管内流体振荡强化换热的机理探讨

ON MECHANISM OF ENHANCED HEAT TRANSFER OF FLUIDS WITHIN PIPES BY OSCILLATION

解析解、数值计算以及实验研究均得到一个一致的结论:管内流体的振荡可以大大地强化其轴向传热。本文说明,这种强化换热的根本原因是由于流体的振荡引起了导热面积和温度梯度骤增的结果。

Theoretical and experimental studies show that axial oscillation of a fluid within pipes can lead to enhancing heat transfer of the fluid. The enhancement multiple of hey ans-fer is a function of (△x/R)2, Womersley number (Worn) and Prandtl number (Pr). Under lerinar conditions, intensive mixture of fluid lumps is impossible. It can be considered that the heat trans'er of the oscillated fluid is completed in form of conduction. In the case of lower Womersley number. the velocity and displacement profiles of the fluid are paraboloids. Normal temperature gradient on the displacement profile for the oscillated fluid is greater than that for the static fluid. Also, the effective conduction area of the oscillated fluid is greater than that of the static fluid. Therefore, the conductive heat transfer rate of the oscillated fluid is obviously greater than that of the static fluid. The oscillation is only the means to make a enhanced area of heat transfer and enhanced temperature gradient continuously. According to this mechanism, the relation of (a1/a) - 1∝ (△x/R)2 is derived . Also, the effects of Womersley number, Prandtl number and wall of the pipe on the enhanced heat transfer are elaborated in this paper.