Effect of Heat Transfer on Flow Field at Low Reynolds Numbers in Vertical Tubes

摘要

Variation of density and viscosity with temperature may cause dis¬tortions in the flow field and affect the rate of heat transfer to fluids flowing in vertical tubes. Under relatively mild conditions of heating and cooling with a constant temperature wall these distortions may be large enough to change the parabolic velocity profile associated with isothermal flow to such an extent that the flow becomes unstable and breaks down into turbulence. For heating in up flow it was found experimentally that unstable flows exist when the center line velocity drops to zero (inversion point) and may even exist under milder conditions. For cooling in up flow unstable flows appeared to arise under only slightly more severe conditions than are necessary to cause the velocity gradient at the wall to go to zero.