TURBULENT HEAT-TRANSFER TO POWER-LAW FLUIDS IN HELICAL PASSAGES

The fully developed turbulent Fanning friction factors and Nusselt num bers for purely viscous power-law non-Newtonian fluids in helical coil s were measured experimentally. The flow passage is about 600 hydrauli c diameters long. The test section wall was heated by passing direct e lectric current through it, yielding constant peripheral wall temperat ure and constant heat flux per unit length along the flow direction. F or turbulent power-law fluid flows through helical coils, over the ran ge of the coil-to-tube diameter ratio from 10 to 26, the generalized R eynolds number (Re) from 25,000 to 50,000, the Prandtl number from 6 to 14, and the power-law exponent (n) from 0.78 to 1, improved correla tions for friction factor-prediction and a new correlation for Nusselt number are proposed. Other than space saving, helical coils do not of fer any advantages over a straight tube for heat-exchanger application s involving turbulent flow of Newtonian or power-law non-Newtonian flu ids.