Experimental studies on heat transfer to Newtonian and non-Newtonian fluids in helical coils with laminar and turbulent flow

摘要

Experimental studies on isothermal steady state and non-isothermal unsteady state conditions were carried out in helical coils for Newtonian and non-Newtonian fluids. Water, glycerol-water mixture 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. These experiments were performed for coils with curvature ratios δ=0.0757, 0.064 and 0.055 in laminar and turbulent regimes. An innovative approach of correlating Nusselt number to dimensionless number '. M' for Newtonian fluids based on experimental data is presented which is not available in the literature. Several correlations for the first time are proposed based on heat transfer data generated from the experiments performed for Newtonian fluids under isothermal and non-isothermal conditions (total 138 tests). These developed correlations were compared with the work of earlier investigators and were found in good agreement. Further, comparison of overall heat transfer coefficient U _o, and Nusselt numbers for Newtonian and non-Newtonian fluids under isothermal and non-isothermal conditions (total 276 tests) is presented in this paper. From the experimental results, it was found that overall heat transfer coefficient and Nusselt numbers for water are higher than glycerol-water mixture and non-Newtonian fluids. It was also observed from experimental results that as helix diameter increases, overall heat transfer coefficient and Nusselt numbers of both fluids decreases for the same flow rates.