US2654226A - Automatic defrosting evaporator - Google Patents

Description

Oct. 6, 1953 T. w. DUNCAN ET AL 2,654,226

AUTOMATIC DEFROSTING EVAPORATOR Filed Aug. 18, 1951 4 Sheets-Sheet l OUTLET l I l I I I I I I l I l l l I INVENTORS; Zia/m5 Q/Zzazcazz I 115 19 Z6622 C. Zosencfrazz Oct. 6, 1953 Filed Aug. 18 1951 T. W. DUNCAN ET AL AUTOMATIC DEFROSTING EVAPORATOR 4 Sheets-Sheet 2 INVENTORS; 57760222625 dflcuzcarz Oct. 6, 1953 T. w. DUNCAN ETAL AUTOMATIC DEFROSTING EVAPORATOR 4 Sheets-Sheet 5 Filed Aug. 18 1951 Oct. 6, 1953 'r. w. DUNCAN ET AL 2,654,226

AUTOMATIC DEFROSTING EVAPORATOR Filed Aug. 18, 1951 4 Sheets-Sheet 4 INVENTORS; Qka/aas Mfia/ZCa/Z Patented Oct. 6, 1953 AUTOMATIC DEFROSTING EVAPORATOR Thomas W. Duncan and Albert C. Rosencranz,

Evansville, Ind., assignors to Seeger Refrigerator Company, St. Paul, Minn., a corporation of Minnesota Application August 18, 1951, Serial No. 242,462

7 Claims.

The present invention relates to automatic defrosting evaporators, and is particularly concerned with evaporators of the type adapted to be used in household refrigerators.

The present invention relates also to an improved evaporator to be used inan automatic defrosting system of the type disclosed in the prior application of Thomas W. Duncan, Serial No. 144,641, filed February 17, 1950, for Automatic Defrosting Mechanism, which application is hereby incorporated herein by reference thereto.

One of the objects of the present invention is the provision of an improved evaporator in which the refrigerant can be caused to circulate during the defrost part of the cycle by the action of heat applied at a particular area of the evaporator, which heats the refrigerant that is circulated throughout the evaporator.

Another object of the invention is the provision of an improved evaporator fluid circuit, including a header for the suction tube in which the evaporator conduits are designed in the form of a complete loop connected at both ends to the header, and provided with portions of substantially equal resistance to flow so that by the application of a heater to an intermediate part the heated refrigerant can be caused to circulate throughout substantially the entire length of the evaporator conduits to heat the evaporator uniformly and melt the frost off all its areas within a short time.

Another object of the invention is the provision of an improved evaporator heating arrangement which heats the evaporator by heating the refrigerant, and which is adapted to effect a defrosting of the evaporator so quickly that the food which is stored in the evaporator or in the food storage space will remain substantially in its previously frozen state without being damaged by the introduction of heat into the evaporator.

Another object of the invention is the provision of an improved defrosting evaporator in which substantially equal static fluid pressure is maintained in both of the circuits of conduits, which are parallel to each other relative to the evaporator inlet and outlet, but which are also in series with each other from one header connection to the other header connection of the conduits.

Another object of the invention is the provision of an improved defrosting evaporator which provides a quick freeze shelf for freezing ice cubes and a relatively large frozen food storage space equally adaptable to the storage of frozen food, or the initial freezing of the food, which is simple in construction, capable of economical manufacture and adapted to perform its functions for a long period of time without necessity for repair.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the drawings, of which there are four sheets, accompanying the specification,

Fig. 1 is a top plan view of an evaporator embodying the invention;

Fig. 2 is a front elevational view;

Fig. 3 is a side elevational view taken from the right side of Fig. 2;

Fig. 4 is a bottom plan view;

Fig. 5 is a top plan view of a modification;

Fig. 6 is a front elevational view of the modification of Fig. 5;

Fig. '7 is a side elevational view taken from the right side of Fig. 6;

Fig. 8 is a side elevational view taken from the left side of Fig. 6.

The present evaporators may be embodied in the type of construction in which conduits are formed by grooves in one or both of two adjacent sheets, or they may be embodied in evaporators of the type in which a freezing chamber and shelf are formed by sheet metal, and the conduits for refrigerant comprise metal tubing secured to one or the other sides of the sheet metal.

For example, the evaporator shown in Figures 1 and 2 is indicated in it entirety by the numeral l0, and it comprises a box-like sheet metal housing II, which has its side l2, its bottom l3, and opposite side I4 formed of a single sheet of suitable metal, such as aluminum.

This aluminum sheet is folded backwardly upon itself along the front edge to form a hairpin bend l5, which is rounded instead of sharp, and the same is true at a similar bend I 6 at the rear edges of the evaporator.

The rear of the evaporator may be closed by means of a plane metal sheet IT, having a right angle attaching flange l8 along its two side edges and along its bottom edge for overlapping the sides 12 and I4 and the bottom l3, to which the rear wall may be secured by rivets or other suitable fastening means.

The front of the evaporator is preferably provided with a suitable'door, such as the door is, which may be pivoted at the bottom, top or either side of the evaporator, and which preferably effects a substantial closure of the front end.

The shelf preferably comprises a plane sheet of aluminum having a downwardly turned flange 2| at each of its side edges engaging the walls 12 and M, to which these flanges are secured respectively by rivets or other suitable fastening means. 3

The front and rear edges of the rectangula shelf 20 are also preferably provided"with the depending border flange 22-, which may also have a backwardly turned flange: 23undern'e'ath the tubing 24, carried by the shelf.

The width of the evaporator may be made as desired, depending upon the amount of food storage space desired below the shelf or the amount of shelf area desired. The evaporator illustrated is of such a Width that, it substantially fills the compartment ,of the refrigerator cabinet and 00-- cupies, all of the inside liner space-at the upper end of the cabinet, leavingonly sufficient space between the liner and evaporator for air circulation.- a

The evaporator casing I I ispreferably provided with a plurality of brackets which are used for its support on the rear wall and the ceiling of the liner. For example, the two right angle brackets 25, which are secured to the top of the side walls 12 and near the front'of the evaporator are provided with rearwardly open slots 26 for receivingheaded securing members carried by the top of the liner.

The two right angle brackets-21, which are carried by the bottom wall J3 at its rear edge, are provided with downwardly-open slots 28 for engagement with headed members carried by the rear liner wall.

As shown in Fig..-1, the horizontal flanges 29 of the brackets Z'Lare extended sufficiently so that they extend past the header 3!); but they are forwardly-of the loop 3| so that the'loop3l'may be located in a recess in the rear wall of the liner, if desired, whilethe header 30 may be in front of the rear liner wall. 1-.

The rear liner wall may be providedwith an elongated vertical depression formed therein-for receiving the depending legs H3, H4, which are then disposed in front of the liner, outside the insulation,-- and covered with a suitable cover plate. 1

The header 30, may consist of a metaltube, such as aluminum, ofuniform diameter and of a size sufficient to permit space for the bubbling and boiling refrigeranttodischarge itsbubbbles; so that the suction tube 32 may carry off what is mainly vaporizedrefrigerant. 1

Each end of the header 30 is closed by a circular end wall member 33, having an outwardly directed cylindrical flange 34-,--which has a tight frictional fit in the end of the header tube 30, and which may beweldedor otherwise suitably secured.

The suction tube 32 which leads to-the inlet of the compressor may extend-into the right end wall 35, preferably near. its upper edge; as shown in Figure 2, to be located above any liquid level in the header.

The header is secured to the back wall I I by a pair of .half cylindrical. sheet metalstraps 35, having a pair of attaching flanges 31, which may be riveted or otherwise secured 'to the back wall .11 near its upper edge. Thus the header is at an elevation which is above'all of the refrigerant Iii conduits except the suction tube 32, which itself is connected to a point adjacent the top of the header.

The header is preferably connected to the refrigerant conduits at a pair of symmetrical points, such as the header inlets 38 and 39, which are equally spaced from the ends of the header and located in' the bottom of the header.

The refrigerant conduits of the evaporator are preferably in the form of aluminum tubing secured to thesides of the aluminum shell or casing l I; and to the shelf 20, by welding or by means of a suitable'heat conducting compound whichadheres to both the tubing and the casing and increases the amount of heat conduction between the casing and tubing by intimate contact of the tubing and casing and by passing through the compound which may have aluminum filings incorporated in it. The tubing is preferably so arranged that there is no. possibility of a gas pocket forming which might prevent circulation of the refrigerant from the inlet 40 to the header 1 30.

Referring to,Figure l, the refrigerant tubing leads from the header inlet 38, with a laterally extending portion 4 l ,and then extends forwardly at 42 underneath the shelf. Thereafter it has a -U-bend at 43, and is provided with a succession of parallel portions 44-41.,connected by U -bends 48-50, until half the shelf has been traversed.

In a similar way the other right half of the shelf in Figure 1 carries the sinuous tubing leading from the header inlet 39, and having the parallel portions 51-55 joined by the easy bends 56-59.

The shelf tubing is preferably applied to. the lower side of the shelfand is concealed by the depending flange 22, leaving the top of the shelf smooth and plane for better heat conducting contact with the bottoms of the ice trays or other subjects to be frozen which may be placed on the shelf. 7

The forwardly extending parallel portions 41 and are preferably bent laterally at and 6!, and have the laterally extending portionsv 62, 63 along the forward edge of the shelf.

Adjacent the side walls 12 and [4 these laterally extending portions '62 and 63, have a right angle bend 64 and 55, respectively, and backwardly extending parallel portions 66 and 61, terminating in U-bends at and 69 near the rear wall and having projecting parallel portions'lfl and H to be joined to the tubing which is carried by the side walls. j-

The side walls [2 and H are provided with suitable apertures for passing the tubingadj acent the u-bends 6B and 68. All-ofv the parallel portions of the tubing carried by the shelf are preferably equally spaced so that the. cooling effect may be as uniform as possible throughout the shelf area.

The side walls l2 and i4, and the bottom l3 are provided below the shelf with .thesinuous coils extending in each case from the joints l2 and 13, backwardly and forwardly, with parallel portions and U-bends. Thus the right wall in Figure l, as seen in Figure 3, has the parallel portions 14-11 and theU-bends 18-8|, While the parallel portion 82 of the tubing-is substantially at the corner.

The Li-bends 8i and 83 extend about the corner and thereafter the bottom is provided with the 'ogrgglel portions 84-88 and joined by the U-bends In a similar way the left side 14 of the casing, Figure 2, is provided with the parallel portions of the tubing indicated at 93-91, the last one being substantially at the corner and with the U-bends 98-IOI.

The adjacent left side of the bottom I3 in Fig. 2 is provided with the parallel tubing portions I02-I06 joined by the U bends I08-I I I. Like the shelf tubing arrangement, the parallel portions of the tubing on the casing walls I2, I3, and I4 are preferably equally spaced for uniform cooling effect. The last mentioned parallel tubing portions 88 and I06 on the bottom of the evaporator preferably extend to the rear edge; and they have diagonally extending portions H2 leading to a pair of depending tubular legs H3, H4, which are joined at the bottom of a U bend H5.

The depending loop I I3I I5 may be arranged inside the liner. The lower U bend H5 is preferably provided with a copper inlet tube I I 6 extending upwardly from the U bend and having a smaller end portion H! of a sizesuitable to be joined to a capillary tube. Therefore III indicates the capillary inlet to the evaporator. Either leg I I3 or I I4 of the depending loop may be provided with one or more electric heating elements I I8; and these are preferably clamped to the tube with aluminum jackets to facilitate heat exchange from the electric heating elements to the depending U-shaped tube, and thence to the refrigerant contained in the tube.

The heaters are preferably of the type in which the resistance wire is enclosed in a powdered insulating refractory, which in turn is enclosed in a metal tubular jacket so that the resistance wire cannot be short circuited by contact of its jacket with water or other materials.

The leg I I3, which has the heater attached, is preferably provided with an enlargement comprising a tubular portion I I3a of larger diameter, thereby increasing the volume of the refrigerant in that leg, which is subjected to heat. The leg II3 also carries an elongated clamp H3b welded thereto or extruded therewith, and shaped to engage and hold the heater I I8. The leg I I3 preferably carries a bulb II3c of a thermostat arranged to actuate a switch in the heater circuit to out off the heat in case of overheating at that point by failure of the control mechanism to cut off the heater.

Leg I I4 preferably carries a bulb I Ila adjacent its upper end and actuating a switch for terminating the defrosting action by increase of temperature at that point. When the heated refrigerant has traversed the entire circuit of the evaporator it will reach and heat the bulb H4a, at which time the heating element should be cut out of circuit and the control of the evaporator I restored to the usual thermostatic switch which controls the operation of the motor compressor.

The operation of this evaporator during cooling operations is as follows: The compressed and liquefied refrigerant comes in at the capillary inlet H1, being metered from the condenser by a suitable length of capillary tubing, and the liquid refrigerant under pressure from the compressor passes into the depending U-shaped loop I I3- I I5, where its evaporation starts and the bubbles pass upward into the coils on the bottom of the evaporator and thence to the coils on the sides of the evaporator.

The refrigerant passes up the sides of the evaporator through the sinuous tubing to the central portion of the shelf, through the tubeportions 62, 63, and thereafter it passes through the sinuous tubing carried by the shelf laterally toward both edges of the shelf, finally reaching the header 30 at the header inlets 38 and 39.

The compressor being connected to the suction outlet 32, of the header, maintains a suitable low pressure in the header during operating periods of the compressor and pumps off the evaporated refrigerant to be again compressed by the compressor and liquefied by removal of its heat in the condenser in the usual manner. 7

The course of the refrigerant through the tubing of the evaporator of Figs. 1 to 4 is through two parallel paths leading from the capillary tube H'I upward through both legs of the depending U-shaped loop I I3--I I5 to the receiver 30, which has its suction outlet at 12, and these parallel paths are shown by the arrows applied to Figs. 1 to 4.

The operation of the evaporator during the defrosting part of the cycle is as follows: When the defrosting mechanism reaches the defrosting part of the cycle the compressor circuit is turned off by a switch in saidmechanism, and the electric heater circuit of the heaters H8 is turned on and energized by the defrosting switch mechanism.

Since the heaters are applied only to one leg I I3 of the depending loop, the refrigerantin that leg is heated, causing boiling and bubbling and vaporization, which produces an unbalance be,- tween the liquids, gases, and vapors contained in the two legs I I3, I I4.

Refrigerant tends to pass up the leg H3 and down the leg H4; and this refrigerant becomes .heated and passes through all of the sinuous coils to the header, warming the left side of the evaporator of Fig. 2.first; and thereafter the heated refrigerant passes out of the header inlet 39 into the sinuous coils of the right hand of the shelf and the right-hand wall I2, and right portion of the bottom of the evaporator, until the entire system of sinuous tubing is filled with hot refrigerant. The refrigerant is constantly recirculated throughout the evaporator as long as the heater is energized.

The hot refrigerant heats the evaporator walls and melts the frost during a defrosting period, which may consume a certain number of minutes, and the time of which depends upon the size of the heater, size of the evaporator, and the amount of frost accumulated.

As soon as the frost has been melted off, the defrosting mechanism terminates the defrosting period by cutting off the electric heater circuit and turning on the compressor energization circuit. In a few more minutes the evaporator is again cooled to a freezing condition without any substantial amount of heat having been transmitted to the frozen food stored in the evaporator.

Referring to Figs. 5 to 8, these are similar views of a modification in which the evaporator is of similar shape, but of slightly different construction. In this embodiment of the invention the sheet metal casing of the evaporator is similar in shape and provided-with the same side walls, I2, I4, and bottom I3.

This evaporator has similar top mounting brackets 25 and rear mounting brackets 21. The shelf 20 is similar in construction but has its sinuous tubing indicated by H9, passing backwardly and forwardly from side to side, with parallel portions joined by U-bends.

The sinuous coils I20 on the bottom I3 of this evaporator extend backwardly and forwardly with parallel portions that extend from side to side of the evaporator, as seen in Figures 7 and 8, and these are joined by U-bends.

ass-sage 7 The sinuous coils on the sides i2 and I I-of the evaporator are shown inFigures 7 and 8, and indicated by: the numerals- I2 I' and I22, and-these extend backward and forwardwith' parallel portions extending "from the "front to back or the evaporator." '1 1 1 V The header' :I23:is preferably arranged adjacentfthe-topf the right wall l2,'which has a slot oil-rectangular aperture "for receiving a part of the header'which'iswelded, brazed or other- 'wlse suitably'secured in this rectangularaperture- 12T; *1 r I The-'iheader outlet is indicated at I25, leading to a'suctiontube I26, top, Figure I, while the two header inlets are indicated at I21, I28. I

The capillarytubeinlet'to the evaporator coils is preferably chosen at such'a point I29, Figure atone o'fthe-bends of the 'shelf' tubing 9., so located;thatpaths of substantially, equal resistancer-to' liquiwflow are providedfr'om the capi11ary iri1et .I29-to both of the header inlets Header inlet I2'I is preferably connected to theuppermost end of the sinuous coils. I2I on the, wall" 11: The lowermost or these coils lextends to and is-connected to and forms. an integral part of -the'bottom coils I20, which extend backward and forward laterally with respect to .the

evaporator.

The bottomcoils I2II-are continued up the left side If as'tube I34.v The side coils I22 .pass through-an-aperture"I3 I;in the side wall I4, below thc shelf-2B in Fig. 8, and extend to the coils I'flkwhich are located beneath the shelf 20. The joint between the shelicoils andthe side wall coils l22 is-indicated at I32. The othercnd of the shelf coil'sf I -I-"'9. is connected at I33, (Fig. .5) to 2; depending tubular portion "I34, whlchextends under the bottom wall I3 as a horizontal portion-185; :Th'e other-end of the bottom coils I20 is connected to the -side coils I2I, ,(Fig. .7). The depending U-shaped tube I36 has its legs I31, I38; connected-at a suitable point in the circuit of the-bottom tubes I20. One. of .the legs I38 isconnectedntothe tube I39, leading. to header inlet I28; The other leg I3Iv is connected to the tube which'extends across the bottom. of the evaporator parallelvto tubes I20 and. at the point I30 -becomes coil-I22. 4 0neof=the:-legs,such as le I31 of the depending loop-I36, is provided with one or more electric heating, elements clamped to the ,tube. with aluminum jackets to *facilitate heat exchange. Thus, the, heaters are; again located to heat only one legorthe depending loop, causingan. upward circulation in that 1eg, -which eventually carries hot refrigerant to every part of the evapor rator tubing. I 1,, I

'Ihis-modified evaporator is also preferably providedwith an enlargement, a clamp carried thereby, anda heater,-and with the two controlling thermostatic bulbs previously described with respect to legs II 3-, I I4 p a, y

The defrosting evaporator of this modification operatesinsubstantially the same manner as that previously described. In this case, however, the refrigerant is carried first to the shelf where the capillary inlet is located at I29, and there the refrigerant goes in both directions through two paths of substantially equal resistance to the header I23, passing from the shelf to the sinuous coils on-thesidesand bottom of the evaporator before reaching the header.,

The course of the refrigerantthrough the tubing of the evaporator of Figs. 5 to 8 is shown as extending in two parallel paths beginning at the capillary tube inlet which communicates with the Shelf tubing at I the point 129,: Fig-15, where it separates into-two parallel paths which are; indicated by arrows. r One-of these paths includes the sinuous tubing' l I 9, which is above'the point I29 in Fig. 5, and which extends backwardly bn the shelf 20- to the point-I32. i

From this 'point the course of-refrigerant extends down the sinuous tubing-1M, I22 on the side "of the evaporator-to the point -I30,-'where the tubing makes:astraight pass I35'ovcr-to the leg I36 of :the LI-shape :formation down which it passes; The course ofthe refrigerant is thenupward through the leg'i3'8, which extends laterally-onthe bottom of the evaporator to the tube I39, which extends upwardly on the side I2 tothei-receiver. I23. w

The other parallel path in" the course of the refrigerant extends from the-point 129'; Fig; 5, sinuously across the-frontupart of the shelf "20 and downwardly on the side::I4,Fig. 8, through the tubing I 34, Thereafter the tubing or this path extends ,sinuously from left to right across the bottom andbackwardly on the'bottom until it communicates, in Fig.- '7, with the sinuous tubing IZI, on the side lz-through which therefrigerant passes upward tothe dischargeendi 21 into the receiver I23. Thecsuctiontubeis again indicated at I26, extending from the upperpart of :the header; 1

It will thus be observed that we have invented improved evaporator structures and a" circulating system for refrigerantwhich permits the application of electric heaters to such a point that a positive circulationiis induced in the conduitso'f the evaporator. "L17"? The-electric heater being placed low and below every part of the evaporator, except the connecting bend-ofthe depending sloop; reirigerant'which is heated tends tobubble upward from theelectrio heater, This causes ;a corresponding "downward current: in the other leg of the "depending loop, feeding new refrigerant to'bezheated. 1' The present evapora-torxand its heating at"- rangements permitathe; defrosting" of a large evaporator with a light amount of'frostin a matterlofa few minutes. The amount or time requireddepends upon the amount-of frost-deposit, sizeof, the. evaporaton'tsize of tubes and size of heaters; but a. positivercirculation or heated refrigerant :is assured withl'these arrangements. The enlargement I5I3a and the clamp carried thereby :may be part. of an integral extruded metal member, the, ends of-rthe-tub'e being spun after the .ad-iacentrclamp portions have been-cut Ofi. 4;. 1111", I e While we have illustrated a preferred embodiment of our inventionmany modifications'may be made without departing-from the spirit of the invention, and wekdo notwishto be limitedto the precise details of ccnstructionsetforth, but desire to avail ourselves of all 'changes within the scopeof thelappendediclaims. ;Havinglthus describedour invention; what we claim; as new -and:desire to' secure by Letters Patent of the United-States,:is: 1 r

1. A defrosting evaporator comprising a metal housing havingza pair: of .side walls'j'oinedby a bottom 'walLandiprovided with a sheli extending from-side wall to :side wall, a rear wall closing the reanspacebetween saidside walls, asuction header carried by an u'pper -part of-one wall and having a suction tube extending into the header with the tube'inlet adj acentthe topo'f said header,

sinuous tubing carried by the bottom of saidshelf and extending sinuously down both side walls and across the bottom of said bottom wall,

an inlet tube communicating with the sinuous tubing at a point remote from said header to cause the refrigerant to be supplied through two paths in parallel leading to said header, and

outlets from said sinuoustubing communicating? with both ends of the lower part of said header, said tubing also including a depending U-shaped portion having a pair of legs extending down ward from said bottom wall, and an elongated metal enclosed electric heater engaging one of said legs and causing the heating and upward boiling of refrigerant in said latter leg, to circulate heated refrigerant through said tubing and header to defrost said evaporator.

2. Adefrosting evaporator comprising a metal housing having a pair of side walls joined by a bottom wall and provided with a shelf extending from side wall to side wall, a rear wall closing the rear space between said side walls, a suction header carried by an upper part of one wall and having a suction tube extending into the header with the tube inlet adjacent the top of said header, sinuous tubing carried by the bottom of said shelf and extending sinuously down both side walls and across the bottom of said bottom wall, an inlet tube communicating with the sinuous tubing at a point remote from said header to cause the refrigerant to be supplied through two paths in parallel leading to said header, and outlets from said sinuous tubing communicating with both ends of the lower part of said header, said tubing also including a depending U-shaped portion having a pair of legs extending downward from said bottom wall, and an elongated metal enclosed electric heater engaging one of said legs and causing the heating and upward boiling of refrigerant in said latter leg, to circulate heated refrigerant through said tubing and header to defrost said evaporator, said U- shaped portion being symmetrically located with respect to the housing side walls and at the rear of the bottom wall.

3. A defrosting evaporator comprising a metal housing having a pair of side walls joined by a bottom wall and provided with a shelf extending from side wall to side wall, a rear wall closing the rear space between said side walls, a suction header carried by an upper part of one wall and having a suction tube extending into the header with the tube inlet adjacent the top of said header, sinuous tubing carried by the bottom of said shelf and extending sinuously down both side walls and across the bottom of said bottom wall, an inlet tube communicating with the sinuous tubing at a point remote from said header to cause the refrigerant to be supplied through two paths in parallel leading to said header, and outlets from said sinuous tubing communicating with both ends of the lower part of said header, said tubing also including a depending U-shaped por-- tion having a pair of legs extending downward from said bottom wall, and an elongated metal enclosed electric heater engaging one of said legs and causing the heating and upward boiling of refrigerant in said latter leg, to circulate heated refrigerant through said tubing and header to defrost said evaporator, and a thermally responsive member having its bulb located to be heated by the upper part of said latter leg, to control said electric heater and prevent overheating of the evaporator.

4. A defrosting evaporator comprising a metal sinuous tubing carried by the bottom of said shelf and extending sinuously down both side walls and across the bottom of said bottom wall, an inlet tube communicating with the sinuous tubing at a point remote from said header'to cause the refrigerant to be supplied through two paths in parallel leading to said headers and outlets from said sinuous tubing communicating with both ends" of the lower part of said header, said tubing also including a depending U-shaped portion having a pair of legs extending downward from said bottom wall, and an elongated metal enclosed electric heater engaging one of said legs and causing the heating and upward boiling of refrigerant in said latter leg, to circulate heated refrigerant through said tubing and header todefrost said evaporator, said heater having a pair of elongated partially cylindrical clamping flanges engaging said latter leg.

5. A defrosting evaporator comprising a metal housing having a pair of side walls joined by a bottom wall and provided with a shelf extending from side wall to side wall, a rear wall closing the rear space between said side walls, a suction header carried by an upper part of one wall and having a suction tube extending into the header with the tube inlet adjacent the top of said header, sinuous tubing carried by the bottom of said shelf and extending sinuously down both side walls and across the bottom of said bottom wall, an inlet tube communicating with the sinuous tubing at a point remote from said header to cause the refrigerant to be supplied through two paths in parallel leading to said header, and outlets from said sinuous tubing communicating with both ends of the lower part of said header, said tubing also including a depending U-shaped portion having a pair of legs extending downward from said bottom wall, and an elongated metal enclosed electric heater engaging one of said legs and causing the heating and upward boiling of refrigerant in said latter leg, to circulate heated refrigerant through said tubing and header to defrost said evaporator, said latter leg having a cylindrical enlargement extending over the major portion of its length, increasing the heat conduction from said heater to a larger amount of refrigerant.

6. A defrosting evaporator comprising a metal housing having a pair of side walls joined by a bottom wall and provided with a shelf extending from side wall to side wall, a rear wall closing the rear space between said'side walls, a suction header carried by an upper part of one wall and having a suction tube extending into the header with the tube inlet adjacent the top of said header, sinuous tubing carried by the bottom of said shelf and extending sinuously down both side walls and across the bottom of said bottom wall, an inlet tube communicating with the sinuous tubing at a point remote from said header to cause the refrigerant to be supplied through two paths in parallel leading to said header, and outlets from said sinuous tubing communicating with both ends of the lower part of said header, said tubing also including a depending U-shaped portion having a pair of legs extending downward from said bottom wall, and an elon- W iqn l ls i beat a in one at said ,legs" and. causing; ;the ;l hea tingl and upward of refrigerant in; said latter leg, in .,.cl. .cu at at r i e an t r u Said tubing andheader to defrost said. evaporator,

said header beinglocated onthe -rear,wall .and'

effecting a heating: and defrosting; of said rear walk A defrosting evaporator comprising a;metal header carriedlhy'anunper partof one wall-and halving a'suction tub extending into the header 1 viiththe tube. inlet adjacent the top of saidheadrj sinuou's'.tubingibarriedby the bottom of said extendingvsinuously down both side walls across the 'hottom of said bottom wall, tiibe'jfcoin'l nunicatirig with the sinuous tubingat a' point remote mm said header to Cats? the i f t t e supplied through two 9w? Para l d t said outlets from said sinuous tubing communicating with both ends of the lower part of said header,-

said tubing also including a. depending U-shaped portion having a pairof legsextending downward from said bottom wall, for the purpose of establishinga refrigerant liquid circuit to cause circulation through said pair'of legs by the ap-- plication of heat to one of said legs, causing the upward boiling in-said latter leg and a downward circulation -in the other leg due to theihead differential in said refrigerant between said legs.-

THOMAS W. DUNCAN. ALBERT c. ROSENCRANZ.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Y 20 1,970,340 Rufi Aug. 14, 934

2,095,014 Stark Oct. 5, 1937 2,487,662 McClay Nov. 8. 1949 2,554,848 Warren May 29, 1951

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