The development of technology and drying equipment tackles a triune task: to intensify drying processes, to save energy, to ensure that proper product quality is achieved. This issue is resolved by modern advancements by supplying thermal energy throughout the entire sample volume. The simplest option among the known techniques is to heat wet raw materials by passing an electric current directly, with an external blowing by a hot heat carrier. This paper reports an experimental study of the combined process of drying apple raw materials using direct electric heating. The influence of control factors such as the field intensity and a heat carrier temperature on the kinetic parameters of the process has been determined, namely: the duration of the combined drying of apples, the rate of moisture removal, and a change in the temperature of the sample. It was established that the application of additional electric heating with an electric field intensity of 20–40 V/cm during convective drying with a heat carrier temperature of 25–55 °C reduces the duration of apple dehydration by 3‒5 times. Permissible limits for changing the combinations of basic technological parameters have been determined, as well as the rational modes for treating raw materials in order to ensure the predefined quality of finished products. Such combinations of technological parameters of heating, in particular the intensity of the electric field and air in the dryer, are 30 V/cm+40 °C, and 25 V/cm+55 °C. The energy parameters of the proposed combined technique of drying apple raw materials have been determined. It was established that the specific energy consumption for the removal of 1 kg of moisture at direct electric heating is 2,350–2,400 kJ/kg (0.66 kWh/kg). The study performed could provide a prerequisite for devising an energy-efficient technique for the combined drying of fruit and vegetable raw materials using direct electric heating
Object of research: the process of heating a biological object with various methods of supplying thermal energy, in particular, convective, direct electric and combined methods. Solved problem: intensification of heating of high-moisture biological objects during the drying process. Main scientific results. The expediency of using a combined (direct electric and convective) supply of thermal energy for intensifying heating of raw materials in the drying process has been established. In terms of the duration of the heating process, combined heating is much more effective than using purely convective or direct electric heating. Comparison of the values of the duration of the heating process for a body weighing 0.0028 kg shows that the combined heating occurs 1.5–2.5 times faster. At the same time, the consumption of electrical energy for the selected processing modes is 279–254 J, which is 80–87 % of the total required energy. It has been found that the main control factor in the combined heat supply is the applied voltage of direct electric heating. The area of practical application of the research results: enterprises of the processing industry, specializing in the production of dried products. Innovative technological product: a combined method of heating high-moisture objects during the drying process, which will provide intensive and energy-efficient processing modes while maintaining the established quality of the finished product. Scope of application of the innovative technological product: production of finished food products and semi-finished products.
The object of research is the process of convective and combined drying of apple raw materials treated before dehydration in an ultrasonic bath. The use of pretreatment solves the issue of intensifying the dehydration process and maintaining the quality of the product. Sonication for 5 min reduces the dehydration process by 13.7 %, and at 10 min processing – by 27.8 % compared to traditional convective drying. With increasing processing time to 20 minutes, the dehydration rate deteriorates. Sonication of raw materials for 5 minutes under combined heating does not intensify the dehydration process, and within 10 and 20 minutes it reduces the efficiency of moisture removal. When processed for 10 minutes, the time to reach the final moisture content is increased by 17.2 %, and at 20 min – by 23.4 % compared to control samples. Regardless of the processing time, there is a decrease in the maximum temperature of the samples in the combined drying process. When processed for 5 minutes, the maximum temperature of the samples decreased by 4.3 %, and with 10 and 20-minute processing – by 8.6 % and 12 % compared to the temperature of samples without sonication. The results are explained by the "sponge effect" caused by ultrasonic vibrations and the phenomenon of cavitation that occurs in the liquid during the action of the ultrasonic field. The peculiarity of the pre-sonication before drying is the possibility to intensify the convective dehydration process without increasing the heat carrier's temperature. The use of this type of processing in a combined energy supply will solve the problem of preserving the quality of the finished product by reducing the maximum temperature of the raw material. The research reported here could be a prerequisite for practial design of an energy-efficient electrical system for drying fruit and vegetable raw materials.
This paper gives examples of the implementation of energy-saving measures in public premises. The introduction of energy-saving measures at enterprises significantly reduces the fixed component of industrial expenditures. As a rule, educational institutions, for example, public premises, are financed from the state budget, and saving money on utilities will enable redirecting finances to the development of the university’s educational and scientific base. Thus, the main purpose of implementing such measures is to reduce the cost of maintaining buildings. The measures are divided into three stages. At the first preparatory stage, the problem elements of a building and communications, which require the introduction of energy-saving measures using a special Fluke Ti25 device, are identified. Problem elements of the building structure were determined by complete scanning of the ceiling, walls, and floor with the help of a thermal imager. A large (more than 10 %) difference between indoor air temperature and the temperature of the building element indicates a problem element. The research method is thermographic. The study contains an example of scanning the wall of the premises. The temperature difference between the left and the right sides of the wall is 2.6 °C (the difference with the room temperature is 21 %). This indicates significant heat losses through the wall. At the second stage of information processing, measures to reduce energy consumption were determined. At the third stage of the introduction of energy-saving measures, the measures that directly affect the energy consumption of a building and effective functioning of communications were implemented. The practical relevance of the study is to obtain results and practical recommendations that can be applied in practice to improve the energy efficiency of premises and buildings.
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