US2876630A

US2876630A - Refrigeration system including defrosting apparatus

Info

Publication number: US2876630A
Application number: US489074A
Authority: US
Inventors: Boling Cecil
Original assignee: Dunham Bush Inc
Current assignee: Dunham Bush Inc
Priority date: 1955-02-18
Filing date: 1955-02-18
Publication date: 1959-03-10
Anticipated expiration: 1976-03-10

Description

Man-ch10, 1959 c. BOLING 2,876,630 4 REFRIGERATION SYSTEM INCLUDING DEFROSTINC APPARATUS Filed Febjls, 1955 /08 I k? g4, 2

INVENTOR eel ll B06611;

, ATTORN s 5 Sheets- Sheet 1 March 10, 1959 C. BOLING REFRiGERATION SYSTEM mcwnmc DEFROSTING APPARATUS Filed Feb. 18, 1955.

5 Sheets-Sheet 4 lg l March 10, 1959 c. BOLING 2,876,630 I REFRiGERATION SYSTEM INCLUDING'FDEFROSTING APPARATUS} l' i led Feb. 18, 1955 5 Shegts-Sheet 5 ATTORNE Unite REFRIGERATION SYSTEM INCLUDING DEFROSTING APPARATUS Application February 18,1955, Serial N 0. 489,074

12 Claims. (Cl. 62-234)" This" invention relates to refrigeration, andr'n'ore in particular to defrosting refrigeration systems of the-type which are adapted to maintain refrigerated compartments at low' temperatures, for example, considerably below freezing. 7

An object of this invention is to provide refrigeration systems which may be defrosted in an improved manner. Another object is to provide refrigeration systemsgwhich a re'superior to prior systems for certain types of applications and which are adaptable to various conditions of nseand ope'ration'. A further objectis to provide an improved arrangement for defrosting low temperature evaporaters. A still further object'is to provide refrigeration systemswhichare defrosted with the use of hot refrigerant in an improved manner. A further object is to provide such systems which-require the use of a' minimum numberof components and parts. A further objectis to provide systems of the above character which occupy minimum space and which are provided with components which arestur'dy in construction, efiicient and dependable in' use, and which are adaptable to meet various demandsand'practice's. These and other objects will be in part obvious and in part pointedout below.

In the drawings:

Figure 1 is a somewhat schematic representation of one ernbodinient'of the invention; I

Figure 2 is" a rear elevation of the evaporator assembly ornigure' 1; v

Figure? is a side'elevation of the assembly of Figure 2;

Figure 4 is a sectionalview with the central portion broken away on the line 44 of Figure 3;.

Figure 5 is a' side elevation of the evaporator unit of Figure 4 with the associated parts;

Figure 6 is a sectional view on the line 6-6 of Figure 4; I, Figure-7 is a" schematic representation of the refrigerant flowiri" thes'ystern of Figure 1 during. the defrostingopstation; and,

States Patent 0 I 2,876,630 Patented Mar. 10, 1959 through a line 32 anda constant pressure expansionvalve 34 to line. 19.

EvaporatorZDis constructed, as shown best in Figures 4,5, and 6 of three vertical rows. of evaporator tube as semblie's-36 which are identical in construction. Each of the'tubeassemblies'36 is formed by an outer tube'38 (see also Figure 8') an inner tube wand an internal fin assembly 42. Hence, each tube has an internal refrigerant passageway 44 within tube 40 and an annular refrigerant passageway 46 between tubes 38 and' 40, and the fin assembly 42 is positioned" within this annular passageway.

An external fin assembly 48 is provided ontubes'38. This.

assembly of

tubes

38 and 40 and finas'sem'bly 42 is'constructed in accordance with the disclosure of my copending'ap'plication, Serial No. 310,820, filed September 22, 1952, and incorporates certain features of the iniventions of my prior U. S. Patents Nos; 2,611,585 and 2,611,587. The fin assembly comprises a corrugated strip of sheet metal positioned spirally in space 46, and after assembly of tube 4il'a'nd fin assembly 42 within tube38, the inner'tube 4i isexpanded to place the fin assembly under uniform'radial compression between the concentric tube walls. Hence, good heat transfer relationships are provided between fluids in each of the passageways 44 and 46and the external fin assembly 48. The heat transfer'relationship between. the fluid in passageway 46 and the external fin assembly is through the internal fin assembly 42 and tube38, and the fluid in passageway'44 is in good heat transfer relationship through tube 40 with fin assembly'42, and thence through tube 38 to the fin assembly 48. Hence, refrigerant in either of passageways 46 or 44'isin good heat transfer relationship with the external fin assembly.

As indicated above, in this embodiment of the invention three vertical rows of tube assemblies 36 are arranged in eight horizontally positioned groups of three tubes each. For convenience, the vertical rows are indicated at 50, 52, and 54', and the eight horizontal rows are indicated at 56, 58, 60, 62, 64, 66, 68, and 70. The refrigerant distributor assembly 24 has four

distributor tubes

72, 74, 76;, and 7 8 ext'endingLto the tube assemblies 36in the left-hand" vertical row 56, and respectively in the alternate

horizontal rows

68, 64, 60 and 56. Each ofthese distributor tubes is connected through the wall of the outer tube 38 of its tube assembly as shown in Figure 6, so that the liquid refrigerant is delivered to the annular passageway 46. An annular cover or cap 80 closes" the Figure 8 is an enlarged sectional view on the line 88 of Figure 6. I

Referring particularly to Figure l, the refrigeration system hasa' compressor 4, a condenser 10, a receiver 12, and an evaporator 20. Compressor 4' is driven by. a motor 6, and delivers hot compressed refrigerant gas through'a line S to condenser 10. The liquid-refrigerant flo'wsfrom' thec'o'ndenser info receiver 12- which is connected' to the evaporator through a line 14,- theliquid circuit of a heat exchanger 16, a line 18, an expansion valve 22, and a line 19. The refrigerant is delivered to the" various;s.'e' ';tionsof the evaporator through a distributor assembly 24'.

The evaporator is connected through a gas returnline 26, having. the gas circuit of the heat exchanger 16-therein,

back to the compresser 4. The hot gas line 8 is connected I manner described below. Evaporator 20 is connected adjacent end of this annular passageway.

The opposite end of this annular passageway is con nected through a U-tube 82' to the adjacent end of the annular passageway in the tube assembly in the same horizontal row and in the next vertical row 52. Similarly, the opposite end of this annular passagewayis connected through a U-tube 84 to the annular passageway of the other tube assembly in that horizontal row, i. e., in the vertical row 54. The opposite end of that annular passageway'is connected through a vertical U-tube 86 (see Figure 4*) to the annular passageway in the tube assembly directly above it, i; e., in the next higher horizontal row but in-the same'vertical row 54. The three tubes of each horizontal row' have their annular passageway interconnected by a=pair of U-tubes similar to 82 and 84, as ex plained above. The end of each annular passagewaydire'ctly above the one to which a distributor tube'is attached is connected through a U'-tube 88 to a refrigerant outlet or gas header 90. Hence, the annular passageways for the two

bottom rows

56 and 58 of tube assemblies are connected in a series circuit between the liquid distributor tube-78 and a U-tube88 which discharges into header90. The annular passageways of the tube assemblies of each ofthe pairs of rows, 60" and 62, 64* and 6'6, and 68- and are similarly connected. Hence, in this embodiment,

' during the defrosting operations.

3 there are four evaporator circuits connected in parallel, receiving liquid refrigerant through the distributor tubes and discharging refrigerantfgas into header 90.

Each of the inner tubes 40 extends beyond the con nection to the annular passageway around it, and all of theseinner tubes 40 of the tube assemblies in each of the vertical rows are connected in series between a bottom header (Figures 4 and 5) 92 and an upper header 94. The bottom tube 40 opens directly into header 92, and its opposite end is connected through a U-tube 96 to the inner tube 40 of the next higher tube assembly. Identical U-tubes 96 connect each similar tube end to the next, and the right-hand end of the top tube 40 opens into the top header 94. The'circuits for the tubes 4i) in all of the vertical rows are identical Header 92 (see Figure 5) is connected directly to the hot gas line 30, and header 94 is connected through a line 32 to the constant pressure expansion valve 34 which, as indicated above, is

connected to line 19. A control tube 98 extends from header 90 to valve 34.

The entire evaporator assembly is rigidly mounted in a pair of end plates 100 (see Figures 2 and 3), and is enclosed within a casing 102. The casing is supported by a pair of channel bars 104 from which a fan motor 106 with its fan 108 is supported by a bracket 110. A cowl 112 is provided which has an opening for the passage of air which is blown through the coil by the fan. The bottom of casing 102 is formed by a drip pan 114 (Figure 3) which has an electric heater 116 therein to melt the ice and warm the water which drops into the pan A drain connection (not shown) carries away the condensate as it is melted and collected in pan 114. Air is blown through the unit from the left in Figure 3, and is deflected upwardly from the face of the unit at the right by a deflector 117.

As has been indicated above, the system is operated I to perform a cooling operation, for example, to maintain a food-storage compartment at a selected low temperature. During such operation, frost or frozen condensate in the form of ice accumulates upon the evaporator within the interstices between the fins, thus interfering with the flow of air through the coil, and also interfering with the transfer of heat from the air to the refrigerant. During this operation, refrigerant is condensed in condenser 10, and the liquid refrigerant flows to receiver 12 and thence through line 14 to the expansion valve 22. The refrigerant passes through the expansion valve and line 19 to the distributor assembly 24 which delivers equal streams of refrigerant to the four evaporator circuits of the evaporator. Each of these circuits is formed by the annular spaces 46 of six of the tube assemblies connected in series. The gas refrigerant [flows to header 90, and returns through line 26 to the compressor. During this time, motor 106 operates fan 1'08 continuously to circulate air through the coil.

' When sufficient frost or ice is accumulated upon the evaporator to interfere materially with the cooling of the air, a defrosting operation is initiated. This involves stopping the fan motor 106 so as to discontinue the circulation of air through the unit and the opening of solenoid valve 35 so as to permit the hot compressed gas to flow through line 30 directly to the evaporator. Simultaneously, the electric heater 116 in the drip pan is energized. In Figure 1, an illustrative electrical circuit is disclosed for controlling the defrosting operation.

This circuit includes an adjustable timer 120 which may be set to initiate the defrosting operation automatically at pre-determined intervals. The duration of the defrosting operation may also be controlled.

asvaoso heat from the refrigerant gas within these tubes passes radially outwardly through the tubes 40 (Figure 8), and thence through the fin assemblies 42 and tubes 38 to the fin assemblies 43. The heat thus transferred melts the ice free so that particles of ice and condensate water fall from the evaporator intothe drip pan 114 (Figure 3). The ice particles are melted and the water is somewhat warmed by the electric heater 116.

The refrigerant within tubes 40 is maintained at an increased pressure by virtue of being connected to the output or high side of the compressor, and the cooling of the refrigerant at this pressure causes it to condense. The condensed refrigerant flows through header 94, line 32, and the expansion valve 34 to line 19. From line 19, it is delivered through distributor assembly 24 to the four evaporator circuits referred to above. The refrigerant is at the reduced pressure of the low" side of the compressor so that it is evaporated in the same manner as during the cooling operation, and refrigerant gas is returned to the compressor. During this defrosting operation, the heat from the electric heater unit 116 which is not picked up by the melting ice and water tends to heat the evaporator and increases the rate of defrosting. Furthermore, the hot gas is delivered to the bottom of the evaporator so that the lower tube assemblies are heated first, and this insures that the ice and water which are freed will not be refrozen onto fin or tube surfaces.

In accordance with the present invention, the heat given off because of condensation of the refrigerant within the tube assemblies is readily transferred through the fin assemblies to the external surfaces. This heat is the heat of compression of the system, and is the heat which is dissipated through the condenser during the cooling operation. However, during the defrosting operation this heat is not dissipated but is accumulated in the evaporator, and the temperature of the evaporator gradually rises. There is some simultaneous cooling by virtue of the evaporation of the refrigerant, but the heating effect is greater than. the cooling effect so that the evaporator temperature is raised above the melting point of water. The fin assemblies 42 permit the free flow of refrigerant through them so that the spaces or passageways 46 provide for the efiicient distribution and evaporation of the refrigerant. The connecting of the herizontal rows of tube assemblies in series provides efficient cooling of the air and flow of the refrigerant. The connecting of the tubes 40 of each vertical row of tube assemblies in series provides for eflicient defrosting, even under very adverse conditions of operation.

The invention contemplates that the electric heater 116 of the embodiment of the drawings is replaced under some circumstances by a tube or line carrying hot refrigerant gas which heats the condensate and ice. The invention also contemplates replacing the constant pressure expansion valve 34 with a fixed orifice or one or more other restrictors. Furthermore, under some circumstances the hot refrigerant gas is delivered to the annular passageways 46, rather than to the internal passageways 44, and then the internal passageways act as the re-evaporator. With such an arrangement, the hot gas delivers its heat directly through the tubes 38 to the fin assemblies 48, and the liquid refrigerant is then delivered through a restrictor to the internal passageways 44. The liquid refrigerant is then re-evaporated as explained above.

The system herein disclosed provides efiicient defrost ing under varying conditions of operation. No ex ternal heat source is required, and ambient temperatures do not elfect the operation, since the evaporator and the re-evaporator are a single piece of apparatus positioned within the refrigerated space at constant temperature. Hence, the system avoids the difliculties which have been encountered with systems which rely upon external heat sources where ambient temperature variations and other conditions cause variations in the length germ-see of time required for'defrosting; It'isthus-seen that the present system-may be operated automatically, withfull assurance that the defrosting will be carried on e'fficien'tly and withoutundesirable heating of the evaporator, which could result from carrying on the defrosting operation for an excessive period of time. As many possible embodiments may be made of the mechanicalfeatures of the above invention and as the art herein described might be varied in various parts, all without departing from th'escope ofthe invention,-it is to be understood that all matter h'ereinabove set forth, or shown in the accompariying drawings is to be interpreted as illustrative and not'in a limiting sense.

1; In a refrigeration system of the character described, refrigerant condensing means comprising compressor means and condenser means, an evaporator assembly comprising a plurality'o'f tubea'ssemblies, each of which has an inner tube and an outer tube positioned concentrically with an annular space therebetween and a fin construction positioned within said annular space and maintained in heat conducting relationship with the outer surface of the inner tube and the inner surface of the outer tube, means interconnecting said inner tubes to form a first passageway circuit and interconnecting said annular spaces to form a second passageway circuit, means to supply liquid refrigerant at a reduced pressure from said condenser means to one of said passageway circuits which then acts as the evaporator space of the system, means to deliver refrigerant gas from said one of said passageway circuits to the intake of said compressor, means to defrost said evaporator by supplying hot refrigerant gas from said compressor to the other of said passageway circuits whereby the heat from the compressed gas is transmitted through said fin assemblies and thence through said outer tubes and said refrigerant is condensed, and means including restrictor means to deliver the liquid refrigerant from said other of said passageway circuits to said one of said passageway circuits at a reduced pressure whereby the liquid refrigerant is reevaporated and delivered back to said compressor.

2. A system as described in claim 1 wherein one of said passageway circuits is formed by the annular spaces of the respective tube assemblies and said other of said passageway circuits is formed by the internal passageways of the respective inner tubes.

3. Apparatus as described in claim 1 wherein said restrictor means is an expansion valve.

4. A system as described in claim 1 which includes a drip pan positioned beneath said tube assemblies and an electric heater positioned within said drip pan and adapted to be energized during the defrosting operation.

5. A system as described in claim 1 wherein each of said tube assemblies includes external fins, and wherein said evaporator assembly includes a fan which directs a stream of air into heat transfer relationship with said fins.

6. A system as described in claim 1 wherein said annular spaces are connected serially to form a plurality of parallel circuits and said inner tubes are connected serially to form a plurality of parallel circuits.

7. A system as described in claim 1 wherein said tube assemblies are positioned horizontally and there are pluralities of both vertical and horizontal rows of tube assemblies, wherein the annular spaces in the tube assemblies of each horizontal row are connected in series, and wherein the inner tubes of the tube assemblies of each vertical row are connected in series.

8. A system as described in claim 7, which includes a pair of headers through which refrigerant flows to and from said inner tubes.

9. In a refrigeration system which includes an evaporator upon which frost tends to accumulate, a com pressor, a condenser, and refrigerant lines connecting to' deliver hot refrigerant gas to said internal passage ways, and restrictor means providing a flow connection from said internal passageways to said annular passageway's whereby liquid" refrigerant condensed within said internal passageway/sis delivered to said annular'pas'sageways" at areduced pressure.

10. Iri a 1fefrigeration system of the charactefi de scribed;- refrigerant cdnde'nsingme'aiis' comprising coinpre's'sor means-arid condenser means, airevaporatoras sembly comprising a plurality of tube assemblies, each of which has an inner tube and an outer tube positioned concentrically with an annular space therebetween and a fin construction positioned within said annular space and maintained in heat conducted relationship with the outer surface of the inner tube and the inner surface of the outer tube, means to supply liquid refrigerant at a reduced pressure from said condenser means to the annular spaces between the inner and outer tubes of the respective tube assemblies, means to deliver refrigerant gas from said annular spaces to the intake of said compressor whereby said annular spaces act as the evaporator for the system, means to defrost said evaporator by supplying hot refrigerant gas from said compressor to the internal passageways formed by said inner tubes whereby the heat from the compressed gas is transmitted through said inner tubes and said fin assemblies and thence through said outer tubes and said refrigerant is condensed, and means including restrictor means to deliver the liquid refrigerant from said inner tubes to said annular spaces at a reduced pressure whereby the liquid refrigerant is re-evaporated and delivered back to said compressor.

11. In apparatus of the character described, the combination of, an evaporator assembly comprising a plurality of tube assemblies each of which comprises a plurality of concentrically positioned tubes and annular fin means therebetwecn, each of said fin means being in good heat conducting relationship with the walls between which it is positioned, said evaporator assembly including connecting means interconnecting each passageway through each tube assembly with the corresponding passageways in the other tube assemblies thereby to form a plurality of concentrically positioned refrigerant passageway circuits, means to supply liquid refrigerant at a reduced pressure to one of said refrigerant passageway circuits and to withdraw gaseous refrigerant therefrom, means to supply hot refrigerant gas to one of said refrigerant passageway circuits during a defrosting operation thereby to raise the temperature of the various tube assemblies and to condense the refrigerant, means to pass the refrigerant thus condensed at a reduced pressure through another of said refrigerant passageway circuits whereby the liquid refrigerant is i e-evaporated.

12. In a refrigeration system, the combination of, a compressor having a low pressure inlet and a high pressure outlet, a condenser connected to said high pressure outlet, an evaporator having a plurality of evaporator passageways and a plurality of defrosting passageways, said evaporator including heat conducting wall means and heat transfer surfaces providing heat transfer relationship between said evaporator passageways and air being cooled at surface temperatures whereby frost tends to accumulate, said defrosting passageways extending substantially parallel with said evaporator passageways, said evaporator including heat conducting means between said defrosting passageways and said evaporator passageways which includes said heat conducting wall means and which transmits heat from said defrosting passageways to said heat transfer surfaces thereby to defrost said surfaces, means including'pressure reducing means connecting said evaporator passageways to receive liquid refrigerant from said condenser at reduced pressure, means connecting said evaporator passageways to said low-pressure inlet of said compressor thereby to provide for the evaporation of refrigerant in said evaporator passageways, and defrosting means comprising means forming a bypass circuit from said high pressure outlet of the compressor to said defrosting passageways and thence from said defrosting passageways to said evaporator passageways, said bypass circuit including a normally closed valve which is opened to permit hot gas to flow through said bypass circuit, said system including means providing a drop in pressure of the refrigerant flowing from said defrosting passageways to said evaporator passageways, whereby the opening of said valve delivers 8 hot refrigerant gas'to said defrosting passagewaysand thereby defrosts said heat transfer surfaces and the refrigerant then passes at a reduced pressure into said evaporator passageways and is returned to said low pressure inlet of the compressor.

References Cited in the file of this patent UNITED STATES PATENTS 2,059,992 Gould Nov. 3, 1936 2,080,358 Kucher May 11, 1937 2,128,386 Warren Aug. 30, 1938 2,611,585 Boling Sept. 23, 1952 2,611,587 Boling Sept. 23, 1952 2,688,850 White Sept. 14, 1954 2,759,339 Kundert Aug. 21, 1956 FOREIGN PATENTS 676,924 Great Britain Aug. 6, 1952