US3830063A

US3830063A - Energy storage and removal methods for rankine cycle systems

Info

Publication number: US3830063A
Application number: US00346397A
Authority: US
Inventors: D Morgan
Original assignee: Thermo Electron Corp
Current assignee: Thermo Fisher Scientific Inc
Priority date: 1973-03-30
Filing date: 1973-03-30
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20
Also published as: CA1001018A; DE2415338A1; JPS49128102A

Abstract

A system and method for handling excess energy encountered under load conditions substantially higher than those attendant upon ordinary running conditions in a variable power vapor cycle engine. Secondary cooling is employed only as needed during periods of high load. The secondary cooling may be in the form of a heat exchanger immersed in a liquid contained in an air-cooled thermal storage chamber or, in the alternative, may be obtained by spraying a conventional primary condenser with coolant from a pressurized storage tank during high load periods. In the first-mentioned secondary cooling arrangement, the vapor or working fluid of the engine may be subjected to secondary cooling before or after the vapor passes through the primary condenser.

Description

United States Patent 11 1 Morgan Aug. 20, 1974 OUT [ ENERGY STORAGE AND REMOVAL METHODS FOR RANKINE CYCLE Primary ExaminerEdgar W. Geoghegan SYSTEMS Assistant ExaminerH. Burks, Sr. [75] Inventor: Dean Thomas Morgan, Sudbury, Attorney Agent or firm-James Neal M s. as 57 ABSTRACT [73] Asslgnee: a r g i Corpomnon A system and method for handling excess energy ena countered under load conditions substantially higher [22] Filed: Mar. 30, 1973 than those attendant upon ordinary running conditions in a variable power vapor cycle engine. Secondary [21] App! 346397 cooling is employed only as needed during periods of high load. The secondary cooling may be in the form [52] US. Cl. 60/645, 60/670, 60/691, 70/692, of a heat exchanger immersed in a liquid contained in 60/693 an air-cooled thermal storage chamber or, in the alter [51] Int. Cl. F0lk 25/00 native, y be Obtained y p y g a conventional [58] Field of Search 60/36,38, 95 R p y Condenser with Coolant from a Pressurized storage tank during high load periods. References Cited In the first-mentioned secondary cooling arrangement, UNITED STATES PATENTS the vapor or working fluid of the engine may be 3,040,528 6/1962 Tabor et al.. 60/36 Subjected to Secondary Cooling before Or after the 3,194,021 7/1965 Peake et al.. 60/95 R vapor Passes through the P y Condenser- 3,237,403 l/l966 Feher.... 60/36 3,516,249 6/1970 Paxton. 60/38 16 Clams 6 Drawmg F'gures 3,584,457 6/l97l Davoud 60/36 4 v 2 EXPANDER TURBO OR BOILER POSITIVE DISPLACEMENT) 38 l 1 s 36- REGENERATOR ./l2

FEED PUMP AIR COOLED l9 CONDENSER CONDENSED AND SUBCOOLED LIQUID 3O PATENTl-imuczo mm H 3. 830.983

SHEET 10F 2 1 2\ EXPANDER BOILER (TURBO OR POSITIVE DISPLACEMENT) FIG. I

36- REGENERATOR /|2 FEED PUMP AIR coon-:0

CONDENSER CONDENSED AND SUBCOOLED LIQUID 3o 24 OUT 24 I? 28 I6 FIG. 2 g: 5

PATENTEDAUBE'O m4 3.830.063

sum 20F 2 mwrrrw'w' AIR FLOW FIG. 5 l6 AIR FLOW ENERGY STORAGE AND REMOVAL METHODS FOR RANKINE CYCLE SYSTEMS BACKGROUND OF THE INVENTION Vapor cycle engines, particularly when used in automotive or similar applications, frequently have peak loads imposed upon them which are substantially higher than those encountered under ordinary running conditions. In open cycle engines, the vapor or working fluid is vented into the atmosphere after it has performed useful work and no condenser is utilized in the system. However, because the fluid is vented and must be replaced, it is necessary to carry a large reservoir of working fluid which must be transported by the vehicle being driven by the engine.

In closed cycle engines a condenser is used to convert the working fluid from vapor to liquid to be used once more in the cycle of the engine. To cope with the peak loads, conventional practice is simply to employ a condenser of sufficient capacity to handle those peak loads. In the specific case of automotive applications,

the engine must be capable of accelerating in quick bursts and the power needed for such bursts is much greater than that needed for driving at relatively unchanging speeds. Stated otherwise, the engine must be operable for short periods at power levels far above those considered maximum for sustained operation. In engines of the type with which the present invention is concerned, air-coolant condensers of capacity great enough to handle the peak load on a sustained basis are commonly used. This constitutes a brute force solution to the problem and the extra cooling capacity of the large condensers is used inefficiently.

The large condenser design is disadvantageous for other reasons. In any automotive vehicle, the permissible engine weight is limited and, also, the amount of space available is limited in size and frequently'in configuration. Moreover, engine efficiency is reduced because parasitic air flow cooling losses increase as condenser size is increased. Finally, the larger the con denser is, the more expensive it becomes.

SUMMARY OF THE INVENTION This invention is concerned with vapor cycle engines suitable for automotive applications. According to this invention, the capacity of the engines primary condenser may be reduced below that required for peak power operation. During high power transients, the heat of the working fluid, in excess of the primary condensers capacity, 'is absorbed by a liquid contained in a secondary cooling system. In this manner, The load imposed on the primary condenser is reduced.

In one embodiment of the secondary cooling system, the working fluid passes through a heat exchanger immersed in a liquid contained in an air cooled thermal storage chamber. This liquid partially cools the working fluid, thus reducing the load imposed on the condenser. The heat absorbed by the liquid is released through the walls of the chamber. Cooling vanes or impingement cooling apparatus are employed to increase the heat rejection rate of the chamber. Dueto the fact that heat can be absorbed rapidly by thevliquid during high power transients and released at a slower rate during lower sustainedpower operations, the total amount of cooling surface in both the primary condenser and the secondary cooling system is less than that required by a single condenser in a conventional system.

The thermal storage cooling system is compatible with various vapor cycle engine designs. It can be arranged to cool the working fluid before, or after, it passes through the primary condenser, or it can be placed in line with each condenser stage. It can also be designed to operate on demand by means of a simple valving arrangement.

In another embodiment, a liquid is stored in a pressurized tank and is sprayed against the cooling surfaces of the condenser during high power transients to incease the condensers cooling capacity. It is also possible to combine this system with the thermal storage cooling system to meet a wide range of design requirements.

The employment of secondary cooling as in this invention in an automotive vapor cycle engine significantly reduces the required size of the engine s primary condenser. Thus engine weight is reduced, space is conserved and condenser costs are are minimized. Furthermore, engine efficiency is increased because the condensers parasitic load is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description of a preferred embodiment of the invention which should be read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic of a vapor cycle engine with a secondary cooling system,

FIG. 2 is a plan view, in section, of a condenser and its associated secondary cooling system,

FIG. 3 is a schematic showing of a condenser and its associated secondary cooling system,

FIG. 4 is a plan view, in section, of another form of condenser and its associated secondary cooling system,

FIG. 5 is a schematic representation of the device illustrated in FIG. 4; and,

FIG. 6 is a schematic showing of a condenser and its associated secondary cooling system.

DESCRIPTION OF THE PREFERRED EMBODIMENT system 19. The heat exchanger 18 is immersed in a liquid 20, such as water or water mixed with a non-volatile anti-freeze contained in an air cooled thermal storage chamber 16. The liquid 20 absorbs heat from the fluid as it passes through the heat exchanger 18. The chamber 16 is provided with a pressure release valve 22 and an impingement heat transfer mechanism 40. The working fluid passes from the chamber 16 via a conduit .24 into a primary condenser 26. After being recondensed, the fluid passes-through a conduit 30 into a feed pump 32. From there it is pumped through a conduit 34 into the regenerator 10 where it passes-through another heat exchanger 36 and absorbs the heat rejected by the heat exchanger 12. In this preheated state it passes through a conduit 38 into the boiler 2, thus completing the cycle.

During steady state operation at or below a given maximum sustained power level, the liquid 20 reaches an equilibrium temperature at which the rate of heat absorption from the heat exchanger 18 equals the rate of heat rejection through the walls 17 of the chamber 16. The air flow over both the chamber 16 and the primary condenser 26 is normally generated by a fan and the pressure differential created by vehicle motion. The rate of heat rejection through the walls 17 can be improved, and the equilibrium temperature of liquid 20 lowered, by increasing the surface area of walls 17, or preferably, by providing air impingement nozzles 40 on the upstream side of the chamber 16. The condenser 26 and the chamber 16 are designed to meet the cooling requirements of the engine during continuous operation at the given maximum power level for sustained operation.

During each power transient in excess of the engines steady state cooling capacity, more heat is produced than can be immediately rejected. The secondary cooling system 19 is provided with a sufficient volume of the liqiud 20 to absorb and thermally store this excess thermal energy. The heat exchanger 18 is designed to insure that all of this excess energy is transferred to the liquid 20. To avoid dissipation of the liquid 20 and the necessity of carrying a reserve, a sufficient liquid volume must be contained in the chamber 16 to insure that its overall temperature does not reach the boiling point of the liquid. For example, assuming an average overall engine efficiency of percent, and a 15 second peak power requirement of approximately 50 horsepower above the vehicles maximum sustained power requirement, the liquid must be capable of absorbing an extra 3,000 BTUs of heat energy, approximately. The minimum amount of water required by the secondary cooling system 19, in' this case, would be approximately 9 gallons, assuming a 40F. temperature rise available in its sensible heating range at the worst design conditions. However, if reduction of the size of the chamber 16 is essential, the latent heat capacity of liquid 20 can also be brought into play.

The heat absorbed by the liquid 20 during high power transients is rejected through the walls 17 of the cham ber 16 during the longer periods of lower power operation. In other words, transient high heat can be rapidly absorbed by the secondary cooling system 19 and slowly rejected during the more quiescent and generally longer intervals between high power transients. Hence, the cooling capacity of the primary condenser 26 is substantially less than that which would be required in a single condenser operating alone. Furthermore, the necessary cooling surface area 26 and the thermal storage cooling system 19 combined is less than that required by a single condenser operating alone.

As shown in FIG. 1, the chamber.l6 and the condenser 26 are at approximately the same level. If the secondary cooling system 19 totally recondenses the working fluid and this is not desired, such may be avoided as shown in FIGS. 4 and 5. Here, the working fluid enters a first stage 21 of the condenser 26 via conduit 14. After passing through that stage of the condenser, it enters a cooling system stage. From the cooling system, it flows through a subsequent stage 23 of the condenser. The condenser 26 and cooling system 19 may be constructed so that this sequence occurs once (e.g., by flow through parallel passages in each stage) or repetitively (e.g., by flow through a plurality of alternating condenser and cooling system stages).

Although it is desirable to have as few valves as possible in 'a vapor cycle engine, the employment of

valves

42 and 48 as shown in FIG. 3 to switch in the secondary cooling system reduces the amount of heat absorbing liquid needed in the secondary cooling system 19 because the equilibrium temperature of the liquid 20 may be lower. In this system, the valve 42 normally directs the working fluid through a conduit 14 directly into the condenser 26. When the engine is operating at power levels in excess of the condenser capacity, the

valves

42 and 48 are opened to admit all or part of the working fluid flow into the secondary cooling system, thus reducing the load that would otherwise be imposed on the condenser.

In another embodiment, now shown, the secondary cooling system is located directly in line with the condenser 26, but the working fluid first passes through the condenser 26. Here again, the equilibrium temperature of the heat absorbing liquid 20 is lower and a smaller amount of the heat absorbing liquid is required by the secondary cooling system 19. However, since the working fluid, within the coil 18 may be already condensed, a greater amount of working fluid is carried by the engine than is otherwise required.

Referring to FIG. 6, another embodiment of this invention is illustrated. Here again, the condenser 26 is sized for the maximum sustained power demands of the system, but the working fluid is not diverted through any secondary cooling system. Instead, a pressurized tank 54 of heat absorbing liquid, water for example, is associated with the condenser. When the engine is operating at power levels in excess of the condenser capacity, a control 52 is actuated. The control 52 opens a valve 50 allowing the heat absorbing liquid to pass through the

conduits

56 and 58 and be emitted as a spray 62. The spray 62 impinges upon the condenser 26 where it is vaporized and significantly increases the cooling capacity of the condenser. Ideally, because the heat absorbing fluid vaporizes on contact with the condenser coil, the latent heat of the heat absorbing liquid contributes greatly to cooling efficiency. A combination of the spray system and any of the other embodiments described above may be utilized to meet a wide range of design conditions.

In all of the above embodiments, the total amount of cooling surface required by the vapor cycle engine is less than that required by earlier designs. Thus the engines parasitic cooling load is reduced and its efficiency increased. Clearly, also, the invention significantly reduces the required cooling capacity of a condenser in a variable power vapor cycle engine. Accordingly, great savings in space, weight and engine cost are achieved. As a result, closed cycle vapor engines which are almost pollution-free may be realistically considered for automotive applications.

Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative andnot interpreted in a limiting sense.

What is claimed is:

1. In a vapor cycle engine in which working fluid is vaporized in a boiler, fed therefrom to an expander to perform useful work, condensed thereafter to a liquid, and then fed to said boiler to complete a cycle, the improvement which comprises, a first means for extracting heat from said working fluid and discharging it into a gaseous environment to condense continuously said working fluid to a liquid during operation levels of said engine not exceeding a predetermined operating level and a second means adapted to contain a heatabsorbing liquid for producing heat transfer from said working fluid to such heat-absorbing liquid to augment said first means and for thereafter rejecting heat from said heat-absorbing liquid into a gaseous environment, thereby permitting operation of said engine at levels above said predetermined operating level.

2. The improvement described in claim 1 wherein said second means comprises a thermal storage chamber for containing heat-absorbing liquid, 21 first heat transfer means communicating with said first means, said first heat transfer means being at least partially immersed in said heat-absorbing liquid, means for passing said working fluid through said first heat transfer means so that heat is transferred to said heat-absorbing liquid, and a second heat transfer means externally mounted on said storage chamber for rejecting heat from the heat-absorbing liquid tosaid gaseous environment.

3. The improvement described in claim 2 wherein said second means is interposed between said expander and said first means.

4. The improvement described in claim 2 wherein said second means is interposed between said first means and said boiler.

5. The improvement described in claim 2 further comprising valving means for directing said working fluid through said first heat transfer means, and means responsive to the cooling requirements of said engine for actuating said valving means.

6. The improvement described in claim 2, wherein said second heat transfer means externally mounted on said storage chamber comprises a jet impingement heat exchanger.

7. The improvement, described in claim 1 wherein said second means comprises a pressurized tank containing heat-absorbing liquid; and spraying means connected to said pressurized tank for directing said heatabsorbing liquid against the external surfaces of said first means, thereby increasing the cooling capacity of said first means.

8. The improvement described in claim 7 further comprising valving means disposed between pressurized tank and said spraying means and means for actuating said valving means in response to the cooling requirements of said engine.

9. The improvement described in claim 2 further comprising a pressurized tank, containing heatabsorbing liquid; and spraying means connected to said pressurized tank for directing heat-absorbing liquid therefrom against the external surfaces of said first means, thereby further increasing the cooling capacity of said first means connected to said spraying means.

10. The improvement described in claim 2 wherein at least a portion of said first heat transfer means is between adjacent stages of said first means.

11. in a vapor cycle engine in which working fluid is vaporized in a boiler, fed therefrom to an expander to perform useful work, condensed thereafter to a liquid and then fed to said boiler to complete a cycle, an improved compact condenser adapted for mobile use comprising:

a. air cooled means for extracting heat from said working fluid to condense continuously working fluid to a liquid during operating levels of said engine not exceeding a predetermined midrange operating level of said engine; and

b. a second means for extracting heat from said working fluid to augment said first means; said second means comprising:

1. a thermal storage chamber for confining a fixed supply of heat absorbing liquid,

2. a first heat transfer means at least partially immersed in said heat-absorbing liquid, for placing said working fluid in heat exchange relationship with said heat-absorbing liquid, said first heat transfer means being in communication with said air cooled means, and

3. a second heat transfer means external of and affixed to said storage chamber for rejecting heat from the heat-absorbing liquid into said gaseous environment; said second means thereby permitting transient operation of said engine at operating levels above said predetermined mid-range level.

12. In a vapor cycle engine in which working fluid is vaporized in a boiler, fed therefrom to an expander to perform useful work, condensed thereto to a liquid, and then fed to said boiler to complete a cycle, a method for condensing said working fluid to a liquid comprising the steps of accepting working fluid from said expander, continually extracting heat from the working fluid in a condenser in a first heat exchange step wherein the maximum rate of heat extraction corresponds to the rate of heat extraction required when the engine is operating at a predetermined level and rejecting said heat to a gaseous environment, transferring additional heat from said working fluid to a heatabsorbing liquid in a second heat exchange step to augment said extracting step and thereby permit operation of said engine at operating levels above said predetermined operating level, and thereafter discharging said additional heat to said gaseous environment.

13. The method as described in claim 12 wherein the transferring step comprises the steps of placing said working fluid in heat exchange relationship with said heat-absorbing liquid contained within a thermal storage chamber, and storing said additional heat in said heat-absorbing liquid.

14. The method as defined in claim 13 wherein the discharging step comprises the steps of transmitting said additional heat from said heat-absorbing liquid to a heat dissipating means external of and affixed to said storage chamber and rejecting said additional heat by means of said heat dissipating means to said gaseous environment.

15. The method as described in claim 14 comprising the additional step of measuring the operating level of said engine, and controlling by a valve means the amount of said working fluid placed in heat exchange relationship with said heat-absorbing liquid in response to the operating level of said engine.

16. The method as described in claim 12 wherein the transferring step comprises the steps of confining a heat-absorbing liquid under pressure, directing a spray 3,830,063 7 8 of said pressurized heat-absorbing liquid against exterevaporating at least some of said heat-absorbing liquid nal surfaces of said condenser during the first heat exto thereby produce heat transfer from the external surchange process in response to operating levels of said faces of said condenser to said heat-absorbing liquid. engine above said predetermined operating level, and

Claims

1. In a vapor cycle engine in which working fluid is vaporized in a boiler, fed therefrom to an expander to perform useful work, condensed thereafter to a liquid, and then fed to said boiler to complete a cycle, the improvement which comprises, a first means for extracting heat from said working fluid and discharging it into a gaseous environment to condense continuously said working fluid to a liquid during operation levels of said engine not exceeding a predetermined operating level and a second means adapted to contain a heat-absorbing liquid for producing heat transfer from said working fluid to such heat-absorbing liquid to augment said first means and for thereafter rejecting heat from said heat-absorbing liquid into a gaseous environment, thereby permitting operation of said engine at levels above said predetermined operating level.

2. The improvement described in claim 1 wherein said second means comprises a thermal storage chamber for containing heat-absorbing liquid, a first heat transfer means communicating with said first means, said first heat transfer means being at least partially immersed in said heat-absorbing liquid, means for passing said working fluid through said first heat transfer means so that heat is transferred to said heat-absorbing liquid, and a seCond heat transfer means externally mounted on said storage chamber for rejecting heat from the heat-absorbing liquid to said gaseous environment.

7. The improvement, described in claim 1 wherein said second means comprises a pressurized tank containing heat-absorbing liquid; and spraying means connected to said pressurized tank for directing said heat-absorbing liquid against the external surfaces of said first means, thereby increasing the cooling capacity of said first means.

9. The improvement described in claim 2 further comprising a pressurized tank, containing heat-absorbing liquid; and spraying means connected to said pressurized tank for directing heat-absorbing liquid therefrom against the external surfaces of said first means, thereby further increasing the cooling capacity of said first means connected to said spraying means.

11. In a vapor cycle engine in which working fluid is vaporized in a boiler, fed therefrom to an expander to perform useful work, condensed thereafter to a liquid and then fed to said boiler to complete a cycle, an improved compact condenser adapted for mobile use comprising: a. air cooled means for extracting heat from said working fluid to condense continuously working fluid to a liquid during operating levels of said engine not exceeding a predetermined midrange operating level of said engine; and b. a second means for extracting heat from said working fluid to augment said first means; said second means comprising:

12. In a vapor cycle engine in which working fluid is vaporized in a boiler, fed therefrom to an expander to perform useful work, condensed thereto to a liquid, and then fed to said boiler to complete a cycle, a method for condensing said working fluid to a liquid comprising the steps of accepting working fluid from said expander, continually extracting heat from the working fluid in a condenser in a first heat exchange step wherein the maximum rate of heat extraction corresponds to the rate of heat extraction required when the engine is operating at a predetermined level and rejecting said heat to a gaseous environment, transferring additional heat from said working fluid to a heat-absorbing liquid in a second heat exchange step to augment said extracting step and thereby permit operation of said engine at operating levels aBove said predetermined operating level, and thereafter discharging said additional heat to said gaseous environment.

16. The method as described in claim 12 wherein the transferring step comprises the steps of confining a heat-absorbing liquid under pressure, directing a spray of said pressurized heat-absorbing liquid against external surfaces of said condenser during the first heat exchange process in response to operating levels of said engine above said predetermined operating level, and evaporating at least some of said heat-absorbing liquid to thereby produce heat transfer from the external surfaces of said condenser to said heat-absorbing liquid.