Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S20/00—Solar heat collectors specially adapted for particular uses or environments
  • F24S20/20—Solar heat collectors for receiving concentrated solar energy, e.g. receivers for solar power plants
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S40/00—Safety or protection arrangements of solar heat collectors; Preventing malfunction of solar heat collectors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S50/00—Arrangements for controlling solar heat collectors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S80/00—Details, accessories or component parts of solar heat collectors not provided for in groups F24S10/00-F24S70/00
  • F24S80/60—Thermal insulation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S21/00—Solar heat collectors not provided for in groups F24S10/00-F24S20/00
• • 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
• • 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 invention relates generally to an air curtain control system and method and, in particular, to an air curtain control system and method for a solar thermal receiver and a solar thermal receiver.
• FIG. 1 shows an example of a solar thermal receiver 101 as part of a single dish solar collector 103.
• FIG. 2 shows a conceptual temperature field 201 of a solar thermal receiver 203 losing heat from a receiver aperture 205.
• significant temperature stratification develops as a stagnant region trapped within the cavity receiver for all angles of inclination slightly greater than 0 degrees.
• Air curtains have generally been available for use in shop front environments to minimise loss of heat from the shop. These types of air curtains use a minimal approach sealing mechanism that is only required to generate an air curtain that extends to the floor. In other words, the floor provides a mechanism for redirecting and containing the air curtain by reducing the vertical component of the flow to zero. Solar thermal receivers do not have the equivalent of a floor to enable an equivalent system to be useful. Further, these types of air curtain are generally limited to reducing heat transfer between horizontally connected volumes. Such units act to suppress the convective exchange of air between a temperature controlled interior environment and an uncontrolled exterior environment.
• air curtains have been used in systems with a falling stream of solid particles being used to absorb thermal energy directly.
• air curtains are directed upwards to help stabilise and confine the stream of particles.
• it is not their purpose to suppress heat loss due to convection from heated surfaces of the thermal receiver.
• an air curtain control system for a solar thermal receiver comprising: at least one air jet arranged to produce an air curtain over at least a portion of a receiver aperture of a solar thermal receiver, an air flow control device for controlling a speed of air flow out of the air jet, at least one angular control device for controlling an angle of the air curtain relative to the receiver aperture, and a system controller arranged to control the air flow control device to isolate the receiver aperture from ambient elements external to the receiver aperture.
• an air curtain control method for a solar thermal receiver comprising the steps of: producing an air curtain from at least one air jet over at least a portion of a receiver aperture of a solar thermal receiver, controlling a speed of air flow out of the air jet, controlling an angle of at least one air jet relative to the receiver aperture, wherein the air flow speed and angle of the air curtain are controlled to isolate the receiver aperture from ambient elements external to the receiver aperture.
• a solar thermal receiver comprising at least one air jet arranged to produce an air curtain over at least a portion of a receiver aperture of a solar thermal receiver, an air extraction device for extracting air out of the receiver aperture and an air injection device for injecting air into the receiver aperture.
• FIG. 1 shows a prior art arrangement for a solar thermal receiver
• FIG. 2 shows a conceptual temperature field of a solar thermal receiver
• FIG. 3 shows a representation of a mathematical model of the behaviour of air emitted from an air jet
• Fig. 4 shows the air curtain effectiveness as a function of air curtain velocity for varying cavity inclinations according to the herein disclosure.
• Fig. 5 shows a schematic diagram of an air curtain control system according to the herein disclosure.
• FIG. 6 shows an example of a solar thermal receiver according to the herein disclosure
• FIG. 7 shows an example of a solar thermal receiver according to the herein disclosure
• FIG. 8 shows an example of an air jet module according to the herein disclosure
• FIGs. 9A - 9D show various configurations of an air jet according to the herein disclosure
• Fig. 10 shows individual jets of air merging to form a planar air curtain according to the herein disclosure
• Figs. 1 1 A - 1 1 C show further examples of air jet configurations on solar thermal receivers according to the herein disclosure
• Figs 12A and 12B show a thermal image of a thermal receiver controlled using a first mode of operation according to the herein disclosure
• Figs 13A and 13B show a thermal image of a thermal receiver controlled using a second mode of operation according to the herein disclosure
• FIGs. 14A -14E show contour plots indicating the effectiveness of two modes of operation of an air curtain system using different configurations according to the herein disclosure
• Convective heat transfer constitutes any heat transfer occurring between a solid surface and an adjacent body of fluid, such as air. Such heat transfer can be further classified as forced or natural convection. Natural convection refers to a fluid motion occurring as a result of fluid density differences such as those arising from conductive heating of a fluid near receiver surfaces. Forced convection refers to the heat transfer caused by an externally forced flow such as a wind gust.
• FIG. 3 shows a representation of a mathematical model of air jet behaviour which describes in mathematical terms the relationship between the air at the jet outlet (nozzle) 301 and the air a certain distance y away from the jet outlet (nozzle) 303, where the expanding jet corresponds with the air curtain 509.
• the term air jet is understood to mean in certain examples a single air jet and co-existing nozzle. In other examples, an air jet may incorporate one or more nozzles.
• jet density p (corresponding to the air temperature T of the jet)
• a(z) describes the entrainment into the turbulent jet; a(z) may take a constant value ⁇ 0.08, for example, over the range of heights where the jet entrains, and a negative value over the range of heights where detrainment occurs.
• the model results compare well with computational fluid dynamics simulations over the initial range of heights where the jet entrains (and the entrainment constant a is known).
• the model equations need to be generalised both to allow for jets directed initially at an angle to the vertical and to calculate the curved trajectory of jets subjected to transverse forces.
• Fig. 2 shows the modelled temperature field in a thermal receiver that is subject to convective heat loss at an inclination of around 45 degrees.
• the effectiveness ⁇ of the air curtain can be defined as: [0047] where Q AC D is the heat loss with the air curtain applied and Q 0 is the heat loss without an air curtain for a given angle.
• the effectiveness as a function of air curtain velocity is shown for each cavity inclination in Fig. 4. From Fig. 4 it can be seen that the horizontal cavity had a maximum effectiveness of 55 - 70%, with an air curtain velocity of 1 .4 - 2.2 m/s.
• the air curtain effectiveness reaches a maximum in the range of 30% to 60% when the cavity is inclined between 15° and 75°, which is notably less than that for a horizontal cavity as seen in Fig. 14C. Furthermore the relative effectiveness of the air curtain is demonstrated to become far more sensitive to air curtain velocity as cavity inclination increases.
• FIG. 5 shows a schematic diagram of an air curtain control system 5001.
• the system has a system controller 501 for controlling a solar thermal receiver 1 01 .
• the system controller 501 may be any suitable electrical or electronic device that may operate to control an electro-mechanical system.
• the system controller may be a computer system that includes: a computer module; input devices such as a keyboard and a mouse pointer device; and output devices including a display device and loudspeakers.
• An external Modulator-Demodulator (Modem) transceiver device may be used by the computer module for communicating to and from a communications network via a network connection, such as WAN, LAN or the Internet.
• a network connection such as WAN, LAN or the Internet.
• the computer module typically includes at least one processor unit, and a memory unit 502, such as random access memory (RAM) and read only memory (ROM).
• the computer module also includes a number of input/output (I/O) interfaces including: an audio-video interface that couples to the video display, loudspeakers and microphone; an I/O interface that couples to the keyboard and mouse; and an interface for an external modem and printer.
• the computer module may also have a local network interface, which permits coupling of the computer system via a connection to a local-area communications network, known as a Local Area Network (LAN).
• LAN Local Area Network
• the I/O interfaces may afford either or both of serial and parallel connectivity, the former typically being implemented according to the Universal Serial Bus (USB) standards and having corresponding USB connectors (not illustrated).
• Storage devices are provided and typically include a hard disk drive (HDD).
• HDD hard disk drive
• Other storage devices such as a floppy disk drive and a magnetic tape drive (not illustrated) may also be used.
• An optical disk drive is typically provided to act as a non-volatile source of data.
• the components of the computer module typically communicate via an interconnected bus and in a manner that results in a conventional mode of operation of the computer system known to those in the relevant art.
• the method of controlling the thermal receiver may be implemented using the computer system, wherein the algorithm may be implemented as one or more software application programs executable within the computer system.
• the software may be stored in a computer readable medium, including the storage devices described below, for example.
• the software is loaded into the computer system from the computer readable medium, and then executed by the computer system.
• a computer readable medium having such software or computer program recorded on the computer readable medium is a computer program product.
• the software is typically stored in the HDD or the memory.
• the software is loaded into the computer system from a computer readable medium, and executed by the computer system.
• the software may be stored on an optically readable disk storage medium (e.g., CD-ROM) that is read by the optical disk drive.
• CD-ROM optically readable disk storage medium
• a computer readable medium having such software or computer program recorded on it is a computer program product.
• the schematic diagram in Fig. 5 shows a single air jet/nozzle 505. However, it will be understood, as explained below, that there may be more than one air jet arranged to produce an air curtain 507.
• the air curtain may be a planar air curtain where the air curtain is substantially spatially arranged to form a sheet of air.
• the air curtain may be a non-planar air curtain where the air curtain is shaped according to the arrangement of the air jet(s), such as in a circular or semi-circular manner, for example.
• the air curtain may be a spatially continuous or spatially semi-continuous air curtain over at least a portion of the air curtain.
• an initial portion of the air exiting the air jet(s) may not form a spatially continuous air curtain, but may form into a spatially continuous air curtain a distance away from the air jet.
• the air curtain may be a temporally continuous or temporally semi-continuous air curtain.
• the air curtain control system may pulse the air coming out of the air jet(s) to produce an intermittent flow of air.
• the intermittent flow of air may form together to produce a spatially continuous of spatially semi-continuous air curtain.
• the air curtain 507 is generated so that it covers or encloses at least a portion of the thermal receiver aperture 509.
• the entire length and width of the aperture of the thermal receiver may be covered by the air curtain, or only a portion of the length and width of the aperture may be covered by the air curtain. It will be understood that the aperture references the aperture plane of the housing of the thermal receiver across the opening at which the air curtain is being generated.
• the angular displacement of the air jet 505 relative to the aperture 509 may be adjusted by an angular control device 503. It will be understood that there may be more than one angular control device.
• the angular control device controls the angle at the source of the air curtain, i.e., the source angle relative to the aperture of the receiver. It may also control the air curtain, or air jet/nozzle angle, or the direction the air is emitted from the nozzle relative to the aperture of the receiver.
• the air jet through adjustment of the air jet or air jet nozzle or housing, may be angularly adjusted so that the air curtain is directed parallel to the aperture 509. Alternatively, the air jet may be angularly adjusted so that the air curtain is directed at a source angle ⁇ relative to the aperture 509.
• the angle ⁇ may be a positive or negative value such that the air curtain is directed either towards or away from the thermal receiver (and therefore towards or away from the aperture).
• the angular control device 503 may, for example, be a motorised device that rotates the air jet 505 according to a control signal generated by the system controller 501 .
• Other suitable angular displacement devices are also envisaged.
• the position of the air jet relative to the aperture may be adjusted or configured depending on the requirements of the system.
• the air jet may be arranged to direct the air curtain from a position located vertically above the receiver aperture.
• the horizontal positioning of the air jet may be adjusted so that the nozzle of the air jet produces an air curtain that is parallel and coplanar with the aperture 509 of the thermal receiver.
• the horizontal positioning may be offset by a value ⁇ so that the nozzle of the air jet produces an air curtain that is parallel and not coplanar with the aperture 509 of the thermal receiver.
• the positioning of the air jet along the horizontal axis may be fixed, or may be adjusted either manually or by any suitable means.
• the horizontal position of the air jet may be adjusted by the system controller 501 , which outputs a control signal to move a horizontal support upon which the air jet 505 is located.
• Other suitable horizontal displacement devices are also envisaged.
• the source of the air curtain i.e., the air jet
• the direction that the air is emitted from the air jet may be modified.
• the air curtain source may be located vertically above the aperture.
• the air curtain source may be located anywhere along the x-axis (where the aperture plane is the y-axis) and the angular direction away or towards the aperture plane may be adjusted.
• the air curtain source may be located in between the upper and lower points of the aperture plane and directed towards the aperture at any angle.
• An air flow generator 516 such as an air fan, provides the air to the air jet 505 via an air flow control device 517 that controls the speed of air flow out of the air jet. It will be understood that the air flow control device 517 and air flow generator 516 may be a single device that combines the two functions. The motion of air generated by the air flow generator passes along a suitable conduit to the air flow control device, and thereon to the air jet 505 via another suitable air conduit.
• One or more pressure sensors may be located in, near or around the receiver cavity (or aperture) to measure the air pressure in those locations. Further, one or more temperature sensors 521 may be located within the receiver cavity to measure the temperature in the receiver cavity. Also, one or more ambient wind sensors 523 may be located externally to the receiver cavity to measure ambient wind variables such as temperature, direction and velocity. Each of these sensors (519A, 519B, 521 , 523) are in communication with the system controller 501 to send the sensed readings to the controller 501.
• the system controller 501 is arranged to control the air flow control device 517 and the angular control device 503 to generate the air curtain and thus isolate the receiver aperture from ambient elements that are external to the receiver aperture.
• the system controller 501 may be arranged to control the air flow control device 517 and the angular control device 503 by controlling one or more of the speed of air flow and the angle of the air curtain based on a predetermined algorithm.
• the predetermined algorithm may be stored in a memory module 502 that is in communication with the controller 501 .
• the predetermined algorithm may be configured or adjusted based on one or more of the detected temperature(s) in the receiver cavity, the detected inclination of the receiver aperture, one or more computational fluid dynamics models, one or more measured
• the system controller memory 502 may also incorporate therein a look up table.
• the look up table may be used by the system controller to adjust one or more of the speed of air flow and the source angle of the air curtain based on an inclination of the receiver aperture.
• a correlation equation, polynomial expression or any other suitable technique may be used.
• the system controller 501 may be arranged to control the air flow control device 517 and angular control device 503 based on one or more input signals. These input signals may be, for example, one or more of the inclination of the receiver aperture, the temperature(s) in the receiver cavity of the solar thermal receiver, the angle of the air curtain relative to the receiver aperture, the speed of the air flow out of the air jet, ambient wind speed, ambient wind direction, ambient wind temperature and sun position.
• the inclination of the receiver aperture may be detected and sent to the system controller 501 by an inclination module 525.
• the inclination module may detect the angle of inclination of the solar thermal receiver. Further, the inclination module 525 may also adjust the inclination of the solar thermal receiver.
• the temperature(s) in the receiver cavity of the solar thermal receiver may be detected by a temperature gauge(s) within the cavity of the thermal receiver and sent to the system controller.
• the angle of the air curtain relative to the receiver aperture may be determined by the angular control device and sent to the system controller.
• the speed of the air flow out of the air jet may be determined by the air flow control device and sent to the system controller.
• the ambient wind speed, wind direction and wind temperature may be detected by suitable wind measurement devices positioned externally from the solar thermal receiver aperture.
• the system may also include one or more air extraction devices 513 for extracting air out of the solar thermal receiver.
• the system may include one or more air injection devices 515 for injecting air into the solar thermal receiver.
• the system may incorporate both air extraction and injection devices. These air extraction and injection devices may be in communication with the controller to receive control signals from the system controller 501 that control how much air is being extracted from or injected into the thermal receiver cavity 51 1 . The adjustment of these air extraction and injection devices may adjust the profile of the air curtain to adjust how much of the receiver aperture is isolated.
• the air extraction devices 513 and air injection devices 515 may be connected together to enable the air being extracted to be injected. For example, the air may flow from the air extraction devices to the air injection devices via a heat exchanger.
• the herein described system generates controlled air flows that are directed so as to partially suppress the convective flows that would otherwise remove thermal energy from the high temperature heat-collecting surface in a concentrating solar thermal receiver.
• the heat-collecting surface may be recessed to some degree in a housing such as the cavity 51 1 of Fig. 5 or Fig. 6 or Fig. 7.
• the air curtain may be generated and controlled in conjunction with extraction (or injection) of air from (to) the volume trapped in the housing.
• the system can assist in suppressing thermal losses for receivers that are either fixed in space or inclined at a variety of angles during operation, and/or are exposed to ambient wind and turbulence.
• Optimum suppression of convective heat loss can be achieved by a control system that can adjust the speed of the air curtain, the angle that the air curtain makes with respect to the aperture plane (i.e. that through which the heated receiver surface is exposed to ambient conditions) and the rate at which air is extracted from (or injected to) the housing.
• Fig. 6 shows a vertical section of a cavity receiver type configuration
• Fig. 7 shows a vertical section of a tower receiver type geometry. It will be understood that other types of configuration or geometry may be used in accordance with the herein disclosure. It will also be understood that the receiver shown in Fig. 7 is not required to be positioned vertically as shown in order for it to operate effectively and that any suitable range of inclination angles may be used.+
• a heat collecting surface (601 and 701 ) consisting of tubes containing working fluid.
• a receiver housing (602 and 702) is provided.
• Air jet nozzle(s) (603 and 703) are provided for directing air over the aperture plane (604 and 704) of the housing.
• Individual jet(s) of air (605 and 705) exit the air jet nozzle(s).
• the initial plane (606 and 706) of the air curtain is shown.
• An extraction valve (607 and 707) shown in one possible position may be used for extracting air from the receiver housing.
• An injection valve (608 and 708) shown in one possible position may be used for injecting air into the receiver housing.
• a cavity inclination axis 609 is shown for the cavity receiver type configuration.
• incoming solar radiation (610 and 710) is directed and focussed into the cavity (61 1 and 71 1 ) of the receiver to heat the heat collecting surface(s) (601 and 701 ).
• a combination of either or both of the air jets (603, 703) and the injection and/or extraction valves (608, 708 and 610,710) are controlled by the system controller 501 , which controls the speed and angle of the air jets, as well as the speed of air extraction and injection. The adjustment of one or more of these components may be made based on input variables received as described herein. It will be understood that any combination of air extraction (608, 708), air injection (607, 707), and air-jets (603, 703) may be used at any point in time according the optimal performance settings of the control system.
• Fig. 8 shows an example of an air jet module 801 that could be used with either of the receiver units shown in Fig. 6 and Fig. 7.
• the air jet module 801 includes a single air jet 803 for generating an air curtain 805.
• the air flow control device 517 may also form part of the air jet 803, or may be separate and in fluid communication with the air jet 803.
• the air flow generator 516 may also be part of the air jet 803 or separate from the housing but in fluid communication with the air flow control device 517. As mentioned earlier, the air flow generator and air flow control device may be combined as one unit.
• the angle of the air curtain 805 may be adjusted using the angular control device 503. That is, the entire air jet 801 may be moved to adjust the angle of the air curtain 805, or a nozzle within the air jet 801 may be adjusted. It will be understood that other alternative mechanisms may be used to adjust or control the angle of the air curtain. For example, by locating two air jets close to each other where the air jets operate at different speeds, the differential speed of the two jets may be used to control the angle of the combined air jet. As a further example, a further air jet may be directed into the air curtain, where the air jet is directed perpendicular (or at any other suitable angle) to the main air curtain in order to add lateral momentum.
• FIG.9A - 9D various configurations of air jet nozzles as viewed from the jet nozzle orifice end are provided.
• the generated air curtain is a continuous and approximately planar turbulent jet of air that is formed by the flow of air exiting either a single linear rectangular nozzle or a series of closely spaced nozzles.
• the nozzles may be, for example, round or rectangular.
• the air jet nozzle 801 may be a single rectilinear nozzle as shown in Fig. 8.
• a series of rectilinear nozzles 901 may be provided as shown in Fig. 9B.
• four individual evenly spaced rectilinear air jets (or nozzles) are provided.
• a series of closely-spaced round nozzles 905 may be provided within each air jet 903 as shown in Fig. 9C.
• a zig-zag array of closely-spaced round nozzles 909 in each air jet 907 may be provided as shown in Fig. 9D
• Fig. 10 shows how individual jets of air 1001 from an air jet module 1002 may merge to form a planar air curtain 1003 as viewed normal to the jet of air direction.
• the spacing d between individual air jets or nozzles should be small enough to allow the jets of air to merge into a continuous planar air curtain by the downstream point where the upper edge of the receiver aperture is first encountered. For example, this may occur by applying a downstream distance of 15x the air jet (or nozzle) spacing as shown in Fig. 10.
• the nozzle width for an air jet is a function of the receiver operating temperature, the aperture size of the receiver and the jet of air velocity (as described in more detail below).
• nozzle widths may be in the range of 4-20 mm for smaller receiver apertures of 0.2 m, and up to 0.2-1 m for large apertures of 10 m. Therefore, the width of the one or more nozzles (or air jets as the air leaves the nozzle) may be between 4 mm and 1 m. It will be understood that the technology described herein may be scaled up to apply to cavity receivers of any suitable size.
• the air jet (and nozzle) arrangement should preferably collectively span at least the full width/periphery of the aperture through which the heated receiver surface is exposed to ambient conditions.
• Figs. 1 1 A— 1 1 C show further examples of air jet configurations on solar thermal receivers.
• the air jets are configured into a circumferential arc.
• the arc of air jets are placed around a circular aperture, as shown facing the aperture.
• the arc of air jets are placed around the periphery of the housing. It will be understood that in the arrangements described herein the system may be configured so that the flow velocity of the air jets may be controlled locally, i.e. each individual jet is controlled independently.
• Figs. 11 A— 1 1 C the air jets are shown mounted on axisymmetric cavity receivers. Jet nozzles may be mounted in a linear fashion as shown in Fig. 1 1A, or a series of linear jet modules mounted to approximate a semi-circular arc as shown in Fig. 1 1 B and 1 1 C.
• Fig.1 1 A shows a receiver housing 1 101 , heat collection tubes 1 103, jet nozzle module(s) 1 105 and an approximately planar air curtain 1 107.
• Fig.1 1 B shows a receiver housing 1 109, heat collection tubes 1 1 1 1 , jet nozzle module(s) 1 1 13 and an approximately planar air curtain 1 1 15.
• Fig. 1 1 C shows a receiver housing 1 1 19, heat collection tubes 1 1 17 in a louvred arrangement, jet nozzle module(s) 1 121 and an approximately planar air curtain 1 123.
• each air jet nozzles produce a unidirectional jet of air without radial convergence of flow.
• the angle of each air jet module (or nozzle) with respect to the aperture plane may be controlled or adjusted by the system controller 501.
• the configuration of the air jets and/or nozzles in Fig. 1 1 C may be adapted for receiver housings 1 1 19 that subtend angles less than 360 degrees in the horizontal plane by adding vertical radial walls (not shown) at the limits of the desired angular extent.
• Vertical radial "blade-like" walls could also be included to subdivide the receiver into several compartments.
• the blades may be cooled by incorporating a cooling channel and cooling medium therein.
• the air jets may be supplied with air at an arbitrary temperature. However, as an alternative, the air may be supplied at ambient temperature air. Further, the air jets may be supplied using air extracted from the cavity such that the air is at a non-arbitrary, non-ambient temperature. [0097]
• the continuous and approximately planar jet is directed across the receiver aperture through which the heated receiver surface is exposed to ambient conditions.
• the plane of the air jet nozzle(s) need not be coincident with the plane of the aperture, but the angle between them (when projected into the vertical plane normal to the aperture) will be typically less than 30° for best suppression of heat loss.
• the optimum angle for the jet of air depends on the inclination of the aperture plane and the ambient conditions. Typically the ability to suppress heat loss is improved when the vertical component of the jet or air velocity is in the downward rather than upward direction.
• the air curtain control system may operate in two distinct modes to control thermal losses from the heated receiver surface.
• the first mode is termed “partially sealed”, and generates an air curtain that is directed with a component in the downward direction, but with insufficient momentum to fully traverse (and “seal") the receiver aperture through which the heated receiver surface is exposed to ambient conditions. That is, the system controller is arranged to operate in a first mode of operation where the air jet(s) is arranged to direct the air curtain over less than a full portion of the receiver aperture.
• One or more of the air flow control device, angular control device, air extraction device and air injection device may be controlled by the system controller based on detected input variables to direct the air curtain over less than a full portion of the receiver aperture.
• the jet nozzle(s) or air jet may be oriented between 0 degrees and 20 degrees, or between 5 degrees and 20 degrees, or between 10 degrees and 20 degrees, or between 15 degrees and 20 degrees, or between 5 degrees and 15 degrees, or between 10 degrees and 15 degrees.
• the jet nozzle(s) or air jet may be activated at 5 degrees, 10 degrees, 15 degrees or 20 degrees, either side of the aperture plane (when projected onto the vertical plane normal to the aperture) depending on the operating conditions for the receiver. Directing the air curtain slightly towards the aperture will reduce the jet strength required to maintain optimum conditions.
• the system controller may operate in the first mode of operation to control the angular control device so the source angle of the air curtain relative to the receiver aperture is any value or range as listed directly above from a plane lying across the receiver aperture. Therefore, in the partial mode of operation, an inwardly angled jet of air (i.e. directed towards the aperture) only partially traverses the aperture.
• the system controller may operate in the first mode of operation to control the angular control device so the angle of the air curtain relative to the receiver aperture is substantially 15 degrees from a plane lying across the receiver aperture.
• the system controller may also be arranged to operate in the first mode of operation using any of the other values or ranges listed directly above.
• the angle of the air curtain relative to the receiver aperture is either directed away from the solar thermal receiver or towards the solar thermal receiver.
• the second mode is termed "fully sealed", and employs an air curtain directed with a component in the downward direction, but with greater momentum such that the jet fully traverses the aperture through which the heated receiver surface is exposed to ambient conditions. That is, the system controller is arranged to operate in a second mode of operation where the air jet(s) is arranged to direct the air curtain over a full portion of the receiver aperture.
• One or more of the air flow control device, angular control device, air extraction device and air injection device may be controlled by the system controller based on detected input variables to direct the air curtain over a full portion of the receiver aperture.
• the system controller controls the air jet and/or nozzle so that the generated air curtain is oriented outwards from the aperture plane, between 0 degrees and 20 degrees, or between 5 degrees and 20 degrees, or between 10 degrees and 20 degrees, or between 15 degrees and 20 degrees, or between 5 degrees and 15 degrees, or between 10 degrees and 15 degrees, when projected onto the vertical plane normal to the aperture, such that the air curtain just returns to the aperture plane after traversing past the heated receiver surface. That is, the system controller is arranged to operate in the second mode of operation to control the angular control device so that the source angle of the air curtain relative to the receiver aperture is any value or range as listed directly above from a plane lying across the receiver aperture and directed away from the solar thermal receiver.
• the system controller may be arranged to operate in the second mode of operation to control the angular control device so that the angle of the air curtain relative to the receiver aperture is between 5 degrees and 15 degrees from a plane lying across the receiver aperture and directed away from the solar thermal receiver.
• the system controller may also be arranged to operate in the second mode of operation using any of the other values or ranges listed directly above.
• Figs. 12A and 12B show temperature variations for a thermal receiver 1201 within its cavity 1203 as a result of the system controller 501 operating in the partial mode. In this partial mode, the air curtain 1205 only partially covers the upper portion of the aperture 1207 of the receiver 1201 .
• Fig. 12A shows the receiver at a first inclination of approximately 30 degrees with the velocity of the air emitted from the air jets at 0.8 m/s.
• Fig. 12B shows the receiver at a second inclination of approximately 60 degrees with the velocity of the air emitted from the air jets at 0.4 m/s. Both Fig. 12A and 12B show the results where the jet width is 5mm and the aperture height is 70 mm.
• the temperatures reached in a solar receiver are typically in the region of 400-900°C, reducing the density of the heated air to between 50 and 25% of that under ambient atmospheric conditions.
• the density difference across the air curtain plays a significant role in the operational dynamics of this system.
• the air curtain entrains a sufficient volume of hot air from the cavity 1203 of the receiver housing that buoyancy acts on the air curtain 1205 to overcome its initial momentum, deflecting the air curtain 1205 away from the aperture plane 1207.
• buoyancy acts on the air curtain 1205 to overcome its initial momentum, deflecting the air curtain 1205 away from the aperture plane 1207.
• the most effective air curtain strength at a given inclination angle corresponds to the largest stagnant region and a reduction in the convective heat loss (by approximately 40% for a range of inclination angles between 15 degrees and 60 degrees).
• Figs. 12A and 12B indicate that as cavity inclination is increased, the sealing effect can become detrimental to cavity performance and a reduction in air curtain velocity may be required to maintain effective operation.
• Figs. 13A and 13B show temperature variations for a thermal receiver 1301 within its cavity 1303 as a result of the system controller 501 operating in the fully-sealed mode. In this filly-sealed mode, the air curtain 1305 fully covers the aperture 1307 of the receiver 1301.
• Fig. 13A shows the receiver at a first inclination of approximately 30 degrees with the air jet pointing away from the aperture at an angle of 10 degrees and with the velocity of the air emitted from the air jets at 2 metres/sec.
• Fig. 13B shows the receiver at a second inclination of
• the air curtain 1305 acts to largely isolate the volume housing the heated receiver surface from the ambient conditions.
• the initial momentum of the air curtain generated by the air jet(s) (or nozzle(s)) is not significantly affected by the buoyancy of the hot air that is entrained into the air curtain.
• This sealing mode works by lowering the pressure in the housing relative to the ambient, drawing the air curtain back to the aperture plane 1307, as seen in Figs. 13A and 13B.
• Both the partial and fully sealed modes may be operated over a wide range of aperture inclinations, typically offering similar reductions in convective loss.
• Optimum partial-sealing can typically be achieved over a range of initial jet angles and speeds; this range of optimum operating conditions is much narrower for full-sealing, and requires higher initial jet velocities.
• a receiver operated at approximately 500°C and with an aperture size to the heated surfaces of order 1 m may be shielded by a linear air curtain generated by a nozzle (or air jet) width 0.07 m and jet of air speeds in the range 1.2-28 m/s. It will be understood that the speed of air from the air jet/nozzle may be based on the orientation of the aperture plane.
• a large vertical receiver surface of order 10 m, operated at the same temperature, may be shielded by a linear air curtain with nozzle (or air jet) width 0.7 m and jet or air speeds in the range 4-90 m/s. It will be understood that other jet widths and air speed ranges may also be suitable as disclosed herein.
• the system controller may be arranged to control the air flow control device so that the speed of air flow out of the air jet is between 1 and 90 metres per second.
• the system controller may be arranged to control the air flow control device so that the speed of air flow out of the air jet is between 2 and 7 metres per second.
• the system controller may be arranged to control the air flow control device so that the speed of air flow out of the air jet is between 7 and 20 metres per second.
• the system controller may be arranged to control the air flow control device so that the speed of air flow out of the air jet is within other ranges as disclosed herein.
• the air curtain may be used to shield convective heat loss at the heated receiver surfaces from the ambient wind.
• the optimum operating conditions for each sealing mode may be modified by the system controller based on one or more of the strength of the ambient wind and its direction.
• the ambient wind may induce a large-scale pressure distribution around the receiver. For certain wind directions, this will lead to a pressure drop or suction effect that will tend to increase the local convective loss from the receiver surface.
• Effective shielding of the surface by the air curtain relies on inducing a similar pressure drop in the vicinity of the heated surface, and this can be characterised by the dimensionless parameter p a U 2 /(p a -p r ) , where U is the wind velocity, and p a -p r is the maximum pressure difference between the ambient air and that inside the receiver at a given height.
• Effective shielding may be possible in general for wind speeds up to approximately 40% of the jet speed, and possibly more depending on the orientation of the wind direction with respect to the receiver.
• operation of these two modes may be assisted by the extraction (and/or injection) of air from (to) the housing surrounding the heat receiver surface using the air extraction device 513 and air injection device 515.
• Extraction or injection of air from the housing surrounding the heated receiver surfaces can be used in conjunction with the above features to enhance the effectiveness of the air curtain.
• the process of air extraction or injection modifies the pressure distribution in the housing, and hence the forces acting on the air curtain. It can be used to lower the jet velocities required in either full or partial sealing modes, and may increase the robustness of the air curtain to ambient wind.
• the pressure distribution inside the receiver housing 51 1 strongly affects the behaviour of the air jets forming the air curtain.
• the housing may be sealed with the exception of the injection and extraction devices (515 & 513) and the aperture 509.
• the air curtain acts to at least partially isolate the receiver interior from the ambient conditions external to the receiver cavity. Much of the interior of the cavity is at a slightly lower pressure than the external pressure. This produces a suction effect that retains the air curtain seal across the aperture.
• the suction effect also means that the jet turbulence is strong enough to entrain hot air only in the upper part (approximately 20%) of the air curtain.
• the injection/extraction of air to the receiver housing provides significant ability to control the air curtain seal.
• the receiver cavity may also be shielded against ambient wind conditions.
• one or more pumps may be coupled to the extraction, injection points or ports. This pump may provide an overpressure or suction in order to produce pressure changes that are comparable to a maximum rated wind speed.
• the external pressure outside of the cavity may be tapped to the receiver housing. This may be done, either directly or via the control system, For example, the control system may select the height in the housing at which the tapping could be connected.
• the most suitable tapping may be a surface near to and parallel to the aperture plane. Alternatively, the tapping may be connected to a "stack" acting as a chimney.
• This arrangement may be used to effectively equalise the ambient pressure and the pressure in the receiver housing, automatically compensating for much of the suction and overpressure effects caused by the ambient wind. It will be understood that such a tapping does not necessarily require a rate of injection and/or extraction to be maintained.
• the air curtain may be driven from an active control system that can respond to the operating conditions to maintain optimum suppression of convective heat loss.
• the primary inputs to the control system are inclination angle of the aperture plane (for a mobile, sun- tracking receiver), receiver operating temperature and ambient wind strength and direction.
• the control system may adjust the speed of air forced from the nozzle(s) or air jet(s), the angle that the air curtain produced by the air jet(s) or nozzle(s) makes with the aperture plane, and the rate at which air is extracted from, or injected into, the housing.
• the appropriate air jet/nozzle parameters will be set by a pre-determined algorithm based on a combination of predictions using fundamental flow physics, (previously conducted) simulations using computational fluid dynamics (CFD) models and measured performance characteristics.
• CFD computational fluid dynamics
• Fig. 14A shows the effectiveness of the two modes of operation for a range of air curtain angles and speeds.
• the cavity is inclined at 45 degrees. It will be understood that other cavity inclinations may be used.
• the angle of the air window may be directed away from the receiver between 0 and 10 degrees or directed towards the receiver between 0 and 10 degrees.
• the air window may be directed away from the receiver between 0 and 8 degrees or directed towards the receiver between 0 and 8 degrees.
• the jet velocity is set between 1 m/s and 1.5 m/s, or optionally between 1 .1 m/s and 1 .3 m/s.
• the angle of the air window may be directed away from the receiver between 5 and 15 degrees.
• the air window may be directed away from the receiver between 8 and 1 1 degrees.
• Figs 14B-14E show a contour plot of the effectiveness as a function of air speed out of the air jets and the cavity inclination angle for the two modes of operation.
• Fig. 14B shows a cavity inclination of 0 degrees
• Fig. 14C shows a cavity inclination of 15 degrees
• Fig. 14D shows a cavity inclination of 30 degrees
• Fig. 14E shows a cavity inclination of 45 degrees.
• Each of the values generated for the different configurations and parameters may be recorded in a look up table and retrieved and used by the system controller to effectively control the air curtain system. It will be understood that the invention is not limited to these specific examples and that further set up parameters may be added to the look up table based on further modelling and testing of the air curtain system, for example at different scales.
• these angular and velocity values may be adjusted to counter measured ambient wind effects.
• the pressure field will force the air curtain to be deflected towards the aperture plane.
• the angle of the air curtain directed away from the receiver may be increased, along with the jet air velocity to help counteract this effect and thus shield the receiver chamber.
• Pressure could also be applied to the receiver chamber by injection of air 515.
• the ambient wind will tend to be accelerated around a receiver or nearby structures, and the associated pressure fields are complicated.
• the air curtain will tend to be drawn out of the aperture plane.
• the angle of the air curtain directed towards the receiver may be increased, along with the jet air velocity to help counteract this effect. Suction could also be applied to the receiver chamber by extraction of air 513. Therefore, one or more pressure sensors located in, near or around the receiver cavity may provide pressure measurements to the system controller 501 .It will be understood that, as an alternative, the system controller may be a mechanical controller that controls the air curtain to a limited extent. For example, a wind-powered ejector may apply control to a pressurised plenum leading to the air curtain jets.
• aperture may also be interpreted to include a localised area of a surface in cases where the solar thermal receiver is in a common form such as a solar tower receiver.
• control system may be configured to control one or more air jets independently.
• the system may be configured such that one or more air jets are associated with their own air flow generator 516 and/or air flow control device 517.
• the angular control device may be a passive device that is not controlled by the system controller, but is instead fixed in a static position to generate an air curtain that effectively seals or partially seals the cavity as described herein.

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• 2015
  • 2015-12-09 EP EP15867874.8A patent/EP3230657A4/de not_active Withdrawn
  • 2015-12-09 WO PCT/AU2015/000742 patent/WO2016090410A1/en not_active Ceased
  • 2015-12-09 AU AU2015362065A patent/AU2015362065A1/en not_active Abandoned
  • 2015-12-09 US US15/534,844 patent/US20170328601A1/en not_active Abandoned
  • 2015-12-09 CN CN201580073995.7A patent/CN107208931B/zh not_active Expired - Fee Related

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