CFD analysis of rotation effect on flow patterns and heat transfer enhancement in a horizontal spiral tube heat exchanger

Abstract

This study explores the enhanced thermal performance of heat exchangers utilizing spirally coiled tubes, particularly in applications such as heating saltwater in solar desalination plants, which require elevated heat transfer coefficients. A numerical investigation is conducted to assess the impact of mechanically rotating horizontal spiral tubes on flow patterns and temperature profiles along their length. A detailed physical model was developed using COMSOL Multiphysics software. The findings from computational fluid dynamics simulations indicate that mechanical rotation significantly modifies both velocity and temperature gradients at each cross-section of the tube. This rotation effectively reduces the formation of thermal hotspots in the outer regions, thereby improving and accelerating heat dispersion. Notably, substantial variations in velocity and temperature profiles occur at rotation speeds up to 4 rpm; however, these changes diminish beyond this speed threshold. The study reveals that rotation increases the Nusselt number of the heated flow within the tube by over 145 %. Furthermore, the effects of rotation are more pronounced in smaller diameter tubes compared to larger ones. Ultimately, the performance factor indicates that the benefits of enhanced heat transfer outweigh the increased pressure drops associated with tube rotation, validating the effectiveness of the proposed heating system.