CONVECTION HEAT TRANSEER COEFFICIENTS AT CONVECTIVE DRYING OF POROUS MATERIALS*

Our measurements proved that the convective heat transfer coefficient (h) has a larger value h_wet at the constant drying rate period and after that it falls down to a minimum one: h_dry 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 h_wet and h_dry heat transfer coefficients as function of Reynolds number. All of these measurements confirmed our establishment that h_wet is far greater than h_dry.