RU2792781C1 - Method for adaptive increase of efficiency of heat exchange processes in cold accumulators - Google Patents

Abstract

FIELD: cooling technique.

SUBSTANCE: invention relates to methods for cooling heat-generating facilities, in particular structures with autonomous operation, and can be used to intensify heat exchange processes in cold accumulators. The cold accumulators are filled with water, which is pre-frozen with the help of a refrigeration unit, and then in the process of heat removal from the heat-generating object is melted. In charging mode, the system of metal grids is lifted and fixed using a tension system made in the form of a system of cables fixed to the four corners of the frame of the grid system with the possibility of their uniform lifting/lowering when the cable system is stretched/loosened. In the autonomous mode of operation, the tension system is released, ensuring uniform melting of ice under the own weight of the mentioned grids.

EFFECT: efficiency of heat exchange processes, in particular the heat transfer process, in cold accumulators increases.

1 cl, 7 dwg

Description

The invention relates to methods for cooling heat-generating objects, in particular, structures with an autonomous mode of operation, and can be used to intensify heat exchange processes in cold accumulators by introducing special heat-conducting elements into their volume - adaptive dynamic thermal bridges with a developed heat exchange surface.

Cold accumulators are currently quite widely used as part of systems for ensuring the temperature and humidity regime of various structures. The simplest cold accumulator is a heat-insulated container filled with a working fluid, for example, water, which is pre-frozen using a refrigeration unit of any type, and then melted in the process of removing heat from a heat-generating object.

There are also structurally more complex systems, which are a heat-insulated container, inside which there is a tubular heat exchanger [Efremov V.V., Naumov A.L., Serov S.F. The use of cold accumulators in air conditioning systems / Internet Bulletin of VolgGASU. Polythematic ser., Vol. 3 (13), 2010. (www.vestnik.vgasu.ru)]. The heat exchanger consists of separate cassettes, which are installed in the tank in parallel at a fixed distance from each other. The cassettes are combined by collectors into a single heat exchanger. Each cassette is a coil of pipes laid in a certain way. The principle of its operation is that the battery capacity is filled with water, and a refrigerant (freon or ethylene glycol solution) with a negative temperature circulates through the tubes of the heat exchanger. As a result, ice forms on the surface of the heat exchanger pipes, and then in the volume of the cold accumulator.

The processes of freezing (charging mode) and ice melting (offline mode) in the cold accumulator are carried out cyclically.

In the mode of charging the cold accumulator, an ice layer is formed near the cooled surface of the accumulator, the thickness of which increases with time. Due to the fact that the thermal conductivity of ice is low, this layer has a significant thermal resistance, which increases with time in direct proportion to the thickness of the frozen layer [Bryukhanov O.N., Shevchenko S.N. Heat and Mass Transfer: Textbook. - M.; INFRA-M, 2012. - 464 p., Chumachenko A.D. Study of the phase transition process in an ice accumulator. //Chemical and oil engineering, No. 12, 1994. - p. 14-15]. This leads to an increase in the freezing time of water in the volume of the cold accumulator and an increase in energy consumption in the process of charging the cold accumulator.

Removal of heat from a heat-generating object in autonomous mode also has its own specifics. A liquid layer is formed near the surface of the heat-generating object, which significantly impairs heat removal. This is due to the low thermal conductivity of water. It is 0.556 W / (m ⁰ C), which is close in value to the thermal conductivity of materials used as thermal insulation. Therefore, over time, the temperature of the fuel object increases, that is, heat removal from the object is carried out at a variable temperature difference between the fuel object and the melting working fluid, which in some cases does not allow cooling the fuel object within the specified temperature change tolerance and leads to a reduction in battery operation time cold offline.

A known system contains an air cooler that absorbs excess heat released in the structure, a pump that pumps melt water through the air cooler and cold accumulator capacity, a heat exchanger that provides freezing and maintaining ice, the heat exchanger is connected to an external refrigeration machine.

In the autonomous operation mode of the system, the heated water from the air cooler enters the evaporative section of the thermosiphon, where it is cooled due to the boiling of the working fluid of the thermosyphon, and again enters the air cooler. Vapors of the working fluid of the thermosiphon enter the condensation section along the adiabatic section, where, falling on the outer surface of the vessel wall, they condense and drain into the evaporation section. This causes the ice in the container to melt.

In charge mode, the refrigerant cooled by the chiller enters the heat exchanger, the additional heat exchanger, and back to the chiller. An additional heat exchanger serves to reduce the size of the thawed zone, and, consequently, to increase the amount of ice in the cold accumulator in offline operation. The operation of the thermosyphon is similar to its operation in the autonomy mode. As a working fluid of a thermosyphon, for example, an azeotropic mixture of freons boiling at 0°C at a pressure close to atmospheric can be used. The expansion tank is used to compensate for the volumetric expansion of water when it freezes.

The disadvantage of this device is the insufficient efficiency of the heat exchange processes occurring in it, as a result of which, in both modes of operation, a temperature difference arises between the heat-generating object and the working fluid of the cold accumulator, leading to a significant increase in the time of the battery charging mode and short battery life due to the inability to use fully stored in the battery cold.

Closest to the invention and simple in composition are cold storage units, consisting of containers of various shapes and sizes filled with a working fluid, for example, water, which is pre-frozen using a refrigeration unit of any type, and then melted in the process of removing heat from a heat-generating object .

The disadvantage of this system is the non-uniformity of ice melting, caused by the distance from the place of heat supply in the tank, while the ice that is closer to the place of heat supply melts faster, and the ice that is located as far as possible in the tank from the place of heat supply melts the slowest. This leads to a decrease in the reserve of autonomous operation due to the inability to fully use the ice stored in the battery due to the formation of a layer of water, which is less thermally conductive, which can lead to a sharp jump in temperature at the heat-generating object and disable it.

The objective of the present invention is to create a method that allows, in offline operation, to increase the battery life of the cold accumulator, taking into account the allowable range of temperature changes of the fuel object by increasing the uniformity of ice melting and its maximum use, to reduce the charging time of the cold accumulator, and, accordingly, to reduce energy costs by freezing ice in this mode.

The technical result, which the proposed method is aimed at, is to increase the efficiency of heat transfer processes, in particular the heat transfer process, in cold accumulators through the use of an adaptive dynamic system of thermal bridges with a developed heat exchange surface (hereinafter referred to as the grid system). For example, a metal frame with a metal mesh fixed inside it (for example, copper or steel) or a steel grid with high thermal conductivity, or several similar frames fixed to each other at different heights.

Under the adaptability of the thermal bridge system, we mean their adaptability to efficient operation in two modes (charging and autonomous operation). A dynamic system is a moving system.

According to the heat conduction equation, the introduction of heat-conducting elements from materials, in particular metals, with high thermal conductivity and a developed surface into the volume of the battery makes it possible to largely distribute the heat flow throughout the volume of the battery and significantly even out the temperature field in it [Grachev A.B., Katenev G .M., Lesyuk E.A. Cryoaccumulator optimization. // Chemical and oil and gas engineering, No. 3, 1998. - p. 35-37]. The charging mode is shortened, thereby reducing the energy consumption for freezing water.

The proposed method is implemented as follows.

In the charging mode, the grid system is raised by any possible solution to the maximum possible height inside the cold accumulator tank and fixed in this position. By transferring well not only heat, but also cold coming from the refrigeration machine to the grid system, an ice supply is formed faster and more evenly, while growing evenly up to the very bottom. Moreover, the more branched the heat exchange surface of the grid system or the more layers of these grids, the faster the process of ice formation, thereby reducing energy consumption for freezing water.

When switching to autonomous mode, the devices fixing the grid system in the upper position are turned off, for example, the tension of the cable system is loosened, and it receives a vertical degree of freedom (mobility). The mobility of the grid system in the autonomous mode of operation leads to a positive impact. In the process of ice melting, the cold accumulator of the grid system under the action of its own gravity is in constant contact with the ice, thereby leveling the negative impact on the heat transfer process of the water layer. The rate of growth of the temperature difference between the heat-generating object and the melting ice decreases, uniform and complete melting of ice occurs and, thus, the duration of the autonomous operation of the cold accumulator increases.

The essence of the method for adaptively increasing the efficiency of heat transfer in cold accumulators lies in the fact that the presence of a movable grid or grid system in the cold accumulator charging mode contributes to faster and more uniform ice formation, first around the grid system and then throughout the entire internal volume of the cold accumulator due to a significant improvement in heat transfer conditions , and offline allows for a more uniform and complete use of ice for its intended purpose.

Comparative analysis showed that the proposed method differs from the known analogues in that the presence of a dynamic thermal bridge leads to the intensification of heat exchange processes in cold accumulators in both operating modes and allows to reduce energy costs for ice freezing in one mode and increase the autonomy of the system in another operating mode.

The essence of the proposed method is illustrated by diagrams, which show:

in fig. 1 - scheme of the initial position when implementing the method of adaptive increase in the efficiency of heat exchange processes in cold accumulators,

in fig. 2 - diagram of the beginning of heat removal - freezing of water in the cold accumulator (charging mode),

in fig. 3 - diagram of the end of heat removal - freezing of water in the cold accumulator (charging mode),

in fig. 4 - diagram of the beginning of the heat supply - autonomous operation of the cold accumulator (autonomous mode),

in fig. 5 - scheme of adaptive movement of the grid system - autonomous operation of the cold accumulator (autonomous mode),

in fig. 6 - diagram of the further movement of the grid system - autonomous operation of the cold accumulator (autonomous mode),

in fig. 7 is a diagram of the final position in the implementation of the method of adaptive increase in the efficiency of heat exchange processes in cold accumulators (autonomous mode).

The following designations are used in the diagrams:

1 - cold accumulator case;

2 - support and tension system;

3 - adaptive dynamic system of thermal bridges with a developed heat exchange surface (grid system);

4 - standard cooling system;

5 - water;

6 - ice;

7 - standard heat supply system (cooled object).

The method can be implemented as follows.

1. In the charging mode of the cold accumulator 1, by means of the tension system 2 (for example, a system of cables fixed to the four corners of the frame of the net system with the possibility of their uniform lifting / lowering when the cable system is tensioned / loosened), lift the net system 3 to the maximum possible height ( leaving a margin to the top cover of ≈10-15% of the total distance of the vertical degree of freedom).

2. Using any standard cooling system 4, remove heat from the cold accumulator until water 5 turns into the maximum possible amount of ice 6. Then stop the operation of the cooling system 4.

3. In the offline mode, loosen the tension of the grid system as much as possible, allowing it to lie under its own weight on the formed ice 6.

4. Supply heat to the cold accumulator (through any existing standard supply system 7) for its subsequent cooling due to interaction with ice 6.

5. Due to the higher thermal conductivity of the branched metal grid system 3 located in the cavity of the cold accumulator, the bulk of the heat flux 7 will be transferred faster to the metal surface of the grid system 3, increasing its temperature. Further, ice 6 begins to melt faster near this system. The newly supplied heat flow continues to heat the grid system 3 faster through the tension system 2 than the water 5 formed during the melting process.

Own gravity and stable shape of the grid system 3 make it possible to constantly contact the ice surface 6, while reducing the water layer 5 between the ice and the grid system, and increasing the efficiency of the heat exchange process by maximizing the use of the entire volume of ice in the occupied area.

6. At the end of the autonomous operation mode, use the tension system 2 to perform the operations in paragraph 1.

The proposed method, through the use of an adaptive dynamic system of thermal bridges with a developed heat exchange surface, allows solving the problem of increasing the efficiency of heat transfer processes, in particular, intensifying heat transfer processes in cold accumulators in both operating modes, which leads to a reduction in energy consumption for ice freezing in charging mode and increase the time of the system in stand-alone operation mode.

Literature

1. Efremov V.V., Naumov A.L., Serov S.F. The use of cold accumulators in air conditioning systems / Internet Bulletin of VolgGASU. Polythematic ser., Vol. 3 (13), 2010. (www.vestnik.vgasu.ru).

2. Bryukhanov O.N., Shevchenko S.N. Heat and Mass Transfer: Textbook. - M.; INFRA-M, 2012. - 464 p.

3. Chumachenko A.D. Study of the phase transition process in an ice accumulator. //Chemical and oil engineering, No. 12, 1994. - p. 14-15.

4. Grachev A.B., Katenev G.M., Lesyuk E.A. Optimization of the cryoaccumulator // Chemical and oil and gas engineering, No. 3, 1998. - p. 35-37.

Claims (1)

A method for adaptively increasing the efficiency of heat exchange processes in cold accumulators, which consists in the fact that in cold accumulators filled with water, which is pre-frozen using a refrigeration unit, and then melted in the process of removing heat from a heat-generating object, characterized in that in the charging mode they raise and the system of metal meshes is fixed with the help of a tension system made in the form of a system of cables fixed to the four corners of the frame of the mesh system with the possibility of their uniform lifting / lowering when the cable system is tensioned / loosened, and in the autonomous mode of operation, the tension system is released, ensuring uniform melting of ice under own weight of the mentioned grids.

Images