LU83927A1 - AIR-LIQUID SOLAR COLLECTOR - Google Patents

Description

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TITLE

HISTORICAL AIR-LIQUID SOLAR COLLECTOR OF THE INVENTION

The invention generally relates to solar collectors and more particularly to a unitary assembly. solar energy collector comprising a plurality of evacuated collector elements and a gas-liquid heat exchanger.

The ever increasing energy needs and the increasing cost of hydrocarbon extraction have pushed the search for other sources of energy.

Perhaps the most promising source variant from the immediate point of view is represented by solar energy, and developments and refinements in the design of solar collectors over the past decade have been dramatic. Nevertheless, each physical conception, for example, flat plate or tube, shows certain anomalies in performance which call for improvements. In evacuated tube collectors that use air as the heat recovery medium, a common problem has been the uniform distribution of air to the manifold elements. Insufficient air flow in certain manifold elements due to poor distribution within a central pipe results not only in the operation of certain manifold elements at high temperatures likely to affect their useful life, but also by a reduction in the efficiency of the entire collector assembly.

In the prior art, it is known that the non-uniform distribution of the fluid is generally capable of improvement by increasing the operating pressure of the system and, consequently, of the pressure drop across the constituent elements of the system. Unfortunately, such an increase in the operating pressure of the system can only be achieved with a corresponding increase in energy consumption, i.e. admission of energy to the air movement elements. In a solar energy recovery system, this increase in energy consumption may turn out to be greater than the increase in recovered energy resulting from better air distribution. In the light of a thermodynamic system, the

The overall efficiency of the solar collector may possibly decrease, in fact, as a result of the increase in energy consumption associated with achieving the goal, ie. better air distribution.

This situation suggests that low system pressures and minimal pressure losses would have some merit. A system of this type is described in US Patent No. 4,016,860, previously issued and of which I am co-owner.

Another area of difficulty in the use of solar energy collectors concerns the mode of energy transfer. In many solar collectors making use of air as the recovery medium, the air is directed from the solar collector assembly through a pipe to the place, such as a living room, or thermal energy is intended to be used. This pipeline presents several problems. First of all, paths of a certain length are the cause of significant pressure losses which aggravate the problems of power supply to the system and of overall efficiency which have been mentioned above. Secondly, the problems of loss of energy to the atmosphere relating to the low air density, the large diameter and the circumferential area of said pipe are significant. It is obvious that this pipe can, and must, be well insulated but this increases the outside diameter of the pipe. Finally, installing such a large outside diameter pipe in existing structures can also present problems that a more compact energy transfer device could reduce or alleviate. An example of a solar energy collector making use of such a compact energy transfer device is described in US Patent No. 3,960,136, of which I am co-owner. In the embodiment described, the air circulated in a collector mounted on the roof heats a liquid such as water, and water is used as the heat transfer medium.

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SHORT DESCRIPTION OF THE INVENTION

The present invention relates to a unitary design solar energy collector comprising a plurality of evacuated collecting elements fixed on and in communication with a centrally disposed double-passage pipe which houses a gas-liquid heat exchanger and a device for circulating the gas heat recovery medium. The manifold elements are arranged in staggered rows on the opposite sides of the tubing. Each of the collecting elements comprises a double-walled glass tube of elongated shape, one end of which is open and defining between the glass walls an evacuated annular volume. A thin-walled metal dispensing tube having a diameter somewhat smaller than the inside diameter of the interior glass wall is disposed therein and extends beyond the open end of the manifold. The annular space defined by the distributor tube and the inner wall of the collecting element communicates with the passage closest to the tubing and the interior of the distributor tube communicates with the passage farthest from the tubing. The air circulation device supplies air at low pressure in the direction of one of the passages and this air is directed into all the annular spaces and inside the distributor tubes with which they communicate. The air then directs away from the tubing and inward either of the annular spaces or of the distributor tubes, arrives at the end of the collecting elements and directs inwardly towards the other passage of the tubing; the air previously found in the annular spaces now circulating in the distributor tubes and vice versa. The air flow is then combined with the other passage of the tubing and passed through the heat exchanger in which the energy of the air is transferred to the liquid, namely water, circulating through the heat exchanger. The air leaving the heat exchanger is returned to the blower and from there to the collecting elements while the water or other liquid which has absorbed the thermal energy of the air is eliminated from the heat exchanger and conveyed through a suitable pipe to the place of use.

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Consequently, one of the objectives of the present invention is to provide a solar collector of the unit type and the output of which is a heated liquid.

Another object of the present invention is to create a unitary type solar energy collector providing high efficiency.

Yet another object of the present invention is to create a solar collector with an evacuated tube and of the unitary type capable of being easily installed in existing and new structures.

Yet another object of the present invention is to create a solar collector with an evacuated tube and of the unitary type which uses an air distribution device operating at low pressure capable of causing an excellent distribution of the air with a minimum absorption of energy.

Other objects and advantages of the present invention will become apparent with reference to the following specifications and the accompanying drawings.

SHORT DESCRIPTION OF THE PLANS

Figure 1 is a perspective view of a unit type solar energy collector according to the present invention;

Figure 2 is an enlarged perspective view of a portion of the heat exchanger used in a solar collector according to the present invention;

Figure 3 is an elevational view of the end of a solar collector according to the present invention, mounted on an inclined surface;

Figure 4 is a schematic view of the air flow through the tubing and the collecting elements of a solar collector according to the present invention;

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Figure 5 is a full sectional view of the tubing of a unit type solar collector according to the present invention taken along line 5-5 of Figure 1;

Figure 6 is a sectional view, fragmentary and enlarged, of the mounting of the distributor tubes in the tubing; and

FIG. 7 is a fragmentary section view of the tubing of a collector, of solar energy of the unit type according to the present invention taken along line 6-6 of FIG. 1,

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to Figures 1 and 3, a unitary type solar energy collector is generally designated by the reference number 10. The solar collector 10 comprises a set of tubing 12 disposed centrally and having a plurality of collecting elements 14 arranged in staggered rows on the opposite faces of said tubing. The tubing assembly 12 and the collecting elements 14 are all supported by a frame assembly 16 of generally rectangular shape. The frame assembly includes a pair of elongated Z-shaped beams 18 which securely secure and lift the tubing assembly 12 above the surface, such as a roof 20, to which the manifold 10 is attached. The frame assembly 16 also includes a pair of L-shaped collector support beams 22 which are generally fixed perpendicularly between the ends of the Z-shaped beams 18. Each of the support beams 22 has a plurality of slots 24 in U-shape serving to receive the collecting elements, these slots supporting the ends of the collecting elements 14 furthest from the tubing assembly 12. The frame assembly 16 can be made of galvanized metal, aluminum or any other analogous material.

The Z-shaped beams 18 can be fixed to the tubing assembly 12 and to the L-shaped beams 22 by any suitable means, for example thread screws, rivets, spot welding or the like.

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As shown in Figure 2, the solar collector 10 can be installed on the roof 20 of a dwelling house or other structure. Preferably, the solar collector 10 is oriented in the southern direction and at an angle of inclination which best captures the solar energy available at the latitude of the installation. The collecting elements 14 are independent, i.e. that the collector 10 does not include a mirror, reflector or specular reflecting device for concentrating the rays of the sun, but is based above all on the diffuse reflection from the surface of the roof 20 or from other horizontal or inclined surfaces acting on the side of the collecting elements 14 facing the sun to reflect energy there.

Referring now to Figure 5, the tubing assembly .12 is generally rectangular in section and has an outer metal casing 30 and a smaller inner metal casing 32. Between the outer metallic envelope 30 and the inner metallic envelope 32 are preformed insulating tiles ~ 34 of appropriate dimensions and orientation. The insulating slabs 34 are preferably made of polyurethane isocyanate or similar material capable of withstanding maximum temperatures of at least 325 degrees Fahrenheit. The uniform thickness of the preformed insulating slabs 34 as well as the perpendicular edges formed with precision ensure the tight fit of the slabs 34 as well as the total filling of the volume between the outer metallic envelope 30 and the inner metallic envelope 32. A baffle 36 in sheet metal is arranged centrally inside the inner metal casing 32; this baffle divides the interior volume of the interior metal casing 32 all along its length into an intake or supply passage 40 and an exhaust or return passage 42.

Referring now to Figures 5 and 6, the centrally arranged baffle 36 defines a plurality of circular orifices 44 each of which receives an elastomeric annular seal element 46. The seal 46 has a frustoconical surface 48 which facilitates the insertion of the seal 46 in the circular orifice 44 and a re-entrant annular groove 50 disposed around its periphery which securely fixes the seal 46 in one of the circular orifices 44. A tube *

The thin-walled metal distributor 52 is housed inside each of these seals 46. The distributor tube 52 is retained axially inside the seal 46 by a veil 54 projecting outwards formed in the distributor tube 52 adjacent to one end which cooperates with a semi-circular recess 56 of complementary configuration formed in the interior surface of the seal element 46. Each of a plurality of distributor tubes 52 is arranged concentrically in one of the collector elements 14 and extends axially beyond the open end of the associated collecting element 14 by a sufficient distance to be able to be fixed in the baffle 36 as described. At the opposite end of the distributor tube 62, i.e. the end disposed in the collecting element 14, a plurality, preferably three ears or tongues 58 directed towards the outside, maintain the distributor tube 52 in a coaxial arrangement inside the collecting element 14.

In axial alignment and concentrically around each of the distributor tubes 52 there is a first circular orifice 60 defined by the outer metallic casing 30 and a second circular orifice 62 defined by the inner metallic casing 32. A portion of the insulating tiles 34 disposed between the orifices 60 and 62 is deposited a circular cavity 64 which receives a molded annular seal 66. The molded seal 66 is preferably made from an elastomer based on silicon and can be retained in the assembly of tubing 12 by application of a thin layer 68 of a silicon-based adhesive product coincide with the annular contact space between the molded joint 66 and the insulating slabs 34. The molded joint 66 has an outer lip 70 which functions as a caulking element and which moreover comprises a plurality of triangular veils 72 circumferential directed inwards which act as a chevron joint to ensure the sealing ity and tightening of the collecting elements 14 in the tubing assembly 12.

As indicated above, one of the plurality of collecting elements 14 is arranged coaxially around each of the distributor tubes 52. The collecting elements 14 are preferably circular in section and are made of glass. Each of the collecting elements 14 has an outer wall 80 and

An inner wall 82 of smaller diameter. The walls 80 and 82 define an elongated annular zone 84 between the latter which is subjected to a high vacuum of approximately 10- ^ torr. The vacuum is obtained by removing the air from the region 84 at the end of the collecting elements 14 and a tab 86 at this location is hermetically sealed according to methods known in the art. The vacuum in region 84 essentially eliminates conduction and convection losses from the conductive elements 14. The interior walls 82 of the collector elements 16 preferably have an energy absorbing surface 88. The energy absorbing surface has a selective coating wavelength with high absorbency and reduced emissivity of the order of 0.1 or less in the infrared region which can be manufactured by vacuum deposition of a thin layer (1,000 Angstroms) of aluminum on the external surface of the internal walls 82 of the vaporized collecting elements 14. A layer of chromium is then. electrically and deposited on the aluminum substrate in the form of black chromium at a thickness of approximately 1,500 Angstroms. Otherwise, the surface 88 can be blackened with a coating of infrared energy absorbing material such as magnesium oxide, magnesium fluoride, etc.

Referring now to Figures 3, 5 and 7, the tubing assembly 12 further includes a blower assembly 90 disposed centrally. The blower assembly 90 comprises an electric motor 92 of essentially conventional type which is fixed by removable means 94 on the external metal casing 30 of the tubing assembly 12. Preferably, the electric motor 92 is suitably waterproofed . Otherwise, the motor 92 can be housed in a protective fairing (not shown). The electric motor 92 comprises a receiving shaft 96 provided with a coupling member 98 S selective attachment which drives the shaft 100 of a blower projecting through the insulating slabs 34 in a coated passage 102 and in the passage 40 intake or supply. At the end of the shaft 100 arranged in the feed passage 40 is fixed the wheel 104 of a squirrel cage blower of conventional type. A suitable fairing 106 fixed on the baffle 36 defines an inlet orifice 108 which is arranged concentrically with and in close proximity to the wheel 104 of the blower.

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Referring now briefly to Figure 7, the tubing assembly 12 also includes an air barrier 110 disposed in the supply passage 40 between the baffle 36 and the inner metal casing 32, and an arcuate panel 112. The air barrier 110 and the arcuate panel 112 both have a symmetrically arranged curved surface 114 which ensures uniform distribution of the air coming from the wheel 104 of the blower towards all the regions of the passage 40 of intake or supply. Access to the blower wheel 104 is easily ensured by manufacturing the arcuate panel 112 and a corresponding external panel 116, which forms a portion of the external metal casing 30, in the form of removable sections which can be fixed by means 118 removable as desired.

Referring now to Figures 2 and 5, the tubing assembly 12 also includes an elongated heat exchanger assembly 120 which is disposed in the exhaust or return air passage 42. The heat exchanger assembly 120 comprises a pair of parallel and elongated plates 122 used for mounting the heat exchanger assembly 120 between the baffle 36 positioned centrally and for blocking approximately two thirds of the width of the passage 42 d 'exhaust or return. A pair of tubes 124 fluid conductors, flat and parallel, is hermetically fixed on the pair of elongated plates 122. The pair of tubes 124 defines an elongated rectangular passage 126 in which is disposed a fin or surface 128 in heat transfer coil. . The heat transfer surface 128 is preferably made of metal such as copper, having good heat transfer characteristics, and its general configuration can conform to the conventional practice of heat transfer in order to optimize the heat exchange from the air passing through the passage 126 to the fluid passing through the tubes 124. At each end of the flattened tubes 124 there is a tube 130 which ensures the communication and the distribution of the flow between the flattened tubes 124 and a single line 132 of fluid. At one end of the heat exchanger assembly 120, the fluid line 132 describes a direction reversing elbow (not shown) and the fluid line 132 is juxtaposed on the heat exchanger assembly. heat 120 lengthwise

Page 10 so that the two fluid intake and exhaust lines 132 extend from the same end of the tubing assembly 12 as shown in Figure 1.

Referring now to FIG. 4, the air circulation inside the tubing assembly 10, the collecting elements 14 and the distributing tubes 52 will be described. As indicated above, the wheel 104 of the blower is positioned inside the supply passage 40, which allows the passage of air therein. A portion of the air supplied by the wheel 104 of the blower enters the plurality of circular passages defined by the thin-walled distribution tubes 52 and goes to the left, outwards and away from the tubing assembly 12 Likewise, a substantially equal portion of the air supplied by the wheel 104 of the blower enters the annular spaces defined by the thin-walled distribution tubes 52 and the interior surfaces of the interior glass walls 82 of the manifold elements 16. This air is directed to the right, outwards and away from the tubing assembly 12. In both cases, as the air flow reaches the end of the distributor tubes 52 and the walls of interior glass 82, the flow direction is reversed. In the first case, the air circulating in the circular passage of the distributor tube 52 begins to flow inward towards the passage 42 back into the annular spaces defined by the distributor tubes 52 and the inner glass walls 82 of the elements collectors 14. In contrast, the air which previously circulated outwards in the annular regions again flows towards the passage 42 in the circular passage defined by the distributor tubes 52. The air then passes through the passage 126 from the heat exchanger assembly 120 and releases the thermal energy collected in the collecting elements 14 in favor of the surface 128 of the heat exchanger and possibly towards the fluid circulating through the flattened tubes 124 of the assembly 120 heat exchanger. The air is then drawn through the circular orifice 108, through the wheel 104 of the blower, and is recirculated.

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Also with reference to FIG. 4, the preferred spacing, without however being compulsory, is shown between adjacent collector elements. As mentioned above, the collecting elements 16 are preferably circular in cross section. Where "T" indicates the diameter of a collecting element 14, it has been found that the optimum density, and consequently the best efficiency from the point of view of energy collection, are obtained when the collecting elements 16 are spaced apart from one another. approximately equal distance. to "T". In other words, the spacing on centers between collecting elements is preferably equivalent to "2T". It should be noted, however, that this preferred spacing should not be considered as a limiting factor of the present invention or as an absolute condition which should not be changed.

As indicated above, the common approach to improving the distribution and transfer of heat in conventional air treatment systems followed in the prior art has involved increasing the operating pressure of the system. Unfortunately, attempts to apply this logic to solar heat recovery systems may require such an increase in the supply of energy to the system to create the desired operating pressures that the overall efficiency of the system will be reduced. In the solar energy collector 10 of the present invention, the location of the pressure losses, hence of turbulence and better heat transfer, has been carefully studied with a view to occurring essentially at the locations of heat transfer and therefore allowing operation at an exceptionally low air pressure and energy input. As regards the collecting elements 14, it should be noted that the cross-sectional areas of the circular passages defined by the thin-walled distributor tubes 52 and the annular passages defined by the outer wall of the distributor tubes 52 and the inner surfaces of the inner walls 82 of the collecting elements 14 are uneven, the cross-sectional areas of the former being substantially larger. Such a disparity between areas in cross section results in an increased flow speed in the annular zones accompanied by turbulence which disturbs the boundary layers adjacent to the interior and exterior surfaces of the annular spaces, thereby improving the transfer of heat to the air. .

As an example, a thin-walled dispensing tube 52 having a diameter of about 1.25 inches will have an internal cross-sectional area equal to approximately 1.2 square inches. When it is positioned concentrically in the interior wall 82 of a collecting element. 14 having an internal diameter of about 1.54 of an inch, the resulting annular space has a cross-sectional area of about 0.6 square inch, or approximately half the cross-sectional area of the interior passage of the tube distributor 52.

In this way, not only is the air more turbulent inside the annular space and therefore less likely to form insulating boundary layers, but the loss of energy and the pressure drop associated with the turbulence occur precisely at the place of energy supply and thus significantly improve energy recovery and overall efficiency.

Furthermore with regard to the flow rate and the pressure drop, it should be noted the construction of the assembly 120 of heat exchanger. The elongated plates 122 close off about two thirds of the cross-sectional area of the exhaust or return passage 42 defining the neck of the passage 126 and throttling the air flow. The air flow through the passage 126 is thus significantly faster and turbulent than that occurring in other portions of the tubing assembly 12. Thus, again, the location of a pressure drop coincides with the place of energy transfer.

An air-liquid solar energy collector using liquid as the last heat transfer medium also has structural advantages. The open arrangement of collectors, i.e. the absence of continuous reflective panels and / or transparent protective covers, as well as the cylindrical outer surfaces of the collecting elements 14 result in very low aerodynamic resistance and virtually eliminate any wind load considerations. This reduced resistance also decreases the need for large, heavy and expensive support structures which can significantly increase the overall cost of the solar energy collector system. Furthermore, the use of a gas such as

Air as the primary heat recovery medium reduces the operating weight of the collector, further reducing the size and cost of the associated structural elements. The fact that the secondary and final heat recovery medium is a fluid such as water having a high specific heat is also advantageous. Specifically, the transfer of the solar energy recovered from the collector 10 to the place of use in a building can be accomplished by the use of a conventional copper pipe or pipes, more recently developed, made plastic and well insulated. Typically, this pipe will have an outside diameter of less than half an inch and not more than an inch in diameter after application of suitable insulation. This reduced diameter makes the installation, especially in existing buildings, ordinary and generally uncomplicated because the piping can be routed through beams, uprights and walls without extraordinary complications.

- Also with regard to the heat transfer fluid circulating in the tubes 124 of the heat exchanger assembly 120, it should be clear that water is a good choice from the start because of its reduced cost, availability, safety and high specific heat. An equally obvious disadvantage of using water is its susceptibility to phase changes, i.e. the gel and the consequent volumetric expansion which occurs when it passes from the liquid phase to the solid phase. It should therefore be clearly understood that other liquids such as glycols or mixtures of glycols must be taken into account with a view to their use as recovery fluid in the collector 10. 1 will also appear that the overall size and therefore the capacity energy recovery of the unitary air-liquid solar energy collector 10 will typically be determined by its application. However, provision can be made for the collector 10 to typically comprise seventy-two collecting elements 14 staggered in two rows of thirty-six elements each. The number as much as the length of the elements 14 can vary significantly.

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Finally, the staggered arrangement of the distributor tubes 52 and the elements 14 is worth noting. This arrangement greatly simplifies the construction of the tubing assembly 12, particularly of the baffle 36.

In many collectors of the prior art, several baffles and passages were necessary to distribute the air towards the various elements of heat recovery. This complexity, in addition to increasing the cost of the manifold, often resulted in poor air distribution.

. In the solar energy collector 10 of the present invention, two essentially identical parallel passages 40 and 42 ensure the direct and uniform distribution of the air to the collecting elements 14 and the distributing tubes 52.

The previous mode is the best mode imagined by the inventor for the implementation of the present invention. It is evident, however, that devices with modifications and variations will appear to those skilled in the art of solar energy recovery. Given that the description which has just been made is intended to enable those versed in the art to implement the present invention, it should also be interpreted so as to understand the said obvious variations and to be limited only by the spirit and scope of the following claims.

Claims (16)

1. Air-liquid solar collector comprising in combination a tube having two passages, a plurality of solar collecting elements having an interior wall, an elongated hollow member disposed inside each of said collecting elements, each of said hollow members defining a passage. interior communicating with one of said passages of the tubing and each of said respective collecting elements defining an external passage between said interior wall of said collecting element and said elongated member communicating with the other of said passages of tubing, and a heat exchanger air-liquid heat disposed in one of said passages. 2. Solar collector 'of claim 1 further comprising means for circulating air through said manifold elements, said hollow members, said passages and said heat exchanger. 3. The solar collector of claim 1 further comprising a frame structure serving to support said tubing and said collecting elements. 4. The solar collector of claim 1 wherein said collecting elements are arranged in two rows on the opposite faces of said tubing in a co-planar arrangement. 5. The solar collector of claim 1 in which said collector elements are cylindrical and are arranged in two rows on the opposite sides of said tube in parallel relationship with said cylindrical elements and all of said elements in one of said rows are offset laterally λ by relative to said elements of the other of said rows by a distance approximately equal to said diameter. 1 2 3 4 The solar collector of claim 1 wherein said heat exchanger cha 2 extends substantially along the entire length of one of said steps 3 wise of the tubing and comprises elongated means for sealing a portion 4 the width of said passage. Page 16 7. Air-liquid solar collector comprising in combination a tube having two adjacent passages, a plurality of sets of evacuated collecting tubes, each of said sets comprising an elongated collecting element having an inner wall and an elongated hollow member disposed inside and defining an interior passage in said member and an exterior passage between said member and said interior wall of said collecting element, said interior passage of each of said assemblies communicating with one of said two * passages of the tubing and the exterior passages of each of said communicating assemblies with the other of said two passages of the tubing, an air-liquid heat exchanger disposed in one of said two passages of the tubing and means for circulating air through said passages, said manifold assemblies and said heat exchanger heat. 8. Solar air-liquid collector of claim 7 wherein said collecting elements are cylindrical and are arranged in two co-planar rows on opposite sides of said tubing in parallel relationship and spaced apart by a distance approximately equal to the diameter of said elements and said elements in one of said rows are offset laterally with respect to said elements in the other of said rows by a distance approximately equal to said diameter. 9. The air-liquid solar collector of claim 7 in which the said air circulation means comprise an electric motor, a blower wheel, "and said tube also comprises means intended to aid the uniform distribution of air. inside at least one of said passages of the tubing 1 2 3 4 5 An air-liquid solar collector of claim 7 in which said heat exchanger 2 comprises a pair of parallel liquid transport tubes 3 defining a air passage, means arranged in said air passage 4 for increasing the heat transfer between the air circulating in said air passage 5 and the liquid circulating in said tubes and means for closing a portion of one of said two passages of the pipe in which the heat exchanger is arranged. 11. solar air-liquid collector of claim 7 wherein said tubing comprises an outer sheath and an inner sheath defining between them a volume, said volume occupied by an insulating material, a baffle, disposed substantially centrally inside said sheath inside and defining said two passages of the tubing and a plurality of orifices intended to receive one end of said elongated hollow member. 12. Solar air-liquid collector comprising in combination a tube having an outer sheath, an inner sheath, a baffle disposed substantially centrally in said inner sheath and defining two adjacent passages, an air-liquid heat exchanger disposed in one of said passages. and means for circulating air, a plurality of sets of evacuated manifold tubes, each set having an elongated manifold having an inner wall and an outer wall and an elongated hollow member disposed therein and defining an interior passage in said member and an exterior passage between said member and said interior wall of said collecting element, said interior passage of each of said manifold assemblies communicating with one of said two passages of the tubing and the exterior passage of each of said assemblies communicating with the 'other of said two passages of the tubing. 13. The air-liquid solar collector of claim 12 wherein the cross-sectional area of said interior passages is approximately twice the area. in cross section of said outer passages. 14. The air-liquid solar collector of claim 12 wherein said elongated hollow members comprise means for maintaining them in a substantially coaxial relationship in said interior wall of said collecting elements. 1 * solar air-liquid collector of claim 12 further comprising insulating tiles disposed between said outer sheath and said inner sheath. Page 18 16. The air-liquid solar collector of claim 7 wherein said heat exchanger comprises a pair of parallel liquid transport tubes defining an air passage, means arranged in said air passage and intended to increase the transfer of heat between the air circulating in said air passage and the liquid circulating in said tubes and means serving to close off a portion of one of said two passages of the pipe in which the heat exchanger is placed, 17. Solar air-liquid collector of claim 12 further comprising a frame structure for supporting said tubing and said manifold assemblies. 18. The solar air-liquid collector of claim 12 in which said means for circulating air comprise an electric motor and a blower wheel and said tube also comprises means intended to aid the uniform distribution of air in the 'at least one of said two passages. 19. The air-liquid solar collector of claim 12 wherein said collecting elements are cylindrical and are arranged in two co-planar rows on opposite sides of said tubing in parallel relationship and spaced apart by a distance approximately equal to the diameter of said elements and said elements in one of said rows are offset from said elements of said other rows by a distance approximately equal to said diameter. i # "*