| The present empirical correlations to calculate flow resistance coefficient are all achieved under stable flow, but flow always fluctuates, such as marine thermal loop could be rocked by ocean condition. The study of applicability of present empirical correlations under flow fluctuation conditions is needed. So characteristics of flow friction resistance under flow fluctuation conditions are studied with theory and experiment in this dissertation.In the theoretical study, the phase difference between the flux and pressure drop fluctuating curve was analyzed. And the correlation of flow resistance under flow fluctuation was achieved through analysis of experimental result.Under flow fluctuation, the experiment of flow resistance of periodic forced circulation is carried on. Water was used as the working fluid. Experimental study was conducted under general pressure and temperature. The flow fluctuations were achieved by changing the speed of the pump using the frequency converter. Experimental data were recorded and analyzed to study the characteristics of the flow resistance.The result of experiment indicated that, the flow resistance coefficient of flow fluctuation is bigger than the flow resistance coefficient of the stable flow. The characteristics of flow friction resistance under flow fluctuation conditions do not only influenced by the amplitude of fluctuation, but also by the average flow rate. The amplitude of flow resistance coefficient increased as the amplitude of fluctuation increased. But it decreased with the increasing of the average flow. The acceleration was the direct reason of the change of the flow resistance coefficient under flow fluctuation. The flow resistance coefficient was trending to increase when the acceleration is positive.
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