Abstract
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
Highlights
In providing the population of the Earth with food, the fruits and vegetables that are rich in vitamins play an important role
The simplest classification is to divide them into natural drying and the drying involving special energy sources
The study results indicate a significant increase in the drying rate due to the pre-treatment using a pulsating electric field (PEF)
Summary
In providing the population of the Earth with food, the fruits and vegetables that are rich in vitamins play an important role. With one or two-time harvesting per year, the consumer properties of produce are ensured by long-term storage in fresh form or when canned. One of the oldest and most reliable techniques of conservation is drying. The activity of microorganisms stops, and nutrients are saved [1]. In the technology of moisture removal, the main energy process is thermal drying. Review papers [2,3,4] often mention drying techniques in the historical aspect along with different sources of thermal energy and appropriate methods of supplying heat to the dried material. The simplest classification is to divide them into natural drying and the drying involving special energy sources
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