GB2498771A - A Generator for an Absorption Chiller and an Absorption Chiller Using such a Generator - Google Patents

Abstract

A generator 20 for an absorption chiller (1 fig 1) has a bath 21 for receiving a refrigerant mixture. The bath has at least one side wall 26, 27, and each side wall has a plurality of laminar heat exchangers 29. Each heat exchanger has a rim 30 from which extends at least one heat exchange fin 31. The laminar heat exchangers are stacked together with the at least one fin extending away from the bath. The rim of each heat exchanger may include many extending fins, and the fins of one heat exchanger may interdigitate or stagger with respect to the fins of an adjacent heat exchanger. The bath may contain a refrigerant mixture that may be heated by a burner 32, and a flue pipe 22 may carry heat from the burner over the heat exchange fins that may extend towards the centre of the flue pipe. The laminar heat exchangers may also extend from the bath outer side wall. The invention also relates to an absorption chiller using such a generator.

Description

A generator for an absorption chiller and an absorption chiller comprising such a generator The present invention relates to a generator for an absorption chiller. More particularly, but not exclusively, the present invention relates to a generator comprising a bath having a side wall, the side wall comprising a plurality of laminar heat exchangers at least partially defining the wall. In a further aspect of the invention there is provided an absorption chiller comprising such a generator.

Absorption chillers including generators are known. The generator comprises a bath which in turn comprises a refrigerant mixture. In use a heated gas, typically from a gas fired heat source, is provided over a side wall of a bath so heating the contents of the bath.

In order to improve the thermal contact between the bath and the heated gas heat exchange fins are provided on the side wall of the bath. Typically a central flue runs through the bath and the fins extend from the flue wall into the flue. Manufacture of such a generator is difficult and can be both expensive and time consuming.

The present invention seeks to overcome the problems of the prior art.

Accordingly, in a first aspect, the present invention provides a generator for an absorption chiller comprising a bath for receiving a refrigerant mixture, the bath comprising at least one side wall; the side wall comprising a plurality of laminar heat exchangers, each heat exchanger comprising a rim having at least one heat exchange fin extending therefrom; the laminar heat exchangers being stacked together with the fins extending away from the bath.

The side wall can comprise a sheet and the rims are connected to the sheet.

Alternatively, the rims can define the side wall.

The bath can comprise a flue pipe extending between input and output ports and a jacket wall surrounding the flue pipe and spaced apart therefrom, the flue pipe and jacket wall defining the bath therebetween, the flue pipe defining an inner side wall and the jacket wall defining an outer side wall.

Preferably, the inner side wall comprises the plurality of heat exchangers with the heat exchange fins extending towards the centre of the flue pipe.

Preferably, the outer side wall comprises the plurality of heat exchangers with the fins extending away from the bath.

The rims of the heat exchangers can be circular.

The generator can further comprise a filling rod within the flue pipe.

Preferably, the diameter of the filling rod varies with distance along the rod.

Preferably, each of the heat exchangers comprises a plurality of fins, the heat exchangers being stacked such that the fins of one heat exchanger interdigitate with the fin of an adjacent heat exchanger.

The thickness of the fins can vary with distance from the rim.

Preferably, the bath contains a refrigerant mixture.

The refrigerant mixture can be a mixture of ammonia and water.

The generator can further comprise a burner to supply heat to the bath.

The generator can further comprise an outer jacket surrounding the bath and heat exchangers and spaced apart therefrom defining a volume for receiving a heated fluid.

In a further aspect of the invention there is provided an absorption chiller comprising a generator as claimed in any one of claims 1 to 15; a condenser connected to the generator and adapted to receive refrigerant gas from the generator and to condense it in to a refrigerant liquid; and, an evaporator comprising first and second fluid paths in thermal contact with each other, the first fluid path being adapted to receive the refrigerant liquid from the condenser.

The present invention will now be described by way of example only and not in any limitative sense with reference to the accompanying drawings in which Figure 1 shows, in schematic form, an absorption chiller; Figure 2 shows a generator according to the invention in vertical cross section; Figure 3 shows a laminar heat exchange of the generator of figure 2; Figure 4 shows a further embodiment of a generator according to the invention; Figure 5 shows a further embodiment of a generator according to the invention; Figure 6 shows a further embodiment of a generator according to the invention; and, Figure 7 shows a further embodiment of a generator according to the invention.

Shown in figure 1 in schematic form is an absorption chiller 1 for chilling a liquid. The absorption chiller 1 comprises a generator 2. Inside the generator 2 is a bath 3 which contains a refrigerant mixture, typically a water/ammonia mixture. A heat source 12 heats the mixture in the bath 3 as described below. When the bath 3 is heated the ammonia boils and separates in the generator 2 creating a high pressure which drives the process.

The ammonia gas exits a refrigerant gas pod 4 of the generator 2 and is received by a condenser 5. In the condenser 5 the ammonia is converted back to a liquid. From here the ammonia is passed to an evaporator 6. The ammonia flows along a first fluid path 7 in the evaporator 6. The fluid to be chilled flows along a second fluid path 8 within the evaporator 6 which is in thermal contact with the first 7. Within the evaporator 6 a heat exchange takes place, chilling the fluid to be chilled and causing re-evaporation of the ammonia back to the gaseous state.

The ammonia gas output from the evaporator 6 is passed to a heat exchanger 9. The gas rises up through the heat exchanger 9 whilst a weak ammonia/water solution obtained from a mixture port of the generator 2 is passed down through the heat exchanger 9 as shown.

Heat exchange between the two components causes the ammonia gas to re-condense within the heat exchanger 9. The output from the heat exchanger 9 is then passed via an absorber 10 and a pump 11 back to the generator 2 and the cycle starts again.

A flue (not shown) is provided which runs up the center of the generator 2. A heat source 12, typically a gas fired heat source, is arranged below the generator 2 and provides a hot gas which passes up the flue. The gas heats the flue which in turn heats the mixture within the bath 3. In order to improve the thermal contact between the flue and the bath 3 gas fins (not shown) are provided on the inner face of the flue. Such fins can be very difficult to manufacture.

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It is often desired to heat the generator 2 with an additional heat source. The additional heat source can be a heated gas. The heated gas is typically provided to the generator 2 by a turbine (not shown). Turbines do not function well when there is a significant back pressure and so this heated gas cannot be piovided to the central flue. Instead, a housing 13 is provided surrounding but spaced apart from the generator 2 and the heated air flows in the gap 14 between the two. Fins 15 designed to produce a low back pressure are often included in this gap 14. Manufacture of the housing 13 and fins 15 is again expensive and difficult.

Shown in figuie 2 in cross section is a first embodiment of a genelatol 20 according to the invention. The generator 20 comprises a bath 21 for receiving a refrigerant mixture. In this embodiment the refrigerant mixture is a mixture of water and ammonia.

The bath 21 comprises a flue pipe 22 extending between input and output ports 23,24. A jacket 25 surrounds the flue pipe 22 and is spaced apart therefrom. The jacket 25 and flue pipe 22 between them define the bath 21 and the refrigerant mixture is received in the gap between the two. The flue pipe 22 partially defines an inner side wall 26. The jacket 25 defines an outer side wall 27.

The flue pipe comprises a thermally conductive sheet 28. Attached to sheet 28 is a plurality of laminar heat exchangers 29 so defining the inner side wall 26. Each heat exchanger 29 complises a rim 30 having a plurality of heat exchange fins 31 extending therefrom. In this embodiment the rim 30 is circular and the heat exchange fins 31 extend inwardly from the rim 30. The rim 30 is a push fit within the flue pipe 22. During manufacture the outer face of the rim 30 is coated with a low melting point metal such as copper. The heat exchangers 29 and flue pipe 22 are typically a high melting point, high thermal conductivity metal such as stainless steel. The laminar heat exchangers 29 are stacked within the flue pipe 22 and the temperature of the assembly raised so braising the laminar heat exchangers 29 to the flue pipe 22 and creating a good thermal bond therebetween.

Figure 3 shows a laminar heat exchanger 29 of figure 2 in plan view. As can be seen, in this embodiment the rim 30 is circular and the fins 31 extend inwardly from the rim 30. The width of the fins 31 in the plane of the heat exchanger 29 decreases with increasing distance from the rim 30. The laminar heat exchangers 29 are arranged with the fins 31 of one heat exchanger 29 interdigitating with the tins 31 of an adjacent heat exchanger 29 in the heat exchanger stack. The fins 31 of the adjacent heat exchanger 29 are shown dotted. Because the width of the fins 31 narrows away from the rim 30, the air gap formed by fins 31 on adjacent heat exchangers 29 remains constant with distance away from the rim 30. This improves air flow along the flue pipe 22 and in particular reduces back pressure. In an alternative embodiment the fins 31 of the heat exchangers 29 are aligned with each other.

Arranged under the bath 21 is a burner 32, typically a gas or oil burner. Air heated by the burner 32 passes up the flue pipe 22, flowing over the heat exchange fins 31 and so heating the mixture in the bath 21. Arranged in the flue pipe 22 is a filling rod 33. The filling rod 33 is typically a ceramic or other none reactive material. The filling rod 33 can be manufactured from the same material as the generator 20. The filing rod 33 diverts air flow from the center of the flue pipe 22 over the heat exchange fins 31. It is often preferred that heat is applied to the bath 21 uniformly along the length of the flue pipe 22. Accordingly, in this case the diameter of the filling rod 33 varies with distance along the rod 33, increasing with increasing distance from the burner 32. In this way as the temperature of the heated gas drops a greater proportion of the gas flows over the fins 31, so providing heat to the bath 21 at a substantially uniform rate along the length of the flue pipe 22.

Figure 4 shows an alternative embodiment of a generator 20 according to the invention. This is similar to that of figure 2 except the inner side wall 26 is made up of the rims 30 of the laminar heat exchangers 29, rather than the rims 30 being braised to the sheet 28 of a flue pipe. The rims 30 are directly connected together (again typically by braising) to form the flue pipe 22.

Figure 5 shows a further embodiment of a generator 20 according to the invention. In this embodiment a plurality of laminar heat exchangers 33 are connected to the outer side wall 27 of the bath 21. The fins 35 of these heat exchangers 33 extend away from the bath 21 as shown.

Extending around the bath 21 and heat exchangers 35 is an outer jacket 36. The outer jacket 36 comprises input and output ports 37,38. In use a heated fluid, typically a gas, flows from the input port 37, over the heat exchange fins 35 to the output port 38. This heats the fins 35 and so provides further heat to the mixture in the bath 21. The heated fluid can be a heated gas, for example a waste product from other machinery such as a generator or the like. Alternatively, the heated fluid could be a heated liquid, for example from a solar generator. This embodiment of a generator 20 according to the invention further comprises a burner 32 for supplying heater gas to the flue pipe 22. The outer jacket 36 of this embodiment is manufactured in two semi-circular halves which are connected around the bath 21. The two halves can be taken apart to enable easy cleaning of the outer heat exchange fins 35.

Figure 6 shows a further embodiment of a generator 20 according to the invention. In this embodiment there are no heat exchange tins inside the flue pipe 22. A annular gas burner 32 is arranged under the tins 35 of the outer side wall 27 as shown. In a further embodiment (not shown) the bath 21 lacks the flue pipe 22 and inner side wall 26. Alternatively, the flue pipe 22 may exist but may be substantially blocked with a filler tube 33.

Figure 7 shows a further embodiment of a generator 20 according to the invention. This embodiment is similar to that of figure 6 except it lacks the gas burner. Heat is provided to the bath 21 by the heated fluid flowing over the fins 35 of the outer side wall 27. In this embodiment the central flue pipe is closed with a filler tube 33. In an alternative embodiment the bath 21 lacks the flue pipe.

The heat exchange fins 31 are shown as smooth in figure 3. In alternative embodiments the fins 31 have grooves on their surface or are rough to increase the contact area between the heated fluid and the heat exchange fin 31. Similarly, the side wall at the base of the fins 31 may be rough, again to increase the contact area.

In the above embodiments the flue pipe 22 and the bath 21 are circular. Other shapes are possible. One or more of the flue pipe 22 or bath 21 may be elliptical, rectangular or square.

The generator 20 is manufactured from components having a high thermal conductivity and melting point. Stainless steel is a preferred alternative although other metals including but not limited to mild steel, Inconel, Nimonic alloys, cast iron and cast steel are also possible.

Similaily, other methods of thermally connecting the heat exchangers 29,34 to the one or more side walls are possible including but not limited to electron beam welding, diffusion bonding, laser welding, heat shrinking and friction welding.

The generator 20 according to the invention forms part of an absorption chiller 1. The generator comprises a retrigerant gas port (not shown). The ammonia gas generated in the generator 20 exits the genelator 20 via the refrigerant gas port and is received by a condenser 5 which condenses it back to a liquid. An evaporator 6 receives this refrigerant liquid and uses it to chill a fluid to be chilled. The warm refrigerant which exits the evaporator 6 is received by a heat exchanger 9. The heat exchanger 9 furthei receives a weak ammonia/water mixture from a mixture port of the generator 20 which is used to cool and at least partially condense the refrigerant output from the evaporator 6. This is then returned to the genelatol 20 via an absorbei 10 and a solution pump 11.

Claims (1)

1. <claim-text>CLAIMS1. A generator for an absorption chiller comprising a bath for receiving a refrigerant mixture, the bath comprising at least one side wall; the side wall comprising a plurality of laminar heat exchangers, each heat exchanger comprising a rim having at least one heat exchange fin extending therefrom; the laminar heat exchangers being stacked together with the fins extending away from the bath.</claim-text> <claim-text>2. A generator as claimed in claim 1, wheiein the side wall complises a sheet and the rims are connected to the sheet.</claim-text> <claim-text>3. A generator as claimed in claim 1, wherein the rims define the side wall.</claim-text> <claim-text>4. A generator as claimed in any one of claims 1 to 3, wherein the bath comprises a flue pipe extending between input and output ports and a jacket wall suiiounding the flue pipe and spaced apart therefrom, the flue pipe and jacket wall defining the bath therebetween, the flue pipe defining an inner side wall and the jacket wall defining an outer side wall.</claim-text> <claim-text>5. A generator as claimed in claim 4, wherein the inner side wall comprises a plurality of heat exchangers with the heat exchange fins extending towards the centre of the flue pipe.</claim-text> <claim-text>6. A generator as claimed in either of claims 4 or 5, wherein the outer side wall complises a plurality of heat exchangers with the fins extending away from the bath.</claim-text> <claim-text>7. A generator as claimed in either of claims 5 or 6, wherein the rims of the heat exchangers are circular.</claim-text> <claim-text>8. A generator as claimed in any one of claims 4 to 7, comprising a filling rod within the flue pipe.</claim-text> <claim-text>9. A generator as claimed in claim 8, wherein the diameter of the filling rod varies with distance along the rod.</claim-text> <claim-text>10. A generator as claimed in any one of claims 1 to 9, wherein each of the heat exchangers comprises a plurality of fins! the heat exchangers being stacked such that the fins of one heat exchanger interdigitate with the fin of an adjacent heat exchanger.</claim-text> <claim-text>11. A generator as claimed in any one of claims ito 10, wherein the width of the tins varies with distance from the rim.</claim-text> <claim-text>12. A generator as claimed in any one of claims 1 to 11, wherein the bath contains a refrigerant mixture.</claim-text> <claim-text>13. A generator as claimed in claim 12, wherein the refrigerant mixture is a mixture of ammonia and water.</claim-text> <claim-text>14. A generator as claimed in any one of claims 1 to 13, further comprising a burner to supply heat to the bath.</claim-text> <claim-text>15. A generator as claimed in any one of claims 1 to 14, further comprising an outer jacket surrounding the bath and heat exchangers and spaced apart therefrom defining a volume for receiving a heated fluid.</claim-text> <claim-text>16. An absorption chiller comprising a generator as claimed in any one of claims 1 to 15; a condenser connected to the generator and adapted to receive refrigerant gas from the generator and to condense it in to a refrigerant liquid; and, an evaporator comprising first and second fluid paths in thermal contact with each other, the first fluid path being adapted to receive the refrigerant liquid from the condenser.</claim-text> <claim-text>17. A generator substantially as hereinbefore described.</claim-text> <claim-text>18. An absorption chiller substantially as hereinbefore described.</claim-text>