Subcooled flow boiling in a horizontal circular pipe under high heat flux and high mass flux conditions

Abstract

Subcooled flow boiling of water is widely observed in high heat flux and high mass flux (HHHM) cooling applications such as heat exchangers, refrigeration equipment, boiler tubes and nuclear reactor core fuel channels in pressurized heavy water reactors (PHWR). In this study, the focus is on investigating the local heat transfer coefficient (HTC) and pressure drop in a horizontal tube experiencing subcooled boiling of water under low pressure and HHHM conditions. The study encompasses different geometrical parameters such as tube diameter (5.5 mm, 7.5 mm, 9.5 mm and 12 mm) and length (550 mm for each of the tubes). The operating parameters that are varied include mass flux (248–2000 kg/m^2.s) and heat flux (0–1837 kW/m²). Infrared thermography is used to measure the local wall temperature. A non-dimensional correlation for the diabatic pressure drop ratio (ratio of diabatic pressure drop to adiabatic pressure drop) as a function of Jakob number ($\mathrm{Ja}$), Boiling number ($\mathrm{Bo}$) and diameter ratio is developed. Subcooled boiling pressure drop ratio for 5.5 mm, 7.5 mm and 9.4 mm diameter tubes is 2.23 which is independent of diameter. A correlation for the two phase local HTC during subcooled flow boiling conditions as a function of $\mathrm{Ja}$, $\mathrm{Bo}$ and Prandtl number ($\mathrm{Pr}$) is also developed.