IL44785A - A refrigeration system provided with variable length capillary tube - Google Patents

Abstract

A refrigerant system with mechanical compression and refrigeration cycle wherein the refrigerant is expanded through a set of capillary tubes of which the length is adjustable in response to a temperature transducer located within the evaporator section of the system. The means for regulating the capillary tubes length comprises a threaded cylinder slidably received within a tube, the trough of the screw thread functioning as a capillary tube. The system further comprises a trap means for capturing any liquid refrigerant escaping through the capillary tubes when the compressor is not running and for circulating the captured liquid refrigerant when the compressor is re-started. [US3884663A]

Description

A refrigeration system provided with- variable length capillary tube Ettore FUNAHO C:- 42938 44785/2 The present invention relates to a refrigerator system.

In known refrigerator systems, a refrigerator fluid is pumped by a compressor between an evaporator, which is copied by evaporation of the fluid, to a condenser in which gaseous refrigerant rom the evaporator is condensed to a liquid. The liquid in the condenser is evaporated into th evaporator either by a mechanical expansion valve or by means of a capillary tube. As will be explained hereinafter by way of specific example, such prior systems suffer from several disadvantages, and in particular, prior systems utilising capillary tubes tend to be inefficient especially at operating temperatures differing from a particular fixed temperature at which the system was designed to operate.

The present invention now provides a refrigerator system comprising an evaporator, a condenser, a compressor arranged to pump refrigerant fluid from the evaporator to the condenser, capillary tube means providing for the refrigerant fluid a variable length flow path from the evaporator to the condenser, sensing means for sensing the temperature of the condenser, and control means arranged to vary the length of said tube in dependence upo said sensed temperature.

The invention will be more fully understood from; the following descriptio of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic diagram of a known ref igeratio system utilising an expansion valve Figure 2 shows a diagram of another know refrigeratio system utilising capillary tube expansion; Figure 3 shows a diagram of an embodimen of a refrigeration system in accordance with this invention; Figure shows in detail the flow regulating device and the related actuating mechanism of the system of Figure 3 Figure 5 shows a detailed view of the sypho associated with the collecting tank of the system of Figure 3 Figure 6 shows a diagram of the electric circuit for controlling the device of Fig. 4; Figure 7 is an end view of the refrigeration system of Fig. 3 as seen from the high pressure side; Figure 8 is a side view of the refrigeratio system of Fig. 3; Figure 9 is an end view of the ref igeration system of Fig. 3 as seen from the high pressure side, the louvre being removed therefrom.

Referring firstly to Figs. 1 and 2, the prior art systems will be described briefly. The cycle of both the known systems is a vapour-compression cycle that is : a fluid in its gaseous state (in general ammonia, Freon, registered trade mark, or methylchloride) is taken in by a compressor, its volume is reduced by compression and its temperature is increased; from the compressor the fluid is fed to an air or water cooled condenser wherein it is cooled and liquefied at constant pressure. The refrigerant from the condenser is collected in its liquid state into a receiver tank and therefrom it is supplied to an expansion valve and from this to an evaporator wherein it suddenly expands and reverts to its gaseous state by means of heat transferred to it from the space to be refrigerated. From the evaporator, the 44785/2 The known refrigeration system that is provided with an expansion valve (Fig. 1) comprises a compressor 1, a suction line 2 to the compressor, a discharge line 3 from the compressor, a condenser 4, a liquid receiver-separator tank 5, an outlet pipe 6 depending from the top of tank 5, the open end of which reaches nearly the bottom of the tank, an expansion alve 7 and an evaporator coil 6. The purpose of tank 5 into which the still warm refrigerant from condenser 4 is fed, is for causing said refrigerant to slowl flow over the inner sides of the tank walls dow to the bottom thereof whereby the refrigerant is cooled to a temperature closely approaching room temperature. In fact it is known that the lower the temperature of the refrigerant co ing from tank 5 the higher is the efficiency of the plant. Through pipe 6 the refrigerant arrives at the automatic expansion valve 7 through which it is urged to flo when, within the refrigerating coil 8, there is a vacuum produced by compressor 1.

T e refrigeration system utilising capillary tube expansion (Fig. 2) comprises a compressor 9, a suction line 10 a discharge line 11, a condenser 12, a capillary tube 13, a refrigerator coll 14.

Through the capillary tube 13, the refrigerant passing along the tube sectio between A and A' undergoes a pressure drop in the same way as across the expansion valve. The capillary tube is a very simple mechanical component and therefore more reliable and long lasting than an expansion valve. However it has the following disadvantages: Firstly, the capillary tube is in practice a passage permanently open between the high pressure and the low pressure sections of the system and therefore there is always a refrigerant flow even if the compressor is not running. In consequence, some Q liquid refrigerant will enter the condenser 14. -When the compressor starts up again, the liquid in the condenser can cause piston knocking in the compressor which can cause the compressor to fail. For this reason in such a type of system the charge of refrigerant is reduced to a minimum, and the receiver-separator tank that is provided in the expansion valve system is not utilised.

Due to the absence of said tank, the refrigerant entering the capillary tube is at a highe temperature than it would be if the tank were provided and therefore the efficiency of the system is very low and becomes lower the greater the system power. Hence, as a practical matter, the system power cannot be increased above 1.5 HP.

When designing, a refrigerator system of this type, the capillary tube is dimensioned to produce a pressure drop as required for achieving th maximum effectiveness at a give room temperature. However the room temperature is far from constant and in certain environments it may increase to a value . such that the restriction caused by the capillary: tube dimensioned as above will not be great enough for building upstream of the tube the pressure required for condensing the refrigerant at such increased value of the room temperature. As a consequence, a portion or even the total of said refrigeran circulates along the system at its vapour state with a loss of work proportional to the percentage of non condensed fluid within the condenser.

From this the requirement ensues of a device for modifyin the flow rate capacity of the capillary tube during the system operation.

Various means have bee devised by the prior art for changing, the flow rate through the capillary tube in a f refrigerator system. For instance the USA Patent No. 3.677.028 to Glendon A.Raymond discloses a refrigeration system wherein the total cooling load is split among several evaporator circuits each circuit being controlled by a shut-off solenoid valve and a fixed restrictio consisting of a capillary tube. The valve is utilised as a first stage restriction providing at least 50 percent of the total pressure drop through the valve and the capillary.

The means for controlling said solenoid valves is not specified in the Patent, but presumably they are controlled by means of sensors of the evaporator temperature, each valve being shut when the cooling load served by the respective evaporator circuit is satisfied.

According to the British Patent No. 910.070 to Pressed Steel Company the refrigerant flow from the condenser to the evaporator i a refrigerator circuit is dealt with by more than one capillary tube, each capillary tube being connected at one end thereof to the end of the evaporator farthest from the compressor and at the other end to the condenser at a level thereof different from the other capillaries. In this way one or more capillary tube progressively become operative or become inoperative in response to variations in the mass flow of vapour pumped by the compressor. In fact the mass flo of the ref igerant through the capillaries increases proportionally to the amount of liquid within the condenser.

Differently from what has been disclosed in the aforementioned patents, in the refrigerator system of this invention the length of the capillary passage betwee the condenser and the evaporator is continuousl changed to fit More specifically, according to this invention, a capillary of variable length is provided upstream of one or * more capillary tubes of fixed length, the capillary tubes being connected in parallel to one the others when more than one are provided.

The length of the variable capillar tube is controlled by a device which senses the temperature within the condenser.

Considerung now a embodimen of a refrigerator system in accordance with the present invention which is shown in Fig. 3, the system comprises a refrigerant receiver tank 19 to which a condenser 18 is connected and which is provided with a pipe 20 which depends from the top of the tank with its ope end almost at the bottom of the tank, a compressor 15 , a suction line 16 to the compressor, a discharge line 17 from the compressor and a normally closed solenoid controlled valve 27 'included between a regulating device 30 which, as will be explained hereinafter, functions as a set of adjustable length capillary tubes, and a set of fixed length capillary tubes 28.

The capillary tubes 28, of which three are shown in Pig. 3, are connected at one end thereof to a vertical , conduit 22. Conduit 22 at th lower section thereof betwee 45 and 46 in Fig. 5 is formed as a syphon A which communicates with evaporator 24. Syphon A is connected to a collector vessel 49 in two wayss through a capillary tube 48 (Fig. 5) or/and also through a solenoid controlled valve 29 which closes when compressor 15 is running and a check valve 47 which opens towards vessel 49 (see arrow in Fig. 5) but closes the other way.

For better clarity, in Fig. 3 the lines which lead from the receiver-separator tank 19 to the regulating device 30 44785/2 When the compressor is operating, the solenoid control- . led valve 27 is open but is closed when the compressor is not running.

Considering now the regulating device 30 and the related electronic control which are illustrated in Figs. 4 and 6, the regulating device comprises a solid cylinder 35 having two opposed threaded end portions and a central section turned down to a diameter smaller than the threaded portions. Cylinder 35 is slidably mounted withi a coaxial tube 3 with precision fitting between the screw thread ridge and the inner surface of the tube. Tube 36 at one end thereof, the left end in Fig. 4, has a chamber B which communicates with one of the two branches of pipe 20 which terminate near the bottom of receiver 19. The other end of tube 36 penetrates one wall of a fluid tight housing 42 wherein an electromechanical device is contained for controlling the movement of cylinder 35 along tube 36.

Such electromechanical device comprises a motor 41 whose shaft 43 is threadingly fitted through a transverse arm 44 which is therefore moved along the motor shaft 43 when this is turned. Arm 44 is firmly attached to an extension of cylinder 35 and to a slider of a potentiometer so that when arm 44 moves along shaft 43, cylinder 35 and the potentiometer slider are also moved.

The centre section of tube 36 is provided with two peripheral rows; of through holes 37 which, when cylinde 35 is moved to the left to the end of its stroke, are both exposed, while when cylinder 35 is moved to the right, the left row Is covered by the left threaded section of cylinder 35. The centre section of tube 36 includin holes 37 is surrounded by a sleeve 38 which is provided with an outlet pipe 34. 44785/2 The screw threads with which the end sections of cylinder 35 are provided function as a pair of capillary tubes in parallel. In fact the refrigerant flowing through pipe 20 is divided in tw streams one of which enters chamber B and the other enters housing 42. From both ends of cylinder 35 the refrigerant flows along the grooves of the threaded surfaces of cylinder 35, any direct flow from the cylinder ends towards the centre section of tube 36 being prevented by the precision fitting between the scre thread ridge and the inner surface of tube 36. For this reason, the clearance between said two elements should be kept as low as 0.05 mm. By moving cylinder 35 to the right from the end of its stroke as shown in Fig. 4, the length of path of the refrigerant along either threading of cylinder 35 decreases. In this way a means is provided for regulating the flow rate of the refrigerant through a capillary tube.

The operation of electric motor 41 is controlled by an element sensitive to temperature which is located at a position where the temperature of the condensing refrigerant can be detected, which in the case of an air cooled condenser is the room temperature.

The temperature sensing element is made to function as one of the two resistances of one of the two branches of a Wheatstone bridge (see Fig. 6) . In Fig. 6, 50 and 51 are the lead of the electrical source of the bridge; 52 , 39, 54 and 55 are the resistances of the same bridge; of said resistances: 39 is the variable resistance of the potentiometer included in said electromechanical device; 52, as already mentioned, is the resistance Of the temperature sensing element and specifically its resistance coefficient is negative, that is 44785/2 In the same Figure, 56 indicates a voltage amplifier; 57 and 58 are two triggers; 59 and 60 are two relays adapted for inverting the rotational motion of motor 41 and 62 is a source of electricity.

The operation of the regulating device is as follows: When a change occurs in th condenser temperature, the electrical resistance of sensitive element 52 will also change whereby the heatstone bridge balance will be modi ied and a sighal will be produced. Such signal, amplified by amplifier 56 is fed to triggers 57 and 58 by which relays 59,60 are controlled.

Relays 59, 60 will cause motor 41 to be connected to one or the other of the two polarities of source 62 i accordance with the direction of the bridge unbalance and motor 41 will be rotated accordingly. Because potentiometer 39 is driven by motor 41, resistanc 52 will b changed until it becomes equal to the resistance of element 52 whereby the output from the Wheatstone bridge will be null and moto 41 will be stopped.

The above regulating device does not cover the' hole range of length of the capillary path to be traversed by the refrigerant. In fact in no case will a path of zero length be required. For this reason, a set of capillary tubes of fixed length is provided which tubes are mounted in parallel with one another and in series with the regulating device.

The latter is designed for adding the required length Of capillary path to the fixed length provided by the set of fixed capillary tubes 28. ' "' ' ' '.■' A refrigerator system is thus provided in which!, although the refrigerant is expanded through capillar tubes, a receiver tank 19 is included between the compressor and the 44785/2 If no corrective measures were taken the presence of a large amount of liquid refrigerant within receiver tank 19 and within housing 42 of the regulating device could cause, when compressor 15 is stopped, a flow of liquid refrigerant towards the evaporator 24 and from this to compressor 15 wherein it could cause damage when the compressor is started up again.

Two means are provided for preventing such danger. The solenoid controlled valve 27 is inserted between the regulating device and the set of capillary tubes 28 Which valve is closed when the compressor is not running.

Another safety means for preventing any flow of liquid refrigerant towards compressor 15 comprises the collecting tank 49 which is connected to the vertical manifold 22 which communicates with the set of fixed capillary tubes 28. Manifold 22 at its lower section is formed as a siphon including a downwardly arcuated pipe section, which is followed by an uprising pipe section, an upwardly arcuated pipe section and a depending pipe section which is connected to evaporator 24. The lowermost point of th downwardly arcuated pipe section is connected to tank 49 through a normally open valve 29 - that is a valve which is open when compressor 15 is not running -and a check valve 47. A capillary tube 48 connects a part close to the bottom of tank 49 to a point along said uprising pip section of said siphon.

The operation of said safety device is as follows: Supposing that compressor 15 is not running and some leaking of liquid refrigerant occurs through valve 27. Then there will be a flow of liquid refrigerant to tank 49 through capillary tubes 28, a portion of the siphon, valve 29 and Simultaneously with the starting of compressor 15 valve 27 will open and valve 29 will shut. Due to the suction by compressor 15. the pressure within evaporator 24 will be lowered with respect to tank 49.

Due to check valve 47 no liquid refrigerant will flow through this valve and valve 29 towards evaporator 24 howeve some liquid refrlgieraht will flow throug capillary tube 48 from tank 49. Such flow of liquid in addition to the liquid flowing through capillary tubes 28 will totally evaporate withi evaporator 24 and will not cause any damage to th compressor.

Claims (13)

44785/3 CLAIMS:

1. A refrigerator system comprising an evaporator, a condenser, a compressor arranged to pump refrigerant fluid from the evaporator to the condenser, capillary tube means providing for the refrigerant fluid a variable length flow path from the evaporator to the condenser, sensing means for sensing the temperature of the condenser, and control means arranged to vary the length of said tube independence upon said sensed temperature.

2. A system in accordance with claim 1 and including a receiver tank connected between the condenser and the capillary tube means, the tank being arranged to cool refrigerant liquid emanating from the condenser.

3. A system in accordance with claim 1 or 2 and including a collector vessel arranged to collect any refrigerant fluid in liquid form that passes through the capillary tube means.

4. A system in accordance with claim 3 and including a further capillary tube connected between the evaporator and the collector vessel to permit re rigerant liquid in said vessel to evaporate into said evaporator.

5. A system in accordance with claim 3 or 4 and including a valve arranged to prevent flow of said liquid into the collector vessel whilst the compressor is running.

6. A system in accordance with any preceding claim wherein said capillary tube means comprises a set of fixed length capillary tubes and a variable length capillary tube connected mutually in parallel to provide said flow path. 44785/2

7. A system in accordance with claim 6 and including a control valve arranged for selectively disconnecting said fixed length capillary tubes from the flow path.

8. A system in accordance with any preceding claim wherein said variable length capillary tube comprises a threaded member slidably received in a tube with a close fit.

9. A system in accordance with claim 8 wherein the control means includes a motor arranged to slide the threaded member along the tube in dependence upon said sensed temperature.

10. » A system in accordance with claim 9 wherein the sensing means comprises an electrical resistor the resistance of which varies with temperature.

11. A system in accordance with claim 9 including a Wheatstone bridge having said resistor connected in one: arm thereof, another arm thereof having connected therein a variable resistor having a resistanc arranged to depend upon the relative position of said tube and said threaded member said motor being arranged to be driven in response to any out of balance current pertaining across the bridge.

12. A system according to any one of claims 9 to 11 wherein said variable length capillary tube, comprises a solid cylinder having two opposed threaded end portions separated by a central portion of smaller diameter, and a tube of substantially the same length as the cylinder and in which said cylinder is slidably received with a close fit, said tube being provided with two peripheral rows of holes which communicate with the space between the central 44785/2 section of said cylinder when said cylinder is longitudinally centered with respect to said tube, the centre section of said tube being enclosed within a cylindrical sleeve which extends at both ends beyond said rows of holes and which defines a fluid tight space around said tube, said tube being closed at one end by a cap defining a chamber, the other end of said cylinder being open to the inner space of a housing in when said motor is received, said chamber and said inner space being connected to the receiver tank.

13. * A refrigerator system substantially as herei described with reference to Figures 3 to 9 of the accompanying drawings. HE:dn