Buoyancy and Velocity Field Synergy Principle in Convective Heat Transfer and its Role in Thermo-Hydraulic Performance Improvement

Abstract

This study proposes the buoyancy and velocity field synergy principle and aims to enhance thermo-hydraulic performance in convective heat transfer. A mechanical energy conservation equation concerning synergy between buoyancy and velocity was derived, which describes the mechanical energy transport and dissipation in convective heat transfer. Two new field synergy numbers, Fsu,g and Fsu,p, were proposed to characterize the degree of synergy between velocity and buoyancy, and the degree of synergy between velocity and pressure gradient over the fluid domain, respectively. The pressure drop of a channel subjected to convective heat transfer is related to not only Gr/Re2 but also Fsu,g. Under a same Gr/Re2, a larger | Fsu,g | leads to a smaller | Fsu,p |, and thus the pressure drop is decreased. Furthermore, the multi-field synergetic relationships among buoyancy, velocity, temperature gradient and pressure gradient were analyzed for convective heat transfer in channels. The correlation between Fsu,p and Fsu,g *Gr/Re2, and the correlation between Fsu,g and a traditional field synergy number characterizing convective heat transfer capability, Fc, were derived, which reveals the coupled mechanisms of mechanical energy dissipation and thermal energy transport. The proposed principle was applied in typical channel flows subjected to convective heat transfer, and its benefits were demonstrated. It is noted that both pressure drop reduction and convective heat transfer enhancement can be achieved in using the proposed principle. This paper provides a new insight for improving thermo-hydraulic performance of heat exchangers.