Experimental investigation of pressure drop in helical coil during flow boiling at subatmospheric pressures

The thermal phenomenon of flow boiling in the helical coil is compelling due to the secondary flow. This work presents a pioneer experimental investigation of pressure drop during flow boiling in the helical coil using water under subatmospheric pressure conditions. The test section is made of SS-304, length 5330 mm, coil diameter 282.7 mm, and tube diameter 9.5 mm. The experiments are performed at 0.25, 0.5, 0.75 and 1 bar absolute pressure at the exit of the helical coil. The mass flux is varied from 140 to 425 kg/m2s, and vapor quality from 0 to 0.9. The effect of system pressure, accompanying mass flux, quality and heat flux on two-phase pressure drop has been studied. The two-phase pressure drop at the subatmospheric system pressure is higher than that at the atmospheric system pressure for identical operating conditions. The two-phase pressure drop in the helical coil is higher for maximum mass flux at higher vapor quality and lower subatmospheric pressure. The two-phase pressure drop in the helical coil increases linearly by increasing the heat flux at all subatmospheric system pressure. The pressure fluctuations are not affected significantly by the mass flux and heat flux in the saturated region. Experimental subatmospheric and atmospheric pressure drop data are compared with available correlations. The available correlations predict the atmospheric and subatmospheric pressure drop data with reasonable accuracy.