GB2213258A

GB2213258A - Solar collectors

Info

Publication number: GB2213258A
Application number: GB8828189A
Authority: GB
Inventors: Hossein Valizadeh
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-12-03
Filing date: 1988-12-02
Publication date: 1989-08-09
Also published as: IE873292L; GB8828189D0; ZA889063B

Abstract

A solar collector comprises an evacuated envelope 10 transmissive of solar radiation, an absorber plate 11 within the envelope for absorbing solar radiation passing through the envelope, and a heat pipe 12 in thermal contact with the plate internally of the envelope and which extends out of the envelope to a condenser 14. The heat pipe contains a working fluid which is evaporated in the envelope by heat from the plate and condensed externally of the envelope in the condenser. The condenser 14 comprises a thermally conductive transfer pipe 15 for containing a heat transfer fluid and a jacket 17 surrounding the transfer pipe, the interior of the jacket being in communication with the heat pipe externally of the envelope so that working fluid vapour may enter the jacket from the heat pipe for condensation in the jacket. <IMAGE>

Description

Title: "Improvements in evacuated solar collectors" This invention relates to a solar collector of the kind comprising an evacuated envelope transmissive of solar radiation, an absorber plate within the envelope for absorbing solar radiation passing through the envelope, and a heat pipe in thermal contact with the plate internally of the envelope and which extends out of the envelope to a condenser, the heat pipe containing a a working fluid which is evaporated in the envelope by heat from the plate and condensed externally of the envelope in the condenser.

Solar collectors of the aforementioned kind are described in UK Patent Specifications GB 2 103 350, GB 2 117 104 and GB 2 131 155, whose contents are hereby incorporated by reference.

The condensers associated with solar collectors of the above type can be classified in two main groups, so-called "dry coupling" and "wet coupling" condensers.

In the first group, the part of each heat tube extending out of the envelope is held by a heat conducting clamping block which is also clamped onto a metal pipe carrying a heat transfer fluid (usually water) to be heated. Thus the heat released by the condensing working fluid must first heat the clamp before the heat is transferred to the water. Hence there is a considerable amount of heat loss and a high heat inertia associated with this method.

The second group is exemplified by Figure 1 of GB 2 117 104, wherein the exposed (condenser) end of each pipe is inserted into a manifold containing the heat transfer fluid, for example water, to be heated.

Manifolds are available to accomodate 15, 20 and 30 individual solar collectors, and all are made from rectangular metal boxes. It is therefore appreciated that this method also suffers from a high heat inertia.

It is therefore an object of the present invention to provide a solar collector of the above type with a condenser arrangement which provides an efficient transfer of heat from the working fluid in the heat pipe to the heat transfer fluid with little heat inertia.

Accordingly, the present invention provides a solar collector of the kind comprising an evacuated envelope transmissive of solar radiation, an absorber plate within the envelope for absorbing solar radiation passing through the envelope, and a heat pipe in thermal contact with the plate internally of the envelope and which extends out of the envelope to a condenser, the heat pipe containing a working fluid which is evaporated in the envelope by heat from the plate and condensed externally of the envelope in the condenser, wherein the condenser comprises a thermally conductive transfer pipe for containing a heat transfer fluid and a jacket surrounding the transfer pipe, the interior of the jacket being in communication with the heat pipe externally of the envelope so that working fluid vapour may enter the jacket from the heat pipe for condensation in the jacket.

Preferably, the jacket is formed as a T-junction at the end of the heat pipe.

The advantage of the invention is that the hot vapour of the working fluid in the jacket surrounds the transfer pipe so that the heat released by the condensation of such vapour is transferred directly through the walls of the transfer pipe to the water or other heat transfer fluid circulating therein with minimal heat loss and heat inertia.

Another advantage is that the transfer pipes of a plurality of solar collectors may be connected in series using short lengths of flexible tubing, so that in any given assembly of such collectors there is complete freedom to install as few or as many as is desired, rather than being limited to the number which can be accomodated in the prior manifold arrangements or multiples thereof.

An embodiment of the present invention will now be described with reference to the accompanying drawing, whose single figure is a diagrammatic view of the upper end of a solar heat collector.

It will be understood that the invention lies primarily in the construction of the condenser arrangement of the solar collector, so that the construction of the main body of the collector is not shown and will be described only briefly. It may, however, be constructed generally according to known techniques, for example as described in the aforementioned Patent Specifications.

The solar collector comprises a highly elongated evacuated envelope, in the form of a lead glass tube 10, transmissive of solar radiation. The tube 10 contains one or a number of absorber plates disposed in the axial direction thereof, such plates being in the form of elongated metal fins 11 which have a coating of a material which increases the efficiency of absorption of solar energy falling on the fins. The fins 11 are welded to and supported in the tube 10 by a cupro-nickel heat pipe 12 which is likewise disposed axially of the tube 10 and maintained in position by clips, not shown.

The heat pipe 12 extends out of the upper end of the tube 10 via a glass-to-metal seal 13 to be described later, and terminates in a condenser generally shown at 14.

The condenser 14 comprises a transfer pipe 15 of, for example, high purity copper with a wall thickness of 0.5mm. The transfer pipe contains, in use, water or other heat transfer fluid which circulates in the direction of the arrows 16. The condenser 14 further comprises a cylindrical cupro-nickel jacket 17 which coaxially surrounds the transfer tube 15 so as to form a space between it and the tube 14. The jacket 17 is welded to the pipe 15 at each end to form a hermeticallly sealed interior 18.

The jacket 17 is further welded to the end 19 of the heat pipe 12 so that the interior 18 of the jacket communicates with the interior of the heat pipe 12, the jacket 17 forming a T-junction with the end 19 of the heat pipe.

As is well known, the heat pipe 12 contains a working fluid (which may be water under reduced pressure) which is heated up and evaporated in the envelope by heat absorbed by the fins 11, the vapour 20 rising up the pipe 12 and, still within the pipe 12, passing out of the tube 10 at the top. In the present embodiment, such vapour enters the interior 18 of the jacket 17.

The interior 18 constitutes a condensation space, wherein the vapour 20 condenses and releases heat which passes across the walls of the pipe 15 to the water or other fluid flowing through the pipe 15. The condensed vapour now flows back into the heat pipe 12 and down into the tube 10. This cycle is operating continuously while the solar collector is in use.

In a practical installation, a number of solar collectors as described above may be connected together by connecting their transfer pipes 15 in series using short lengths of flexible tubing, so that a complete circuit for the circulating heat transfer fluid in the pipes 15 may be constructed.

Returning now to the glass-to-metal seal 13, this seal is made between a metallic collar 21 welded at 22 to the exterior of the heat pipe 12 and a reduced diameter portion or neck 23 of the tube 10, and may be of the "knife-edge" type described in GB 2 103 350.

However, we have found that this provides a weak joint which can crack.

cTAqzcordingly, we have found it preferable to use NILOL475 as the metal of the collar 21, which is particularly suitable for sealing to lead glass since it has a coefficient of expansion very similar to lead glass. Accordingly, a robust seal 13 may be made.

NIL08475 has the following constituents: Nickel 47% Carbon 0.15% Manganese 0.5% Silicon 0.5% Copper 0.5% Chromium 5.0%

Claims

CLAIMS: 1. A solar collector of the kind comprising an evacuated envelope transmissive of solar radiation, an absorber late within the envelope for absorbing solar radiation passing through the envelope, and a heat pipe in thermal contact with the plate internally of the envelope and which extends out of the envelope to a condenser, the heat pipe containing a working fluid which is evaporated in the envelope by heat from the plate and condensed externally of the envelope in the condenser, wherein the condenser comprises a thermally conductive transfer pipe for containing a heat transfer fluid and a jacket surrounding the transfer pipe, the interior of the jacket being in communication with the heat pipe externally of the envelope so that working fluid vapour may enter the jacket from the heat pipe for condensation in the jacket.
2. A solar collector as claimed in Claim 1, wherein the jacket is formed as a T-junction at the end of the heat pipe.
3. An array of solar collectors as claimed in Claim 1 or Claim 2 having their transfer pipes connected in series.
4. A solar collector as claimed in Claim 1, substantially as described herein with reference to the accompanying drawing.
5. Any novel feature or combination of features described herein.