Temperature in the Period of Decreasing Drying Rate of Thin Flat Capillary-Porous Wet Materials

The article is devoted to the development of new methods for processing experimental data for drying processes based on the dependence of dimensionless temperature on generalized complex variables characterizing the most general patterns of drying in the period of its rate decreasing. The generalized drying time, the ratio of drying time over drying periods, and the ratio of the current moisture content to the critical one are used as generalized complex variables. The dimensionless temperature complex represents the relationship between the ratio of the temperature difference in the period of rate decreasing and the temperature difference in the period of constant rate. A method for determining the average temperature from the solution of an unsteady heat equation for thin flat bodies based on the Predvoditelev and Fourier criteria is considered. For the case of heating a thin flat body at a constant ambient temperature, a method for calculating the average temperature using the heating rate of a wet body is given based on the heat balance equation for the second drying period. The methods for determining the average temperature for the period of decreasing drying rate are presented; they are based on complex variables, viz. generalized drying time and the ratio of drying time by period. Processing the experiment using a dimensionless temperature complex makes it possible to determine the average temperature of the material, taking into account the influence of important characteristics of drying kinetics on the process. The processing of the experiment based on the temperature coefficient of drying using experimental temperature curves is presented. The obtained formulas are checked to establish the accuracy of the calculated temperature values from the experimental temperature curve. A comparison of the obtained calculated temperature values with the experiment is given in the tables for all the materials under study.

1. Lykov A. V. (1968) Drying Theory. Moscow, Energiya Publ. 472 (in Russian).

2. Akulich P. V. (2010) Calculations of Drying and Heat Exchange Installations. Minsk, Belaruskaya navuka Publ. 443 (in Russian).

3. Krasnikov V. V. (1973) Conductive Drying. Moscow, Energiya Publ. 288 (in Russian).

4. Sazhin B. S. (1984) Scientific Fundamentals of Drying Technique. Moscow, Khimiya Publ. 320 (in Russian).

5. Rudobashta S. P. (2015) Thermal Engineering. Moscow, Pero Publ. 672 (in Russian).

6. Vasiliev V. N., Kutsakova V. E., Frolov S. V. (2013) Drying Technology. Fundamentals of Heat and Mass Transfer. St. Petersburg, GIORD Publ. 222 (in Russian).

7. Lykov A. V. (1967) Theory of Heat Conductivity. Moscow, Vysshaya Shkola Publ. 599 (in Russian).

8. Lykov A. V. (1961) Theoretical Foundations of Construction Thermal Physics. Minsk, Publishing House of the Academy of Sciences of the BSSR. 519 (in Russian).

9. Lykov A. V., Mikhaylov Y. A. (1963) Theory of Heat and Mass Transfer. Moscow–Leningrad, Gosenergoizdat Publ. 535 (in Russian).

10. Kuts P. S., Ol’shanskii A. I. (1977) Some Features of Heat and Moisture Transfer and Approximate Methods of Calculating the Drying Kinetics of Moist Materials. Journal of Engineering Physics, 32 (6), 650–656. https://doi.org/10.1007/BF00862568.

11. Rabinovich G. D. (1966) Calculation of Radiative-Convective Recuperators. Journal of Engineering Physics, 10, 140–143.

12. Ol′shanskii A. I. (2016) Regular Thermal Regime and Influence of Heat and Mass Transfer Similarity Criteria on the Process of Convective Drying of Porous Ceramics. Journal of Engineering Physics and Thermophysics, 89 (1), 38–49. https://doi.org/10.1007/s10891-016-1351-6.

13. Filonenko G. K., Lebedev P. D. (1952) Drying Plants. Moscow, Energia Publ. 263 (in Russian).

14. Lykov A. V. (1954) The Phenomena of Transfer in Capillary-Porous Bodies. Moscow, The State Publishing House of the Technical-Theoretical Literature. 296 (in Russian).

15. Ol’shanskii A. I. (2016) Investigation of the Drying of Thin Materials with the Use of Generalized Complex Variables. Journal of Engineering Physics and Thermophysics, 89 (4), 886–895. https://doi.org/10.1007/s10891-016-1450-4.

16. Ol’shanskii A. I., Zhernosek S. V., Gusarov A. M. (2022) Investigation of Heat and Mass Transfer in the Processes of Heat Treatment and Drying of Thermal Insulation Materials. Enеrgеtika. Izvestiya Vysshikh Uchebnykh Zavedenii i Energeticheskikh Ob’edinenii SNG = Energetika. Proceedings of CIS Higher Education Institutions and Power Engineering Associations, 65 (2), 156–168. https://doi.org/10.21122/1029-7448-2022-65-2-156-168 (in Russian).

17. Ol’shanskii, A. I., Gusarov, A. M. (2017) Experimental Study of the Kinetics of Drying of Thin Plane Moist Materials by the Regular-Regime Method Using Generalized Complex Variables. Journal of Engineering Physics and Thermophysics, 90 (3), 665–678. https://doi.org/10.1007/s10891-017-1614-x.