Effects of Boundary Layer Turbulence Promoters on the Local Film Coefficients of ML-1 Fuel Elements

Abstract

Local convective heat transfer coefficients for a surface with integral boundary-layer turbulence promoters were determined by conducting naphthalene-to-air mass transfer tests and invoking the heat transfer-mass transfer analogy. The turbulence promoters were machined into the convex surface of an annulus. The experimental results were normalized relative to mass transfer coefficients on a smooth surface with parallel flow.On the faces of the turbulence promoters local heat transfer coefficients up to six times the smooth surface value were encountered. High transfer coefficients were found on the upstream and top faces. Coefficient values on the downstream surfaces were low and independent of geometry. Corner areas showed heat transfer coefficients lower than those for a smooth surface with parallel flow.The data from surfaces between two turbulence promoters were correlated in terms of a dimensionless location index. A broad heat transfer coefficient peak of 2.4 times the smooth surface magnitude was found 4 turbulence promoter heights downstream from a promoter. Each test also showed a narrow coefficient peak at the point about 0.5 height preceding a turbulence promoter. When correlated in this manner, the results revealed a unique generalized distribution of the transfer coefficient for surfaces with boundary layer turbulence promoters of rectangular cross section. The upstream and downstream regions of boundary layer separation were independent of the dimensions of the turbulence promoters.The estimated error for this series of tests was approximately ±20 % of the maximum relative transfer coefficient values.