Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D23/00—General constructional features
  • F25D23/06—Walls
  • F25D23/061—Walls with conduit means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/14—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D2201/00—Insulation
  • F25D2201/10—Insulation with respect to heat
  • F25D2201/14—Insulation with respect to heat using subatmospheric pressure
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B40/00—Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Definitions

• the present invention is related to the refrigerators with Stirling cycle heat pumps, wherein heat exchangers are used in order to remove the thermal energy from the cooled chamber of the refrigerator to the external environment.
• the cooling systems with compressors that have been used for many years in the cooling applications such as refrigerators and airconditioners, mainly consist of four units; namely, a compressor, an evaporator used to draw out the thermal energy from the cooled refrigerator cabinet, a condenser used to discharge the thermal energy and a throttle valve or a capillary pipe to regulate the flow of the fluid circulating through the system, from high pressure to low pressure.
• the heat exchangers generally referred to as evaporators, that serve to absorb the thermal energy from the cooled air inside the refrigerator cabinet, are manufactured of metal pipes with various diameters depending on their functional properties.
• the function of the compressor within the system is to compress the refrigerant being at a low pressure and temperature while leaving the evaporator, to a high pressure ( Figure 1).
• the dimensions of the evaporators used in the conventional systems are determined after the required surface area is calculated according to the cabinet heat gain, the desired temperature of the air inside the cabinet, the evaporation temperature of the refrigerant, and the coefficients of thermal conduction and convection.
• the limited heat transfer surface area requires high temperature differences whereas heat transmission at such a high temperature difference, increases the irreversibilities, which in turn leads to a decrease in the coefficient of performance of the system.
• the research and development studies made by various institutions show that the efficiency of the compressors used in such systems approach to an upper limit.
• the refrigerants or cooling fluids used in the refrigerators having compressors damage the ozon layer and cause a global warming.
• the Stirling-type heat pump is a system consisting of a cold surface exposed to the air that absorbs heat energy from outside, a warm surface dissipating heat to air and a piston-displacer mechanism driven by a motor to compress and expand the gas within the heat pump in oscillation at a preselected frequency. While the piston driven by a linear electric motor is compressing the gas within the heat pump, an isothermic compression is realized due to the heat transmission from the warm surface to the external environment, and the temperature of the gas remains constant. Whereas at the cold side of the Stirling heat pumps, as heat energy is drawn in from outside by using the cold surface during the expansion of the gas within the heat pump, an isothermic expansion occurs and the temperature of the gas remains constant.
• the Stirling heat pumps have a cold surface capable of absorbing heat energy from outside and a warm surface, capable of dissipating heat energy to outside.
• heat exchangers which can also be referred to as cold-side- and warm-side- heat exchangers are placed on the above described cold and warm surfaces.
• a heat exchanger must be placed within the refrigerator cabinet in order to convey the heat energy in the air to the cool surface, and this heat exchanger must be connected to the cold-side heat exchanger to create a secondary circulation circuit.
• a fluid containing water and additives, that circulates in the secondary circulation circuit will absorb the heat energy from the air within the refrigerator cabinet by flowing through the internally mounted heat exchanger.
• the fluid carrying this heat reaches the cold-side- heat exchanger, placed on the Stirling heat pump.
• the gas (usually helium or nitrogen) within the Stirling heat pump absorbs the heat energy from the fluid flowing in the secondary circulation circuit due to the above mentioned reasons and transmits the heat energy absorbed by the said fluid from the air within the cabinet to the Stirling heat pump by means of the cold-side- heat exchanger.
• a circulation similar to that provided between the heat exchanger mounted in the cabinet and the cold-side- heat exchanger mounted on the Stirling heat pump, must also be provided between an external heat exchanger and the warm-side- heat exchanger on the Stirling heat pump, in order that the refrigerator can fully perform the cooling function.
• the cooling fluid which is compressed at a constant temperature at the section where the warm side heat exchanger is installed, will transmit the heat energy absorbed from the air inside the refrigerator cabinet to the secondary fluid consisting of water, which circulates in the external side heat exchanger circuit mounted externally with respect to the refrigerator, by the assistance of the warm- side heat exchanger.
• the cycle is completed.
• nitrogen or helium is used as the cooling fluid in the Stirling heat pump, and mostly water is used in the secondary circuits, this technology has no adverse effects on the environment.
• the object of the present invention is to provide the construction of the heat exchangers used to absorb heat energy from the cooled volume and to dissipate the absorbed heat energy to the external environment, in compliance with the heat pumps operating by Stirling cycle.
• Figure 1 is the general view of the cooling system of the prior art.
• Figure 2 is the general view of the free-piston type Stirling heat pump.
• Figure 3 is the general view of the system using the Stirling heat pump.
• Figure 4 is the general view of the heat exchanger.
• Figure 5a is the view showing the parallel flow of the fluid in the heat exchangers.
• Figure 5 b is the view showing the serial flow of the fluid in the heat exchangers.
• Figure 6 is the view of the heat exchangers applied in the refrigerator.
• Figure 7 is the view of the heat exchanger with the insulation material.
• the flow character of the fluid flowing through the channels in the heat exchangers (1) i.e whether the flow is laminar or turbulent, is important to determine the properties and channel dimensions of the said heat exchangers (1).
• the heat exchangers (1) are made of parallel channels with square or rectangular sections.
• the dimensions of the channels vary within a range from 2x2 mm to 20x20 mm ( Figure 4).
• the Stirling heat pumps (2) Differing from the conventional compressors (4) the Stirling heat pumps (2) have the opportunity for capacity modulation and for this reason the value to be taken into consideration in the construction of an interior heat exchanger (1) is the heat gain in continuous operation.
• the Stirling heat pumps (2) can operate at a higher capacity in order to meet the added thermal load and when the heat gain attains the level of continuous operation, the refrigeration capacity of the heat pump (2) decreases to the normal value.
• These thermal loads are required to be added to the continuous operation heat gain so that food in the refrigerator are cooled in a sufficiently short time.
• the maximum operational capacity of the heat exchanger (1) is obtained by adding the heat gain created by opening/closing the door or putting new objects in the refrigerator cabinet to the continuous operation heat gain.
• the maximum cold side heat exchanger (1) capacity obtained by adding the average thermal load due to the opening/closing the door or putting new objects in the refrigerator cabinet to the continuous operation heat load, is around 40 W.
• Another factor to be taken into consideration for designing the heat exchanger ( 1 ) is the difference between the inlet and outlet temperatures of the fluid flowing within the heat exchanger (1).
• this difference is big, the heat transmission within the heat exchanger (1) from the warmer section to the colder, will increase which in turn will have a negative effect on the process of heat absorption from the cabinet (3).
• This problem is solved by keeping the evaporation temperature of the cooling fluid, almost constant in the evaporator which provides the absorption of heat from the air within the refrigerators wherein conventional compressors are used. Whereas this problem is avoided in the heat exchangers compatible with Stirling heat pumps (2) by keeping the difference between the inlet and outlet temperatures of the fluid flowing within the heat exchanger (1 ), maximum at 1 °C.
• the flow rate of the fluid used must be approximately 9-10 g/s depending on its specific heat, in order to attain the said temperature difference of 1 °C.
• this value rises up to 25 g/s.
• the geometrical shape i.e being square or rectangular, of the flow channels plays an important role with regard to the production methods and cost considerations.
• 10x10 mm square or 10x40 mm rectangular cross sectioned channels are used for a 9-10 g/s flow rate in a heat exchanger designed to absorb 40 W of thermal energy from the air inside a refrigerator with 150x50x50 cm dimensions, the flow rates of 9.5 cm/s and 2.3 cm/s are obtained respectively, in the channel.
• the heat exchanger (1) consisting of square or rectangular sectioned channels, depending on the capacity of application, is manufactured so that it covers the rear wall or side walls and the rear wall of the refrigerator. All these operations are also valid for the externally mounted heat exchanger ( 1 ) that provides heat transfer from the fluid flowing in the secondary circuit to the environment; as well as for the heat exchanger (1) produced to absorb thermal energy from the air within the cabinet (3). From said heat exchangers (1 ), the one to be used on the cold side is manufactured together with the cabinet (3) inner liner or adhered to said inner liner after being produced separately.
• the Stirling heat pump (2) has the capability to absorb heat energy from outside at the cold side and to dissipate heat energy to the external environment at the warm side.
• heat exchangers (1) compatible with the Stirling heat pump (2) are used in the refrigerators, a heat transfer surface area required for the absorption of the thermal energy is provided at low temperature differences between the air within the cabinet (3) and the fluid circulating in the secondary circuit. Heat transfer realized at low temperature differences, reduces the irreversibilities, thus enhances the cooling performance of the heat pump (2) and the refrigerator while decreasing its energy consumption.
• the heat exchanger ( 1 ) can be placed with a modification in the configuration of the heat exchanger ( 1 ), so that it covers the rear surface of the refrigerator entirely, a more homogeneous temperature distribution can be provided in the refrigerator cabinet (3).
• the heat exchangers (1) are produced as integrated with the refrigerator cabinet (3) inner liner, a decrease in the production cost of the refrigerator is attained.
• the heat exchanger is produced by utilizing thermo- forming or plastic injection method.
• the heat exchanger (1 ) which is 75 cm high and 40 cm wide, consists of channels with square or rectangular cross sections, and can be placed as one piece on the cabinet (3) rear wall or as three pieces on the rear and side walls of the cabinet (3) of a refrigerator with the dimension, 150x50x50 cm.
• the heat transfer surface area is 0.3 m 2 for a heat exchanger ( 1 ) placed as one piece on the cabinet (3) rear wall whereas it is 0.9 m 2 for a heat exchanger ( 1 ) placed as three pieces on the rear and side walls of the cabinet (3).
• the required temperature difference between the air inside the cabinet (3) and the fluid in the heat exchanger (1) is approximately 22 °C for a heat exchanger (1) placed as one piece on the cabinet (3) rear wall whereas it is 7.5 °C for a heat exchanger (1) placed as three pieces on the rear and side walls of the cabinet (3).
• the temperature of the fluid within the heat exchanger (1) is -18 °C for a heat exchanger (1) placed as one piece on the cabinet (3) rear wall, whereas it is -3 °C for a heat exchanger (1) placed as three pieces on the rear and side walls of the cabinet (3).
• the heat exchanger (1) placed as three pieces on the rear and side walls of the cabinet (3) is used to increase the temperature of the said fluid within the heat exchanger (1) by increasing the heat transfer surface area, thus to enhance the heat pump (2) performance and to reduce energy consumption.
• the temperature of the fluid providing the absorption of the thermal energy from the cabinet (3) is almost the same as the evaporation temperature of the refrigerant within the evaporator used in the applications with compressors, in case the heat exchanger (1) is placed only on the cabinet (3) rear wall.
• the heat exchanger to provide the absorption of the heat energy from the cabinet absorbs a certain amount of thermal energy also from the external surrounding i.e environment of the cabinet (3), which leads to an increase in the energy consumption of the refrigerator.
• a material with a lower thermal conductivity than the traditional insulation materials, such as a vacuum insulation panel (8) is placed at the rear side of the heat exchanger (1) ( Figure 7).

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Chemical & Material Sciences (AREA)
• Devices That Are Associated With Refrigeration Equipment (AREA)
• Refrigerator Housings (AREA)
• Polarising Elements (AREA)
• Inorganic Insulating Materials (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (7)

Citations (18)

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• 2000
  • 2000-11-30 TR TR2002/01186T patent/TR200201186T2/xx unknown
  • 2000-11-30 DE DE60029616T patent/DE60029616T2/de not_active Expired - Lifetime
  • 2000-11-30 JP JP2001542147A patent/JP4902080B2/ja not_active Expired - Fee Related
  • 2000-11-30 AT AT00980211T patent/ATE334363T1/de not_active IP Right Cessation
  • 2000-11-30 AU AU17505/01A patent/AU1750501A/en not_active Abandoned
  • 2000-11-30 EP EP00980211A patent/EP1234149B1/en not_active Expired - Lifetime
  • 2000-11-30 WO PCT/TR2000/000061 patent/WO2001040724A1/en not_active Ceased

Patent Citations (18)

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