Internal heating effect and enhancement of drying of ceramics by microwave heating with dynamic control

  • Yoshinori Itaya
  • Shigeru Uchiyama
  • Shigekatsu Mori
Chapter

Abstract

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.

Keywords

Microwave drying Internal heating Ceramics Molding Crack formation Heat and mass transfer Dynamic control Drying enhancement 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Araszkiewicz, M., Koziol, A., Oskwarek, A., Lupinski, M.: Microwave drying of porous materials. Dry. Technol. 22(10), 2331–2341 (2004)CrossRefGoogle Scholar
  2. Di, P., Chang, D.P.Y., Dwyer, H.A.: Heat and mass transfer during microwave steam treatment of contaminated soils. J. Environ. Eng. 126(12), 1108–1115 (2000)CrossRefGoogle Scholar
  3. Gong, Z.X., Mujumdar, A.S., Itaya, Y., Mori, S., Hasatani, M.: Drying of clay and nonclay media: Heat and mass transfer and quality aspects. Dry. Technol. 16(6), 1119–1152 (1998)Google Scholar
  4. Islam, Md. R., Ho, J.C., Mujumdar, A.S.: Simulation of liquid diffusion-controlled drying of shrinking thin slabs subjected to multiple heat sources. Dry. Technol. 21(3), 413–438 (2003)CrossRefGoogle Scholar
  5. Itaya, Y., Taniguchi, S., Hasatani, M.: A numerical study of transient deformation and stress behavior of a clay slab during drying. Dry. Technol. 15(1), 1–21 (1997)Google Scholar
  6. Itaya, Y., Mori, S., Hasatani, M.: Effect of intermittent heating on drying-Induced strain-stress of molded clay. Dry. Technol. 17(7&8), 1261–1271 (1999)Google Scholar
  7. Itaya, Y., Okouchi, K., Mori, S.: Effect of heating modes on internal strain-stress formation during drying of molded ceramics. Dry. Technol. 19(7), 1491–1504 (2001)CrossRefGoogle Scholar
  8. Itaya, Y., Uchiyama, S., Cabrido, E.F., Hatano, S., Mori, S.: Uniformity of microwave field intensity by random reflection in a fluidized bed of electrically conductive beads. Kagaku Kogaku Ronbunshu (J. Chem. Eng. in Japanese) 29(3), 339–344 (2003)CrossRefGoogle Scholar
  9. Kowalski, S.J., Rybicki, A.: Qualitative aspect of convective and microwave drying of saturated porous materials. Dry. Technol. 22(5), 1173–1189 (2004)CrossRefGoogle Scholar
  10. Kowalski, S.J., Rajewska, K., Rybicki, A.: Mechanical effects in saturated capillary-porous materials during convective and microwave drying. Dry. Technol. 22(10), 2291–2308 (2004)CrossRefGoogle Scholar
  11. Lehne, M., Barton, G.W., Langrish, T.A.G.: Comparison of experimental and modelling studies for the microwave frying of ironbark timber. Dry. Technol. 17(10), 2219–2235 (1999)Google Scholar
  12. Liu, F., Turner, I.W., Bialkowski, M.E.: A finite-difference time-domain simulation of the power density distribution in a dielectric loaded microwave cavity. J. Microwave Power Electromag. Energy 29(3), 138–148 (1994)Google Scholar
  13. Perre, P., Turner, I.W.: A complete coupled model of the combined microwave and convective drying of softwood in an oversized waveguide. Proceedings of the 10th International Drying Symposium (IDS’96), Krakow, Poland, vol. A, pp. 183–194 (1996)Google Scholar
  14. Turner, I.W., Jolly, P.G.: The modelling of combined microwave and convective drying of a wet porous material. Drying Technology 9(5), 1209–1270 (1991)Google Scholar
  15. Turner, I.W.: Astudy of the power density distribution generated during the combined microwave and convective drying of softwood. Proceedings of the 9th International Drying Symposium (IDS’94), Gold Coast, Australia, pp. 89–111 (1994)Google Scholar

Copyright information

© Springer Science+Business Media B.V. 2006

Authors and Affiliations

  • Yoshinori Itaya
    • 1
  • Shigeru Uchiyama
    • 1
  • Shigekatsu Mori
    • 2
  1. 1.Department of Chemical EngineeringNagoya UniversityNagoyaJapan
  2. 2.Center for Cooperative Research in Advanced Science & TechnologyNagoya UniversityNagoyaJapan

Personalised recommendations