Theoretical and experimental substantiation of volumetric infrared irradiation in the thermal processing of medicinal plants

Abstract

Theoretical and experimental substantiation of volumetric infrared (IR) irradiation methods in the thermal treatment of medicinal plants is discussed. The study is based on thermodynamic principles for improving the energy efficiency of optical electrotechnologies formulated in the works of Prof. V. N. Karpov. Within the framework of the theory of irreversible processes, it is shown that the magnitude of the useful energy flux is determined by the combination of thermodynamic forces, kinetic coefficients, and the conditions of interaction between radiation and the treated medium. It is found that the key factor in intensifying thermoradiative processes is the improvement of the uniformity of radiant energy distribution within the material volume rather than increasing temperature gradients. This approach ensures an increase of the “potential driving force” without raising transfer resistance or entropy generation, thereby significantly enhancing energy efficiency. The possibilities for improving efficiency through the control of kinetic coefficients, the use of coupled thermodynamic effects (free convection, thermodiffusion), and the increase of the interaction surface are considered. A hydromechanical principle of coordinated movement of the irradiated medium relative to the gradient of absorbed radiation is proposed providing uniform volumetric irradiation. Based on this principle, a multi-tier technological scheme was developed implementing layer-by-layer processing of the material and efficient utilization of radiant energy without losses. Experimental studies of the drying process of medicinal plants, including fireweed leaves, confirmed that increasing the number of layers enhances moisture removal intensity and reduces specific energy consumption. It is shown that a rational combination of preliminary convective heating and subsequent IR irradiation allows accounting for different forms of moisture binding and prevents the degradation of biologically active substances. Energy savings achieved through the application of the developed methods increase with the initial moisture content of the raw material which confirms their high efficiency and prospects for industrial implementation.