热水解污泥在扭曲管中流动换热的数值模拟

Numerical Simulation of Heat Transfer and Fluid Flow of Thermal-Hydrolyzed Sewage Sludge in Twisted Oval Tube

采用数值模拟方法研究了热水解污泥在扭曲换热管中的流动换热特性,分析了扭曲管的强化传热机理.获得了扭曲管不同纵横比和扭曲比条件下的温度场与速度场分布,阐述了不同雷诺数对流动传热的影响.该结果与传统光滑圆管的流动换热特性进行了比较,研究结果表明,扭曲管产生的旋流和二次流可以有效地提高换热效率,但是也增加了流动阻力.另外,综合换热因子随着扭曲比的增大而减小,随着纵横比先增大后减小,在纵横比为1.96时达到最大.与传统光滑圆管相比,发现在低雷诺数(小于5 000)情况下扭曲换热管具有更高的换热效率.

The flow and heat transfer performances of thermal-hydrolyzed sewage sludge in twisted oval tubes were numerically investigated and the mechanism of enhanced heat transfer was analyzed in this paper. The velocity and temperature distributions at different aspect ratios and twist ratios were obtained, and the effect of Reynolds number on the flow and heat transfer was clarified. The results reveal that the heat transfer efficiency could be greatly increased by the generation of vortex and secondary flow but with the growth of pressure drop. Furthermore, a larger twist ratio leads to a smaller thermal performance factor, and as the aspect ratio increases to 1.96, the thermal performance factor reaches the maximum value and then descends. By compared with the results of smooth round tubes, the twisted oval tubes show much improved heat transfer efficiency at a low Reynolds number（〈5 000）.