ELECTROMAGNETIC DRYING OF WET MATERIALS WITH A SMALL DEPTH OF PENETRATION OF MICROWAVE RADIATION IN THE CONDITIONS OF HEAT REMOVAL BY RADIATION AND CONVECTION. III. STAGE OF FALLING DRYING RATE

• Main Authors: Vladimir V. Salomatov, Vadim A. Karelin, Vasiliy V. Salomatov
• Format: Article
• Language: Russian
• Published: Tomsk Polytechnic University 2020-04-01
• Series: Известия Томского политехнического университета: Инжиниринг георесурсов
• Subjects: microwave radiation; electromagnetic drying; capillary-porous array; heat radiation; convection; a.v. lykov heat-moisture transfer equation; stage of falling drying speed
• Online Access: http://izvestiya.tpu.ru/archive/article/view/2601/2208
• ISSN: 2500-1019; 2413-1830

The relevance of the research is dictated by the need to develop mathematical models of microwave heating and MV-drying of wet materials to obtain technologically optimal and cost-effective modes. This publication is a continuation of the articles of the same authors in The Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, in which using mathematical modeling, the authors have studied in details the process at the first and second stages of drying – the heating stage, when heat exchange between the surface of a wet body and the environment occurs due to radiation and convection, and microwave energy is absorbed by the surface layer owing to its small penetration depth, as well as the stage of constant drying rate. The authors constructed the asymptotic solutions of this nonlinear problem for small and large values ​​of dimensionless time, which are demanded by engineering practice, both for parametric analysis and for performing operational calculations. The approach associated with the consideration of the third stage – the stage of the falling drying rate, is based on determination of the basic drying equation, which provides the relationship between heat transfer and moisture exchange using the Rebinder criterion. The aim of the researchis tostate the problem of the third stage of microwave drying of a wet material – the stage of a falling drying rate, and to implement a theoretical solution to determine temperature field distribution over the layer thickness and the drying rate. The object of the research is a flat layer of wet material – coal, sand, wood, etc. capillary-porous arrays, which are affected by microwave radiation. Such materials have a high dielectric constant and, as a result, very effectively absorb microwave radiation, which is almost 100% converted to thermal energy. The research methodsare associated with mathematical modeling, which are based on the equations of Maxwell’s electrodynamics and heat and moisture transfer by A.V. Lykov. In this article, when assessing the parameters of heat and moisture transfer, heat transfer accounting is conducted in more details than mass transfer. One of the features of this problem is the consideration of materials with a small depth of absorption, whereby the source term in the system of equations for heating is in the boundary condition. The temperature and moisture content of the body to be dried were determined in the mode of the falling drying speed, the calculated analytical ratios for small and large parameters of time were obtained.