Thermal Analysis and Wall Temperature Distribution during Flow Boiling under Subatmospheric System Pressure

This study investigates subcooled flow boiling at subatmospheric system pressure for high heat flux transfer applications where higher surface temperatures are a concern. The experimental setup includes an SS-304 tube with a 11.7 mm diameter, a 1500 mm heated length, and 0.5 mm thickness. The mass flux ranges from 90 to 300 kg/m2s with a varying heat flux of 30-145 kW/m2. Results indicate that the subcooled flow boiling heat transfer coefficient is enhanced at lower subatmospheric system pressure due to more nucleation sites activated by higher wall superheat. The surface temperature is radially symmetric at subatmospheric system pressure, and the onset of nucleation is achieved earlier in the axial direction with higher heat flux. The mass flux does not significantly affect the subcooled flow boiling heat transfer coefficient. These findings may be useful in designing subcooled flow boiling systems for various applications.