Flow and heat transfer characteristics of water in eccentric micro annuli

Abstract

Considering the few studies on eccentric micro annuli, in view of the extensive use of microchannels, experimental and numerical studies on the thermal–hydraulic performances are conducted. Results show that the flow is turbulent in the Reynolds number range of 992–3491. The velocity and temperature distributions at cross-section are nonuniform and two or four vortexes are formed. As the mass flow rate and heat flux increase, the friction factor decreases and the Nusselt number increases. As the eccentricity increases, the friction factor and Nusselt number decrease. When the buoyancy is negligible, the local Nusselt number for peripheral surface declines rapidly at first and then steadily declines. The larger mass flow rate and smaller eccentricity cause the quasi-stationary state local Nusselt number to occur early. When the buoyancy is not negligible, the local Nusselt number for peripheral surface drops quickly at first and then rises. The larger heat flux causes an increase in the local Nusselt number at a shorter heating length. The flow and thermal entropy production rates in most flow regions are small. The thermal entropy production rate far outweighs the flow entropy production rate. Finally, the correlations for the Nusselt number and friction factor are presented.