Patent Grant
8065876
This disclosure relates to the conversion of heat energy to mechanical energy. The disclosure further relates to such conversion where the heat energy source is concentrated solar energy.
Several different types of heat engines have been used in practice to convert concentrated solar radiation to mechanical power, notably Stirling cycle engines and Rankine cycle engines, however, all such known engines have had disadvantages relating to complexity, cost or low efficiency. Apparatus which convert heat energy into mechanical energy, namely the heat energy of concentrated beam of solar radiation into the movement of a piston through the explosion or expansion of a droplet of substantially uncompressed liquid targeted by the concentrated solar beam are described in patent application Ser. No. 11/512,568, referred to above. In patent application Ser. No. 11/512,568, a method of utilizing a droplet or thin film of water or other liquid, which is heated and explosively expanded in a six-sided expander, is described. The six-sided expander absorbs substantially all of the energy in the droplet and converts a large fraction of that energy to mechanical power through the motion of a linear piston. Mechanical power is in turn converted to electrical power by a linear generator on each of the six sides complete with field excitation and output coil.
In theoretical, conventional Rankine cycles, expansion of working fluid takes place under reversible adiabatic conditions. Also in conventional Rankine cycles as applied to solar energy conversion, the fluid is first vaporized in a boiler then passed into an expander.
Methods whereby liquid is injected into a working space above a piston have also been described. Conventionally, the hot liquid vaporizes at the point of injection, with consequent loss of available energy or exergy. Some of the initial energy loss on vaporization of liquid injected into the cylinder may be regained as heat transferred from the compressed vapor already within the cylinder; however, the energy thus transferred comprises no net heat addition from outside but merely constitutes energy re-circulated within the system. Such recirculation cannot, of itself, produce a useful energy output by the system.
Thus, in the liquid injection prior art, fluid is injected, with exergy loss into a chamber, during which relatively uncontrolled vaporization takes place reducing the amount of available energy, then work is done by adding heat back into the already partially expanded vapor to cause the further expansion of the vapor which moves a piston to perform useful work.
In one practical embodiment, a concentrated beam of solar radiation is directed through a high temperature resistant window, for example, of sapphire or any other suitable material, onto a thin film or droplet of water. The thin film or droplet can be sitting on or near a “target” disk or plate. The target disk or plate can be a material with high absorptivity, high emissivity in the near and far infra red range and very high surface area. The thin film or droplet of liquid is heated and subsequently expanded or exploded, to provide mechanical power.
Some embodiments use a boiler-less, thermodynamic cycle in which the working fluid is heated in contact with the expansion system and the expansion takes place whilst heat input is still going on. Fluid heating takes place at near constant volume, and with substantially no pre-compression resulting in achievement of pressures much higher than conventional Rankine cycles. Also, uniquely, expansion and heating take place on the constant pressure, constant temperature line in the liquid T-s and h-s diagrams, unlike in conventional, Rankine cycle devices hitherto described in the prior art.
According to some embodiments, another part of the cycle comprises a constant volume heat recovery which pre-heats the unexpanded working fluid, while the exhausted, expanded working fluid experiences a constant pressure and constant temperature compression back to the liquid state. Due to the aforementioned heat recovery step whilst exhausting, in a particularly efficient embodiment, the cycle will receive input energy during the expansion process only.
According to an embodiment, an engine comprises a chamber defined by at least one fixed wall and at least one movable wall, the volume of the chamber variable with movement of the movable wall; an injector arranged to inject liquid into the chamber while the chamber has a substantially minimum volume; apparatus through which energy is introduced that is absorbed by the fluid which then explosively vaporizes, performing work on the movable wall; and apparatus which returns the movable wall to a position prior to the work being performed thereon so the chamber has the substantially minimum volume, substantially evacuating the chamber of vaporized fluid without substantially compressing the vaporized fluid.
According to another embodiment, a method of converting energy from one form to another in a system comprises confining a quantity of substantially unexpanded liquid within a chamber; adding energy to the system, so as to heat the liquid sufficiently to vaporize the liquid and expand a resulting vapor; and receiving mechanical energy from the expanding vapor in a form of movement of a wall of the chamber responsive to the expansion.
According to yet another embodiment, a method of converting energy from one form to another by passing a working material through a closed liquid-vapor thermodynamic cycle, comprises expanding the working material from a liquid phase into a vapor phase by addition of heat; recovering heat from the working material in the vapor phase so as to condense the working material from the vapor phase into the liquid phase to await expansion; and adding the recovered heat to working material awaiting expansion, without changing the phase thereof.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing”, “involving”, and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
A single sided expander and its working cycle is now described. The single sided expander includes an oscillating piston and linear electrical generator. The single sided expander is derived from actual experimental rig results. It will be understood that expanders operating on the principles illustrated by the single-sided expander but employing more than one moveable wall element are possible. Moreover, the single sided expander is described in the context of a cylindrical chamber having a piston which moves to vary the size of the chamber; however, it will be understood that other expander configurations are possible, for example based on a rotary configuration similar to the Wankel internal combustion engine, which also has an expansion chamber having a single side which moves to vary the size of the chamber. Any suitable expander chamber configuration in which the expander chamber varies in size responsive to the force of the expanding vapor within and which is returned to a starting position by excess energy temporarily stored in a flywheel or other device for the purpose.
The operating thermodynamic cycle for the expanders, according to various embodiments, is a closed cycle, having relatively high conversion efficiency. It will be contrasted with a conventional Rankine thermodynamic cycle. It is based on the heating and expansion of a droplet or thin film of any suitable liquid, without any substantial pre-compression of the liquid or any substantial pre-compression of any gas surrounding the liquid.
Reference will now be made to
The Expander 101 includes a piston 107 in a cylinder 108, the piston having a piston top 109, which forms a suitable cavity boundary, together with the cylinder 108 and a cylinder head 110. When it is in top dead centre (TDC) position a water droplet or film 111 is injected into this cavity, with necessary propellant force being provided by the liquid pump 104.
A concentrated solar beam 105 is applied intermittently through a sapphire window 112 or other means provided in the cylinder head 110, such that the trapped water droplet or film 111 is vaporized and expands against the piston top 109, producing mechanical power, during an expansion stroke. See also
In addition to utilizing a beam of concentrated solar radiation, any other suitable method of introducing heat into the chamber may be used. For example, a heat exchanger with flow passages on the outside of the chamber may be configured to heat up a flat surface or surface with enhanced area (e.g., textured to have additional surface area), which is directly in contact with the water film inside the cylinder and trapped between piston and cylinder head. Alternatively, a porous block or plate may be fitted between the piston and cylinder head. The porous block, which, as a result of its porosity, has a very substantial surface to volume ratio, can be heated by applying heat externally, which is then transferred through the cylinder head into the block. In yet another alternative, a series of heat pipes embedded in the cylinder head, may enable heat to be transferred at a very high rate from external sources. This last alternative can be combined with the use of the porous block or heat transfer surface explained above.
Exhaust of spent vapor at point 2 on the T-s diagram is carried out by a rotation of the piston such that exhaust ports 122 on the cylinder wall line up with grooves 120a and 120b in the piston, as shown in
In addition to piston rotation, any other suitable method for exhausting spent vapor may be used. For example, a poppet type valve can be disposed in the cylinder head, operated by a solenoid, mechanical lifters or any other suitable means. Alternatively, a valve can comprise a combination of a slot in the piston together with a slot disposed in a rotating sleeve disposed to the outside of the piston. The rotating sleeve may comprise the whole of the cylinder. A cyclical rotation of the sleeve can alternately bring into alignment and take out of alignment the slot in the piston wall in relation to the corresponding slot in the cylinder wall. In yet another alternative, a poppet valve may be disposed on the top surface of the piston, exhausting spent vapor to the area behind the piston. This last alternative has some advantages, notably that the constant pressure condensation step (step 4-5 in
Spent vapor can be condensed, also referred to herein as Process 3-4, prior to re-injection into the cylinder, for example, in condenser 103. The process pathway is given as line 3-4 in the T-s diagram. The spent vapor condensation, Process 3-4, is represented as a constant pressure process. At point 4, the spent vapor is wholly in liquid form, ready for injection into the expander cylinder to start a new cycle. Thus, a continually refreshed supply of working fluid is not required, as the cycle is closed.
Condensed liquid from the condenser 103 is pumped up to injection pressure by means of pump 104, through heat exchanger 102 and then injected into cylinder 108 as a liquid droplet or thin film. The heat exchanger 102 permits otherwise wasted heat in the vapor to be recovered for the useful purpose of increasing the energy available in the next expansion cycle, rather than simply disposing of waste heat. This part of the cycle is indicated as lines 4-5 (liquid pumping, Process 4-5) and 5-6 (constant volume heat gain, Process 5-6), in the T-s diagram. Notably, because the heat recovered by the heat exchanger 102 provides insufficient energy to the liquid to vaporize the liquid prior to or during injection into the cylinder 108, the full energy of expansion of the liquid into expanded vapor after adding some quantum of externally supplied heat is available to perform work on the piston 107.
The inventive cycle is distinguished from conventional Rankine cycles in part by eliminating the boiler and also because inward heat transfer occurs while the working fluid is in the cylinder 108. Other differences include the presence of two constant volume heat transfer processes, (1) Process 2-3, and (2) Process 5-6, in the T-s diagram, and a low pressure compression step, 3-4. The portion 6-1 is an external heat addition step, because the total recovered heat in the 5-6 step is insufficient to heat the condensed fluid awaiting expansion to the fluid's saturation temperature at point 1.
In comparison with conventional Rankine cycles, the ability to do external work during the heat addition process has not previously been considered practical by those skilled in this art, possibly because of the difficulty of implementation. The described and heretofore unknown embodiment, and the variations suggested herein, each demonstrate a way to accomplish this useful result.
In contrast with conventional Rankine cycles a very high expansion ratio is achieved by embodiments in a single cylinder. Because the working fluid is expanding directly from a condensed liquid state to vapor within the cylinder of the expander, expansion ratios of over 80:1 may be achieved in a single cylinder with a four inch diameter and 5 inch stroke. See
Embodiments further employ a single piston on a rod; to the opposite end of this rod a linear generator 106 is mounted, capable of absorbing mechanical energy produced and converting that mechanical energy in the form of motion to electrical energy, at high efficiency. The linear generator consists of permanent magnet 116 and/or coil 114 type system for excitation field and a coil 114 based electrical output system, with necessary software based field current control for production of sinusoidal power output. A rotary crank and suitable connecting rod can also permit connection to a conventional, rotary generator.
In general terms, the invention consists of a unique liquid film-based, constant-temperature, wet-region, expansion heat engine device, running on a unique, hitherto unexploited thermodynamic power cycle, with heating during expansion resulting in an expansion with no internal energy change, constant volume heat transfer, isothermal compression, leading to very high conversion efficiency.
The theoretical basis for the operation of the inventive engine is now presented using non-flow, 1st Law analyses. The theoretical underpinning of each of the processes discussed above is given.
Process 1-2:
Q1-2−W1-2=δU1-2
In the general case, δU is non zero. Therefore, rearranging, the heat input during Process 1-2 is
Q1-2=W1-2+(U2−U1)
Process 2-3:
Q2-3=(U2−U3)
Process 3-4:
Q3-4−W3-4=U4−U3
Process 4-5:
This process constitutes pressurization of the liquid to operating pressure P1 and is a work input term. Since the pressurization is being done on a liquid and not vapor, the magnitude of this term is usually low.
W4-5=(P1−P3)×v1
Process 5-6:
This process constitutes a constant volume heat gain to the pressurized liquid and receives heat from the heat output process of process 2-3. No external or internal work is done, in this process. This is the transfer of heat from spent vapor which is to be condensed back to liquid (for subsequent injection into the expander), into the liquid that is presently awaiting injection into the expander, thus recovering heat that would otherwise be discarded as waste heat. Since the working fluid at 6 is in liquid form whereas the working fluid at 2 is a mixture of vapor and liquid, the total quantum of heat that may be recovered and introduced to the liquid in the process 5-6 is limited by the fluid temperature at 2.
Therefore, Q5-6=Q2′-3,
where point 2′ represents the liquid condition pertaining to the pressure and temperature at point 6. Therefore the internal energy at 6 is given by
U6=(U2′−U4)+U5
Generally U5=U4, hence
U6=U2′
To bring the working fluid up to the working temperature and pressure, additional heat input, for example by transferring into the expansion chamber concentrated solar energy, is required, as follows:
Q6-1=U1−U6
Hence
Q6-1=U1−U2′
Therefore total heat input to the cycle is
Qin total=Q6-1+Q1-2,
or
Qin total=(U1−U2)+W1-2+(U2−U1).
Hence,
Qin total=(U2−U2′)+W1-2.
Thus,
Net work output from the cycle is given by
In the thermodynamic cycle disclosed, the heat input is equal to the gross work output plus a difference in the recovered energy in the constant volume heat transfer and the net work output is equal to gross work out less the low pressure vapor compression work and the liquid compression work.
Part of the heat available at point 2 of the cycle, after expansion, is recovered and utilized for preheating of the fluid prior to commencement of the cycle, at point 1 of the cycle, with additional heat addition to make up any shortfall.
One example of a novel thermodynamic cycle has been described, above. Further specific, novel modifications of a general class of cycles, based on the above cycle, are now presented.
The novel thermodynamic cycle described above, and the related cycles described now are part of a general class of cycles characterized by the Trilateral Flash Cycle described in U.S. Pat. No. 5,833,446, issued to Smith et al. The Trilateral Flash Cycle is presented in
The work described in the Smith at al. patent indicates the Trilateral Flash Cycle is suitable for low grade and geothermal heat recovery and highly suited to utilization with organic fluids. Smith et al. were unable to identify any wider range of suitable application for the particular cycle they describe.
During any Rankine cycle process in the wet vapor region, heat may be recovered during expansion. The quantity of heat recovered affects the improvement achieved in the power output and the efficiency.
According to an aspect of an embodiment, as illustrated by
This bypass ratio may theoretically vary from 0 to 1 but very low bypass ratios result in low specific power outputs hence a more practical approach would be in the range 0.2 to 1.0. The expansion processes resulting from finite stepwise variation of bypass flow is generally shown as lines 2-3a, 2-3b, 2-3c etc. In each of these cases, there is a progressive increase in specific power output and a decrease in overall efficiency as the line from 2-3n approaches vertical (not shown).
To describe the cycle more fully, feedwater at point 1 is pressurized by the pump (see
The Trilateral Flash Cycle identified by Smith et al. is a special case of the general class of liquid to vapor expansion bypass cycles, with a bypass ratio equal to 1, thereby resulting in a high specific power output but a low overall efficiency, for this class of cycles.
A conventional Rankine cycle calculation may be applied to the liquid to vapor expansion bypass cycle; the resulting pressure volume diagram is given in
Although it was not apparent to Smith et al., we have discovered that lower bypass ratios lead to a substantial efficiency increase. As a result of these high efficiencies water, which is readily available in many locales, may be used as the working fluid, whereas Smith et al. propose organic fluids due to perceived low efficiencies using water. Low efficiency using water in the trilateral cycle appears unavoidable in the literature, but we have discovered that low bypass ratio cycles lift this ceiling and permit consideration of water as a working fluid.
The new cycle with bypass may be logically and rationally extended to the supercritical region of the fluid, see
The new cycle when extended to the superheated region shows higher efficiency than in the wet vapor region, in keeping with Carnot efficiency temperature dependence correlations. There is, however, substantial improvement in work done per unit mass of fluid, which is clearly apparent from the fact that internal energy and enthalpy are much higher in the supercritical region. A cycle with a reversible, adiabatic expansion directly from point 2 down to condensing temperature and pressure, as in the case of the trilateral flash cycle of
The general class of liquid to vapor expansion cycles in the wet vapor and supercritical region with bypass constitute a new class of thermodynamic cycles and provides enhanced efficiency possibilities in a multitude of applications: fixed bypass ratio systems may be used in constant output applications such as geothermal power generation; and, variable bypass ratio systems may be considered for hybrid vehicle applications, wherein a low bypass ratio is used during cruising only to charge a battery at a high efficiency, with a momentary high bypass ratio used to produce higher power output for overtaking, etc.
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/719,327, entitled “PIEZOELECTRIC SELECTABLY ROTATABLE BEARING,” filed on Sep. 21, 2005, and Application Ser. No. 60/719,328, entitled “SOLAR HEAT ENGINE SYSTEM,” filed on Sep. 21, 2005, both of which are herein incorporated by reference in its entirety. This application claims the benefit under 35 U.S.C. §120 of U.S. application Ser. No. 11/512,568, entitled “SOLAR HEAT ENGINE SYSTEM,” filed on Aug. 30, 2006, which is herein incorporated by reference in its entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 0659450 | McHenry | Oct 1900 | A |
| 2791881 | Denker | May 1957 | A |
| 3939819 | Minardi | Feb 1976 | A |
| 4024715 | Scragg et al. | May 1977 | A |
| 4103151 | Chromie | Jul 1978 | A |
| 4135367 | Frosch et al. | Jan 1979 | A |
| 4144716 | Chromie | Mar 1979 | A |
| 4195481 | Gregory | Apr 1980 | A |
| 4198826 | Chromie | Apr 1980 | A |
| 4209983 | Sokol | Jul 1980 | A |
| 4229076 | Chromie | Oct 1980 | A |
| 4259841 | Thomas | Apr 1981 | A |
| 4423599 | Veale | Jan 1984 | A |
| 4471617 | De Beer | Sep 1984 | A |
| 4601170 | Flege | Jul 1986 | A |
| 4636325 | Greene | Jan 1987 | A |
| 4788823 | Johnston | Dec 1988 | A |
| 4821516 | Isshiki | Apr 1989 | A |
| 4981014 | Gallagher | Jan 1991 | A |
| 5101632 | Aspden | Apr 1992 | A |
| 5809784 | Kreuter | Sep 1998 | A |
| 6128903 | Riege | Oct 2000 | A |
| 6272855 | Leonardl | Aug 2001 | B1 |
| 6282894 | Smith | Sep 2001 | B1 |
| 6442937 | Stone et al. | Sep 2002 | B1 |
| 6568386 | Agata | May 2003 | B2 |
| 6735946 | Otting et al. | May 2004 | B1 |
| 6786045 | Letovsky | Sep 2004 | B2 |
| 7051529 | Murphy et al. | May 2006 | B2 |
| 7084518 | Otting et al. | Aug 2006 | B2 |
| 20040154299 | Appa et al. | Aug 2004 | A1 |
| 20090100832 | Loeffler | Apr 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 8233373 | Sep 1996 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20100083658 A1 | Apr 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60719328 | Sep 2005 | US | |
| 60719327 | Sep 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11512568 | Aug 2006 | US |
| Child | 12246127 | US |
