GB1596696A

GB1596696A - Solar radiation receiving apparatus

Info

Publication number: GB1596696A
Application number: GB7180/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-02-23
Filing date: 1978-02-23
Publication date: 1981-08-26
Also published as: AU4446179A; FR2418426A1; AU528932B2; BR7901168A; CH635918A5; ES477963A1

Abstract

The device has at least one receiver element, which in turn has a tube (2) and at least one metal longitudinal rib (1) arranged on the tube. To this there is associated a channel (5) which is closed at both ends and which has a mirror-like reflecting inner surface (6) for reflecting the direct and diffuse radiation, which strikes the tube (2) and rib (1) indirectly, and also a heat exchanger for transmitting the heat developed in the tube (2). The tube (2) can be a heating tube, and the heat exchanger is then situated at the end of the heating tube (2). The tube (2) can also have a chamber for the delivery and discharge of liquid to be heated. <IMAGE>

Description

(54) SOLAR RADIATION RECEIVING APPARATUS (71) We, DAVID PETER WALKER and NIGEL GEOFFREY ALAN COBHAM, both British Subjects, and both of 63, Sydney Road, Haywards Heath, Sussex RH16 1QD, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for receiving both direct and diffuse solar radiation and converting it into useful heat. In particular the invention relates to a solar radiation receiving element intended to form at least part of such apparatus.

Thus in accordance with the invention in its widest aspect a solar radiation receiving and converting apparatus comprises at least one closedended channel having specular inside curved and end surfaces, a solar radiation receiving element comprised of at least one tube with at least one attached fin and which is disposed at or outside the entrance to said channel or channels opposite the whole length but only part of the width of the channel or channels so as to receive solar radiation both directly and by reflection from specular surfaces, and means for transferring thermal energy from said element to a place of utilisation. Each tube may if required be a heat pipe and the heat transfer means may be situated at an end thereof.

The finned heat pipe - that is to say a sealed low pressure boiling and condensing device, utilises gravity and/or capillary action for condensate to return to an evaporator section. In such a device thermal energy is transported by means of the latent heat of evaporation of the working fluid. The finned heat pipe will normally be made wholly or in part of metal or other suitably conductive material coated with a radiation absorptive coating, which may be a composition having a low thermal emissivity and a high absorptivity (selective coating). The composition may consist of a metal base electroplated firstly with nickel and then black chrome plated to a thickness of the order of the wavelength of the incoming short wave solar radiation.

The reflective surface may be provided by a closed ended channel shaped structure which may be of semi-cylindrical shape, such that the finned heat pipe covers approximately 50% of the area of the entrance to the structure and at least one side of the fin(s) being coincident with the centre line of the closedended channel shaped reflector. A suitable reflective surface may be aluminium or silver.

Solar radiation elements as foresaid may be of any suitable length or configuration and may be arranged side by side as a parallel or series connected set through which fluid to be heated is caused to flow by convection, gravity or pump pressure.

Various embodiments of the invention are hereinafter described by way of example with reference to the accompanying drawings in which: Figure 1 is a plan view of a typical radiation receiving element.

Figure 2 is a section on line A-A of Figure 1.

Figure 3 is a section on line B-B of Figure 1.

Figure 4 is a section similar to that of Figure 3 showing an alternative embodiment.

Figure 5 is a plan view of a solar radiation receiving apparatus comprised of two seriesconnected elements as foresaid.

Figure 6 is a section on line A-A of Figure 5.

Referring firstly to Figures 1 to 3, the solar radiation receiving element therein shown comprises a conductive fin 1 made of metal with a heat pipe 2, also made of metal bonded to it. The heat pipe and the fins are such as to cover approximately 50% of the aperture 3 of a closed-ended semi-cylinder 5 having a reflective surface 6 constituted by a coating of aluminium. An heat exchanger 4 is located at one end of the heat pipe and provides a flow passage for a fluid, such as water, which is to be heated.

As shown in Figure 3, the part of the reflector aperture not covered by the heat pipe and fins allows access of solar radiation to the reflector 5, 6.

Referring to Figure 6, it can be appreciated that on exposure of the elements to the sun, direct and diffuse solar radiation enters the elements through the transparent cover plate 7. Some of this energy impinges directly on the heat pipes and fins and is absorbed by a selective coating whilst a high proportion of the remainder of the direct and diffuse radiation impinges on it after reflectance from the surface 6. The absorbed energy which is now in the form of thermal energy is transferred to the heat pipe working fluid by conduction through the fins and pipe walls to the evaporator region whereupon the action of the heat pipe transports the thermal energy to the condenser region which forms part of the heat exchanger 4 thus the energy is given to the fluid which is to be heated.Loss of energy by reradiation is reduced by the selective coating, and the insulating properties enhanced by the reflective surfaces surrounding the absorber.

Figure 4, shows an alternative embodiment in which two closed-ended channel shaped reflectors disposed longitudinally side by side are utilised. In this embodiment the two reflectors have an aperture equivalent to that of the first embodiment. However the depth of the reflector is now reduced to half.

Referring now to Figures 5 and 6, there is shown an assembly of two solar energy receiving elements as described with reference to Figures 1 to 3 connected side by side, surrounded by a thermal insulating material 8 and overlaid with a transparent cover plate 7, which faces the direction of solar radiation.

Heat exchangers 4 at the ends of the pipes 2 are series-connected and have a fluid flow inlet pipe 9 and a fluid flow outlet pipe 10, respectively connected thereto.

When the tube is not a heat pipe, any number of solar energy receiving elements as aforesaid, preferably parallel with one another, may be coupled together by a common fluid inlet pipe and a common fluid outlet pipe.

These pipes themselves may also be formed with at least one metal fin and at least one reflective surface so as to function in the same manner as the individual solar energy receiving elements which they serve to connect.

Although in Figures 4 and 6 the pipes 2 and associated fins 1 are shown as being located in a common plane diametric to the adjacent closed-ended semi-cylindrical reflectors it may be preferable in certain circumstances - for instance to avoid risk of reflector damage - to space the nearest point of the pipe/fin element slightly outside the confines of the reflector. Thus referring to Figure 4, the fins in consequence would be inclined at an angle of about 10 to the plane of the entrances of the reflectors, and referring to Figure 6, the pipe/fin on either side of the length centre line of the common fin would then be inclined at an angle of about 10 to the plane of the entrances of the reflectors.

These alternatives are suggested by the chain dashed lines in Figs 4 and 6.

Although reference has been made to closedended semi-cylindrical reflectors and closed ended channel-shaped reflectors, it is important that the shape of the closed-ended channel should be such that direct and diffuse radiation entering the system from any particular angle is reflected not into a line focus but into a band focus of which the width should approximately correspond with the width of the fin or fins on which the reflected radiation is required to impinge. "Closed-ended channel" is thus defined for the purpose of the present disclosure.

The major advantage of the present apparatus over conventional apparatus using flat plate and focussing collectors lies in the fact that it may be regarded as a combination of the two types, in that it combines the smaller absorber plate size, and hence lower heat losses associated with the focussing type of collector, with the ability of the flat plate type to absorb diffuse as well as the direct component of solar radiation. This gives a higher energy flux which increases the nett useful heat transfer rate in the fin/pipe heat exchanger, and combined with the lower heat losses, results in higher efficiencies.

Hence the design of the apparatus allows for redirection of both direct and diffuse radiation onto a reduced absorber plate size, - which is not possible in conventional focussing devices - in conjunction with higher energy flux in the absorber plate than that associated with the conventional flat type of collector.

WHAT WE CLAIM IS: 1. A solar radiation receiving and converting apparatus comprising at least one closed-ended channel having specular inside curved and end surfaces, a solar radiation receiving element comprised of at least one tube with at least one attached fin and which is disposed at or outside the entrance to said channel or channels opposite the whole length but only part of the width of the channel or channels so as to receive solar radiation both directly and by reflection from specular surfaces, and means for transferring thermal energy from said element to a place of utilisation.

2. Apparatus according to Claim 1 wherein each tube has two fins extending outwardly from it 3. Apparatus according to Claim 2 wherein the two fins extend outwardly from the tube in a plane diametric to the tube.

4. Apparatus according to any of Claims 1 to 3 in which each tube is a heat pipe and the means for transferring thermal energy is situated at an end of the heat pipe.

5. Apparatus according to any of Claims 1 to 3 in which each tube provides a space for the admittance and discharge of a fluid to be heated.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. that on exposure of the elements to the sun, direct and diffuse solar radiation enters the elements through the transparent cover plate 7. Some of this energy impinges directly on the heat pipes and fins and is absorbed by a selective coating whilst a high proportion of the remainder of the direct and diffuse radiation impinges on it after reflectance from the surface 6. The absorbed energy which is now in the form of thermal energy is transferred to the heat pipe working fluid by conduction through the fins and pipe walls to the evaporator region whereupon the action of the heat pipe transports the thermal energy to the condenser region which forms part of the heat exchanger 4 thus the energy is given to the fluid which is to be heated.Loss of energy by reradiation is reduced by the selective coating, and the insulating properties enhanced by the reflective surfaces surrounding the absorber. Figure 4, shows an alternative embodiment in which two closed-ended channel shaped reflectors disposed longitudinally side by side are utilised. In this embodiment the two reflectors have an aperture equivalent to that of the first embodiment. However the depth of the reflector is now reduced to half. Referring now to Figures 5 and 6, there is shown an assembly of two solar energy receiving elements as described with reference to Figures 1 to 3 connected side by side, surrounded by a thermal insulating material 8 and overlaid with a transparent cover plate 7, which faces the direction of solar radiation. Heat exchangers 4 at the ends of the pipes 2 are series-connected and have a fluid flow inlet pipe 9 and a fluid flow outlet pipe 10, respectively connected thereto. When the tube is not a heat pipe, any number of solar energy receiving elements as aforesaid, preferably parallel with one another, may be coupled together by a common fluid inlet pipe and a common fluid outlet pipe. These pipes themselves may also be formed with at least one metal fin and at least one reflective surface so as to function in the same manner as the individual solar energy receiving elements which they serve to connect. Although in Figures 4 and 6 the pipes 2 and associated fins 1 are shown as being located in a common plane diametric to the adjacent closed-ended semi-cylindrical reflectors it may be preferable in certain circumstances - for instance to avoid risk of reflector damage - to space the nearest point of the pipe/fin element slightly outside the confines of the reflector. Thus referring to Figure 4, the fins in consequence would be inclined at an angle of about 10 to the plane of the entrances of the reflectors, and referring to Figure 6, the pipe/fin on either side of the length centre line of the common fin would then be inclined at an angle of about 10 to the plane of the entrances of the reflectors. These alternatives are suggested by the chain dashed lines in Figs 4 and 6. Although reference has been made to closedended semi-cylindrical reflectors and closed ended channel-shaped reflectors, it is important that the shape of the closed-ended channel should be such that direct and diffuse radiation entering the system from any particular angle is reflected not into a line focus but into a band focus of which the width should approximately correspond with the width of the fin or fins on which the reflected radiation is required to impinge. "Closed-ended channel" is thus defined for the purpose of the present disclosure. The major advantage of the present apparatus over conventional apparatus using flat plate and focussing collectors lies in the fact that it may be regarded as a combination of the two types, in that it combines the smaller absorber plate size, and hence lower heat losses associated with the focussing type of collector, with the ability of the flat plate type to absorb diffuse as well as the direct component of solar radiation. This gives a higher energy flux which increases the nett useful heat transfer rate in the fin/pipe heat exchanger, and combined with the lower heat losses, results in higher efficiencies. Hence the design of the apparatus allows for redirection of both direct and diffuse radiation onto a reduced absorber plate size, - which is not possible in conventional focussing devices - in conjunction with higher energy flux in the absorber plate than that associated with the conventional flat type of collector. WHAT WE CLAIM IS:

1. A solar radiation receiving and converting apparatus comprising at least one closed-ended channel having specular inside curved and end surfaces, a solar radiation receiving element comprised of at least one tube with at least one attached fin and which is disposed at or outside the entrance to said channel or channels opposite the whole length but only part of the width of the channel or channels so as to receive solar radiation both directly and by reflection from specular surfaces, and means for transferring thermal energy from said element to a place of utilisation.

2. Apparatus according to Claim 1 wherein each tube has two fins extending outwardly from it

3. Apparatus according to Claim 2 wherein the two fins extend outwardly from the tube in a plane diametric to the tube.

6. Apparatus according to any of Claims

1 to 5 in which each element is opposed to approximately half the width of a channel.

7. Apparatus in accordance with Claim 6 in which the element is disposed wholly to one side of the longitudinal plane of symmetry of each said channel.

8. Apparatus according to any of Claims 1 to 7 having two said channels in parallel side by side adjoining relation with the tube extending along the longitudinal junction line between said channels.

9. Apparatus according to any of Claims 1 to 7 having two of said channels in parallel side by side adjoining relation and wherein said element comprises two tubes each having a radially directed fin and which are connected together by a common fin, said element being symmetrically disposed relatively to the longitudinal plane of symmetry between said channels and passing through the junction between said channels.

10. Apparatus in accordance with any of the preceding claims wherein each tube is situated outside the confines of the or each channel and fins are inclined from each said tube in different planes between curved specular surfaces of said channels.

11. Apparatus according to any of the preceding claims in which heat transfer means at one of the ends of each of a plurality of said tubes are connected together in series.

12. Solar radiation receiving and converting apparatus substantially as hereinbefore described with reference to, and as shown in, Figs. 1 to 3, Fig. 4 or Figs. 5 and 6 of the accompanying drawings.