GB2117104A

GB2117104A - Heat pipe for collecting solar radiation

Info

Publication number: GB2117104A
Application number: GB08207140A
Authority: GB
Inventors: Faramarz Mahdjuri-Sabet
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-11
Filing date: 1982-03-11
Publication date: 1983-10-05

Abstract

A solar collector comprises a heat-pipe having an absorber plate in heat transferring contact to its evaporation compartment. The condenser compartment (2) is constructed to be secured in a water/air manifold. The interior surface of the condenser compartment is increased by inserting a metal heat conducting member or members in thermal contact with the condenser body. The heat conducting member may be a helical body (22). Alternatively, the condenser compartment may contain perforated discs (24), a wavy metal sheet or metal mesh. <IMAGE>

Description

SPECIFICATION Solar radiation collectors This invention relates to solar radiation collectors.

Solar radiation collectors are designed to convert solar radiation into heat and to transfer the heat, with the maximum possible efficiency, to a fluid heat transferring means which is, for example, water or air.

Solar radiation collectors include a heat pipe, the essential function of which is to transfer and to distribute heat by vaporisation and condensation of a working fluid (heat-transfer medium). The principal feature of a heat pipe is that the energy which is requried for the flow of the liquid and the vapour, in the presence of gravity, is completely provided by the heat source, so that no external pumping source is needed. The use of heat pipes in solar collectors is known (see for example my U.K. patent application publication 202380A).

Solar collectors also include a heat exchange system, the condenser of which is one of the most important parts of the collector. The condenser is normally positioned in a manifold through which heat transferring fluids are passed which extract and carry away heat from the condenser. It is necessary to provide efficient heat transfer from the compartment of the condenser to the heat transferring means circulating through the manifold. Also, it is necessary to design the condenser to be appropriate to the collector output. It is required, moreover, to have a small thermal resistance between the compartment of the condenser and the fluid heat transferring means in the manifold.

Another requirement of solar radiation collectors is that they be easily assembled from their component parts and that they be capable of taking up the tolerances which are usual in this field. In addition, it is desirable that the component parts be easily replaceable.

I have now devised a heatpipe solar radiation collector having a high efficiency and which can be constructed cheaply, and can readily be assembled and overhauled.

In a preferred aspect, the present invention relates particularly to a solar radiation collector, having a transparent cover and an absorbing compartment. The absorbing compartment has a planar configuration, for absorbing solar radiation, bonded to at least a closed metallic channel (metal tube) extending longitudinally and enclosing a working fluid (heat-transfer medium) capable of being vaporised. A vaporisation compartment is provided in thermal contact with the absorber, and also a condensing compartment which, during the operation of the system, is spatially at a higher level, the condenser being adapted to be received in a manifold wherein a fluid heat transferring means is caused to flow.

In the use of solar radiation collectors, when the sun does not shine, the working fluid is collected in the bottom end portion of the vaporisation compartment (evaporator) of the heat pipe. When subsequently the sun shines once again, the entire plate of the absorbing compartment, and thus also the evaporator channel, will be heated. The temperature of the part of the evaporator channel with no working fluid will rise much quicker than the bottom part of the evaporator with working fluid. The working fluid which is in the end bottom portion of the evaporator channel begins to vaporise and during the run towards the condenser, the vapor temperature is increased as a result of the high temperature of the evaporator channel wall.The condenser cannot perform any condensation, due to the superheating of the vapour, until the vapour temperature has dropped to the condensation temperature (equivalent to evaporation temperature on the bottom of the evaporator).

This procedure is such as to hamper the starting of the operation, and it results in reduced efficiency.

One proposal to overcome this problem is to provide a cascade-like arrangement of pockets along the length of the interior of the evaporator compartment for receiving the condensation (see specification number GB 2023804 A). However, this arrangement is difficult and expensive.

According to one preferred feature of the present invention, I have found that this problem can be advantageously reduced or overcome by increasing the internal surface area of the condenser. It is generally desirable for various reasons to keep the overall size of a condenser as small as possible and I prefer, therefore, to achieve an increased internal surface area by providing extra surfaces inside the condenser, rather than by simply increasing its overall size. The extra surfaces can be provided in a variety of ways, but principally I prefer to include one or more solid members in the condenser compartment, e.g.

perforated plates, metal mesh, spiral or otherwise convoluted metal bodies particulate materials or the like (such members being shaped to maximise their surface areas). Preferably, the solid member(s) will not substantially reduce the internal volume of the condenser available to working fluid.

The increase in condensation rate achievable by substantially increasing the internal surface area greatly improves the efficiency of the solar collector. This measure is even more important as a reflecting system when the collector tube is used.

The condenser compartment of a heat pipe collector has to be in direct contact with the heat transferring means (for example water) in the manifold, and because of the usual tolerances in this field, it has to be capable of taking up the tolerances when it is being fixed in the manifold.

One water tight connection for heat pipe solar collectors is described in patent publication GB 2023803 A. However, the system there described is not always entirely satisfactory. A certain amount of tension always exists in the weakest part of the collector, namely the glassmetal joint, which may damage the unit during the assembly or may reduce the life of the unit.

According to a second preferred feature of the present invention, I have now found that this problem can be reduced or alleviated. In the arrangement of GB 2023803 A, a seal is formed by a resilient gasket pressed against the conical end wall of the condenser. In the arrangement of the present invention, the seal is not made in this way, but rather by providing a sealing means between the manifold and the glass neck (or glass cover tube thereof).

In order that the various features of the invention may be more fully understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawing, wherein: FIGURE 1 is a longitudinal view in part section of a complete solar collector; FIGURES 2, 3 and 4 are part-sectional views of different condensers for use in solar radiation collectors: and FIGURE 3A is a transverse section on the line A-A of Figure 3.

In Figure 1, the collector comprises a cover glass tube (1), a condenser (2) on the absorber plate (3) welded to an evaporator compartment of the heat pipe (4). A flange (5) is provided capable of absorbing tolerances of the fixing of the supporter end (13) in all directions. This flexible flange (5) is glued directly to the glass neck (71).

The flange is made out of soft plastic material, such as soft PVC or silicon rubber. A water-sealing gasket (6) seals the flange (5) against the manifold (10). The metal ferrule (7) as described in my patent application GB 8123829, is sealed at one end with the neck of the glass tube (71), and at the other end engages around the heat pipe tube (4). A so-called 'frost protection ring' (9) is made out of a closed pore sponge, and fills the space between the manifold neck (101) and the ferrule 70. The ring (9) does not allow fluid heat transfer means (water) to stay in that area in volume, so that in a cold winter period the small amount of water (film) which may freeze during the night would not damage the manifold neck (101) or the ferrule (7).

The manifold (10) has the insulation (102). The supporter springs (11) keep the absorber plate (3) in a fixed position in the glass tube (1). Other components include the getter ring (12) and the supporter end (13) which is made out of a plastic material glued to the internal glass neck part (131): retaining cap (14) and neck sealing (132).

FIGURE 2 shows a condenser compartment (2), in which the interior surface area is increased by inserting a spiral shaped (22) metal body (for example, a spring).

FIGURE 3 shows a condenser compartment (2) in which the interior surface area is increased by inserting a waved metal sheet (23). In the metal sheet (23), holes (230) are punched to provide free circulation of the working fluid vapour in the condenser.

FIGURE 4 shows a condenser compartment (2) in which the interior surface area of the condenser has been increased by inserting a number of metal discs (24). In the discs (24), holes (240) are punched to provide free circulation of the working fluid vapour and liquid in the condenser.

Claims

1. A solar collector comprising a planar metallic asborbing apparatus for capturing solar radiations, and at least a closed channel confined by metallic walls and containing a vaporisable heattransferring fluid medium, said channel having a vaporization compartment placed in heattransferring contact relationship with said absorbing apparatus, and a condensation compartment (called condenser) which, during operation, is at higher spatial level than said vaporization compartment, wherein internal surface of the condenser of the channel is substantially increased by inserting one or more thermal conducting members into it, which are in thermal contact with the body of the condensation compartment (condenser).

2. A solar collection according to the claim 1, wherein the interior surface area of condenser is increased by inserting a spiral shape metal body.

3. A solar collector according to the claim 1, wherein the interior surface area of the condenser is increased by inserting a waved metal sheet.

4. A solar collector according to the claims 1 and 3, wherein the waved metal sheet is perforated.

5. A solar collector according to the claim 1, wherein the interior surface area of the condenser is increased by inserting a metal mesh.

6. A solar collector according to the claim 1, wherein the interior surface of the condenser is increased by inserting a number of perforated metal disks.

7. A solar collector according to the claim 1-6, wherein a flexible flange is bonded to the condenser/glass tube assembly to act as the water sealing gasket against the manifold outlet.

8. A solar collector according to the claims 1-7, wherein a closed pore sponge fills the space between the bottom of the condenser/glass neck and the manifold neck.