Heat or Mass Transfer in Laminar Flow in Conduits With Constriction

Analytical solutions are obtained on the effects of boundary constriction on heat or mass transfer at the entrance region in a well-developed steady laminar flow in symmetric and axisymmetric conduits subjected to uniform wall temperature or mass concentration. The solutions are limited to the fluids of constant properties with negligible viscous dissipation, moderate Reynolds number, and large Peclet or Schmidt number, and the spread of the wall constriction is large compared to the mean width or radius of the conduits. It is found that both the bulk temperature and heat transfer rate at the wall are oscillatory in nature, and their amplitudes decrease drastically as the fluid moves away from the entrance. Near thermal entry length, the bulk fluid temperature approaches its mean value with vanishing oscillation, but the heat transfer rate at the wall stays oscillatory in nature due to the irregularity of the wall. The thermal entry length changes very little from the corresponding straight-wall conduits. These results are also true for the mass transfer.