WO2000068622A1

WO2000068622A1 - An absorption chiller

Info

Publication number: WO2000068622A1
Application number: PCT/GB2000/001621
Authority: WO
Inventors: Robert James Tucker; David Anthony Clark; Jeffrey David Sadler; Aik Beng Lua
Original assignee: Lattice Intellectual Property Ltd.
Priority date: 1999-05-11
Filing date: 2000-05-08
Publication date: 2000-11-16
Also published as: GB9910758D0; GB2349941B; MXPA01011460A; AR023965A1; GB2349941A; GB0011000D0; CN1370262A; JP2002544462A; EG22662A; HK1046727A1; EP1179164A1; BR0010414A

Abstract

An absorption chiller (2) including a generator (4) to boil-off water from a lithium bromide/water solution. The generator (4) comprises an upper tank (42) and a lower tank (36) interconnected by vertical heat exchange tubes (38) which are disposed in cross-flow relation with the hot products of combustion coming from a fuel gas pre-mix package burner (50) and flowing through a combustion chamber (46) and in which the solution flows upwardly, and by insulated thermo-syphon tubes (58) which are separated from the hot products flow by a thermal barrier and in which the solution flows downwardly. The weak solution is introduced into the upper tank (42) through an inlet (68) opposite the upper end of a thermo-syphon tube (58). The upper tank (42) comprises baffle plate (76), a demister pad (74), an outlet (72) for steam, vertical baffle plates (80, 82) forming a calm zone (78) and an outlet (70) for concentrated lithium bromide.

Description

AN ABSORPTION CHILLER

This invention concerns an absorption chiller wherein refrigerant is dissolved in liquid absorbent to form a solution of refrigerant in said absorbent.

More particularly the invention concerns a generator of such an absorption chiller in which generator the solution is heated to boil -off said refrigerant from absorbent to separate aforesaid refrigerant in gaseous phase from said absorbent .

An object of the invention is to provide an absorption chiller in which the efficiency of transfer of solution is improved .

According to the invention there is provided an absorption chiller wherein refrigerant is dissolved in liquid absorbent to form a solution of refrigerant in said absorbent, the absorption chiller comprising a generator in which the solution is heated to boil-off the refrigerant in gaseous phase from the absorbent, the generator comprising an upper tank and relative thereto a lower tank, the tanks, in use, containing the solution, means for upwardly transferring solution from the lower tank to the upper tank, means for downwardly transferring solution from the upper tank to the lower tank and means to provide a supply of hot heating gas along a hot gas flow path, the means for upwardly transferring solution being disposed in the flow path so that the solution is heated by the heating gas whereas the means for downwardly transferring solution is disposed wholly or substantially wholly outside the flow path.

Preferably the means for upwardly transferring solution from the lower tank to the upper tank comprises heat exchange tubes which are disposed in the flow path for heat exchange between the heating gas and solution within the tubes.

Preferably the means for downwardly transferring solution from the upper tank to the lower tank comprises at least one thermo-syphon tube extending from one tank to the other and opening into each tank, the solution flowing from the upper tank to the lower tank through the thermo-syphon tube or tubes .

Suitably the upwardly transferring solution means extends at substantially a right angle to the direction of hot gas flow along the flow path.

Relative to the direction of hot gas flow along the flow path one or more of the heat exchange tubes may be upstream relative to one or more other of the heat exchange tubes, and advantageously the one or more other heat exchange tubes may have external heat collecting formations thereon which may be fins . The heat exchange tubes may be disposed in an array comprising a plurality of rows extending across the flow path. Each row comprises a plurality of spaced said heat exchange tubes, the rows are disposed one after another along the flow path, and the heat exchange tubes in a said row may be staggered relative to the heat exchange tubes in an adjacent row.

Preferably, the or each thermo-syphon tube is separated from the flow path by thermal barrier means .

An inlet for supplying said solution may open into a said tank, and the or a thermo-syphon tube may open into that tank adjacent to or opposite to the inlet. Advantageously, an inlet for supplying the solution opens into the upper tank, and the or a thermo-syphon tube opens into the upper tank adjacent to or substantially opposite to the inlet for receiving weak solution discharged by the inlet, the solution being weakened by the refrigerant dissolved in the absorbent .

In another embodiment, an inlet supplying said solution may open into the or at least one of the thermo-syphon tubes.

In relation to the direction of flow of hot gas along the flow path each tank has an upstream end and a downstream end. The or a thermo-syphon tube may open into the lower tank adjacent to the upstream end of the lower tank. A plurality of heat exchange tubes may open into the lower tank adjacent to the upstream end thereof. The or a thermo-syphon tube may open into the upper tank adjacent to the upstream end thereof. An inlet for supplying the solution may open into the upper and/or into the lower tank adjacent to the upstream end(s) thereof.

An outlet for absorbent may lead from the upper tank. If desired, a calm zone may be provided in the upper tank adjacent to the absorbent outlet.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic view of an adsorption chiller formed according to the invention with the regenerator shown in perspective;

Figure 2 is a side elevation of the regenerator in Figure 1 with a side casing panel and insulation removed;

Figure 3 is a plan view of the regenerator in Figure 2; Figure 4 is a side view partly in section of the upper and lower tanks, heat exchange tubes and thermo-syphon passages of the regenerator in Figure 2 ;

Figure 5 is a view on arrow V in Figure 4;

Figure 6 is a plan view of Figure 5 ;

Figure 7 is a section on line VII-VII in Figure 4 ;

Figure 8 is a section on line VIII-VIII in Figure 4 ;

Figure 9 is a view on arrow IX in Figure 4 of a top portion of the regenerator components in Figure 4 ;

Figure 10 shows an enlargement of region X in Figure 4 ;

Figure 11 diagramatically shows a fuel gas supply and control train layout of a fuel gas burner used to heat the regenerator in Figure 1 ; and

Figure 12 are graphs representing efficiency and heat exchange tube wall temperature in a generator illustrated in Figures 1 to 11 having eleven rows of heat exchange tubes and heated by a fuel gas burner rated at 350k . In the drawings like references identify the same or comparable parts.

With reference to Figure 1, an absorption chiller 2 comprises a regenerator 4 supplying refrigerant in its vapour or gaseous phase along line 6 to a condenser 8 (known per se) and supplying concentrated liquid absorbent along line 10 via one-way valve 12 and a pump 14 to an absorber 16 (known per se) . From the condenser 8 liquid refrigerant is supplied to an expansion arrangement 18 (known per se) in line 20 and thence the refrigerant enters evaporator 22 (known per se) . Line 24 carries refrigerant vapour to the absorber 16 in which the refrigerant dissolves in the absorbent to form a weak solution of absorbent containing refrigerant. That solution is conveyed via one-way valve 26 in line 28 and a pump 30 to the regenerator in which the weak solution becomes concentrated absorbent by boiling-off the refrigerant.

Preferably the refrigerant is water (H₂0) in which case the refrigerant vapour on line 6 can be steam, and the liquid absorbent is lithium bromide (LiBr) though other refrigerant and absorbent combinations may be used, for example ammonia as refrigerant and water as absorbent .

Now with reference to Figures 1 to 10 aspects of regenerator 2 will be described in more detail . The regenerator 2 comprises a base frame 32 supporting an outer casing 34 of parallel piped shape (shown in dotted line in Figures 5 to 7) and a lower tank 36 of substantially rectangular cross- section having a flat top 37 from which ascend a plurality of substantially vertical heat exchange tubes 38A and 38B, tubes 38A having cylindrical, plain outer surfaces whilst the tubes 38B have heat collecting formations formed by fins 40. The heat exchange tubes 38A, 38B open through a flat base 41 of an upper tank 42 of substantially rectangular cross-section and greater volume than the lower tank 36.

Between the casing 34 and the structure comprising the tanks 36 and 42 and the heat exchange tubes 38A, 38B is heat insulating material having an upper inner face 44A (Figure 2) , lower inner face 44B (Figure 2) , and two opposite side inner faces 44C and 44D (Figure 5) defining between them a combined combustion chamber and flue 46 also defined in part by surfaces of the tank top 37 and tank bottom 41. The heat insulation may comprise one or more layers of suitable material, for example ceramic fibre board and/or ceramic blanker and/or Rock wool. The heat exchange tubes 38A, 38B are substantially wholly within the combustion chamber 46. At an upstream or front end 48 of the casing 34 is a gas burner, preferably a package burner 50 of a pre-mix type having an electrically driven fan or impeller propelling combustion air pre-mixed with a fuel gas to a burner outlet orifice or combustion surface which may be disposed within a vertically elongate substantially rectangular frame 52 (Figure 2) within the casing 34 having longer side walls 54 (only one shown, Figure 2) . If desired the aforesaid burner outlet orifice may comprise a metal fibre burner. Externally of the casing 34, a downstream flue path within a rectangular tube 56 leads from combustion chamber 46. From the above it will be understood that the heat exchange tubes 38A, 38B are in cross-flow relation with, more particularly at a right- angle to, flow direction X of hot heating gas or products of combustion through the combustion chamber 46 from the burner 50. It can also be seen that the heat exchange tubes 38A, 38B are arranged in a plurality of rows, in this particular example eleven rows, spaced one from another along the flow direction of the hot products of combustion of each row extending transversely to the direction of flow X of the combustion products - there being at least two heat exchange tubes per row, in this example four heat exchange tubes per row. With respect to flow direction X, the finned heat exchange tubes 38B are disposed at or towards the downstream end of the array of tubes 38A, 38B, whereas the plain heat exchange tubes 38A are upstream of the finned heat exchange tubes in the array. In the example there are seven rows of plain heat exchange tubes 38A and four rows of finned heat exchange tubes 38B.

Two thermo-syphon tubes 58A and 58B are disposed substantially vertically and extend from the lower tank 36 to the upper tank 42 and open into each. As will be understood from Figures 5 to 7 the thermo-syphon tubes 58A, 58B are surrounded by the heat insulating material which screens the tubes from the combustion chamber 46 and opposes heat transfer from the combustion chamber to the thermo-syphon tubes. With respect the direction X of products of combustion flow in the combustion chamber 46, 60 and 62 are upstream ends respectively of the tanks 36 and 42 and 64 and 66 are the respective downstream ends. The thermo-syphon tube 58A opens into the upper and lower tanks 42, 36 adjacent to the respective upstream ends 62, 60. With respect to direction X, the thermo-syphon tube 58B is downstream of the tube 58A and opens into the lower tank 36 about substantially mid-way therealong and opens into the upper tank 42 nearer to the upstream end 62 than the downstream end 66. The number of thermosyphons, their size and inlet/outlet positions can be adjusted. An inlet tube 68 to supply weak refrigerant/absorbent solution from line 28 (Figure 1) to the upper tank 42 opens thereinto opposite to the entrance to the thermo-syphon tube 58A (see Figures 4 and 5) . An outlet tube 70 for carrying off concentrated absorbent solution to line 10 (Figure 1) leads from the downstream end 66 of the upper tank, and an outlet tube 72 to carry off refrigerant vapour or gas to the line 6 (Figure 1) leads from the top of the upper tank.

The unit comprising upper and lower tanks 36, 42, the heat exchange tubes 38A, 38B and the thermo-syphon tubes 58A, 58B can be formed of metal, for example carbon steel. However because the absorbent used may be corrosive, it may be preferred to form the aforesaid unit of corrosion resistant metal, for example cupro-nickel .

With weak refrigerant/absorbent supplied to the upper tank 42 continuously through the inlet 68 and with the burner 50 operating, the weak solution descends to the lower tank 36 through the thermo-syphon tubes 58A, 58B and then ascends to the upper tank through the heat exchange tubes 38A, 38B. As the solution rises in the heat exchange tubes 38A, 38B the refrigerant boils off to a vapour which leaves through the outlet 72, whereas the remaining concentrated absorbent leaves the upper tank through the outlet 70. The heat exchange tubes 38A, 38B may be substantially half full of aforesaid boiling off vapour.

As mentioned, in this example there are eleven rows of heat exchange tubes 38A, 38B which may be identified as rows 1 to 11 in which row 1 is, relative to direction X at the upstream end of the array of heat exchange tubes and row 11 is at the downstream end. Thus the plain tubes 38A form rows 1 to 7 and the finned tubes 38B form rows 8 to 11. The products of combustion tend to be hotter at the upstream end of the array of heat exchange tubes 38A, 38B than at the downstream end. To ensure a more even extraction of heat along the flow path X, the tubes 38B are finned to increase therein ability to extract heat from the relatively cooler downstream combustion products. It will thus be appreciated that the position of the thermo-syphon tube 58A tends to receive the initially input weak solution from the inlet and feed it to a position in the lower tank 32 from which the solution is more likely to ascend through upstream heat exchange tubes 38A, say tube rows 1, 2, and 3, which are exposed to the hottest combustion products .

A vapour permeable demister pad 74 which may be of metal mesh or fibre is disposed in front of the entrance to the outlet pipe 72, and in front of or below the pad is a baffle plate 76 to prevent upward surges of solution hitting the pad or entering the outlet pipe.

A calm zone is established in the upper tank 42 at its downstream end and in front of the entrance to the outlet pipe 70. The calm zone 78 is designed to reduce the chance of absorbent in a turbulent state entering the outlet 70 and to increase the chance of only the more concentrated absorbent being supplied to the outlet. Thus the calm zone comprises two substantially vertical baffle plates 80 and 82 extending across the upper tank 42. The taller baffle plate 80 is spaced at 84 (see Figure 10) from the floor of the upper tank 42 and somewhat higher than the space 84 is the other baffle plate 82 acting as a weir. Since the more concentrated absorbent tends to be lower in the upper tank 42, only such more concentrated absorbent can pass under the baffle plate 80 through the space 84 and over the baffle plate 82 to the outlet 70.

Since the combustion products passing down flue pipe 56 may still contain recoverable heat, the pipe 56 may be lined with heat insulating material and may contain a further heat exchanger 86 exposed to the flue gases, this further heat exchanger acting as a regenerator/economiser/pre-heater . Heat exchanger 86 may be a tube in serpentine form or a plurality of serpentine forms disposed side by side and connected for liquid to flow through them in succession from one serpentine arrangement to the next, the vertical straight tube lengths in the or each serpentine form being in cross- flow relation with flue gases flow direction. An inlet to the heat exchanger 86 is indicated at 86A and an outlet at 86B.

It is preferred that the further heat exchanger 86 be used to pre-heat the weak refrigerant/absorber solution delivered by the pump 30. To this end the section of line 28 between points a and b in Figure 1 is omitted and the line 28 extended by a section 28A leading to the inlet 86A. From the outlet 86B another section of line 28B leads to the inlet tube 68. When the apparatus uses the further heat exchanger 86, an H₂0/LiBr solution and a 350kW burner 50 burning fuel gas, for example natural gas, provided with about 20% excess combustion air, the following operational conditions may obtain. The boiling temperature of the solution may be about 160°C, the concentrated solution supplied to outlet 70 may be about 64% LiBr salt, and the velocity of the mixture entering the upper tank 42 from the heat exchange tubes 38A, 38B may be about 1.5m/s. The temperature of the flue gases in the flue 56 may be about 210°C. Shown in Figure 12 is a variation in heat exchange tube wall temperature for the tubes in row 1 to the tubes in row 11 and how the cumulative efficiency of the generator may progressively (and relatively uniformly) increase along the array of heat exchange tubes from one row to next. The pressure within the upper tank 42 may substantially approach or be 0.5 barg.

In the drawings, reference 88 indicates a union for mounting a pressure relief valve on the upper tank 42, reference 90 indicates access tubes to receive liquid level sensors inserted into the calm zone of the upper tank, and reference 92 indicates a normally closed drain passage. Sight glasses enabling a view of the main interior of upper tank 42 and the calm zone 78 are indicated at 94 and 96 respectively. Temperature sensors may be provided in the lower and upper tanks 36, 42. In the above description supply of weak refrigerant/absorbent solution is to the upper tank 42 through the inlet pipe 68, instead that pipe 68 may be blocked-off or omitted and the weak solution from line 28 or line 28, 28A, 28B be supplied to the lower tank 36 through an inlet pipe 98 opening into the lower tank opposite to the lower opening of the thermo- syphon tube 58A.

A package burner 50 rated at 350kW has been referred to above. Package burners of different ratings may be used for example from a few kW to MW ratings.

In a gas supply system for the package burner 50 in Figure 11, the burner comprises a fan or impeller 100 driven by an electric motor 102 to draw combustion air along a duct 104 in which the air pre-mixes with fuel gas from a gas supply line 106 before supply to the burner outlet orifice. An electrical control (not shown) comprises a motor control 108, a pressure switch 110 observing the output pressure of the air/fuel gaseous mixture from the impeller 100, a pressure switch 112 observing the pressure of the fuel gas supplied, solenoid controlled valves 114 and 116, and an air/fuel ratio controller 118 arranged to respond to signals representative of air pressure in the vicinity of an orifice plate 120 in the duct 104. A manual valve 121 has to be open before any fuel gas may be supplied. If the pressure of the supplied gas observed by the pressure switch 112 falls outside a pre- determined range the control may operate one or other of the solenoid valves 114, 116 to shut off gas supply to the burner. Should the pressure observed by the switch 110 fall outside a pre-determined range the control may operate to shut one or other of the valves 114, 116 and may also stop the motor 102. The control may be responsive to a demanded firing rate at the burner and thus operate the motor control 108 so that the impeller 100 speed is varied to supply combustion air in desired quantity. Alternatively the control 108 may be omitted and the impeller 100 driven at a constant speed, the amount of combustion air supplied being varied by operation of the throttle valve 122, in the duct 104, driven by a throttle motor 126 in accordance with signals thereto initiated by the control.

Instead of using a package burner 50, some other means of generating hot gases to heat the heat exchange tubes 38A, 38B may be used, for example hot exhaust gases from a gas turbine .

By choosing a thermo-syphon tube or tubes as the solution transfer means and/or by locating the thermo-syphon tube or tubes outside the hot gas flow path, there is no or at least little or a reduced heat transfer from the combustion gas to the tube or tubes promoting better thermo-syphon action. Weak solution can enter the top chamber and a lower volume of solution can be used. In addition, by locating the thermo-syphon tube or tubes outside the hot gas flow path, there is greater freedom in the choice of the size, shape and position of the tube or tubes. By carefully selecting the appropriate design features a weak solution can be selected and its flow rate controlled. When the thermo-syphon tube or tubes are located outside the hot gas flow path it or they is/are easier to install in the generator, the tube or tubes can be used for flow level measurements and the overall weight of material can be reduced.

Claims

1. An absorption chiller wherein refrigerant is dissolved in a liquid absorbent to form a solution of refrigerant in said absorbent, the absorption chiller comprising a generator in which the solution is heated to boil-off the refrigerant in gaseous phase from the absorbent, the generator comprising an upper tank and relative thereto a lower tank, the tanks, in use containing the solution, means for upwardly transferring solution from the lower tank to the upper tank, means for downwardly transferring solution from the upper tank to the lower tank and means to provide a supply of hot heating gas along a hot gas flow path, the means for upwardly transferring solution being disposed in the flow path so that the solution is heated by the heating gas whereas the means for downwardly transferring solution is disposed wholly or substantially wholly outside the flow path.

2. An absorption chiller in which the means for upwardly transferring solution from the lower tank to the upper tank comprises heat exchange tubes which are disposed in the flow path for heat exchange between the heating gas and solution within the tubes .

3. An absorption chiller as claimed in claim 2 in which one or more of the heat exchange tubes are upstream relative to one or more other of the heat exchange tubes .

4. An absorption chiller as claimed in any of claims 1 to 3 in which the means for downwardly transferring solution from the upper tank to the lower tank comprises at least one thermo-syphon tube extending from one tank to the other and opening into each tank, the solution flowing from the upper tank to the lower tank through the thermo-syphon tube or tubes .

5. An absorption chiller as claimed in any of the preceding claims, in which fluid flows in the means for upwardly transferring solution along directions extending across the direction of hot gas flow along the flow path.

6. An absorption chiller as claimed in any of the preceding claims, in which each means for upwardly transferring solution extends at substantially a right angle to the direction of hot gas flow along the flow path.

7. An absorption chiller as claimed in any of the preceding claims, in which relative to the direction of hot gas flow along the flow path first heat exchange tubes are upstream relative to second heat exchange tubes which have external heat collecting formations thereon.

8. An absorption chiller as claimed in claim 7, in which the external heat collecting formations are fins.

9. An absorption chiller as claimed in claim 7 or claim 8, in which first heat exchange tubes have plain external surfaces .

10. An absorption chiller as claimed in any of claims

2 to 9, in which the heat exchange tubes are disposed in an array comprising a plurality of rows extending across the flow path, each row comprising a plurality of spaced heat exchange tubes, the rows being disposed one after another along the flow path, and the heat exchange tubes in a row being staggered relative to heat exchange tubes in an adjacent row.

11. An absorption chiller as claimed in any preceding claim, in which the means for downwardly transferring solution is separated from the flow path by thermal barrier means.

12. An absorption chiller as claimed in any of the preceding claims, in which the means for downwardly transferring solution is provided externally with thermal insulation.

13. An absorption chiller as claimed in any of the preceding claims, in which walls of the tanks receive heat from the hot gas in the flow path.

14. An absorption chiller as claimed in any of the preceding claims, in which walls of the tanks form walls of the flow path.

15. An absorption chiller as claimed in any of the preceding claims, in which in relation to the direction of flow of hot gas along the flow path each tank has an upstream end and a downstream end.

16. An absorption chiller as claimed in claim 15, in which the or a thermo-syphon tube opens into the lower tank adjacent to the upstream end of the lower tank.

17. An absorption chiller as claimed in claim 16, in which a plurality of heat exchange tubes open into said lower tank adjacent to said upstream end thereof.

18. An absorption chiller as claimed in any one of claims 15 to 17, in which the or a thermo-syphon tube opens into the upper tank adjacent to said upstream end thereof.

19. An absorption chiller as claimed in claim 18, in which a plurality of the heat exchange tubes open into the upper tank adjacent to the upstream end thereof.

20. An absorption chiller as claimed in any one of claims 16 to 19, in which there are at least a first thermo-syphon tube and a second thermo-syphon tube, the first thermo-syphon tube opening into each tank adjacent to the upstream end thereof and the second thermo-syphon tube opening into each tank downstream of the first thermo-syphon tube but no further from the upstream end of each tank than substantially mid-way between the upstream and downstream ends of the tank.

21. An absorption chiller as claimed in any one of claims 1 to 14, in which an inlet for supplying solution opens into the upper tank.

22. An absorption chiller as claimed in any one of claims 1 to 14, in which an inlet for supplying solution opens into the lower tank.

23. An absorption chiller as claimed in claim 21 and in any one of claims 15 to 20, in which the inlet opens into the upper tank adjacent to the upstream end thereof.

24. An absorption chiller as claimed in claim 22 and in any one of claims 15 to 20, in which the inlet opens into the lower tank adjacent to the upstream end thereof.

25. An absorption chiller as claimed in any one of claims 1 to 14, 21 or 22, in which an outlet for the absorbent leads from the upper tank.

26. An absorption chiller as claimed in claim 25 and in any one of claims 15 to 20, 23 or 24, in which the absorbent outlet leads from the downstream end of the upper tank.

27. An absorption chiller as claimed in claim 25 or claim 26, in which a calm zone is provided in the upper tank adjacent to the absorbent outlet.

28. An absorption chiller as claimed in claim 27, in which the calm zone comprises a baffle arrangement wherein at least one baffle is spaced from the floor of the upper tank for flow of absorbent under at least one baffle.

29. An absorption chiller as claimed in any of the preceding claims, in which a refrigerant vapour outlet leads from the upper tank.

30. An absorption chiller as claimed in claim 29, in which de-mister means is provided for passage of refrigerant vapour therethrough to said outlet.

31. An absorption chiller as claimed in claim 29 or claim 30, in which baffle means is disposed in an upper part of the upper tank, the baffle means being in front of the refrigerant vapour outlet .

32. An absorption chiller as claimed in any one of claims 21 to 24, in which further heat exchange means is disposed in the flow path downstream of the heat exchange tubes for heat transfer from the hot gas to the further heat exchange means for which at least a portion of the solution is subject to initial heating prior to supply to the inlet .

33. An adsorption chiller as claimed in any of the preceding claims, in which the hot gas comprises products of combustion.

34. An absorption chiller as claimed in claim 33, in which the products of combustion are provided by burning gas .

35. An absorption chiller as claimed in claim 34, in which the products of combustion are provided by burning fuel gas at a fuel gas burner.

36. An absorption chiller as claimed in claim 35, in which the gas burner is a pre-mix burner.

37. An absorption chiller as claimed in claim 36, in which the gas burner comprises a driven fan providing combustion air.

38. An absorption chiller as claimed in any one of claims 4 to 14, in which an inlet for supplying the solution opens into a tank, and the or a thermo-syphon tube opens into that tank adjacent to or opposite to the inlet.

39. An absorption chiller as claimed in any one of claims 4 to 14, in which an inlet for supplying the solution opens into the upper tank, and the or a thermo-syphon tube opens into the upper tank adjacent to or substantially opposite to the inlet for receiving weak solution discharged by the inlet, the solution being weakened by the refrigerant dissolved in the absorbent.

40. An absorption chiller as claimed in any one of claims 4 to 14, in which an inlet for supplying the solution opens into the or at least one of the thermo-syphon tubes.

41. An absorption chiller as claimed in any of the preceding claims, in which the refrigerant is water and the absorbent is lithium bromide.

42. An absorption chiller wherein refrigerant is dissolved in liquid absorbent to form a solution of refrigerant in the absorbent, and the absorption chiller comprising a generator substantially as hereinbefore described with reference to the accompanying drawings .