US3163997A - Method of and apparatus for defrosting absorption cooling systems - Google Patents

Description

Jan. 5, 1965 H. STIERLIN 3,163,997

METHOD OF AND APPARATUS FOR DEFROSTING ABSORPTION COOLING SYSTEMS Filed July 6, 1960 4 Sheets-Sheet 1 FIG.

Jan. 5, 1965 H. STIERLIN 3,163,997

METHOD OF AND APPARATUS FOR DEFROSTING ABSORPTION COOLING SYSTEMS Filed July 6, 1960 4 Sheets-Sheet 2 Nl E/V TOR By HAX/s sr/mu/v A T TORNE V Jan. 5, 1965 H. STIERLIN METHOD OF AND APPARATUS FOR DEF'ROSTING ABSORPTION COOLING SYSTEMS Filed July 6, 1960 4 Sheets-Sheet 3 FIG. 4

l nln l I I I H INVENTOR HANS ST/ERL /N 81 A T TORNEV Jan. 5, 1965 H. STIERLIN 3,153,997

v METHOD OF AND APPARATUS FOR DEFROSTING ABSORPTION COOLING SYSTEMS 4 Sheets-Sheet 4 Filed July 6, 1960 FIG. 6'

TTORNEV //v l/ENTOR By HANS ST/ERL/N United States Patent Ofifice 3,l3,97 Patented Jan. 5, 1.5%65

3,163,;97 NETHGD OF AND AlfARATUS FQR DEFRQSTING ABSQRPTIUN CQULENG SYSTEMS Hans Stierlin, l Rainweg, Schlieren, Zurich, Switzerland Filed July 6, 1969, Ser. No. 41,162 Claims priority, application Switzerland, July 19, E59, 75,590/59 11 Claims. (Cl. 62--2i8) The present invention relates to a method of, and apparatus for, defrosting absorption type refrigeration apparatus, in which some of the circulating cooling medium is removed into an auxiliary system not a part of the main cooling medium circulating system, the Withdrawn portion of cooling medium being stored in an auxiliary reservoir.

Defrosting of evaporators of refrigerators is desired for several reasons, (a) the insulating effect of a coating of snow or ice decreases the temperature gradient which can be obtained in relation to the ambient temperature, (12) the removal of the ice-cube drawer or of the refrigerated material involves difiiculties when the evaporator compartment is covered with ice and includes the danger of mechanical damage of the casing, and (c) a thick coating of ice takes up valuable space.

Defrosting by means of electrical switches and con trollers, for example, by reversing the circulatory path of the cooling medium, is prior known for refrigerators having compressor units. However, such methods can technically not be used with refrigerators operated by gaseous or fluid fuels. Also prior known is the use of an auxiliary pump connected to the cooling medium circulatory system which conveys the solution from the generator into the evaporator. However, the last mentioned method has specific disadvantages, as follows: (a) absorption type refrigerators usually use chromates in the circulatory medium as rust preventatives. If an auxiliary pump of the above described type, pumps chrome containing circulatory medium into the evaporator, chrome salts are deposited, which accordingly are lost to the circulatory medium thus decreasing the effective life of the apparatus; and (b) this crystallization of the rust preventing material may result in blocking up the system.

A further structure for defrosting includes a line from the condenser opening into the gas circulation system, the line having a fluid seal in which the liquid cooling means coming from the condenser, is accumulated. This liquid seal is in the form of a siphon which, after a certain amount of condensate has accumulated, automatically by the displacement of the liquid by suction, unblocks the path for the vapor, coming from the generator, to the gas circulation path. Such vapor interferes with the gas cycle and hence the entire cooling process. This arrangement has, in addition to others, the disadvantage that rapid and complete defrosting of the desired evaporator region is impossible due to its low efiiciency.

In still another prior suggested system, a line having a liquid seal is provided from the gas line between the generator and the condenser and opens into the evaporator. One arm of the liquid seal is heated by an electrical heating element so that the liquid therein stored is brought to its boiling point and flows into the evaporator. This prior art arrangement obviously necessitates an auxiliary heating element having special control elements for initiating the defrosting phase.

According to still another defrosting system, generator gases are condensed and accumulated in a liquid seal. Connected thereto is a second fluid seal located in a vapor line between the rectifier and the evaporator. By means of an individual heater, the liquid is removed from the second seal so that hot vapor from the generator streams into the evaporator to defrost the apparatus. Here also, additional elements are required to permit defrosting and to heat and evaporate the liquid seal. Furthermore, it developed that such equipment was difficult satisfactorily to control. 7

In addition, there is prior known a fully automatic defrosting apparatus having a liquid seal incorporated between the generator and the condenser to which a vapor line opening into the evaporator is connected. After a predetermined amount of condensate is stored in the seal, the seal is automatically drawn off by a siphon and hot vapor from the generator can flow into the evaporator to effect the defrosting action until such time as sufiicient condensate has again accumulated in the seal thereby to close the vapor line outflow opening. The sealing liquid outflowing by siphon action does not actively participate in the defrosting action. While this prior known method is fully automatic, it has the disadvantage that the defrosting power dependent solely upon the generator power, is very low. But defrosting requires a certain amount of energy, deliverable in the shortest time interval, so that, simultaneously with a very intensive defrosting effect, a mechanical effect may be produced by virtue of which the ice cracks and drops and slides off as pieces of ice into the drip tray without complete melting of the ice formation on the evaporator being necessary. Thereby the defrosting time is reduced to a minimum. Such minimum defrosting time is highly desirable so that defrosting may be had practically without change of temperature within the refrigerator.

The object of the instant invention is to provide a method of, and apparatus for, attaining the minimum possible defrosting time. In accordance with this invention, the method includes the steps of removing a portion of the cooling medium from the closed main circulating system into an auxiliary system branched from the main system at a region not part of the liquid circulating system, storing the removed cooling medium portion in liquid form in the auxiliary system, and suddenly bringing the stored liquid into heat exchanging relationship with the hot generator of the refrigerator such that the stored liquid immediately withdraws a great portion of the heat content of the generator and its contents, and thereupon reintroducing the now heated Withdrawn medium into the evaporator of the main system to powerfully defrost the evaporator.

The apparatus for practicing the instant invention has a closed main system, including a condenser, an evapora tor and a generator, in which a cooling medium circulates, the improvement for defrosting the refrigerator, comprising an auxiliary system branched by a branch pipe from the closed system at a region not a part of the liquid containing portion of the circulating system, and having a liquid reservoir, a siphon connected to said reservoir, a first tubing connected to the siphon output and forming a heat exchanger with the generator, and a second tubing connecting the first tubing to the evaporator.

The invention will be explained in detail in connection with the drawing in which FIGURESl through 7 disclose, in schematic form, a number of illustrative embodiments.

In the partially shown cyclic path schematic of an absorption type refrigerator, there is connected to the generator 1 a condenser 2, which in turn connects to an evaporator 3 and the coil 4 of the gas cycle system. The mode of operation of gas absorption refrigerators is well known and hence not here further described.

In the illustrative embodiment of the invention in FIG- URE 1, immediately before condenser 2, a collector and storage reservoir element 5 branches from the system and 'ervoir an upper region of the chamber 3, a line is connected into the evaporator 3. The defrosting transpires as follows: Having the normal production of cold, a portion of the cooling medium vapor, prior to its entrance into the condenser, flows into the reservoir element 5, where it condenses and collects. The amount of the condensate in reservoir 5 increases and its level in the reservoir, as also in siphon 6, rises until the level of the liquid is above the highest point in siphon 6. At such time, this structure acts as a suction lift pump, all liquid stored within resis siphoned oil, and it all flows through line 6 into the vaporizing chamber 8. As a result of the heat exchange, the cooling medium is heated and vaporized in that the medium draws heat from the generator system. The vapor, so formed, streams through line 9 into the evaporator 3 and instantaneously heats the evaporator so that the coating of ice adhering to the evaporator melts from the inside outwardly and drops off.

The size of reservoir 5, together with the disposition of the siphon 6, determines the magnitude of the heat carrier medium flowing in one defrosting cycle. The disposition, as also the insulation properties, of the reservoir 5 and the siphon 6, determine the period of the defrosting. The configuration of the vaporizing chamber 8 is such that the heat transfer rate and the quantity of heat exchanged result in the desired high efliciency of the defrosting, so that the defrosting is sudden. After a few minutes, for example two to four minutes, after the reservoir '5 has been emptied by siphon 6, the defrosting is similarly suddenly terminated.

Such action has the following advantages over the prior methods initially above described. The heat transmission medium which is a part of the contents of the apparatus or aggregate and at the same time the control element for the periodic initiation and cessation of the defrosting sequence, evaporates in the vaporizing chamber 8 and again enters, as the result of its condensation, the circulating system by way of the evaporator. Due to the phase changes of such heat transmission medium, very favorable relations exist in chamber 8 and in evaporator 3 in respect of the heat transfer and heat content such that with small amounts of the medium great quantities of heat are transferred in short time intervals. The boiling temperature of the heat transmission medium is about 55 C., while the temperature of the generator and of vaporizing chamber 3 is about 180 C. Theoretically it is thus possible to withdraw from the generator such an amount of heat that the generator will have cooled to the boiling temperature of the heat transmission medium. In the prior known systems which pump generator solution into the evaporator, such a large heat transfer from the generator is not possible in that the boiling temperature of the pumped solution is about 150 C. and below such boiling temperature a gas bubble pump can no longer convey or operate. Heat transfer in an increased amount must be produced either by the normal heating of the generator or by auxiliary heating elements, as takes place in the prior known methods, and the hot vapors from the generator must be conducted to the evaporator for defrosting intervals of from 30 to 60 minutes, resulting in the danger of melting the refrigerator goods. Increasing the defrosting interval has to date been possible only by additional heating elements of high capacity, which capacity is substantially greater than that of the normal heaters for the generators. \Vith the instant invention, however, due to the large temperature differential available between the generator temperature and the boiling temperature of the heat transfer medium, as also the excellent heat transfer relation, defrosting of high efficiency is possible with the defrosting time reduced and limited to about two to four minutes so that the temperature of the refrigerated goods will not, in practice,-be increased to that of the defrosting.

In addition, the instant method retains the following advantages, some of which are known: (a) no rust preventative material is withdrawn from the circulatory system thus increasing the life of the apparatus and, by preventing stoppages or blocking, increases the etfective operation thereof; (b) the defrosting operation involves no drain on, or interference with, the normal heating source, which fact is of particular advantage for apparatus fired by gas or a liquid fuel; (c) and the defrosting is periodically initiated automatically as also terminated automatically without any added control devices subject to possible error.

In the embodiment of my invention shown in FIGURE 2, the collecting and storage reservoir 5 is connected directly after the condenser 2. A pressure equalizer 4a connects the coil t of the gas cycle system with the end (output side) of condenser 2-. The condensate to be conducted to reservoir 5 is sucked from the level of the normal circulation path by means of a suction element it), which may for example be in the form of a wick. In this embodiment, the vaporizing chamber 11 is formed as a housing or vessel enclosing the generator 1.

As is well known, when the warm gas is coo-led in the gas cycle, liquid condenses from the gas, and in the third embodiment of my invention such condensate is used for defrosting, as is shown in FIGURE 3. This structure has the advantage that no appreciable quantity of cool medium is withdrawn from the circulation system. The composition of the branched liquid corresponds about to that filling the system and, as a result, deconcentration or thinning of the circulating solution is impossible. Furthermore, in the bird embodiment, an auxiliary gas bubble pump 12 is provided instead of a vaporizing chamber, pumping gas-liquid mixture into the evaporator 3 for the purpose of defrosting. This gas bubble pump 12 is joined to the generator 1 by a welding seam 12a.

The apparatus of the embodiment of FIG. 4 operates for defrosting in the same manner as that of FIG. 1, hereinabove described in detail. In coil 4 hereof, liquid is condensed from that co lected in reservoir 5 on cooling of the warm gas. The level of the condensate rises until it reaches the top of siphon s whereupon the lifting action takes place and empties reservoir 5. The liquid flows through the piping 7 and into the bottom of gas bubble pump 12 which is Welded lengthwise at 12a to generator l, the latter delivering suflicient heat to at least partially vaporize the inflowing liquid. This vaporization is again very turbulent since a large amount of heat is available in generator 1, and the hot vapors flow through the duct to the evaporator 3. The evaporator is instantly heated to such a degree that the coating of ice adhering to its exterior is thawed and melted from the inside outwardly and drops away.

It is also possible to position the top of the siphon tube 6 at a higher elevation than the inlet of the condenser 2, as indicated in broken lines 4% in FIGURE 5.

In this elevated position the siphon will never discharge the reservoir 5. If, however, one wants to defrost the evaporator it is possible to dip the siphon 6 into a lower position, for instance as indicated with full lines in FIG- URE 5. By this very important fact the user can choose the moment of defrosting at will. The dipping of the siphon can be done by hand, by a magnet relay, etc.

A further illustrative embodiment of my invention is shown in FIGURE 4 in which the medium necessary for defrosting is withdrawn from the system in the form of non-evaporated cooling medium from the evaporator 3 at one end thereof. The liquid cooling medium flows, by the suction of siphon 6, through the line '7 into the annular vaporizing chamber Ill enveloping generator 1, Where it vaporizes. In vapor form it leaves chamber 11 and streams through line 9 into the exterior jacket 13 of a heat exchanger Where the therein contained heat is delivered mainly to the coating of ice on the exterior jacket 13. In this configuration, the defrosting time is automatically controlled by the degree of icing of the evaporator. The more ice that is formed, the better insulated is the evaporator, resulting in incomplete vaporization of the cool liquid medium which thus drips into the reservoir 5. Therefore the more ice is formed the more of the cool liquid medium drips into the reservoir 5, which will be filled in shorter time and bring the cooling liquid by siphon 6 for defrosting in the defrosting cycle as described above. The quicker the ice on the evaporator 3 is formed, the shorter is the period of the defrosting cycle. The liquid condensed in the heat exchanger is returned to the circulatory system by the line 14.

As shown in the embodiment of FIGURE 4, it is not absolutely necessary that the defrosting medium be di rected into the evaporator. Because of this it is possible to defrost solely those particular portions of the evaporator as may be desired. With an evaporator having two or more different temperature level compartments, it is particularly desirable not to affect the deep freeze compartment by, or during, the defrosting. In view thereof, the thawing or defrosting medium is conducted to the Warmer region of the evaporator 3, whereas the initial region of the evaporator operates normally. By so doing, an increase in the freezing time is prevented should the defrosting occur unavoidably in a time interval while ice cubes are being frozen. In addition, during defrosting the temperature in the deep freeze compartment rises but little so that no thawing, or in the extreme case, spoilage, of the deep-freeze foodstuffs in such compartment, occurs.

FIGURE discloses three further modes of controlling the defrosting period. The storage reservoir 5 is provided with heat insulation 20 which may be displaced in both directions as indicated by arrow 21 from externally the refrigerator. By such displacement the condensation speed, and hence the time when the siphoning level is reached, may be controlled. It is also possible, however, to pass cooling air in variable amount over the reservoir 5, thereby varying the speed of condensation and hence the timing and duration of the defrosting. This cooling air can be drawn through opening 24 by natural draft leaving the apparatus as heated up air stream 23. The amount of cooling air passing through the opening 24 can be controlled by a flap 25. Such time and duration can also be varied by a siphon tube 6 which, for instance by its elasticity, is variable in height.

The method which operates with storage of the cooling medium results in that the cooling medium concentration of the solution conveyed by the pump, decreases with increasing quantity of the stored medium. This, in turn, increases the temperature of the generator which can, under circumstances, have a detrimental effect. It

is, however, possible to operate the structure between successive defrostings at substantially constant generator temperature by providing the structure shown in FIG- URE 6.

In the illustrative embodiment of FIGURE 6, the noninsulated portion of the storage reservoir 5 fills with condensate in relatively a short time. During such filling, an increase occurs in the temperature of the generator system corresponding to the volume of the cooling medium branched off. The condensation within the insulation region, which is relatively small as compared to the non insulated portion of the storage reservoir 5, until the time when the siphon operates, takes the major portion of the time between successive defrosting periods. Thus a relatively flat or small increase in the temperature of the generator occurs during this long time so that on appropriately filling or charging the system, the desired operating values may be maintained practically constant. A pressure equalizer 27 connects the upper part 28 of the filling reservoir 29 and the end of the condenser 2.

Instead of utilizing insulation 20 to slow down the condensation to reservoir 5 as explained and shown in FIG. 6, direct or indirect heating of the upper part of reservoir 5 may be used, where a metallic connectingpiece 30 is welded between the two parts as shown in FIG. 7.

It must also be mentioned that with proper selection of the volume and heat transfer relations of generator 1 and the vaporizing chamber 8 or 11, or the auxiliary gas bubble pump 12, the generator gas bubble pump may be interrupted for predetermined intervals because of the heat withdrawn therefrom, thus further increasing the defrosting efficiency.

What I claim is:

l. A closed absorption refrigeration apparatus comprising a main system including a generator from which refrigerant vapor is driven off, a condenser in which said refrigerant vapor is condensed to a liquid, and an evaporator in which a part of the liquid refrigerant evaporates, the improvement for defrosting comprising an auxiliary system including a branch pipe which leads part of the liquid refrigerant to a reservoir in which said part of the liquid refrigerant collects, a siphon connected to the reservoir for emptying the reservoir of liquid refrigerant when the liquid refrigerant therein accumulates to a given level, a first tub-ing connected to the siphon outlet and having a portion thereof forming a heat exchanger with the generator, and a second tubing connecting the top of the heat exchanger so formed to the evaporator.

2. The improvement according to claim 1 in which the branch pipe to the liquid reservoir is connected to the main system at the input side of the condenser thereof.

3. The improvement according to claim 1 in which the branch pipe to the liquid reservoir is connected to the main system intermediate the ends of the condenser.

4. The improvement according to claim 1 in which the branch pipe to the liquid reservoir is connected to the main system immediately after the output side of the condenser.

5. The improvement according to claim 4 in which a capillary suction means is provided in the branch pipe to said liquid reservoir to suck liquid refrigerant into this reservoir.

6. The improvement according to claim 1 in which the branch pipe connects the liquid reservoir to the main system immediately beyond the evaporator.

7. The improvement according to claim 1 in which the second tubing connects the first tubing to an exterior jacket of the evaporator.

8. The improvement according to claim 1 in which the liquid reservoir is provided with a sheathing of heat insulation variably positionable thereon.

9. The improvement according to claim 1 in which means variably condition the liquid reservoir thermally.

10. The improvement according to claim 9 in which the variable thermal conditioning means is an air current circulated about the reservoir.

11. The improvement according to claim 1 in which the height of the siphon is variable.

References @ited in the file of this patent UNITED STATES PATENTS 2,285,884 Ashby Jan. 9, 1942 2,468,105 Anderson Apr. 26, 1949 2,942,431 Kogel June 28, 1960 2,956,415 Kogel Oct. 18, 1960

Claims (1)

1. A CLOSED ABSORPTION REFRIGERATION APPARATUS COMPRISING A MAIN SYSTEM INCLUDING A GENERATOR FROM WHICH REFRIGERANT VAPOR IS DRIVEN OFF, A CONDENSER IN WHICH SAID REFRIGERANT VAPOR IS CONDENSED TO A LIQUID, AND AN EVAPORATOR IN WHICH A PART OF THE LIQUID REFRIGERANT EVAPORATES, THE IMPROVEMENT FOR DEFROSTING COMPRISING AN AUXILIARY SYSTEM INCLUDING A BRANCH PIPE WHICH LEADS PART OF THE LIQIUID REFRIGERANT TO A RESERVOIR IN WHICH SAID PART OF THE LIQUID REFRIGERANT COLLECTS, A SIPHON CONNECTED TO THE RESERVOIR FOR EMPTYING THE RESERVOIR OF LIQUID REFRIGERANT WHEN THE LIQUID REFRIGERANT THEREIN ACCUMULATES TO A GIVEN LEVEL, A FIRST TUBING CONNECTED TO THE SIPHON OUTLET AND HAVING A PORTION THEREOF FORMING A HEAT EXCHANGER WITH THE GENERATOR, AND A SECOND TUBING CONNECTING THE TOP OF THE HEAT EXCHANGER SO FORMED TO THE EVAPORATOR.

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