水平柱群通道全氟己酮过冷沸腾传热特性研究

Study on Subcooled Flow Boiling Heat Transfer Characteristics of Novec 649 in a Horizontal Finned Channel

为提升散热量不断增加的电力电子器件冷却系统的高效换热能力,提出采用全氟己酮为工质的水平双直角五边形肋柱通道流动沸腾换热系统对其进行冷却。通过实验的方法制作了入口当量直径为3.81 mm的五边形柱群通道结构,对通道内流动沸腾的平均及沿程换热特性展开了研究,实验工况如下:壁面热流密度为50~400 kW·m^(-2),入口流速为0.1~0.9 m·s^(-1),入口过冷度为15~35℃。结果表明:当热流密度低于100 kW·m-2时,单相对流占主导,增加流速与过冷度能够明显促进壁温降低;当热流密度高于200 kW·m^(-2)时,沸腾吸热占主导,增加流速与过冷度时壁温的降低幅度不明显;在热流密度为400 kW·m^(-2)、过冷度为15℃的工况下,柱群通道的平均传热系数最高;通道沿流向的局部传热系数总体呈现上升趋势,随着热流密度的增大、流速与过冷度的降低,通道出口传热系数相比进口的增长更加显著,此时通道内流体沿流向的沸腾剧烈程度发展速度更快、通道出口的沸腾程度更剧烈。该研究可为水平柱群通道内流动沸腾传热的最佳工况设计提供理论基础。

In order to meet the increasing demand for heat dissipation of power electronic device and improve the heat transfer capability of its cooling system,a horizontal flow boiling heat transfer system with double right angle pentagonal pin finned channel using Novec 649 as the working fluid was proposed.A pentagonal pin finned channel structure with an inlet equivalent diameter of 3.81 mm was fabricated to experimentally study the average and local flow boiling heat transfer characteristics in the pin finned channel.The working conditions are as follows:heat flux ranges from 50 to 400 kW·m^(-2),the inlet flow velocity ranges from 0.1 to 0.9 m·s^(-1),and the inlet subcooled temperature ranges from 15 to 35℃.The results show that when the heat flux is less than 100 kW·m^(-2),single-phase convection heat transfer dominates,and increasing the flow velocity and subcooled temperature can significantly reduce the wall temperature.When the heat flux is higher than 200 kW·m^(-2),boiling heat transfer dominates,and increasing the flow velocity and subcooled temperature has a slight impact on the reduction of the wall temperature.When the heat flux is 400 kW·m^(-2)and subcooled temperature is 15℃,the finned channel displays the highest average heat transfer coefficient.Generally speaking,the local heat transfer coefficient along flow direction presents an upward trend.With the increase of heat flux,decrease of the flow velocity and subcooled temperature,the heat transfer coefficient at the outlet of the channel increases more significantly than that at the inlet.At present,the boiling intensity of the fluid in the channel along flow direction develops faster,and the boiling intensity at the outlet also becomes more intense.The study results in this paper can provide a theoretical guidance for the design of flow boiling heat transfer in a horizontal pin finned channel.