Study On Flow Resistance Under Rolling

Experimental study and theoretical analysis on the flow resistance of the natural circulation for single-phase water under rolling condition is carried out.The natural circulation and forced circulation experiments are performed under non-rolling and rolling conditions by using water as the working fluid. The test section is a horizontal stainless steel tube.The reason for the phase difference of half period between flow rate and pressure drop under rolling condition is analyzed. The phenomenon that two flow rate crests appear in one period in natural circulation under rolling is found when the flow rate is small. An explanation is given. For the flow rate fluctuation problem, the frictional pressure drop is separated from the fluctuating total pressure drop. By analyzing the influence of the inertia forces on pressure measurement under rolling, a relatively good method of measuring the pressure drop is adopted, and the data-processing methods are determined.Through processing the experimental data, natural circulation and forced circulation flow friction coefficients are obtained. They are compared with the calculating results of traditional friction coefficient correlations. Under the same thermal conditions, the friction coefficients are compared between natural circulation and forced circulation, under rolling and non-rolling conditions. The effect of different system pressures, rolling periods and rolling angles on the friction coefficients are also analyzed The semi-empirical correlations of the horizontal pipe flow friction coefficient of natural circulation under rolling and non-rolling condition are fitted out.The results of the experiment show that, the natural circulation friction coefficients of horizontal pipe flow coincide with those of forced circulation in laminar flow, but the friction coefficients of the forced circulation are bigger than that of the natural circulation in turbulent flow. The influence of rolling condition on the natural circulation resistance characteristics is that, the shorter the rolling period, the bigger the natural circulation friction coefficient. The influence of system pressure on the resistance characteristics is not obvious under non-rolling condition, but under the rolling condition, with the increase in system pressure, the friction coefficient of the natural circulation significantly increases.