Compression refrigeration system

A compression refrigeration system having a compressor, a condenser, an evaporator, and a liquid refrigerant in which a capillary tube is positioned within an enclosure. The liquid refrigerant from the condenser is connected to the enclosure inlet and then flows to the inlet of the capillary tube and out of the capillary tube to the evaporator, whereby the refrigerant in the enclosure forms a heat exchange relationship with the exterior of the capillary tube for providing a self-regulating flow through the capillary tube. Improved charging of the system is provided by positioning the inlet to the capillary tube above the bottom of the enclosure and providing a refrigeration adding valve to the enclosure to insure that the enclosure is filled to a predetermined level in order to enter the capillary tube. Preferably, a reserve of liquid refrigerant is inserted into the enclosure above the capillary inlet for compensating for variations in density of the refrigerant. Preferably, the outlet of the capillary tube is positioned above the inlet to the capillary tube to aid in charging of the system in the field by allowing the enclosure to be filled with the proper amount of refrigerant by tilting the enclosure to a proper angle in accordance with the operating variables while filling the enclosure with refrigerant. Preferably, it is desired that the capillary inlet be at the top of the capillary coil and the capillary outlet be above the capillary inlet.

BACKGROUND OF THE INVENTION 
A conventional compression refrigeration system such as air conditioning 
generally includes a compressor which compresses a vapor refrigerant to a 
high pressure and high temperature, a condenser which removes the latent 
heat of condensation causing the gas to condense to a liquid, a capillary 
tube which provides a restriction for reducing the pressure, and an 
evaporator which absorbs heat from the medium to be cooled thereby causing 
the liquid refrigerant to evaporate back into a gas. 
The capillary tube has the advantage of being inexpensive, but has the 
disadvantage of being fixed. That is, the outlet pressure from the 
capillary tube is a function of the inlet pressure. In systems using air 
as the condensing medium, and to a lesser extent in those systems which 
use water, the temperature of the condenser varies as the temperature of 
the condensing medium varies. For example, on hot afternoons, the 
condenser temperature and thus its pressure increases thereby increasing 
the pressure to the inlet of the capillary tube, increasing the 
temperature and pressure from the outlet of the capillary tube causing 
refrigerant gas going to the compressor to be at a higher pressure and 
therefore more dense and causing the compressor to pump more pounds of 
refrigerant thereby further increasing the condenser pressure and further 
compounding the build up of pressure problem. One of the features of the 
present invention is the provision of an improvement for self regulating 
the refrigerant flow through the capillary tube for overcoming the buildup 
of the pressure cycle by means of the heat exchange from hot liquid to 
flash gas. Otherwise, carried to its extreme conclusion, pressure cycle 
buildup will cause loss of efficiency, overloaded equipment, safety trip 
outs and equipment failures. 
Another problem with conventional systems is that while the system can be 
satisfactorily charged with refrigerant under factory conditions, it is 
difficult under field conditions to obtain an accurate charging of the 
refrigeration system with the refrigerant. Another feature of the present 
invention is the provision of an improvement in a refrigeration system 
which allows service personnel to more accurately charge the refrigeration 
system in the field with the correct amount of refrigerant. 
Another problem with conventional systems is to provide compensation for 
refrigerant density which is dependent upon several variables. The present 
invention provides an improved system for establishing and storing a 
reserve capacity of refrigerant in the system and an improved means for 
allowing the service personnel to determine the amount of the reserve 
refrigerant which should be placed in the system. 
SUMMARY 
One feature of the present invention is the improvement in a compression 
refrigeration system having a compressor, a condenser, an evaporator, a 
liquid refrigerant, and a capillary tube in which the restriction to flow 
through the capillary tube increases as the pressure drop across the 
capillary tube increases thereby providing a more stable evaporator 
temperature. The capillary tube is positioned in an enclosure and the warm 
liquid refrigerant coming from the condenser flows into the enclosure in a 
heat exchange relationship with the capillary tube, enters the capillary 
tube, and flows to the evaporator. The liquid refrigerant, when hotter, 
tends to cause more refrigerant in the capillary tube to boil and flash 
into gas thereby restricting the flow through the capillary tube and 
resulting in a larger pressure drop than when the liquid is cooler 
providing a trend toward self-regulating flow through the capillary tube. 
A further object of the present invention is the improvement in a 
restriction between the condenser and evaporator of a capillary tube with 
an inlet and an outlet, an enclosure surrounding the capillary tube, the 
outlet of the capillary tube extending through the enclosure and connected 
to the inlet of the evaporator and the inlet of the capillary tube being 
in fluid communication with the interior of the enclosure. The enclosure 
has an inlet connected to the outlet of the condenser for receiving liquid 
refrigerant from the condenser which is placed in a heat exchange 
relationship with the exterior of the capillary tube and also flows into 
the capillary tube inlet for regulating the flow through the capillary 
tube. 
Still a further object of the present invention is the provision of 
positioning of the inlet of the capillary tube at a predetermined distance 
above the bottom of the enclosure for aiding in correctly charging the 
system with refrigerant. Preferably, the liquid level of the refrigerant 
in the enclosure is above the inlet of the capillary tube to provide a 
reserve capacity of refrigerant. In addition, a refrigerant adding valve 
is connected to the enclosure for adding refrigerant to the enclosure. 
Still a further object of the present invention is the provision of the 
enclosure inlet and the outlet of the capillary tube being adjacent to 
each other for increased heat exchange. 
Still a further object of the present invention is the provision of 
positioning the inlet of the capillary tube at the top of a coil and 
positioning the outlet of the capillary tube above the inlet of the 
capillary tube. Thus the enclosure may be positioned at various angles for 
aiding in properly filling the enclosure with refrigerant until the 
refrigerant flows from the capillary tube outlet. 
Yet a further object of the present invention is the provision of an 
improved system for storing a reserve capacity of refrigerant in an air 
conditioning system to compensate for the differences in the density of 
the gas in the system by providing an enclosure having an inlet and an 
outlet, the inlet being connected to the outlet of the condenser, the 
outlet being in communication with the inlet of the evaporator. A flow 
tube is positioned in the enclosure having an inlet in communication with 
the interior of the enclosure and the outlet of the flow tube being 
connected to the enclosure outlet. The inlet of the flow tube is 
positioned above the bottom of the enclosure and the outlet of the tube is 
positioned above the inlet whereby the enclosure can be filled with the 
proper amount of refrigerant by tilting the enclosure to a predetermined 
angle while filling until the refrigerant comes out of the outlet. 
Other and further objects, features and advantages will be apparent from 
the following description of presently preferred embodiments of the 
invention, given for the purpose of disclosure and taken in conjunction 
with the accompanying drawings.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, the schematic of a compression system for 
refrigeration, such as for air conditioning, is generally indicated by the 
reference numeral 10. As is conventional, the vapor of the refrigerant, 
which may be freon, in line 12 is compressed by the compressor 14 into 
line 16 at a high pressure and temperature such that the liquefaction 
temperature is above that of the atmospheric air or other coolant. From 
the compressor 14, the refrigerant goes to a liquefying condenser 18 where 
the heat of condensation is removed by air or cooling water causing the 
gas to condense to a liquid and passes through line 20. The now liquid 
refrigerant passes through a restriction such as a capilllary tube 22 
which separates the high pressure region from the low pressure region as 
the capillary tube reduces the pressure as it passes to line 24. The 
evaporator 26 absorbs heat from the medium to be cooled and the liquid 
refrigerant evaporates back into a gas and completes the cycle by 
returning to line 12. The capillary tube 22 has the advantage of being 
inexpensive but has the disadvantage of being fixed as compared to an 
expansion valve. Therefore the outlet pressure in line 24 is a function of 
the inlet pressure in line 20 to the capillary tube 22. This creates 
severe problems as the discharge pressure and temperature in line 20 from 
the condenser 18 varies widely as the temperature of the condensing 
medium, and particularly air, varies. 
Since the capillary tube is a fixed device, an increase in the pressure in 
line 20 will cause more refrigerant to pass through the capillary tube 22 
which causes the following undesirable results: 
(1) An increase in the outlet pressure from the capillary tube 22 and a 
corresponding increase in temperature, 
(2) An increase in the density of the gas in the low pressure side of the 
system in the line 22 and evaporator 26 further reducing the high pressure 
liquid available, and 
(3) An increase in the low side pressure in line 12 which causes the 
compressor 14 to handle more pounds of gas with each stroke thereby 
further elevating the pressure on the high side beginning in line 16. 
Therefore the cycle accentuates itself, that is, an increase in high side 
pressure 16 increases the low side pressure which further increases the 
high side pressure. 
Referring now to FIG. 1, the present invention is directed to providing an 
enclosure 30 about the capillary tube 22. The enclosure 30 includes an 
inlet 32 connected to the line 20 and thus connected to the outlet of the 
condenser 18 for receiving liquid refrigerant from the condenser 18. The 
capillary tube 22 includes an inlet 34 in communication with the interior 
of the enclosure 30 for receiving the liquid refrigerant returning from 
the condenser 18 and an outlet 36 connected to line 24 and thus connected 
to the inlet of the evaporator 26. The capillary tube 22 functions to 
reduce the pressure from the high pressure side to the low pressure side 
of the system 10. As the refrigerant passes through the capillary tube 22 
a portion of the refrigerant vaporizes as the pressure reduces thereby 
causing a refrigerating effect on the remaining liquid refrigerant and 
lowering its temperature. The refrigerant entering the inlet 32 of the 
enclosure 30 is in a heat exchange relationship with the exterior of the 
capillary tube 22, which is preferably helically wound, therefore, on hot 
days when the temperature and pressure of the incoming refrigerant in the 
enclosure 30 is greater, the refrigerant entering the enclosure 30 tends 
to cause the refrigerant in the capillary tube 22 to boil and flash into 
gas thereby restricting the flow through the capillary tube 22 resulting 
in a larger pressure drop than when the incoming refrigerant into the 
enclosure 30 is cooler. Therefore, the present system compensates as the 
temperature of the condensing medium, either air or water, over the 
condenser 18 varies. That is, in the event of increased pressure and 
higher temperatures in the condenser 18 and line 20, there is an increased 
heat exchange between the high temperature liquid inside of the enclosure 
30 and the low pressure and flash gas vapor in the capillary tube 22 which 
causes an increase of gas in the capillary 22 resulting in a greater 
pressure drop across the capillary tube 22 which tends to compensate for 
the higher pressure and temperatures in the line 20. Thus, the present 
system provides a self-regulating flow through the capillary tube in the 
face of varying ambient conditions. 
One conventional method of attempting to overcome the problem of increased 
flow through the capillary tube upon an increase of pressure and 
temperature is to limit the amount of refrigerant in a system to a 
"critical charge". In this method only a given amount of refrigerant is 
placed in the system such that the amount of liquid available at the 
capillary tube 34 would be less than 100% to break up the buildup of 
pressure cycles. This is inefficient as it requires expenditure of energy 
for no other purpose than to limit a system from malfunctioning. However, 
in the present system the heat from the warm refrigerant in the enclosure 
30 heats the mixture of cooler liquid and flash gas in the capillary tube 
22 causing more flash gas to be developed and in turn causing a greater 
restriction through the tube 22 which further causes more flash gas to be 
developed. But also, the heat which comes out of the warm liquid in the 
enclosure 30 tends to subcool that liquid prior to entering the capillary 
tube 22 and therefore less flash gas is required to effect the desired 
pressure reduction. The net result is that a higher quality of liquid is 
available for passage to the evaporator 26 than is possible under the 
"critical charge" method. 
Preferably, the inlet 32 of the enclosure 30 is adjacent to the outlet 36 
of the capillary tube to provide an increased heat relationship between 
the refrigerant in the enclosure 30 and the capillary tube 22. 
Another problem encountered in refrigeration systems is the problem of 
accurately and correctly charging the system with the proper amount of 
refrigerant. Another feature of the present invention is to improve the 
charging methods used in the field. Thus, the inlet 34 of the capillary 
tube 22 is positioned a predetermined distance above the bottom of the 
enclosure 30 thereby requiring that the refrigerant level in the enclosure 
level be sufficient to enter the capillary tube 22. Service personnel can 
quickly detect if the refrigerant level has reached the inlet 34 of the 
capillary 22 by feeling the temperature of the capillary tube outlet 36. 
The temperature will be warm if the liquid level of the refrigerant in the 
enclosure 30 is below the inlet 34 and will be cold when the liquid level 
in the enclosure 30 is at or above the inlet 34. In addition, the service 
personnel can also determine by the sound of the fluid passing through the 
capillarly 22 whether or not the liquid level is sufficiently high. While 
other portions of the system 10 may have inlets for charging refrigerant 
into the system 10, it is desirable to provide a refrigerant adding valve 
40 such as a conventional Schrader valve or needle valve to facilitate the 
adding of refrigerant at this more desirable point in the system 10. 
Another feature of the present invention is the provision of a reserve 
capacity of refrigerant in the system to compensate for differences in 
density of the gas in the system. While the apparatus of FIG. 1 could be 
utilized by inserting an extra amount of liquid refrigerant into the 
enclosure 30 above the capillary tube 22, the preferred embodiment is best 
seen in FIG. 2 which is generally similar to the apparatus shown in FIG. 1 
except in an upright or vertical position and in which like parts are 
designated by like numbers with the suffix "a". In FIG. 2 the liquid 
refrigerant in the enclosure 30a has a reserve capacity equal to the 
distance 42 above the inlet 34a of the capillary tube 22a which serves as 
a small reservoir refrigerant available to compensate for the variations 
in the density of the refrigerant. However, the amount of the reserve 
capacity 42 as well as the amount of the charge of refrigerant in the 
system 10 depends upon several variables which may include the ambient 
temperature, size and length of the lines, and design efficiency. The 
present invention is particularly applicable to assisting the service man 
by providing a more accurate method of charging a system and providing for 
the desired reserve capacity. That is, the volume inside of the enclosure 
30 is known. And by placing the enclosure 30a in a tilted position as best 
seen in FIG. 3, the volume below the inlet 34a and the outlet 36a will 
vary with the angle at which the enclosure 30a is set relative to 
horizontal. Therefore, the volume of liquid refrigerant placed in the 
enclosure 30a through the valve 40a and filling the space below the dotted 
line 50 before the liquid flows out of the outlet 36a will be determined 
by the angle from horizontal that the container 30a is set while filling. 
Thus, a suitable charging chart can be provided with emperical values 
based upon the measured variables to determine the angle at which the 
container 30a should be set. In addition, suitable indicating lines 50 can 
be placed upon the exterior 30a to aid the service personnel in tilting 
the container 30a to the proper angle for filling. 
While the feature of properly charging the enclosures 30 and 30a are 
particularly applicable for use in combination with the temperature 
compensation of the capillary tubes 22 and 22a, the structure of improving 
the accuracy of charging an air conditioning system 10 in the field by a 
service man may be utilized independently of a capillary tube system. 
Referring now to FIG. 4, an enclosure 60 is provided having a refrigerant 
adding valve 62 and an inlet 64 which is connected to and receives liquid 
refrigerant from a condenser. An unrestricted flow line 66 is positioned 
in the enclosure 60 having a fluid inlet 68 positioned above the bottom of 
the enclosure 60 and an outlet 70 which may be connected to any suitable 
restriction such as an orifice, or an expansion valve. The enclosure 60 is 
suitable for allowing a service man to accurately charge a refrigeration 
system with the correct amount of refrigerant and provide a reserve 
capacity indicated by the level 72 above the inlet 68. The enclosure 60 is 
charged similarly to the charging of the container 30a as described in 
connection with FIGS. 2 and 3 by tilting the enclosure 60 to an angle from 
the horizontal as determined by indicating lines 74 which are determined 
by an emperical charging chart based upon the known variables and 
thereafter the enclosure 60 is placed in the upright position as shown in 
FIG. 4. 
It should be noted that while the reserve capacity of refrigerant in the 
system will increase the efficiency of the system by increasing the 
quality of liquid refrigerant going into the evaporator, the safety 
feature of a limited charge is maintained, and even enhanced by having a 
more accurate means of charging the system with only a small amount of 
reserve refrigerant. 
The present invention, therefore, is well adapted to carry out the objects 
and attain the ends and advantages mentioned as well as others inherent 
therein. While presently preferred embodiments of the invention have been 
given for the purpose of disclosure, numerous changes in the details of 
construction and arrangement of parts will readily suggest themselves to 
those skilled in the art and which are encompassed within the spirit of 
the invention and the scope of the appended claims.