Method for converting one form of energy into another form of energy

Method for converting one form of energy into another form of energy by isobarically heating a gas, adiabatically expanding the gas while converting the heat energy of the gas into the kinetic energy of a moving body, converting the kinetic energy of the moving body into another form of energy, and approximately isothermally compressing the gas to a higher pressure. Improved efficiency is achieved by virtue of the fact that this system employs approximately isothermal compression, which is preferably achieved by injecting liquid into an adiabatically-expanded gas, thereby effecting a thermodynamic cycle which more closely approximates the efficiency of a Carnot cycle.

BACKGROUND OF THE INVENTION 
While the present invention is not limited to any particular type of energy 
converter, it will be described herein in connection with a undirectional 
energy converter such as that shown in U.S. Pat. No. 3,859,789, issued 
Jan. 14, 1975. In an energy converter of this type, a closed, continuous 
loop passageway contains a plurality of freely-movable bodies which travel 
around the passageway in one direction only. Force is applied to 
successive ones of the bodies in one region of the passageway to thereby 
propel them around the passageway. At points around the passageway, at 
least a portion of the kinetic energy of the propelled bodies is converted 
into another form of energy. Thereafter, successive ones of the bodies are 
returned back to the starting region where they are again propelled in one 
direction by application of a force thereto. The unidirectional energy 
converter shown in the aforesaid patent may be operated in accordance with 
various well-known thermodynamic cycles such as the Brayton, Otto and 
Diesel cycles. Such thermodynamic cycles employ adiabatic expansion of a 
gas during the power stroke. This is followed by an exhaust stroke, during 
which heat is rejected, and adiabatic compression back to a higher 
pressure. With isothermal compression of a gas, however, variations can be 
visualized in thermodynamic cycles which more closely approximate the 
Carnot cycle. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a method for operating an energy 
converter is provided which employs a thermodynamic cycle of higher 
efficiency than conventional cycles by virtue of the fact that 
approximately isothermal compression of a gas is employed during part of 
the cycle rather than adiabatic compression. Such isothermal compression 
can be approximated by injecting into the gas, at the completion of 
adiabatic expansion, a fluid such as water at a temperature that is 
preferably approximately equal to that of the expanded gas. 
In one embodiment of the invention, the cycle is comprised of isobaric 
(i.e., constant pressure) heating and expansion, adiabatic expansion, and 
approximately isothermal compression. The advantage of this cycle is that 
it can utilize hot air at atmospheric pressure and thus has important 
applications in waste-heat utilization from low-temperature hot air. In 
another embodiment of the invention, the cycle is comprised of adiabatic 
compression, isobaric heating and expansion, adiabatic expansion and 
finally approximately isothermal compression. The primary advantage of 
this cycle is a thermodynamic efficiency greater than the Brayton cycle 
for similar temperature-pressure ranges and potentially significantly 
higher than other practical cycles currently in use. 
In the case of a unidirectional energy converter such as that shown in U.S. 
Pat. No. 3,859,789, which employs freely-movable bodies within a 
continuous loop passageway, hot gas at ambient pressure is introduced into 
the expander region of the passageway and is then expanded adiabatically 
below ambient pressure. As the working body within the passageway nears 
the end of the expander section, a liquid such as water at a temperature 
that is preferably approximately equal to the temperature of the expanded 
gas is sprayed into the expander section. The gas-liquid mixture ahead of 
the ensuing piston is then compressed approximately isothermally to 
ambient pressure and expelled from the expander section when the expander 
section exit port is opened by the passage of the preceding piston. The 
liquid is then separated from the gas by a centrifugal separator and the 
heat is removed by a heat exchanger.

With reference now to the drawings, and particularly to FIG. 1, a 
unidirectional energy converter is shown comprising a closed-loop, 
circular passageway 10 having a plurality of freely-movable bodies or 
pistons 12 therein. The pistons may comprise cylindrical, curved elements 
having a radius of curvature corresponding to the radius of curvature of 
the closed-loop passageway 10. Alternatively, the pistons 12 may comprise 
spheres or other geometries conforming to the geometry of the passageway. 
The tolerance or clearance between the surfaces of the pistons 12 and the 
inside walls of the closed-loop passageway 10 is such as to permit the 
pistons to move freely through the passageway. However, fluid flow past 
the pistons within the passageway is substantially prevented. Piston rings 
may be used as required. The continuous, closed-loop passageway 10 is 
provided with four ports 14, 16, 18 and 20 spaced around the passageway at 
intervals of about 90.degree.. The region between ports 14 and 16 includes 
an expander section where hot gases entering port 14 cause successive ones 
of the pistons 12 to be propelled around the passageway 10 in a 
counterclockwise direction as viewed in FIG. 1. That is, the hot gases 
entering the port 14 expand adiabatically, imparting kinetic energy in the 
form of increased forward velocity to each piston 12. After the hot gases 
are expanded adiabatically, they are then compressed approximately 
isothermally as will be explained hereinafter. 
In the region between ports 16 and 18, the pistons 12 move without 
acceleration or deceleration except for deceleration caused by frictional 
forces. Between ports 18 and 20, the unit gas cells between successive 
pistons are compressed. This compressed gas exits through port 20 and is 
fed to a gas heater 22 where it is heated and then fed back into port 14 
prior to adiabatic expansion. Between ports 20 and 14 is a thruster region 
where the pistons 12 move downwardly under the force of gravity to the 
port 14 where they are again propelled in a counterclockwise direction. It 
should be understood, however, that other forms of force in the thruster 
region may be employed. 
Part of the kinetic energy of the propelled pistons may be extracted by 
means of electromagnetic coils 24 which surround the passageway 10 
assuming, of course, that the pistons 12 are formed from a 
magnetically-permeable material such as iron. Other materials and other 
forms of energy extraction may also be used. Beyond the region of energy 
extraction, shown as coil 24, but ahead of the port 16 is a nozzle 26 
adapted to spray a liquid, such as water, into the interior of the 
passageway 10. The mixture of liquid vapor and gas is exhausted through 
port 16 to a liquid-gas separator 28. The separated liquid is then fed to 
a heat exchanger 30 where heat is extracted and then back to the nozzle 
26. On the other hand, the separated gas is applied through conduit 32 to 
port 18 where it is again compressed in the region between ports 18 and 
20. It will be appreciated, of course, that the air/liquid mixture from 
port 16 can simply be exhausted to the atmosphere and that atmospheric air 
can be drawn into port 18. Likewise, instead of recycling the liquid 
through a heat exchanger 30, a continuous or new supply of liquid at the 
proper temperature can be injected into the passageway 10. The coil 24 can 
be replaced by other types of power take-offs such as that shown in U.S. 
Pat. No. 4,280,325 or U.S. Pat. No. 3,859,789. In this system, the kinetic 
energy of the pistons and the spacing (and thus the pressure-volume 
relations) are interrelated. Therefore, the useful power must be removed 
in the expander section between ports 14 and 15 and optimally between the 
liquid spray nozzle 26 and port 16, or an appropriate pressure gate, as 
described later, must be used at the expander exit. 
The operation of the unidirectional energy converter of FIG. 1 can best be 
understood by reference to FIGS. 2 and 3. In FIG. 3, positions of 
successive ones of the pistons in the region between ports 14 and 16 are 
shown, the ports in passageway 10 being separated by an angle less than 
90.degree. in FIGS. 3A-3D for illustrative purposes only. In the thruster 
region between ports 20 and 14, the unit gas cell between successive 
pistons is collapsed to essentially zero volume at point 1 shown in the 
P-V diagram of FIG. 2. The hot, high pressure gas from gas heater 22 then 
enters the inlet port 14 and expands the lead piston (piston A in FIGS. 
3A-3D) at constant pressure to point 2 in FIG. 2, until the trailing 
piston B (FIG. 3B) seals off the unit cell. The unit cell now undergoes 
adiabatic expansion between points 2 and 3 shown in FIG. 2 to 
subatmospheric pressure p.sub.3 at point 3. At this time (FIG. 3C), the 
lead piston A moves against the pressure (assumed to be atmospheric 
pressure) at the outlet 16 and tends to slow down. On the other hand, the 
trailing piston B sees high pressure behind it and vacuum ahead of it, 
such that it still accelerates for a period of time. The result is 
compression of the gas in the unit cell. However, to avoid just climbing 
back up the adiabatic curve between points 2 and 3 in FIG. 2, a liquid 
spray from nozzle 26 is injected into the unit cell between pistons A and 
B. This liquid absorbs the heat of compression, forcing the compression 
process to be approximately isothermal compression up to atmospheric 
pressure p.sub.a at point 4 shown in FIG. 2. At this juncture (FIG. 3D), 
the unit cell exhausts its moist gas through the outlet 16. The liquid is 
then separated from the gas in separator 28 and the dry gas compressed 
between ports 18 and 20 where the gas in a unit cell is adiabatically 
compressed from point 4 to point 5 in FIG. 2. The exhaust gases from port 
20 are then exhausted to the heater 22 and the unit cell collapses to 
point 1 in the thruster region between ports 20 and 14. The gain in the 
net work of this cycle over the Brayton cycle is shown as the 
cross-hatched area in the P-V diagram of FIG. 2. Thus, very high 
efficiencies are possible with the cycle of the invention, approaching the 
Carnot efficiency. Heat is absorbed by the liquid during isothermal 
compression. Consequently, the temperature of the liquid entering the unit 
cell through nozzle 26 should be approximately that of the 
adiabatically-expanded gas in the unit cell. The temperature of the liquid 
in the unit cell increases slightly during the approximately isothermal 
compression, but this temperature is again decreased in the heat exchanger 
30 where heat is extracted. 
In FIG. 4, another embodiment of the invention is shown in which adiabatic 
compression is eliminated and points 1, 2 and 5 in FIG. 2 are, in effect, 
reduced to atmospheric pressure p.sub.a. In the embodiment of FIG. 4, the 
ports 18 and 20 in the continuous, closed-loop passageway 10 are 
eliminated and the pistons are permitted to move freely without 
compression of a gas between ports 16 and 14. The gas separated in 
separator 28 at atmospheric pressure is simply fed back to the gas heater 
22. The result is the thermodynamic cycle shown in FIG. 5 wherein isobaric 
heating occurs between points 2 and 4 in heater 22 followed by adiabatic 
expansion and then approximately isothermal compression between points 3 
and 4. Heat is again extracted by the heat exchanger 30 to lower the 
temperature of the entering liquid. 
In FIG. 6, a further embodiment of the invention is shown which employs two 
expander regions and two power takeoff stations. Ambient air is introduced 
into a combustion chamber 40 where it is heated and then fed through 
conduits 42 and 44 into two expander regions formed in a continuous, 
closed-loop passageway 46. As in the embodiments of FIGS. 1 and 4, water 
is sprayed into the expander sections via nozzles 48 and 50; while energy 
is extracted from the continuous loop passageway by means of a pair of 
linear generators 52 and 54. As the pistons 56 leave the expander 
sections, they pass through pressure gates 58 and 60 located just beyond 
the nozzles 48 and 50. The gates 58 and 60, which may take the form of 
segmented rubber diaphragms as shown in FIG. 7, act as check valves. That 
is, the segments 61 will separate along seams 63 to permit a piston 56 to 
pass through in one direction. After the piston passes through the gate, 
the segments are forced back into sealing engagement along seams 63 due to 
the fact that the pressure in the unit cell at the point of water 
injection is below atmospheric pressure existing at exhaust duct 62. In 
this respect, the gates assume the function of the piston A in FIG. 3C, 
for example, and prevent atmospheric air from entering the unit cell in 
the area adjacent the nozzles 48 and 50. As each piston leaves the 
expander, it passes through a pressure gate; and behind the piston the 
pressure gate closes and maintains a pressure below atmospheric in the 
region of the nozzles 48 and 50. Water is injected at a rate appropriate 
to the heat rejected by the gas ahead of the piston moving out of the 
expander to effect approximately isothermal compression as in the previous 
embodiments of the invention. 
Although the invention has been shown in connection with certain specific 
embodiments, it will be readily apparent to those skilled in the art that 
various changes in form and arrangement of parts may be made to suit 
requirements without departing from the spirit and scope of the invention. 
In this regard, it will be apparent that instead of extracting energy from 
the moving pistons with the use of an electromagnetic coil such as that 
shown in FIGS. 1 and 4, any of the methods for extracting energy from a 
unidirectional energy converter as shown, for example, in the aforesaid 
U.S. Pat. No. 3,859,789 can be used equally as well.