US2782596A - Elastic fluid actuated power systems - Google Patents

Description

Feb. 26; 1957 'r. 1. LINDHAGEN ETAL ELASTIC FLUID ACTUATED POWER SYSTEMS Original Filed Sept. so, 1947 ELASTIC FLUID ACTUATED POWER SYSTEMS Teodor Immanuel Lindhagen, Stockholm, and Hans Robert Nilsson, Ektorp, Sweden, assignors, by mesne assignments, to Svenska Rotor Maskiner Aktiebolag, Nacka, Sweden, a corporation of Sweden Original application Serial No. 776,928, September 30, 1947, now abandoned; Serial No. 289,161, May 21, 1952, now Patent No. 2,627,161, dated February 3, 1953. Divided and this application January 30, 1953, Serial No. 334,222

Claims priority, application Sweden April 3, 1947 The portion of the term of the patent subsequent to February 3, 1970, has been disclaimed 6 Claims. (Cl. 6039.61)

This application is a division with respect to our copending application Serial No. 289,161, filed May 21, 1952 (now Patent No. 2,627,161 granted Feb. 3, 1953) and as such is a division with respect to our copending application Serial No. 776,928, filed September 30, 1947 and allowed August 11, 1952 (now abandoned) and relates back to said application Serial No. 776,928 as a division thereof.

The present invention relates to elastic fluid actuated power systems and has particular reference to such systems of the kind in which motive fluid generated by the heating of a gaseous medium compressed in the system is directly employed for the production of power by expansion in the system.

In all such systems the attainable thermal efliciency of the cycle is largely influenced by the eflective heat drop that can be obtained from the motive fluid in the expansion phase, which in turn is largely influenced by the initial temperature of the motive fluid and the 'amount of heat rejected to the surfaces with which the motive fluid comes into contact while expanding. Consequently, one object constantly sought has been the provision of a system enabling the highest possible initial temperature of the motive fluid to be used that can effectively be employed. For that reason the heating means employed to produce the motive fluid has to be designed to give the motive fluid a high initial temperature which according to the invention is accomplished by combustion of a compressed gaseous combustion supporting medium in a suitable chamber to produce high temperature motive fluid comprising products of combustion. In order to obtain the best efliciency of the system a portion of the compressed gaseous combustion supporting medium is heated by means of the combustion products before being introduced into the combustion chamber. As-in acombustion process the temperature at which the fuel is burned is to be held as high as possible, it is of advantage that the gaseous combustion supporting medium is introduced into the combustion chamber in apreheated state. However, certain wall parts of the combustion chamber will have to endure a temperature in excess of that permissible for the material employed in said walls and as the introduced preheated gaseous combustion supporting medium is not sufliciently effective to cool said wall parts, a second portion of the compressed gaseous combustion supporting medium is utilized as means for directly cooling said Wall parts of the combustion chamber. This second portion of the compressed gaseous combustion supporting medium is conducted to the combustion chamber directly from the compressor and as this second portion enters the combustion chamber without any lossof pressure and unpreheated it constitutes an efficient cooling agent of high velocity. I v j For a better understanding of the more. detailed nature of the invention, reference may be had to the ensuing nited States Patent 2,782,596 Patented Feb. 26, 1957 portion of this specification, taken in conjunction with the accompanying drawings, which disclose suitable examples of apparatus for carrying the invention into effect.

In the drawings:

Fig. 1 shows in a longitudinal, transverse section an arrangement of a system embodying the invention comprising a compressor and an engine of the positive displacement type together with a combustion chamber and a regenerator built up to form a single power unit in which the air supply is utilized partly for engine cooling and partly for cooling the combustion chamber, the section being take on line Il of Figs. 2 and 3.

Figs. 2 and 3 are cross-sections on the lines 11-11 and III-Ill of Fig. 1 showing engine and compressor structure.

While in certain of its broader aspects the invention is not restricted to the utilization of rotary positive displacement compressors, the use of such a type, for at least one or more stages of compression, is much to be preferred to Wholly dynamic compression. The basic reason for this is that because of the similarity of operating characteristics between the power producing and the compressing units of a system wherein positive displacement apparatus is used in both, the variations in elflciency, capacity and other factors of the two sides of the system, under diflferent conditions of speed and load, so closely match one another that highly efficient operation of the system as a whole may be maintained over a relatively wide range of speeds and loads. Also, with positive displacement compression embodied in the system, a degree of stability is obtainable, even with sudden speed and load changes of considerable magnitude, that is diflicult if not impossible to obtain with wholly dynamic compression.

While for the purpose of obtaining the desired cooling of the engine by liquid or other fluid media is within the scope of the broader aspects of the invention it will be evident that the use of a gaseous medium is highly advantageous, particularly for the purpose of cooling the rotors. At the high temperature levels contemplated, cooling in the liquid phase, even with high boiling point liquids, would be difflcult if not impossible, except with a high pressure system, to keep tight. Moreover, from the standpoint of uniformity of cooling, the cooling passages should be asclose as practical to the surfaces requiring cooling. This requires, for the most satisfactory rotor cooling, passages at considerable distances from the axis of. rotation, with consequent increase in centrifugal force stresses with liquid versus gaseous cooling. Additionally, the preferred gaseous cooling by a cooling medium which is subsequently utilized to produce motive fluid for operating the system, avoids the thermal loss inherent in any system, liquid or gaseous, which employs an independent cooling system to which heat is rejected.

The initial temperature level of the motive fluid usable with the present invention is so high that in some instances it is desirable to provide for special cooling of the combustion chamber. This of course can be accomplished by a separate cooling system for the combustion chamber. Such an expedient, however, results in a thermal loss from the system which is undesirable. Since the total quantity of compressed air available is more than required to adequately cool the engine, the air supply is divided with one portion being utilized for engine cooling and another for cooling the combustion chamber. An arrangement of this kind is illustrated in Figs. 1 to 3. In this embodiment a compressor 15, having rotors 1.6 and 32, through coupling 12 and shaft 11, is driven by engine 23 having rotors 35 and 36. The engine rotors are provided with hollowshafts, those of the rotor 36 appearing at 10 and 24 in Fig. 1. As shown in Figs. 1 and 2 the body of rotor 36 is provided with spaced radially extending diaphragms or bafiles provided with ports 21 and 22 located to produce zig-zag flow of cooling air through the rotor as indicated by the arrows in Fig. 1. The rotor 35 is similarly provided with baffles 34 similarly ported to produce zig-zag flow, certain of the ports appearing at 33 in Fig. 2. As will be evident from the drawing the internal baiiles provide extended cooling surface and further provide for flow of the cooling air giving elfective and uniform skin cooling of the working surfaces of the rotors.

Air from the compressor 15 passes through the duct 13 to the distributing chamber 19. From this chamber a portion of the air flows through the rotors to the duct 5 leading to the negenerator 7. Another portion flows through one or more passages 9 to the jacket spaces 8 in the housing structure of the engine and from the latter to duct 5 through connections 6. Still another portion flows through connection 17 to the combustion chamber 29 to which air also flows from the regenerator 7 through duct 14.

In the construction shown the combustion chamber is provided with an inner shell 28 providing an inner chamber 27 to which fuel is supplied through burner 31. Air for combustion is supplied to chamber 27 through ports 30 communicating with duct 14. An intermediate shell 26 is provided which surrounds the burner end of the inner shell in relatively closely spaced relation to provide an annular cooling chamber to which cooling air from connection 17 is admitted and from which the air flows to the main chamber space of the combustion chamber.

From inspection of Fig. 1 it will be evident that the air reaching the combustion chamber through connection 17 will be at a higher pressure than that reaching the chamber through duct 14, since the latter supply has a certain pressure drop caused by its flow through the engine cooling system and the regenerator, while the former flows through a direct connection from the distributing chamber 19. This pressure diflerential is utilized to create high velocity flow of cooling air through the jacketing chamber 25, capable of exerting substantial cooling to the inner shell 28 which is subjected to the most intense heat of the combustion zone.

While for the sake of simplicity the embodiment shown in Figs. 1 to 3 has been illustrated more or less diagrammatically it will be understood that advantageous details of construction shown in the aforesaid Patent .No. 2,627,161 may equally well be utilized in the embodiment just described.

In the embodiment above described, labyrinth or leakage type seals are employed for both the engine and compressor components, the leakage air from which is usefully returned to the system to aid in externally cooling the ends of the rotors exposed to the high temperature motive fluid. Such seals are indicated more or less diagrammatically at Ma and 24a in Fig. 1, and as will be observed from that figure, operate to substantially isolate the flow of cooling air delivered from the compressor and flowing through the hollow shafts and the rotors of the engine 23, from the high temperature motive fluid supplied to the chambers formed between the rotors for operating the engine.

From the standpoint of the overall thermal efiiciency of the system, however, it is advantageous to convert all of the fluid upon which work of compression has been done to high temperature motive fluid at the desired inlet temperature for expansion from that temperature in the system. To secure such a result in a system embodying the principles of the present invention requires that the compressed fluid passed through the engine rotors and (or casing for cooling purposes be sealed ofi or isolated from the passages and) or working chambers for the expanding motive fluid.

While specific details of rotor profiles, numbers of lobes, helix angles, etc. are not critical and may vary as between different specific designs, there are certain fundamental characteristics of the apparatus employed, particularly the engine, that are of major importance for reasons hereinafter explained.

It is characteristic of rotary machines of the kind herein disclosed and also disclosed in the application of Hans R. Nilsson, Ser. No. 584,495, filed July 18, 1946, abandoned in favor of his continuation-in-part application Ser. No. 761,265, filed July 16, 1947, and granted December 23, 1952, No. 2,622,787, that the total wrap angle of the rotor lands is less than 360, usually ma terially less. When the wrap angle is less than 360, the working chambers vary in axial length as the rotors revolve, the axial length being defined between a place axially fixed relative to the rotors and casing, such as an end wall of the casing, and a place at which a rotor land meshes with a cooperating groove, the latter place moving axially relative to the rotors and casing as the rotors revolve, to vary the length of the chamber. This characteristic construction is of great importance from the standpoint of enabling sufficient cooling of the rotors to be effected to maintain the great degree of temperature difference between high inlet gas temperature and the moderate rotor temperature, which is characteristic of the invention, while at the same time not rejecting to the cool ing system so much heat from the high temperature part of the thermal process :as to materially reduce or cancel the thermal advantage accruing from the high initial gas temperature. Primarily, the reason for this is due to the fact that with the kind of rotor construction and Working chamber under consideration, the inlet ends of the rotor lands are subjected to the high initial gas temperature only during the inlet or admission phase of the cycle. As soon as any one expansion chamber is cut oif from the inlet port the temperature of the gas in the chamber drops as the gas expands and continues to drop until the exhaust phase of the cycle is reached. However, during both the expansion and exhaust phases of the cycle the chamber is still in part defined by the inlet end portions of the rotor lands, so that these portions, which are the only parts of the rotors exposed to the high initial gas temperature, are exposed to that temperature for only a minor portion of. the total time of the cycle, since the inlet phase of the cycle is ordinarily only of very short duration as compared with the duration of the combined expansion and exhaust phases of the cycles. Thus the average gas temperature to which the hot or inlet ends of the rotors are subjected is very much lower than the inlet gas temperature and since the cold or exhaust ends of the rotors are only subjected to exhaust gas temperature, there is ample opportunity for flow of heat by conduction along the lands from the hot to the cold ends of the rotors, thus even Without additional cooling tending to maintain a relatively great temperature difiference between inlet gas temperature and the highest rotor temperature.

Much test operation has been carried out at 1200 C. and at speeds of 18,000 R. P. M. or better with external load of the order of 50 to H. P. It is therefore appropriate to consider the heat conditions prevailing with such an inlet temperature. With inlet temperature of 1200 C. the exhaust temperature is of the order of 600 C. but the mean gas temperature to which the rotors are exposed is only of the order of 700 C. for the reason that each land is exposed to the temperature of partially expanded or exhaust gas for the greater portion of the time. The extent to which this is so is shown by the fact that with rotors of the specification given above, the inlet phase of the cycle for a given land covers some 7080 of rotation, the expansion phase covers some -140 of rotation while the exhaust phase (which is equal to the wrap angle plus the pitch angle between successive lands) coverstsome 290;

Under such conditions and with the rotors skin cooled by compressed air flowing through passages of the kind shown, .the rotor temperature at the inlet end is of the order of 500" C. andiat the outlet end of the'order of 400 C. giving a mean rotor temperature of the order of 450 C.

With a mean gas temperature of the order of 700 C., it is thus evident. that the cooling system has to absorb only enough heat to maintain a difference of some 250 C. between mean values, even though at the inlet end of the machine a temperature difference of the order of 700 C. is maintained between gas temperature and rotor temperature.

A further factor enabling a relatively large temperature difference to be maintained between the high temperature inlet gas and the walls of the chambers formed by the rotors and the casing is the fact that the velocity of the hot gases relative to the walls of the chambers is quite low as compared with other kinds of machines. In an engine of the kind under discussion, the relative velocity of the gas over these working surfaces at normal operating speed is only of the order of 100 meters per second, even with straight axial inlet and outlet flow, which gives the highest relative velocities in this type of machine. Since the rate of heat transfer from gas to solid is a function of the relative 'velocity between the two, a low rate of heat absorption is immediately evident.

As a result of the several factors discussed above and other minor factors, both calculations and test results show that in a system embodying an engine of the kind herein disclosed the overall heat rejection to the cooling air is of the order of only 20% and of that only approximately 4% is taken from the motive fluid before commencement of the exhaust phase of the cycle, the latter percentage corresponding to only approximately 2% of the work done. Since the major portion of the heat rejected to the cooling air is rejected at relatively low temperature level from partially expanded or exhaust gases, and is returned to the system, the engine, when cooled by air subsequently converted to motive fluid, is substantially a true regeuerator in contrast to those types of apparatus in which working surfaces are continuously exposed to inlet gas and from which they absorb large quantities of heat at high temperature level if attempt is made to cool them.

While as previously noted, the invention in its broader aspects is not restricted to the use of positive displacement compressors of the helical rotor type herein disclosed, such type, in addition to the advantages heretofore pointed out, is productive of further advantage from the standpoint of heat transfer for engine cooling purposes, when employed inpower units of the type herein disclosed. Such further advantage is due primarily to the fact that the several positive displacement compression chambers, coming successively into communication with the outlet port, produce a high frequency pulsating discharge, the frequency of which is a function of the speed of rotation of the compressor and the number of chambers discharging per revolution. With apparatus of the kind herein disclosed this frequency may be of the order of 60,000 to 80,000 or more per minute. If, now, as in the power units herein disclosed, the discharge from such a compressor is delivered more or less directly to the cooling passages of the engine and of the combustion chamber, the pulsating or vibratory character of the flow insures a high rate of heat transfer from the walls of the passages to the air, since such flow is effective in preventing the formation and/ or maintenance of the wall known stagnant molecular boundary layer of fluid which materially reduces the rate of heat transfer. When advantage is taken of the pulsating character of the discharge from a compressor of the preferred type, adequate cooling of the engine may be effected with the minimum quantity of cooling air, which, as shown in the system illustrated in Fig. 1 may be substantially less than the total quantity required to produce the motive fluid for operating the engine. In many other specific systems coming within the purview of this invention, it may be highly advantageous to be able to effect the necessary engine, cooling with less than the total quantity of fluid delivered by the compressor side of the system.

Novel features of construction of the prime mover per se disclosed but not claimed herein, form the claimed subject matter of our copending application Ser, No. 289,162, filed May 2i, 1952, as a division and continuation-in-part of our aforementioned application Ser. No. 776,928.

From the foregoing it will be apparent that in its several aspects the invention may be embodied in widely different specific forms and combinations of apparatus, and that certain of the novel features disclosed may be used to the exclusion of others. The invention is therefore to be understood as embracing all forms of apparatus and modes of Operation falling within the scope of the appended claims.

What we claim is:

1.-An elastic fluid power plant comprising compressor means, heating means for producing high temperature motive fluid from compressed elastic fluid delivered by said compressor means, power producing expander means operated by said motive fluid comprising a rotary positive displacement engine of the expansible chamber type having intermeshing rotors, passages for flow of cooling fluid through said rotors in proximity to the surfaces thereof, means for dividing the compressed medium into different portions, means for supplying a first of said portions as cooling fluid to and exhausting the same from said passages, means for cooling walls of said heating means by a second of said portions, and means for introducing both of said portions into said heating means for conversion into high temperature motive fluid.

2. An elastic fluid power plant comprising compressor means, heating means for producing high temperature motive fluid from compressed elastic fluid delivered by said compressor means, power producing expander means operated by said motive fluid comprising a rotary positive displacement engine of the expansible chamber type having intermeshing rotors, passages for flow of cooling fluid through said rotors in proximity to the surfaces thereof, means for dividing the compressed medium into different portions, means for supplying a first of said portions as cooling fluid to and exhausting the same from said passages, heat exchanger means for heating said first of said portions by the expander motive fluid after fl w through said rotor passages, means for cooling walls of said heating means by a second of said portions, and means for introducing both of said portions into said heating means for conversion into high temperature motive fluid.

3. Apparatus as defined in claim 1, in which the conduit system for flow of cooling fluid from the compressor means through the cooling passages to the heating means includes sealing means for substantially isolating the flow of cooling fluid from the flow of motive fluid.

4. A power unit for plants operated by elastic motive fluid comprising a rotary compressor of the helical rotor type providing positive displacement working chambers operative as the rotors revolve to compress and discharge in rapid succession a series of separate increments of compressed elastic fluid, whereby to deliver a pulsating supply of compressed fluid, a rotary positive displacement motor of the helical rotor type for expanding high temperature elastic motive fluid to provide power for operating the compressor, said rotors being provided with passages for cooling fluid adjacent to the working surfaces of the rotors exposed to the motive fluid, heating means for producing the motive fluid from the compressed fluid and connections for supplying one part of pulsating fluid from said supply to said passages to cool said rotors and another part of pulsating fluid from said supply to said heating means to cool the walls thereof.

5. A power unit for plants operated by elastic motive fluid comprising a rotary compressor of the helical rotor type having a casing enclosing the rotors and providing positive displacement workingzchambers operative asthe rotors revolve to compress and discharge in rapid succession a series of separate increments of compressed elastic fluid, whereby to deliver a pulsating supply of compressed fluid, a rotary displacement motor of the helical rotor type for expanding high temperature elastic motive fluid, said motor having a casing and rotors mounted therein, said rotors having shaft parts and body portions, said portions being provided with cooling passages adjacent to the working surfaces of the rotors exposed to the motive fluid, a housing structure connecting said compressor and motor casings and providing a chamher therebetween, the shaft parts of the rotors of said motor extending into said chamber and having passages therein providing communication between said chamber and the cooling passages in the body portions of the rotors, said compressor casing having a discharge port, communicating with said chamber, heating means for producing the motive fluid from the compressed. fluid, and a connection for supplying compressed elastic fluid from said chamber to saidv heating means to cool the walls of said heating means.

6. An elastic fluid power system comprising compressor means for compressing a gaseous fluid to produce high temperature motive fluid, heating means forv producing the motive fluid from the compressed fluid, a positive displacement rotary motor of the helical rotor type having expansible working chambers for expanding said motive-fluid: for driving said compressor means, the rotors having body partsrprovided with. internal passages therein for cooling fluid and shaft parts providing inlets and outlets communicating with said passages for flow of said cooling fluid, a conduit for supplying compressed fluid from said compressor means to said passages, a conduit for conducting said fluid from said passages to said heating means, sealing means associated with said shaft parts for substantially isolating the path of flow of said cooling fluid through the rotors of the motor from the path of flow of the motive fluid through the motor, and a conduit for supplying compressed fluid from said compressor means directly to said heating means to cool the walls of said heating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,287,268 Edwards Dec. 10, 1918 2,470,184 Pfenninger May 17, 1949 2,618,120 Papini Nov. 18, 1952 FOREIGN PATENTS 665,762 Germany Oct. 3, 1938

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