Numerical investigation on performance comparison of non-Newtonian fluid flow in vertical heat exchangers combined helical baffle with elliptic and circular tubes

In the present study, heat transfer and flow resistance characteristic in the shell side of a vertical heat exchanger combined helical baffles with elliptic tubes were experimentally and numerically investigated. An aqueous solution with 3% weight fraction of carboxymethyl cellulose exhibits non-Newtonian fluid behavior selected as the working fluid whose stability is excellent found in our previous investigation, and flows in the shell side of the tested heat exchanger. A helical baffle heat exchanger with circular tubes based on the same equivalent outside diameter of the elliptic tubes was also numerically studied for the performance comparison. The numerical results showed that, the heat transfer rate per unit outside surface area and shell side Nusselt number of the elliptic tubes heat exchanger are 14.7%-16.4% and 11.4%-16.6% higher than those of the circular tubes heat exchanger, and the shell side friction factor is lower by 29.2%-36.9%. The comprehensive thermal performance factor is given to evaluate both heat transfer coefficient and pressure drop. The thermal performance factor enhances by 30-35%, which demonstrates that the elliptic tube can effectively improve the heat transfer performance of non-Newtonian fluid flowing in the helical baffle heat exchanger when compared to the circular tube. Based on experimental results, correlations for predicting the shell side Nusselt number and friction factor of the heat exchanger combined helical baffle with elliptic tubes were presented.