Flow Regime Transition of Accelerated （Decelerated） Flow in Rectangular Channel

Flow regime transition under constant pressure drop rate in rectangular channel is investigated by theoretical and experimental study. Laminar velocity distribution and the method to determine the critical Reynolds number is obtained by theoretical study. The factors that affect the critical Reynolds is analyzed.The results show that the critical Reynolds number of accelerated（decelerated） flow is smaller（larger） than that of the steady flow. The pressure drop rate has little effect on the critical Reynolds number while the starting steady part pressure drop does. The critical Reynolds number approaches to the steady condition value while the steady part pressure drop approaches to the steady condition value. The pressure drop rate hardly affects the critical Reynolds number.The experimental data supports the smaller（larger） critical Reynolds number in accelerated（decelerated） flow, but is not consistent with the effect of pressure drop rate.