US2454344A - Absorption refrigeration system - Google Patents

Description

Nov. 23, 1948. E J. N. ROTH 2,454,344

ABSORPTION REFRIGERATION SYSTEM Filed Aug. 21, 1944 4 Sheets-Sheet 1 Nov. 23, 1948. ROTH 2,454,344

ABSORPTION REFRIGERATION SYSTEM Filed Aug. 21, 1944 4 Sheets-Sheet 2 Nov. 23, 1948. J. N. ROTH 2,454,344

ABSORPTION REFRIGERATION SYSTEM Filed Aug. 21, 1944 v 4 She ets-Sheet 3 Nov. 23, 1948. N; ROTH 2,454,344

ABSORPTION REFRIGERATION SYSTEM Patented Nov. 23, 1948 ansoamou REFRIGERATION SYSTEM Joseph N. Roth, Beldlng, Mich, assignor, by memo assignments, to Montcalm, Incorporated, Greensvillc, Mich, a corporation of Michigan Application August 21, 1944, Serial 'No. 550,402

8 Claims.

This invention relates to an absorption refrigerationsystem, and more particularly to an improved control arrangement for a continuous absorption refrigeration system of the transfer chamber type.

One feature of this invention is that it provides improved operation of the absorption system and eliminates shut-down failures wherein abnormal conditions prevent completion of the transfer operation returning liquid from the absorber to the still, and thus cause cessation of proper refrigeration; another feature of this invention is that better control of the length of the transfer period is achieved; yet another feature of this invention is the provision of an improved heat transfer relationship between the temperature responsive portion of the control arrangement and liquid returningfrom the absorber to the still; still another feature of the invention is the provision of means for varying the heat exchange relationship between the temperature responsive portion and the still, and more specifically for normally providing good heat exchange relationship between the temperature responsive portion and the still but for interrupting such relationship during transfer operations; a further feature of this invention is the provision of two alternative fiow paths for refrigerant vapor boiled out of liquid in the still, one of these paths coinciding in part with the flow path for returning liquid from the absorber to the still; and yet a further feature of this invention is the provision of resistance means, in the form of a liquid trap, in the other flow path to cause vapor to flow normally through thefi rst-mentioned flow path, this latter flow path being in heat exchange relation to the temperature responsive portion of the control arrangement. Other features and advantages of this invention will be apparent from the following specification and the drawings, in which:

Figure 1 is a schematic diagram of a continuous absorption refrigerating system embodying my improved control arrangement; Figure .2 is a fragmentary view, principally in vertical section, of the still and certain associated. parts; Figure 3 is a fragmentary transverse sectional view along the line 3-3 of Fig. 2; Figure 4 is a fragmentary view, principally in vertical section, of the still and associated parts embodying a modified form of my invention; Figure 5 is a fragmentary vertical sectional view of still another modification of my invention; and Figure 6 is a chart .showing certain pressure relatil 2 tionships in the operation of a system of the character shown in Figure 1.

In the particular embodiment of the invention disclosed herewith, the system in general comprises a still adapted to have a mixture of a refrigerant and an absorber, as ,ammonia and water, boiled by the application of heat to boil of! refrigerant vapor; a condenser connected by a vapor conduit to the still to liquefy the refrigerant vapor; an evaporator or cooling unit in which the liquefied refrigerant is permitted to vaporize, the evaporator having restricted connection with the condenser; an absorber in which the gas (the low pressure vapor) from the evaporator is reabsorbed in liquid; and means for effecting fiow of weak liquor from the bottom of the still to the absorber and flow of rich liquor from the bottom of the absorber to the still. This latter means includes a transfer chamber intermediate the absorber and the still and a valve arrangement so constructed that the chamber first receives liquid from the absorber and then is connected to the still to deliver the liquid thereto.

Referring now more particularly to the specific system diagrammatically illustrated in Figure 1, the still I0 is adapted to contain a mixture of water and ammonia. A flue H is provided within the still and heat is delivered thereto by the combustion of gas or some other fuel delivered by the burner l2. An analyzer tower l3, in the form of a long cylindrical tubing enclosing the flue I I, is located immediately above the still and rises vertically for a substantial distance. The analyzer tower is provided with bailie plates, here identified as l4, these plates serving to improve the efllciency of the apparatus; and, although they are not shown here, the vertical cylindrical vessel comprising the'still l0 would in practice also have baflle plates therein. As will be noted from the drawings, the lower end of the analyzer tower I3 is closed and does not make open communication with the still. Instead, refrigerant vapor boiled out of the liquid in the still is delivered to the lower end of the analyzer tower through either of two alternative flow paths, as will later be described in more detail.

Rich ammonia vapors boiled off the liquor in the still pass upwardly through the analyzer tower l3 and then through the pipe connection It to the rectifier ll, a finned inclined tube at the top of the system. From there the ammonia vapors, any entrained water vapor having been removed by the rectifier, pass down through the connection l8 to a condenser is at the lower end of the apparatus. This condenser comprises one or ore loops of piping, finned to increase the heat radiation. The ammonia vapor is here condensed into liquid ammonia, and then elevated by the vapor pressure behind it through the connection 20 to the receiver 2|. '1

The amount of ammonia boiled off and liquefied is a function of'the concentrationof the liquor in the still and of the amount of heat supplied to it, so that if the concentration of liquor is kept relatively constant the rate of delivery of liquid ammonia to the receiver 21 will be practically a direct-function of the amount of heat supplied to the still. The amount of fuel delivered to the burner l2, and thus the amount of heatsupplied and the rate of delivery of liquid ammonia to the receiver, can be regulated in any desired manner, as by a valve (not here shown) actuated in conventional manner by athermostat in the' cooling chamber of the refrigerator.

Liquid ammonia passes from the receiver 2| to the dry evaporator 22, preferably comprising several coils of piping, through the restriction interposed by a' valve 23 controlled by the float 24. The float and valve are so arranged that, as more liquid ammonia is delivered to the receiver, the valve opens further to permit increased flow to the evaporator to maintain the level of liquid in the receiver substantially constant.

Absorbing apparatus is provided in the form of an upper chamber or vessel 25 having extending downwardly therefrom a cooling and absorption loop. This loop is formed by a pipe 26 extending down from the bottom of the absorber vessel; the absorber cooling coil 21, finned for better heat radiation; and the upwardly extending pipe or leg 28, terminating in the vessel 25 slightly above the --level of absorption liquid therein.

Expanded ammonia vapor from the evaporator 22 first passes through a small loop or coil 29, to cool liquid in a chamber surrounding it, then through the pipe 30 into the rising leg 28 of the absorber loop, near the lower part thereof. The incoming vapor creates bubbles in the leg 28 of the absorber loop which provide a liquid lift or pump ensuring circulation of absorption liquid through the loop. Inasmuch as the liquid in this rising leg is at all times the weakest liquor in the absorber, and cool as a result of passing through the coil 21, all absorption takes place in the pipe 28 under normal conditions, the liquid flowing out of the top of this pipe being quite rich.

The level of liquid in the absorber vessel 25 is maintained by a. float 3| and valve 32 controlling delivery of weak liquor from the still. The pipe 33 leads from the lower end of the still (where the liquor is weakest) through a heat exchanger 34 and then on up to open into the absorber, the flow into the absorber being controlled by the valve 32, which opens whenever the level of liquid in the vessel 25 drops below a desired point.

The means for returning rich liquor from the absorber to the still comprises as its principal parts a transfer chamber 35, a valve assembly 36, a pressure chamber 31, and associated operative interconnections. A flow connection is provided from the leg 28 of the absorber loop, out of the open-ended short cross tube 28a, through the jacket 38, pipe 39, and check valve 40, into the pressure chamber 31. When the valves are set in a certain position a flow path is provided from the pressure chamber, and thus from the absorber, through the pipe 4|, the valve mech- -transfer chamber 35, any vapor therein being vented through the pipe 43 and the pipe 44 (interconnected by the valve assembly) into the pressure chamber.

When the valve device is actuated, in accordance with a condition of the system, to move the valves to another position, the pipe 43 is connected to the pipe 45 which is open to high pressure vapor in the pipe l8; and the pipe 42 is connected to the pipe 46, connected through the outer of the concentric paths of the heat exchanger 34 to a Jacket 41 around a thermostat bulb 48 and through a pipe.49 into the still. The transfer chamber and connecting pipes now being at high pressure, the rich liquor therein flows from the transfer chamber to the still until the valves are again moved to the position first described above.

When the interconnection between the pressure chamber and the transfer chamber is again completed, there is, of course, a rush of high pressure vapor through the pipes 43 and 44 to the chamber 31. The check valve 40, however, prevents these vapors from getting back into the low pressure side of the system; and the solid body of liquid maintained in the chamber 31, cooled by the coil 29, rapidly absorbs this high pressure vapor, assisted in this respect by a fine stream of weak liquor bled into the chamber 31 through the conduit 58 branching from the weak liquor pipe 33, the portion of this conduit making connection with the pressure chamber having an internal diameter approaching that of a. capillary tube. The rapid absorption of ammonia vapor in the pressure chamber causes the pressure in the chambers 35 and 31 to drop below the pressure of the absorber 25 for a brief time so that there is a positive flow of rich liquor from the absorber to the transfer means completely refilling the chambers 35 and 31. When these are completely filled with liquid, the weak liquor entering through the bleeder connection 50 immediately starts to raise the pressure therein, the check valve closing; and, in a very short period the chambers 35 and 31 are at full still pressure.

There is thus only a brief interval during which the valves in the assembly 36 must withstand the full difference of pressure between the high and low sides of the system.

No further description of the general construction and operation of a continuous absorption system of this type will be given, as reference may be had to a. number of issued patents to supplement the present disclosure. The basic ele ments of a continuous absorption refrigeration system of the transfer chamber type are the subject matter of a number of patents which issued someyears ago, of Ralph E. Schurtz, namely: 1,414,527; 1,627,808; 1,796,410; 1,891,028; 1,890,- 531; and 1,905,308. In addition, the particular system illustrated diagrammatically in Figure 1 hereof is the subject matter of a number of more recent patents of the said Schurtz and of myself, namely: 2,334,219; 2,305,640; 2,337,067; 2,339,811; 2,339,812; 2,339,813; 2,339,814; 2,339,- 815; 2,339,816 and 2,339,817. The present application is particularly concerned with improvements in the control arrangement for effecting movement of the valves in accordance with a desired predetermined condition of the system, in this case the concentration of liquor in the still, the present application being directed particularly to improvements in a control arrangement of the same general type as that to'which my Patent 2,339,811 is directed, reference being made particularly, to this patent. Other improvements on the general system are more specifically described and claimed not only in the abovementioned recent patents, but also in other co-pending applications by myself and the sa d Schurtz, namely: Serial Nos: 409,576; 400,089; 382,420; and 389,248, which have respectively matured into: Patent No. 2,372,684, granted April 3, 1945; Patent No. 2,354,705; granted August 1, 1944; Patent No. 2,386,817, granted October 16, 1945; and Patent No. 2,346,875, granted April 18, 1944.

The optimum in the way of smoothness of operaton, response to variation in load, efficiency of the system, and the like can be achieved if predetermined quantities and concentrations of liquid are maintained in the various parts of the system, as the still, the receiver and the absorber. In order to maintain the quantity and concentration of liquor in the still relatively constant, it is best, as is more fully described in my said Patent 2,339,811, to deliver relatively small quantities of rich liquor to the still periodically, and to determine the time of initiation of-each delivery by an arrangement such that transfer operation is effected when the liquor in the still has boiled down to a predetermined minimum preferred concentration. In order to accomplish this, the movable valve member in the valve assembly36 is actuated by an arrangement wherein still pressure is balanced against pressure derived from the thermostat bulb48. This is accomplished by using a bellows 5| as the actuating means for the valve, the interior of this bellows being open at all times to the pipe 46, this pipe in turn always being open to the still and containing fluid at still pressure, and the exterior of this bellows being open to pressure generated in the bulb 48 and delivered through the pipe connection 52 to a chamber surrounding the bellows. The bulb is preferably filled with a refrigerant-absorbent mixture of the desired minimum refrigerant concentration or just slightly thereabove. Under these conditions, the pressure developed in the still is higher than that developed in the bulb so long as the concentration of the liquid in the still is above the desired minimum concentration; but the pressure in the bulb exceeds that in the still when the still concentration falls below that of the mixture in the bulb,.and the excess of pressure on the exterior of the bellows 5| causes movement of the valve member in the valve assembly 36 to connect the transfer chamber 35 to the still and effect delivery of rich liquid to the still.

In order that the valve member may be moved back to its original position to terminate the transfer action, it is necessary that the pressure in the bulb 48 be reduced below that in the still shortly after transfer has been initiated and before the chamber 35 has emptied. In order to do this, it is desirable rapidly to cool the bulb 48, and, as was also the case in the arrangement shown in my Patent No. 2,339,811, this is here shown as accomplished by passing the rich liquor flowing back from the transfer chamber to the still in heat exchange relation with the bulb after it has gone through the heat exchanger 34 and before it passes into the still.

Under normal conditions of refrigerator operation, the cooling action of the returning rich liquor, in the arrangement shown in my Patent No. 2,339,811, is fully effective to reduce the pressure in the bulb sufficiently below that in the still to cause termination of the transfer operation; a. definite predetermined pressure differential being required because of the inclusion of snap acting mechanism in the valve arrangement. In the arrangement shown in this earlier patent, however, the cooling effect on the bulb of the returning rich liquor is minimized by continuing heat input from the hot liquid in the still,

and under certain very abnormal conditions the pressure in the still would drop faster than that in the thermostat bulb. For example, if the burner should have been shut down to pilot conditions just before a transfer operation was initiated, and then the condenser should be very rapidly and unusually cooled (as, for example, by spilling a pan full of cold water on it), conditions might arise which would prevent termination of the transfer operation before the chamber was empty, and the system would be thrown outof balance and fail to continue proper operation. I have obviated any chance of dimculty in this regard in the arrangements illustrated herewith in Figures 1-4 by taking the bulb or temperature responsive portion of the valve actuating means out of the still and by providing two alternative flow paths for refrigerant vapor leaving the still, one of these paths being in heat transfer relationship with the bulb and the other path having no such relationship; and by so constructing and arranging these paths that refrigerant vapor normally traverses the path in heat exchange relationship with the bulb, but, upon initiation of a transfer operation, traverses the other path until such transfer is completed, this completely removing any possibility of heat input tothe bulb and therefore ensuring an exceedingly rapid reduction in pressure in the bulb and consequently operation of the valves despite abnormal conditions resulting in rapid decrease in pressure in the still at the same time.

Referring now more particularly to Figures 2 and 3, the still I!) is shown as a vertical cylindrical vessel with the analyzer tower l3 extending vertically thereabove, and with the temperature responsive bulb and its jacket to one side, here being shown as immediately over the heat exchanger 34. It will be noted that while the flue H rises through the top of the still and enters the bottom of the vertical analyzer tower l3, there is no direct connection, in this form of my invention, between the analyzer tower and the still.

The level of the liquid in the still, under normal conditions, is as indicated by the uppermost dashed line in Figure 2. With liquid at this level, one normally unobstructed vapor path between the still and analyzer tower is provided through the following path: the pipe 49; the flow passages provided by the space between the bulb 48 and the jacket 41, and by the heat transfer tubes 48a-c; and the pipe rising from the end of the jacket 41 farthest removed the absorber .to the still, as described earlier. Accordingly, when the concentration ofliquid in the still has boiled down to the point where the control-apparatus causes movement of the valves to initiate a transfer operation, returning liquid fills this path and prevents vapor from taking this path to the analyzer tower, particularly since the level of liquid in the still immediately rises above the lower end of tube 49.

As soon as vapor is prevented from passing through this first vapor path it travels a second 4 vapor path provided as an alternative. This sec. ond vapor path comprises the upwardly extending pipe 56 and the smaller downwardly extend-- ing pipe 51 making connection to the bottom of the analyzer tower at the point 51a. The bottom of the analyzer tower l3 always contains a certain amount of liquid condensed by the analyzinto the still to a point well below the lowest' level ever taken by the liquid therein, operates to prevent an undue depth of liquid in this trap, and to maintain the trap depth constant. Making pipe 56 of much larger diameter than pipe 51 to which it is connected prevents any possibility of a siphoning back of liquid, and accordingly, the liquid trap in the bottom of the analyzer tower would in practice always have a depth of four or five inches. As soon as transfer action starts and returning liquid begins to flow into the still through the pipe 49, any attempt of refrigerant vapor to travel the first flow path backs liquid up the pipe 55; and the liquid trap opposing movement of the vapor is capable of achieving a much greater height and a much one end to the other. It will be understood that these tubes communicate with the space to the exterior of the bulb, being-welded or otherwise permanently fastened into the end plates of the bulb cylinder, and that the bulb is still completely closed and any pressure developed therein is effective only through the pipe 52. However, these longitudinally extending heat transfer tubes 48H greatly improve the transfer of heat to fluid near the center of the bulb, removed from the cylindrical wall.

Referring now more particularly to Figure 4,

a somewhat modified form of my invention will be described, the reference numerals used being analogous to those used in the description of Figures 1-3. In this form of my invention the greater liquid head than that of the liquid trap in the bottom of the analyzer tower. Accordingly,

path for liquid returning from the absorber through the transfer chamber includes the heat exchanger I34, the pipe 148a, the flow passage comprising the space between the bulb I48 and the shell I41 and the interior of the heat transfer tubes Milo-c, and the outlet pipe I49. The first or normal vapor flow path is through the pipe I49 (normally slightly above the level of liquid in the still), this same space around the bulb and within its heat transfer tubes, and through the pipe 155 to the analyzer tower H3. The second fiow path for refrigerant vapor is through the pipes I58 and IE1 to the lower end of the analyzer tower, a liquid trap in the bottom of the tower (with a level determined by the overflow tube I59) again providing sufficient hindrance to vapor flow normally to prevent passage of vapor through this latter path. This arrangement primarily differs from that shown in Figuers 1-3, in that the temperature responsive bulb and its jacket are arranged vertically above the still, rather than to one side thereof.

Referring now more particularly to Figure 5, andusing reference numerals analogous, in so far as possible, to those previously used, it will be seen that the temperature responsive bulb 248 is as soon as transfer action is initiated, refrigerant vapor leaving the still travels the second path (comprising the pipes 56 and 51) rather than the first path.

This provides a very considerable difference in heating effect upon the bulb 48. Dining normal operation of the system, betweentransfer actions, the bulb is in good heat transfer relation with outgoing refrigerant vapor; and this vapor is at the temperature of the liquid in the still. During this phase of the operation, therefore, the bulb and its contents will at all times be kept at or very near still temperature. On the other hand, as soon as transfer action starts, the refrigerant vapor travels the second or altemative path, and the fluid in heat transfer relation with the temperature responsive bulb 48 is the rich liquor returning from the transfer chamber 35 to the still. This liquid is relatively cool, normally being within 10 or 20 of room temperature; and the result is a very rapid and very effective cooling of the bulb 48 and reduction of the pressure in the bulb and the pipe 52 leading to the exterior of the bellows 5|. 'Moreover, the cooling effect of the returning liquid is not minimized or reduced by continuing heat transfer from the still, heat transfer being interrupted during this portion of the refrigeration cycle.

I have also found that, as may be best seen in Figure 3, the desired heat transfer relationships with the bulb are greatly improved by the use of a plurality of heat transfer tubes, as the tubes 48a-c, extending through the bulb from arranged with the improved heat exchange or heat transfer tubes 24811-0 which were previously described. In this modification of my invention, the analyzer tower 2i; is mounted directly on and opens directly into the top of the still 2, there being only one outgoing path for refrigerant vapor. In this respect, the arrangement shown in Figure 5 is similar to that shown in my Patent No. 2,339,811. It provides an improved, more rapid and more positive transfer action, however, by the provision of the heat transfer tubes 2480-0 through the bulb 248; and by having the incoming rich liquor delivered directly into the still from the short outflow pipe 249, rather than by having this liquid delivered up into the analyzer tower. The lower delivery point of the rich liquor increases the head between the transfer chamber and the point of delivery, and thus increases the rate of flow of liquid; and this increased rate of flow, together with the improved heat exchange relation, provides a quicker and more positive termination of transfer action.

Referring now more particularly to Figure 6, the advantages of having an exceedingly rapid drop of pressure in the temperature responsive bulb will be more fully explained. The upper solid line,.here identified as 65, is indicative of a normal generator pressure curve under normal home conditions, with the flame shutting down to pilot and then rising again as the refrigeration load demands it. With a generator pressure curve of this type proper termination of transfer operations presents no particular problem.

I tions would normally take place to replenish the liquid in the still; and to terminate these transfer operations before emptying of the transfer chamber, the transfer bulb pressure would have to drop sufficiently below the generator pressure to overcome the resistance of the snap action mechanism and draw the valves back to a position closing the transfer chamber off from the still. With the arrangement here illustrated and described, wherein heat transfer from the still to the bulb is interrupted and very good heat exchange relationship exists between the bulb contents and the returning cool liquid, this desired action is achieved with considerable margin of safety, as may be seen from an examination of the curve identified as 61, representing pressures in the transfer bulb. At the point marked transfer on this curve 61, at about six minutes, transfer action was initiated; and it will be seen that the transfer bulb pressure dropped with exceeding rapidity from about 190 pounds to well below 140 pounds within about three minutes. Despite the fact that the curve of generator pressure, as illustrated by the line 66, was dropping with considerable rapidity, it will be seen that the transfer bulb pressure dropped much faster, and that the transfer operation terminated and flow of vapor from the still re-established through the first path, in heat exchange relationship with the bulb, so that the transfer bulb temperature began to rise. By the time about 17 minutes had been reached, the transfer bulb pressure was sufficiently above generator pressure to cause a transfer action to be initiated; and this time, within about a minute,

transfer bulb pressure dropped sufliciently below generator pressure to terminate transfer operation. At about 24 minutes flame was again turned on under the still and generator pressure began to-climb so that it was not until about 36 minutes that another transfer operation took place, as may be seen from the curves. The present invention, and more particularly the forms thereof shown in Figures 1-4, provides means ensuring against the generator pressure overrunning or out-dropping bulb pressure under abnormal conditions and causing the machine to shut down.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim: V

1. In an absorption refrigerationsystem having a still adapted to have refrigerant vapor boiled out of liquid therein, a condenser, an evaporator, an absorber, and operative connections therebetween, these connections including liquid flow circuit connections between the still and the absorber, one of these latter circuit connections flow of fluid therethrough, control apparatus ineluding; actuating means 'for moving said movable element, this means having a temperature responsive portion; means providing a first flow path for refrigerant vapor leaving the still this path being in heat exchange relation with said temperature responsive portion and coinciding in part with the path of flow of liquid returning from the absorber to the still; and means providing a second flow path for refrigerant vapor leaving the still, the construction and arrangement being such that vapor flows through said second path only when vapor flow through said first path is blocked by liquil returning to the still.

2. In an absorption refrigeration system having I a still adapted to have refrigerant vapor boiled out of liquid therein, a condenser, an evaporator, an absorber, and operative connections therebetween, these connections including liquid flow circuit connections between the still and the absorber, one of these latter circuit connections including a movable element for controlling the flow of fluid therethrough, control apparatus-including: actuating means for moving said movable element, this means having a temperature responsive portion; means providing a first flow path for refrigerant vapor leaving the still, this path being in heat exchange relation with said temperature responsive portion and coinciding in part with the path of flow of liquid returning from the absorber to the still; and means providing a second flow path for refrigerant vapor leaving the still, this path including resisting means having its resistance so proportioned that vapor normally flows through said first path but flows through said second path when liquid is returning from the absorber to the still.

3. Apparatus of the character claimed in claim 2, wherein the temperature responsive portion comprises a bulb having heat exchange tubes therethrough and a spaced shell therearound, these tubes and the space between the bulb and shell being adapted to form part of the circuit connection for flow of liquid from the absorber to the still and of the first flow path for refrigerant vapor.

4. In an absorption refrigeration system having a still adapted to have refrigerant vapor boiled out of liquid therein and delivered through a vertical analyzer tower above the still, control apparatus including: a temperature responsive portion; means providing a first flow path for refrigerant vapor leaving the still, this path being in heat exchange relation with said temperature responsive portion, coinciding in part with the path of flow of liquid returning from the absorber to the still, and making connection with said tower; and means providing a second flow path for refrigerant vapor leaving the still, this path also making connection with said tower and including a liquid trap having its resistance so proportioned that vapor normally flows through said first path but flows through said second path when liquid is returning from the absorber to the still.

5. In an absorption refrigeration system having a still adapted to have refrigerant vapor boiled out of liquid therein and delivered through a vertical analyzer tower above the still, control apparatus including: a temperature responsive portion; means providing a first flow path for refrigerant vapor leaving the still, this path being in heat exchange relation with said temperature responsive portion and making connection with said tower, this path coinciding in part with also making connection with'said tower and in- .cluding a liquid trap comprising liquid in the bottom'oi the tower, whereby condensation in the tower maintains the desired amount of liquid in the trap, the resistance of the trap being so proportioned that vapor normally flows through said first path but flows through said second path when liquid is returning from the absorber to the still.

6. Apparatus of the character claimed in claim 5, including a liquid overflow pipe having one end connected to the'tower at the desired level of liquid therein and the other end opening into the still below the level of liquid therein;

7. In an absorption refrigeration system having a still adapted to ha ve ref,r ig,erant vapor.

boiled out of liquid therein, a condenser, an evaporator, an absorber, and operative connections therebetween, these connections in-- cludingliquid flow circuit connections between 4 the still and the absorber, one of these latter circuit connections including a movable element for controlling the flow of fluid therethrough, control apparatus including: actuating means for moving said movable element, this means having a temperature responsive portion; means providing a first flow path for refrigerant vapor leaving the still, this path being in heat exchange relation withsaid temperature responsive portion; 1 and means providing a second alternative flow path for refrigerant vapor leaving the still, this path flow is normally through said first path and is only periodically and temporarily through .said second path.

' 8. In an absorption refrigeration system having 'a still adapted to have, refrigerant vapor boiled out of liquid therein, acondenser, an evaporator, an absorber, and operative connections therebetween, these connections including liquid -fiowcircuit connections between the still and the absorber, one of these latter circuit connections including a movable element for controlling the flow of fluid therethrough, control apparatus including: actuating means for moving said movable element, this means having a temperature responsive portion; means providing a first flow path for refrigerant vapor leaving the still, this path being in heat exchange relation with said temperature responsive portion; and means providing a second alternative flow path for refrigerant vapor leaving the still, this path coinciding in part with said first path and including a trap preventing flow of vapor therethrough, the construction and arrangement being such that vapor flow is periodically and temporarily blocked through said first path and permitted through said second path.- JOSEPH N. ROTH.

,REFERENCES CITED The following references are of record ,in the file of this patent:

UNITED STATES PATENTS Name Date Casterline Mar. 4, 1902 Milker May 31, 1927 Schurtz Apr. 25, 1933 Ryden May 21, 1935 Roth Dec. 22, 1942 Number

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