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We have tested the microwave device of continuous operation for the thermal treatment of plant materials, which was developed and designed to implement microwave technologies in the industry. The purpose of the tests was to assess the effectiveness of the microwave device by the indicators of quality of the obtained material and energy consumption determined by the efficiency of the conversion of microwave energy into the internal energy of the material. The effects of microwave treatment of a straw substrate for tree-destroying fungi were studied. The treatment quality was determined by the yield of Oyster (Pleurotus) mushrooms, grown on the obtained substrate. Microwave treatment was carried out in various modes, which differed in the value of specific power. When analyzing the effectiveness of microwave treatment, the results were compared with the data obtained during the application of the traditional technology of straw sterilization. It was shown that the harvest of Oyster mushrooms increased by 11%. It was found that under the optimal mode, specific power was qv=8.68·105W/m3, final temperature was t=96°С, duration of treatment was 180 s. Based on the thermal calculations, the values of the microwave chamber efficiency ηcwere calculated; under the optimal mode, ηc=62%. The influence of the microwave treatment on the sowing characteristics of seed wheat grain was studied. The effectiveness of the microwave treatment was determined by the values of laboratory germination and seed germination energy. Under the optimal mode, the output power of magnetrons was ΣPout=0.6kW, the grain consumption was G=2.1·10-2kg/s. The study of the microwave device operation showed that for this design, in order to ensure stable and uniform movement of the material along the product pipeline, it is necessary to maintain the movement speed that is not higher than 0.5 m/min. It is recommended to apply the tested microwave device of continuous operation on specialized farms

The object of research: the process of heat exchange in a packing in the form of a dense layer of crushed stone as part of a thermal regenerator designed to utilize the low-grade heat of the air in a greenhouse. Investigated problem: increasing the efficiency of air heat accumulation in the greenhouse during the daytime by a regenerative heat exchanger with a granular packing. Conducting experimental tests of regenerator models with a packing in the form of a dense layer of granular material under natural conditions is necessary to improve the design and optimize technological parameters. The main scientific results: the analysis of temperature curves of air changes at the inlet and outlet of the regenerator installed in the mock-up greenhouse with a volume of 0.25 m3, and the packing material was carried out. During the heating period of the nozzle, the accumulated heat was Q=8•104 J, which can be used when the temperature in the greenhouse decreases. During the pause, the loss from the heat exchange channel to the environment is 48,000 J. The duration of the period was 358 min, while the average heat flux corresponded to 2.2 W. Heat losses during the pause period are significant due to its duration, however, the average heat transfer coefficient has a low value of k=2.3 W/m2K, so strengthening the insulation of the heat exchange channel is irrational. The area of practical use of the results of the study: greenhouses, allowing the possibility of installing additional heat exchange equipment. Innovative technological product: the innovativeness of the technical solution is determined by the possibility of using the heat of the air in the greenhouse and the implementation of contact heat exchange between the air flow and the packing particles. The design of the regenerator, the simplicity of its manufacture and operation, as well as the efficiency of air heat accumulation in the greenhouse during the daytime, allow to recommend it for use in greenhouse farms. The scope of the innovative technological product: regenerative heat exchangers with a dense layer of granular material for the utilization of low-grade air flows generated in food production enterprises, ventilation systems and greenhouses

The object of research is the pulsating flow of drilling fluid in the drill string. One of the most problematic places is pressure loss due to friction forces distributed along the length of the flow and concentrated in its nodes (threaded joints and pipe bends). In the course of the study, transformation methods were used that allow the drill string to be represented in the form of straight pipes – elements with distributed parameters connected by different inhomogeneities. This makes it possible to reduce the characteristics of the pulsating flow of the drilling fluid to the determination of the lumped parameters of the inclusions, the limiting conditions at the beginning and end of the drill pipes, as homogeneous sections of the drill string. In turn, pressure losses in the drill string during rotary drilling were divided into two types of losses. These are losses along the entire length of the column (flow) and local pressure losses, which are obtained only in certain places of the liquid flow (for example, tool joints, etc.), due to the fact that the flow suffers local deformation. It has been found that from a technological point of view, the most favorable well diameter is the one at which the flow resistance in the pipes is equal to the resistance in the annulus. This is due to the fact that during the flow of the drilling fluid, the speed of the turbulent flow decreases only at the walls of the pipe. Therefore, under the action of centrifugal forces on pipe bends, as in heterogeneities, when local pressure losses occur due to separation of the transit flow, the pipe diameter narrows due to the accumulation of solid particles in whirlpool zones and flow velocities. With a smooth turn of the pipe, the specified separation may be absent. In this case, local pressure losses are largely due to the occurrence of a «steam vortex» at the turn (a helical movement caused by the action of inertial forces). Therefore, a necessary condition for rotary drilling is the continuous circulation of the flushing solution, the complete or partial cessation of which makes further drilling impossible. In this case, the drilling process slows down or leads to an accident. This is due to the accumulation of the hard phase in the places where whirlpools appear. The research results will be useful to scientists and specialists in the oil and gas industry in the physical modeling of well flushing processes in the process of drilling and designing technological flushing processes.

The results of the development of a regenerative-type heat exchange unit for greenhouses are presented. The creation of a soil regenerator is conditioned by energy and economic expediency. In spring in the daytime, the air in greenhouses is intensely heated by solar radiation, and at night it can be cooled below the allowable temperature. Heat accumulation during the day and using this heat at night will reduce the need for heaters even to their complete exclusion. The soil regenerator contains a dense layer of granular material that is blown through by the air from the inner space of a greenhouse. This solution makes it possible to intensify significantly the heat exchange. To determine the mean intercomponent heat exchange factor, the empirical dependence, taking into consideration the effect of duration of the heat exchange process, was obtained. We developed the procedure of thermal design calculation of a regenerator, using which the main geometric characteristics of the heat exchange area are determined. The results of the calculation of the soil regenerator for a greenhouse with the surface area of 18m2for the conditions of the warm continental climate were presented. The developed soil regenerator contains 5channels that are 5.75m long, filled with rubble. It was obtained that for the average solar radiation flow Qc=2,160W and the duration of operation of the soil regenerator τΣ=6hours, the accumulated heat at night can be consumed for 2.6hours at the average ambient temperature t1=7°C. As the ambient temperature rises, the time of regenerator operation will increase. The proposed soil regenerator is characterized by the design simplicity and its application will lead to an increase in energy costs to maintain the temperature mode in a greenhouse

We present results of experimental work on studying the drying of a dense layer of grain using microwave heating. We investigated a series of techniques to supply heat to grain to assess energy efficiency of a microwave field. We studied the following ways of drying: a microwave method, a pulsating microwave method, a microwave-convective cyclic method with blow of a layer with heated air flow and air without preheating, simultaneous microwave-convective drying method. Studying the kinetics of drying in a microwave field showed that we can divide the process into heating periods (zero drying rate), constant (first drying rate) and falling (second drying rate). These periods are characteristic for drying of colloidal capillary-porous bodies at other methods of heat supply. We obtained empirical relationships for the drying rate and the average temperature of grain in the first period based on the generalization of experimental data on the study on drying of grain of buckwheat, barley, oats, and wheat. We presented kinetic dependences in a dimensionless form. They summarize data on the studied grains. The aim of comprehensive studies of various methods of heat supply during drying was determination of the optimal method and rational operational parameters, which ensure high intensity of the process and the required quality of the finished product with minimal energy consumption. All studies took place under identical conditions and for the same grain (oats) to ensure the accuracy of the comparison. We determined that the most preferable method is a simultaneous microwave-convective energy supply without air preheating, which minimizes specific energy consumption. Experimental studies on drying using a microwave field made possible to select the required process parameters: power, heating rate, mass, and form of loading. We plan to develop a technology for drying of grain using microwave energy based on the study data

We considered problems of water scarcity elimination in arid regions of the planet and analyzed modern water producing systems. We showed the prospects of obtaining of water from atmospheric air directly while cooling it below the dew point using refrigeration units. We proposed to use absorption-type cooling systems with a water-ammonia solution as a working liquid as cooling units in regions with an excess of solar energy. We noted that low energy characteristics of heat-using refrigeration cycle, with main problems associated with non-calculated losses of refrigerant (ammonia) during transportation through AWRU refluxer hamper a widespread use of absorption water-ammonia refrigerating units (AWRU) in systems for obtaining of water from atmospheric air. This contribution is particularly noticeable in operation of AWRU in a wide range of outdoor air temperatures. We performed modeling of heat and mass exchange processes of a lifting section of an AWRU refluxer to find methods for elimination of ammonia transportation losses. At the heart of model representations were equations of heat and mass balances, and we took into account resistance of a diffusion process at radial movement of a vapor flow to a wall of a refluxer in modeling. A preliminary analysis of thermal resistance of reflux film showed its small contribution to the total resistance and we ignored it subsequently. As a result of modeling, we found a significant (up to 36 °C) temperature difference between a flow inside a refluxer and its wall. Experimental studies of a serial AWRU confirmed the modeling results. The obtained results made possible to propose the original design of a heat-insulating casing of an AWRU refluxer with variable thermal resistance with a corresponding change in the outside air temperature. This gave possibility to increase energy efficiency from 18 to 36 % and productivity of systems for obtaining of water from atmospheric air.

We report results of experimental research into effects of heat treatment of different plant materials in a microwave field. The effects of seed bio-stimulation are investigated, as well as features of drying and the influence of thermal treatment on the properties of moistened straw. A procedure is proposed for calculating a threshold time of seed exposure to a microwave field, compiled on the basis of hypothesis on the emergence of a bio-stimulation effect. We identified a cascade pressure growth in a container with humid grain when the layer’s temperature exceeds 70 о С. The moisturizing effect of the lower layer of grain was established during its drying in MW field under conditions of a leakproof bottom. It is shown that at an initial moisture content in grain of 20 %, after 14 minutes of drying, the moisture content of the upper layer reached 15.5 %, of the middle layer – 14.5 %, of the lower layer – 21.6 %. It was established that performance efficiency of a microwave chamber substantially depends on the loading volume, material’s type, and moisture content. The chamber’s performance efficiency while heating water can reach 90 %, the chamber’s performance efficiency when loaded with grain does not exceed 67 %. To estimate energy effectiveness of using microwave energy, a dependence is proposed, which includes power output of the magnetron, load volume, and the value of performance efficiency. Dependences for the calculation of performance efficiency when loading a material are proposed to be established experimentally

Experimental studies of heat exchange between a dense layer of granular material and a stream of heated air have been carried out. As a granular material, claydite and gravel were used in a moving and a stationary layer. Temperature curves were obtained for the air flow and the solid component at the inlet and outlet of the installation. The shape of the curves indicates presence of two distinct zones with different heating rates. It was stated that it is expedient to set the heating period in the heat accumulators with a stationary bed within the first period which is characterized by a high heating rate. When calculating duration of the heating period, it is rational to take the value of the final material temperature 10 ‒ 15 % lower than the temperature of the heating air at the inlet. It was established that the coefficient of intercomponent heat exchange depends on the gas velocity, the velocity of the bed motion, the gas temperature at the input to the installation and the process duration. It was found that the curves of the dependence of the coefficients of intercomponent heat exchange on the process duration are described by a sigma function. Intensity of heat transfer for a moving layer in the investigated region was commensurable or somewhat higher than that for a stationary layer. It was shown that claydite is the preferred material for a granular packing. The time to onset of a stationary mode for a moving claydite layer was reduced by 2.4 times in comparison with gravel layer and by 2.2 times for a stationary layer.

This paper reports a study of the thermoacoustic phenomena in steam-generating channels of the cooling system of heat-loaded devices. The examined cooling modes are characterized by surface boiling of the heat carrier, which occurs due to high heat flows at the cooled surface and large underheating of the flow core to the saturation temperature. Under such conditions, high-frequency pulsations of acoustic pressure may occur in cooling channels. It has been established that the emergence of thermoacoustic oscillations could lead to the formation of a standing wave in the channel, one of the conditions for whose formation is the presence of a wave reflection boundary. We have proposed a mathematical model describing the generation of thermoacoustic vibrations in a cooling channel. It was assumed that fluctuations with a high amplitude arise due to the resonance observed when the frequency of forced vibrations of steam bubbles coincides with the vapor-liquid column's natural frequency of vibrations or their harmonics. To calculate the amplitude of pressure fluctuations in the channel, the dependence has been derived, which takes into consideration the viscous dissipation of energy and energy losses at the ends of the channel. It has been shown that when approaching the resonance, the contribution of volumetric viscosity to the viscosity absorption factor increases. It has been established that for the examined conditions the losses of energy on the walls of the channel and losses in the boundary layer could be neglected. We have calculated the amplitude of thermoacoustic pressure fluctuations for conditions corresponding to actual processes in surface-boiling cooling channels. The reported procedure is proposed to be used in the design of liquid cooling systems for heat-loaded devices for which cooling modes imply a significant underheating of the heat carrier to a saturation temperature, as well as surface boiling

The paper considers the issue on ensuring a thermal regime of the magnetron's anode unit by replacing an air-cooling system with the system of liquid cooling. It has been argued that a liquid cooling system is most suitable for magnetrons, for which currently an air-cooling system is implied, although they are not designed for a continuous operation in the structure of industrial microwave installations. Arranging the system of liquid cooling would makes it possible for a magnetron to work over long time without overheating and under favorable conditions, which rule out a possibility to clog the heat exchange surface with particles and dust, as well as the occurrence of overheating of the anode unit's surface. The basic element of the proposed system for liquid cooling is a cooling jacket, which represents an annular channel made from a heat-conducting material. Cooling jacket is mounted directly on the anode unit; in this case, a compression ratio of surfaces and the thickness of an air gap must ensure a minimum total thermal resistance. In order to determine heat transfer coefficients, an empirical dependence was established, which reflects the fact that when cooling the anode units the rational regimes are the viscous and transitional motion modes. The basic thermal characteristics of the cooling process have been defined, which include a coefficient of heat transfer, change in a heat-carrier temperature, the maximally permissible temperature at inlet. Calculations were carried out for two types of heat-carriers: water and a 54% aqueous solution of ethylene glycol. A circuit for the system of liquid cooling has been proposed, which implies cooling from 1 to 6 magnetrons. Applying a given circuitry and choosing the rational estimated modes make it possible to solve the task on improving production efficiency, as well as reliability of microwave equipment.

Mathematical models of heating wet materials in a microwave field are analyzed. A thermal conductivity model is presented that considers two internal sources of heat, positive and negative. A negative heat source considers moisture output during drying of the material. A formula is obtained for calculating the temperature of a semi-bounded body under the action of internal heat sources for boundary conditions of the first kind. The results of calculations of the temperature of water and a dense layer of wheat grain are presented, depending on the duration of the microwave field and the specific power for the heating period. It is shown that in order to obtain reliable results, it is necessary to correctly set the efficiency of the microwave chamber. The results of calculations of moisture content and temperature of a layer of wheat grain for a period of constant drying speed are presented.