Heat transfer characteristics of enhanced single and two-phase alternative refrigerant mixture flow in meso-channels.

摘要

The dissertation presents results from an experimental study on refrigerant mixture flow (R-407C) in which the heat transfer coefficient was measured over a range of heat and mass fluxes. Heat transfer characteristics in smooth horizontal meso-channels and in meso-channels enhanced by wire coils of varying geometry. Experiments were conducted under three different flow types: single-phase, two-phase subcooled, and two-phase saturated boiling flows in channels of diameters of 1.59, 2.78, and 3.97 mm. Experiments were performed at heat fluxes of 2 and 6 kW/m2 for the subcooled boiling flow and 15 and 29 kW/m 2 for the saturated boiling flow. The mass flow rate ranged from 0.45 to 1.85 kg/min and the refrigerant subcooled by 8°C. The saturated boiling experiments were conducted for ΔT_sat of 0 to 13°C. The heat transfer coefficient was found to be dependent on channel size, heat flux, and mass flow variations. For smaller channel diameters, the heat transfer rate significantly increased as compared to larger channel diameters. The results showed an increase of up to 100% in the heat transfer coefficient when compared to traditional and micro-channel boiling characteristics. Results also show that micro-coil inserts enhanced the heat transfer performance over that in smooth meso-channels by 250%. This study also presents correlations-based on the experimental database developed for R-407C flow in meso-scale horizontal channels. The purpose of this study is to present new design correlations for flow boiling in a ternary refrigerant mixture at a meso-scale size. Single-phase, two-phase subcooled, and two-phase saturated boiling flow correlations were developed. The effects of essential design parameters, such as, channel diameter, coils pitch and diameter, and flow variables, Reynolds number, Prandtl number, wall superheat, mass flow rate, subcooling, and heat flux were considered in the correlation. The relative influences of enhancement design parameters on friction factor and heat transfer were carried in this parametric analysis of the flow boiling correlations. The resulting correlations are compared to available published correlation.