Flow fluctuations and flow friction characteristics of vertical narrow rectangular channel under rolling motion conditions

Experimental investigations on flow fluctuations and friction characteristics of a vertical narrow rectangular channel under rolling motion condition are carried out. This experiment is designed to acquire the flow rate fluctuation boundary of forced single-phase flow in rolling motion and to get an insight into the flow friction characteristics under large flow rate fluctuation amplitudes. The results show that the amplitude of flow rate fluctuations increase with increasing rolling amplitude and the valve opening while decrease with the increase of the rolling period and driving head. The time average friction coefficient can be obtained by two kinds of methods, one calculated by integrating the instantaneous friction coefficient in one period is related to the viscous dissipation and the other acquired by the Darcy equation which employs time average pressure drop and velocity represents time average frictional pressure drop. A correlation for the instantaneous friction coefficient is developed, which could also apply to steady condition when the rolling frequency or rolling amplitude approaches zero.