US2769311A - Defrosting evaporators - Google Patents

Description

Nov. 6, 1956 T. w. DUNCAN DEFROSTING EVAPORATORS 6 Sheets-Sheet l Filed July 2, 1953 ii @i INVENTOR.

Nov. 6, 1956 T. w. DUNCAN 2,769,311

DEFROSTING EvAPoRAToRs Filed July 2, 1953 e sheets-sheet 2 NOV 6, 1956 T. w. DUNCAN DEF'ROSTING EVAPORATORS 6 Sheets-Sheet 5 Filed July 2, 1955 Nov. 6, 1956 T. w. DUNCAN DEFRosTING EvAPoRAToRs 6 Sheets-Sheet 4 Filed July 2, 1955 Nov. 6, 1956 6 Sheets-Sheet 5 Filed July 2, 1953 ISCHARGE COHPKE550R LINE INVENTOR.

Filed July v 2, 1953 6 Sheets-Sheet 6 ln* l l i l t dv 1) L 1 INVENTOR. of/zza WMM WW United States Patent O DEFROSTING EVAPORATORS Thomas W. Duncan, Bedford, Ind., assignor, by mesne assignments, to Whirlpool-Seeger Corporation, a corporation of Delaware Application July 2, 1953, Serial No. 365,694

6 Claims. (Cl. 62-3) The present invention relates to defrosting evaporators, and is particularly concerned with an improved form of defrosting evaporator of the same general type covered by the prior application of Thomas W. Du-ncan and Albert C. Rosencranz, Serial No. 242,462, filed August 18, 1951, for Automatic Defrosting Evaporators, now Patent No. 2,654,226.

One of the objects of the invention is the provision of an improved construction for defrosting evaporators by means of which the coldest part of the evaporator is defrosted last, so that the frozen articles stored therein are subjected to the least amount of heat.

Another object of the invention is the provision of an improved evaporator of the type in which the refrigerant may be caused to circulate during the defrost part of a cycle by the action of heat applied at a particular area of the evaporator, heating the refrigerant which is then circulated throughout the entire 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 evaportor 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 quickv ly 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 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 s'helf for freezing ice cubes and a relatively large frozen food storage space equally adaptable tothe storage of frozen food, or the initial freezing of the food, which is Vsimple 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 Vthe accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views. Y

Referring to the drawings, of which lthere are six sheets accompanying the specification,

ICC

Fig. l is a fragmentary front elevational View of a r'efrigerator cabinet equipped with an evaporator embodying the invention with the evaporator door removed;

Fig. 2 is a fragmentary side elevational view of the upper part of the refrigerator equipped with such an evaporator;

Fig. 3 is a top plan view of the evaporator;

Fig. 4 is a side elevational view taken from the bottom of Fig. 3;

Fig. 5 is a fragmentary rear elevational view of the evaporator;

Fig. 6 is a front elevational view of the evaporator door;

Fig. 7 is a side elevational View of the evaporator door;

Fig. 8 is a fragmentary section taken on the plane of the line 8 8 of Fig. 2;

Fig. 9 is a diagram of the refrigeration system ernployed in the evaporator;

Fig. l0 is a wiring diagram of one form of control for the defroster.

Referring to Figs. l Vand 2, 10 indicates in its entirety a defrosting evaporator embodying the invention, which is shown installed in a refrigerator cabinet 11, having an outer shell 12, and an inner liner 13 separated from the outer shell by insulation 14.

The cabinet is provided with an inwardly turned facing ilange 15 on its outer shell surrounding a door opening 16, and the opening is closed by a suitable insulated door 17, having an inner panel 18 and an outer panel 19, separated by insulation 20.

The door carries a suitable resilient seal 21, engaging the facing llange 15, all around the door opening a-nd assuring an airtight closure.

The evaporator 10 may be wide enough laterally to occupy substantially the full width of the upper part of the cabinet, and may comprise a rectangular sheet of aluminum which is bent to form a substantially U-shaped member having side walls 22 and 23, joined by easy bends 24 and 25 to the integral bottom wall 26.

Evaporator walls 22 and 23 are ben-t backwardly upon themselves at their upper edges to form a smooth upper edge 27, by means of the backwardly bent flange 28.

At the front edge the side walls 22 and 23 are also bent backwardly at the llange 29, the bend forming a smooth front edge surface 30 which also extends across the front edge of the bottom 26. The flanges 28 and 29 are mitered at 31, where they meet at the top front corner, Fig. 2.

While the blank sheet of which the evaporator is made is substantially rectangular, the side walls 22 and 23 are preferably slightly longer at the back, making the side walls trapezoidal, causing the bottom 26 to slope downward toward the back when the evaporator is installed with its upper edges in horizontal position in a cabinet having a horizontal liner top 34.

Upper edges of the two side walls are provided with pairs of angle brackets 32, 33, one flange of which is riveted to the side walls of the evaporator, and the horizontal flange of each bracket is secured to the top wall 34 of the liner.

The liner may have four evaporator hanger supports Welded on the outside of the liner above the brackets 32, 33. Each hanger support comprises a strip of steel with an easy bend to fit the corner of the liner, and having a threaded tubular formation 32a for receiving screw bolts passing through the brackets and through a registering hole in the liner.

Thus the evaporator may be installed with its top edges substantially horizontal and its bottom wall 26 and its shelf both sloping downward toward the back, and the top of the liner closes the top of the evaporator.

The back of the evaporator is preferably closed by means of a back plate 35 of aluminum, comprising a plate of sufficient size to cover the back, the plate being provided with forwardly extending attaching flanges 36, 37, for each side wall, and being secured to the side walls by means of a plurality of rivets 3S.

A bottom attaching llange 39 also engages below the bottom wall 26 and assures a substantial closure of the rear side of the evaporator. 35 conforms substantially in shape to the U-shape of the evaporator with its rounded corners 24, 25 about which the attaching lianges fit sinuously.

At its upper edge the back plate 35 may have a rear- The rear evaporator plate wardly turned horizontal ange 40 engaging the top of the liner. The upper edges of the side walls and back plate of the evaporator have a substantial lit against the walls of the liner so that the top of the evaporator is closed by the liner.

The side walls 22 and 23 of the evaporator support an upper shelf 41, which is preferably spaced from the top of the evaporator by a distance suitable for receiving ice trays.

The shelf is substantially rectangular in shape, having a length corresponding to the width of the evaporator and having a front to back width corresponding to the front to back depth of the evaporator.

At each side the shelf 41 is provided with a depending attaching flange 42, which is secured by rivets 43 to the side walls 22 or 23. At its back edge the shelf 41 is Y provided with an upwardly extending attaching flange 44 engaging the inside of the back` panel 35, to which it is secured by rivets 45.

At its forward edge the Shelf 41 is provided with a depending ange 46, having its edge backwardly turned at 47. The depending and backwardly turned flange 46, 47 gives the shelf a more substantial appearance and presents a blunt or flat forward facing, and also conceals the coils from an observer whose eyes are substantially at the level of the shelf or above the shelf.

The back panel 35 may be provided with a multiplicity of circular apertures 48, located at the bottom level 26 so that any moisture collecting on the bottom 26 will drain downwardly and backwardly out of the apertures 48.

The side wall 23 is preferably formed with an elongated, oval aperture 49, having parallel upper and lower edges 50 and 51, and rounded end portions 52 adjacent a stamped partially cylindrical groove 53 and groove 54.

In order to drain the shelf, the back panel is provided with a plurality of shelf drain apertures 48a, located just above the shelf level.

The front groove 53 terminates in a rounded end 55, short of the front edge of the evaporator, but the rear groove 54 may extend to the back edge of the side wall 23. The purpose of the oval aperture 49 and grooves 53, 54 is to house a receiver or header 56, which is substantially complementary in its diametrically located outline from end to end.

The header 56 comprises a substantially cylindrical aluminum tube 57, which has its tapered end portions 5S and 59 spun inward to provide a substantially tubular conduit 69 at the rear end and to provide a closure 61 at the front end.

rl`he receiver 56 is provided with spaced integral diametrically located attachment anges 62 at the top, and 63 at the bottom. These attachment flanges engage the outside of the side wall 23 when the receiver is disposed in the oval aperture 49, and the attachment anges are riveted to the side wall 23 by rivets 64, 65.

The receiver 56 is provided with a suction tube 66, which extends into its top wall and terminates at 67, close to the inside of the top wall for sucking olf vapor which will be located at the top of the receiver above any liquid refrigerant in the receiver.

The suction tube 66 extends parallel to the top of the receiver 56 at 63, and at the rear end of the receiver it is bent and provided with a downwardly extending portion 69, and with a forwardly extending portion 70, leading to the inlet of the compressor which is used to supply the evaporator with liquid refrigerant and which draws olf the refrigerant vapor.

The sides and bottom of the evaporator are provided with sinuous coils 71, 72, 73, Figs. 2 and 4. For example, the sinuous coils 71 may communicate with the inside of the receiver 56 at 74, from which the coils '71 extend backward at 75 and have a hairpin bend at 76. They extend forward and downward at 77, and have a hairpin bend at '78 and extend backward and downward at 79.

At the coils 71 are bent downward and are bent under the bottom at 81. The coils extend sinuously back and forth from side to side across the bottom at 72, with the same easy bends adjacent each side wall, terminating at the bottom, near its front edge at 82, where the coils are curved upwardly at 83 on the outside of the side wall 22.

Here again the coils 73 extend horizontally at 84, have an easy bend at S5, horizontally at 86, with an easy bend at 87. horizontally at 8S, with an easy bend at 89, and a horizontal portion at above the shelf 41.

The arrangement and distribution of these coils is such that every part of the side Walls has contact with some of the coils in proportion to the amount of frost which is likely to gather thereon, and when the coils contain heated refrigerant they effectively melt all of the frost from the side walls and bottom.

At 91 the side coils 73 are bent downward with a diagonal portion 92 that extends to an aperture 93 in the side wall 22, near its rear edge so that the coil may extend into the evaporator for arrangement on the lower side of the shelf.

The coils on the bottom of the shelf have been indicated in their entirety by the numeral 94, and beginning at the aperture 93, Fig. 3, the shelf coils include a straight pass 95, adjacent the front ange 46 of the shelf for eX- tending the cooling action and melting action well forward on the shelf.

Thereafter the coil on the bottom of the shelf has an easy bend at 96, a parallel lateral pass at 97, easy bend at 98, and another side to side pass at 99. This leads to an easy bend at 1119 and a straight side to side pass 191, an easy bend at 102, and a straight pass 1113, which stops short of the side wall 23 at a U-shaped easy bend 104, from which there is a straight pass 195 extending laterally of the bottom of the shelf adjacent the rear panel 35 and passing through the side wall 23 at an aperture 106.

From the aperture 106 the tubing is bent downward of the side wall 22, Fig. 4, and has a straight pass downward indicated at 107. The straight downward pass 107 is bent at 108 to conform to the curvature of the shell and extends inwardly along the bottom of the evaporator at 109, with a Asubstantially straight pass which is bent backwardly at 110, leading to a backwardly and downwardly extending diagonal portion 111.

The tube is bent downward at 112 and communicates with a vertically extending portion 113. This extends to a U-shaped bend 114, which has an upwardly extending short tube 115. Tube 115 communicates with a tubular extension 116 of an enlargement or receiver 117, which extends parallel to the tube 113.

Receiver 117 comprises a tubular member having its end portions spun down to be tapered at 118 and pro* vided with the tubular formations 116 and 119. The upper tubular formation 119 is connected by a diagonal portion 120, with a laterally ex-tending pass 121, Fig. 3 at the bend 122.

' The laterally extending pass 121 extends across the bottom to .the side 23, and is provided with an easy bend at 123 and extends upward at 124.

The upwardly extending portion 124 is shown in Fig. 2

toward the rear wall 35, and it extends upward on the side wall 23 to the point 125, whereit is .bent at an obtuse angle having a diagonally extending portion 126 to permit an easy bend at 127, leadingto'the horizontal portion 128 which extends into` the tubular endv 129 of the receiver 56.

Thus the depending legs 113, 117 extend on the right side of the evaporator up to the receiver 56,' and on the left side of the evaporator the leg 113 extends over across the bottom and upward to the shelf. l

The enlargement `117 is provided 'with an integral metallic clamping member 130, which may also comprise a member welded or brazed tothe enlargementv117 of substantially U-shape for receiving and clamping about a tubular, metal encased electrical resistance used as a heater. Such electrical heaters include a resistance wire which is surrounded and insulated by a heat resistive powder and which may be encased with an aluminum or copper tubing.

A thermostatic switch has its bulb attached to the leg 113 near the top of the leg land adjacent the electric heater 130g, for the purpose of cuttingoif the electricheater and restoring the `system to normal refrigeration control when the bulb reaches a predetermined temperature.

Ordinarily defrost may be terminated by this switch when the circulating hot refrigerant which goes up the leg 117 has traversed the entire evaporator and arrived in a hot condition at the bulb 113a at sufficient temperature to raise the bulb to lthe cutoff temperature.

At this time the entire evaporator will have been heated sufficiently to melt ol all the' frost. In the case of a failure of circulation of the refrigerant, the bulb may be sufficiently heated by conduction and radiation from the heater 130g, due to its proximity to the`heater, to cut otf `the electric heater before any damage is done.

The bulb 113:1 is connected by a small bore to a bellows which actuates a switch'and is preferably charged with a sub-atmospheric charge of refrigerant or other volatile gas so that in the event thebulb is punctured the natural resiliency of the bellows willcause it to lexpandldue to the admission of air pressure and'the'expanding bellows ywill cutotftheheater. f. 1 ,w `m- Y The mode of securing the control bulb to the leg3113 is shown in Fig. 8. A pair of two-part clamps 150 are employed and the clamping :members are heat insulated from the leg 113 and the bulb 113a `by a -layer vof heat insulation such as aber sheet. f f1 Clamping members 151, 152 have partially cylindrical formations at each end of the' proper size'to engage the leg 113 and the bulb 113a.- l, Y

Screw bolt 153 passes through the clampingmernber 151 and is threaded into a tubularformationin clamp 152, but is kept out of 'contact with the heater. The heat insulation provides a suitable time lag betweenvthe heating of leg' 113 and the heating of bulb `11311. v

The electric heater 130e is preferably of the type having an electric heating element which is insulated by a heat resistive powder from an outer tubularVcasing-which may be made of copper or aluminum. v u Y The clamp 130 is bent tightly about such a metal clad electric heater for maximum heatrconduction of heat ,to the enlargement 117 and theliquidrefrigerant,contained therein. Y Y. Q l

Theinlet to the evaporator from .the compressor, condenser and capillary tube is indicated Vby the capillary end 131 of the inlet tube 132, extending'horizontally on the side23, Fig. 2. Y Y

This inlet extends behind theevaporatorwhere it is curved laterally and upwardly at 133, having aportion 134 extending upward to the` shelf level, whereitis curved forwardly toward the shelf at 135, Fig.r2. n

The inlet tube extends through the back wall at 136, Fig. 3, and forwardly to theV curve 13 7," whichturns `'the tube toward the easy.bend,104, V 'y ,y

A short portion 138 extends totlrefeasybendJ104, where the tube 138 may be tapered at 139;.t0'a capillary ,end which communicates at 140 with the tube 104 at the U-shaped bend. Thus the refrigerant is introduced into the tubing of the shelf adjacent .the rear wall, and it travels in two parallel paths as follows:

d From the inlet 140 the refrigerant travels forwardly across the bottom of the shelf, as indicated by the arrows, through the tubing portions 103, 102, 101, 100, 99, 98, 97, 96, 95, 92, 91 and 90.

Thereafter the refrigerant in this path passes down the sinuous coils 73, Fig. 4, as follows:

90, 89, 88, 87, 86, 85, 84, 83, to the bottom coils 72 of the evaporator, beginning at 82. From the point 82 the refrigerant passes sinuously back and forth from side to side across the bottom of the evaporator in the coils 72, ending at 81, Fig. 4, Fig. 2.

From 81 the refrigerant passes upward through coils 80, 79, 78, 77, 76, 75, entering the receiver 46 at 74.

The other parallel path of the refrigerant from the inlet point 140 extends across a rear pass 105, below the shelf, emerging at 106 and extending downward at 107 to the bottom 26, inward across the bottom at 109 to the point 110, backward at 111, downward at 112, downward in leg 113, turning upward lagain at 114, 115, through enlargement 117, upward at tube 120, bending laterally at 110, across the bottom to the side 23 at 121, upward at 123, upward at 124, 125, 127, and into the receiver 56 at 128.

, The brackets 32, 33 for the top of the evaporator have their upper anges provided with rearwardly open slots 141, Vso that depending headed fasteners carried by the liner may be received in the slots 141 as the vevaporator is pushed backwardly into the liner.

The rear wall 142 of the liner is preferably formed with a pressed groove 143 of suicient size to receive the legs 113, 117, and the heater and these are covered in the groove 143 by means of a cover plate 144.

The groove 143 in the liner is provided with a plurality of bowedmetal straps 154, secured tothe liner inthe groove at each end rivets, for engaging the U-shaped legs 113, 117 and spacing them from the liner in the groove to minimize the transmission of heat to the liner during defrost.

The cover plate 144- may consist of an elongated substantially rectangular molded plastic member formed on its back side with a longitudinally extending groove `156, and providedat its top with an open top funnel 157. The cabinet may be provided with a suitable drip tray, larger in area than the bottom of the evaporator for receiving 'dr'i'ppage from the evaporator and discharging the water from a rear spout.

The funnel 157 is adapted to receive condensate which comes from the discharge spout and runs down the groove v143 to the bottom of the liner. The water runs out of a drain in the bottom of the liner into a suitable evaporation pan (not shown) below the cabinet, where it is evaporated into the surrounding air.

The front of the evaporator is preferably closed by means of an inner evaporator door 158. The evaporator door 1'58 may consist of a substantially rectangular molded plastic member provided with an inwardly extending border flange 159, all about its edge and with a separate handle 160 projecting downward on the front 0f the door and secured to the door by an `angular attaching flange 161 and screws 162.

The inside of the door 158 may be closed by means of a back panel, having inwardly extending border anges A164, the two border anges being secured together by a plurality of screws 165, thus providing a head air space inside the doorf158.

The` back panel 163 may have a pair of circular holes 166 for receiving circular rubber bumpers 167, the head 16S of which lies on the inside of the door in position to engage the front side edgesof the evaporator.

TheV rubber bumper167 has a reduced shank fitting` in the hole 166, and a smaller pointed head 169 which may be forced through the hole 166 until the back panel is located between the two heads 168 and 169 to secure the bumpers in place.

The door is provided on each side adjacent the lower edge with a stop bracket 170, secured to the door edge by a plurality of screw bolts 171, and having an outwardly turned flange 172 to act as a stop by engaging a hinge bracket 173 when the door is open at substantially horizontal position.

Stop bracket 170 also serves as a hinge arm and has an aperture registering with an aperture in the border flanges 159 and 164 for receiving the trunnions 174. Trunnions 174 are carried by the hinge brackets 173 by having a reduced end riveted over at 175, outside the hinge bracket.

The hinge brackets 173 have a body 176 for supporting the trunnions, an offset at 177 and an attaching ange 17S, which is secured to the liner wall. Thus the door 158 is pivoted on the liner wall and is preferably of sufricient width to cover not only the evaporator but the space between the evaporator and the liner, substantially closing the upper front of the liner at the evaporator.

The door trunnions 174 are preferably provided with axially extending diametric slots 179 and a torsion spring wire 180 extends from end to end of the bottom of the door, and has a V-shaped portion 181 at each end anchored against rotation in the slots 179.

The extreme end 182 of the wire extends into a bore in the trunnion 174. The torsion wire 180 is bent upward to the point 183, where it is bent downward and provided with an open U-forrnation 184, which is anchored xedly to the door by means of a bracket 185 and a screw bolt 186.

The U-shaped formation 184 turns with the door while the V-shaped formations 181 are held fixed by the trunnion slots. Spring 180 is under initial torsion, tending to hold the door closed when it is closed and its tension is increased when the door is opened through 9() degrees, but is not suiiicient to close the door from the fully open position.

The details of the door are not of my invention and any suitable type of evaporator door may be used.

The refrigerating system of the present refrigerator is shown in Fig. 9. It includes a motor compressor 187, having an upper motor housing 188, joined to a lower oil sump 189, surrounding a motor compressor 190, directly driven by the motor shaft. Y

The outlet 191 of the compressor is connected by conduit 192 to the coils 193 0f a separate precooling condenser section having heat dissipating tins or wires 194.

The precooler coils 193 are connected by conduit 19S to the top of the motor housing to carry back the partially cooled and condensed refrigerant and oil to the top of the motor housing, where it drains down through the motor parts, the oil settling in the oil sump 189.

There is some revaporization of refrigerant in the motor housing in cooling the motor parts 196. The refrigerant passes from the top of the motor housing 188 by conduit 197 which leads to the main condenser coils 198, which may be provided with heat dissipating fins 199 or wires or may be any other suitable form of condenser.

From the main condenser coils 193, the now liquid refrigerant may pass through a drier 200 and through a capillary tube 131 to the inlet of the evaporator, indicated at 140.

The course of the refrigerant through the evaporator has already been described in two parallel paths which lead to the receiver 55.

The suction tube 66 extends from the receiver 56 to the inlet 201 of the motor compressor.

Referring to Fig. lO, this is a wiring diagram of one form of manual control for the refrigeration system. In this diagram 187 indicates the motor compressor, which is usually of the induction type having three conductors 202 CFI ' 8 leading to a starter switch 203 for controlling starting windings and running windings.

One conductor 204 leading from the starter switch passes through the usual thermostatic controlling switch 205, 206, having a bulb mounted on the evaporator shelf and adapted to start the motor compressor whenever the shelf rises above a predetermined temperature, which is always below freezing.

The thermostat, usually called the cold control, is connected by conductor `207 with the refrigeration contact 210 of a defrost control switch. The defrost control switch has a movable cotnact arm 209, which is shown in the heater position engaging heater contact 20S. Y

Contact arm 209 is connected by a conductor 211 to the usual llO volt lighting circuit. The heater contact 208 is connected by conductor 2,12 to the heater coil a, the other end of which is connected to the other line conductor 213.

The line conductor 213 also extends to the starter switch 203. Themovable contact arm 209 may be moved by a plunger 214 against spring 215 to the heater position as shown, where it-may be latched by a latching lever 216 pivoted at 217, and urged into latching position by spring 218. Y

A ther-mostatic bellows 219 isl connected by a capillary tube 220 to the bulb 11341,v which is fastened to the leg 113 of the evaporator. Thus the defrost may be initiated by pressing on the plunger 214 manually compressing the spring 215, and latching the plunger in the heater position.v

When the bulb113a is heated sufficiently the thermostat 219 will unlatch the plunger 214 and cause it to move back into engagement with the refrigerator contact 208, cutting out the heater 130e: and restoring the system to controlI of the usual cold control thermostat 205, 206;,

The operation of the system is as follows: When the cold control thermostat 205, 205 has its bulb elevated at temperature toa predetermined point, which is still below freezing, the motor compressor is started and it compresses refrigerant which is carried away from the motor compressor 187 to a condenser precooling coil 193, where it is partially condensed and returned to the top of the motor housing.

The refrigerant then passes from the top of the motor housing to the main condenser 198 where it is condensed and passed through the drier 200 and through the capillary tube to the evaporator inlet at the rear of the evaporator shelf.

The refrigerant passes in two parallel paths through the evaporator, the rst path being forwardly through the sinuous coils of the shelf which are cooled to an ultra below-freezing temperature capable of maintaining frozen food in a frozen condition at all times.

From the shelf front end the refrigerant passes outwardly to the left side of the evaporator and down the sinuous coils to the bottom. It then passes through the sinuous coils on the bottom of the evaporator and upward through sinuous coils on the right side of the evaporator to the receiver 56.

The other parallel path from the evaporator inlet 140 is across the evaporator shelf through a straight pass 109 downwardly through tubing 107, on the left side of the evaporator, to the depending evaporator leg 113, upwardly in the leg 117 and across the bottom of the evaporator at 121, and upwardly through conduit 125 to the receiver 56.

The refrigerant vapor is pumped off the top of the receiver 56 through suction tube 66, which leads back to the inlet of the motor compressor 187.

When itis desired to defrost the evaporator, all parts of which are preferably maintainedy at a below-freezing temperature,'the user may push the plunger 214, moving the defrost switch arm 209' to break the contact 210 and engage the contact 208, which closes the circuit through the heater 13011. This stops the motor compressor during defrosting by breaking the motor compressor circuit, and the defroster contact arm 209 is latched in the heater closed position.

The heater 130a by heat conduction heats the refrigerant in the enlarged tube 117, causing it to boil upward and to circulate up the tube 121, 124, 126 to the receiver 56. Hot refrigerant may run down from receiver 56 through the sinuous tubing on the right side of the evaporator, shown in Fig. 2, through the sinuous tubing 72, on the bottom of the evaporator, and up the sinuous tubing 73 on the left side of the evaporator.

From thence the hot refrigerant passes into the tubing on the evaporator shelf which communicates with the downwardly extending leg 113, leading the hot refrigerant back to the heated leg 117.

As the hot refrigerant circulates it heats the evaporator coils and adjacent evaporator casing, which are progressively heated until they melt all the frost from the evaporator. When the refrigerant is still hot at the time it arrives at the upper part of the tube 113, it heats the bulb of the cutoff thermostat 219, which expands and unlatches the latch 216, permitting the spring 21S to move the plunger back to the refrigeration contact and breaking the heater circuit at the heater contact 208.

In the event of a failure of the circulation of refrigerant the bulb 112m is, nevertheless, heated by radiation due to its proximity to the heater, the upper end of which is the hottest, and the heater circuit is broken before the evaporators or other parts are so overheated that they may become damaged.

In the event of failure of the thermostat 219 by a puncture or loss of its volatile uid, this thermostat is preferably filled with refrigerant at subatmospheric pressure so that the air will leak in and cause it to expand and cut off the heater in this event also.

Thus the present system is safe against damage to the evaporator by overheating by the electric heater element. When the defrost is terminated the system is again` restored to the normal coldcontrol thermostatic switch 205, 206, and refrigeration proceeds as before.

The shelf is the last part to be heated and defrosted so that frozen food inside the evaporator is subjected to a minimum amount of heat, and the defrost is accomplished so quickly that the frozen food is not melted or heated to any appreciable extent.

It will thus be observed that I have invented an improved defrosting evaporator and an improved defrosting refrigerator and refrigeration system, in which heat is applied to depending tubing connected with the tubing of the evaporator in such manner as to cause the circulation of hot refrigerant throughout the evaporator until all the frost is melted from the evaporator and the freezing shelf is last to be defrosted so that the adjacent contents are subjected to a minimum amount of heat.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a defrosting system for a household refrigerator, the combination of an insulated cabinet, comprising an outer metal shell, an inner liner, and insulation between them, said cabinet having a door opening, and an insulated door, an evaporator comprising a substantially U-shaped metal casing provided with a transverse freezing shelf, said evaporator being supported from the top of the liner, below freezing coils on the bottom of the shelf for producing an ultra-below freezing zone above the wasn shelf, below freezingcoils'on the sides and bottom of said casing for cooling the space outside said evaporator to an above-freezing temperature, and the space inside the evaporator, below the shelf, to a below-freezing temperature, and a depending U-shaped leg of tubing connected to said coils, and having an electric heater applied to one of the branches of said U-shaped leg, for heating the refrigerant and causing it to circulate upward in the heated branch and downward in the other branch, the hot refrigerant heating all the evaporator coils and casing and melting the frost on them, and a cut-off thermostatic switch in circuit with said electric heater, and having a bulb connected to the unheated branch adjacent said heater, to be heated by conduction and radiation in the event of a failure by circulation of the refrigerant, said bulb being secured to said unheated branch by opposed clamping members, and a layer of insulation interposed between the said clamping members and said bulb and branch to produce a time lag in the heating of said bulb by radiation and conduction from said heater.

2. In a defrosting system for a household refrigerator, the combination of an insulated cabinet, comprising an outer metal shell, an inner liner, and insulation between them, said cabinet having a door opening, and an insulated door, an evaporator comprising a substantially U-shaped metal casing provided with a transverse freezing shelf, said evaporator being supported from the top of the liner, below freezing coils on the bottom of the shelf for producing an ultra-below freezing zone above the shelf, below freezing coils on the sides and bottom of said casing for cooling the space outside said evaporator to an above-freezing temperature, and the space inside the evaporator, below the shelf, to a below-freezing ternperature, and a depending U-shaped leg of tubing connected to said coils, and having an electric heater applied tov one of the branches of said U-shaped leg, for heating the refrigerant and causing it to circulate upward in the heated branch and downward in the other branch, the hot refrigerant'heating all the evaporator coils and casing and melting the frost on them,said casing having a rear wall closing the rear of the evaporator, said rear wall having drainage apertures at the shelf level and the bottom level of said evaporator, for draining condensate.

3. In a defrosting system for a household refrigerator, the combination of an insulated cabinet, comprising an outer metal shell, an inner liner, and insulation between them, said cabinet having a door opening, and an insulated door, an evaporator comprising a substantially U-shaped metal casing provided with a transverse freezing shelf, said evaporator being supported from the top of the liner, below freezing coils on the bottom of the shelf for producing an ultra-below freezing zone above the shelf, below freezing coils on the sides and bottom of said casing for cooling the space outside said evaporator to an above-freezing temperature, and the space inside the evaporator, below the shelf, to a below-freezing temperature, and a depending U-shaped leg of tubing connected to said coils, and having an electric heater applied to one of the branches of said U-shaped leg, for heating the refrigerant and causing it to circulate upward in the heated branch and downward in the other branch, the hot refrigerant heating all the evaporator coils and casing and melting the frost on them, said casing having a rear wall closing the rear of the evaporator, said rear wall having drainage apertures at the shelf level and the bottom level of said evaporator, for draining condensate, said casing having its side walls slightly longer in a vertical direction at the rear of the evaporator, causing a downward tilt of the shelf and the bottom toward the rear drainage openings.

4. In a defrosting system for a household refrigerator, the combination of an insulated cabinet, comprising an outer metal shell, an inner liner, and insulation between them, said cabinet having a door opening, and an insulated door, an evaporator comprising a substantially U-shaped metal casing provided with a transverse freezing shelf, said evaporator being supported from the top of the liner, below freezing coils on the bottom of the shelf for producing an ultra-below freezing zone above the si ei, below freezing coils on the sides and bottom of said casing for cooling the space outside said evaporator to an above-freezing temperature, and the space inside the evaporator, below the shelf, to a below-freezing temperature, and a depending U-shaped leg of tubing connected to said coils, and having an electric heater applied to one of the branches of said U-shaped leg, for heating the refrigerant and causing it to circulate upward in the heated branch and downward in the other branch, the hot refrigerant heating all the evaporator coils and casing and melting the frost on them, a drip pan carried by the liner Walls under said evaporator for receiving con- .,sate from the evaporator, said pan discharging into a funnel carried by the rear wall of the liner, said rear w 'i having a pressed groove for receiving said leg and Mtl tonnel discharging into said groove.

5. In a defrosting system 4for a household refrigerator, the combination of an insulated cabinet, comprising an outer metal shell, -an inner liner, and insulation between them, said cabinet having a door opening, and an insulated door, an evaporator comprising a substantially U- shaped metal casing provided with a transverse freezing shelf, said evaporator being supported from the top of the liner, below freezing coils on the bottom of the shelf for producing an ultra-below freezing zone above the shelf, below yfreezing coils on the sides and bottom of said casing for 4cooling the space outside said evaporator to an above-freezing temperature, and the space i11- side the evaporator, below the shelf, to a below-freezing temperature, and a depending U-shaped leg of tubing connected to said coils, and having an electric heater applied to one of the branches of `said U-shaped leg, for heating the `refrigerant and causing it to circulate upward in the heated `branch and downward in the other rbranch, the hot refrigerant heating all the evaporator coils and casing and melting the frost on them, a drip pan carried by the liner Walls under said evaporator for receiving condensate from the evaporator, said pan dischargingpinto a funnel carried by the rear wall of the liner, said rear wall lhaving a pressed groove for receiving said leg Iand said tunnel discharging into said groove, and a cover for closing the front of said groove and covering said leg.

6. In a defrosting system for a household refrigerator, the combination of an insulated cabinet, comprising an outer metal shell, `an inner liner, and insulation between them, said cabinet having a door opening, and an insulated door, an evaporator comprising a substantially U- shaped metal casing provided vvith a transverse freezing shelf, said evaporator being supported from the top of the liner, 'below freezing coils on the bottom of the shelf for producing an ultra-below Ifreezing zone above the shelf, below freezing coils on the sides and bottom of said casing for cooling the space outside said evaporator to an above-freezing temperature, and the space inside the evaporator, below the shelf, to a below-freezing temperature, and a depending U-shaped leg of tubing connected to said coils, and having an electric heater applied to one of t-he branches of said U-shaped leg, for heating `the refrigerant and causing it to circulate up-ward in the heated branch and downward in `the other branch, the hot refrigerant heating all the evaporator coils and casing and melting the frost on them, said liner having a vertically extending pressed groove in its rear wall, and said U-shaped leg extending rearwardly to said groove and vertically in saidl groove of said liner and conveying condensate along lthe tubes down said groove, and a cover member `for said groove, said cover including an upper funnel formation, and Iforming a conduit for condensate in said groove.

Atchison Aug. 4, 1942 Duncan et al. Oct. 6, 1953

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