US20090260361A1

US20090260361A1 - Isothermal power system

Info

Publication number: US20090260361A1
Application number: US12/245,224
Authority: US
Inventors: Melvin L. Prueitt
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-26
Filing date: 2008-10-03
Publication date: 2009-10-22
Also published as: US20080264062A1; WO2008134283A2; WO2008134283A3

Abstract

This invention provides means for producing power by using isothermal compressors and isothermal expanders. One embodiment has an isothermal compressor that compresses air (or other gas), passes the air through a counter-flow heat exchanger, which heats the air, uses the heated air to drive an isothermal expander for power generation, and passes the expander exhaust back through the counter-flow heat exchanger to heat the input air to the expander. Another embodiment has a boiler that produces vapor that flows through a counter-flow heat exchanger to superheat the vapor. The vapor then flows through an isothermal expander for power generation. The exhaust from the isothermal expander flows back through the counter-flow heat exchanger to supply heat to super heat the vapor coming from the boiler. The description presents several devices that can perform at near isothermal conditions, including a modified Tesla turbine.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This Continuation in Part application claims priority to and the benefit of U.S. patent Utility application Ser. No. 12/104,797, filed Apr. 17, 2008, the entirety of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Most of the heat engines in use today use adiabatic expansion of gases to produce power. The Rankine, Brayton, Otto cycles, and others use adiabatic expansions, and some of them also use adiabatic compressions. This disclosure shows that isothermal expansion and compression have some important efficiency advantages.
The isothermal cycle can use a working fluid such as water, ammonia, or propylene that are boiled and then expanded isothermally in an engine to produce power. The vapors are then condensed back to a liquid to repeat the cycle. It can also use a gas such as air or helium that can be compressed isothermally, heated, and then expanded isothermally in an engine that drives an electric generator or drives some other machine. Since the exhaust gas from the expander is still hot, its heat can be used to heat the compressed gas flowing from the compressor to the expander.
Some U.S. Pat. Nos. that are somewhat related to embodiments of the present invention are 4,023,366, 4,207,027, 4,455,825, 4,676,067, 5,641,273, 6,186,755, 6,205,788, 6,225,706, 7,062,913, and 7,124,585.

SUMMARY OF THE INVENTION

In order to have isothermal compression and expansion of gases, heat must be removed from the gas while it is being compressed, and heat must be supplied to the gas during expansion. One purpose of this invention is to provide means of transferring heat to and from gases quickly.
By providing appropriate heat exchangers at appropriate points in the design, the disclosed isothermal systems provide a method that allows the exhaust from the expander engine to flow through the heat exchangers to supply superheat for the vapor flowing from the boiler or compressor to the expander engine. For a two-phase fluid, the gas from the expander that flows through the heat exchanger still has enough heat left over to partially preheat the feed liquid flowing to the boiler. This cannot be done with an adiabatic expander, because the vapor exhaust from the adiabatic expander is normally cooler than the superheat temperature.
Another important feature of the isothermal engine is that the same amount of gas can be expanded to much larger volumes than the adiabatic machine, and this provides more output energy.
We can consider an example to compare the isothermal steam engine with a Rankine cycle steam engine. As an example, suppose we begin with liquid water and boil it at 400 K (127° C.). If one kilogram (0.731 m³) per second of steam flows from the boiler at a pressure of 2.455 bar and is superheated to 800 K (527° C.), the power produced by an isothermal expander is defined (for an ideal gas) by
W=P _s V _sln(V _e /V _s)
where P_sis the pressure of the superheated gas (same as the boiler pressure), V_sis the volume of the superheated gas, and V_eis the volume of the expanded gas flowing out of the expander. The “ln” is the natural log function. The volume V_sis 1.462 m³(since the temperature is twice as high as the boiling temperature at constant pressure). If we let the gas expand in the isothermal expander to the condenser pressure, 0.03531 bar, the vapor volume will be 101.65 m³, and the power will be 1.522 MW. The efficiency will be 38.77%.
For an adiabatic expander, the power is defined by
W=(P _e V _e −P _s V _s)/(1−γ)
where γ is the ratio of specific heats of the gas. For this example, we let γ=1.32. If we let the superheated gas expand adiabatically to P_e=0.03531 bar (same as in the isothermal case), the volume will be only 36.35 m . The power will be 0.72 MW. This is only 47% of the power output by the isothermal system. The isothermal case requires 15% more heat input, but it uses that heat more efficiently. The efficiency of the adiabatic (Rankine) cycle is 21.16%.
For an ideal gas, the internal energy depends only on the temperature. Thus, all the heat input to the isothermal engine is used to generate power as it maintains the gas temperature at a constant value (no change in internal energy of the gas). Then, when the gas is exhausted from the expander, it is still at the same temperature as the input temperature, and its energy can be used to superheat the boiler vapor in the counter-flow heat exchanger as its temperature theoretically drops down to the boiler temperature. In an actual machine, we would want the input heat to the isothermal engine to be at a little higher temperature than the superheat temperature in order to provide the temperature differential to cause adequate heat flow.
For the adiabatic case, after the gas expands to 36.35 m³, its temperature is only 286 K, which is too cold to supply any heat to superheat the gas flowing out of the boiler.
The following table gives some calculated values for the performance of the isothermal heat engine that uses steam as the working fluid. These calculations were made by a computer

TABLE I

				Isothermal
Boiler	Condenser	Superheat		Engine	Rankine	Rankine
Temperature	Temperature	Temperature	Power	Efficiency	Cycle Eff.	Cycle with
(Degrees C.)	(Degrees C.)	(Degrees C.)	(MW)	(%)	(%)	Reheat, Eff.

80	27	90	0.446	15.53	9.81	10.52
127	27	227	0.951	28.35	16.05	17.82
127	27	727	1.903	44.18	23.70	25.10
200	27	700	2.577	52.47	27.68	30.21
300	27	800	2.760	56.80	25.66	27.98
300	27	1000	3.276	60.94	27.46	29.61
200	27	1000	3.371	59.10	31.15	33.39
300	27	1200	3.900	64.36	28.95	30.93
22	12	27	0.095	3.68	2.66
22	12	127	0.126	4.86	3.28
22	12	227	0.158	6.00	3.82
22	12	480	0.237	8.77	4.90
22	12	800	0.339	12.05	5.88

program called “Isoengine.exe.” For comparison, the next-to-the-last column gives the efficiency of an ordinary Rankine cycle steam engine. The last column gives the performance of a Rankine cycle steam engine with single reheat. The power values are for a flow of one kilogram per second of steam. The values in the Rankine columns were calculated with a single gamma value and constant heat capacity of the steam, which provide slightly inconsistent values, since the gamma varies with temperature and pressure. The values in the table are theoretical values, but the comparison between the isothermal engine and the Rankine steam engines is valid.

The first row in the table represents values that would be appropriate for a system that uses heat from a solar pond where the temperature of the pond might be 90° C.
The last five rows are for OTEC applications. No multi-staging is involved. Efficiencies could be higher if multi-stages were used. The Rankine cycle with reheat is not listed for these five rows, because the temperature differences are too small to use reheat.
Using a system that has isothermal compression and expansion of single-phase gases provides performances that are even better than isothermal system of the two-phase fluids, such as water-steam (Rankine cycle). Air can be used as the working fluid. Helium has high heat transfer properties and might be used. It is used in Stirling engines.
Table II gives some calculations of performance for this design that were made by a program called “Isotherm5.exe.” Again, these are theoretical calculations that do not include friction and thermal conduction losses. For each item in the table, the air pressure at the entrance to the isothermal compressor is 10 bar, the temperature is 27° C., and the volume is 1 cubic meter per second. The air is compressed in the compressor to 0.2 m³.
Note that at the same temperatures of superheat, the efficiencies for this apparatus with an isothermal compressor and an isothermal expander are significantly higher than those for the device that has a boiler and an isothermal expander, as shown in Table I. In fact, when the single-phase simulations were run with the computer program, the efficiencies turned out to be Carnot efficiencies. When friction and heat conduction losses are included, the efficiencies will be less, but they should still be higher than the devices in Table I, when losses are included in those calculations.

TABLE II

Superheat
Temperature	Power Output	Efficiency
(Degrees C.)	(MW)	(%)

100	0.3916	19.57
200	0.9281	36.58
300	1.4650	47.64
400	2.0010	55.40
500	2.5375	61.19
600	3.0740	65.65
700	3.6105	69.17
800	4.1470	72.04
900	4.6835	74.43
1000	5.2199	76.43
1200	6.2929	79.63

It is therefore an object of the present invention to provide an economical means of producing power using isothermal compressors and isothermal expanders.
It is another object of the present invention to utilize available heat sources to provide energy to generate electrical power using isothermal compression and expansion engines.
It is another object of the present invention to utilize available heat sources to provide energy to generate electrical power using a boiler and an isothermal expansion engine.
It is another object of the present invention to utilize available heat sources to provide the heat required to maintain near-isothermal conditions in isothermal expanders.
It is another object of the present invention to utilize the hot exhausts gas from an isothermal expander to superheat the compressed gas from an isothermal compressor in a counter-flow heat exchanger.
It is another object of the present invention to utilize the hot steam, or other two-phase working fluid, that exhausts from an isothermal expander to superheat the vapor from a boiler in a counter-flow heat exchanger.
It is another object of the present invention to provide means for reducing mechanical losses in the compression and expansion devices.
It is another object of the present invention to provide methods to effectively produce substantially isothermal compression and expansion of gases.
It is another object of the present invention to provide an efficient Tesla-like turbine that operates isothermally.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:

FIG. 1 is a schematic side view of an embodiment of an apparatus according to the present disclosure showing an isothermal compressor, an isothermal expander, a counter-flow heat exchanger, a heater, and a cooler.

FIG. 2 is a schematic side view of an embodiment of an apparatus according to the present disclosure that illustrates the use of a boiler, counter-flow heat exchangers, an isothermal expander, a heater, and a condenser.

FIG. 3 is a schematic sectional side view of an embodiment of an isothermal compressor or isothermal expander according to the present disclosure, which has a piston in a cylinder and has tapered plates that transfer heat to and from the gas.

FIG. 4 is a schematic isometric view of another embodiment of an apparatus according to the present disclosure, having tapered concentric circular forms for increasing surface contact with gases for isothermal compressors and expanders.

FIG. 5 is a graphic depiction of an inside top view of a rotating piston engine according to the present disclosure.

FIG. 6 is a schematic top view of a modified rotating piston engine according to the present disclosure, featuring tapered plates for isothermal operation.

FIG. 7 is a schematic end view of another embodiment of an apparatus according to the present disclosure, showing the stator blades of an isothermal turbine.

FIG. 8 is a schematic end view of a rotor blade of an isothermal turbine, such as may be used in the embodiment seen in FIG. 7.

FIG. 9 is a schematic side view of an embodiment of a bellows compressor and/or expander according to the present disclosure.

FIG. 10 is an axial or end view of a cross section of an isothermal Tesla turbine compressor according to the present disclosure.

FIG. 11 is a cross-sectional side view of two disks mounted on the shaft of an isothermal Tesla turbine compressor, as may be used in the embodiment seen in FIG. 10.

FIG. 12 is an end view schematic of the cross section of an isothermal Tesla turbine expander.

FIG. 13 is an axial or end view of a cross section of a disk of an isothermal Tesla turbine expander showing a method of reducing the vapor pressure required to remove the heating liquid from the disk chamber.

FIG. 14 is an end view schematic of a disk showing curved vanes attached to the side of the disk.

DETAILED DESCRIPTION OF THE INVENTION

Single-Phase Gas Isothermal Heat Engine

FIG. 1 shows a layout for the single-phase gas isothermal engine system. The gas is compressed in the isothermal compressor 120. In order to keep the gas at constant temperature, a cooler 128 is necessary, since compression of a gas tends to heat it.
For efficient heat transfer, the cooler 128 can supply a liquid to channels beneath the surfaces in the compressor 120. The liquid evaporates as it removes heat from the surfaces. The vapor flows to the cooler 128, where it is condensed and returned to the compressor 120.
For adequate heat flow, a heater 127 should supply heat at slightly higher temperature than the isothermal temperature of the expander 123, and the cooler 128 should supply a fluid that is at slightly lower temperature than the compressor isothermal temperature.
In FIG. 1, the isothermal compressor 120 draws air (or other gas) in through pipe 126 and compresses it. The compressed gas from the isothermal compressor then flows through the counter-flow heat exchanger 122, where it is heated by the exhaust from the isothermal expander 123. After the gas leaves the heat exchanger 122, it flows through the isothermal expander 123 to produce power, which drives electrical generator 130. The exhaust gas from the isothermal expander 123 flows back through the counter-flow heat exchanger 122 and returns to the isothermal compressor 120 to repeat the cycle.
For this design, the cooler 128 keeps the compressor 120 cool. The cooler 128 could use water-cooling, evaporative cooling, or even ambient air to dispose of the heat. The isothermal expander 123 is kept hot by heater 127. The heat can be supplied by solar energy, fossil fuels, nuclear energy, geothermal, or other heat source.

Steam Isothermal Power Generator

An isothermal expander can be used to produce power with steam (or other two-phase working fluid). In FIG. 2, steam is produced in boiler 140. The steam flows through a counter-flow heat exchanger 141, which superheats the steam. From there, the steam flows through an isothermal expander 142, which produces power by the steam expansion and drives the generator 148. Since the expander is isothermal, there would be no problem with steam condensation. After the steam leaves the expander 142, it flows back through the counter-flow heat exchanger 141 where its temperature decreases as it provides heat to superheat the steam coming from the boiler 140.
Exiting the first counter-flow heat-exchanger 141, the steam still has sufficient heat to preheat the boiler feed water in a second counter-flow heat exchanger 143. The steam is then condensed in the condenser 144. The condensate is then pumped by pump 146 back into the boiler 140 through counter-flow heat exchanger 143.
Even though the engine is called “isothermal,” in order to have heat transfer into the expanding steam, the fluid flowing from the heater 147 is at a higher temperature than the “isothermal” temperature. The steam flowing out of the isothermal engine 142 is hotter than the steam coming from the counter-flow heat exchanger 141.

Designs for Isothermal Compressors and Expanders

In my co-pending U.S. patent application Ser. No. 11/739,580 entitled “Water Extraction from Air and Desalination,” incorporated herein by reference, some designs for isothermal compressors and expanders are described. Some of the drawings and descriptions from that disclosure are provided here to show some types of isothermal engines that can be used to keep the gases close to isothermal.
FIG. 3 schematically illustrates an isothermal compressor or expander. To increase heat transfer from the gas to the metal, the metal surface area is greatly increased by placing components such as tapered plates 22 on the front of the piston 21 and complementary tapered plates 23 on the bottom of the isothermal engine cylinder 20, leaving channels for gas flow. (The piston and cylinder combination is referred to as an “isothermal engine,” because it may function either as a compressor or as an expander). These components 22, 23 could have planar surfaces as shown in FIG. 3. Alternatively, the components 38 could have circular concentric configurations extending from a base 39, as seen in FIG. 4.
In operation as a compressor, as the piston 21 in the isothermal engine 20 moves upward, it draws in air (or other gas) through check valve 26. When the piston 21 reaches its maximum height, valve 26 closes, and the piston is forced downward, compressing the gas. As the gas is compressed, it tends to increase in temperature, but the tapered plates 22, 23 absorb the heat of the gas. Since the heat capacity of the metal plates is about 2000 times greater than the gas (per unit volume), the temperature of the plates 22, 23 does not rise very much during one half cycle.
When the piston 21 has traveled down far enough to provide the appropriate pressure the gas, check valve 36 opens to allow the gas to flow out. The piston 21 continues to move downward to force the compressed gas out.
When the apparatus is in operation as an expander, check valve 26 is replaced by a controlled valve. As the piston 21 in the cylinder 20 moves upward, it draws in air (or other gas) through controlled valve 26. When the piston reaches the designed height, valve 26 closes, and the piston continues to rise, expanding the gas and extracting energy from the gas. As the gas is expanded, it tends to decrease in temperature, but the tapered plates 22, 23 provide heat for the gas. When the piston 21 moves downward, it forces the gas out through check valve 36.
For the compressor, the tapered plates 22, 23 can have interior channels in which a cooling fluid can flow. The cooling fluid could be a liquid that evaporates to absorb the heat. For the tapered piston plates 22, the fluid would have to be delivered and retrieved through channels in the piston rod 27. The fluid can be delivered to tapered cylinder plates 23 through channels in the cylinder 20. Calculations show that the gas will remain near isothermal during both compression and expansion, since the gas has close proximity to the plates 22, 23 for heat transfer, and the motion of the plates create turbulence that further enhance heat transfer.
For the expander, heating fluids are required. The heating fluids could be gas or liquid, or they could be vapor that condenses to a liquid in the channels of the tapered plates to release the heat of condensation.
In this disclosure, components that are used to increase the surface area in contact with the working gas are mostly referred to as “tapered plates,” because it is easy to illustrate the tapered plates in the drawings. Heat-transfer components having other shapes and configurations may be contemplated, and are within the scope of the invention. In many applications, it may be better to use tapered concentric circular forms that are approximately cylindrical. FIG. 4 shows the tapered concentric circular forms 38 mounted on a base 39. Such circular forms 38 would fit better in a cylinder (such as cylinder 20 in FIG. 3) than would planar plates. Thus, the tapered plates 23 seen in FIG. 3 could actually be the tapered concentric circular forms 38. Similar complementary arranged circular forms could be attached to piston 21 in FIG. 3. The radii of the upper circular forms and the lower circular forms must be defined so that the circular forms “mesh” or fit together as the piston descends.

More Efficient Compressors and Expanders

One of the main sources of inefficiency for a compressor or expander that is needed for the isothermal engine is sliding friction of the piston. My U.S. Pat. No. 6,401,686, which is incorporated herein by reference, discloses an apparatus referred to as “MECH,” which stands for motor, expander, compressor, and hydraulics. As the MECH apparatus uses rolling friction between two rotating pistons rather than sliding friction of a standard piston engine, the friction losses are much less. The rotating pistons do not touch the cylinder walls. There is sliding friction on the ends of the pistons, but this can be relatively small by making the pistons long relative to their diameters.
It is well known that rolling friction is only about 1/100 as large as sliding friction. A MECH prototype demonstrated only 8% as much energy loss as a comparable size piston engine. It provides an engine with unprecedented economy for producing water from the air or for desalinating seawater.
FIG. 5 depicts a MECH engine 65 with an end plate removed to reveal how the two rotating pistons 66 roll together at the contact line 67. The engine 65 could be used as a compressor or as an expander. Cavities 68 and 69 within the engine 65 are locations in which gases are compressed or expanded. Similar cavities are present on the other side of the engine next to the other rotating piston.
FIG. 6 shows a top view of a compressor/expander that is similar to a MECH engine in that it has two rotating surfaces that roll together. It is designed to be an isothermal compressor or expander. The MECH compressor already has one advantage over standard compressors for isothermal compression: it has larger surface areas of the cylinder walls and piston surfaces for absorbing heat during compression and for returning heat to the gas during expansion. The rotating pistons rotate almost 180 degrees in one direction and then reverse directions for almost 180 degrees. The pistons do not touch the cylinder walls. Sliding friction occurs only at the ends of the pistons where they meet the ends of the cylinders. The seal to prevent gas leakage is formed at the rolling contact point between the two pistons.
FIG. 6 is a schematic top view of such a modified MECH compressor. Cylinders 75 are machined out of a block 70. Each rotating piston 71 consists of a hollow half-cylinder that is open on one side. The half-cylinder is connected to the shaft 77 by partition 74. Tapered plates 72, similar to those in FIG. 3, are placed inside the rotating piston 71. (FIG. 6 shows a top view of the plates, whereas FIG. 3 shows the plates edge-on). The top and bottom of the rotating piston are closed with half-circle plates; they are not shown, because they are on the near end and far end of the half-cylinder (i.e., above and below the plane of the page). When the right piston rotates to the right and the left piston rotates to the left, the upper tapered plates 72 will move into the volume where stationary tapered plates 73 are located and will fit between the stationary plates. The gas in the spaces will be compressed and squeezed out (for a compressor) the exhaust/intake pipes 76. At the same time, gas will be drawn into the bottom half of the engine through the pipes 78. When it rotates the other direction, gas in the bottom half will be compressed. For an expander, the gas is drawn in, expanded, and pushed out.
The tapered plates 72, 73 provide large surface areas for the transfer of heat to and from the gas. The motion of the tapered plates 72 relative to the stationary plates 73 causes gas turbulence in the small gaps between them to enhance heat flow.
In order for the expander or compressor of FIG. 6 to perform isothermally, heating or cooling fluid needs to be supplied to the surfaces inside the device. To supply heating or cooling fluid to the rotating tapered plates 72, the fluid can flow through an axial hole in the center of the shaft 77 and flow through channels in the rotating plates to cool or heat the rotating plates. After the fluid flows through the channels, it flows back to near the other end of the shaft 77 and enters a hole in the shaft allowing the fluid to exit the other end of the shaft. The stationary plates 73 can receive fluid through the separator 79. The walls can have fluid channels on the outside.
Instead of flat tapered plates, this embodiment of the invention could use tapered concentric circular forms as described above and illustrated in FIG. 4. In this case, the circular forms would not be complete circles, but would be partial circular configurations.

Isothermal Turbines

In an isothermal turbine expander, the heating fluid can flow through the turbine walls, stator blades, and rotating blades. Reference is made to FIG. 7 showing an expander. Although there are cases in which the heating fluid can be a liquid or a gas, in the following disclosure, the heating fluid enters as a vapor and condenses to release the latent heat of condensation. FIG. 7 is a schematic drawing showing the stator blades and the flow paths of the heating fluid. The hot vapor flows in the inlet pipe 161 into the top of the turbine 160, and flows through a vapor channel 162 on the upper half of the turbine. It flows through channels (not shown) within the upper stator blades 163 toward the center of the turbine. The turbine shaft 169 is at the center of the turbine. Part of the vapor condenses and releases the latent heat of condensation. The condensed liquid and the remaining vapor flow into the vapor and liquid channel 164.
From there, the vapor and liquid flow to the lower stator blades 165 and flow through channels in those blades. In the stator blade channels, more of the vapor condenses. The liquid and the remaining vapor flow into the liquid channel 166 on the lower half of the turbine. They return to the heating fluid boiler (not shown) through the condensed liquid outlet 167. After boiling, the vapor returns again to the isothermal expander turbine.
For an isothermal turbine compressor, the geometry looks much like the expander of FIG. 7. The cooling liquid enters from the top 161. It is designed so that the liquid is directed into each of the upper stator blades. As the liquid flows down through channels in the blades, some of it evaporates and provides cooling by the latent heat of evaporation. The vapor and the remaining liquid flow to the vapor and liquid channel near the center of the turbine. Appropriate guides are designed to direct liquid into each of the lower stator blades. The vapor flows along with the liquid. More liquid vaporizes in the lower stator blade channels.
Finally, the vapor and any remaining liquid flow out the bottom and flow back to a cooler, which condenses the vapor to a liquid. The liquid is pumped back to the turbine compressor to repeat the cycle.
Alternatively, the liquid can be pumped into the bottom of the compressor. As it flows up through the lower stator blades, it boils. The vapor it creates blows liquid as a mist up through the rest of the system. The mist droplets strike surfaces and evaporate, removing heat and continuing the process of blowing liquid droplets up through the upper blades.
If the stator blades do not provide sufficient heat removal for the compressor, the rotating blades may be configured to receive liquid that evaporates and removes heat. The liquid enters one end of the shaft that holds the turbine blades. The liquid then flows through a channel in the shaft until it reaches the channels in the blades. As it flows through the blade channels, it evaporates and removes heat. The vapor flows back to the shaft and flows through another channel in the shaft to the other end of the shaft and then flows back to the cooler.
It is not so simple for an isothermal expander turbine. If vapor is put into the rotating blades, it condenses to a liquid, which has high density. Centrifugal force causes the liquid to move to the tips of the blades. High pressure is required to force the liquid back to the shaft against the centrifugal force. The density of the liquid can effectively be reduced by mixing it with the vapor. By supplying more vapor than is necessary to deliver the required heat, the extra vapor flows back to the shaft through a small-diameter channel and carries with it a mist of liquid.
A schematic drawing of a single rotating turbine blade 180 for an expanding turbine is shown in FIG. 8. Hot vapor flows from one end of shaft 181 through channel 182 inside the shaft 181 to the vapor channel 183 and flows through vapor channel 183 in the blade. Part of the vapor condenses in the vapor channel and releases heat to keep the blade hot. The condensed liquid flows by centrifugal force to the space 184 near the end of the blade. The vapor at high pressure is forced to flow through the small-diameter liquid and vapor return pipe 185 at high speed back to the shaft and into the liquid and vapor output channel 186. Since it is flowing at high velocity, it will carry a mist of liquid with it. The vapor and the liquid will flow through the channel 186 to the other end of the shaft, where they will flow into a coupling that takes the vapor and liquid back to the boiler.
Another alternative would be to use a liquid to transfer heat to the rotating blades. The liquid flowing from the shaft to the tip of the blade would provide the pressure to push the liquid back to the shaft. The liquid flowing back to the shaft would be slightly denser than the liquid flowing toward the tip, because it is cooler. Extra pressure in the input channel would be required.
In order to enhance the heat transfer between the turbine blades and the gas, the blades should probably be closer together and be wider than blades in standard turbines.

Other Isothermal Designs

FIG. 9 shows a compressor/expander design that incorporates bellows 83 to compress and expand gas. The bellows is connected to the top 80 and to a base 85. Push rod 81 moves the top up and down. The purpose of the displacer 84 is to push out as much gas as possible when the bellows is compressed as far as possible. Gas flows in and out of pipe 86.
For an isothermal compressor, the tapered plates like those of FIG. 3 can be connected to the displacer 84 and to the base 85. Rather than use flat tapered plates, it would probably be better to use tapered concentric circular forms as illustrated in FIG. 4.
If we can increase the efficiency of standard power generating plants by replacing the adiabatic engines with isothermal engines, it would reduce the release of greenhouse gases into the atmosphere. For solar thermal or geothermal power plants, the isothermal engines would produce more power for the same size heat source.

Isothermal Tesla Turbine

The Tesla turbine allows the flow of gas between rotating disks to transfer momentum between the gas and the disks. The Tesla turbine expander produces power from the flow of compressed gas as the gas expands, while the Tesla turbine compressor pumps gas from low pressure to high pressure. Since it provides large surfaces that are exposed to the gas, it would be ideal for isothermal use, but the Tesla turbine requires special modifications, as now described.
U.S. Patent Application Publication number US 2005/0172624 A1, entitled “Method and Device for Converting Thermal Energy into Kinetic Energy,” by Holecek, et al., describes several methods of compressing and expanding a gas to produce power. The Holecek et al. application mentions that with a Tesla turbine, in particular, better isothermal expansion or compression is possible. But the Holecek et al. application does not describe how to make a Tesla turbine “isothermal.” Normally the gas in a Tesla turbine expands or compresses nearly adiabatically. Methods must be provided to remove heat from a gas that is being compressed or to add heat to a gas that is expanding.
A Tesla turbine features of a number of closely spaced disks that rotate about a shaft in a cylindrical enclosure. In a Tesla turbine expander, the compressed gas flows into the housing tangential to the outside edges of the disks and flows between the disks as it imparts energy to the disks by transfer of momentum. The gas flows out through holes in the disks near the shaft. In a compressor, gas flows in through the holes in the disks and is compressed as it flows outward toward the periphery of the disks.
FIG. 10 provides a cross-sectional end view of one of the disks 101 of a Tesla turbine compressor 100. Each disk defines in its interior a narrow hollow chamber 102, which may be referred to as a “disk chamber.” To define the disk chamber 102, the disk 101 may be formed by two disks that are sealed together at their outer edges and sealed near their centers where the disk supports 103 connect the disk 101 to the shaft 104. A cooling fluid flows through a channel 105 from one end of the shaft and flows through the disk supports 103 via the fluid distributor pipe 106 into the narrow disk chamber 102. After absorbing heat, the cooling fluid flows out the outlet pipe 107 to the exit channel 108 in the shaft. From there, the fluid flows to the opposite end of the shaft 104 from the end where the fluid entered and flows back to the cooler 128 of FIG. 1.
One effective method of transferring a large quantity of heat is to use a liquid to flow into the disk chamber 102. The liquid spreads over the inside walls of the chamber as it is thrown outward by centrifugal force. The liquid evaporates and removes heat from the chamber walls. The amount of heat removed is equivalent to the latent heat of evaporation of the liquid. This cools the gas that is flowing outside the disks.
The vapor from the evaporating liquid flows to the outlet pipe 107 and then flows into a fluid exit channel 108. From there, it flows to the end of the shaft opposite the end where the liquid enters, and is transmitted via a sealed connection that takes the vapor to a cooling unit. The fluid is condensed in the cooling unit and pumped back to the turbine 100 to flow again in the liquid entry channel 105.
The gas that is being compressed enters through gas entry ports 109 between the disk supports and after flowing radially outward between the rotating disks, it flows out the gas exit port 110.
FIG. 11 is longitudinal cross section view of selected internal parts of the isothermal Tesla turbine compressor. The shaft 104 runs from left to right. For simplicity of illustration, only two disks 101 are shown. A complete Tesla turbine has at least two and preferably a number of disks mounted for rotation on or with the shaft 104. The cooling fluid flows through pipe 114 into the shaft and flows through the cooling fluid entry channel 105. It flows into the disk chambers 102 through the fluid distributor pipes 106, which are not shown in FIG. 11, because they are perpendicular to the page of the drawing. After absorbing heat, the fluid flows out the fluid outlet pipes 107 and then flows through the fluid exit channels 108 to the right end of the shaft and exits pipe 115. From there it flows back to the cooler, where it will be condensed and pumped back to the compressor.
FIG. 12 is a schematic showing an end view cross section of one of the disks of a Tesla turbine expander. It may look very similar to the compressor disk if a single-phase liquid or gas is used for heat removal (in the compressor) or heat deposit (in the expander). In this case, the pressurized gas enters the cylinder via the entry ports 150 and flows tangentially to the edges of the disks 101 and flows between the disks as it imparts rotational energy to the disks. The gas expands as it flows radially inward between the disks to the gas exit ports 151. As the gas expands, it tends to cool. In order to maintain it substantially near isothermal conditions, heat must be supplied. A hot fluid is pumped through the disk chamber 102 to keep the disk surfaces hot and transfer heat to the gas.
One embodiment of the apparatus utilizes a vapor flowing through a vapor entry channel 149 and vapor injector tube 154 into the disk chamber 102 of the expander. As the vapor condenses, it releases heat to the walls of the chamber. The condensed liquid is heavy and is thrown radially outward toward to the outer part of the chamber 102. FIG. 12 illustrates extended liquid collector tubes 152 to collect the liquid where it accumulates near the peripheral rim of the disk. If the incoming vapor has sufficient pressure, the liquid will be forced to flow through the liquid collector tubes 152 to the liquid exit channel 153 in the shaft, and then flow to a heater where the liquid is pumped into a boiler, which boils the liquid. The vapor then flows back to the expander.
If the liquid filled tube runs from the center of the shaft to the outside of the disk chamber, the pressure at the outer end of the tube is
P=0.5 ρv ²
where P is the pressure in Pascals, ρ is the density in kilograms per cubic meter, and v is the velocity of the end of the tube in meters per second. If the disk is rotating at 12,000 rpm and the outer end of the tube is 10 centimeters from the center of the shaft and the density is that of water, the pressure is 7.896 MPa (1,145 psi). It might be difficult to provide the appropriate pressure to force the liquid out of the disk chamber.
A solution is to have the liquid collector tube 152 have a small inside diameter and provide more vapor than is necessary during operation. The liquid droplets moving radially inward in the tube are mixed with vapor so that the average density is reduced. Thus, less vapor pressure is required to move the liquid toward the shaft.
Another solution is to design the liquid collector tube 156 with a spiral shape, as shown in FIG. 13. As the liquid 155 enters the outer end of the tube 156 and starts to flow toward the center of the shaft, due to the vapor pressure, the liquid has to slow down, because portions of the tube closer to the disk axis of rotation (e.g., at the shaft) move more slowly than portions farther from the rotational axis. This deceleration generates a force that promotes movement of the liquid toward the shaft 104. Thus, as the liquid flows through the spiral tube 156 toward the output channel 153, it decelerates due to the decreasing absolute, or linear, speed at which the part of the tube adjacent to the liquid moves as the liquid approaches the disk's axis of rotation. This progressively decreasing speed results from the fact that those portions of the tube having a relatively smaller radius (measured from the axis of rotation) move more slowly than those portions having a larger radius. Stated differently, an axiom from rotational dynamics dictates that the closer a point on a rotating body is to the body's axis of rotation, the slower is that point's movement speed in a frame of reference exterior to the body itself. The resulting deceleration force on the liquid promotes movement of the liquid 155 toward the output channel 153 in the shaft 104.
FIG. 1 shows the layout of the complete isothermal engine, which could use isothermal Tesla turbines. The compressor 120 compresses the gas at near isothermal conditions as the fluid from the cooler 128 removes the heat of compression. The compressed gas flows through a counter flow heat exchanger 122 that heats the gas. It then flows into the expander 123 where it expands as it generates power that turns the generator 130 and the compressor. The fluid from the heater 127 keeps the gas hot in the expander.
The gas is still hot as it leaves the expander. It flows to the heat exchanger 122 where it delivers its heat to the gas coming from the compressor. The cooled gas then returns to the compressor to repeat the cycle.
The heater can be any heat source, such as solar energy, geothermal energy, fossil fuel, or nuclear energy. The cooler can be a cooling tower, air cooler, or any source of cool water.
The isothermal Tesla turbine expander can also be used in a two-phase working fluid engine with a boiler as shown in FIG. 2. In this case, a compressor is not needed. The isothermal Tesla expander is 142 in FIG. 2. A detailed description of FIG. 2 is provided previously herein.
FIG. 14 shows a method of providing higher performance of a Tesla-like turbine. Curved vanes 170 on outer faces of the disks extend axially between disks 101 to provide additional surface area to promote heat transfer between the disks and the fluid flowing between them for both the compressor and the expander turbine modes. The vanes 107 also help to guide the gas flow between the disks 101. For the expander turbine, the gas flowing from the outer periphery of the disk 101 toward the center imposes a rotational torque on the vanes, which increases the power delivered to the shaft. For the compressor turbine, the vanes impart a force on the gas to more effectively pump the gas.
The vanes 107 are mounted on or attached to at least one surface of the disk 101, and extend axially to the adjacent disk to contact the face of that disk. Alternatively, vanes 107 could extend axially from both sides of all disks, in which case corresponding vanes on respective disks may contact each other. Additionally, the vanes 107 optionally may extend radially inward onto the disk supports 103.
Although an apparatus and method have been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present disclosure will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all patents and publications, cited above are hereby incorporated by reference.

Claims

1. An isothermal power generating system comprising:

an isothermal compressor for compressing a gas;

a cooler, which supplies a cooling fluid to the isothermal compressor to cool the gas flowing through the isothermal compressor;

a counter-flow heat exchanger for heating the compressed gas;

an isothermal expander for expanding the heated compressed gas to produce mechanical power;

a heater for supplying a heating fluid to the isothermal expander to heat gas flowing through the isothermal expander; and

means for conducting the expanded gas back through the counter-flow heat exchanger to supply heat to the compressed gas flowing from the compressor through the counter-flow heat exchanger;

wherein the isothermal compressor draws in and compresses cooled and expanded gas flowing from the isothermal expander through the counter-flow heat exchanger.

2. An isothermal power generating system according to claim 1, wherein the isothermal compressor is an isothermal Tesla turbine comprising:

rotatable disks spaced along a shaft;

a chamber within each disk;

input channels for conducting the cooling fluid from the cooler into the chamber within each disk; and

output channels for conducting the cooling fluid out of the chamber within each disk and returning the cooling fluid to the cooler;

wherein the rotating disks compress gas flowing between the disks, and wherein the cooling fluid flowing through the chamber within each disk absorbs heat from walls of the chamber, and wherein the chamber walls thus absorb heat from the gas to maintain the gas at near isothermal conditions, and wherein the cooling fluid flows from the chamber to the cooler for further cooling.

3. An isothermal power generating system according to claim 2 further comprising disk supports for attaching the disks to the shaft, and wherein the input channels are defined within the shaft and within at least one of the disk supports, and wherein the output channels are defined within at least one of the disk supports and within the shaft.

4. An isothermal power generating system according to claim 2, wherein:

the cooling fluid is a liquid as it enters the chambers in the disks and evaporates to cool the disks thereby to cool the gas flowing between the disks; and

wherein vapor produced by the evaporation of the liquid flows through the output channels to the cooler, where the vapor condenses back to a liquid.

5. An isothermal power generating system according to claim 1, wherein the isothermal expander is an isothermal Tesla turbine comprising:

rotatable disks spaced apart along a shaft;

a chamber within each disk;

input channels for conducting the heating fluid from the heater into the chamber within each disk; and

output channels for conducting the heating fluid out of the chamber within each disk and returning the heating fluid to the heater;

wherein the flow of expanding gas between the disks produces torque on the disks to produce shaft power, and wherein the heating fluid flowing into the chamber within each disk heats the walls of the chamber, and wherein the chamber walls thus heat the expanding gas to maintain the gas at near isothermal conditions, and wherein cooled heating fluid flows out of the chamber back to the heater to be reheated.

6. An isothermal power generating system according to claim 5 further comprising disk supports for attaching the disks to the shaft, and wherein the input channels are defined within the shaft and within at least one of the disk supports, and wherein the output channels are defined within one or more of the disk supports and within the shaft.

7. An isothermal power generating system according to claim 5, wherein the heating fluid is a vapor as it enters the chambers in the disks and condenses to heat the disks, thereby to heat the gas flowing between the disks.

8. An isothermal power generating system according to claim 7, wherein:

liquid produced by the condensation of the vapor is forced by vapor pressure to flow through radial tubes fluidly connected to the output channels and extending away from the periphery and toward the center of the chamber within each disk, and

the liquid flows through the output channels and returns to the heater where it is boiled to a vapor, and

the vapor flows back to the isothermal expander.

9. An isothermal power generating system according to claim 7, wherein:

the liquid produced by the condensation of the vapor is forced by vapor pressure to flow through a spiral tube running from the outer periphery of the chamber in each disk to output channels in the shaft, and

as the liquid flows through the spiral tube toward the output channels, it decelerates due to a decreasing absolute speed of the liquid as the liquid approaches the disk axis of rotation, and a deceleration force on the liquid promotes movement of the liquid toward the output channels in the shaft, and

the vapor flows back to the isothermal expander.

10. An isothermal power generating system for two-phase working fluids comprising:

a boiler for boiling a working fluid;

a first counter-flow heat exchanger for superheating working fluid vapor;

an isothermal expander for expanding the superheated working fluid vapor to produce mechanical power;

a heater for supplying a heating fluid to an isothermal expander to heat the working fluid vapor flowing through the isothermal expander;

a means for conducting the expanded working fluid from the isothermal expander back through the first counter-flow heat exchanger to heat the working fluid flowing from the boiler;

a condenser for condensing the working fluid vapor to a liquid;

a pump for pumping working fluid into the boiler; and

a second counter-flow heat exchanger for preheating the working fluid flowing to the boiler;

wherein working fluid vapor from the boiler flows through the first counter-flow heat exchanger, and wherein the isothermal expander extracts mechanical energy from the working fluid vapor as the working fluid vapor expands, and wherein the working fluid flows back through the first counter-flow heat exchanger and releases heat to superheat the working fluid vapor flowing from the boiler, and wherein the working fluid flows through the second counter-flow heat exchanger to preheat the working fluid liquid, and the working fluid vapor flows into the condenser to be condensed to a liquid, and wherein the working fluid liquid is pumped through the second counter-flow heat exchanger to the boiler.

11. An isothermal power generating system for two-phase fluids according to claim 10, wherein the isothermal expander is an isothermal Tesla turbine comprising:

rotatable disks spaced along a shaft; and

a chamber within each disk;

output channels conducting the heating fluid out of the chamber within each disk and returning the heating fluid to the heater;

wherein a flow of working fluid between the disks produces torque on the disks to produce shaft power, and wherein the heating fluid flowing through the input channels and into the chamber within each disk heats the walls of the chamber, which chamber walls provide heat to expanding working fluid to maintain the expanding working fluid at near isothermal conditions, and wherein cooled heating fluid flows out of the chamber through the output channels and back to the heater to be reheated.

12. An isothermal power generating system according to claim 11 further comprising disk supports for attaching the disks to the shaft, and wherein the input channels are defined within the shaft and within at least one of the disk supports, and wherein the output channels are defined within one or more of the disk supports and within the shaft.

13. An isothermal power generating system according to claim 11, wherein the heating fluid is a vapor as it enters the chamber in each disk, and the vapor condenses to provide heat to the disk thereby to heat the working fluid flowing between the disks, and wherein the liquid produced by the condensation of the vapor is forced by vapor pressure to flow through tubes disposed radially in the disk and fluidly connected to the output channels, and wherein the liquid flows through the output channels and into the heater.

14. An isothermal power generating system according to claim 11, wherein:

the heating fluid is a vapor as it enters the chamber in each disk, and the vapor condenses to provide heat to the disk thereby to heat the working fluid that is flowing between the disks, and

wherein the liquid produced by the condensation of the vapor is forced by vapor pressure to flow through a spiral tube running from the outer periphery of the chamber in each disk to output channels in the shaft, and

as the liquid flows through the spiral tube toward the output channels, it decelerates due to a decreasing absolute speed of the liquid as the liquid approaches the disk axis of rotation, and a deceleration force on the liquid promotes movement of the liquid toward output channels in the shaft, and

the liquid flows out through the output channels in the disk supports and in the shaft and returns to the heater where it is boiled to a vapor, and

the vapor flows back to the isothermal expander.

15. An isothermal power generating system according to claim 1, wherein the isothermal compressor is an isothermal Tesla turbine comprising:

a set of closely spaced rotatable disks operatively connected to a shaft by disk supports;

a set of curved vanes on outside faces of each disk, wherein the vanes comprise a spiral configuration to guide the gas from the center of the turbine toward the periphery of the turbine to increase compression of the gas, and wherein the vanes further comprise surface area for promoting heat transfer between the disk and the gas;

a chamber within each disk;

input channels within the shaft and within at least one of the disk supports for conducting the cooling fluid from the cooler into the chamber within each disk; and

output channels within at least one of the disk supports and within the shaft for conducting the cooling fluid out of the chamber within each disk and for returning the cooling fluid to the cooler;

wherein the rotating disks aided by the curved vanes compress gas flowing between the disks, and wherein the cooling fluid flowing through the input channels in the shaft and disk supports into the chamber within each disk absorbs heat from the walls of the chamber, and wherein the chamber walls absorb heat from the compressing gas to maintain the gas at near isothermal conditions, and wherein the cooling fluid flows out of the chamber through output channels in the disk supports and the shaft and back to the cooler where it cooled and then returns to the isothermal compressor.

16. An isothermal power generating system according to claim 1, wherein the isothermal expander is an isothermal Tesla turbine comprising:

a set of curved vanes on outside faces of each disk, wherein the vanes comprise a spiral configuration whereby gas flowing from the periphery of the turbine toward the center of the turbine presses on the vanes to increase torque on the shaft, and wherein the vanes comprise surface area for promoting heat transfer between the disk and the gas;

a chamber within each disk;

input channels within the shaft and within at least one of the disk supports for conducting the heating fluid from the heater into the chamber within each disk; and

output channels within at least one of the disk supports and within the shaft for the purpose of conducting the heating fluid out of the chamber within each disk and returning the heating fluid to the heater;

wherein the flow of gas between the disks imposes torque on the disks and on the vanes, to produce shaft power, and wherein the heating fluid flowing through the input channels in the shaft and disk supports into the chamber within each disk heats the walls of the chamber, and wherein the chamber walls provide heat to the expanding gas to maintain the gas at near isothermal conditions, and wherein the cooled heating fluid flows out of the chamber through output channels in the disk supports and shaft back to the heater to be reheated, and then to return to the isothermal expander.