GB2099980A

GB2099980A - Heat transfer panels

Info

Publication number: GB2099980A
Application number: GB8200404A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-05-06
Filing date: 1982-01-07
Publication date: 1982-12-15
Also published as: GB2099980B

Abstract

A heat radiator comprises a panel type casing (1) containing a vapourizing fluid (3) in an amount which, when the radiator is cold, has a liquid phase which is contained within the bottom channel of the casing, through which passes with clearance a pipe (2) for a heating fluid such as hot water, said pipe being sealed from the space for the vapourizing fluid, whereby the liquid phase of the vapourizing fluid is heated by heat exchanger to condense and give out heat at the main heat-radiating surface of the panel above the bottom channel and thence to trickle back to the bottom channel. In a preferred arrangement the pipe (2) is disposed above the level of the liquid phase of the vapourizing fluid and a wick means (5) depends from said pipe to dip into the liquid phase. The pipe (2) may be replaced by an electrical heating element. In an alternative arrangement, the casing is inverted and constitutes a solar heater. <IMAGE>

Description

SPECIFICATION Improvements in fluid-containing radiators This invention relates to fluid-containing radiators such as panel radiators as are widely used in the majority of central heating systems, but is not limited to that use. The invention also extends to devices which can be of analogous construction but are used in the converse manner for heat absorption, such as solar panels.

In, for example, a conventional private house, the living areas are heated by any one of a variety of heating means, such as coal fire or gas or oil fired boilers. The heat from the boiler is transferred usually through a circuit by hot water which fills the radiators, thereby heating the radiator and heat is given off by natural convection of air over the radiator. Even though modern pressed steel radiators are of a compact size, a typical 1 KWhr rated output radiator will contain over one gallon of water. Thus in a house of say eight radiators, it is necessary to heat up eight gallons of water before that heat is being transferred fully to the air heating application for which it is intended. Eight gallons heated from say 60"F to 1 60"F will require 8000 BTU (21/2KW) of heat.This heat, however, is not totally wasted, even in a simply controlled system, since after thermostat shutdown this heat is gradually convected from the radiators to the room. Nevertheless, since the thermostat was not demanding this heat, the effect is to overshoot the temperature required, so that heat has been used unnecessarily.

Systems with more sophisticated controls can partly solve this problem by storing hot water, but substantial heat wastage still occurs. Furthermore, high temperature fluctuations are not desirable, and also the time taken in heating up the water to its circulating temperature means that a lengthy time elapses between thermostat switch on at the time heat is required and the time at which heat is actually received into the rooms.

According to one aspect of the present invention, there is provided a heat radiator (or absorber) which comprises a sealed panel-type casing containing space for heated fluid within a heat-radiating (or heat-absorbing) surface, a vapourising first fluid contained within said casing, and a pipe for a second fluid joined to the casing but hermetically sealed from the first fluid space therein to pass with clearance therearound through and along the bottom, for a heat radiator, (or the top, for a heat absorber) of said fluid space, so that in use heat exchange between the first and second fluids takes place as the first fluid condenses (or evaporates) behind the heat-radiating (or heat-absorbing) surface and evaporates (or condenses) at the bottom (or top) of the casing adjacent the said pipe.

A principal application of the invention is in a panel-type radiator for a central heating system. By arranging the pipe through the bottom channel of the space within the radiator, joined to but hermetically sealed from that radiator, the only water required is the amount which flows through the pipe.

Heat exchange is enabled by submerging the pipe in the vapourising liquid contained in the radiator, but only sufficient vapourising liquid as to cover or partially cover the pipe. The panel radiator then is evacuated of all other gases other than the vapour of the vapourising liquid and hermetically sealed.

When hot water is circulated through a central heating circuit including a radiator of the form outlined above, it enters the pipe in the radiator, giving heat out by conduction through the pipe and into the vapourising liquid. The vapourising liquid boils taking in latent heat of vapourisation and the vapour travels to the colder parts of the radiator where it condenses, giving out the latent heat of vapourisation into the radiator surface, which is then convected to the air in the room. The condensed vapour then trickles down the panel radiator inside surface to the bottom, to be re-vapourised.

It has been shown that less than a pint of vapourising liquid needs to be used in a panel radiatorwhich previously contained over a gallon of water.

The liquids suitable for use for vapourising are varied but suitable likely candidates are refrigerants such as Freon, alcohols such as methanol, acetones, such as carbon tetrachloride, and ammonia, but any liquid which vapourises and then condenses within the operating temperature range, without degradation eitherto itself orthe radiator casing, would be suitable.

Comparing panel radiators a) filled with water; b) partially filled with vapourising liquid as described above.

a) Capacity of water eight pints = 1 Olbs weight; heating from 600to 160"F requires 1000 BTU to get to 160"F ignoring the thermal capacity of the radiator material itself.

b) Vapourising liquid, one pint = 1 Ib weight of, for example, methanol, assume half of this is vapourised in heating the radiator from 60'to 160"F.

Latent heat of vapourisation of methanol is approximately 400 BTU/lb. Therefore, heat absorbed in raising the radiator to 160"F is 200 BTU, ignoring the thermal capacity of the radiator material itself. Thus, the heat required to raise the radiator to an equivalent operating temperature is reduced to only 1/5 of that required with a standard water filled panel radiator.

The radiator circuit will thus reach its operating temperature five times quicker when radiators in accordance with this invention are used compared to conventional radiators. Several advantages are therefore apparent in use of the radiator containing vapourising fluid: 1) As mentioned above, the radiator has a low thermal capacity requiring less heat to get to operating temperature; 2) This in turn means that a heating circuit will have a much faster temperature rise; 3) As soon as heating demand has been met the radiator quickly cools and so there is less temperature overshoot and thus energy is saved by not raising the temperature too high; 4) Asmallercirculating pump is required since the path of the circulating water is shorter and less tortuous;; 5) The radiator can be presealed during manufacture, which in turn means that a) it does not ever require bleeding or venting, and b) it cannot and need never be drained for service; 6) Because the radiator is sealed the formation of rust in the circuit is prevented.

It has been shown that a conventional panel radiator can be used as a solar heat collector, but, although cheap, the drawback is that it contains a large amount of liquid within it which has to be heated before a supply of heated liquid to the water storage tank is established.

Another aspect of the above invention is that the panel-type casing can be made into and used directly as a solar panel but with a much lower thermal capacity and thus faster heating response than a conventional panel radiator. Thus, it can be used as an inexpensive solar collector, with characteristics equivalent to those of purpose built collectors but with the advantage of manufacture by the mass production technology already used in manufacturing panel-type radiators. A major difference is that, for use as a solar collector or any other kind of heat absorber (such as an absorber in a waste, hot gas stream), the pipe for passage of the second fluid will pass through and along the top of the first fluid space within the panel, e.g. along the top channel thereof.In the case of a mass manufactured panel, this may simply mean that the panel is used in an inverted orientation when compared to its use as a radiator.

One disadvantage of the device, as thus far described, and in the context of use as a heat radiator, is that the direct contact which takes place between the liquid phase of the first fluid and the pipe containing heated water can cause a bubbling of the first fluid as it locally boils, giving rise to undesirable noise from the radiator. Another aspect of the present invention is concerned with this problem.

Thus according to another aspect of the present invention, there is provided a heat radiator which comprises a sealed panel-type casing containing space for a heated fluid within a heat-radiating surface, a vapourising first fluid contained within said casing, a pipe for a heated second fluid passing through the first fluid space, and a wick means, such as a metal gauze wick, depending from the pipe in the first fluid space, the quantity of first fluid in said space being selected so that, at least during usage, the second fluid pipe lies above the level of the liquid phase of the first fluid and the wick means dips into said liquid phase.

In this way, during use, only a thin film of first fluid is presented to the heated pipe, and this is evaporated very rapidly without bubbling, banging or other unwanted noise.

Preferably, thetotal quantity offirstfluid in the radiator will be such that, even when the radiator is cold, the liquid phase of said first fluid is below the bottom of the pipe. Assuming the pipe extends, as before, through the bottom channel of the radiator, i.e. at the bottom of the first fluid space, the employment of a wick enables a lesser quantity of first fluid to be employed than would otherwise be the case, giving rise to the further advantage that the lesser quantity of first fluid has a reduced latent heat capacity, thus further reducing the thermal hysteresis of the radiator.

An embodiment of the invention is shown by way of example in the accompanying drawings, in which Figure 1 is a perspective view of a panel radiator; Figure 2 is a diagrammatic cross-sectional view thereof; and Figure 3 shows a modification in diagrammatic cross-sectional view.

The panel radiator 1 is conventional and as currently manufactured except for the inclusion of the straight through hot water pipe 2, e.g. fed from a boiler, entering at one end of the bottom channel of the radiator and leaving at the other end. Vapourising liquid 3 is filled within the radiator 1 to such a level as to cover or partially cover the pipe 2.

Evacuation and filiing of the radiator 1 is effected through a valve 4 at the top end of the radiator As soon as water circulates through the pipe 2, at the pressure within the radiator, the vapourising liquid 3 boils, taking in latent heat of vapourisation and rises to the colder parts of the radiator where it condenses on the inside of the heat radiating surface to give latent heat thereto and then trickles back to the heat source 2 by gravity.

In the application for use as a solar heat collector the panel orientation is reversed with the pipe 2 at the top and the vapourising liquid at the bottom. As heat is absorbed from the sun the liquid vapourises and rises to the pipe at the top, where the vapour condenses, giving up latent heat to the liquid within the pipe, and then trickles down the channels in the radiator to be re-vapourised at a later stage.

In the modification of the radiator 1 shown in Figure 3, a metal gauze wick 5 is attached around the hot water pipe 2 in the bottom channel of the panel.

A reduced quantity of vapourising fluid 3 is employed, so that the pipe 2 is positioned wholly above the liquid level of said fluid. However, the wick 5 depends from the pipe 2 to dip into the vapourising liquid 3, and thereby continuously supply a thin film of said liquid around the pipe for rapid, noiseless evaporation.

Various modifications of the above-described arrangements are possible within the scope of the invention and, in particular, it is to be appreciated that the second fluid, passing or contained in the pipe, can be any suitable liquid or gas.

Any form of heating can be used to heat the vaporisingfirstfluid:forexample,thiscan be achieved by direct firing or by an electrical heating element instead of the described second fluid within the pipe. Also, the material of the wick 5 need not necessarily be made of metal, but can be of any material which is compatible with the working fluid and the container and which is capable of capillary flow. For example, the material of the wick could be glass fibre felt, a sintered material or a textile material.

Claims

CLAIMS (Filed 19.4.82)

1. A heat radiator comprising a sealed panel-type casing containing space for a heated fluid within a heat-radiating surface, a vapourizing fluid contained within said casing in an amount such that, when the radiator is cold, the fluid has a liquid phase which occupies a bottom region of the casing the volume of which is only a small fraction of the total interior volume of said casing, and means for heating said vapourizing fluid in the bottom region of the casing.

2. A radiator according to claim 1, wherein the heating means comprises a heating member passing with clearance therearound through and along said bottom region of said casing.

3. A radiator according to claim 2, wherein said heating member is a pipe for a second fluid, joined to the casing and hermetically sealed from the space therein containing the vapourizing first fluid.

4. A radiator according to claim 2 or claim 3, wherein the amount of vapourizing fluid in the casing is sufficient, when the radiator is cold, only just to cover or partially to cover the heating member.

5. A heat absorber comprising a sealed panel type casing containing space for a heated fluid within a heat-absorbing surface, a vapourizing first fluid contained within said casing in an amount such that, when the radiator is cold, the fluid has a liquid phase which occupies a volume which is only a fraction of the total interior volume of said casing, and a pipe for a second fluid passing through a top region of the casing in sealed relationship from the vapourizing fluid space and for extracting heat absorbed by its heat-absorbing surface due to heat exchange in said top region where the vapourizing fluid condenses.

6. A heat absorber according to claim 5, wherein said casing constitutes a solar panel.

7. A radiator or absorber according to any of claims 1 to 6, wherein the space within the casing is evacuated of all gases other than the vapour of the vapourizing fluid.

8. A radiator or absorber according to any of claims 1 to 7, wherein the vapourizing first fluid is a Freon, an alcohol, an acetone or ammonia.

9. A heat radiator comprising a sealed panel type casing containing space for a heated fluid within a heat-radiating surface, a vapourizing fluid contained within said casing, a heating member passing through a bottom region of said casing with clearance therearound and a wick means depending from said heating member, the quantity of vapourizing fluid in said space being such that, at least during usage, the heating member lies above the level of the liquid phase of said vapourizing fluid and the wick means dips into said liquid phase.

10. A radiator according to claim 9, wherein said heating member is a pipe for a second fluid, joined to the casing and hermetically sealed from the space therein containing the vapourizing first fluid.

11. A radiator according to claim 9 or claim 10, wherein said wick means is a wick of a material affording capillary flow.

12. A radiator according to claim 10 or claim 11, wherein said wick means is a metal gauze wick.

13. A radiator according to any of claims 9 to 12, wherein the space within the casing is evacuated of all gases other than the vapour of the vapourizing fluid.

14. A radiator according to any of claims 9 to 12, wherein the vapourizing first fluid is a Freon, an alcohol, an acetone or ammonia.

15. A heat radiator or absorber substantially as hereinbefore described with reference to Figures 1 and 2 or to Figure 3 of the accompanying drawings.