Development and Identification of a Mathematical Model for Nonstationary Heat and Mass Transfer in the Water/Air System with Forced Convection

摘要

Mathematical description of nonstationary heat and mass transfer in the water/air system in a glass round weighting cup has been developed for air in the Memmert UFE 400 drying cabinet equipped with forced circulation. The liquid surface is in contact with air at the constant temperature. The liquid is constrained by a glass plate underneath through which heat exchange with the air is also ensured. The incoming heat includes the heat transferred by means of convection to the upper surface of the water; the heat transferred by means of convection to the glass plate and the heat generated by not equimolar transfer of the substance. Equations are given to calculate mass transfer coefficients in case of forced convection for water/air systems, and air-to-water, air-to-glass-plate and free-convection-in-air heat transfer coefficients. The equation has been recorded to determine the water surface temperature that causes evaporation to start. To identify the mathematical model, two experiments have been done to measure the water heating temperature and study the kinetics of its evaporation. Experimental and calculation data have been satisfactorily reconciled.