GB2088549A

GB2088549A - Heat transfer apparatus

Info

Publication number: GB2088549A
Application number: GB8128168A
Authority: GB
Original assignee: Ruetgerswerke AG
Current assignee: Ruetgers Germany GmbH
Priority date: 1980-11-28
Filing date: 1981-09-17
Publication date: 1982-06-09
Also published as: IT1172091B; DE3044855C2; FR2495289B1; PT74039B; BE891209A; PT74039A; GR77291B; IT8149757A0; ES507465A0; DE3044855A1; GB2088549B; FR2495289A1; ES8300193A1; NL8104780A

Abstract

Heat transfer apparatus with a fluid heat carrier comprises at least one flat heat exchanger 1 for receiving or delivering heat, a conduit system 2 with a circulating pump 4, a heat exchanger and a pressure regulating device 5. The pipes of the conduit system 2 which lead downwards are dimensioned as a function of the volumetric delivery of the circulating pump 4 such that the flow speed of the heat carrier is higher than 0.5 m/s, and the pressure-regulating device 5 regulates the pressure in the conduit system. The heat exchanger 1 consists of two thin foils 19,20, connected together at the edges and separated by a porous layer 21 of open-pored foam or a fleece, and may be a solar collector or a radiator. <IMAGE>

Description

SPECIFICATION Heat transfer apparatus The present invention relates to a heat transfer apparatus with a fluid heat carrier which comprises at least one flat heat exchanger for receiving or delivering heat, a conduit system of pipes with a circulating pump and pipe line fittings and mountings, a heat exchanger and a pressure-regulating device.

Such an apparatus can be used, for example, as part of a heating plant for using solar energy or for room heating with large-surface heat exchangers on walls, floors or ceilings.

German Offenlegungsschrift 2,714,901 discloses a heat exchanger element of a double fabric length coated on both sides, which can be used both as a heat-adsorbing element for using solar energy and as a heating element in the form of a carpet. The element is loaded with an internal pressure which is higher than that of the atmosphere. The enormous forces arising on account of the large surface are absorbed by a plurality of connecting threads, which firmly connect the upper and lower fabric. Flat heat exchangers of this type are very expensive to produce.

German Offenlegungsschrift 2,818,154, together with the application of addition, German Offenlegungsschrift 2,909,027, disclose a collector element for receiving solar energy which consists of two foils with an interadjacentdiaphragm layer, e.g. of fleece or foam. According to the application of addition, the foils are either glued or welded to the diaphragm layer, or the diaphragm layer is provided with holes at a plurality of points, so that the foils can be directly glued or welded together at these points.

These heat exchangers are also expensive to produce. The design suggest that the flat heatexchan- gers should be operated with a pressure above that of the atmosphere, as is usual in heating plants. The force components acting at right angles to the adhesion surface area have a disadvantageous effect on the durability of the elements.

Heat transfer apparatus are now also known which operate entirely or partially in a pressure range which is below atmospheric pressure.

The German Offenlegungsschrift 2,601,673 describes a method and a device for using solar energy which utilizes heat of vaporization for the transfer of heat. Water is particularly used as a heat carrier. As the boiling temperature of the water is not reached with atmospheric pressure in the collector, the apparatus must be carefully evacuated. The very low system pressure can only be maintained with difficulty.

German Offenlegungsschrift 2,809,690 also discloses a device for heating and for using solar energy which can be acted upon by different pressures and therefore also at an underpressure. This is a closed system in which the pressure is prevented from rising above an admissible degree by changes in volume, ag. as a result of temperture variations with a determined pressure which is lowerthan, or the same as, that of the atmosphere. A safety valve is thus unnecessary and the components of the apparatus can be of a smaller size. There is no information asto howthis underpressure is produced. Irrespective of this, it is not possible to deaerate the apparatus during operation if the pressure in the gas chamber above the diaphragm is lower than atmospheric pressure.This apparatus is not therefore suitable for constant operation in the subatmospheric pressure range.

The object of the invention is to develop a design for a heat transfer apparatus which can allow the use of easily assembled, light, flat heat exchangers, the connection points of which are not exposed to any force components acting at right angles thereon.

The object is solved according to the invention by a heat transfer apparatus which operates at partially reduced pressure and which is characterised in that the or each pipe of the conduit system which leads vertically downwards is dimensioned as a function of the volumetric delivery of the circulating pump such that the flow speed of the heat carrier is higher than 0.5 mls and the pressure regulating device regulates the pressure in the conduit system such that, irrespective of the temperature of the heat carrier in the flat heat exchanger it is lower than the atmospheric pressure and is maintained substantially constant under operating conditions.

The flow speed of above 0.5 m/s is necessary in order to be able to convey the gases which may arise owing to any leaks or the degasificaion of the heat carrier or which are present when the apparatus is started into the overpressure range. The gas can be removed from the circuit in a known manner, e.g. by a float-controlled air vent valve.

The pressure can be regulated in various ways. In an open conduit system, regulation can be carried out in a simple manner using a ventilated liquid column being maintained at a certain level below the flat heat exchanger. This takes place in the most simple manner using a vertical pipe line that runs upwards to a container from a lower, horizontal pipe line of the conduit system.

The capacity of the container should be large enough to receive the expansion volume without considerable alteration in the filling height. When there is not sufficient space for such a container, the level can be maintained constant by means of an overflow dam. The connecting branch, which is open to the atmosphere, together with the overflow dam and overflow collector such as an annular cap, can be directly mounted in a downward leading pipe of the conduit system below the flat heat exchanger.

Superflous heat carrier flows over the overflow dam into the overflow collector and then reaches for instance a lower reservoir via a pipe line. If required, such s for filling the apparatus or reducing the circulating volume by lowering the temperature, provision can be made that the heat carrier is pumped back into the conduit system for the reservoir via a pipe line by means of, e.g. a float-controlled charge pump.

If there is no space for a reservoir below the connecting branch, the level in the connecting branch can also be adjusted by, e.g. a charge pump which can be controlled by level probes and whose direction of discharge is reversible. The pump is then connected via a pipe line to the connecting branch and the reservoir. In all these arrangements the pressure regulating device, which is open to the atmosphere, can also be used to deaerate the apparatus, so that air vent valves are unnecessary.

Such float-controlled air vent valves or the like devices are indispensable in a closed conduit system and must be arranged in the overpressure range such that no gas can collect in the pressureregulating system; they must therefore be arranged in front of or on the pressure-regulating device.

The pressure regulating device then suitably comprises a container which is closed by, e.g. a diaphragm, bellows or a piston and on whose easily movable lid a constant force, e.g. a weight acts. The container and the lid must be dimensioned such that no large forces arise owing to the movement of the lid following the change in volume.

The apparatus according to the invention enables large surface, flat heat exchangers to be used for the transfer of heat which can consist of two thin foils arranged one on top of the other. Such foils need only be connected together at the edges in a gastight manner and be be separated from on another by a compression-proof, porous intermediate layer of open-pored foam or a fleece, for example. Instead of the intermediate layer the foils can be provided with stampings which, according to the use, can withstand pressures of at least 0.5 bar and hold the foils apart under this load, so that the heat carrier can freely flow through the foils. As the flat heat exchanger is only acted upon by external forces which are adsorbed by the spacers, the delicate connection points of the foils remain almost unloaded.Apart from the fact that the manufacture of such flat heat exchangers is simplified, their working life is also considerably increased.

As the heat carrier should not evaporate, the pressure reduction in the flat heat exchanger is limited. The pressure at entry of the heat carrier should be below atmospheric pressure, e.g. 0.9 bar; the total pressure loss of the flat heat exchanger should not then exceed the difference, reduced by 0.1 bar, between atmospheric pressure and the boiling pressure of the heat carrier at the respective operating temperature, which can reach a maximum of 80"C. If water is used as the heat carrier, the maximum admissible pressure loss is 0.43 bar. This total pressure loss is composed of the resistance to flow and the static height in a flat heat exchanger when not arranged horizontally. A bypass with an air vent valve can provide in the immediate vicinity of the flat heat exchanger in order to facilitate the starting of the apparatus.The flat heat exchanger is then by-passed while the apparatus is completely filled. The pressure-regulating device is advantageously separated from the conduit system during this procedure. The circulating pump is then switched on and the pressure-regulating device reconnected to the conduit system. As an underpressure has developed in the upper part of the apparatus, the flat heat exchanger can now be slowly connected.

Operation can be started more quickly if the flat heat exchanger is already evacuated when filling is carried out. A particularly suitable device for this is a water-jet pump installed at the point in the conduit system where the bypass again leads into the conduit system in the flow direction. The heat carrier flowing from the bypass into the conduit system forms the driving jet.

The present invention is further illustrated by way of non-limiting example in the following description of specific embodiments.

In the description, reference is made to the accompanying drawings in which the Figures 1 to 5 are schematic circuit diagrams of apparatus of the invention.

Figure 1 shows heat transfer apparatus with a heat exchanger 1, an open conduit system 2 and a pressure regulating device 5 in the form of an expansion tank.

The pipes of the conduit system 2 which lead vertically downwards are dimensioned as a function ofthevolumetric delivery of a circulating pump such that the flow speed of the heat carrier is higherthan 0.5 m/s. The pressure regulating device 5 regulates the pressure in the conduit system such that, irrespective of the temperature of the heat carrier in the flat heat exchanger 1, it is lower than the atmospheric pressure and is maintained almost constant in the operating condition.

In the open conduit system 2 of Figure 1, regulation of pressure is carried out in a simple manner using a ventilated liquid column connected to the conduit system 2. The height of the liquid column is maintained at a certain level below the flat heat exchanger. To this end a vertical pipe line 6 runs upwards to a container from the lower, horizontal pipe line of the conduit system 2. The diameter of the container is large enough to receive the expansion volume without a considerable alteration in the filling height.

When there is not sufficient space for such a container as shown in Figure 1, the level can also be maintained constant by means of an overflow dam 7, as shown in Figure 2. The connecting branch, which is open to the atmosphere, with the overflow dam 7 and the annular cup 8, can also be directly mounted in the downward leading pipe of the conduit system 2 below the flat heat exchanger 1.

Superflous heat carrier flows over the overflow dam 7 into the annular cup 8 and then reaches a lower reservoir 10 via a pipe line 9. If required, e.g. when filling the apparatus or reducing the circulating volume by lowering the temperature, the heat carrier is pumped back into the conduit system 2 from the reservoir 10 via the pipe line 11 by means of, e.g. a float-controlled charge pump 12.

If there is no space for the reservoir 10 below the connecting branch the level in the connecting branch can also be adjusted by, e.g. as shown in Figure 3 a charge pump 12 which is controlled by conventional level probes 13 and whose direction of discharge is reversible. The pump is then connected via a pipe line 11 to the connecting branch and the reservoir 10.

In all these arrangements the pressure regulating device, which is open to the atmosphere, can also be used to deaerate the apparatus, so that air vent valves are unnecessary. Such, e.g. float-controlled air vent valves are indespensable in a closed conduit system 2 and must be arranged in the overpressure range such that no gas can collect in the pressureregulating system 5; they must therefore be arranged in front of or on the pressure-regulating deviceS.

The pressure regulating device 5 can then comprise a container which is closed by, e.g. a diaphragm 14, bellows 15 or a piston 16, see Figures 4 to 6, and on whose easily movable lid a constant force, e.g. a weight 17 acts. The container and the lid must be dimensioned such that no large forces arise owing to the movement of the lid following the change in volume.

The apparatus of the various figures according to the invention enables large surface, flat heat exchangerms to be used which consist of two thin foils 19,20 arranged one on top of the other. The foils are connected together only at the edges, in a gastight manner, and are separated from one another by a compression-proof, porous intermediate layer 21 of open-pored foam or a fleece, for example. Instead of the intermediate layer 21 the foils can also be provided with stampings which, according to the use, can withstand pressures of at least 0.5 bar and hold the foils 19,20 apart under this load, so that the heat carrier can freely flow through the foils.

The operating pressure of the heat carrier should be below atmospheric pressure, e.g. 0.9 bar at entry; the total pressure loss of the flat heat exchanger 1 should not then exceed the difference, reduced by 0.1 bar, between atmospheric pressure and the boiling pressure of the heat carrier at the respective operating temperature, which can reach a maximum of 80"C. If water is used as the heat carrier, the maximum admissible pressure loss is 0.43 bar. This total pressure loss is composed of the resistance to flow and the static height in a flat heat exchanger 1 if not arranged horizontally.

A bypass 22 with an air vent valve is provided in the direct vicinity of the flat heat exchanger 1 in order to facilitate the starting of the apparatus of the figures. The flat heat exchanger 1 is by-passed when the apparatus is completely filled. The pressureregulating device 5 is advantageously separated from the conduit system 2 during this procedure.

The circulating pump 4 is then switched on and the pressure-regulating device 5 reconnected to the conduit system 2. Once an underpressure has developed in the upper part of the apparatus, the flat heat exchanger 1 can now be slowly connected.

Operation can be started more quickly if the flat heat exchanger 1 is already evacuated when filling is carried out. A particularly suitable device for this water-jet pump 23, as shown, which is installed at the point in the conduit system 2 where the bypass 22 again leads into the conduit system 2 in the flow direction. The heat carrier flowing from the bypass 22 into the conduit system 2 forms the driving jet.

Claims

1. Heat transfer apparatus with a fluid heat carrier, the apparatus comprising at least one flat heat exchanger for receiving or delivering heat, a conduit system with a circulating pump, a heat exchanger and a pressure-regulating device, characterised in that the pipes of the conduit system which leads downwards are dimensioned as a function of the volumetric delivery of the circulating pump such that the flow speed of the heat carrier is higher than 0.5 mis, and the pressure-regulating device regulates the pressure in the conduit system such that, irrespective of the temperature of the heat carier in the flat heat exchanger, it is lower than the atmospheric pressure and is maintained substantially constant during operation.

2. Apparatus according to claim 1, characterised in that the pressure-regulating device consists of a container arranged below the flat heat exchanger, which container is connected to the conduit system, is open to the atmosphere and can receive at least the expansion volume of the heat carrier without a considerable alternation in the filling height.

3. Apparatus according to claim 1, characterised in that a connecting branch, which is open to the atmosphere, together with an overflow dam and an overflow collector, are mounted in the conduit system below the flat heat exchanger to form the pressure regulating device, the overflow collector being connected to a reservoir arranged below the connecting branch and from which a pipe line with return pump runs to the connecting branch.

4. Apparatus according to claim 1, characterised in that a connecting branch, which is open to the atmosphere and connected to the conduit system, is mounted below the flat heat exchanger as a pressure-regulating device, is provided with a level switch and is connected to a reservoir, arranged as desired, via a pipe line and a charge pump, which is controlled by the level switch and whose direction of discharge is reversible.

5. Apparatus according to claim 1, characterised in that a container, closed by a diaphragm, bellows, a piston, or equivalent closure means is used as pressure-regulating device in a closed conduit system with a constantly operating force acting on the movable lid of the container, and that an automatic vent is arranged in the overpressure range in advance of and/or on the pressure-regulating device.

6. Apparatus according to any of claims 1 to 5, characterised in that the flat heat exchanger comprises a lower and an upper foil connected together only at the edges and in a gastight manner, and interjacent spacers.

7. Apparatus according to any of claims 1 to 6, characterised in that the flat heat exchanger has a total pressure loss which is smaller by 0.1 bar than the difference between atmospheric pressure and the vapour pressure of the heat carrier at operating temperature, which can be a maximum of 80"C.

8. Apparatus according to any of claims 1 to 7, characterised in that it is provided with a bypass with ventilation in the immediate vicinity of the flat heat exchanger.

9. Apparatus according to any of claim 8, characterised in that a device which produces an underpressure is installed at the point where the bypass leads back into the conduit system when viewed in the flow direction.

10. Heat transfer apparatus substantially as hereinbefore described with reference to any of the Figures 1 to 5 of the accompanying drawings.