CONVECTION HEAT TRANSEER COEFFICIENTS AT CONVECTIVE DRYING OF POROUS MATERIALS*

ABSTRACT Our measurements proved that the convective heat transfer coefficient (h) has a larger value hwet at the constant drying rate period and after that it falls down to a minimum one: hdry in the equilibrium dried state (see Fig.1). Our measurements showed also that the heat of vaporisation in the last phase of the falling drying rate period is far greater than it was in the constant drying rate period (see Fig.10). Our first measurements were made on a gypsum plate. Afterwards we carried out measurement research with fine glass powder and cement-perlite plate and determined hwet and hdry heat transfer coefficients as function of Reynolds number. All of these measurements confirmed our establishment that hwet is far greater than hdry .