Abstract:
An absorption provided with a refrigerant management method and apparatus for temporarily storing liquid refrigerant during cooling mode operation and releasing refrigerant to the evaporator sump as needed to prevent refrigerant pump cavitation during periods of part load operation and causing dilution of solution in the absorber when the system is shut down. The refrigerant is stored in a tank located in the evaporator, with the tank fluidly communicating with the evaporator sump both by way of a side opening in the tank and by way of overflowing the tank. Refrigerant replenishment to the tank occurs during normal operation either by refrigerant flow from the condenser or by way of a bleed line from the refrigerant pump.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to absorption cooling systems and to absorption heating and cooling systems and, in particular, to the management of refrigerant for release into the system during part load and shut down conditions. 
     In an absorption type cooling system, an absorbent is dissolved in a liquid refrigerant to produce a refrigerant-absorbent solution that is suitable for use in the process. When such a system operates under cooling loads that vary, the amount of refrigerant necessary to keep the system running efficiently will also vary. As a result, it is a common practice to equip such a cooling system with a refrigerant adjusting system which includes a refrigerant storage reservoir, and to store refrigerant in or release refrigerant from this reservoir as necessary to keep the concentration of the solution within an acceptable range of concentrations as the cooling load fluctuates. This storage reservoir often takes the form of a sump that is located in or in close association with the system condenser. 
     One example of a cooling mode refrigerant adjusting system of the above-described type is described in unexamined Japanese application 62-178858, which is assigned to Ebara Ltd. of Tokyo, Japan. In the latter application, there is disclosed an absorption machine in which the gravity flow of liquid refrigerant between the system condenser and the system evaporator is controlled in response to a sensed condition of the system, such as the solution temperature as it is leaving the absorber. A reservoir for liquid refrigerant is provided inside the condenser and the refrigerant is supplied to the evaporator through a first flow path under normal operating conditions. Upon the sensing of a condition that calls for an increase in the quantity of refrigerant, a second flow path is opened which supplies additional refrigerant from the condenser to the evaporator. Another example of a refrigerant adjusting system is described in copending U.S. patent application Ser. No. 09/244,910, filed Feb. 4, 1999, which is commonly assigned herewith, and which is hereby expressly incorporated by reference herein. In this application, there is disclosed an absorption type machine in which refrigerant is stored in a holding tank that is separate from the condenser sump and that is filled via a refrigerant bleed line. The desired refrigerant concentration is then maintained by releasing refrigerant from the holding tank under the control of a microprocessor in response to the sensing of a need for additional refrigerant. 
     An example of a refrigerant adjusting system that is specially adapted for use in an absorption type refrigerator is described in U.S. Pat. No. 5,806,325 (Furukawa et al). In that patent there is described an absorption type refrigerator in which a storage reservoir is formed in the condenser by a dam with an array of holes that allows the rate at which refrigerant is released to vary as a function of the rate at which refrigerant condenses and, consequently, as a function of the cooling load that the refrigerator must support. 
     When an absorption type cooling system is shut down, it is necessary to release into the system, within a time known as the dilution time, a quantity of refrigerant which is sufficient to dilute or reduce the concentration of the absorbent-refrigerant solution within the absorber to a value low enough to prevent crystals of the absorbent from forming therein. The diluting of this solution during the shut down process is known as the dilution cycle of the system. Historically, the additional refrigerant necessary to enable the system to complete its dilution cycle has been provided in various ways. One approach was to pump the additional refrigerant from a specially provided storage tank. This approach is not cost effective, however, not only because of the cost of providing such a storage tank, but also because of the cost of providing the associated pump and pump control circuitry. 
     Another way of providing the additional refrigerant necessary to complete the dilution process has been to release into the system the contents of the refrigerant storage reservoir or tank that is used as a part of its cooling mode refrigerant adjusting system. 
     This way of diluting the solution, however, has a deficiency that limits its usefulness. This is that the reservoir outlets and piping through which refrigerant is released during the cooling mode refrigerant adjusting process are too small to allow the refrigerant necessary to complete the dilution process to be released within the available dilution time. As a result, the released refrigerant may not be able to mix with the absorbent-refrigerant solution rapidly enough to prevent crystals from forming in the absorber. 
     While the above-mentioned deficiency may be overcome by providing circuitry which senses the occurrence of a shut down condition, and which opens valves that controllably increase the rate at which refrigerant is released into the evaporator, the provision of such circuitry and valves substantially increases the cost of the shut down portion of the cooling system. The provision of such control circuitry and valves also increases the complexity of the system and thereby introduces failure modes that decrease the overall reliability thereof. 
     Another approach for providing the refrigerant necessary for dilution has been that shown in U.S. patent application Ser. No. 09/580,182, filed May 26, 2000 which is commonly assigned herewith and which is expressly incorporated herein by reference. There, a refrigerant storage tank is provided in the condenser for storage during the cooling cycle for release along two flow paths during part load and shut down conditions, respectively. 
     Finally, there is another common approach wherein the refrigerant is stored in the evaporator sump and the level of the refrigerant is sensed so that when it reaches a certain predetermined level, a solenoid valve is opened and refrigerant is dumped to the solution pump either by gravity feed or by using a refrigerant pump. This approach, of course, requires a sensor, a solenoid valve and possibly an additional refrigerant pump. 
     It is therefore an object of the present invention to provide an improved refrigeration management apparatus for an absorption system. 
     Another object of the present invention is the provision in an absorption system for a refrigeration management apparatus which stores refrigerant during the cooling process and selectively releases refrigerant to accommodate part load and shutdown conditions. 
     Yet another object of the present invention is the provision in an absorption system for the storage of refrigerant in a location other than in the condenser. 
     These objects and other features and advantages become readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings. 
     SUMMARY OF THE INVENTION 
     Briefly, in accordance with one aspect of the invention, a refrigerant storage tank is placed in the evaporator of an absorption system, in fluid communication with both the condenser and an evaporator sump. During cooling mode operation, liquid refrigerant flows from the condenser to the storage tank by way of a conduit, and from the storage tank to the evaporator sump by way of an opening in the side of the storage tank and by way of overflowing the refrigerant tank during full load operating conditions. The size of the opening is such that, under part load conditions, there is sufficient flow of refrigerant to the sump to prevent cavitation of a refrigerant pump associated with the sump. At shutdown, the opening allows for drainage of the refrigerant storage tank into the sump and for the subsequent overflow of the sump into the absorber so as to sufficiently dilute the absorber solution to prevent the formation of crystals. 
     In accordance with another aspect of the invention, the condenser is fluidly connected to the refrigerant storage tank by way of a J-tube, which provides a liquid seal between the condenser and the evaporator. Also, a liquid/vapor separator may be provided downstream at J-tube such that any vapor that results from a flashing of the refrigerant can be passed to the absorber, with only liquid refrigerant remaining to be passed to the storage tank. 
     In accordance with another aspect of the invention, the opening in the side of the refrigerant storage tank is a slot which extends vertically to the bottom of the storage tank such that, upon shutdown, the storage tank drains completely to the evaporator sump. 
     In accordance with another aspect of the invention, the storage tank is replenished by way of a bleed line from the refrigerant pump rather than from the condenser. 
     In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified schematic diagram of a two-stage absorption machine of a type which is known in the art; 
     FIG. 2 is a simplified schematic diagram of a refrigerant management apparatus as contemplated by the present invention; 
     FIG. 3 is a simplified schematic illustration of an absorption machine with a refrigerant management system incorporated therein in accordance with the present invention 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is shown a simplified schematic diagram of an absorption cooling system  10  of one type that is know in the art, in this case a two-stage, series cycle cooling system. Other types of absorption systems may use more or fewer stages, may be able to operate in both a cooling mode and a heating mode, and may use a parallel rather than a series cycle. It will therefore be understood that the cooling system of FIG. 1 comprises only an exemplary one of the many types of absorption systems that might have been used as a descriptive background for the present invention. As will be explained more fully later, the refrigeration management apparatus of the present invention may be applied to the cooling portions any of these types of absorption systems. 
     Absorption system  10  of FIG. 1 comprises a closed fluidic system which contains a refrigerant that exists in both a vapor phase and a liquid phase, an absorbent, and a solution of the absorbent in the refrigerant. In the following description, it will be assumed that machine  10  employs water as a refrigerant and lithium bromide, which has a high affinity for water, as an absorbent. 
     Absorption system  10  of FIG. 1 includes an evaporator  20  and an absorber  30  mounted in a side-by-side relationship within a common shell  40 . System  10  also includes a high temperature generator  50  and a low temperature generator  60  for generating refrigerant vapor from the absorbent-refrigerant solution, and condenser  70  for receiving that refrigerant vapor and condensing it to produce liquid refrigerant. Condenser  70  is located immediately adjacent to and above evaporator  20 , and is disposed in side-by-side relationship with low temperature generator  60  within a common shell  80 . 
     When system  10  is operating in its cooling mode, liquid refrigerant from condenser  70  is supplied to evaporator  20 , where it is vaporized to absorb heat from a fluid, usually water, that is being chilled. The water being chilled is brought through the evaporator through a chilled water line  22  and a heat exchanger assembly, not shown. Vaporized refrigerant developed within evaporator  20  passes to absorber  30 , through a partition P 1 , where it is absorbed by a relatively strong solution to form a relatively weaker solution. Heat developed in the absorption process is taken out of the absorber by cooling water flowing through a cooling water line  32  and a heat exchanger assembly, not shown. 
     The solution in absorber  30  collects in an absorber sump  34  and is pumped therefrom by a suitable solution pump  36 . Part of this solution is recirculated through interior of the absorber through a spray head  39  to enhance the absorption process. The remainder of the solution passes through a first, low temperature solution heat exchanger  55  and a second, high temperature solution heat exchanger  57 , and is supplied to high temperature generator  50  via solution inlet line  52  thereof. As the solution within high temperature generator  50  is heated by a suitable heat source  53 , refrigerant vapor is driven off and supplied to low temperature generator  60  and condenser  70  through vapor lines  54  and  64 . The heated solution remaining within the high temperature generator then exits through a solution outlet line  56  and is supplied to absorber  30  through a solution inlet line  33 . On the way, this solution passes through heat exchanger  57 , valve orifice  59 , low temperature generator  60 , via inlet and outlet lines  62  and  64  thereof, and heat exchanger  55  to assure that much of the thermal energy stored therein is recovered, thereby reducing the amount of heat that must be supplied by heat source  53 . The machine shown in FIG. 1 may also be provided with an overflow path, which may take the form of a J-tube  67 , through which excess solution within low temperature generator  60  may be supplied to absorber  30  through a suitable inlet  37 . 
     Refrigerant vapor which is released into condenser  70  via vapor lines  54  and  64 , along with refrigerant vapor which is released into condenser  70  by low temperature generator  60 , via a partition P 2 , is cooled by cooling water flowing through cooling water line  32  and a heat exchanger, not shown. This vapor condenses to form liquid refrigerant which collects in a condenser sump  74 . From condenser sump  74 , the liquid refrigerant flows toward evaporator  20 , under the force of gravity, through a suitable J-tube  75  and refrigerant inlet line  23 , and collects within an evaporator sump  24 . 
     Liquid refrigerant is pumped out of evaporator sump by a suitable refrigerant pump  26  and supplied through a refrigerant discharge line  28  and an orifice plate  27  to a spray head  29 , which sprays the refrigerant into the interior of the evaporator chamber. There it evaporates as a result of the low pressure maintained therein by absorber  30 , through partition P 1 , to produce the already described cooling effect on fluid, usually water, flowing through chilled water line  22 . The refrigerant vapor then passes through partition P 1  into the interior of evaporator  30 , where it is absorbed by the solution that is pumped from absorber sump  34  by solution pump  36  and sprayed thereover through spray head  39 . The solution that collects within absorber sump  34  as this occurs is then either recirculated through spray head  39  or directed back to high temperature generator  50 , in the manner described earlier, to complete the cycle. 
     Because cooling systems of the-above-described type are well known to those skilled in the art, the operation of the system of FIG. 1 in its cooling mode will not be further described herein. Because the manner in which the system of FIG. 1 may be modified for operation in a heating mode is also well known to those skilled in the art, the operation of the system of FIG. 1 in a heating mode will also not be described herein. 
     When system  10  is operating in its cooling mode, it is desirable for the refrigerant-absorbent solution to have a concentration which is relatively high, i.e., to be relatively strong or refrigerant-poor, but which varies over a range of concentrations that fluctuates with the cooling load thereon. More particularly, it is desirable for the concentration of the solution to increase as the cooling load on the system increases. This increase in concentration is preferably accomplished by providing the cooling system with a cooling mode refrigerant adjusting system that causes liquid refrigerant to be withdrawn from the solution, (i.e., withdrawn from active circulation within the system) as the cooling load increases, and which releases liquid refrigerant into the system as the cooling load decreases. 
     In absorption cooling systems of the type described in unexamined Japanese application 62-178858, in U.S. Pat. No. 5,806,325 (Furukawa et al), and in pending application Ser. No. 09/580,182, the refrigerant adjusting system includes a refrigerant storage reservoir that forms a part of the condenser and may comprise the condenser sump. The present invention, on the other hand incorporates the refrigerant management system as a part of the evaporator as shown in FIGS. 2 and 3. Referring now to FIG. 2, there is shown an evaporator  20  with its associated sump  24 , along with a condenser  70  mounted thereabove in a conventional manner. However, unlike the conventional machine, there is positioned in the top portion of the evaporator  20 , a refrigerant storage tank  80 . The condenser  70  and the refrigerant storage tank  80  are interconnected by a J-tube  85  so as to provide for fluidic communication between the two, while maintaining a liquid seal therebetween. 
     Formed in the side of the refrigerant storage tank  80  is an opening,  86 , to provide for direct fluidic flow between the storage tank  80  and the evaporator sump  24  below. While the opening is shown as a vertical slot, it may take any of other appropriate forms such as a single round opening on a plurality of openings arranged in horizontal or vertical spacings. As will be seen, the opening  86  preferably extends downwardly to the bottom surface of the tank  80  so that, so long as there is liquid refrigerant in the storage tank  80 , there will be a flow out of a opening  86  and into the evaporator sump  24 . The storage tank  80  has an open top  87  so that, if refrigerant continues to flow into the tank  80  by way of the J-tube  85  after it is full, the tank will overflow, with the refrigerant flowing to the evaporator sump  24 . 
     In operation, as refrigerant forms in the condenser, it flows to the storage tank  80  by way of the J- tube  85 , but the refrigerant will immediately begin to flow from the slot  86  to the evaporator sump  24 . As the machine continues to operate, the volume of condensate coming from the condenser  70  will exceed that which is flowing from the slot  86 , so that the storage tank  80  will eventually fill up and overflow to the sump  24 . Under part load conditions, however, the supply of condensate from the condenser  70  will not keep up with the flow of refrigerant from the slot  86 , and the level of refrigerant in the tank  80  will drop, but the flow of refrigerant from the slot  86  will continue to flow to the sump  24  so as to provide sufficient refrigerant to prevent the cavitation of refrigerant pump  26 . At shutdown, all of the refrigerant will be drained from the storage tank  80  by way of the slot  86 , thereby filling up the sump  24  and causing it to overflow into the absorber so as to thereby dilute the solution and prevent crystallization from occurring. 
     As will be understood from the above description, the size of the slot  86 , as well as the volumes of the storage tank  80  and the sump  24  are critical to proper operation of the system. Generally, these are selected such that, at the anticipated the minimum load conditions, there is sufficient refrigerant in the sump  24  to prevent cavitation of the refrigerant pump  26 , at full load operating conditions the storage tank overflows to the sump  24  but the sump  24  does not overflow to the absorber  30 , and at shutdown there is sufficient refrigerant stored in the storage tank  80  that, when it is drained to the sump  24  and overflows to the absorber, there is sufficient refrigerant to lower the concentration of solution in the absorber to prevent crystallization thereof. Also, at  80  percent load, the flow from the slot  86  will be such that it will be exceeded by the flow of refrigerant from the condenser such that the storage tank  80  will overflow to the sump  24 . 
     Referring now to FIG. 3, the conventional system of FIG. 1 is now shown to include modifications to incorporate the above described refrigerant management apparatus into the system. As will be seen, rather than placing the refrigerant storage tank in the condenser, it is located in the evaporator. In doing so, with the condensed refrigerant passing to the storage tank  80  by way of the J-tube  85 , there will be a tendency for some of the liquid refrigerant to flash to a vapor form as it passes into the tank. This will, in turn, complicate the relative volume relationship as discussed hereinabove. That is, if there is a liquid/vapor mixture passing to the storage tank  80 , the volume of the two phase flow will be substantially greater than it would have been in a single phase form, thereby presenting the tank with a condition in which the volume is exaggerated for that particular operating condition. Accordingly, it is desirable to locate a liquid/vapor separator  90  in the circuit between the J-tube  85  and the storage tank  80 . Any resulting refrigerant vapor can then be conducted along line  91  to the absorber  30 , thereby leaving only liquid refrigerant to flow from the separator  90  to the storage tank  80 . 
     As an alternative to the supplying of refrigerant from the condenser  70  to the storage tank  80  as described above, the storage tank  80  may be kept supplied with refrigerant by way of a line  93  (shown as the dotted line and FIG. 3) coming from the refrigerant discharge line  28 . With this arrangement, the J- tube  85  and the liquid/vapor separator  90  can be eliminated and, although the feature of ensuring that there is sufficient refrigerant in the evaporator sump at part load, will no longer be available, the feature of diluting the solution at shutdown will operate in the same manner as described above. 
     Although preferred embodiments of the present invention have been illustrated and described, other changes will occur to those skilled in the art. For example, although the invention has been described with reference to a two-stage, series cycle of absorption cooling system, it could just as well have been described with reference to cooling systems of any of a variety of other types, including a single stage, parallel cycle system, among others.