Heat transfer characteristics of R-134a in a converging-Diverging nozzle

Abstract

Heat transfer characteristics of cavitating flows in the diverging section of a converging-diverging nozzle, with R-134a as the working fluid were investigated for mass fluxes from 11.3-52.3 kg m −2 s −1 and heat fluxes from 52.6-693 kW m −2 . Eleven different nozzle configurations were examined with different divergence angles, throat diameters, inlet profiles, and lengths. Heat flux measurement assumptions were analyzed using numerical conduction simulations with ANSYS Fluent. Experimental results indicated two different heat transfer regimes at high Reynolds number-one high and one low-likely due to wall dryout. A temperature drop with a strong correlation to Reynolds number as well as inlet profile was recorded due to the cavitationinduced phase change. Additionally, data showed two-phase heat transfer coefficients from 3.7 to as high as 285kW m −2 K −1 . Chen's correlation compared well with the recorded heat transfer coefficients for low Reynolds numbers. Variation of heat transfer coefficients with different geometry parameters were given, and potential sonic effects were discussed. With such high heat transfer coefficients, cavitation enhanced heat transfer in converging-diverging nozzles could be of significant use in electronics cooling applications.

On the influence of thermal phenomena during cavitation through an orifice

“…Several authors evidenced with experiments this thermodynamic effect in the framework of engineering applications such as propulsion systems [8,9] , or electronics cooling [10,11] , and many of them used Liquid Nitrogen (LN 2 ). Tani and Nagashima [12] studied cavitation formed at the throat of a nozzle using both water and LN 2 .…”