EFFECT OF FREEZING TEMPERATURE AND HEAT FLOW IN SUBLIMATION DRYER ON DRYING EFFICIENCY

ABSTRACT

During the research work, it was achieved to distribute the temperature in the drying chamber by one norm to the raw material by changing the freezing and heat transfer pipes of a conventional vacuum sublimation device from a circular shape to an oval shape and installing an additional heat transfer pipe structure. It was found that the heat capacity released increased by an average of four times due to an increase in the working surface of the heat transfer pipe. Using the optimal heat load in sublimation drying of dates, figs and melons, the technological efficiency of the process was proven, and on this basis an improved new construction of a vacuum-sublimation dryer was developed. During the experiments carried out, the effect of heat flow on the duration of the drying process and the effect on the final moisture content of the product, freezing temperature and the summing drying time of the form and sizes of raw materials were studied, and the results obtained were reflected in a tabular and graphical view. The level of organoleptic indicators (shape, size, color, smell and taste,) of dried products was achieved by 95÷98% preservation.

АННОТАЦИЯ

В ходе научно-исследовательской работы было достигнуто распределение температуры в сушильной камере на одну норму по отношению к сырью путем изменения формы труб для замораживания и теплопередачи обычного вакуумного сублимационного устройства с круглой на овальную и установки дополнительной конструкции труб для теплопередачи. Было установлено, что выделяемая теплоемкость увеличилась в среднем в четыре раза за счет увеличения рабочей поверхности теплопередающей трубы. При использовании оптимальной тепловой нагрузки при сублимационной сушке фиников, инжира и дынь была доказана технологическая эффективность процесса, и на этой основе была разработана усовершенствованная новая конструкция вакуумно-сублимационной сушилки. В ходе проведенных экспериментов было изучено влияние теплового потока на продолжительность процесса сушки и влияние на конечное содержание влаги в продукте, температуру замораживания и суммарное время сушки формы и размеров сырья, и полученные результаты были отражены в табличном и графическом виде. Уровень органолептических показателей (форма, размер, цвет, запах и вкус) сушеных продуктов был достигнут при сохранении 95÷98%.

Keywords: vacuum, sublimation, device, drying, fruits, vegetables, fig, persimmon, melon, parameter, traditional, experimental, shape, size, half, quarter.

Ключевые слова: вакуум, сублимация, устройство, сушка, фрукты, овощи, инжир, хурма, дыня, параметр, традиционный, экспериментальный, форма, размер, половинка, четверть.

Introduction

With the growing population in the world, their demand for food is also growing in parallel. In many areas, climate change, drought conditions have led to a shortage of food in the population, resulting in increasing demands for agricultural production, processing, quality food production, and safety from year to year. The increasing demand for quality food in the world requires a high-quality implementation of the processes carried out in terms of storage of products. One effective method for drying is the sublimation method. With this method, the demand for built products is increasing every year. In particular, in the markets of Europe (Spain, Great Britain, Germany, France, Italy, Russia and the rest of Europe), the segment of products obtained by sublimation drying is becoming wider depending on the type of product. Sublimated fruits, vegetables, drinks, coffee, tea, etc., sublimated dairy products, sublimated meat and seafood are rapidly entering the ranks of common types of products in supermarkets, hypermarkets and round-the-clock shops, online stores, retail outlets [1]. Scientific and practical research on the creation of modern technological processes and devices with high efficiency and automated control, ensuring the receipt of high-quality products to meet the ever-increasing demand for quality food, determines the relevance of the topic. In the sublimation process, factors such as vacuum capacity, initial moisture content of the product, freezing temperature, drying time duration depend on the physicochemical, thermal-physical properties of the product being dried. For this reason, one of our important tasks is to study the duration of the heat flow drying process and the effect of the product on the final moisture content, freezing temperature and the influence of the shape and dimensions of the raw materials on the summing drying time in order to choose the optimal varint of drying.

 Methods

The sublimation method was used to dry raw materials. Dehydration of materials under high vacuum when Frozen is called sublimated drying. Under these conditions, the moisture in the material is in the ice state, and then this ice turns directly into steam without changing to a liquid state. In this method of drying, the removal of moisture from the material composition is carried out in three stages: with a decrease in pressure in the drying chamber, self-freezing of moisture occurs, and at the expense of the heat from the material itself, the transformation of ice into steam occurs (on average, 15% of the moisture contained in it is released); the separation of the bulk of moisture by sublimation corresponds to a period of constant rate of drying; separation of the remaining moisture from the material under the influence of heat. The sublimation drying method has higher total energy and operational consumption than other drying methods (except dielectric drying). For this reason, this drying method is used to dry materials (meat, fruits, vegetables, medical and pharmaceutical products), which are valuable substances, resistant to high temperatures and whose biological properties must be maintained for a long time. But, in this process, the product retains almost 95÷98% of its vitamins, and the appearance practically does not change.

Results and discussion

During the research work, the first experiments were carried out to determine the effect of heat flow in the drying chamber on the duration of the drying process, and the results obtained were reflected in Table 1. Figs and persimmons were selected from the fruits and melon were selected from the vegetable products as the object of the study.

Table 1.

From the data presented in Table 1, an increase in the temperature of the heating agent to 20÷40⁰ C led to a significant change in the drying process.

The results of the experiment studying the effect of hot temperatures inside the sublimation device on the final moisture content of the product are shown in Figure 1.

Figure 1. The effect of hot current temperature on the final moisture content of the product

Changes in the diagram show that the moisture content of dates decreases from 2,6 % to 2,1 % as the heat flow in the sublimation process changes at temperatures of 20÷40⁰ С. A decrease in the last moisture content of figs was observed from 2,8 % to 2,2 %. The humidity of the melon was found to decrease from 2,9 % to 2,1 % as the temperature increased. By lowering the temperature of food products to -20÷-25⁰ С, it will be possible to freeze 85÷90 % of the moisture contained in them. To freeze 90÷98% of the moisture content of the product, it is required to lower it to a temperature of -30÷-40⁰ C. This affects the duration of sublimation drying. The results of the experiment carried out on the effect of persimmons, figs and melon on the duration of the sublimation process at temperatures of -20÷-40º C and drying under a vacuum of 125÷150 Pa are presented in figures 2.

Summing up the cumulative experimental data on both diagrams, it can be concluded that by carrying out the sublimation process-at a vacuum pressure of 30⁰ С and 150 Pa, the time spent on the process was achieved by an average of 2÷3 hours and a decrease in the final moisture content by 10÷12 % compared to the final moisture content of.

Conclusion

An analysis of the research carried out to improve the effectiveness of the process of drying fruits and vegetables in a sublimated way was carried out, and based on the results obtained, the goals and objectives of the research work were formulated;

During drying in a sublimation device, it was found that drying time and vacuum power depend on the final moisture content. The time spent by increasing the temperature of freezing persimmons to -30⁰ C, and the humidity in the vacuum 100 Pa indicator was 2,9 %, while the time spent was 32 hours, while the vacuum indicator increased by 125 Pa, the time spent decreased by 2 hours, humidity by 0,3 %. As the vacuum value increased by 150 Pa, the required time for the process was observed to be 5 hours, while the humidity decreased by 0,7 %;

As the heat flux in the sublimation process changes at temperatures of  20÷40⁰ C, it was found that the final moisture index of Persimmon decreases from 2,6 % to 2,1 %. The last moisture content of figs decreased from 2,8 % to 2,2 %. The humidity of the melon was found to decrease from 2,9 % to 2,1 % as the temperature increased;

By carrying out the sublimation drying process-under vacuum pressure of 30 ^oC and 150 Pa, the time spent on the process was achieved by an average of 2÷3 hours and a decrease in the final moisture content by 10÷12 % compared to the final moisture content of dried products in a conventional vacuum sublimation device.

References:

1. Morgunova E.M., Kondratenko S.A. The innovative and competitive potential of food products of directed effectiveness. Bulletin of the Plekhanov Russian University of Economics. 2022;(1):203-218. https://doi.org/10.21686/2413-2829-2022-1-203-218.
2. Khudaiberdiev T.L. Agricultural products drying technology and devices, textbook. - T: “Мухр пресс”. 2022. - 232 PP.
3. Vasiev M. G., Dadaev K.O., Ihaboev I. B., Sapaeva Z. Sh., Gulomova Z. Zh. Fundamentals of food technology. Textbook. –T: “Successor-publishing”. 2012. – 400 PP.
4. O.K. Ergashev, A.A. Egamberdiev. Possibility of using energy-saving vacuum-sublimation dryer in fruit and vegetable drying. Scientific and Technical Journal Namangan Institute of Engineering and Technology. Volume 7, Issue 3, 2022. ISSN 2181-8622. Pp. 62-67.
5. O.K.Ergashev, A.A.Egamberdiev, A.M. Khamdamov, O.T.Mallabaev. Исследование процесса сублимatsiонной сушки плодов сливы. UNIVERSUM: ТЕХНИЧЕСКИЕ НАУКИ. Release: 12(105) December 2022. Part 4. Moscow. Pp. 22-25.
6. O.K. Ergashev, A.A. Egamberdiev, M.F. Meliboev. Study of energy and resource efficiency of sublimation drying of fruits and vegetables. UNIVERSUM: ТЕХНИЧЕСКИЕ НАУКИ. Issue: 3(108) March 2023, Part 5. Moscow. Pp. 15-18.
7. O.K. Ergashev, A.A. Egamberdiev. Choosing acceptable parameters for experiment on new energy-saving vacuum sublimation drying equipment. Scientific and Technical Journal Namangan Institute of Engineering and Technology. Volume 8, Issue 2, 2023. ISSN 2181-8622. Pp. 92-96.
8. Meliboev, M. F. "Mamatov Sh. M., Ergashev OK Energy consumption and economic indicators in sublimation and microwave sublimation dry plum." Universum: technical science 5.98 (2022): 9-12.
9. Ergashev Oybek, Egamberdiev Azizbek, Meliboev Mirazam STUDY OF ENERGY AND RESOURCE EFFICIENCY OF SUBLIMATION DRYING OF FRUITS AND VEGETABLES // Universum: технические науки. 2023. №3-5 (108). URL: https://cyberleninka.ru/article/n/study-of-energy-and-resource-efficiency-of-sublimation-drying-of-fruits-and-vegetables (date of application: 03.04.2024).