Heat transfer enhancement in smooth tube with wire coil insert in laminar and transitional non-newtonian flow

Abstract

This work presents an experimental study on the heat transfer enhancement by means of a tube with wire-coil insert,for non-Newtonian laminar and transitional flow. The dimensionless pitch and wire diameter (based on the plain tube inner diameter) were chosen as p/D= 1 and e/D=0.09. Two pseudoplastic test fluids have been used: 1% by weight aqueous solutions of carboxymethyl cellulose (CMC) with high viscosity and medium viscosity. A wide range of flow conditions has been covered: Reynolds number from 10 to 1200 and Prandtl number from 150 to 1900. Isothermal pressure drop tests and heat transfer experiments under uniform heat flux conditions were performed on both the plain tube and the tube with wire-coil. The plain tube results have shown an excellent agreement with the available data. At Reynolds numbers below Re=400, the wire-coil insert has no effect in heat transfer. However, it becomes more effective as turbulence is established: at Re=1200, the wire-coil increases the heat transfer rate by 350%, with a pressure drop increase of 250%. At Reynolds number Re=1800, if a wire-coil is inserted in a smooth tube the heat transfer rate will be increased by 300% with no increase in pumping power.