FIELD OF THE INVENTION

The present invention relates to a cooling system expansion device which is suitable for regulating the mass flow of the cooling fluid.

BACKGROUND OF THE INVENTION

As it is generally known, a cooling system basically comprises a compressor, a condenser, an expansion device and an evaporator. The cooling fluid (in the gas phase) is compressed in the compressor and flows into the condenser, where it is cooled, for example, by means of either ambient air or water, and passes into the liquid phase. The cooling fluid, at high pressure, flows into the expansion device, where its pressure is decreased, and then, it flows into the evaporator, where it absorbs , heat from the load (food, for instance) and passes into the gas phase. Finally, the coolant is drawn by the compressor, therefore accomplishing the refrigeration cycle.

STATE OF THE ART AND ITS DRAWBACKS

The expansion devices further promote the decreasing of the cooling fluid pressure and, according to the prior art, they comprise expansion valves (thermostatic or pressostatic ones, for example) and capillary tubes, which are tubes having a small diameter, that is, with a diameter smaller than that of the tube through which the cooling fluid flows. For small cooling systems, for example, in refrigerators for domestic use, it is used capillary tubes, while for large size systems, it is used expansion valves.

In case of capillary tubes, they are sized to a single room temperature, provided the best performance of the cooling system, which results in decrease in performance when the heat load to be cooled is small or when the room temperature decreases, as it happens in winter. Likewise, when the room temperature gets high, such as in the summer, system performance declines.

Thus, in order to combine the maximum performance of a cooling system with the lowest use cost, it was found that it was necessary to vary the system cooling capacity according to the load to be cooled. Then, it was created the variable capacity - compressors.

Thus, when the compressor works in low capacity (low rotations), the capillary tube has the greater capacity of flowing the cooling fluid than the flow released by the compressor, which causes losses of 5% to 15% depending on the system and the room temperature.

In order to try to overcome the drawbacks of the aforementioned capillary tubes, variable flow - expansion devices were designed.

A drawback in variable flow - expansion devices of the prior art is the fact that, in small size systems, in which flows are small, the use of this device is constructive and financially unfeasible. Another drawback of the variable flow - expansion devices consists in that, in large size systems, where they show viability, did they do allow constructively the use thereof as heat exchangers in the compressor suction line, which prevents the increase in the performance of the cooling system.

Thus, the variable expansion devices of the prior art are not economically and constructively feasible (in small size systems) or do not allow the use thereof as a heat exchanger (in large size systems), which increases the performance of the system cooling.

OBJECTS AND ADVANTAGES OF THE INVENTION

The present invention directs providing a variable mass flow - expansion device, which enables excellent performance of the cooling system, and may be used in small size systems, and which directs portable and mobile systems, or large size system.

This object is achieved by means of an expansion device of a cooling system, adapted for regulating the mass flow of the cooling fluid, which comprises a tube having an inlet and an outlet of the cooling fluid, said tube having a spindle disposed therein, and said spindle being longitudinally displaceable within the tube. The spindle displacement may be accomplished by electrical, mechanical or pneumatic means.

Conveniently, the expansion device is disposed within a second tube, in the compressor suction line, constituting a heat exchanger.

Thus, an advantage of the invention is the fact of that the expansion device according to the invention moves continuously in order to always operate at the higher efficiency point of the refrigeration system.

Another advantage of the expansion device according to the invention is the fact of that it may be used as heat exchanger in the suction line of the compressor, both in large and small size systems, allowing the increased performance of the cooling system.

Another advantage is the of fact that the second tube acts as a liquid accumulator, and, therefore, the expansion device according to the invention allows to gather in the same space, the heat exchanger, the expansion device itself, and the liquids accumulator, allowing the system compaction, which is a considerable advantage in small size systems, such as household refrigerators or miniaturized and portable cooling systems, having little free space. The liquid accumulator has the function of preventing the coolant from entering the compression chamber in liquid state during thermal load oscillations or room temperature.

Still, there is the possibility of using it in laboratories for the development of cooling systems as a template for determination of equivalent capillary tubes. In those cases, the device is applied to a cooling system and adjusted until the product reaches its best performance. Following, it is measured the flow thereof in a test rig with fluid nitrogen and it is determined the corresponding capillary tube.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is hereinafter further described, by way of example, based on the accompanying figures:

FIGURE 1 - a schematic view of a cooling system having an expansion device according to the prior art; and

FIGURE 2 - a schematic view of a cooling system having an expansion device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a view of a conventional cooling system, where it is noticed a compressor 1 , which pumps the high pressure cooling gas 2, said gas passes through the condenser 3, it condensates and flows as a liquid at a high pressure 4, which passes through the expansion device 5, where its pressure is decreased. Then, the low pressure liquid 6 passes through the evaporator 7, absorbs heat from the load, vaporizes, and the cooling gas 8, flowing through the suction line 9, is again suctioned by the compressor 1 , completing the cycle.

Figure 2 shows a cooling system using a preferred embodiment of the expanding device 10 according to the invention. The expansion device 10 comprises a tube 1 having an inlet 12 and an outlet 13 of the cooling fluid, and a spindle 14 disposed within it. In the present embodiment the inner surface of tube 1 1 is smooth; however, alternatively, the surface may have a screw having the same thread pitch as the spindle 14. The cooling fluid is admitted into the device through the inlet 12, flows between the fillets of the spindle 14, and exits through outlet 13.

Sensors (not shown) installed in the cooling system send signals to, for example, an electric motor or an actuator (not shown), which drives the spindle 14 by moving it longitudinally either to the right or left, so that the mass flow may be regulated. Alternatively, the spindle may be driven manually or further pneumatically through the pressure differential of the cooling system. For a maximum cooling capacity, the spindle is fully displaced to the left, so that the load loss of the cooling fluid is minimum, thereby allowing the maximum flow of said cooling fluid.

Control logic may be incorporated, so that the flow may vary from 0% to 100%. At 0% position, the device would perform as a blocking valve.

When the system is already stabilized, for example, when the products within the refrigerator have already been cooled to a satisfying temperature, the thermal load of the system tends to decrease, and so does the cooling capacity of the cooling system. Thus, the flow of cooling fluid tends to be reduced, so that the cooling system works at a lower operation level. In this case, an electric pneumatic or mechanical drive drives the spindle by moving it forward to the right. Having the spindle displaced to the right as shown in Figure 2 increases load loss, since the number of fillets of the spindle 14 to be traveled by the cooling fluid is greater, and, thus, the flow of the cooling fluid decreases, by suiting the system to the cooling requirements of the moment. Naturally, the spindle 14 may be moved to any position relative to tube 1 1 , so that the cooling system always works under conditions of greatest efficiency.

Figure 2 also shows that the cooling fluid, when leaving tube 1 1 , passes through the evaporator 15, and, then passes through a second pipe 16, disposed in the suction line 17. Tube 16, together with tube 1 1 , configures a heat exchanger, and additionally serves as a liquid accumulator for the system. In the heat exchanger, the cooling fluid in tube 16 absorbs heat from tube 1 1 , and then, by flowing through the other section of suction line 17, is again suctioned by compressor 18.

Following, by restarting the cycle, the cooling fluid is pumped by compressor 18, passes through the condenser 19, and penetrates again at the expansion device 10 through inlet 12.

Thus, as previously mentioned, the expansion device according to the invention may be used as a heat exchanger in both small and large size systems, thereby increasing system performance.

In large size systems of the prior art, as shown in Figure 1 , the expansion device (expansion valve 5) does not allow constructively to use it as a heat exchanger in the suction line (line 9).

Therefore, the expansion device according to the invention allows having a performance that is the closest to optimum point over different conditions of room temperature and thermal load in both small size and large size systems.

In addition to the embodiment previously shown, the same inventive concept may be applied to other alternatives or possibilities of using the invention.

Thus, it will be understood that the present invention should be broadly interpreted, and its scope should be determined by the terms of the appended claims.