Patent Publication Number: US-2007095512-A1

Title: Shell and tube evaporator

Description:
TECHNICAL FIELD  
      The present invention relates to refrigeration systems. More particularly, the present invention relates to evaporators for use in a refrigeration system.  
     BACKGROUND OF THE INVENTION  
      Centrifugal chillers, which are the workhorses of the comfort cooling industry, have very few moving parts (Prior Art  FIG. 1 ). Therefore, they usually offer high reliability and low maintenance requirements. A moving part is the compressor. A centrifugal compressor of the centrifugal chiller acts very much like a centrifugal fan, compressing the vapor flowing through it by spinning it from the center of an impeller wheel radially outward, allowing centrifugal forces to compress the vapor. Some machines use multiple impellers to compress the refrigerant in stages.  
      The compressor is in fluid communication with a shell and tube evaporator, as depicted in prior art  FIG. 2 . The evaporator acts to change the state of a refrigerant from a liquid to a vapor by warming the refrigerant. Warm water passes into the evaporator tube bundle and warms the liquid refrigerant, causing the refrigerant to change state to a vapor. The refrigerant vapor exits the evaporator at a suction nozzle under the motive force of a suction applied thereto by the compressor. Heat extracted from the liquid refrigerant acts to cool the water in the tube bundle. It should be noted that the prior art evaporator has a plurality of tubes contained within a shell. The tubes are all the same diameter.  
      There is a need in the industry to minimize the pressure drop on the water side of the chiller refrigeration system. Further, there is a need to reduce the cost of refrigeration systems without compromising performance.  
     SUMMARY OF THE INVENTION  
      The present invention meets the aforementioned needs of the industry. By employing greater diameter tubes for each successive pass of the water through the evaporator, pressure loss in the evaporator is advantageously reduced as compared to prior art evaporators. Further, by employing smaller diameter tubes for the initial pass and increasing the size of the tubes for successive passes, the tube cost of an evaporator is reduced by about ten percent as compared to a comparable capability evaporator constructed in the manner of the prior art, as exemplarily depicted in  FIGS. 1 and 2 .  
      The present invention is an evaporator for a refrigeration system wherein a flow of water makes a plurality of passes therethrough. The evaporator includes a tube bundle assembly having a known tube bundle portion associated with each of a plurality of passes of water therethrough, each of a plurality of tubes of a tube bundle portion associated with a first water pass having a lesser diameter than the diameter of tubes of tube bundle portions associated with successive passes of water. The present invention is further a method of forming an evaporator.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a partial cut away centrifugal chiller system;  
       FIG. 2  is a partially cut away depiction of a prior art evaporator; and  
       FIG. 3  is an end sectional view of an evaporator of the present invention depicting the tube bundle. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      The evaporator of the present invention is shown generally at  10  in  FIG. 3 . The evaporator  10  is constructed generally in accordance with the construction of the evaporator of the prior art depicted in  FIG. 2 . Reference may be made to prior art  FIG. 2  for the general portion of the description of the evaporator  10 .  
      Generally, the evaporator  10  is of the shell and tube type construction. Accordingly, the evaporator  10  has a cylindrical shell  12  and a tube bundle  14 .  
      The cylindrical shell  12  is preferably an elongate cylinder formed of a metallic material. The evaporator  10  is designed to be mounted in a horizontal disposition. Accordingly, a plurality of base supports (not shown) may be fixed to the underside of the cylindrical shell  12  for mounting the evaporator  10  in such disposition.  
      An insulation jacket  18  may be disposed immediately interior to the cylindrical shell  12 . The insulation jacket  18  preferably has a fluid-tight interior liner  19 . The cylindrical shell  12  is sealingly capped at either end by shell head  28 .  
      A water inlet  20  and a water outlet  22  are coupled to a one of the endplates  28 . Preferably, the water inlet  20  is disposed lower than the water outlet  22 .  
      A refrigerant inlet  24  and a refrigerant outlet  26  (also known as a suction nozzle) are coupled to the cylindrical shell  12 . As noted, the refrigerant outlet  26  is in fluid communication with the centrifugal compressor, depicted in  FIG. 1 . Liquid regrigerant enters the shell through inlet  24  and the bottom of the shell  40 .  
      Referring to  FIG. 3  for the particulars of the present invention, the tube bundle assembly  14  includes endplates  30  disposed at either end of the tube bundle assembly  14 . Each of the endplates  30  is spaced apart from the adjacent shell head  28  in order to define a fluid passage for communication of the water from the first pass to the second pass. Each of the endplates  30  has a plurality of tube ends  32  sealingly disposed therein.  
      As depicted in  FIG. 3 , the first pass tube bundle portion  36  is disposed in the lower portion of the cavity  40  defined within the cylindrical shell  12 . The second pass tube bundle portion  38  is disposed above the first pass tube bundle portion  36 . It is understood the certain evaporators employ a side to side flow of the refrigerant. There are preferably fewer of the second pass tubes  44  in the second pass tube bundle portion  38  than there are first pass tubes  42  in the first pass tube bundle portion  36 . The diameter of each of the first pass tubes  42  is preferably 0.50 inches in diameter to 1.0 inches in diameter and is most preferably 0.75 inches diameter. The diameter of the second pass tubes  44  is always greater than the diameter of the first pass tubes  42 . Preferably, the diameter of the second pass tubes  44  is 0.75 inches to 1.5 inches and most preferably is 1.0 inches diameter. In a preferred configuration of the evaporator  10 , the diameter of the first pass tubes  42  is 0.75 inches and the diameter of the second pass tubes  44  is 1.0 inches.  
      Preferably, the total area ( the total area being arrived at by taking the inside crosssing area of each tube in the tube bundle portion and multiplying it by the total number of tubes in the tube bundle portion) of all the first pass tubes  42  is substantially equal to the total area of all the second pass tubes  44 . In evaporators  10  having more than two passes, each successive tube portion for successive passes has a greater tube diameter than the tubes of the previous pass and has a substantially equal total area as that of the tube bundle portion of the preceding pass and, in fact all other tube bundle portions.  
      In operation, liquid refrigerant flows into the refrigerant inlet  24  and floods the cavity  40 , thereby, submerging the tube bundle assembly  14 . Warm water is pumped into the water inlet  20  and into the first pass tubes  42  of the first pass tube bundle portion  36 . As the warm water passes through the first pass tube bundle portion  36 , it acts to vaporize the liquid refrigerant. The refrigerant must be in a vapor state in order to be compressed by the compressor.  
      After passing through the first pass tube bundle portion  36 , the water temperature reduces and enters the second pass tubes  44  of the second pass tube bundle portion  38 . As the water passes through both the first pass tube bundle portion  36  and the second pass tube bundle portion  38 , the refrigerant transitions from a liquid state to a vapor state. Heat energy is transfered from water to refrigerant by vaporizing the liquid refrigerant. The now cooled water then exits the second pass tubes  44  of the second pass tube bundle portion  38  and passes out of the evaporator  10  by the water outlet  22 . It should be understood that a third or a fourth pass could be made by the water by installing a third and fourth bundle portion above the second pass tube bundle portion  38 . As noted above, the third pass bundle portion would be greater in diameter than the diameter of the second pass tubes  44  and lesser in diameter than the tubes comprising the fourth bundle portion, but each pass bundle portion would have the same total area and therefore the same flow volume, as noted above.  
      The above disclosure is not intended as limiting. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the restrictions of the appended claims.