EXPERIMENTAL AND CFD INVESTIGATIONS OF HEAT TRANSFER IN HELICAL COILS FOR THE DEVELOPMENT OF CORRELATIONS FOR NEWTONIAN AND NON-NEWTONIAN FLUIDS IN TRANSIENT STATE-SPACE CONDITIONS

摘要

Experimental studies and CFD investigations were carried out under laminar and turbulent flow regimes in isothermal steady state and non-isothermal unsteady state conditions in helical coils for Newtonian and non-Newtonian fluids. Water and glycerol-water mixture (10 and 20% glycerol) as Newtonian fluids and dilute aqueous polymer solutions of sodium carboxymethyl cellulose (SCMC), sodium alginate (SA) as non-Newtonian fluids were used in this study. The experiments were performed for three helical coils of coil curvature ratios as 0.0757, 0.064 and 0.055 in laminar and turbulent flow regimes. For the first time, two innovative correlations to calculate Nusselt number (Nu) in terms of new dimensionless 'M' number, Prandtl number and coil curvature ratio under different conditions for Newtonian fluids are proposed in this paper. Third correlation of Nu vs. Graetz number (Gz) including the effects of coil curvature on heat transfer coefficient which was not considered by earlier investigators is developed based on tests conducted in laminar flow for Newtonian fluids. All these three innovative correlations developed based on experimental data which were not found in the literature. These correlations were compared with the work of earlier investigators and were found to be in good agreement. The CFD analysis for laminar and turbulent flow was carried out using the CFD package FLUENT 12.0.16. The CFD calculation results (Nu_i, U) for laminar and turbulent flows were compared with the experimental results, and also the work of earlier investigators was found to be in excellent agreement. Further, the effect of helix diameter on heat transfer for Newtonian and Non-Newtonian fluids are also presented in this paper and it was observed that as helix diameter increases, overall heat transfer coefficient decreases.