水平加热管上气泡动力特性对纳米颗粒悬浮液过冷沸腾的影响

纯水在水平加热管加热下的过冷池沸腾试验揭示出，在热流密度低于24.4 kW/m2时，加热管底部所需的过热度最低，中部次之，顶部最高；随着热流密度的增加，加热管各位置所需的过热度逐渐趋于一致。纳米颗粒悬浮液的试验发现，低热流密度时，各位置处所需过热度的差异较小，但随着热流密度的增加，加热管底部所需的过热度超过了顶部，这种差异随着颗粒浓度的增加而增加。从气泡动力学角度对产生差异的原因进行了分析，主要的结论是，考虑纳米颗粒/团聚体在加热管顶部表面的沉积/吸附，会降低加热管表面粗糙度，同时使得悬浮液微液底层内出现一个吸引力Fa，从而使得悬浮液的相变温度提高，而由于加热管中、底部分粗糙系数降低所带来的换热降低较加热管顶部要强，使得大部分热流密度下加热管顶部沸腾所需的过热度较中、底部分要高。

EFFECT OF BUBBLE DYNAMICS SUBCOOLED POOL BOILING OF NANO-PARTICLE SUSPENSIONS ON A HORIZONTAL TUBE

The experiment of boiling conducted for pure water showed that, when the heat flux was lower than 244 kW/m2, the superheat at the bottom of heated tube is the lowest, lower at the middle and highest at the upper, and when the heat flux is higher than 244 kW/m2, the superheat at different locations was almost the same. However, the experiments of boiling for nano-particle suspensions showed that, the difference at different positions is small at low heat flux, and the superheat at the bottom is larger than at other positions with increasing heat flux, and also increasing with the concentration. The difference is analyzed from bubble dynamics, the main conclusions are the subsidence/attachment of nano-particles on the heated surface resulted in the attaching force Fa and the decrease of the surface roughness, which make the increase of superheat for nano-particle suspension relative to pure water, at the same time, the superheat for upper part is higher than that for middle and lower part at the large heat flux due the worse heat transfer resulted from the decrease of roughness for middle and lower part relative to upper part.