Oct. 1, 1946.- ’ J_G_RE'.D,JR_ 2,408,480 EVAPORATOR FOR LOW PRESSURE REFRIGERANTS Filed‘ Jan. 3., 1945' M/W ATTORNEY Patented Oct. 1, 1946 - 2,408,480 UNITED STATES PATENT-Face EVAPORATOR FOR- LOW-PRESSURE > REFRIGERANTS ' v John G. Reid,>Jr., Evansville, Ind., ,assignor to‘, I Servel, Inc., New York, Y., a oorporationlof . Delaware Application January 3, 1945, Serial No. 571,167 I i 5 Claims. (o1.62_'119) 1 The present invention relates to refrigeration i Fig. 1 is a diagrammatic view of an absorption and more particularly to a refrigeration system refrigeration system incorporating the evapora - including a novel evaporator construction to tor of the presentinvention'; and adapt the system for air conditioning. While ‘the present invention may be used with . g Fig. 2 is a longitudinal sectional view of the up. per portion of an evaporator tubeshowingvthe internal helical groove forming a plurality of ser other absorption refrigeration systems, it is par ticularly adapted for use in a system of the type rations on the inner periphery of the tube ‘andja illustrated and described in the application for wick to facilitate the initial'wetting of the inner United States Letters Patent of Albert R. Thomas, surface of the tube. v _ i . . ; ' Serial No, 560,214, filed October 25, 1944, en 10 In the drawing, the invention 'isshown ap titled “Refrigeration.” The refrigeration system plied to a refrigeration system'of the type illus trated in the‘ Thomas application referred to illustrated and described in the Thomas applica tion operates in a partial vacuum and utilizes water as a refrigerant and a saline ‘solution as an absorbent. above. In a refrigeration system of this type a The refrigerant and absorbent; are 15 introduced into the system as a water solution of a salt such as lithium chloride, lithium bromide, or the like and the absorbent occurs in the sys tem as a dilute or concentrated water solution of the salt. 7 liquid refrigerant-such as, for‘example, water ‘is introduced into the evaporator [0, later 'to be de scribed in detail, from a condenser ll through a path of ?ow including avU-shaped tube l2. rI‘he u-shaped tube !2 has. one end connected to a sump l3 at the bottom of the condenser II and its opposite end extends through the top of the evaporator H3. The refrigerant vapor ‘formed in the evaporator it! flows 'to an" absorber [4 where the vapor is absorbed in aliquid absorbent such ' One of the objects of the present invention is to provide an evaporator or cooling element hav ing vertical tubes extending between upper and lower headers and so constructed and arranged as as, for example, a concentrated water solution of lithium chloride or lithium bromide. The ab sorber M is in the form of a horizontally arranged to distribute liquid refrigerant equally to the plurality of tubes. Another object isqto provide an evaporator of the type indicated in which the liquid refrigerant cylindrical drum positioned below the evaporator it. ‘A pipe l5 extends upwardly from the top of is supplied to the open upper end of each tube in a thin sheet or ?lm around its entire periphery for the absorber l4 and isv connected to the emperortor ‘It to provide a path of flow for refrigerant gravity flow therethrough. vapor from the evaporator to the’ absorber. ‘' ‘ Absorption liquid enriched with refrigerant‘ or, Another object is to provide an evaporator hav ing vertical tubes of the type indicated with ser rations on the-inner periphery of each tube to in other words, a dilute salt solution is conducted from the absorber l 4' to the base of- a generator I 6 in anath of'flow including a conduit l1, pump l8, impede the flow, of liquid refrigerant and main tain a thin ?lm of the liquid refrigerant through out its length. conduits i9 and 2E], liquid heat'exchanger 2| and conduit 22. The generator’l? comprises'a plu ‘ Another object is to provide an evaporator of the type indicated having a pump circuit for re circulating the refrigerant . from header to the upper header. ‘ the > lower rality of riser tubes 23 enclosed Within an outer 40 ' Still another object is to provide an evaporator of the type indicated which is adapted-to accom modate the large volumes of refrigerant vapor formed in a vacuum system. These and other objects will become more'ap parent from the following description and draw ing in which like reference charactersdenote like ' parts throughout the several views. It is to be expressly understood, however, that the draw 50 ing is for the purpose of illustration only and not a de?nition of‘the limits of the invention, refer ence being had for this purpose to the appended claims. In the drawing: shell as to provide ‘a chamber therebetween. Steam is supplied to the chamber in- the genera tor it from a boiler 25 through a conduit 26‘. For purposes of illustration a manually operable valve V is shown in the conduit 25 for controlling the amountof steam’ supplied, to the generator 16 but'it will be understood that a suitable auto matically operable valve may be substituted for controlling the amount of steam delivered to the generator ity in accordance with thevload. ' The boiler 25 isprovided with ?re tubes 21 to which heat is supplied from’ suitable fuel burners 28. An outlet vent 29 is provided adjacent the upper end-of the steam chamber. in the generator l5 and a condensate return line 30' is provided ad jacent the base thereof.v The heating of the riser tubes 23 by the Steam causes refrigerant vapor to 2,408,480 3 4 the upper end of the conduit in the separating chamber is protected by a shield 44. be expelled from the absorption solution and such expelled vapor is effective to raise the absorption When relatively large refrigeration units uti solution in the tubes by gas or vapor lift action. The expelled vapor passes from the upper ends of lizing water as a refrigerant are used for air con the riser tubes 23 into a vapor separator 3| and thence flows through a conduit 32 to the con denser H where the vapor is lique?ed. Liquid tion of refrigerant in different parts of the evap ditioning, a uniform distribution and evapora orator cannot be obtained in the usual types of evaporators due to the low pressure and great volume of refrigerant vapor. A ?ooded type evaporator cannot be used advantageously in such a refrigeration system because of the hy drostatic head of refrigerant in such an evapora refrigerant formed in the condenser ll flows through the U-shaped tube [2 to the evaporator ID, as explained above, to complete the refriger ation cycle. . The raised absorption solution from which re tor which raises the boiling point progressively frigerant vapor has been expelled is conducted from the top to the bottom of the evaporator and from the upper portion of the generator IE to the absorber M in a path of flow including a 15 renders the greaterportion of its surface ine?ec tive for the transfer of heat. To avoid such hy conduit 33, liquid heat exchanger 2| and conduit drostatic head, it is desirable to maintain a thin 34. The end of the conduit 34 extends into the .7 ?lm of the liquid refrigerant on the internal sur upper portion of the absorber I4 adjacent the faces of the evaporator. With relatively small inlet from the pipe [5 and has a plurality of apertures or nozzles therein to provide a dis 20 units using water as a refrigerant, it is the prac tributing pipe 35 for dividing the absorption solu— tion as it is introduced into the absorber to pro mote absorption of the refrigerant vapor. The heat liberated by the absorption of refrigerant vapor in absorber I4 is taken up by a cooling medium such as, for example, water which flows upwardly through vertically disposed banks of pipes or coils 36 in the absorber. The cooling tice to flow the refrigerant from the top to the bottom of the evaporator in a shallow stream through a series of substantially horizontal tubes. In such small units a substantial wetting of the interior surfaces of the tubes is obtained and the design can be such that all of the refrigerant will be evaporated during a single pass through the evaporator at full load conditions. With large units, however, due to the increased amount of water is introduced into the lower ends of the 30 liquid refrigerant supplied to the evaporator it is banks of pipes 38 from a supply main 31 and is practically impossible to maintain a thin ?lm discharged \from the upper ends of the banks of refrigerant on the interior surfaces of such a of pipes through a conduit 38. Conduit 38 is series arrangement of horizontal tubes and the connected to the condenser ll so that the cool liquid refrigerant in the ?rst tubes of the evap ing water also may be utilized to effect cooling orator is apt to be blown out of the tubes by the of the condenser. The cooling water is discharged from the condenser ll through a conduit 39. The system operates in a partial vacuum with the generator [5 and condenser H operating at one pressure and the evaporator IE) and absorber 14 operating at a lower pressure. The pressure differential between the high and low pressure sides of the system is maintained by a liquid col umn in the up-leg of the U-shaped tube l2 be tween a condenser l l and evaporator ID. A simi lar liquid column also is present in the conduit 34 connecting the absorber I 4 and liquid heat exchanger 2!. The pump l8 connected between ‘the absorber M and liquid heat exchanger 2| also maintains the pressure differential between the absorber and generator I 6. . The absorption solution in the absorber I4 is circulated continuously through an auxiliary loop circuit to promote absorption of the refrigerant vapor. The auxiliary loop circuit for the absorp tion solution comprises the conduit l1, pump l8 ‘and conduit l9. The upper end of the conduit l1 extends into a sump 40 in the bottom of the absorber l4 and the lower end of the con duit is connected to the inlet of the pump l8. Conduit [9 is connected at one end to the outlet from the pump I8 and its opposite end extends ‘throughout the length of the absorber l4 adja cent the top thereof. A series of nozzles 4| are provided in the end portion of the conduit I9 ex tending into the absorber M to provide a liquid distributing pipe 42 for dividing the absorption r. liquid into a ?ne spray as it is delivered to the absorber. During operation of the refrigeration ‘system, part Of the circulating absorption solu— tion is diverted from the conduit l9 through the conduit 20 and liquid heat exchanger 2| to the generator l6~as previously described. ' An over?ow conduit 43 is provided between the separating chamber 3| and the absorber l4 and rapidly expanding refrigerant vapor. Further more, it is di?icult to design a horizontal tube evaporator for a large unit which will vaporize all of the refrigerant during a single pass there through under varying load conditions. In accordance with the present invention a novel :form of air conditioning evaporator is pro vided for use with relatively large refrigeration units. The evaporator Hi comprises a casing 59 forming a central rectangular opening 5| through which the air to be conditioned may be circu lated. The casing is of generally hollow con struction to provide an upper header 52 above the opening 5|, a lower header 53 below the opening and a relatively large passageway 54 at one side of the opening. The bottom wall of the upper header 52 constitutes a horizontal tube sheet 55 and the top wall of the lower header 53 constitutes a tube sheet 56. The end of the lower header 53 opposite the passageway 54 ex tends horizontally and vertically to provide a pump chamber 5?. .One end of the upper header 52 converges into a cylindrical pipe section 58 having a ?ange 59 at its end for connection ‘to the pipe 15. A plurality of vertical pipes or cooling tubes 60 extend across the opening 5i and through the tube sheets 55 and 58 in the upper and lower headers ‘52 and 53. .The upper end portions of the tubes 60 extend abovethe tube sheet 55 in the upper header 52 with all of the ends arranged at the same level in ‘a horizontal plane. A wall 6i ex tends upwardly from the tube sheet 55 and be tween the side walls ‘of the header 52 to provide a dam for maintaining a pool of liquid refrig erant around the upwardly projecting ends of the tubes Bil. While a single row of the tubes 65 are illustrated in the drawing, it will be understood that a plurality of rows of tubes may be provided and the tubes are provided with '?ns 63 forfin— 2,408,480 5 . ' creasing the heat transfer. The internal ‘surface .innerperiphery. thereof. Due to the equal‘height of the tubes 60 ‘are roughened or serrated to of the ends of the‘ evaporator tubes 58 above the ' impede the ?ow of refrigerant therethrough and maintain a thin film of liquid refrigerant thereon. As, illustrated in Fig.7. 2, the serrations on the tube sheet 55 the liquid refrigerant will be dis tributed‘ equally in all of the tubes Bi] and will interior of each tube is formed by an internal be supplied’ to each tube in a thin ?lm around its entire inner periphery. When a starting de helical groove 64 in which refrigerant flows from the top to the bottom of the tube, by gravity. vice 82, as illustrated in Fig. 2, is provided on the upwardly projecting end of each of the tubes 58, a small amount of the liquid refrigerant is Due to the size and shape of the helical groove .64 the liquidrefrigerant creeps up along the sur 10 siphoned into the interior of the tube by capillary face of the tube between adjacent grooves due to action to wet the interior before the liquid refrig erant rises to a level above the upper end of the capillary action to wet the entire surface of the tube and form a?lm ofliquid refrigerant thereon. tube. Such a starting device assists in the initial wetting of the tube to insure equal distribution ‘ While not essential to the operation of the evap orator 10, a starting device 62 may be provided 15' of refrigerant in the plurality of tubes, "The liquid refrigerant will flow downwardly by gravity on the upwardly projecting end of each tube 60 to initially wet the inner surface of they tube be > in'the helical grooves 64 from the top to thebot- _ fore the liquid rises to the level of the upper end ~ .of the tube. As illustrated in Fig. 2, the starting tom of the tubes 60 and due to the shape and size of the grooves the. liquid refrigerant will ‘creep device is formed by a ?ne mesh metallic screen 20 between adjacent grooves to wet the interior sur looped over the sides of the upwardly projecting face of the tubes throughout their length. In end of the tube. In place of a metal screen a other words, the helical serrations 64 on the inte rior of the evaporator tubes 68 will cause a thin fabric sleeve or wicking may be used. The liquid refrigerant in the lower header 53 ?lm of the liquid refrigerant to be formed thereon. is recirculated through the evaporator II! by‘a 25 The liquid refrigerant in excess of that evaporated during a single pass through the evaporator tubes pump 65in the pump chamber 51. The pump 55 is positioned below the liquid level in the lower 5i) will flow through the tubes to the lower header 53. . header 53 and the pump'is driven by a shaft 66 extending from an hermetically sealed motor 67 The pump 65 continuously recirculates the re mounted on the evaporator casing. A conduit 63 30 frigerant from the lower header 53 to the upper header '52 and delivers the refrigerant through is connected to the outlet from thepump 65 and the nozzles 69 in the form of a spray to promote extends upwardly and then horizontally through evaporation of the refrigerant._ Due to the rela out substantially the entire length of the upper ’ tively thin ?lm of liquid refrigerant on the inter header 52. The portion of the conduit 68‘ extend ing into the header 52 has aseries of outlet aper 35 nal surfaces of the tubes 60 the evaporation of tures or nozzles 69 and constitutes a liquid dis the refrigerant occurs at the surface of the liquid tributing pipe ‘Hi for supplying the recirculated so that liquid refrigerant will not be blown from refrigerant to the upper header. the tubes. Furthermore the recirculation of the refrigerant insures complete and equal evapora An over?ow conduit 15 is provided in the evap orator IO to prevent the accumulation of an ex 40 tion throughout all parts of the evaporator. The evaporation of the refrigerant in the evap cessive amount of liquid refrigerant therein. The orator l? will reduce the temperature of the re upper end of the conduit ‘l5 extends into the frigerant to a value corresponding to the pres evaporator in to a predetermined height above sure prevailing in the evaporator. Thus the the bottom thereof and below the lower ends of evaporation of the refrigerant acts to cool the the tubes 50. The opposite end of the conduit 15 may be connected to any part of the refrigeration 7body of refrigerant supplied to the header 52 system and as hereinlillustrated it is connected ‘ from the condenser I l and recirculated by the to the conduit 22 adjacent the base of the gen pump‘ 65. The air to be conditioned flows erator 16. When the level of the liquid refrig through the opening 5| and around the tubes 59 erant in the evaporator ill rises to a level above 50 in the evaporator H! and is chilled bv its contact the upper end of the conduit '15 the liquid refrig with the tubes; the air transferring its heat through the tubes to evaporate more of the re‘ erant will overflow to the base of the generator Hi to dilute the absorption solution and maintain . frigerant'to maintain a temperature correspond ins: to the pressure in the] evaporator. the concentration below the saturation point at which crystallization and precipitation of salt The refrigerant vapor flows upwardly through from the solution will occur. One form of the the tubes 6!! to‘the upper header and from invention having now been described in detail the lower header 53 through the relativelylarge the mode of operation is explained as follows. passage‘ 54 to the upper header 52 and thence Steam supplied to the generator 55 vaporizes flows through the pipe 85 to the absorber M the refrigerant therein which flows upwardly 60 where it is absorbed in the absorption solution. through the tubes 23 and raises the absorption The absorption solution in the upper part of the solution by vapor lift action. The refrigerant vapor ?ows from the separating chamber 3! through a conduit 32 to the condenser H where generator 16 flows through the conduit 33, liquid heat exchanger 2! and conduit 34 to the liquid distributing pine 35 where it is delivered into the the vapor is condensed to a liquid. The liouid 65 absorber. The absorption solution in the absorb; refrigerant flows from the condenser H through or M is continuously recirculated through the the U-shaped tube !2 into the upper header 52 conduit-i7. pump it! and conduit 89 to the liquid of the evaporator. vDue tothe dam If! in the upper distributing pipe 42 in the absorber which deliv header 52, a pool of the liquid refrigerant accu ‘ers the absorption solution in a ?ne spray to mulates around the end portions of theevaporator tubes 60 projecting above the tube sheet 55. When a su?icient amount of liquid refrigerant has ac cumulated in the header 52, the liquid level will rise to the horizontal level of the upper ends of the tubes 60 and will ?ow into the tubes at the promote absorption. A portion of the recircu lated absorption solution is continuously diverted through the conduit 2!], liquid heat exchanger 2| and conduit22 back to the base of the generator. If for any reason the liquid refrigerant tends to accumulate in the evaporator Hi, the overflow 2,408,480 8 conduit 15 will drain the refrigerant to ‘the con duit 22 adjacent the base of the generator to maintain the concentration of the absorption so part of the system to control the amount of re frigerant in the evaporator by draining excess refrigerant to the other part of the system. lution within permissible limits. 3. An evaporator for use in a refrigeration sys tem comprising a casing forming a central open It will now be observed from the foregoing speci?cation that the present invention provides ing with a header above the opening, a header below the opening and a relatively large passage way between the upper and lower headers at one an evaporator of novel construction including a plurality of vertical tubes extending between up per and lower headers.‘ It will further be ob served that the evaporator of the present inven side of the opening, said upper header having an inlet for liquid refrigerant and an outlet for re frigerant vapor, the bottom wall of the upper tion is so constructed and arranged as to main header forming a horizontal tube sheet, a plu tain a ?lm of liquid refrigerant in all parts of rality of vertical tubes extending between the up the evaporator and is adapted to accommodate per and lower headers with the ends of the tubes the large volumes of refrigerant vapor which are formed in a vacuum system. It will still further 15 projecting above the tube sheet in the upper header, structure in the upper header for retain ‘be observed that the present invention provides for continuously circulating refrigerant from the lower header to the upper header to provide an 10 ing a pool of liquid refrigerant which over?ows into the upwardly projecting ends of the tubes, a pump in the lower header, and a conduit con ‘ample supply of liquid refrigerant to insure the wetting of the internal surfaces of all of the evap 20 necting the pump and the upper header to re circulate refrigerant from the lower header to orator tubes. the upper header. While a preferred refrigeration system and 4. An evaporator for use in a refrigeration sys evaporator construction are herein illustrated and tem comprising a casing forming a central open described it is to be understood that other re frigeration systems may be used and that modi 25 ing with a header above the opening, a header below the opening and a relatively large passage ?cations may be made in the construction and way between the upper and lower headers at one arrangement of the elements in the evaporator side of the opening, said upper header having an without departing from the spirit or scope of the inlet for liquid refrigerant and an outlet for re invention. Therefore without limiting myself in this respect reference is to be had to the ap 30 frigerant vapor, the bottom wall of the upper header forming a horizontal tube sheet, a plu pended claims for a de?nition of the limits of the rality of vertical tubes extending between the invention. upper and lower headers with the ends of the What is claimed is: tubes projecting above the tube sheet in the up 1. An evaporator for use in a refrigeration per header, a dam in the upper header for re system having an upper header provided with a taining a pool of liquid refrigerant which over horizontal tube sheet, a lower header, a plurality ?ows into the upwardly projecting ends of the of vertical tubes extending between the upper and tubes, said tubes having internal serrations to lower headers and projecting above the horizon impede the flow of refrigerant therethrough and tal tube sheet of the upper header, means for cause a wetting of the internal surface of the supplying liquid refrigerant to the upper header ’ tubes, a pump in the lower header, and a conduit which overflows into the end portions of the connecting the outlet from the pump to the up tubes projecting above the tube sheet, said tubes per header for recirculating refrigerant from the having internal‘serrations to retard the ?ow of lower header to the upper header. refrigerant through the tubes to maintain a ?lm 5. A unitary evaporator comprising a casing of liquid refrigerant on the interior surfaces 45 forming a central opening with a header above thereof, and means for recirculating liquid re the opening, a header below the opening and a frigerant from the lower to the upper header. relatively large passageway between the upper 2. In an absorption refrigeration system, a gen and lower headers at one side of the opening, erator, a condenser, an evaporator, an absorber, conduit means interconnecting the elements to 60 said upper header having an inlet for liquid re frigerant and an outlet for refrigerant vapor, the provide circuits for a refrigerant and absorbent, bottom wall of the upper header forming a hori said system operating in a partial vacuum and zontal tube sheet, a plurality of vertical tubes utilizing water as a refrigerant and a salt solu extending between the upper and lower headers, tion as an absorbent, said evaporator comprising a dam in the upper header for retaining a pool 01 Cl a casing forming a central opening with a header of liquid refrigerant which over?ows into the ends above the opening, a header below the opening of the tubes, the end of the lower header opposite and a relatively large passageway between the the passageway being extended horizontally and upper and lower headers at one side of the open vertically at the side of the opening to provide ing, a plurality of vertical tubes extending be a pump chamber, a pump in the pump chamber, tween the upper and lower headers, means for iii) an hermetically sealed motor mounted on the cas supplying liquid refrigerant to the upper header to cause it to flow by gravity through the plu rality of tubes, said interconnecting means in cluding a conduit connecting the upper header to the absorber, and a conduit having one end ex tending a predetermined height above the bottom of the lower header and connected to another ing and connected to drive the pump, and a con duit connected to the outlet from the pump and extended into the upper header, said pump and conduit recirculating refrigerant from the lower to the upper header. ' - JOHN G. REID, JR.