Heat transfer distribution and pressure drop fluctuations in subcooled flow boiling at subatmospheric system pressure

Abstract

The transfer of higher heat flux at subatmospheric system pressure is relevant to different applications where the higher surface temperature is a constraint. There is a scarcity of literature on subcooled flow boiling at subatmospheric system pressure. The experiments are performed at 50, 75 and 101 kPa absolute system pressure in an SS-304 tube of 5.85 mm radius, heated length of 1500 mm and 0.5 mm thickness. The mass flux of 90–300 kg/m2s is streamed at the varying heat flux of 48–218 kW/m2. The heat transfer coefficient in single-phase flow is not impacted significantly by the subatmospheric system pressure. The subcooled flow boiling heat transfer coefficient is increased at the lower subatmospheric system pressure. The more nucleation sites due to higher wall superheat are activated at the higher heat flux at subatmospheric system pressure. The surface temperature is radially symmetric at subatmospheric system pressure for all values of the Froude number. The gravitational force is suppressed at subatmospheric system pressure. The onset of nucleation is achieved earlier in the axial direction at the higher heat flux. The mass flux has no significant effect on the subcooled flow boiling heat transfer coefficient. The pressure drop and fluctuations are enhanced at the higher mass flux, higher heat flux and lower subatmospheric system pressure.