caa a22 4500 463163168 CHVBK 20180406164754.0 cr unu---uuuuu 170326e20070101xx s 000 0 eng 10.1007/s11242-006-9020-4 doi (NATIONALLICENCE)springer-10.1007/s11242-006-9020-4 Internal Heating Effect and Enhancement of Drying of Ceramics by Microwave Heating with Dynamic Control [Elektronische Daten] [Yoshinori Itaya, Shigeru Uchiyama, Shigekatsu Mori] The effectiveness of internal heating for enhancing the drying of molded ceramics is evaluated by both modeling and experiments. In the theoretical analysis, three dimensional drying-induced strain-stress are modeled, and the numerical solutions show that the internal heating generates lower internal stress than continuous convective heating or intermittent convective heating. Microwave drying is examined experimentally to study the effect of internal heating on the drying behavior of a wet sample of a kaolin slab. The drying behavior is compared among three modes: microwave heating, hot air heating and radiation heating. The transient behavior of temperatures in microwave drying is quite different from conventional drying by external heating. In particular, the temperature of the slab drops once in the progress of drying. This phenomenon cannot be predicted adequately by a simple model of one-dimensional heat conduction and moisture diffusion accompanied with an internal heat generation rate given as a linear function of the moisture content. It should be noted that the temperature behavior takes place due to the combined interactions with internal evaporation of moisture by rise in internal vapor pressure and shift of impedance or interference in the applicator. Microwave heating with a constant power above 100 W results in sample breakage due to the internal vapor pressure. However, if the power is dynamically controlled so as to maintain the temperature less than the boiling point of water, the drying succeeds without any crack generation until completion with a significantly faster drying rate than drying in convective heating or in the oven. Springer Science+Business Media B.V., 2006 Microwave drying nationallicence Internal heating nationallicence Ceramics nationallicence Molding nationallicence Crack formation nationallicence Heat and mass transfer nationallicence Dynamic control nationallicence Drying enhancement nationallicence Bi : Biot number [−] nationallicence C 0 : Initial moisture content defined by water weight per unit volume of layer [kg/m3] nationallicence C * : Dimensionless moisture content normalized by initial moisture content [−] nationallicence c p : Specific heat of layer [J/(kg·K)] nationallicence c pw : Specific heat of water [J/(kg·K)] nationallicence f v : Ratio of overall mass transfer coefficient between interface and air to that between surface and air [−] nationallicence H a : Humidity of air [kg-H2O/kg-dry air] nationallicence H s : Saturated humidity at surface temperature of layer [kg-H2O/kg-dry air] nationallicence Le : Lewis number [−] nationallicence Q * : Dimensionless internal heat generation rate [−] nationallicence Q 0* : Dimensionless internal heat generation rate of sample with initial moisture content [−] nationallicence r w : Latent heat of water evaporation [J/kg] nationallicence T : Local temperature [K] nationallicence T 0 : Initial temperature [K] nationallicence T a : Air temperature [K] nationallicence $$\bar{T}$$ : Average temperature of sample [K] nationallicence $$T*$$ : Dimensionless temperature normalized by initial temperature [−] nationallicence T a * : Air temperature normalized by initial temperature [−] nationallicence V : Volume of a slab [m3] nationallicence w 0 : Initial moisture content of a slab with dry basis [kg-H2O/kg-dry solid] nationallicence $$\overline{w}$$ : Average moisture content of a slab with dry basis [kg-H2O/kg-dry solid] nationallicence x * : Coordinate in depth direction (dimensionless depth from surface normalized by thickness of layer) [−] nationallicence x e * : Dimensionless depth of interface from surface [−] nationallicence θ : Dimensionless time defined as Fourier number [−] nationallicence ρ : Density of layer [kg/m3] nationallicence $$\phi_{1}$$ : Correction factor defined by ratio of thermal diffusivity in dry layer to wet layer [−] nationallicence $$\phi_{2}$$ : Correction factor defined by ratio of thermal conductivity in dry layer to wet layer [−] nationallicence φ : Proportional constant in Eq. (10) [−] nationallicence Itaya Yoshinori Department of Chemical Engineering, Nagoya University, 464-8603, Nagoya, Japan aut Uchiyama Shigeru Department of Chemical Engineering, Nagoya University, 464-8603, Nagoya, Japan aut Mori Shigekatsu Center for Cooperative Research in Advanced Science & Technology, Nagoya University, 464-8603, Nagoya, Japan aut Transport in Porous Media Kluwer Academic Publishers 66/1-2(2007-01-01), 29-42 0169-3913 66:1-2<29 2007 66 11242 https://doi.org/10.1007/s11242-006-9020-4 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11242-006-9020-4 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Itaya Yoshinori Department of Chemical Engineering, Nagoya University, 464-8603, Nagoya, Japan aut NATIONALLICENCE 700 1- Uchiyama Shigeru Department of Chemical Engineering, Nagoya University, 464-8603, Nagoya, Japan aut NATIONALLICENCE 700 1- Mori Shigekatsu Center for Cooperative Research in Advanced Science & Technology, Nagoya University, 464-8603, Nagoya, Japan aut NATIONALLICENCE 773 0- Transport in Porous Media Kluwer Academic Publishers 66/1-2(2007-01-01), 29-42 0169-3913 66:1-2<29 2007 66 11242 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer