Void fraction and pressure drop in subcooled forced convective boiling with refrigerant 12

This paper presents investigations and results of void fraction and pressure drop of dichlordifluormethan (CCl2F2) in forced convective subcooled boiling. The data was taken at different heat fluxes in a 12 to 25 bar pressure range, the mass fluxes have been varied from 500 to 3000 kg/m2s with an inlet subcooling in the range from 10 to 50 K. The experiments have been conducted in an annular test channel, with an 0.016 m inner diameter and 0.03 m outer diameter. The inner tube of the annulus was heated by direct current. The void fraction data was gaged with a γ-densitometer and a specially designed impedance void meter. The experimental results reveal that the void fraction is nearly constant from the onset of nucleation boiling to a subcooling of about Δ=10 K. The pressure drop shows a similar behaviour