Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
  • F02G1/00—Hot gas positive-displacement engine plants
  • F02G1/04—Hot gas positive-displacement engine plants of closed-cycle type
  • F02G1/043—Hot gas positive-displacement engine plants of closed-cycle type the engine being operated by expansion and contraction of a mass of working gas which is heated and cooled in one of a plurality of constantly communicating expansible chambers, e.g. Stirling cycle type engines
  • F02G1/053—Component parts or details
  • F02G1/055—Heaters or coolers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03G—SPRING, WEIGHT, INERTIA OR LIKE MOTORS; MECHANICAL-POWER PRODUCING DEVICES OR MECHANISMS, NOT OTHERWISE PROVIDED FOR OR USING ENERGY SOURCES NOT OTHERWISE PROVIDED FOR
  • F03G6/00—Devices for producing mechanical power from solar energy
  • F03G6/06—Devices for producing mechanical power from solar energy with solar energy concentrating means
  • F03G6/068—Devices for producing mechanical power from solar energy with solar energy concentrating means having other power cycles, e.g. Stirling or transcritical, supercritical cycles; combined with other power sources, e.g. wind, gas or nuclear
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
  • F02G2254/00—Heat inputs
  • F02G2254/30—Heat inputs using solar radiation
• • 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
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/40—Solar thermal energy, e.g. solar towers
  • Y02E10/46—Conversion of thermal power into mechanical power, e.g. Rankine, Stirling or solar thermal engines

Definitions

• the present disclosure refers to an absorber and to the relative method of dimensioning for a Stirling motor, originally designed so as to operate by burning natural gas.
• the present disclosure concerns the design of an absorber, that, when receiving solar energy, is capable of efficiently accumulating and transferring the flow of heat coming from the solar radiation to the head of the Stirling motor, without using vector fluids.
• Stirling motors are external combustion heat engines, with a closed cycle that use a gas as a thermodynamic fluid, usually air, nitrogen or helium in the high performance versions: it proves to be very versatile in relation to different heat sources.
• Stirling motors are made up of one or more cylinders in which one or more pistons slide following the expansion and the contraction of the thermodynamic fluid.
• the gas alternately flows from a hot exchanger and a cold exchanger after having passed through one heat regenerator: the corresponding harmonic movement of the pistons can produce electric energy, through a mechanical-electrical converter.
• the heat is generally supplied to the heat exchanger, which is at one end of the cylinder/s, and provides for heating the inner thermodynamic fluid that moves the piston/s.
• the heat exchanger is formed by a plurality of fins of material having good thermal conductivity, or by a plurality of small ducts in which the working fluid flows.
• the regenerator alternately absorbs and gives back heat from/to the working fluid and increases the transformation efficiency.
• the cold exchanger which constitutes the low temperature source, is usually a cross flow exchanger with tube bundle in which the tubes are licked outside by cooling water, whereas the working fluid flows inside the tubes.
• the fact that the Stirling motor works by external combustion is advantageous since the heat can be supplied externally by a wide array of combustibles, even with low calorific power.
• WO2005/054654 describes a Stirling engine assembly comprising a heat exchanger defined by a ring that internally surrounds one end of the cylinder near to the head.
• a type of heat absorber is not suitable for solar power application, especially since its thermal capacity is so low that it cannot ensure continuous operation of the Stirling motor.
• by eliminating the absorber and directly irradiating the head of the cylinder there is the risk of damaging the motor.
• the present invention proposes to provide a solar radiation heat absorber for Stirling motor, in particular for solar power application, that is capable of collecting the heat of solar radiation and efficiently transfer it to a heat exchanger inside the Stirling motor.
• the present invention proposes to supply, with a concentrated solar radiation, Stirling motors which need heat flows that are lower than 1000 Watt/m 2 in order to operate.
• the object of the present invention is a solar radiation heat absorber for Stirling motors, according to claim 1 .
• the absorber object of the present finding makes it possible to absorb concentrated solar radiation over a well-defined area, optimizing the operating temperatures of the motor and transferring the energy absorbed to the head of the Stirling motor in the form of heat minimizing the losses by radiation and convection.
• the absorber has a thermal capacity such as to keep the motor switched on for a predetermined interval of time even when the solar radiation is lower than 1000Watt/m 2 .
• the absorber that defines a sort of cap of the motor head, thus operates as an interface between a concentrated solar radiation and a heat exchanger inserted inside the head of a Stirling motor.
• Another purpose of the present invention is that of providing a system for converting solar energy that is based on a Stirling motor comprising the aforementioned heat absorber.
• the Stirling motor is of the type capable of producing both mains frequency electrical energy, and hot water.
• a further purpose of the present invention is that of providing a method of dimensioning a heat absorber for a solar application of a Stirling motor comprising a heat exchanger inserted in a motor head.
• a method of dimensioning a heat absorber of a Stirling motor also forms the object of the present invention, according to claim 10.
• a head of a Stirling motor can be shared by two or more cylinders.
• figure 1 represents a longitudinal section of an absorber inserted on a head of a Stirling motor
• figure 2 represents a trend of the temperatures of the section of figure 1 during the collection and heat exchange operations.
• the absorber 1 (or solar cap) has the task of collecting a light radiation and of conveying the heat to a cylindrical area at the heat exchanger 3 of the motor head 2.
• thermocouples are inserted for monitoring the temperature at the interface between heat exchange 2r and absorber 1 .
• thermocouples are used arranged in two opposite parts along the circumference of the motor head 2.
• the section represented in figure 1 thus represents an axial section passing by the slits 4 intended to house respective thermocouples which are not represented.
• the present description discloses how to: determine the thermal capacity and the mass of the solar cap 1 needed for the steady operation of the Stirling motor,
• Tstart 200 °C
• the Stirling motor can operate correctly.
• the surface for the heat to pass through is greatly restricted by the width of the outer diameter of the head of the Stirling, so that it is not possible to reduce the parts of the cap which are not directly irradiated as desired with the purpose of minimizing losses, since there is the risk of not being able to transmit the energy needed for the operation of the motor to the heat exchanger.
• Such dimensioning is further restricted by the mass of the absorber, which can vary in the range previously defined between m min and m max .
• - W is selected to be the power transmitted from the area exposed to solar radiation to the area in direct contact with the heat exchanger of the Stirling;
• T irr is selected to be the average temperature of the surface exposed to solar radiation
• - Tim is selected to be the average temperature of the interface with the heat exchanger
• S is selected to be the collection surface of the solar radiation, and if the reflecting mirror is a portion of a sphere, then S has a circular shape that is smaller or equal to the focusing area with a diameter d e-m ax ;
• - L is at least equal to the height of the cylinder of the piston
• Tint is equal to T ste ady .
• T irr is set to be equal to T max which is the maximum temperature that the preselected material, for example copper, can withstand without becoming damaged.
• Tma f copper is 1 100 °K (1373 °C) and
• S is the exchange surface, the inner diameter of which, that is
• c is the specific heat of the material of the absorber. So that, once a mass of the absorber has been selected, the collection surface S that defines a larger base is joined with a smaller base SM defined by said diameter d e- min, obtaining a solid with a cylindrical symmetry tapered towards the smaller base, i.e. the part for engaging on the head of the Stirling motor, in which the engagement cavity is formed from the smaller base and is concentric with it.
• said absorber 1 can thus have side surfaces 1 1 that are rectilinear, concave or convex in relation to the aforementioned joining operation.
• the absorber protects the head of the cylinder ensuring to keep the temperature of the head within the limits of motor operation
• the absorber collects solar radiation and optimizes the transfer of heat towards the heat exchanger inserted in the motor head

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Photovoltaic Devices (AREA)
• Sorption Type Refrigeration Machines (AREA)
• Engine Equipment That Uses Special Cycles (AREA)

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Cited By (5)

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Citations (7)

Family Cites Families (4)

• 2010
  • 2010-07-30 IT ITRM2010A000428A patent/IT1402134B1/it active
• 2011
  • 2011-07-25 WO PCT/EP2011/062744 patent/WO2012016873A1/en active Application Filing
  • 2011-07-25 CN CN201180037679.6A patent/CN103052788B/zh not_active Expired - Fee Related

Patent Citations (7)

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