R141b在圆形微通道内的沸腾换热实验研究

为提高换热强度、解决设备内部高热流密度散热问题,采用实验方法研究R141b在不同直径(D=0.5mm和1.0mm)水平圆形微通道内的沸腾换热特性,分析了热流密度(q=2.0kW/m~2～47.6kW/m~2)、质量干度(x=0～0.6)、质量流速(G=111.11kg/(m~2·s)～333.33kg/(m~2·s))的变化对平均传热系数h的影响,探究不同情况下影响沸腾换热的主导因素。实验研究表明:平均传热系数h随热流密度q的增加而减小,在不同范围内减小速率有明显差异;热流密度q=2kW/m~2～5kW/m~2时质量流速G对平均传热系数h影响较明显,热流密度较高时质量流速G对换热影响很小;在质量流速G=111.11kg/(m~2·s)～333.33kg/(m~2·s),质量干度x0.3时,平均传热系数h随质量干度x增加而明显下降,在设计微通道换热器时应尽量使R141b处于初始沸腾阶段以获得更好换热效果,并采取一定措施预防干度过高引起的换热恶化。

Experimental Investigation on Flow Boiling Heat Transfer of R141b in Circular Micro-Channel Heat Sinks

In order to intensify heat transfer and solve the problem of high heat flux and heat dissipation inside the equipment, the boiling heat transfer characteristics of R141b in horizontal micro-channels with different diameters (D=0.5mm and 1.0mm) were studied experimentally. The effects of heat flux (q=2.0kW/m²~47.6kW/m²), vapor quality (x=0~0.6) and mass flow rate (G=111.11kg/(m²?s)~333.33kg/(m²?s)) on the average heat transfer coefficient h were analyzed, and the dominant factors affecting boiling heat transfer were explored under different conditions. The experimental study showed that the average heat transfer coefficient h decreased with the increase of heat flux q in significantly different rate according to different range. The effects of mass flow rate G on the average heat transfer coefficient h are obvious when heat flux q=2kW/m²~5kW/m², while when the heat flux is high, the mass flow rate G has little effect on the heat transfer. At different mass flow rate (G=111.11kg/(m²?s)~333.33kg/(m²?s)) when the vapor quality x>0.3, the average heat transfer coefficient h decreased with increasing vapor quality x. Micro-channel heat exchangers should be well-designed to insure R141b working under the initial boiling stage to achieve better heat exchange effect, and certain measures should be taken to prevent the heat deterioration caused by excessive dryness.