A consideration of factors that delay increase in convective heat transfer when turbulent flow in a pipe accelerates rapidly

Abstract

The delay of the heat transfer increase against the rapid acceleration of the pipe flow was investigated through the measurement of fluctuations of flow and heat transfer. Immediately after the rapid acceleration of the flow, the pressure loss increases due to an increase in the wall velocity gradient. However, since the turbulence in the pipe is almost the same as before the acceleration, the heat transfer coefficient is almost unchanged. Then, after a short delay, generation of turbulent spots increases the heat transfer coefficient. By systematically changing the Reynolds number, it was revealed that the delay until the turbulent spots generate after the acceleration strongly depends on the turbulence intensity before the acceleration.