Determinacion coeficiente convectivo de materia en el secado de sólidos

Abstract

A mathematical correlation to determine the mass coefficient, during the evaporation of water from a wet surface, was developed for their application in wet air with low psychometric differential and with air temperature above 60°C. The classic theory that has been used in order to get heat and mass convective coefficients, through non-dimensional parameters and phenomenological analogies, turns out to be valid only for dry air. In the particular case of solids drying, where operation requires to be performed under controlled drying rates, in order to prevent physical damage from affecting the product, is necessary to operate on a wet bulb temperature above 40°C or at moderate psychometric differential. When we work under those ranges of temperature, the expressions that relate heat and mass convective coefficients show errors between 26% and 113% for wet temperature between 30°C and 70°C and psychometric difference of 30°C. The expression that has been given for this application is stated as a function of the following: heat transfer coefficient, wet bulb temperature, and psychometric differential. The obtained results allow to settle down that, for the extreme conditions of wet bulb temperature and psychometric differences assigned before, the error is located among -1.4% to 2.14%, regarding the obtained through the classic methodology. The obtained correlation has polynomial form, of easy operation and viable of being incorporate to any simulation pattern for the prediction of the dynamics of the drying.