Patent Publication Number: US-3875758-A

Title: Plate defrosting system

Description:
United States Patent Fischer 1 Apr. 8, 1975 1 PLATE DEFROSTING SYSTEM Primary Eruminer-Meyer Perlin {75] Inventor: &#34;any C. Fischer Raw] Oak Md Attorney. Agent. or FirmKinzer, Plyer. Dorn &amp;  
  McEuchran [73] Assignee: Dole Refrigerating Company,  
  Chicago. Ill. [57] ABSTRACT 22 Fikd; June 2 1973 A refrigeration system utilizes at least one refrigeration plate filled with a suitable eutectic, The eutectic [2H Appl. No.: 373,668 isfrozen and during use air is drawn across the plate to provide cooling for a closed urea. The plate is de- 521 U.S. Cl. 62/l57; 62/282; 62/439 frosted y means of a distribution System in which a 5 l] 1m. Cl. FZSd 21/10 defrosting q for example 11 glycol Solution iS 53 i l f Search 3 32 15 157 331 9 tributed across the plate. collected at the bottom and then recirculated by a suitable pump. The system for 5 Ref/{fences (j circulating the defrosting liquid includes a still to re- UNITED STATES PATENTS move the water from the defrosting liquid between de 7 607 m 8 1952 Garland 61/78? frost periods so as to restore the liquid to its original 53.69158; W; mm.IIIIIIIIIIIIIIIIIIIIIIIIII 65/585 CPI/Manon m Preparer)&#34; fer the MW 3.727.422 4/1 /73 Apple 62/282 8 Claims, 1 Drawing Figure PNENTEUAPR 8&amp;975  
 IIIIIIHI llll HHIHI PLATE DEFROSTING SYSTEM SUMMARY OF THE INVENTION The present invention relates to a defrosting system for use in connection with refrigeration plates containing a eutectic in which defrosting can occur without the cooling surface temperature rising to 32 F.  
  A primary purpose of the present invention is a de frosting system of the type described using a glycol solution as the defrosting liquid.  
  Another purpose is a defrosting system of the type described including means for circulating the defrosting liquid over the plate, collecting the defrosting liquid and then removing the water therefrom.  
  Another purpose is a closed circuit defrosting liquid circulation system usable with refrigeration plates containing a eutectic.  
  Another purpose is a defrosting system of the type described including means for boiling off the accumulated water from the defrosting liquid.  
  Other purposes will appear in the ensuing specification, drawing and claims.  
 BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated diagrammatically in the attached diagram.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT A defrosting means for refrigeration plates is shown in U.S. Pat. Nos. 3,042,381 and 3,727,422 and includes a system for distributing water over a series of refrigeration plates, each of which contain a suitable eutectic. Water is distributed in such a manner that it flows over the surface of the plates to remove accumulated frost. The distribution system is shown in the abovementioned patents, as in the particular construction of the plate. However, it should be understood that the manner of distribution may vary, as may the construction of the plate. What is important in the present invention is to provide a system for defrosting refrigeration plates of the general type shown in the aforementioned patents utilizing a particular type of defrosting liquid which will not necessitate or cause melting of the eutectic within the plates.  
  In the drawing, a typical refrigeration plate unit or system is indicated generally at and includes an outer cover or container 12 within which are positioned one or more plates 14 which may contain a suitable eutectic. The front cover has been removed in the drawing to illustrate the plates and the air flow pattern. In use, the plates 14 are frozen by means of refrigerant coils that pass through them and air is drawn across the surface of the plates and distributed through blower outlets 16 to a space to be cooled, for example a milk truck, frozen food truck or the like. The air intakes are indicated at 18 and the plate unit 10 may be so constructed that air flows downwardly along the opposite sides of the plate unit, as indicated by arrows 20, and then upwardly through the center, as indicated by arrows 22, to be discharged through the openings 16. A suitable fan or blower may be positioned behind the discharge openings 16. Plate unit 14 is positioned above a reservoir 24 formed at the bottom of the container 12, as described hereinafter.  
  Positioned to distribute a defrosting liquid over the top of plate 14 is a spray tube 26 fed by a header 28. The spray tube will have a series of openings, as particularly disclosed in the above-mentioned patent, to spray liquid over the top of the plate.  
  Below the plate unit 10 is a storage tank 30 which is in communication with the reservoir 24 by means of conduits 32 generally positioned at opposite sides of the reservoir. A pipe 34 connects the storage tank 30 with a valve 36, with the valve 36 in turn being connected to a pump 38. The discharge side of the pump connects to a pipe 40 which in turn connects to the header 28 at the top of plate 14.  
  A still is indicated generally at 42 and is connected by a valve 44 to the discharge side of the pump 38 and by a second valve 46 to the inlet or suction side of the pump 38. In practice, when the pump 38 is operating, it will draw defrosting liquid both from storage tank 30 and from still 42. Although both valves 36 and 46 will be open, they will be adjusted so that the still tank will not be pumped dry. Valve 44 also has to be adjusted to keep the still tank from being pumped dry. These adjustments will be fixed and will not be altered in service.  
  A reflux condenser is indicated generally at 48 and is connected by a pipe 50 to an upper part of still 42. An outlet 52 forms one end of the evaporation column 48 and is effective to discharge water vapor during the distillation process. A packing column 54 is positioned below the reflux condenser and the condensed liquid, after passing over the packing in column 54, will collect in its bottom area 56, after which the condensed liquid will flow through pipe 58 to still 42.  
  A thermostat is indicated at 60 and has a sensing element 62 positioned within the still below the liquid level indicated at 64. Positioned below the thermostat 62 is a heater element 66, with both the thermostat 60 and the heater element 66 being connected to a timer 68. The timer 68 is also connected by suitable electric lines 70 to the pump 38 to the effect that the timer controls the operation of the pump and heater in accordance with the temperature as supplied by the thermostat 60 and in accordance with a predetermined sequential program.  
  The valves 36, 44 and 46 are adjusted so that the still is not pumped dry during defrosting operation, thus causing the pump to cavitate.  
  In operation, normally air circulated along the paths of arrows 20 and 22 will be cooled, after which it is discharged from the openings 16 to pass into the area to be refrigerated. During the normal course of operation, frost will accumulate on the plates and it is necessary to remove the frost as any areas of the plates which are covered by frost are less effective in providing the air circulating about the plates. Frost is a poor conductor of heat and hence there will be reduced heat transfer from areas of the plates covered by frost.  
  A suitable defrost liquid that can remove frost without warming the eutectic plates should have two characteristics. Freezing point should be lower than the temperature at which the eutectic plate is operating, for example 0 F. It should also have a boiling point that is substantially higher than the boiling point of water so that an easy separation can be made by distillation.  
  A suitable defrosting liquid, for example propylene glycol, ethylene glycol, or other satisfactory liquids as described above, will be present in the storage tank 30.  
 The level indicated by line 72 is the level of the liquid before the defrosting operation is started. The liquid level 74 in the still is the same as the liquid level 72 in the storage tank 30, as the storage tank and still are in open circuit through the pump. Liquid passes through valves 36 and 46 to the pump 38 and it is circulated by pipe 40 up to the header 28 and then distributed by the spray tube 26 across the top of the plates. The distribution manner is taught in US. Pat. No. 3,727,422. As the liquid passes over the plates, it will remove the accumulated frost, which is basically water, and thus will dilute the defrosting liquid or glycol. The defrosting liquid will pass down into the reservoir 24 and then into the storage tank 30. After a predetermined operating period. determined by the timer 68, the pump will be shut off. At this time heater 66 will begin operation in order to boil off the collected water from the defrosting liquid. The heater 66 will operate a sufficient period of time to raise the boiling point of the liquid in the still to approximately 240 F. At this point the thermostat 60 will cause the heater 66 to be shut off. As the liquid is heated within the still, the vapor. will pass through pipe 50, through the packing column 54, and up through the reflux condenser 48. Water vapor will pass out of the opening 52 in the top of the evaporation col umn. The glycol solution which is separated from the vapor in the distillation process, will be collected in the bottom 56 of the packing column and will pass through pipe 58 back into the still 42.  
  Thus, the defrosting liquid, for example a propylene glycol solution, is circulated over the plates to be defrosted and the liquid is collected along with water from the defrosting process. The solution of glycol and water from the defrosting process is heated within the still to boil off the water, thus concentrating the defrosting liquid for a further defrosting operation.  
  The invention should not be limited to any particular type of plate structure, although the particular defrosting system shown is advantageously used with an eutectic-type plate. in like manner, the invention should not be limited to a particular type of defrosting liquid, although propylene glycol solutions have been found to be highly satisfactory.  
  Of advantage in the defrosting system described is that defrosting is accomplished without melting the frozen eutectic. Previous systems necessitate raising the plate temperature to a point above 32 F., whereas, in the present system defrosting is accomplished without so raising the temperature of the cooling surface.  
 Whereas the preferred form of the invention has been shown and described herein, it should be realized that there may be many modifications, substitutions and alterations thereto.  
  The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
  1. In a refrigeration system having at least one refrig eration plate unit containing a eutectic, means to defrost the exterior of the plate unit with a liquid solution having a boiling point above that of water and a freezing temperature substantially below 32 F., including a defrost liquid reservoir positioned beneath the plate unit and in communication with the bottom ofthe plate unit, means for distributing the defrost liquid over the plate surface from adjacent the top thereof, pump means for moving the defrost liquid from the reservoir to the distributing means, and means including a reflux condenser for removing at least a portion of the water from the defrost liquid after it has passed over the plate unit and has been received in the reservoir including a still connected to said pump means.  
  2. The structure of claim 1 further characterized in that said plate unit is positioned within a closed container, with said reservoir being in communication with the bottom of said container to receive the defrost liquid after it is passed over the plate unit.  
  3. The structure of claim 1 further characterized by and including a storage tank connected to the reservoir, said pump means being connected to the storage tank and to the still.  
  4. The structure of claim 3 further characterized by and including valve controlled conduits connected between the still and the pump means and the storage tank and the pump means such that said pump means moves liquid from both the still and storage tank during operation thereof.  
  5. The structure of claim 1 further characterized in that said still includes a packed column and said reflux condenser is connected thereto, and a heater positioned within said still.  
  6. The structure of claim 5 further characterized by and including a timer connected to the heater within the still and to the pump for use in coordinating operation of the pump and heater.  
  7. The structure of claim 6 further characterized by and including a thermostat in said still and connected to said heater.  
 8. The structure of claim 1 further characterized in that said defrost liquid includes a glycol.