LOCAL FRICTION AND HEAT-TRANSFER BEHAVIOR OF WATER IN A TURBULENT PIPE-FLOW WITH A LARGE HEAT-FLUX AT THE WALL

The present study investigated the behavior of friction and heat transfer coefficients of water flowing turbulently in a relatively long (i.e., 950 diameter long) circular pipe. When a large heat flux was applied at the wall, the viscosity of water significantly decreased along the axial direction due to the increasing temperature of water. A concept of a ''redeveloping region'' was introduced, where the local heat transfer coefficient increased while the local friction coefficient decreased due to the above-mentioned viscosity change. The present study proposed the use of local bulk-mean temperature to determine local Nusselt numbers by using local Reynolds (Re-LB) and Prandtl numbers (Pr-LB), a method, that automatically took into account the effect of axial viscosity change on the evaluation of local heat transfer coefficients. A new-turbulent heat transfer correlation for the prediction of the local Nusselt number is given as Nu(X) = 0.00425 Re-LB(0.979) Pr-LB(0.4)(mu(W)/mu b)(-0.11).