Effect of length-to-diameter ratio on critical heat flux in porous-coated tubes

The critical heat flux occurring during upflow of boiling water in vertical smooth and porous-coated tubes were investigated experimentally. experiments performed at low pressures from 0.11-0.7 MPa mass fluxes 100-400 kg/m2s, with inlet subcoolings 1-70 K. carried out four test sections, two which porous coated by sintering. each the cases, smooth, had same geometries (L/D = 28.3, L/D 38.75) to ensure a direct comparison measured data those tubes. In addition, for uniformly heated obtained literature. These conducted using inner 14.1, 50) experimental set-up used present study. general, it was found that decreased an increase ratio both effect coating on can be positive, negative, or even neutral.