RU2183307C2 - Vacuum-sublimation drier - Google Patents

Abstract

FIELD: drying equipment used in chemical, microbiological and food-processing industry. SUBSTANCE: vacuum-sublimation drier has vacuumizer composed of hermetically joined sections 1 equipped with branch pipe having lock valve, vacuum pump, desumbimator, and heater. Sections are equipped with double bottom 3 incorporating thermoelectric modules 4 made in the form of semiconductor devices composed of semiconductor branches with conductivity of p-type and n-type. Branches are disposed between two dielectric plates equipped with commutation surfaces, which connect semiconductor branches into single electric circuit. Operation of thermoelectric modules is based on Peltier effect. During passage of direct current one of plates of thermoelectric module is cooled while other plate is heated. In this case upper plates serve as heater and lower plates serve as desublimator, i.e. devices on which moisture is frozen out. EFFECT: reduced power consumed for desublimation process and uniform drying process. 2 cl, 2 dwg

Description

 The invention relates to drying equipment, in particular to equipment for freeze-drying, and can be used in the food, chemical and microbiological industries.

 Known heating and drying unit for a sublimation unit [a.c. 922469, class F 26 In 5/06, 1982] containing sections sequentially mounted one above the other. The disadvantage of this device is the need to use heating elements in each section and the need to use a sealed chamber for the process.

 The closest in technical essence and the achieved effect is a vacuum sublimation unit flow-cyclic action [RF patent 2099658, cl. F 26 B 5/06, B.I. 35, 12/20/1997], containing a vacuum chamber, a vacuum pump, desublimator, heaters, and the vacuum chamber consists of hermetically connected sections, representing a shell having a transverse partition made of a heat-conducting material, dividing the section into two cavities, while the cavity sections are connected by means of a branch pipe with a locking valve, by means of which the pressure in each section is regulated so that it rises with the connection of each subsequent section. Due to the temperature difference between the saturated vapors of neighboring sections, a heat exchange occurs between the sublimation surface of the frozen product and the saturated vapor through a heat-conducting partition. In this case, partial condensation (desublimation) of steam occurs on the heat-conducting partition, and moisture sublimation occurs on the surface of the frozen product.

 The disadvantage of this device is the difficulty of adjusting the pressure drops between sections, the unevenness of the drying process of the product and its high duration.

 An object of the invention is to reduce energy consumption for the desublimation process, achieving uniformity of the drying process and its intensification.

 The problem is achieved in that in a vacuum freeze dryer containing a vacuum chamber, consisting of hermetically connected sections, equipped with a nozzle with a shut-off valve installed with the ability to connect to a vacuum pump, a vacuum pump, desublimator, heater, sections are made with a double bottom in which thermoelectric modules are installed, which are semiconductor devices consisting of semiconductor branches with p- and n-type conductivity located between two dielectric and substrates on the surfaces of which there are switching platform connecting branch into a single semiconductor circuit. The principle of operation of thermoelectric elements is based on the Peltier effect, which consists in heating one and cooling the other junction while passing a constant electric current [Anatychuk L.I. Thermocouples and thermoelectric devices. Directory. M.: lay down. and food. industry, 1986]. In this case, the upper substrates will play the role of heaters, and the lower ones will play the role of a desublimator, i.e. devices on which freezing of moisture occurs. 2 ill.

 Based on studies conducted on the sources of patent and scientific and technical literature, we can conclude that the set of essential features is new and allows to reduce energy consumption for the desublimation process, to achieve uniformity of the drying process and its intensification.

 Technical solutions, the properties of which would coincide with the properties of the claimed, were not found, therefore, the claimed technical solution meets the criterion of "significant differences".

 A positive effect in the implementation of the invention is achieved by reducing energy consumption for the desublimation process, achieving uniformity of the drying process and its intensification.

 In FIG. 1 shows a longitudinal section through a vacuum freeze dryer; figure 2 - arrangement of thermoelectric modules in the section.

 The dryer contains a vacuum chamber, consisting of hermetically connected sections 1, including a baking sheet 2 with a double bottom 3, in which thermoelectric modules 4 are installed with the possibility of connecting to a direct current source, a heater 5, while the sections are equipped with a pipe 6 with a shut-off valve 7, installed for connections to the vacuum pump.

 Vacuum freeze dryer operates as follows. The product is loaded into each section 1 and pre-frozen in a low-temperature refrigeration device. The vacuum chamber assembled from sections 1 is connected to the vacuum pump using nozzles 6, then the pressure inside the vacuum chamber is brought to a value below the triple point for water (<610 Pa). Freeze-drying of the product begins under the influence of the heater 5. At the same time, direct current sources for supplying power to the thermoelectric modules 4 are turned on, which provide cooling of the bottom of the pan 2 to a temperature of 250 ... 255 K, and the moisture removed from the dried product is frozen (desublimated) and turns into ice. At the same time, heat is generated on the hot junctions of the thermoelectric modules, equal to the sum of the cooling capacity and the power spent on powering the thermoelectric modules. This heat is transferred to the product through a partition made of a material with a high coefficient of thermal conductivity. At the same time, moisture is sublimated from the surface of the frozen product of the higher section 1 (transition from a solid state to a gaseous state, bypassing the liquid phase). Similar processes occur in each section.

 After reaching the desired moisture content of the product, the drying process is stopped, the vacuum chamber is evacuated and the product is unloaded. Then the power polarity of thermoelectric modules is changed for 2 ... 3 min, which leads to the heating of cold junctions and the removal of desublimate (ice), after which the installation is switched back to normal operation.

 The number of thermoelectric modules installed in each section depends on their cooling capacity and the required installation performance. Domestic and foreign industry produces thermoelectric elements with known values of thermoelectric coefficient, semiconductor height d, as well as their thermoelectric figure of merit.

The proposed dryer allows you to:
- reduce energy costs for the process of steam desublimation through the use of thermoelectric modules as built-in desublimators;
- to achieve uniformity of the drying process by creating the same pressure in the sections;
- intensify the drying process by achieving a deeper vacuum in the sections, as well as through the use of thermoelectric modules with a high heat flux density.

Claims (1)

 Vacuum freeze dryer containing a vacuum chamber, consisting of hermetically connected sections, equipped with a nozzle with a shut-off valve installed with the ability to connect to a vacuum pump, a vacuum pump, desublimator, heater, characterized in that the sections are made with a double bottom, in which thermoelectric modules are installed, serving simultaneously as heaters for the higher section and desublimator for the lower.

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