Experimental study on subcooled flow boiling heat transfer to water-diethylene glycol mixtures as a coolant inside a vertical annulus

Experimental studies on subcooled nucleate flow boiling heat transfer of dilute water-diethylene glycol (DEG) mixtures inside a vertical annulus have been conducted. The experimental apparatus provides the particular conditions to investigate the influence of heat flux, flow velocity, degree of subcooling, and concentration of mixture on heat transfer coefficient in both the convection and nucleate boiling regimes. Results reveal that increasing heat flux causes the single phase heat transfer coefficient increases slightly until the incipience of bubble formation. Then, the flow boiling heat transfer coefficient dramatically increases when heat flux increases. Increasing the flow velocity increases the flow boiling heat transfer coefficient. Contrary to the expectations; little increase in the heat transfer coefficient is clearly observed in both of the convective and the nucleate boiling regimes when small amount of DEG was added to the mixture. In addition, liquid inlet temperature to the annulus significantly influences the inception heat flux such that increasing the inlet temperature decreases the inception heat flux.