US3267691A

US3267691A - Cooling and lubricating system for absorption refrigeration apparatus

Info

Publication number: US3267691A
Application number: US406011A
Authority: US
Inventors: William L Osborn
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1964-10-23
Filing date: 1964-10-23
Publication date: 1966-08-23
Anticipated expiration: 1983-08-23

Description

Augn'ZB, 1966 w. OSBORN 3,257,691

COOLING AND LUBRICATING SYSTEM FOR ABSORPTION REFRIGERATION APPARATUS 2 Sheets-Sheet 2 Filed Oct. 25, 1964 United States Patent 3,267,691 COOLING AND LUBRKCATING SYSTEM FOR ABSORPTION REFRIGERATION APPARATUS William L. Osborn, York, Pa., assignor to Borg-Warner Corporation, a corporation of Illinois Filed Oct. 23, 1964, Ser. No. 406,011 5 Claims. (Cl. 62-476) This invention relates generally to systems for providing cooling and lubricating fluid to the hermetically sealed, combination pump-motor units in an absorption refrigeration apparatus, and more particularly to a cooling and lubricating system which automatically maintains an adequate supply of dilute absorbent solution of the proper concentration for use as a cooling and lubricating medium.

It will be appreciated that there are several different conventional arrangements used in absorption refrigeration systems. For purposes of illustration only, the description herein will relate to a design comprising a pair of shells arranged one on top of the other, it being understood that the invention is applicable to single shell and various other configurations. In the example, the lower shell houses two tube bundles, the evaporator and the absorber, operating at a pressure on the order of 6.3 mm. of Hg absolute ,5 atmosphere) while two tube bundles in the upper shell provide a generator and a conenser, said shell being maintained at a pressure on the order of 75 mm. of Hg absolute atmosphere).

As is Well-known to those skilled in the art, operation of the system depends on two factors: a refrigerant that boils at a temperature below that of the liquid being chilled and an absorbent possessing great affinity for the refrigerant. At the pressures maintained within the two shells, the water flowing over the bundle from the evaporator boils and extracts heat from the chilled liquid flowing through the tube bundle. Several refrigerant-absorbent combinations are used commercially, but this specification will make reference to a system employing water as the refrigerant and a hydroscopic brine such as LiBr as the absorbent, it being understood that the invention is applicable to other refrigerant-absorbent combinations.

A liquid, usually water, to cool the conditioned space or process is chilled as it passes through the evaporator tubes by giving up hea t to the refrigerant flowing on the outside of the tubes. The heat removed from the chilled liquid causes the refrigerant (water) to evaporate since it is at a pressure (with a corresponding boiling temperature) lower than the leaving chilled water temperature. For example, water is chilled from 54 F. to 44 F. with the evaporator at 6.3 mm. of Hg absolute; this corresponds to a 40 F. boiling point for the refrigerant.

The LiBr solution, which is circulated within the absorber section located underneath the evaporator, has a great affinity for the water vapor released in the evaporator. This vapor flows downwardly and is brought into contact with the intermediate strength solution flowing over the outside of the absorber tubes, thus diluting the solution. The heat of absorption generated in this process is removed by condenser water from a cooling tower or other source flowing through the absorber tubes.

Dilute solution from the absorber is pumped to the generator by the generator pump. In passing through the heat exchanger, it is regeneratively heated by hot, concentrated solution flowing from the generator to the absorber.

The dilute solution from the absorber flows over the outside of the generator tubes, and a portion of the refrigerant in the solution is vaporized by a heat exchange medium, usually steam, passing through the generator tubes. When the refrigerant is driven ofl, the solution is concentrated and the concentrated solution fiows by gravity through the heat exchanger (where it is cooled regeneratively by the cold dilute solution) to the suction side of the absorber pump.

The refrigerant vapor released from the boiling action in the generator flows upwardly and is brought into contact with the outside of the condenser tubes. The vapor gives up its heat of condensation to the condenser water passing through the tubes and the condensed vapor is passed through a conduit to a distributor located above the absorber coil in the lower shell.

The absorption design described above is described more fully in copending application SN 169,969, filed January 30, 1962 now abandoned. The present invention relates more specifically to a system for cooling and lubricating the hermetically sealed pump and motor units which circulate solution and refrigerant through the system. It should be understood that this background description is merely for the purpose of setting forth the essential elements in a typical absorption refrigeration machine, and provides a basis for a clear understanding of the operation of the cooling and lubricating system associated therewith.

It has been found that dilute LiBr provides an excellent cooling and a superior lubricating medium, requiring less maintenance than systems which utilize the re frigerant, i.e. water, for this purpose. However, one problem has been with insuring that an adequate supply of solution having the proper concentration is available to compensate for leakage from the cooling and lubricating circuit into the solution circuit, or vice-versa. For one thing, the system must provide means for maintaining the solution used for cooling and lubricating in a relatively dilute condition; otherwise, when the solution is passed through the heat exchanger, where its temperature is lowered by a secondary coolant, there would be a possibility of LiBr salt crystallizing out of the solution and choking off flow through the cooling circuit. On the other hand, the concentration should be high enough to provide superior lubricating properties. A range which has been found to be satisfactory is between -53% LiBr.

It is therefore a principal object of the present invention to provide an improved system for cooling and lubricating the hermetically sealed pump and motor units in an absorption refrigeration system.

Additional objects and advantages will be apparent from the following detailed description taken in conjunction with the drawings wherein:

FIGURE 1 is a schematic representation of a cooling and lubricating system constructed in accordance with the principles of the invention;

FIGURE 2 is a view, partly in cross-section, of solution chamber;

FIGURE 3 is a cross-sectional view taken along the plane of line 33 of FIGURE 2; and

FIGURE 4 is a cross-sectional view taken along plane of line 44 of FIGURE 2.

Referring now to the drawings, and particularly to FIGURE 1, the reference character A designates a heat the the

exchanger in which the dilute absorber solution used for cooling and lubricating the pump-motor units passes in heat exchange relation with a secondary cooling fluid. In a preferred embodiment, this secondary cooling fluid is provided by tapping off cold refrigerant from the refrigerant line.

Reference character B designates a concentration control and make-up solution chamber. This chamber, hereinafter referred to as the solution chamber, has several functions. First of all, it acts as a make-up chamber for solution which provides additional solution to the coolant circuit in the event the leakage is from the latter into the refrigerant/solution circuit. It also permits any excess solution, due to leakage from the refrigerant/solution circuit, to flow back to the absorber. Another important function is to maintain the coolant solution at the proper concentration; if it is too dilute, water is drawn out of the solution; if it is too concentrated, water is added. How this is accomplished will be clear from a later description of. the operation.

While all of the pump-motor units ordinarily provided in an absorption refrigeration system are not shown, it will be appreciated that most systems include a generator pump for pumping dilute absorbent solution from the absorber to the generator, a refrigerant pump for recirculating refrigerant through the evaporator and an absorber pump for recirculating an intermediate strength solution through the absorber. In each case, solution is passed into and throughthe casing of each unit in a manner similar to that described in copending application SN 317,661, filed October 21, 1963. It will be understood that each of the pump-motor units has a motor section and a pump section, the cooling-lubricating solution passing into and out of the motor section only. Each of the motor shafts, as illustrated in the aforementioned copending application, also carries a small impeller which pumps the solution through the casing and back to the heat exchanger.

As shown in FIGURE 1, the generator pump 10 is provided with discharge line 11 through which dilute solution from the absorber is forwarded to the generator (not shown). A tap-off conduit 12 communicates with the discharge line and carries a portion of this solution to the solution chamber B.

Solution chamber B comprises a cylindrical shell 16 having

end closures

17, 18, a divider plate 2i? extending transversely across the chamber and being provided with aperture 21, a weir 22, and a perforated distributor plate 24. Located in the zone to the right of weir 22 (FIG- URES 1 and 2) is a solution over-flow line 26 leading back to the absorber. Communicating with the zone to the left of divider plate is a conduit 27 which interconnects with the shell side of heat exchanger A. In this same zone is a conduit 28, which may be referred to as an equalizing line, having a terminal portion extending upwardly into the upper part of the solution chamber and the opposite end terminating in the upper portion of the absorber. The function of this equalizing line will be apparent from the description of the operation.

The circuit for the primary coolant, i.e. the coolant which comes directly in contact with the pump-motor units, includes the conduit 27 connecting the solution chamber B with heat exchanger A, conduit 38 leading from the lower portion of the shell side of said heat exchanger, a filter or strainer element 32, and a supply header 34. Individual supply lines for the coolant solution include lines leading to the refrigerant pump 40, line 36 leading to the absorber pump which circulates an intermediate strength solution over the absorber tube bundle (not shown), and line 37 leading to the pumpmotor unit for the generator. As mentioned above, each of the pump-motor units includes an auxiliary pumping device for circulating the coolant solution in the casing in heat exchange relation with the motor armature and bearings. Coolant solution is returned through lines 41, .2,

and 43 to a return header 44 which delivers the solution to an inlet 45 in the upper portion of the heat exchanger A. A portion of the solution from return header flows upwardly through conduit 46 to an opening in the solution chamber B above the distributor plate 24'.

Heat exchanger A may take the form of a conventional tube and shell heat exchanger design comprising a generally cylindrical shell 5t? and a coiled tube 55 arranged therein. The conduit 27 which interconnects the shell side of heat exchanger A with solution chamber B opens into the shell at the upper portion thereof while conduit 3t which carries the cooled solution to the pump-motor units, is connected to the lower portion of said shell. The inlet line 45 which is employed to return solution to the heat exchanger after passing through the pump-motor units is connected at the opposite end of the heat exchanger shell near the upper portion thereof, said inlet line as, in a preferred embodiment, being provided with an orifice 49 to insure that a portion of the returning fluid is directed upwardly to the solution chamber B through conduit 46.

Operation From the individual pump-motor units, the coolant solution flows through

lines

41, 42, and 43 into the header as. The flow of returning coolant is split into two streams, one of which flows through inlet line 45 to the heat exchanger A and the other flowing through line 46 to the solution chamber B where it is discharged downwardly against the perforated. distributor plate 24. The solution impinges against the distributor plate where it is broken into small droplets which fall in rain-like fashion on the surface of the solution. The solution then flows by gravity through line 27 into the heat exchanger where it combines with the solution being returned from the pumpmotor units through line 45. The latter flows from right to left (as shown in FIGURE 1) and is cooled by passing over tube 55 through which cold refrigerant (approximately 40 F.) circulates. The refrigerant, it will be noted, is tapped olf from line 56 by a line 57 connected to coiled tube 55 and is returned to the inlet side of refrigerant pump 40 via line 58. Solution in .heat exchanger A passes downwardly through conduit 30, filter 32, and supply header 34 to the individual branch supply lines lead-' ing to the pump-motor unit through

lines

35, 36, and 37.

Should leakage be encountered in the pump-motor shaft seal, thereby causing fluid in the pump section of one of the pump-motor units, either water or LiBr, to enter the motor coolant-lubricant circuit, the excess fluid will flow through the aperture 21 to the right-hand portion of the solution chamber. This solution will overflow weir 22 and be passed through the over-flow line 26 to the absorber. On the other hand, should the leakage be from the motor coolant-lubricant circuit into the solution/refrigerant circuit, additional make-up solution will be provided from the generator solution entering via conduit 12 chamber 16 through divider plate 20. Solution flow in this case would be from the right-hand half of the chamber through opening 21 to the left-hand half of the chamber.

The system further provides automatic control over the concentration of the motor coolant-lubricant solution. If the concentration of the solution begins to rise, its vapor pressure will be depressed, assuming that the temperature will remain relativelyconstant. This will cause water vapor from the absorber to pass through line 28 and be absorbed by solution in the zone in the upper portion of the solution chamber. This same mass transfer opera tion will work in reverse if the solution concentration drops. In this case, the vapor pressure of the solution will rise, causing water vapor to flow to the lower pressure area in the absorber through line 28. This will restore the chamber equilibrium and, thus, return the solution to its normal operating concentration range.

For example, in a LiBr system which is operating at a 40 refrigerant temperature in the evaporator, the vapor pressure in the absorber would be approximately 6 mm. Hg absolute. Recirculated solution entering the solution chamber B from line 46 is cooled to some temperature in the neighborhood of 75 F., and the equilibrium condition at 6 mm. pressure and 75 F. corresponds to a concentration of 50% LiBr solution by weight. Operating at this condition, the solution will come up to equilibrium at this 50% value. If, however, on start-up, the solution concentration tended to be somewhat greater than this, for example 55% by weight of LiBr, then the corresponding vapor pressure at 75 F. would be approximately 3.2 mm. Hg absolute. Consequently, the solution would tend to absorb water vapor from the absorber through line 29 until equilibrium is established. At 6 mm. of pressure and 75 F. as noted above, this would result in a final equilibrium of 50% solution. In order to insure that this equilibrium condition is established quickly, the perforated plate 24 is used to break up the solution into small droplets which fall through the vapor chamber and thus afford considerable absorber surface.

If solution enters chamber B through line 46 at a lower temperature, say 65 F., then solution would come to a new equilibrium point of approximately 45%. Similarly, if the solution temperature would be at 85 F., the equilibrium point would be approximately 53% LiBr. In any event, the resulting concentration of solution in the lubricant and coolant circuit is kept within a range of about 45 to 53%, appreciably lower than the main solution circuit concentration. Within this range, the solution is sufliciently high in concentration to provide the desirable lubrication surface and at the same time is safely below the concentration where crystallization might result.

While this invention has been described in connection with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of this invention is defined solely by the appended claims which should be construed as broadly as the prior art will permit.

What is claimed is:

1. In an absorption refrigeration system including a generator, a condenser, an evaporator, and an absorber connected in a closed refrigeration circuit, and a plurality of hermetically sealed pump-motor units for circulating solution and refrigerant through said system, a cooling and lubricating circuit comprising a heat exchanger; means for circulating a liquid coolant in a first path through said heat exchanger and said pump-motor units; a solution chamber connected to provide a second path for coolant in parallel with said heat exchanger; means for continuously supplying absorbent solution from said refrigeration circuit to said solution chamber; conduit means for interconnecting said absorber and said solution chamber to provide a passage for water vapor flow to and from said absorber in order to establish a concentration of said coolant solution somewhat below the normal concentration of solution flowing within the refrigeration circuit; and means for supplying a secondary coolant to said heat exchanger such that it passes in indirect heat exchange relation to the solution flowing therethrough.

2. In an absorption refrigeration system including a generator, a condenser, an evaporator, and an absorber connected in a closed refrigeration circuit, and a plurality of hermetically sealed pump-motor units for circulating solution and refrigerant through said system, a cooling and lubricating circuit comprising a heat exchanger; means for circulating a liquid coolant through a first path including said heat exchanger and said pump-motor units; a solution chamber connected in parallel with said heat exchanger; means for circulating liquid coolant in a second path including said heat exchanger and said solution chamber; means for continuously supplying absorbent solution from said refrigeration circuit to said solution chamber in such a manner that additional solution is added to the flow of coolant in said second path as required; means for interconnecting said absorber and said solution chamber to provide a passage for water vapor flow to and from said absorber in order to establish a concentration of said coolant solution somewhat below the normal concentration of solution flowing within the refrigeration circuit; and means for supplying a secondary coolant to said heat exchanger such that it passes in indirect heat exchange relation to the coolant flowing to said pump-motor units.

3. In an absorption refrigeration system including a generator, a condenser, an evaporator, and an absorber connected in a closed refrigeration circuit, and a plurality of hermetically sealed pump-motor units for circulating solution and refrigerant through said system, a cooling and lubricating circuit comprising a heat exchanger; means for circulating a liquid coolant, consisting essentially of an aqueous solution of LiBr having a concentration on the order of 50% by weight LiBr, from said heat exchanger to said pump-motor units and back; a solution chamber connected in parallel with and above said heat exchanger, means in said solution chamber for maintaining the solution therein at a fixed level, said means including an overflow line which permits excess solution to flow back to said absorber and means for continuously supplying absorbent solution from said refrigeration circuit to said solution chamber; means for interconnecting said absorber and said solution chamber to provide a passage for water vapor flow to and from said absorber in order to establish a concentration of said coolant solution somewhat below the normal concentration of solution flowing within the refrigeration circuit, and means for supplying a secondary coolant to said heat exchanger such that it passes in indirect heat exchange relation to the solution flowing therethrough.

4. In an absorption refrigeration system including a generator, a condenser, an evaporator, and an absorber connected in a closed refrigeration circuit, and a plurality of hermetically sealed pump-motor units for circulating solution and refrigerant through said system, a cooling and lubricating circuit comprising a shell and tube heat exchanger having a shell side and a tube side; a solution chamber located above said heat exchanger; means for continuously supplying solution from said refrigeration circuit to said solution chamber; first conduit means interconnecting said solution chamber with said heat exchanger such that solution flows by gravity from the solution chamber through the shell side of said heat exchanger; a weir in said solution chamber, said weir determining the level of liquid within said solution chamber; an overflow conduit for carrying solution overflowing said weir to said absorber; second conduit means for conducting coolant solution from the shell side of said heat exchanger through said pump-motor units in heat exchange relationship therewith, third conduit means for circulating a portion of the coolant being returned to said heat exchanger back to said solution chamber, said solution being introduced in such a manner that said solution is broken up into small droplets to provide a relatively large absorber surface area; fourth conduit means interconnecting said absorber and said solution chamber to provide a passage for water vapor flow to and from said absorber whereby the equilibrium concentration of the coolant solution introduced into the chamber by said third conduit means is quickly established; and means for supplying a secondary coolant through the tube side of said heat exchanger.

5. Apparatus as defined in claim 1 wherein said solution chamber comprises an elongated cylindrical shell; partition means dividing said shell into a first zone and a second zone; aperture means through said partition means to provide fluid communication between said zones; a weir disposed within said first zone, the upper edge of said weir being located above said aperture means; first conduit means interconnecting the lower part of said second zone to said heat exchanger.

References Cited by the Examiner UNITED STATES PATENTS Leonard 62494 Edberg et a1 62-505 X Rayner 62-505 Enibury et a1. 62505 X LLOYD L. KING, Primary Examiner.

Claims

1. IN AN ABSORPTION REFRIGERATION SYSTEM INCLUDING A GENERATOR, A CONDENSER, AN EVAPORATOR, AND AN ABSORBER CONNECTED IN A CLOSED REFRIGERATION CIRCUIT, AND A PLURALITY OF HERMETICALLY SEALED PUMP-MOTOR UNITS FOR CIRCULATING SOLUTION AND REFRIGERANT THROUGH SAID SYSTEM, A COOLING AND LUBRICATING CIRCUIT COMPRISING A HEAT EXCHANGER; MEANS FOR CIRCULATING A LIQUID COOLANT IN A FIRST PATH THROUGH SAID HEAT EXCHANGER AND SAID PUMP-MOTOR UNITS; A SOLUTION CHAMBER CONNECTED TO PROVIDE A SECOND PATH FOR COOLANT IN PARALLEL WITH SAID HEAT EXCHANGER; MEANS FOR CONTINUOUSLY SUPPLYING ABSORBENT SOLUTION FROM SAID REFRIGERATION CIRCUIT TO SAID SOLUTION CHAMBER; CONDUIT MEANS FOR INTERCONNECTING SAID ABSORBER AND SAID SOLUTION CHAMBER TO PROVIDE A PASSAGE FOR WATER VAPOR FLOW TO AND FROM SAID ABSORBER IN ORDER TO ESTABLISH A CONCENTRATION OF SAID COOLANT SOLUTION SOMEWHAT BELOW THE NORMAL CONCENTRATION OF SOLUTION FLOWING WITHIN THE REFRIGERATION CIRCUIT; AND MEANS FOR SUPPLING A SECONDARY COOLANT TO SAID HEAT EXCHANGER SUCH THAT IS PASSES IN INDIRECT HEAT EXCHANGE RELATION TO THE SOLUTION FLOWING THERETHROUGH.