GB2107035A

GB2107035A - Refrigerator

Info

Publication number: GB2107035A
Application number: GB08228246A
Authority: GB
Inventors: George Albert Apoloni Asselman; Mensvoort Adrianus Johanne Van
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1981-10-07
Filing date: 1982-10-04
Publication date: 1983-04-20
Also published as: IT1153204B; GB2107035B; SE8205633D0; AU556603B2; JPS5872860A; DE3235949A1; ES516183A0; SE8205633L; FR2514115A1; AU8912782A; AR229282A1; ES8306858A1; NL8104565A; FR2514115B1; IT8223595A0; CA1193873A

Abstract

The invention relates to a refrigerator having a freezing compartment 2 and a refrigerating compartment 3, which refrigerator comprises a primary refrigerating system which contains a refrigerant and which comprises a primary evaporator 7 arranged in the freezing compartment 2, and a secondary refrigerating system which also contains a refrigerant and which comprises a secondary evaporator 8 arranged in the refrigerating compartment and a secondary condensor 10 which is in heat- exchanging contact with the primary evaporator 7, to which secondary refrigerating system a reservoir 12 is connected which contains an adsorbent 13 for the refrigerant, the adsorbent being a porous solid substance which can be heated by means of an electric heating element 14 included in an electric control circuit, which control circuit comprises a temperature-sensitive element arranged in the refrigerating compartment, which temperature- sensitive element controls the heating element so as to maintain a specific temperature level in the refrigerating compartment. Suitably, the adsorbent is silica gel and the used refrigerant for the secondary refrigerating system is CF2Cl2. <IMAGE>

Description

SPECIFICATION Refrigerator The invention relates to a refrigerator comprising a freezing compartment and a refrigerating compartment, which refrigerator comprises a primary refrigerating system which contains a refrigerant and which comprises a primary evaporator arranged in the freezing compartment, and a secondary refrigerating system which also contains a respective refrigerant and which comprises a secondary evaporator arranged in the refrigerating compartment and a secondary condensor which is in heat-exchanging contact with the primary evaporator, to which secondary refrigerating system a reservoir is connected which contains an adsorbent for the refrigerant.

Such a refrigerator is known from United States Patent Specification 2,433,188. In this refrigerator a mineral oil is employed as adsorbent (in fact absorbent). The amount of absorbent and the amount of refrigerant have been selected in such a way that the temperature in the refrigerating compartment is constant at different temperatures of the space in which the refrigerator is located. The disadvantage of this refrigerator is that the absorbent is a liquid, so that the position of the reservoir and thus the position of the refrigerator may only be changed to a limited extent. Especially during transport of the refrigerator great care must be taken.In any case it must be avoided that the oil or oil vapour enters the refrigerating system, because this oil cannot be extracted from the refrigerating system, thereby reducing both the absorption capacity and the heat transfer capacity of the refrigerating system. A further disadvantage is that the refrigerating capacity of the refrigerating system is adapted to the required refrigerating capacity via the ambient temperature. This adaptation is effected at a very slow rate. In fact, no real control is provided.

It is an object of the invention to provide a refrigerator in which the reservoir is positionedindependent, which enables adjustment of the desired temperature and a fast temperature control.

To this end the refrigerator according to the invention is characterized in that the absorbent comprises a solid substance which is heatable by means of an electric heating element arranged in an electric control circuit, which control circuit comprises a temperature-sensitive element arranged in the refrigerating compartment, which last-mentioned element controls the heating element so as to maintain a specific temperature level in the refrigerating compartment.

The advantage of the use of a solid as absorbent is that the position of the reservoir may be selected freely. In conjunction with the control circuit it is also optional whether the reservoir is arranged inside or outside the refrigerator.

Preferably, silica gel is employed as the absorbent and CF2CI2 is employed as the refrigerant for the secondary refrigerating system.

Other combination of refrigerants and adsorbents suitable for use in such a refrigerator are: CCIF2-CCIF2 (freon R1 14) in zeolite type MS 13 X, CCIF2CF3 (freon R1 15) in zeolite type MS 13 X or in activated aluminium oxide, CH(CH3)3 (isobutane) in zeolite type MS 1 3X NH in zeolite MS type 4A, 5A, or 13X.

The use of the combination CF2CI2 (freon R12) and the solid substance silica gel further has the advantage that the adsorption capacity of the silica gel for CF2CI2 in high at a temperature of approximately OOC and the desorption capacity is high at a temperature of approximately 1 000C.

The adsorption/desorption rate of CF2CI2 in silica gel is also high over the entire temperature range.

There is no hysteresis for adsoprtion/desorption.

Moreover, the combination has a high chemical stability up to 1 800C.

The said other combinations are also chemically stable and have a satisfactory adsorption/desorption capacity.

For a satisfactory fast control of the refrigerating system it is important that a heating element is used for heating the adsorbent in order to increase. the amount of refrigerant in the circuit to assist in the heat transfer. When an oil is used as adsorbent this gives rise to problems because oil becomes chemically unstable when heated above approximately 1 500C. This temperature of 1 500C is at least reached as a spot temperature when the heating element is immersed in the oil which is desirable for a satisfactory and fast control.

From European Patent Application EP O 000 21 7 a refrigerator is known which for the purpose of temperature control varies the size of the secondary condensation-wall area by means of a control gas which is adsorbed or desorbed in a solid substance, zeolite, but during manufacture of this refrigerator such requirements have to be imposed that the cost price of such a refrigerator increases. For example, all extraneous substances, specifically water, have to be extracted from the zeolite. This so-called activation has to be effected by means of evacuation at a comparatively high temperature and for a long time (7.10-2 Torr, 4500C, at least 4 hours). Activating silica gel is a substantially faster process, which may be effected at a lower temperature (7.10-2 Torr, 2000C and 6 minutes).

This means that this process may even be carried out in the production line of the refrigerator. A further requirement is that the refrigerant filling is subject to comparatively tight tolerances. Too much refrigerant results in an impermissibly high pressure in the system during insulation of the refrigerator when the refrigerator is heated to approximately 750C. An insufficient amount of refrigerant means that the evaporator is not completely wetted so that the refrigerating capacity will be reduced. In the refrigerator in accordance with the invention these tolerances are wider because a larger amount of refrigerant CF2CI2 does not result in higher pressures because the adsorbent silica gel retains the refrigerant CF2CI2 and thus keeps the vapour tension low.

Moreover, filling with control gas should also be effected within narrow tolerances. An excess amount would mean that the refrigerating capacity is reduced, whilst lack of refrigerant would mean that the secondary refrigerating system cannot be turned off. In the refrigerator in accordance with the invention no control gas is required.

An embodiment of the invention will now be described in more detail, by way of example, with reference to the drawing.

Fig. 1 schematically represents the two refrigerating systems in a refrigerator, and Fig. 2 shows an electric control circuit for the refrigerator shown in Fig. 1.

The reference numeral 1 designates a refrigerator, which comprises a freezing compartment 2 and a refrigerating compartment 3. The freezing compartment 2 is cooled by means of a primary refrigerating system comprising a compressor 4, a primary condensor 5, capillary 6 which serves as restriction, and a primary evaporator 7. The primary refrigerating system contains a normal refrigerant such as freon R12 (CF2CI2). The temperature in the freezing compartment 2 is thermostatically controlled and the temperature level is adjustable in known manner, not shown.

The refrigerating compartment is cooled by means of a secondary refrigerating system whose secondary condensor tube 9 is located in an insulated outer wall of the freezing compartment 2. The secondary condensor tube 9 comprises a condensation wall 10, which is in heatconducting contact with the primary evaporator 7. Preferably, the secondary refrigerating system also contains fren R12 (CF2CI2) as refrigerant.

The secondary evaporator tube 8 and the secondary condensor tube 9 are formed by one tube. The heat transfer in the secondary refrigerating system is obtained 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 tube 8 by the force of gravity and thus cools the refrigerating compartment 3. The liquid refrigerant flows along the inner wall of the evaporator tube and the size of the wetted evaporator area determines the degree of cooling.

The temperature in the refrigerating compartment 3 is controlled by varying the amount of refrigerant in the secondary refrigerating system. For this purpose the upper end 11 of the secondary condensor tube 9 terminates in a reservoir 12. However, the reservoir may be arranged at any other arbitrary location inside or outside the refrigerator and may be connected to any arbitrary point of the secondary refrigerating system. The reservoir contains a porous adsorbent 13, suitably silica gel, which can be heated by means of a heating element 14 included in the electric control circuit. The control circuit is shown in Fig. 2 and substantially corresponds to the control circuit as described in European Patent Application EP 0 000 217.

However, the temperature-sensitive element RNTC' which is located in the refrigerating compartment should be connected to a different point of the control circuit because the heating element 14 must be switched on when the temperature in the refrigerating compartment 3 decreases.

The temperature in the refrigerating compartment 3 is controlled as follows: Through thermal leakage the temperature in the refrigerating compartment increases. This is detected by the temperature-sensitive element RNTC Via the electric control circuit the heating element 14 is now switched on. The adsorbent is heated and the refrigerant is desorbed from the adsorbent, so that more refrigerant vapour is applied to the secondary refrigerating system. A new pressure equilibrium is established during which more refrigerant in liquid form is present and the evaporator 8 is wetted over a larger area.

As a result of this, the cooling of the refrigerating compartment increases and the temperature decreases until the heating element is switched off again. The adsorbent cools down and the refrigerant is gradually re-adsorbed until the temperature in the refrigerator compartment 3 again reaches a specific temperature level and the heating element is switched on again.

Claims

1. A refrigerator comprising a freezing compartment and a refrigerating compartment, which refrigerator comprises a primary refrigerating system which contains a refrigerant and which comprises a primary evaporator arranged in the freezing compartment and a secondary refrigerating system which also contains a respective refrigerant and which comprises a secondary evaporator arranged in the refrigerating compartment and a secondary condensor which is in heat-exchanging contact with the primary evaporator, to which secondary refrigerating system a reservoir is connected which contains an adsorbent for the refrigerant, characterized in that the adsorbent comprises a solid substance which substance can be heated by means of an electric heating element arranged in an electric control circuit, which control circuit comprises a temperature-sensitive element arranged in the refrigerating compartment, which last-mentioned element controls the heating element so as to maintain a specific temperature level in the refrigerating compartment.

2. A refrigerator as claimed in Claim 1, characterized in that the adsorbent is silica gel and the refrigerant for the secondary refrigerating system is CF2C12.

3. A refrigerator as claimed in Claim 1, characterized in that the adsorbent is zeolite type MS 1 3 X and that the refrigerant for the secondary refrigerating system is one of the refrigerants of the group CClF2-CClF2, CCIF2-CF3, CH(CH3)3, NH3.

4. A refrigerator as claimed in Claim 1, charactertized in that the adsorbent is activated aluminium oxide and the refrigerantforthe secondary refrigerating system is CCIF2-CF3.

5. A refrigerator as claimed in Claim 1, characterized in that the adsorbent is zeolite type MS 4A and the refrigerant for the secondary refrigerating system is NH3.

6. A refrigerator as claimed in Claim 1, characterized in that the adsorbent is zeolite type MS 5A and the refrigerant for the secondary refrigerating system is NH

7. A refrigerator substantially as herein described with reference to the accompanying drawing.