WO2009027700A2

WO2009027700A2 - Solar collector

Info

Publication number: WO2009027700A2
Application number: PCT/GB2008/002943
Authority: WO
Inventors: John Clifford Hobbins
Original assignee: Cct (Hinckley) Limited
Priority date: 2007-08-29
Filing date: 2008-08-29
Publication date: 2009-03-05
Also published as: EP2245382A2; WO2009027700A3; GB0716811D0

Abstract

The solar collector comprises a heat pipe panel (302) and a heat exchanger (303). The heat pipe panel (302) has a series of upwards extending tubes (304), which are hydro-formed inflations of the two metal skins that the panel (302) is made of. Substantially sine wave undulations (U) are formed in the panel (302) with the direction of the wave extending along the tubes (304), each tube (304) having the same undulation. The undulations (U) give the panel stiffness against curvature in the other direction, which is the curvature that the panel (302) tends to experience.

Description

SOLAR COLLECTOR

The present invention relates to a solar collector.

In another international application having the same priority date as this application and filed under Nigel Brooks' reference 2763/PCT, ("Our Co-Pending Application") there is described a heat pipe panel. An extract of the disclosure of that application is repeated here:

Figure 1 is a perspective view of the heat panel; Figure 2 is a cross-sectional view in the X direction through a welding bed set up for welding the heat panel;

Figure 3 is a similar cross-sectional view in the Y direction through the welding bed, showing edge clamps;

Figure 4 is a scrap view in the X direction of the end of the welding bed showing another end clamp;

Figure 5 is a perspective view of an XfY robotic device supporting a welding laser above the welding bed;

Figure 6 is a perspective view of the welded product of Figure 1 after hydroforming into a solar, heat pipe product; Figure 7 is a cross-sectional plan view of the heat pipe product of Figure 6;

Figure 8 is a perspective view of a heat exchanger product for the heat pipe product of Figure 6;

Figure 9 is a cross-sectional plan view of the heat exchanger product, taken on the line VIII-VIII in Figure 8; Figure 10 is a cross-sectional end view of the heat exchanger product, taken on the line IX-IX in Figure 8;

Figure 11 is a diagrammatic cross-sectional side view of a hydro-forming press for forming the heat exchanger product;

Figure 12 is a view similar to Figure 12 of the press tool, taken at right angles to the view of Figure 12, without the heat exchanger sheets in the tool; and Figure 13 is a view similar to Figure 6 of the heat pipe product having the heat exchanger product fitted to the top margin of the heat pipe product, the combination comprising a solar collector. Referring to Figure 1, a welded product comprises a pair of flat, metal sheets 2, 3, typically of steel and typically 0.25mm thick and a metre square. The top sheet 2 is more extensive than the bottom sheet 3. The sheets are welded together at an array in both X & Y directions of welds 7, the welds being intermittent lines parallel with the X direction and spaced in the Y direction. A peripheral weld 10 surrounds the array of welds 7.

Turning to Figures 2 & 3, for making the product, aflat welding support or bed 21 is provided in its face with a series of channels 22 in register with the positions of the welds 7, 10 to be formed. The channels are pneumatically connected together to a vacuum duct 23 having a cock 24 and thence to a source of vacuum 25. The bed has a series of spring loaded pegs 26 extending up from its surface for initial location of the sheet 3. Within these is a channel 27 having a seal 28 for sealing the sheet 3 to the welding bed, whereby application of vacuum pulls the sheet against the bed.

Outside the extent of the sheet 3, an outer vacuum channel 31 is provided. It is connected to the vacuum source via its duct 32 and its cock 33. Around this, an outer seal channel 34 and seal 35 is arranged. Thus the sheet 2 when laid over the sheet 3 can be pulled down by vacuum onto it and the bed around the sheet 3.

Simple clamps 41 are arranged along one pair of edges 42 of the bed 21 for the corresponding edges 43 of the sheet 2. The clamps have outer edge ribs 44 engaging in recesses 45 in the bed. Actuators 46 beneath the welding bed have rods 47 arranged along the middle of the clamps for pulling them down. Their inner edges 48 are formed to grip the sheet 2 and hold it against the bed.

With reference to Figures 4, at the other edges 50 of the bed, more substantial clamps 51 are provided. The welding bed is mounted on a machine structure 52. The clamps 51 are mounted on the structure 52 to be movable away from the welding bed and clamped to the machine structure by actuators 53. Between the clamps and the bed, eccentric driven clamp movers 54 are provided. They have shafts 55 journalled in bearings 56 abuttingly secured to the edges of the bed and eccentrics 57. The clamps have nibs 58 extending towards the eccentrics. A rotary actuator 59 turns the shafts to move the clamps away from the welding bed, by action of the eccentrics on the nibs. The clamps themselves are similar to the edge clamps, although more substantial, having V form jaws 60,61 for tightly gripping the sheet 2 and jaw closure actuators 62.

As shown in Figure 5, over the welding bed is mounted a welding head having YAG laser 71 via an X/Y robotic device 72, which is of conventional design. It is arranged such that as the laser is traversed in its use position, advanced close to the welding bed, the laser head remains at a constant distance D from the welding bed.

For production of the product, a lower sheet 3 is laid on the welding bed, located by the pegs 26. Vacuum is applied to the channels 22 by opening the cock 24, pulling the sheet 3 down against the welding bed. An upper sheet 2 is then laid over the lower sheet, with the side and end clamps open. The cock 33 is opened and the top sheet is pulled down onto the lower sheet.

With the eccentrics turned to allow the end clamps to approach the welding bed, the clamps are all closed. The eccentrics are turned and the top sheet is tensioned. The jaws 60, 61 are set slightly below the surface of the welding table, whereby top sheet is pulled downwards at the edges 50 of the web and the sheets are held firmly against the welding bed, by the combination of the vacuum and the tension.

The result is that with the sheets so firmly held in position and contacting each other across the fully extent of the smaller sheet 3, the free face of the sheet 2 is parallel the face of the welding bed on which the sheet 3 is supported. In other words the face of the sheet 2 is planar.

The X/Y robot and the YAG laser are now controlled to make the welds. Once the laser is advanced to its use spacing from the sheet 2 in one position, this spacing will be maintained wherever the robot traverses the laser to. Thus, the welds can be made wherever desired for their array. Referring now to Figures 6 & 7 of the drawings, a welded (as described above) and hydroformed (in a manner similar to that described below for the heat exchanger 111) heat pipe product or solar collector panel 101 is shown, which is one metre square and has two 0.25mm skins of stainless steel 102,103, with an array of tubes 104 formed in them; that is to say that each tube is comprised of an elongate D- section formation 105 in one skin, aligned with a similar formation in the other skin, the two D-formations providing the tube. At the sides of each tube, the skins radiate from its transverse diameter towards adjacent tubes at lands 106, which abut and are welded together by welds 107, laser formed in the manner described above. The welds unite the skins and enable them to resist the considerable internal pressure generated in the panel during use as a heat pipe. Simple line welds 107 centrally of the lands are shown in the left hand sides of Figures 7 and 8; whilst alternative pairs of parallel, intermittent line welds 108 are shown at the right hand side of these Figures. The welds 108 are close to the D formations in the individual skins and improve stability of the panel at the expense of substantially twice the length of weld.

The tubes are united top and bottom by transverse tubes 109, which act to equalise pressure in the tubes of the array. Hydroforming was performed in a two part tool, having the shape of the D formations cut in their opposed surfaces and an outlet for hydroforming liquid, injected into the panel via a point 1091. This was welded closed after the hydroforming liquid was withdrawn a replaced by a predetermined quantity of heat pipe liquid. A peripheral weld 110 seals the entire panel close to its edges, which are cropped.

Referring to Figures 8, 9 & 10, a heat exchanger product 111 for the heat pipe panel is of more complex form and is long and narrow compared with the square outline of the solar collector, the heat exchanger being designed to co-operate with the top 15% approximately of the collector. It also is of two skins 112,113. They are intermittently welded together at recesses 114 in the outer skinll2, that is where the skin not in contact with the solar panel in use. Apart from the recesses 114 and top and end margins 115,116, the entire outer skin is lifted away 117 from the inner skin, including at D section connection formations 118 in the end margins and between the recesses 114. The inner skin has pressed indentations 119 which are complementary to the tubes 104,109 of the collector. The welded recesses are at the same pitch as the lands 106.

The recesses 114 are opposite webs 120 in the inner skin, which extend between the indentations 119. Further, the recesses and the welds 121 at the bottom of the recesses are arrayed in two dimensions, the first along the webs and the second transverse to the first in the direction of the length of the heat exchanger, that is across the length of the heat pipe tubes 104. Whilst the welds in adjacent webs could be aligned with the second direction, in the preferred embodiment, it is those in alternate webs that are so aligned, with the welds in the adjacent webs being offset at half their pitch P/2 along the webs, whereby heat transfer fluid passing between each pair of welds is displaced up or down to mix thoroughly for enhanced heat pick up. In other words, the recesses 114 and their welds 121 act as flow distributors. Immediately inside the connection formations 118, longer distributors 1141 are provided to act as deflectors, deflecting flow from remaining in the top portion of the heat exchanger only and deflecting at least part of it downwards towards the bottom portion.

Except at the connection formations 118, a peripheral weld 122 is provided around the lifted away portion 117. All the welds 121 and the peripheral weld 122 are in the same plane, namely at the inside face of the inner sheet. For sealing of the heat exchanger at its edge bottom edge 123, which passes across the tubes 104, the webs 120 are bent up to the level of the furthest extent 124 of the indentations 119. The outer skin meets the inner skin at this level with a bottom extent 125 of the peripheral weld. Thus this weld is out of the plane of the other welds.

The heat pipe 1 and the heat exchanger 111 are formed essentially similarly and the formation of the heat exchanger 111 only will now be described.

For forming the heat exchanger product - referring Figures 11 and 12 - a hydroforming press 201 is equipped with upper and dies 202,203. The lower die has upstands 204 corresponding to the indentations 119 and the upper die has generally recessed area 205 corresponding to the inflated portion 117 of the outer skin 112. Arrayed within the area 205 are non recessed pieces 206, which appear as protrusions but in fact extend only as far as the level of a peripheral region 207 of the die. The lower die has location dowels 208 and a hydroforming fluid duct 209, with a surrounding seal 210. The upper die has apertures 2081 for receiving the dowels on closure of the tool. The lower die has an upstand 211 corresponding to the height of the bottom edge of the heat exchanger, with the upper die having a complementary rebate 212.

In the manner described with reference to Figures 1 to 6 above, two flat sheets 112,113 of stainless steel are welded together with the array of welds 121 and the peripheral weld 122 to form a "welded product". At this stage, the sheets are still over-size with respect to their finished size. Two extra welds 126,127 are provided. The inner 126 of these extra welds extends around the top (in use) and sides of the heat exchanger and defines the outer limit of the heater exchanger when cropped to size, around the top and end margins 115,116. The outer weld 127 is limited to defining small regions 128 outwards of the connections formations 118, which are inflated to allow full inflation of these formations to the edge of the heat exchanger, and at one side an additional area that is not inflated, but includes an aperture 129 in the inner sheet, through which hydroforming inflation fluid can be introduced into the product. This aperture is in register with the hydroforming duct 209. It should be noted at this point that the D inflations for connection are more substantial in the extent of the inflation of the outer skin than the main inflation 117. The regions 128 extend in strips of sheet material 130 to be cropped off. These strips include apertures 131 via which the sheets are located on the dowels 208.

The "welded product" is placed on the lower die, located by the dowels 208.

The duct 209 is in registered with the aperture 129. The press is closed with the skins being gripped at the welds 121 by the upstands 204 and the non-recessed pieces 206. It is also gripped by faces of the dies at the margins 115, 116 and at the bottom edge upstand 211 and rebate 212. During the die closing process, the lower sheet rests on the upstands 204 initially and both sheets are formed to an initial extent during complete closure. The edge margins are held in their intended position by the dowels.

Once the die is closed and clamped, hydroforming fluid is applied under pressure to the aperture 129. This inflates the outer skin to its level 117 and to create the connection formations 118. Further, between the upstands 204, the inner skin is pressed back down to the level of the margins causing it to have the indentations. These deformations occur with plastic deformation and are permanent. So far as the inner skin is concerned, the result is formation of the indentations from the original flat form of the sheet.

The heat exchanger product is finished by peripheral trimming to size.

The heat pipe is formed in like manner in a similar die. A measured quantity of water is introduced into the tubes and a vacuum is drawn in them. Its hydroforming aperture is welded closed by conventional means. The heat pipe panel thus becomes an array of heat pipe tubes.

As shown in Figure 13, the heat exchanger is secured to heat pipe product by clinches 140 formed in the margins of the two products. Additionally to further ensure that the two products are kept in close contact remote from the clinches, double U clips 142 are provided. These are in the general configuration of paper clips. They have a short bridging limb 143 with a long gripping limb 144 extending from each end of the bridging limb to bear on opposite sides of the combined product urging the two components together. At the ends of the long limbs remote from the bridging limb, further bridging limbs 145 extend parallel to the main bridging limb. Since one of the long limbs engages the between a pair of the heat pipe tubes, the further bridging limbs are offset 146 out of the plane of the long limbs and extend across to the position of the respective other long limb. Thence further long limbs 147 extend back towards the main bridging limb. Thus the long limbs and their counterpart further long limbs grip the two components between themselves, urging the components into close contact.

Whilst this panel can be formed flat, it has a tendency to deform in use.

The object of the present invention is to stiffen the panel against this deformation.

According to the invention there is provided a solar collector comprising: • a heat pipe panel having

• heat pipe tubes running from a lower end to an upper end thereof and

• undulations in the panel along the length of the tubes, the undulations providing stiffness against curvature about an axis parallel to the general direction of the pipes and

• a heat exchanger in contact with a face at the upper end of the panel.

Preferably, the heat pipe panel has an upper margin - conveniently between 10% to 20% and typically 15% of its height - which is free from undulations where the heat exchanger contacts the panel.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 14 is a side view of a solar co Hector according to the invention;

Figure 15 is a scrap perspective view of a heat pipe panel of the solar collector of Figure 1.

Referring to Figures 14 & 15, a solar collector 1 is primarily comprised of a heat pipe panel 302 and a heat exchanger 303, both formed as disclosed Our Co- Pending Application.

The heat pipe panel 302 has a series of upwards extending tubes 304, which are hydro-formed inflations of the two metal skins that the panel is made of. Between the tubes are lines of welds 305 joining the skins. The tubes are sealed within an outer peripheral weld 306.

The heat exchanger 303 similarly is formed of two welded and hydroformed metal skins. It has one side that has indentations complementary to the tubes of the heat pipe panel, so that the panel and the exchanger can be in good heat transfer contact. The exchanger also has end formations 8 to which connection tubes are brazed, the tubes being for flow of heat exchange liquid. On heating, the heat pipe panel has a (not understood) tendency to deform with curvature when viewed from above, in the direction of the tubes.

In accordance with the invention, substantially sine wave undulations U are formed in the panel with the direction of the wave extending along the tubes, each tube having the same undulation. The undulations give the panel stiffness against curvature in the other direction, which is the curvature that the panel tends to experience.

The undulations can be formed at the stage of hydroforming of the tubes in the panel. However, they are preferably formed in a press with a pair of dies in the usual metal pressing manner.

The top margin of the panel is the part most prone to deformation, apparently because it is the hottest part of the panel in use - the heat pipes transferring heat to it. However the margin, and the heat pipes within it, is kept free of undulations whereby the heat exchanger can be mated to it.

Claims

CLAIMS:

1. A solar collector comprising:

• a heat pipe panel having

• heat pipe tubes running from a lower end to an upper end thereof and • undulations in the panel along the length of the tubes, the undulations providing stiffness against curvature about an axis parallel to the general direction of the pipes and

• a heat exchanger in contact with a face at the upper end of the panel.

2. A solar collector as claimed in claim 1, wherein the heat pipe panel has an upper margin - conveniently between 10% to 20% and typically 15% of its height - which is free from undulations where the heat exchanger contacts the panel.