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To equalize the temperature field in fusion cryoaccumulators, rods with developed fibbed surface or substances with capillary open pores may be used as beat-conducting headpieces. With such a design of the cryoaccurnulator, the heat removal by a solid cryogen in the process of its fusion may continue for a long time with small temperature gradients. This is particularly important for the cryostating of objects not permitting large temperature changes.The processes occurring in fusion cryoaccumulators with beat-conducting headpieces have not been sufficiently studied, and this requires therefore their physical and mathematical modeling for the purpose of subsequent calculation and optimization of such devices.Let us consider a fusion cryoaccumulator, cylindrical in shape, with a headpiece in the form of a fibbed heatconducting rod, and the method of its calculation. The heat-conducting headpiece is a rod with radius R and height H with rectangular ribs soldered to it along the axis (the number of ribs is n, the thickness of each rib is 3).To model the heat transfer in the structure under consideration (see Fig. 1), the following assumptions are made:--with z = 0 the heat Qo is removed from the cryostated object through a rod with the cross-sectional area S = ~rR2; --beat exchange in the working substance does not proceed in a circular sector but in a rectangular layer (such an assumption is possible because when the number of thin ribs is large, the layer of cryogen comes close to being rectangular); --there is no heat exchange over the height of the rib and cryogen, nor radially in the cryogen, heat removal over the height of the rod is effected solely through the r~s (this assumption simplifies the nature of the calculations with the chosen model, the calculation using it is carried out with some safety margin. In reality heat exchange proceeds with greater intensity because of the increased area of the beat-exchange surface of the ribbed rod since in modeling of the beat-transfer process heat exchange between the rod and the cryogen in the space between the ribs is not taken into account, nor is the heat removal from the end faces of the fibs); --in the middle layer of the eryoaccumulating substance (between two adjacent ribs) the temperature changes linearly from the temperature of the phase transition Tp to the running temperature of the rod over the z-axis Trd; --we neglect the temperature distribution within the rod and the fibs; --this is a steady-state problem. Such parameters of the beat-conducting headpiece of the cryoaccumulator have to be chosen (material, geometric dimensions of fibs and rod, number of ribs) so that the headpiece ensures the specified conditions of heat exchange within the eryoaccumulator, i.e., the permiss~le limit of temperature increase of the cryostated object is specified.In connection with the functional purpose of the material, viz., to equalize the temperature field within the cryoaccumulator for attaining lengthy cryostating of the heat-liberating object, the material of the...

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Thermal energy storage devices for cooling have become increasingly used in various areas of technology. Their operation is based on the use of preliminary cooling reserves built up by a heat-draining insert as a result of a first-order phase transition at low temperatures, such as evaporation, sublimation [1], or melting of the working medium [2].Since cooling reserves in the thermal energy storage device diminish as heat is withdrawn from the objects to be cooled, when needed for prolonged operation they are designed to allow for periodic charging. The charging method depends on the operating principle of the cryogenic thermal energy storage device. Repeated charging may be done using a refrigerator, a cryogenerator, or any other cooling device. For short-term operation, generally repeated charging of the thermal energy storage device is not required and thus its operating life is limited by the mount of cooling reserve.The operating life of the cooling thermal energy storage device, all other conditions being equal, is determined not only by the cooling reserve but also in many eases by the unacceptably large temperature difference developing over time as heat is transferred from the object to be cooled to the working medium. Such a limitation usually arises when cryostating ff and optoelectronic devices, in which the objects to be cooled cannot tolerate substantial changes in temperature.Accordingly, cryogenic thermal energy storage devices based on melting of solid cryogens have two major advantages: during heat input from the object to be cooled, the temperature of the melting working medium in the cryogenic thermal energy storage device remains constant; the change in the specific volume of the working medium during melting--freezing phase transitions is relatively small, which makes it possible to create cryogenic thermal energy storage devices without consumption of the working medium and accordingly allowing for periodic charging, i.e., cooling. Such devices are expediently used, for example, to increase the service life of gas-cycle cryogenic micromachines, and cryostating rf and optoelectronic devices which cannot tolerate exposure to noise, vibrations, electric or magnetic fields, etc.Under realistic conditions, withdrawal of heat from a heat-releasing object to a melting working medium occurs with some variable temperature difference between the object and the working medium. This is connected with the fact that a layer of liquid having significant thermal resistance is formed between the heat-releasing object and the melting cryogen. Since many heat-releasing objects do not tolerate a large variation in their temperature during the cooling process, we need to take special measures in designing cryogenic storage devices.In order to decrease the temperature difference between the heat-releasing object and the melting working medium, in the cryogenic thermal energy storage device we can place an insert made of material with high thermal conductivity, designed in the form of different types of fins or ...

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