is realized in the deepenings of the sinusoidal coating. Upon activation of nucleation sites (at heat loads less than 100,000 W/m²), the heat transfer intensity is the same for both studied surfaces having the same coating thickness in the deepenings. On the surface with significantly higher ridges at heat loads \(10,000 < q< 300,000\) W/m² upon activation of nucleation sites, the temperature difference observed is smaller than that on the surface with smaller ridges.

中文翻译：

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氟利昂池沸腾过程中增材制造对表面改性的传热强化

摘要

本文介绍了通过增材制造改性的平面矩形 ( \(16\times 24\)  mm ² ) 传热表面 ( HTS )传热效率的实验研究结果。对一个未改性的高温超导和两个具有不同改性涂层几何参数的改性高温超导进行了比较实验研究。在传热单元的黄铜底座上 3D 打印了由平均直径为 35 μm 的球形青铜颗粒组成的多孔正弦涂层 。涂层厚度在深部为 150  \(\mu\) m，在深部为 300  \(\mu\) m 和 700  \(\mu\)m 在山脊上。在 200– \(5\cdot 10^5\)  W/m ² 和 0.03 的减压下，液体氟利昂 R21 的自由对流沸腾过程中研究了传热。实验表明，对于改性表面，与光滑的未改性表面相比，成核位点的激活开始于显着较低的热流密度。在改性表面激活成核位点的条件下，传热系数增加 4-5 倍。成核位点的激活是在正弦曲线涂层的加深中实现的。成核位点激活后（热负荷小于 100,000 W/m ²), 对于两个研究表面在加深处具有相同涂层厚度的传热强度相同。在热负荷 \(10,000 < q< 300,000\)  W/m ² 激活成核位点时，在脊明显较高的表面上，观察到的温差小于脊较小的表面。