Calculation method of friction coefficient on flat plate in supercritical water laminar boundary layer flow

Abstract

In supercritical water (SCW) gasification reactor, understanding the interaction of SCW with wall surfaces and the boundary layer situation is significant to gasification efficiency improvement. This paper wishes to find a convenient way to calculate the friction coefficient on flat plate in SCW laminar flow with a pseudo-critical incoming state. The velocity profiles characteristics in the SCW boundary layer would be studied using direct numerical simulation (DNS) method, and they would be applied to variable separation of friction coefficient expression. Then, a semi-analytical formula for plate friction applied to the SCW fluid field would be derived, and it would be found to be the extended form of that derived from the Blasius's theory. In this formula, the effects of the unique properties variation around critical points had been isolated as dimensionless parameter Gμ*, dependent on pressure and temperature boundary conditions. The method of obtaining Gμ* by DNS will be given, and two details in the processes will be explained. Finally, the dependence between Gμ* and boundary conditions would be derived by numerical experiments. By the semi-analytical formula and diagram of Gμ*(Tw)|in, the friction coefficient on one side of the plate in SCW laminar flow could be quickly calculated. The applicable inflow states are five pseudo-critical points of 23–27 MPa, the wall temperature is 645–673 K, and the Reynolds number range is above 1×105. The accuracy of this method has been proved by comparing the results obtained by it with DNS results.