Patent Publication Number: US-7707850-B2

Title: Drainage mechanism for a flooded evaporator

Description:
BACKGROUND 
   The present application is directed generally to an evaporator arrangement. Specifically, the present application is directed to a liquid collection and drainage system to remove liquid refrigerant from vapor refrigerant in an evaporator. 
   In a refrigeration circuit, refrigerant vapor passes from the evaporator to the compressor. If the refrigerant isn&#39;t completely changed to vapor in the evaporator, some liquid refrigerant may be passed on to the compressor as liquid carryover. This liquid carryover can affect both the performance and the life of the compressor. 
   For example, in a flooded evaporator that has liquid refrigerant introduced in the lower part of the evaporator shell to exchange heat with a fluid passing through a tube bank, liquid droplets may be entrained in the refrigerant vapor flow leaving the evaporator after exchanging heat with the fluid within the tube bank. One approach to solving this problem is to provide a liquid/vapor separator, either internally or externally of the evaporator. While these separators are effective, they add substantial expense to the system. 
   Another approach to removing liquid refrigerant from the refrigerant vapor in the evaporator has been to provide sufficient vertical space between the top of the tube bank and the suction nozzle at the top of the evaporator shell such that any liquid droplets will be caused to flow downwardly by the force of gravity before they reach the suction nozzle. This approach requires the use of a larger shell, which is costly because of the added materials and space that it requires. 
   Yet another approach for removing liquid refrigerant has been to provide a so-called “mist eliminator” in the form of a wire mesh, between the top of the tube bank and the compressor suction. Such an eliminator tends to interrupt the flow of the liquid droplets, allowing them to collect on the eliminator and to eventually fall by force of gravity. This approach is somewhat effective in controlling liquid carryover and while it requires less space then the approach described hereinabove, it does require some additional space for the eliminator and also involves additional cost. In addition, the eliminator is recognized as being a passive system in the sense that it simply turns back the droplets, which will tend to be entrained in the flow of refrigerant vapor as before. Furthermore, the eliminator causes pressure drop of the vapor flow resulting in degradation of the performance of the chiller. 
   Other approaches for removing liquid refrigerant include providing a baffle above the tube banks for interrupting and collecting the upward flow of liquid refrigerant droplets that would otherwise tend to flow to the compressor along with the refrigerant vapor. Heat may be added to the baffle to cause an evaporation of the liquid droplets such that the resulting vapor passes to the compressor. However, this approach does not offer an effective drainage of the liquid collected by the baffle. 
   Intended advantages of the methods and/or systems satisfy one or more of the needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs. 
   SUMMARY 
   One embodiment is directed to a liquid collection and drainage system to remove liquid refrigerant from refrigerant vapor in an evaporator including a baffle having an inside surface to be disposed adjacent a suction inlet of the evaporator and an outside surface to be disposed adjacent a refrigerant pool of the evaporator. The system also includes a mesh pad and a drainage pipe. The mesh pad is disposed adjacent to the inside surface of the baffle and is configured to trap liquid refrigerant. The drainage pipe has a drain hole at one end and is configured to extend along the baffle to permit liquid refrigerant to flow to the drain hole. Liquid refrigerant is trapped by the mesh pad and collected in the drainage pipe to flow to the drain hole for return to a refrigerant pool. 
   Another embodiment is directed to an evaporator with a drainage system to remove liquid refrigerant from refrigerant vapor including a housing having an upper portion and a lower portion, a tube bank disposed in the lower portion of the housing and a drainage device disposed in the upper portion of the housing. The drainage device includes a suction baffle having an inside surface to be disposed adjacent a suction inlet of the evaporator and an outside surface to be disposed adjacent the tube bank. The drainage device also includes a mesh pad configured and disposed adjacent the inside surface of the suction baffle to trap liquid refrigerant. Further, the drainage device has a tapered pipe configured with a drain hole at one end and extending along the bottom of the suction baffle. Liquid refrigerant is trapped by the mesh pad and flows into the tapered pipe upon operation, where the trapped liquid refrigerant builds a liquid column and flows toward the drain hole. 
   One advantage is the reduction in liquid carryover into the compressor. 
   Another advantage is decreased power consumption and higher system efficiency compared to a system with liquid carryover. 
   Another advantage is the elimination of costly and large devices or systems to remove the liquid carryover. 
   Alternative exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates schematically a refrigeration system. 
       FIG. 2  illustrates a conventional flooded evaporator system. 
       FIG. 3  illustrates a perspective view of one embodiment of a flooded evaporator. 
       FIG. 4  illustrates a side view of the flooded evaporator of  FIG. 3 . 
       FIG. 5  illustrates a perspective view of another embodiment of a flooded evaporator. 
       FIG. 6  illustrates the swirling flow of the refrigerant vapor in the flooded evaporator of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic diagram of a refrigeration system  14 . Refrigeration system  14  includes a compressor  13 , a condenser  10 , an evaporator  12  and an expansion device  11 . Compressor  13  compresses a refrigerant vapor and delivers the vapor to condenser  10 . Compressor  13  can be a centrifugal compressor, scroll compressor, rotary compressor, screw compressor, swing link compressor, turbine compressor, or any other suitable compressor. The refrigerant vapor delivered by compressor  13  to condenser  10  enters into a heat exchange relationship with a fluid, e.g., air or water, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from condenser  10  flows through an expansion device  11  to evaporator  12 . 
   The condensed liquid refrigerant delivered to evaporator  12  enters into a heat exchange relationship with a fluid, e.g., water, brine or ethylene glycol, and undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the fluid. The vapor refrigerant in evaporator  12  exits evaporator  12  and returns to compressor  13  by a suction line to complete the cycle. It is to be understood that any suitable configuration of condenser  10  can be used in system  14 , provided that the appropriate phase change of the refrigerant in condenser  10  is obtained. Refrigeration system  14  can include many other features that are not shown in  FIG. 1 . 
   Now referring to  FIG. 2 , a side view of a prior art flooded evaporator  42  system with a refrigerant pool  40  at the bottom of evaporator  42 . Upper portion  44  of the system has no drainage device, and is an empty cavity where the refrigerant vapor with entrained liquid  48  exits evaporator  42  through a suction connection. In a conventional system as shown in  FIG. 2 , the pool of liquid refrigerant  40  absorbs the heat from the tubes carrying the fluid into and out of the evaporator, and undergoes a phase change from liquid to vapor. In flooded evaporator  42 , the liquid refrigerant droplets may travel through the suction line (not shown) causing damaging effects on the compressor and refrigerant system. 
   Referring now to  FIGS. 3 and 4 , suction baffle  16  is located inside of the upper portion of flooded evaporator  12 . The refrigerant vapor flows around baffle  16  and is eventually returned to compressor  13  through compressor suction piping  18 . In an effort to prevent any liquid from entering into compressor  13  and compressor suction piping  18 , suction baffle  16  is used to impart a swirling flow to the refrigerant vapor as it flows around suction baffle  16  to exit flooded evaporator  12 . As illustrated in  FIG. 6 , the swirling flow is induced by the entry of the refrigerant vapor containing liquid droplets through the slots in the suction baffle and assists in the separation process between the refrigerant vapor and any refrigerant liquid that is carried with the vapor. The swirling flow causes the refrigerant liquid to collide and form larger droplets that eventually collide with mesh pad  22  that is attached to or placed on the inside wall of suction baffle  16  or that fall by gravity into mesh pad  22 . The collected refrigerant liquid collects at the bottom of baffle  16  where a tapered pipe  24  is located. The collected liquid continues to collect in tapered pipe  24  until a column of liquid is formed in pipe  24 . The column of liquid is sized such that it eventually overcomes the pressure difference between the two sides of suction baffle  16  and drains through drain hole  26  into refrigerant pool  28  below, which includes tube bundle  39  (shown only in  FIG. 4 ). 
   Mesh pad  22  is a thin layer of steel, plastic, or other material suitable for absorbing refrigerant liquid that is separated from the refrigerant vapor by suction baffle  16 . Mesh pad  22  is secured in baffle  16  by use of retainers such as clips, rods and other suitable fasteners. In addition, suction baffle  16  may have a grooved surface that is also constructed of any material suitable for collecting liquid refrigerant. The grooves may be formed by manufacturing them with the baffle as one unitary piece. The grooves on the surface of suction baffle  16  are protrusions that allow any liquid in the vapor to collect. As the liquid droplets collect on the grooves and form droplets, the droplets follow the path of the grooves to the bottom of the baffle where the droplets fall into tapered pipe  24 . The protrusions of the grooves form a path extending downward to tapered pipe  24  so that the droplets collected thereon can flow easily to pipe  24  and on to drain hole  26 . 
   Tapered pipe  24  is shaped such that it is sized from a larger diameter end  32  to a smaller diameter end  34  as shown in  FIG. 5 . Smaller diameter end  34  is closed off with no outlet, to ensure that all of the collected drainage exits at larger diameter end  32  of tapered pipe  24 . A drain hole  26  is located at larger diameter end  32  and allows the collected refrigerant to drain from pipe  24  into refrigerant liquid pool  28  below baffle  16  and in the bottom of evaporator  12 . Tapered pipe  24  can be a separate unit that is disposed at the bottom of suction baffle  16 , or it can be a unitary unit or integral with suction baffle  16 . A weld connection or other similar suitable connection can be used to secure the tapered pipe  24  in the suction baffle  16 . In addition to being tapered in shape with a larger diameter end  32  and a smaller diameter end  34 , tapered pipe  24  can also be disposed in suction baffle  16  at a slant or angle, to help with diverting the collected liquid to larger diameter end  32  and drain hole  26 . Tapered pipe  24  is angled such that smaller diameter end  34  is at a higher level than larger diameter end  32  such that the collected liquid tends to flow downward toward drain hole  26 . Alternately, tapered pipe  24  may not have a drain hole  26  and may connect directly to a drainpipe at larger diameter end  32  to drain the collected liquid. 
   It should be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the phraseology and terminology employed herein is for the purpose of description only and should not be regarded as limiting. 
   While the exemplary embodiments illustrated in the figures and described herein are presently preferred, it should be understood that these embodiments are offered by way of example only. Accordingly, the present application is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims. The order or sequence of any processes or method steps may be varied or re-sequenced according to alternative embodiments. 
   It is important to note that the construction and arrangement of the drainage mechanism as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present application.