Effective moisture diffusivity

Although effective moisture diffusivity decreased normally in osmotically treated fruits, there are some quality characteristics that are always better in osmodehydrated-dried than in fresh-dried ones. 

Gabas, A.L., Telis-Romero, J., and Menegalli, EC. Determination of concentration dependent effective moisture diffusivity of plums based on shrinkage kinetics. Transport Phenomena in Food Processing, J. Welti-Chanes, J.F. Velez-Ruiz and G.V. Barbosa-Canovas, eds., CRC Press, Boca Raton, FL, pp. 153, 2002. 

Approximate Ranges of Effective Moisture Diffusivity in Some Materials... 

Effective thermal conductivity and effective moisture diffusivity are related to internal heat and mass transfer, respectively, while air boundary heat and mass transfer coefficients are related to external heat and mass transfer, respectively. The above transport properties are usually coefficients in the corresponding flow rate and driving force relationship. The equilibrium material moisture content, on the other hand, is usually related to the mass transfer driving force. 

Effective moisture diffusivity and effective thermal conductivity are in general functions of material moisture content and tanperature, as well as of the material structure. Air boundary coeffiamts are functions of the conditions of the drying air, that is humidity, tonperature, and velocity, as well as system geometry. Equilibrium moisture content of a given material is a function of air humidity and temperature. The drying constant is a function of material moisture content, temperature, and thickness, as weU as air humidity, tonperature, and velocity. 

Despite the limited data of effective moisture diffusivity, a lot of data are reported in the literature for thermal conductivity. Data for mainly homogeneous materials are available in handbooks such as the Handbook of Chemistry... 

Effective moisture diffusivity Air boundary mass transfer coefficient Effective thermal conductivity Air boundary heat transfer coefficient... 

Tong, C.H. and Lund, D.B., Effective moisture diffusivity in porous materials as a function of temperature and moisture content, Biotechnol. Prog., 6(l) 67-75,1990. 

Several researches have been carried out to understand the mechanism of moisture movement in clay during drying. Newitt et al. [12] and Wakabayashi [13] investigated the moisture movanent in clay by liquid diffusion and vapor diffusion, which affect the drying characteristics particularly the falling rate. They concluded that the liquid diffusion dominates the movement until about 20%-dry basis in moisture content for stoneware clay and 30% for the mixture of 80% Kibushi clay and 20% feldspar. Wakabayashi [14] also evaluated the effective moisture diffusion coefficient of some sorts of clay such as Kibushi, Gairome, stoneware, feldspar, and their mixtures. The effective diffusion coefficient is available for the brief description of the moisture movement behavior. The effective diffusion coefficient D can be defined by... 

The inflnence of the openness of a fiber matrix on the effective moisture diffusion is also observed in the diffusion of water vapor throngh wood pulp and paper sheets. 

Despite the limited data of effective moisture diffusivity, a lot of data are reported in the literature for thermal conductivity. Data for mainly homogeneous materials are available in handbooks such as the Handbook of Chemistry and Physics [91], the Chemical Engineers Handbook [92], ASHRAE Handbook of Fundamentals [93], Rohsenow and Choi [94], and many others. For foods and agricultural products, data are available in Refs. [83,88,95-97]. For selected pharmaceutical materials, data are presented by Pakowski and Mujumdar [98]. 

Dr effective moisture diffusion coefficient AH, heat of sorption... 

If the effective moisture diffusion coefficients are calculated from Eqs 3.2 and 3.3, it can be noted that the coefficient in the case of SSD would be higher when the medium temperature is higher than 140 °C. This corresponds to the experimental drying rate data shown in Fig. 3.7 it can be seen that the inversion temperature of the whole drying process was approximately 140 °C. 

M.A. Ruiz - Cabrera, M.A. Salgado-Cervantes, K.N. Waliszewski-Kubiak and M.A. Garcia-Alvarado, The Effect of Path Diffusion on the Effective Moisture Diffusivity in Carrot Slabs, Drying Techn., 15, 1 (1997) 169-181. 

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