US 3090210 A
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May 21, 1963 J. c. GROFF 3,090,210
REFRIGERATION SYSTEM WITH CONTROLS Filed 001:. 27, 1960 I 45 v. I
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INVENTOR JAMES C. GROFF BY U ATTORNEY United States Patent 3,090,210 REFRIGERATEON SYSTEM WITH CQNTROLS James C. Groif, Anaheim, Calif, assignor, by mesne assignments, to Astro Science Corporation, West Los Angeles, Calif, a corporation of California Filed Oct. 27, 1960, Ser. No. 65,409 7 Claims. (Cl. 62-197) This invention relates to improvements in a refrigeration system of the compressor, condenser, and expander type and to improvements in the control thereof.
The primary object of the invention is to make possible a smaller size heat exchanger with increased efficiency and capacity to thereby enhance the compactness. The attainment of this objective is, of course, highly desirable in aircraft applications where weight and size are at a premium.
As a corollary to the foregoing stated object, other objectives have been realized. One of the further objectives is that of better distribution of liquid refrigerant inside the heat exchanger. By improving the distribution of the liquid refrigerant more effective use is made of the surface inside of the heat exchanger.
Another object is to improve the effectiveness and compactness by utilizing relatively small heat exchangers in series. In combination with this object is that of avoiding excessive pressure drop in the refrigeration side of the heat exchangers and by utilizing a vapor separator between the heat exchangers which by-passes a part of the vaporized gas around the second stage evaporator.
Another object is to achieve capacity reduction or capacity control of the system by providing a point of hot gas injection between the evaporators.
Another object is to realize hermetic type of evaporator by mounting all of the components of the system including the series heat exchanger in a rectangular enclosure and employing a pour-in-place type of insulation.
Another object of the invention is to improve the efficiency, effectiveness, and compactness of the system of the type described by utilizing evaporatons which may be of a shell and tube type in a vertical position with liquid refrigerant being admitted at an end. With this arrangement it is possible to feed all refrigeration tubes with the same quality of mixture emerging from the expansion valve and the capacity is improved by reason of the uniform distribution and more effective usage of all of the heat transfer surface of the unit.
A further object and advantage of the invention is that the liquid passages are connected in series so that the velocity of flow is increased and the efliciency of the heat exchanger is improved.
Another object is to overcome and eliminate the deficiencies of prior art systems in the way of uneven distribution of refrigerant in the evaporators and resulting lack of effectiveness.
Another object is to achieve and realize an efficient, effective, and compact system utilizing a single expansion valve.
Another object of the invention is to realize a system which inherently provides an ideal point of hot gas injection for controlling capacity.
ferred form of the invention.
In the form of the invention, as shown in the figure, the system utilizes relatively small shell and tube type heat exchangers as designated at 10 and 12. These heat exchangers are connected in series as will be described 3,090,210 Patented May 21, 1963 and are mounted on end, that is, vertically for reasons which will become more apparent presently. The flow of liquid to be cooled is through the heat exchangers in series. It enters through pipe 14 at the top of the shell of heat exchanger 12 and passes downwardly therethrough. It then exits from heat exchanger 12 through pipe 15 and enters the bottom of the exchanger 10 passes upwardly therethrough and passes out through the pipe or conduit 16.
The construction of the heat exchangers themselves is conventional. Each comprises a shell as shown at 17 for the heat exchanger 10 having a plurality of vertical tubes 18 therein for passage of refrigerant therethrough. Within the heat exchanger 10 there are provided a plurality of transverse bafiles as shown at 20 providing tortuous passageway through the heat exchanger for the liquid to be cooled.
Referring to the refrigerant side of the heat exchangers,
a pipe 22 having an expansion valve 23 in it, the refrigerant entering the plenum chamber 25 at the lower end of the heat exchanger 10. Heat exchanger 10 is the final chiller of the system. Refrigerant gas and liquid mixture is present in the chamber 27 at the upper end of the heat exchanger 10 and it passes through a pipe 28 to a liquid vapor separator designated by the numeral 32. This separator is shown in the form of a generally cylindrical chamber in which the liquid refrigerant settles to the bottom and the gas is drawn to the top. The liquid refrigerant is then taken to the heat exchanger 12 through the pipe 33 entering at the bottom thereof. It passes vertically through the refrigerant tubes in the heat exchanger 12 exiting at the top through the pipe 35 which connects to the suction side of a refrigerant compressor designated by the numeral 35 which may be of a conventional type. It may be driven by an electric motor or other means. It discharges into condenser shown diagrammatically at 37 which may be of a conventional type having a liquid receiver or collector 38.
Heat exchanger '12 is the primary chiller of the system. Refrigerant vapor taken from separator 32 is taken through a pipe 41 which connects to the pipe 35 so that only the vapor passes from the separator 32 back to the compressor 36.
With reference to the system as so far described, the arrangement includes among other things, as will be referred to, that the shell and tube heat exchangers 10 and 12 are in vertical positions .to improve the refrigerant distribution and make possible the use of a smaller area chiller unit still having the necessary "capacity.
Both the refrigeration circuit and the liquid to be cooled circuit are in series. This keeps the velocity high and the efiiciency of the heat transfer surface high. By reason of the series connection in the refrigerant circuit only one expansion valve 23 is required in the system. This makes possible a much more stable system than one of the type were two expansion valves are used in parallel.
The use of the liquid vapor separator 32 prevents the pressure drop from becoming extremely high in the series connected refrigeration circuit. The separator reduces the amount of gas which is required :to go through the primary chiller 12 and consequently reduces its pressure drop. Furthermore, it provides for a more direct connection of the final chiller 10 to the suction pipe of the compressor 36 and causes the final chiller to operate at a lower evaporator temperature and pressure.
The system provides a point of hot gas by-pass injection between the primary chiller 12 and the final chiller control, hot gas is injected into the pipe 42 as will presently be described.
With reference to the control of the system, the expansion valve 23in pipe 22 may be a conventional type of refrigeration expansion valve controlled in response to the degree of super-heat in the suction conduit 35. It is connected by a tube or line 44 to a sense bulb 4 5 ad jacent to the line 35 and responsive to the temperature therein. The bulb 45, of course, contains a temperature responsive fluid which expands and contracts developing a pressure proportional to the degree of super-heat in the line 35.
. The point of hot gas injection into the evaporator assembly eliminates the need for a separate expansion valve used only for the purpose of quenching the heat in the hot gas. The hot gas line 42 may connect to a suitable point at the compressor outlet and it has in it the control valve 50. The valve 50 is operated by a control motor 51 which preferably may be an electrical type which is connected by linkage 52 to the operating member of the valve 50. The control motor 51 is controlled by a sense bulb, that is a thermostat 54 which is positioned as shown to sense liquid outlet temperature at the pipe 16, that is the outlet of the final chiller 10. The liquid which is cooled by the unit may, by way of example, be ethylene glycol. A hermetically sealed enclosure shown schematically at 58 encloses the components shown there within, and the spaces between the components may be filled with insulation, which may be poured into the enclosure 58. The injection of hot gas through the pipe 42 provides for capacity control of the system, the system ordinarily at normal loads operating under the control of the thermostat 45 and valve 23. The capacity control occurs under conditions of extremely light loads or in cases Where the ambient conditions and consequently the condensing temperatures are reduced and the refrigeration capacity of the system is greatly increased. As the load is reduced on the chillers lll'and 12, the outlet temperature of the liquid leaving the chillers will become too low. At that point, the thermostat 54 in the liquid outlet passage will sense a low temperature and send a signal to open the gas control valve 50 slightly. This gas control valve allows hot gas to enter the pipe 33 and the lower part of the heat exchanger 12. As the chiller load is decreased the gas flow through the control valve 50 is increased so that the suction pressure will not be pulled down to an extremely low value. As will be observed, the point of hot gas injection is such that the hot gases are not injected into the return line to the compressor. The advantage of this is that the hot gas is usually at a temperature such that it would be unsafe for direct return to the compressor. Consequently the necessity of mixing the liquid refrigerant with such hot gas is eliminated and there is no need for an additional expansion valve controlling such liquid refrigerant for quenching the hot gas. It is to be observed that if the two evaporators shown in the FIGURE were used in parallel along with a hot gas quenching system as described, there would necessarily be three expansion valves in the system and hence there would necessarily be a tendency for the expansion valves to effect each other and the result would be a thoroughly unstable system. The system and arrangement of the invention as shown and described overcomes the disadvantages in a very simplified eifective way.
The foregoing describes the principles of the system and its operation. However, from the standpoint of further details, it may be pointed out that representatively the refrigerant leaving expansion valve 23 might be approximately 47% by weight of gas and 53% by weight of liquid. Representative-1y, the primary chiller 12 might carry approximately /3 of the total load; the refrigerant leaving the chiller might be approximately 60 by weight of gas and 40% by weight of liquid. The function of the liquid vapor separator is to separate the majority of the vapor and prevent it from entering the primary chiller 12. By this means, the pressure drop in the primary chiller in the refrigeration side of the heat exchanger is reduced as a great majority of the refrigeration products are thy-passed by way of the separate pipe 41 to the suction gas connection 35. The function of the primary chiller 12 is also to complete the evaporation of refrigerant so that the products exiting through the pipe 35 will be gas. It will be observed that the sense bulb E5 is beyond the connection of the pipe 4135 and the expansion valve 23 is set to provide a proper degree of super heat at that point.
By injecting the hot gas at the point shown into the line 33 space is provided Within the evaporator assembly for mixing \hot gas and liquid refrigerant. The refrigerant circuit tubes provide an excellent place for the mixing required. It should be noted that since the expansion valve sense bulb 45 is located on the outlet suction gas connection for the entire package, any introduction of hot gas will tend to raise the super heat and will conse quently increase the flow of liquid refrigerant to the expansion valve 23. However, the super-heat of the suction gas will remain normal. The entire system including the refrigerant for hot gas quenching is controlled by a single expansion valve, the hot gas injected at 42 being quenched in the manner described within the evaporator assembly. This particular point of hot gas injection also provides for sufficient velocity of refrigerant products in the primary chiller to prevent any possibility of oil trapping. Such refrigerant oil is soluble in liquid refrigerant. It is freely carried through the final chiller due to the large amount of liquid refrigerant still flowing. In the primary chiller 12 where all refrigerant is transformed into vapor, there could possibly be some trapping of some residual oil if the velocity in the refrigerant tubes were cut down to a low value. However, with the present controlled system when the refrigeration load decreases the flow of hot gas through line 42 in the system is increased. Consequently, the velocity of the refrigerant products through the primary chiller is kept at maximum at all times. This eliminates the possibility of trapping oil anywhere in the evaporator system.
From the foregoing those skilled in the art will observe that the invention as described, achieves and realizes the objectives and advantages as stated in the foregoing. The arrangement of the heat exchangers in vertical position provides for the best possible distribution of refrigerant thus providing for the highest possible efiiciency with maximum compactness. By using numerous small heat exchangers connected in series, the required heat transferred capacity can be realized in a much shorter assembly.
The use of the vapor separator decreases the pressure drop in the overall evaporator package and thereby provides for a greater log mean temperature difference between the refrigerant used and the liquid being cooled.
The point of hot gas injection into the evaporator assembly eliminates the need for a separate expansion valve used only for the purpose of quenching the heat in the hot gas. When the liquid outlet temperature becomes too high the gas control valve is opened slightly. As the additional heat is introduced into the evaporator the expansion valve sense bulb senses the additional superheat and signals the expansion valve to increase the flow of liquid refrigerant. It is to be observed that this is done 'by the use of only one expansion valve. The overall effect of introducing hot gas in this location is to create a dummy load and it raises the pressure of the refrigerant within the evaporator thereby increasing the temperature. Consequently the log mean temperature difference between the liquid being cooled and the refrigerant is reduced. With a control system set up in this manner, it is, under certain conditions, possible to reduce the actual refrigeration capacity of the evaporator to nearly 0%.
Introduction of the bypass gas at this point in addition to eliminating the one expansion valve for hot gas quenching eliminates the long length of mixer tube that is normally required to mix the hot gas and the liquid refrigerant. Also elimination of this extra expansion valve provides for a more stable system as there is nothing that will continually fight the expansion valve controlling the main evaporator.
While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiment, it is recognized that de partures may be made therefrom within the scope of the invention which is therefore not to be limited to the details disclosed herein but is to be afforded the full scope of the claims.
What is claimed is:
1. In a refrigerating system of the compressor-, condenser-expander type, in combination, means comprising a plurality of evaporators connected for series flow of refrigerating medium therethrough, means comprising a separator unit between the evaporators for separating gas from liquid, said unit having a connection for flow of gas from the unit to the outlet of the evaporators, means for passing medium to be cooled through said evaporators, and means for injecting hot gas into the flowing refrigerating medium, said last means being connected to the connection between two adjacent evaporators and means for controlling the admittance of the hot gas.
2. The system of claim 1 including a control valve for controlling the admittance of hot gas and means whereby said valve is controlled in response to the outlet temperature of medium to be cooled passing through the system.
3. The system as in claim 2 wherein the flow of medium to be cooled is in series relationship through the evaporators.
4. The system of claim 1 wherein the evaporators are of the shell and tube type and are positioned in a vertical position.
5. The system of claim 1 wherein the refrigerating medium and medium to be cooled pass through the system in counterflow relationship.
6. A refrigeration system comprising a plurality of evaporator units, said evaporator units each including a plurality of upright tubes with a plenum chamber at both bottom and top areas, a baffled liquid flow area around said tubes, a transfer conduit from the top plenum chamber of one unit to the bottom of the following unit, a supply line for liquid refrigerant to the bottom area of one unit, said evaporators being connected for counterflow of medium to be cooled with respect to the direction of refrigerant flow, a separator header as said transfer conduit interconnecting at least two units, said separator header having a sump area for the collection of liquid and a hood area for collection of gasses, said separator header connected to be supplied from said top area of said one unit, a supply line from said sump area of the header to the bottom of the other of said units as a supply line thereto, an exhaust line from said gas hood area, and control means for refrigerant introduction into the said bottom area of said one unit operatively responsive to the exhaust temperature from said exhaust line.
7. A refrigeration system comprising a plurality of evaporator units, said evaporator units each including a plurality of upright tubes with a plenum chamber at both bottom and top areas, a bat-lied liquid flow area around said tubes, a transfer conduit from the top plenum chamber of one unit to the bottom of the following unit, a supply line for liquid refrigerant to the bottom area of one unit, said evaporators being connected for counterflow of mediumto be cooled with respect to the direction of refrigerant flow, a separator header as said transfer conduit interconnecting at least two units, said separator header having a sump area for the collection of liquid and a hood area for collection of gasses, said separator header connected to be supplied from said top area of said one unit, a supply line from said sump area of the header to the bottom of the other of said units as a supply line thereto, an exhaust line from said gas hood area, control means for refrigerant introduction into the said bottom area of said one unit operatively responsive to the exhaust temperature from said exhaust line, and means for injecting hot refrigerant gas into the flowing refrigeration medium, said last means being connected to the supply line from said sump area to the bottom of the other of said units, and means for controlling the admittance of the hot gas.
References Cited in the file of this patent UNITED STATES PATENTS 1,493,016 Bush May 6, 1924 2,138,777 Zellhoefer Nov. 29, 1938 2,323,474 Kraft July 6, 1943 2,669,099 Malakoif Feb. 16, 1954 2,772,076 Matthews Nov. 27, 1956 2,805,555 Schumacher Sept. 10, 1957