On invariants of a convective drying process

The Lewis relation is proved to be valid in the absence of an analogy between heat and mass transfer. Invariance of temperature and equilibrium curves is established for some drying processes.Notation I enthalpy - c heat capacity - t, temperature of the gas and a material, respectively - u, u_s, u_cr.red, u_max.h, u_eq mean, surface, critical reduced, maximum hygroscopic, equilibrium moisture content of the material, respectively - X air moisture content - q_b binding energy of moisture with the material - r₀ heat of liquid evaporation at 0°C - D vapor diffusion coefficient in the gas calculated from the moisture content gradient - f specific contact surface of phases, m²/kg - l determining dimension - X, t moisture content and temperature of the gas in the boundary layer - y normal to the contact surface of phases - , interphase heat and mass transfer coefficients - gas thermal conductivity - density - time - Rb=c_m(–d/du)r Reminder number - Nu=l/, Nu_m=l/D heat and mass transfer Nusselt numbers. Indices - g, gas, m material - s surface - d.g dry gas - l liquid - v vapor - sat saturated - w.t wet-bulb thermometer - f final, index 0 stands for parameters at the dryer inlet Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 442–448, October, 1992.