EP0000217B1

EP0000217B1 - Refrigerator

Info

Publication number: EP0000217B1
Application number: EP78200036A
Authority: EP
Inventors: George Albert Apolonia Asselman; Adrianus Johannes Van Mensvoort
Original assignee: Philips Gloeilampenfabrieken NV; Koninklijke Philips Electronics NV
Current assignee: Whirlpool International BV
Priority date: 1977-06-22
Filing date: 1978-06-12
Publication date: 1981-09-16
Also published as: US4258554A; AU3723378A; ES470936A1; DE2861071D1; CA1088333A; EP0000217A1; IT1096563B; AU519150B2; JPS5410467A; AR217693A1; IT7824625A0; JPS6337303B2

Description

The invention relates to a refrigerator having a freezing compartment and a refrigerating compartment which refrigerator is provided with a primary refrigerating system containing a refrigerant and having a primary evaporator disposed in the freezing compartment, and a secondary refrigerating system containing also a refrigerant, which system is constituted by a single pipe, the lower part of which is a secondary evaporator pipe which is closed at the lower end and disposed in the refrigerating compartment, the upper part of the single pipe being a secondary condenser pipe which is in heat exchanging contact with the primary evaporator, which secondary condenser pipe has a condensation wall on whose surface the refrigerant condenses during operation, and a means for controlling the temperature of the secondary evaporator pipe.
A refrigerator of the said type is known from German Patent Specification 1 601 010.
A problem associated with such two- temperature refrigerators is presented by control of the temperature in the refrigerating compartment independently of the temperature in the freezing compartment.
From German Patent Specification 1,601,010 it is known to provide the secondary refrigerating system with a heating device with independently of the primary refrigerating system, enables liquid refrigerant to be evaporated, so that the amount of the refrigerant available for the secondary evaporator, and hence the temperature in the refrigerating compartment, is controllable. However, a major drawback of such a control system is that the heating device delivers comparatively much heat to the secondary refrigerator, which heat is to be dissipated by the primary refrigeration system.
This has a highly unfavourable effect on the thermal efficiency of the installation.
It is an object of the invention to provide a beter solution for the temperature control of the refrigerating compartment. The refrigerator in accordance with the invention is therefore characterized in that the effective condensation wall area is variable with said means.
When the wall area of the secondary condenser pipe available for condensation is varied, the amount of refrigerant which condensates, and thus the temperature of the secondary evaporator pipe, will vary. It is now in particular possible to adapt the effective condensation wall area in such a way that, when the temperature in the freezing compartment changes, for example for rapidly freezing food, the temperature in the refrigerating compartment remains constant. Moreover, it is possible to defrost the secondary evaporator by adjusting the effective condensation wall area of the secondary condenser pipe to a minimum.
From the United States Patent Specification No. 2 581 044 a refrigerator is known having a primary and secondary refrigerating system both with a closed loop, in which the condenser of the secondary system is in heat exchanging contact with the primary system by means of an intervening fluid (liquid and/or vapour) between two heat exchanging walls. The amount of intervening fluid in the heat exchanger defines the magnitude of the heat-transfer coefficient of the two walls and the intervening fluid (liquid or vapour) and thus the rate of condensation in the secondary condenser. Controlling of the temperature of the secondary evaporator takes place by varying this heat-transfer coefficient.
In the refrigerator according to the invention heat exchange between the primary evaporator and the secondary condenser takes place directly across the wall between them. Controlling of the temperature of the secondary evaporator takes place by varying the effective condensation wall area. The heat exchange is therefore better and the control speed higher than in the above mentioned US patent.
A preferred embodiment of the refrigerator in accordance with the invention is characterized in that said means comprise a reservoir containing a control gas, which reservoir is connected to the upper end of the secondary condenser pipe, which control gas during operation constitutes an interface with refrigerant vapour in the secondary condenser pipe, the interface being movable along the condensation wall. Owing to the movable interface the wall surface available for condensation can be adjusted to a size which corresponds to a desired temperature in the refrigerating compartment.
A further preferred embodiment of the refrigerator in accordance with the invention is characterized in that the reservoir containing the control gas contains a reversible control-gas getter, which can be heated by a heating element for varying the amount of free control gas. Depending on its temperature this control-gas getter may absorb control gas or release control gas, so that the amount of free control gas can be reduced or increased respectively. The displacement of the interface by which this is attended causes an increase or decrease of the effective condensation wall area.
A further preferred embodiment of the refrigerator in accordance with the invention is characterized in that the reversible control gas getter can be heated by means of an electric heating element which is included in an electrical control circuit, which control circuit includes a temperature-sensitive element which is mounted in the refrigerating compartment, which temperature-sensitive element controls the heating element so as to maintain a specific temperature level in the refrigerating compartment.
Preferably, the reversible control-gas getter and the electric heating element are accommodated in a holder of a thermal insulating material, which holder is provided with at least one wall which is permeable to a control gas.
Preferably, the refrigerant is a freon, the control gas is nitrogen, and the reversible control-gas getter is constituted by a molecular filter material, such as a zeolite.
A different embodiment of the refrigerator in accordance with the invention is characterized in that the reservoir has a fixed partition, which divides the reservoir into two section, which is permeable to control gas and not to refrigerant vapour.
The advantage of this embodiment is that the temperature of the secondary evaporator can be controlled without the use of auxiliary energy.
Still another embodiment of the refrigerator in accordance with the invention is characterized in that the reservoir containing the control gas comprises a movable bounding wall for moving the interface. Owing to the movable bounding wall the interface between control gas and refrigerant vapour can be adjusted via the control gas to a position which corresponds to specific size of the effective condensation wall area, which in its turn corresponds to a desired temperature in the refrigerating compartment.
A further suitable embodiment of the refrigerator in accordance with the invention is characterized in that the movable bounding wall, with its side which is remote from the reservoir containing the control gas, forms part of the bounding surface of a further reservoir, which contains a pressure-transfer medium whose pressure is controllable.
In accordance with the invention the pressure-transfer medium can be heated by means of an electric heating element which is included in an electrical control circuit, which control circuit comprises a temperature-sensitive element which is disposed in the refrigerating compartment, which temperature-sensitive element controls the heating element so as to maintain a specific temperature level in the refrigerating compartment.
A further suitable embodiment of the refrigerator in accordance with the invention is characterized in that the secondary condenser pipe is tapered in the direction of the refrigerant flow, the cross-section of which increases in the direction towards the secondary evaporator pipe. Owing to a larger cross-section at the inlet side of the condenser pipe the vapour speed upon entrance in the secondary condenser is low. This facilitates reflux of condensed refrigerant to the secondary evaporator. Moreover, a part of the condenser pipe has a smaller volume, so that in the case of control actions via this section the control speed is high.
The invention will now be described in more detail with reference to the drawing which shows some embodiments schematically and not to scale.

Figure 1 schematically represents the two refrigerating systems in a refrigerator in which the freezing compartment is disposed above the refrigerating compartment.
Figure 2 shows an electrical control circuit for a refrigerator in accordance with figure 1.
Figure 3 shows a cross-section of a control-gas reservoir, which forms part of the refrigerator of figure 1.
Figure 4 shows an other example of the control-gas reservoir.
Figure 5 shows still another example of the control-gas reservoir.
Figure 6 shows a variant of the secondary condenser of the refrigerator of figure 1.
Figure 7 is a cross-sectional view taken on the line VII-VII of figure 6.
Figure 8 schematically represents two refrigerating systems in refrigerator in which the freezing compartment is disposed underneath the refrigerating compartment.
Figure 9 shows the construction of figure 8, in which the secondary condenser is curved.
Figure 10 shows the construction of figure 8 in which the secondary refrigerating system now includes a capillary structure, and
Figure 11 shows another example of the secondary evaporator.

In Figure 1 the reference numeral 1 refers to a refrigerator, which comprises a freezing compartment 2 and a refrigerating compartment 3. In this case the freezing compartment 2 is disposed above the refrigerating compartment 3.
The refrigerating compartment 2 is. cooled by means of a primary refrigerating system which comprises a compressor 4, a primary condenser 5, a capillary tube 6 serving as a restriction, and a primary evaporator 7. The primary refrigerating system contains a normal refrigerant, such as freon. The temperature in the refrigerating compartrpent 2 is adjustable in known manner, not indicated.
The refrigerating compartment 3 is cooled by means of a secondary refrigerating system, whose secondary evaporator pipe 8 is located in the refrigerating compartment 3 and whose secondary condenser pipe 9 is located in an insulated outer wall of the freezing compartment 2. The secondary condenser pipe 9 has a condensation wall 10, which is brought into thermally conducting contact with the primary evaporator 7. The secondary refrigerating system also contains a normal refrigerant, such as freon. The secondary evaporator pipe 8 and the secondary condenser pipe 9 are constituted by a single pipe. Heat transfer in the secondary refrigerating system is effected in that the liquid refrigerant evaporates in the evaporator 8 and subsequently condenses on the surface of the condensation wall 10. The condensed refrigerant flows back into the secondary evaporator pipe 8 as a result of the force of gravity and in this way cools the refrigerating compartment 3.
The temperature in the refrigerating compartment 3 is controlled by varying the effective condensation wall area 10. For this purpose, the upper end 11 of the secondary condenser pipe 9 terminates in a reservoir 12, which is filled with a control gas 13. This control gas 13 constitutes an interface 15 with the refrigerant vapour 14 in the secondary condenser pipe at the location of the condensation wall 10. Below this interface 15 condensation of refrigerant vapour takes place during operation whilst above the interface no condensation takes place. The position of the interface 15 determines the size of the effective condensation wall area. Hence the amount of refrigerant which condenses and thus also the temperature of the secondary evaporator 8.
The interface 15 can be moved along the condensation wall 10 by varying the amount of control gas 13. For this purpose a reversible control-gas getter 16, which can be heated is contained in the reservoir 12. At increasing temperature the control gas getter releases more control gas and moves the interface 15 downwards, so that the effective surface area of the condensation wall 10 is reduced. Conversely the control gas getter will absorb more control gas at decreasing temperature, so that the interface 15 is moved upwards and the effective condensation wall area increases. As refrigerant, for example, freon R12 (CF₂CI₂) is used as control gas nitrogen, and as control gas getter the well-known molecular filter material, zeolite type 4A. This type of zeolite getters nitrogen, but substantially no freon R12. Of course, other combinations are also possible.
The control-gas getter 16 may be heated with the aid of a heating element 17, which is included in the electrical control circuit in accordance with figure 2. This known control circuit is described in the brochure "Design of time-proportional temperature controls using the TDA 1023" (Philips Elcoma Division, Technical Information No 025, 1 March 1977). The integrated circuit TDA 1023 in this control circuit is a time-proportional control circuit. The temperature-sensitive element R_NTC is located in the refrigerating compartment 3.
The operation of the refrigerating system will now be described in more detail with reference to an example.
Assume that the temperature in the freezing compartment 2 is -18°C and the temperature in the refrigerating compartment 3 is +4°C. Food is to be frozen rapidly and the temperature level in the freezing compartment 2 is set to -30°C. As a result of this, the primary evaporator 7 becomes colder and consequently more vapour will condense in the secondary condenser pipe 9. As a result of this, the temperature in the refrigerating compartment 3 decreases. This is detected by the temperature-sensitive element R_NTC in the refrigerating compartment 3. Via the electrical control circuit the heating element 17 is now switched on. The control gas getter 16 is heated and starts to release control gas 13. As a result of this, the interface 15 moves downwards along the condensation wall 10. The size of the effective condensation wall area is reduced and less refrigerant vapour will condense. This compensates for the aforementioned effect that more vapour starts to condense because the primary evaporator 7 has become colder.
The temperature in the refrigerating compartment 3 is consequently maintained at the level of approximately +4°C. When the temperature in the freezing compartment is reset to -18°C the process is reversed.
Thus, the invention enables the temperature in the refrigerating compartment 3 to be maintained constant automatically, irrespectively of the temperature in the freezing compartment 2. Moreover, it is possible to set the temperature level in the refrigerator compartment 3 manually to a desired value via the variable resistor Rp, which is included in the electrical control circuit, which obviously is attended by a displacement of the interface 15.
Defrosting of the secondary evaporator 8 is possible periodically via a timing circuit or counter circuit to be included in the electrical control circuit. When the temperature of the secondary evaporator 8 is above -2°C no ice will be formed on the secondary evaporator pipe. This high evaporator temperature may be used, because of the continuous heat transfer in the secondary refrigerating system.
A preferred form of the reservoir 12 containing the control gas is shown in figure 3. The reservoir has a filling opening 18 for the refrigerant and the control gas. In the reservoir 12 a holder 19 is located, which contains the control gas getter 16 and the heating element 17. The walls 20 of the holder 19 are porous, so as to allow the control gas to pass through and they are thick-walled so as to insure a satisfactory thermal insulation. Preferably, the reservoir 12 is disposed in the thermally insulated outer wall of the refrigerator cabinet, the filling opening 18 being disposed at the outside. This enables the secondary refrigerating system to be filled during one of the last manufacturing stages.
Figure 4 shows a different example of a control-gas reservoir. The reservoir 12 is different example of a control-gas reservoir. The reservoir 12 is divided into two sections 27 and 28 by a partition 26. This partition is permeable to the control gas 13, but not to the refrigerant vapour 14. Thus, no refrigerant vapour can enter the section 28 of the reservoir. Temperature control of the refrigerating compartment 3 is effected automatically. When the temperature in the refrigerating compartment 3 rises, more refrigerant will evaporate and the vapour pressure will increase. The control gas is further pressurised and the interface 15 moves upwards, so that the effective condensation wall area increases and a new vapour pressure equilibrium is established. More vapour will condense and the temperature rise will be eliminated substantially.
As the operating temperature of the secondary evaporator 8 depends on the vapour pressure, filling the reservoir 12 with control gas 13 should be effected accurately. Obviously, the vapour pressure also depends on the temperature of the primary evaporator 7. When the temperature of the freezing compartment 2 is set to freezing-in, the temperature of the primary evaporator 7 decreases, so that more refrigerant vapour condenses in the secondary condenser pipe 9 and the temperature in the refrigerating compartment 3 decreases. The lower temperature of the primary evaporator 7 also results in a reduced vapour pressure in the secondary condenser pipe 9, so that more control gas 13 is withdrawn from the section 28 of the reservoir 12 and the interface 15 moves downwards along the condensation wall 10. The effective condensation wall area is reduced and the temperature drop is substantially compensated for.
However, in the present example changing the temperature level of the refrigerating compartment 3 is not possible. If the section 28 of the reservoir 12 also contains a reversible control gas getter, which can be heated by a heating element which is included in an electrical control circuit, which circuit includes a temperature-sensitive element accommodated in the refrigerating compartment 3 for controlling the heating element, changing the temperature level in the refrigerating compartment is possible.
Figure 5 shows still another construction for moving the interface 15. In accordance with this construction, in which corresponding parts are designated by the same reference numerals as in figure 1, the secondary condenser pipe 9 terminates in a reservoir 21, in which a movable bounding wall, such as a diaphragm or bellows 22 is located. A displacement of the bellows 22 results in the displacement of the interface 15 and thus a change in size of the effective condensation wall area 10. For automatic control of the refrigerating-compartment temperature the displacement of the bellows 22 should be related to the difference between the desired and prevailing temperature in the refrigerating compartment. This can be achieved in different manners. In the present case this is effected by mounting a pressure-transfer medium 24 and a heating element 25 in a space 23 above the bellows 22. The heating element 25 may then again be included in an electrical control circuit as shown in figure 2. As pressure-transfer medium it is for example possible to use a medium, which is the same as the refrigerant. When the heating element 25 is switched on, the vapour pressure increases and the bellows 22 are urged downwards, which in their turn force the control gas 13 in the secondary condenser pipe 9 downwards. The interface 15 is then also moved downwards accordingly.
The bellows 22 can be controlled with the aid of various control systems such as a on-off control system (for example, a bimetallic strip), an analog or a digital control system (for example, a servo system).
Figure 6 shows a variant of the secondary condenser pipe of figure 1. In this case the secondary condenser 9 takes the form of a tapered pipe whose cross-section increases towards the secondary evaporator 8. Owing to the comparatively large cross-section at the entrance side of the condenser pipe 9 the vapour speed upon entrance in the condenser pipe is low. As a result of this, the condensed refrigerant can readily flow back to the secondary evaporator 8. Another advantage of the tapered condenser pipe 9 is that the upper portion of the pipe has a smaller volume, so that for control actions over this portion the control speed is high.
Figure 7 is a cross-sectional view of the secondary condenser pipe 9 and the primary evaporator pipe 7 which is in heat exchanging contact therewith. The primary evaporator pipe 7 is disposed on both sides of the secondary condenser pipe 9. As a result of this the condensation wall is twice as large. The condenser pipe 9 and the evaporator pipe 7 have a slightly flattened shape, so that in comparison with for example round pipes, the volume of the control gas is low and the surface area of the condensation wall 10 is large. When a control-gas getter is employed, the amount of getter material can then also be small. This moreover reduces the electric power required for the temperature control of the control gas getter.
In the refrigerator of figure 1, the freezing compartment is disposed above the refrigerant compartment. Thus, it can be ensured by means of a simple construction of the refrigerating system that the condensed refrigerant flows back to the secondary evaporator by the force of gravity. Figure 8, in which corresponding parts bear the same reference numerals as in figure 1, but augmented by the number 100, schematically shows a refrigerator in which the refrigerating compartment 103 is disposed above the freezing compartment 102. The secondary condenser 109 is located in an insulated outer wall of the refrigerating compartment 103, where it is in heat-exchanging contact with the primary evaporator 107. The refrigerant, which has condensed in the secondary condenser 109, also flows back to the secondary evaporator 108 by the force of gravity.
In the refrigerator construction in accordance with figure 8 the entire secondary refrigerating system is located at the same level as the refrigerating compartment 103, which demands a substantial mounting height of the refrigerating compartment. This substantial mounting height can be reduced by construction as shown in figure 9. The secondary condenser pipe 108a and the part of the primary evaporator 107a, which is in heat exchanging contact therewith, are curved. The length of the secondary condenser pipe 109a and thus the size of the condensation wall area is now equal to that in figure 8, whilst the mounting height of the refrigerator is smaller.
Another construction, where the refrigerating compartment also disposed above the freezing compartment is shown in figure 10. The parts corresponding to figure 1 now bear the same reference numerals, augmented by the number 200. The secondary condenser pipe 209 is located in an insulated wall of the freezing compartment 202 and the secondary evaporator pipe 208 in the refrigerating compartment 203. The secondary evaporator pipe 208 is thus located above the secondary condenser pipe 209. In order to feed the condensed refrigerant back from the condenser pipe 209 to the evaporator pipe 208 a capillary structure 209a is located in the secondary condenser pipe 209 and in the secondary evaporator pipe 208, for example a layer of metal gauze or capillary grooves in the inner wall.
It will be obvious that any arbitrary construction of a refrigerator with a refrigerating compartment and a freezing compartment utilizing the invention, is possible.
Figure 11 shows a favourable construction of a secondary evaporator pipe 8 of the refrigerator of figure 1. The secondary evaporator pipe 8 is locally provided with pockets 8a, which serves as reservoirs for liquid refrigerant. Thus, a uniform evaporation of the liquid is obtained over the entire evaporation area. Moreover, the cooling time for the refrigerating compartment, for example after a defrosting period, is short, because the vapour enters the secondary condenser pipe 9 directly saturated.
Obviously, it is also possible to vary the effective condensation wall area by the use of for example a folding condensation wall, or by covering the condensation wall by mechanical means, for example a plunger.
Instead of a refrigerator with a primary refrigerating system consisting of a compressor, a condenser and an evaporator is alternatively possible to provide the refrigerator with a primary refrigerating system based on absorption.

Claims

1. A refrigerator having a freezing compartment (2) and a refrigerating compartment (3), which refrigerator is provided with a primary refrigerating system containing a refrigerant and having a primary evaporator (7) disposed in the freezing compartment (2), and a secondary refrigerating system containing also a refrigerant, which system is constituted by a single pipe, the lower part of which is a secondary evaporator pipe (8) which is closed at the lower end and disposed in the refrigerating compartment, the upper part of the single pipe being a secondary condenser pipe (9) which is in heat exchanging contact with the primary evaporator (7), which secondary condenser pipe (9) has a condensation wall (10) on whose surface the refrigerant condenses during operation, and a means for controlling the temperature of the secondary evaporator pipe (8), characterized in that the effective condensation wall area is variable with said means.

2. A refrigerator as claimed in claim 1 characterized in that said means comprise a reservoir (12) containing a control gas (13), which reservoir is connected to the upper part (11) of the secondary condenser pipe (9), which control gas during operation constitutes an interface (15) with the refrigerant vapour in the secondary condenser pipe, the interface being movable along the condensation wall.

3. A refrigerator as claimed in claim 2, characterized in that the reservoir (12) containing the control gas (13) contains a reversible control-gas getter (16) which can be heated by a heating element (17) for varying the amount of free control gas.

4. A refrigerator as claimed in claim 3, characterized in that the reversible control-gas getter (16) can be heated by means of an electric heating element (17) which is included in an electrical control circuit, which control circuit includes a temperature-sensitive element which is mounted in the refrigerating compartment, which temperature-sensitive element controls the heating element so as to maintain a specific temperature level in the refrigerating compartment.

5. A refrigerator as claimed in claim 4, characterized in that the reversible control-gas getter (16) and the electrical heating element (17) are accommodated in a holder (19) of a thermal insulating material, which holder is provided with at least one wall (20) which is permeable to a control gas.

6. A refrigerator as claimed in claim 3, 4 or 5, characterized in that the refrigerant is a freon, the control gas is nitrogen, and the reversible control-gas getter is a molecular filter material, such as a zeolite.

7. A refrigerator as claimed in claim 2, characterized in that the reservoir (12) has a fixed partition (26), which divides the reservoir into two sections, which is permeable to control gas and not to refrigerant vapour.

8. A refrigerator as claimed in claim 2. characterized in that the reservoir (12) containing the control gas comprises a movable bounding wall for moving the interface (15).

9. A refrigerator as claimed in claim 8, characterized in that the movable bounding wall, with its side which is remote from the reservoir containing the control gas, forms part of the bounding surface of a further reservoir, which contains a pressure-transfer medium, whose pressure is controllable.

10. A refrigerator as claimed in claim 9, characterized in that the pressure-transfer medium can be heated by means of an electric heating element which is included in an electrical control circuit, which control circuit comprises a temperature-sensitive element which is disposed in the refrigerating compartment, which temperature-sensitive element controls the heating element (17) so as to maintain a specific temperature level in the refrigerating compartment.

11. A refrigerator as claimed in any of the preceding claims, characterized in that the secondary condenser pipe (9) is tapered in the direction of the refrigerant flow, the cross section of which increases in the direction towards the secondary evaporator pipe (8).