Heat transfer and friction characteristics of spirally corrugated tubes for power plant condensers—2. A mixing-length model for predicting fluid friction and heat transfer

Abstract A mixing-length formulation modified in accordance with the suggestion of Rotta is used to predict the Fanning friction factor and the heat transfer coefficient on corrugated (roped) tubes. Several empirical parameters are required in this formulation and they are obtained via experimental data fitting. The experiments are carried out with water flow in corrugated tubes in the ranges 10 4 ⩽ Re ⩽ 6 × 10 4 and 2.2 ⩽ Pr ⩽ 3.4. Simple correlations are suggested for the relations between the two most important empirical parameters—the dimensionless distance Δη that shifts downward the reference wall and the cavity Stanton number, St w , and the geometrical parameters of the ridges of the tubes. These correlations yield the mean value boundary layer profiles, Fanning friction factors and Nusselt (Stanton) numbers through the solution of the momentum and energy transfer equations for one-dimensional time-independent stabilized flow.