AU2007240126B2

AU2007240126B2 - A heat engine/heat pump

Info

Publication number: AU2007240126B2
Application number: AU2007240126A
Authority: AU
Inventors: Noel Geoffrey Barton
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-04-19
Filing date: 2007-04-18
Publication date: 2012-03-01
Anticipated expiration: 2027-04-18
Also published as: AU2007240126A1; WO2007118282A1

Abstract

A heat engine (1) which includes an inlet duct (5) to receive an air stream containing hot dry air; a turbine (15) operatively associated with the inlet duct (5). The turbine (15) in use extracts energy from an inlet air stream as the air stream flows into the inlet duct (5). An evaporator (20) extends from an outlet end of the inlet duct (5) and is operable to evaporate water injected into the air stream. There are means (25) to inject water droplets into the air stream. An outlet duct (35) extends from the evaporator (20). A fan (30) at an outlet end of the outlet duct (35) is operable to extract air from the evaporator (20).

Description

WO 2007/118282 PCT/AU2007/000498 1 A HEAT ENGINE/HEAT PUMP Field of the Invention The present invention relates to devices for power generation, with associated applications to space heating and cooling. In particular, the invention relates to heat 5 engines based on evaporation of water at reduced pressure, and heat pumps based on condensation of water vapour at reduced pressure. The heat engines are suitable for power generation from renewable energy sources, such as passive solar pre-heating of air or the like. Background of the Invention 10 Most heat engines employ a four-stage cycle based on compression-heating expansion-cooling. Notable examples are the Brayton, Otto, Diesel and Stirling cycles for gases, and the Rankine cycle for liquid-vapour systems. Another feasible four-stage power cycle involves expansion as the first step - expansion-cooling-compression heating - and is herein called the expansion-based cycle. This cycle can be used for is power generation when the cooling stage is accomplished by evaporation of microscopic water droplets. Evaporation involves substantial amounts of latent heat (approximately one tenth the energy content of fossil fuels, without need for oxidant) and rapid heat transfer. Conversely, if the expansion-based cycle involves heating at reduced pressure, that is expansion-heating-compression-cooling, then a heat pump is obtained. This heat 20 pump cycle is obtained when the heating stage is accomplished by condensation of microscopic water droplets. Expansion and compression required in these devices can be achieved by two principal techniques: use of an expansion turbine and extraction fan (or compressor) in series, or use of a piston-in-cylinder configuration.

WO 2007/118282 PCT/AU2007/000498 2 Currently most electrical energy is generated from fossil fuels, and this leads to the fundamental problems of increasing levels of atmospheric CO 2 and depletion of fossil fuels. Nuclear energy is heavily used in some countries, but has many costs as well as risks associated with safety and disposal of radioactive waste. 5 There are many technologies for generating electricity from renewable resources. The most widespread of these are hydropower and wind power, both of which have limits to their exploitation. Renewable forms of electricity generation such as photovoltaic cells, solar thermal plants, wind generators, wave and tidal power, geothermal and biomass only have a very small share of the global electricity market because presently 10 they are too expensive to set up, maintain and run, have storage problems, are too large in size, are not efficient, or rely on energy sources that are limited in some way. The use of heat pumps for space heating of air for domestic or industrial purposes is common throughout the world. Existing heat pumps employ a sealed liquid vapour system and deliver heat from a source at low temperature to a location where the 15 temperature is higher. Power is required for this purpose. When applied to the heating of air, the effect is to provide warmth but not drying of the air. For some industrial applications, it is important to remove water vapour from the air at the same time it is heated, which is not done by existing heat pumps. Object of the Invention 20 It is an object of the present invention to overcome or ameliorate some of the disadvantages of the prior art, or at least to provide a useful alternative. Summary of the Invention There is firstly disclosed herein a heat engine which includes: an inlet duct to receive an air stream containing hot dry air; WO 2007/118282 PCT/AU2007/000498 3 a turbine operatively associated with said inlet duct, said turbine in use extracts energy from an inlet air stream as said air stream flows into said inlet duct; an evaporator extending from an outlet end of said inlet duct and operable to evaporate water injected into said air stream; 5 means to inject water droplets into said air stream; an outlet duct extending from said evaporator; and a fan at an outlet end of said outlet duct and operable to extract air from said evaporator. Preferably, said injection means includes a plurality of spray nozzles. 10 Preferably, said evaporator is a low pressure evaporator. There is also disclosed a heat engine which includes: a cylinder of constant cross section having a chamber to receive an air stream containing hot dry air; a plurality of inlet valves through which said air stream can flow into said 15 chamber; a piston within said cylinder and movable relative thereto to alter the volume of said chamber; means to inject water droplets into said chamber; a plurality of outlet valves through which said air can exit said chamber; and 20 means to cause reciprocating motion of said piston. Preferably, said injection means includes a plurality of spray nozzles. There is also disclosed herein a heat pump which includes: an inlet duct to receive an air stream containing moist air; a turbine operatively associated with said inlet duct, said turbine in use extracts 25 energy from an inlet air stream as said air stream flows into said inlet duct; WO 2007/118282 PCT/AU2007/000498 4 means to inject seed water droplets into said air stream prior to said turbine; a condenser extending from an outlet end of said inlet duct and operable to condense water vapour contained in said air stream; means to collect water droplets in said air stream prior to removal of said air 5 stream from said condenser; an outlet duct extending from said condenser; and a fan at an outlet end of said outlet duct and operable to extract air from said condenser. Preferably, said condenser is a low pressure condenser. 10 Preferably, including means to impart a swirl velocity upon said air stream causing the air stream in said condenser to swirl. Preferably, said swirl means includes a plurality of vanes. Preferably, injection means includes a plurality of spray nozzles. Preferably, said condenser includes apertures to aid in the collection of 15 condensed water from walls of said condenser. There is also disclosed herein a heat pump which includes: a cylinder of constant cross section having a chamber to receive an air stream of moist air; a plurality of inlet valves through which said air stream can flow into said 20 chamber; a piston within said cylinder and movable relative thereto to alter the volume of said chamber; means to inject seed water droplets into said chamber prior to an increase in said volume; WO 2007/118282 PCT/AU2007/000498 5 means communicating with said chamber to collect microscopic water droplets prior to a reduction in said volume; a plurality of outlet valves through which said air can exit said chamber; and means to cause reciprocating motion of said piston relative to said cylinder to 5 alter said volume. Preferably, said outlet valves are operable with said piston. Preferably, said piston is a primary piston. Preferably, said injection means includes a plurality of spray nozzles. Preferably, said collection means includes a plurality of cyclones mounted in a 10 secondary piston. Preferably, including attachment means to attach the primary piston to the secondary piston. Preferably, said primary and secondary pistons are attached together during an expansion cycle. 15 Brief Description of the Drawings The preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of the Expansion Cycle Evaporation Turbine (ECET) heat engine as an embodiment of the present invention; 20 Figure 2 is a side view of the Barton Evaporation Engine (BEE) heat engine as an embodiment of the present invention; Figure 3 is a side view of the Expansion Cycle Condensation Heat Pump (ECCHP) heat pump as an embodiment of the present invention; and WO 2007/118282 PCT/AU2007/000498 6 Figure 4 is a side view of the Baron Drying Engine (BDE) heat pump as an embodiment of the present invention. Detailed Description of the Preferred Embodiments Referring firstly to Figure 1, there is disclosed an Expansion Cycle Evaporation 5 Turbine (ECET) heat engine device 1. The device 1 is generally axially symmetric and includes an inlet duct 5 to receive an air stream 10 of hot dry air. A turbine 15 is located within the inlet duct 5 and in use extracts energy from the air stream 10 as the air stream 10 flows through the inlet duct 5. The air stream 10 works against the turbine 15, resulting in decreased pressure, temperature and density. Extending from an outlet end of 10 the inlet duct 5 and after the turbine 15, is a low-pressure evaporator 20 which is operable to evaporate water injected into the air stream 10. The air temperature and pressure will be low in the evaporator 20 due to work done by the air stream 10 against the turbine 15, but not so low that the air stream 10 becomes saturated by any water vapour existing in the inlet air. The evaporator 20 includes means in the form of nozzles or the like 25 to 15 spray or inject microscopic water droplets into the air stream 10. Evaporation of water at approximately constant pressure from these droplets causes the temperature and specific volume to decrease until saturation of the air stream 10 is reached. Extending from the evaporator 20 is an outlet duct 35. An extraction fan 30 is locatable within the outlet duct 35 and is operable to extract air from the evaporator 20. 20 As the air stream 10 is extracted, the pressure, temperature and density increase. Evaporative cooling from the water droplets continues. During the extraction stage, the pressure is brought back to the inlet pressure, and the temperature increases but not back to the inlet temperature. Because the specific volume of the air stream 10 has been decreased in device 1 by evaporative cooling, less work is required by the extraction fan WO 2007/118282 PCT/AU2007/000498 7 30 than is obtained from the turbine 15. Thus the ECET device 1 operates as a heat engine. The length of the evaporator 20 of the ECET device 1 should be sufficient to ensure evaporation to saturation in this low-pressure, low-temperature section. The rate 5 of evaporation depends on the size of the injected droplets, the temperature and relative humidity of the inlet air stream, and the pressure drop across the expansion turbine. Sufficient droplets should be injected such that further evaporation continues as the air stream is removed from the evaporator 20 by the extraction fan 30. This requires that the residence time of the air stream 10 in the extraction fan 30 be sufficiently large for 10 evaporation to continue. Thus the air stream 10 should be saturated with water vapour at the end of the outlet duct 35. If it is desired, the exhaust air stream can be directed through a cyclone device or the like to collect un-evaporated remnant water droplets before release of the cool moist air to the atmosphere. Cyclones are devices that induce a rapidly swirling airflow in a 15 confined geometry, and thereby separate water droplets from the airflow as they are flung outwards by centrifugal force. Referring to Figure 2, there is disclosed herein a Barton Evaporation Engine (BEE) device 40. The device 40 is based on a similar thermodynamic cycle to the ECET heat engine of Figure 1 described above, but uses a reciprocating piston-in-cylinder 20 configuration instead of continuous flow through a turbine and extraction fan. The piston can be given a reciprocating motion by any one of a number of mechanical means, including but not limited to connecting rod and rotating crank shaft, flexible cable and rotating crank shaft, forced oscillation under the effects of gravity and reduced air pressure, or forced oscillation of a water colunm in a U-tube under the effects of gravity WO 2007/118282 PCT/AU2007/000498 8 and reduced air pressure. In the description below, the reciprocating motion of the piston is caused by vertical oscillation under the effect of gravity and reduced air pressure. The device 40 is a two-stroke heat engine. It includes a cylinder 45 of constant cross section having a chamber 50 to receive an air stream 55 of hot dry air. A plurality s of inlet valves 60 is located at one end of cylinder 45 through which the air stream 55 can flow into chamber 50. A heavy piston 65 is locatable within cylinder 45 and operable in use to alter the size of chamber 50. Air located within chamber 50 expands or contracts as the piston 65 moves within cylinder 45. The piston 65 is constrained to move vertically downwards with gravity for expansion and upwards against gravity for 10 contraction. Means in the form of spray nozzles 70 inject water droplets into the air mass in chamber 50. A plurality of valves 75 on piston 65 is operable in use to pennit the air to exit chamber 50. During use, the cycle starts with piston 65 fully inserted into the cylinder 45, that is at the top of cylinder 45, adjacent to the inlet valves 60. During the first part of the first i stroke, the inlet valves 60 are open while piston 65 drops under gravity through cylinder 45. The outlet valves 75 located on piston 65 are closed. Thus hot dry air 55 flows into chamber 50 at approximately atmospheric pressure. When chamber 50 contains sufficient air, the inlet valves 60 are closed and the piston 65 continues to fall under gravity. The pressure, temperature and density of the air in chamber 50 decrease, but not to the extent 20 that any water vapour in the inlet air reaches saturation. The piston 65 comes to rest when the kinetic and potential energy of the piston has been converted into work required to expand the air in chamber 50. At the point of maximum expansion of piston 65, nozzles 70 spray microscopic water droplets into chamber 50. Rapid evaporation of water from these droplets brings the air to saturation. Since the piston 65 is momentarily 25 at rest, the air density is constant, whilst the temperature and pressure decrease. If WO 2007/118282 PCT/AU2007/000498 9 required, piston 65 can be held stationary by airtight clamps (not shown) mounted in the walls of cylinder 45 whilst evaporation proceeds to saturation. The second stroke then begins. In the first part of the second stroke, piston 65 is drawn against gravity into cylinder 45 under the pressure difference between ambient and 5 the inside of chamber 50. Force is transmitted through the spring-loaded flexible cable 80 to generator 85, thereby enabling power take-off. Evaporation continues to occur as the pressure, temperature and density increase. When the pressure in chamber 50 reaches atmospheric pressure, the outlet valves 75 on piston 65 open and moist cool air is ejected. The cycle is completed with the piston 65 moving in free flight against gravity to the top 10 of the cylinder 45. If it is desired, the exhaust air stream can be directed through a cyclone device or the like (not shown) to collect un-evaporated remnant water droplets before release of the cool moist air to the atmosphere. Referring to Figure 3, there is disclosed herein an Expansion Cycle Condensation 15 Heat Pump (ECCHP) device 90 including an inlet duct 95 to receive an air stream 100 containing moist air. A turbine 105 is located within the inlet duct 95 and in use extracts energy from the air stream 100 as it flows through the inlet duct 95. A low-pressure condenser 110 extends from an outlet end of the inlet duct 95 and is operable to condense water vapour contained in the air stream 100 onto seed droplets injected through nozzles 20 115 before the expansion turbine 105. An outlet duct 120 extends from the condenser 110, and an extraction fan 125 located in the outlet duct is operable to extract air from the condenser 110. Device 90 shares some similar features with the ECET device 1 (Figure 1), although it is now essential to collect condensed water droplets prior to compression and 25 adiabatic heating of the air stream by the extraction fan 125.

WO 2007/118282 PCT/AU2007/000498 10 The device 90 is generally axially symmetric. The inlet duct 95 delivers moist air 100 which does work against the turbine 105, resulting in decreased pressure, temperature and density, to such an extent that the air stream 100 becomes super saturated with water vapour existing in the inlet air. In the absence of condensation 5 nuclei, condensation will not occur even at quite high levels of super-saturation. Condensation nuclei are provided by microscopic water droplets which are sprayed through nozzles 115 into the air stream 100. Condensation of water vapour acts to increase the temperature and specific volume at the same time that turbine 105 decreases the pressure, temperature and density. The dominant effect is that of the turbine 105. 10 Condensation therefore commences in turbine 105 and proceeds to saturation in the condenser 110. In this case, the condensed water droplets need to be collected before the extraction fan 125, since otherwise they would re-evaporate as the pressure and temperature increase as the air stream 100 is re-compressed by the extraction fan 125. To 15 collect the droplets, it is desirable for the flow to be given a swirl. This can be achieved either through the action of the turbine 105, or by use of stationary vanes or the like (not shown). Slots, apertures, perforations or the like 130 at the end of the condenser 110 collect condensed droplets which have been flung outwards by centrifugal force in the swirling flow. 20 The design of the expansion turbine 105 should ensure that as much condensation as possible occurs before the air stream reaches the condenser 110. The condenser 110 should be designed so that droplets reach an outside wall under the action of centrifugal force during the time of flight of the air along the condenser 110. As well as the device geometry, key variables are the length of the condenser 110, the inlet 25 conditions, the radius of the injected droplets, and the swirling speed of the flow. It WO 2007/118282 PCT/AU2007/000498 11 should be noted that droplet collection before the extraction fan 125 could be achieved by other means, including passing the air stream through a plurality of cyclones (not shown) or the like. During the extraction stage, the pressure is brought back to the inlet pressure and 5 the temperature increases to above the inlet temperature. Because the specific volume of the air stream 100 has been increased by condensation, more work is required by the extraction fan 125 than is obtained from the turbine 105. Also the exhaust air stream from the outlet duct 120 will be warmer and drier than the inlet air stream. Thus the device 90 is a heat pump with a high coefficient of performance, which will also deliver 10 chilled distilled water as a co-product. Referring to Figure 4, there is disclosed herein a Barton Drying Engine (BDE) device 135. The device 135 is based on a similar thermodynamic cycle to the ECCHP heat pump of Figure 3 described above, but uses a reciprocating piston-in-cylinder configuration instead of continuous flow through a turbine and extraction fan. The piston 15 can be given a reciprocating motion by any one of a number of mechanical means, including but not limited to connecting rod and rotating crank shaft, flexible cable and rotating crank shaft, forced oscillation under the effects of gravity and reduced air pressure, or forced oscillation of a water column in a U-tube under the effects of gravity and reduced air pressure. In the description below, the reciprocating motion of the piston 20 is caused by vertical oscillation under the effect of gravity and reduced air pressure. The device 135 includes a cylinder 140 of constant cross section having a chamber 145 to receive an air stream 150 of moist air. A plurality of inlet valves 155 is located at one end of the cylinder 140 through which the air stream 150 can flow into the chamber 145. A heavy primary piston 160 is locatable within the cylinder 140 and 25 movable relative thereto to alter the volume of chamber 145. Air located within chamber WO 2007/118282 PCT/AU2007/000498 12 145 expands and contracts as the primary piston 160 moves within cylinder 140. The primary piston 160 is constrained to move vertically downwards with gravity for expansion and upwards against gravity for contraction. Means in the form of a secondary piston 165 is locatable further inside chamber 145 than the primary piston 160 5 communicates with said chamber 145 to collect microscopic water droplets prior to a reduction in the volume. Connection means in the form of catches 170 or the like attach the secondary piston 165 to the primary piston 160 during an expansion stage of the thermodynamic cycle of the device 135. Means in the form of spray nozzles 175 or the like inject water 10 droplets into the air stream 150 prior to the inlet valves 155. The catches 170 release when the chamber 145 has a maximum volume, thereby permitting the secondary piston 165 to be driven upwards through chamber 145. A plurality of cyclones 180 mounted on the secondary piston 165 trap any water droplets in chamber 145. A plurality of valves 185 at the outlet end of cylinder 140 is operable in use to permit the air to exit chamber 15 145. Means in the form of motorized wheels 190 are used to drive the primary and secondary pistons upwards against gravity. It should be noted that other drive mechanisms, including permanent magnet electric motors, can also be used for this purpose. The cylinder has a generally vertical longitudinal axis, with the chamber being located above the primary piston. 20 During use, the cycle starts with the secondary piston 165 attached to the primary piston 160, with both at the top of the cylinder 140 adjacent to the inlet valves 155. During the first part of the first stroke, the inlet valves 155 are open while the primary piston falls under gravity within cylinder 140. The outlet valves 185 located on the primary piston 160 are closed. Thus moist air 150 flows into chamber 145 at 25 approximately atmospheric pressure. When chamber 145 contains sufficient air, the inlet WO 2007/118282 PCT/AU2007/000498 13 valves 155 are closed and the primary piston 160 continues to fall under gravity. The pressure, temperature and density of the air in chamber 145 decrease to the extent where the air becomes super-saturated with water vapour. The piston 160 comes to rest when the kinetic and potential energy of the piston has been converted into work required to 5 expand the air in chamber 145. In the absence of condensation nuclei, condensation will not occur even at quite high levels of super-saturation. Condensation nuclei are provided by microscopic water droplets which are sprayed through nozzles 175 into the air stream 150 prior to the expansion stage of the thermodynamic cycle. Condensation of super-saturated water 10 vapour onto the seed droplets begins during the expansion stage and continues until the air in chamber 145 is no longer super-saturated. Condensation is also accompanied by the release of latent heat, which acts to increase the temperature and specific volume. However, the dominant effect is withdrawal of the piston 160, and the pressure, temperature and density continue to decrease. 15 The condensed water droplets should be collected before the compression stage of the thermodynamic cycle, since otherwise they would re-evaporate as the pressure and temperature increase as the air in chamber 145 is re-compressed. To collect the droplets, the secondary piston 165 is released from the primary piston 160 and driven upwards through chamber 145 by motorized wheels 190. During this process the primary piston 20 160 is held in position by airtight clamps (not shown) mounted in walls of cylinder 140. The secondary piston 165 contains a plurality of cyclones 180, through which air flows during the ascent of the secondary piston 165, and which trap microscopic water droplets. The water is permitted to escape through a slider tube (not shown) passing downwards from the secondary piston 165 through the primary piston 160. After the WO 2007/118282 PCT/AU2007/000498 14 upwards passage of the secondary piston 165 through chamber 145, the air in the chamber is saturated but does not contain any microscopic droplets. Once droplets have been cleared from chamber 145, the second stroke begins. In the first part of the second stroke, the primary piston 160 is accelerated upwards into the 5 cylinder 140 under the pressure difference between ambient and the inside of chamber 145. When the pressure in chamber 145 reaches atmospheric pressure, the outlet valves 185 on the primary piston 160 open and air is ejected until the cycle is completed with the primary piston 160 moving in free flight against gravity to the top of cylinder 145. External work is required to complete the compression phase, and this can be supplied by 10 motorized wheels 190 mounted on the primary piston 160. At the completion of the cycle, the catches 170 re-connect the secondary piston 165 to the primary piston 160. In the absence of pre-heating, the ECET and BEE heat engines discussed above should produce power and moist cool air from water and the heat energy in hot dry air, such as is readily available in summer months in Mediterranean or hot arid climates. The is heat engines can also be used for evaporative cooling. Both the ECET and BEE heat engines preferably operate with greater power and efficiency as the temperature of the inlet air increases. Modest pre-heating of inlet air can be accomplished through the use of waste heat, for example from power stations, or use of renewable energy such as passive solar collectors or geothermal energy from hot 20 springs. The water that is evaporated in the ECET and BEE heat engines can be sourced either from pure water, in which case collection of un-evaporated remnant droplets would not be necessary, or from water containing dissolved substances. In the latter case, the heat engines could for example concentrate the solute in remnant un-evaporated water 25 droplets, and hence facilitate extraction of dissolved solute from the water solvent.

WO 2007/118282 PCT/AU2007/000498 15 The ECCHP and BDE heat pumps preferably produce chilled distilled water and a warm dry exhaust from power and moist cool air. All the abovementioned engines/pumps are preferably simple in design and construction. Many design features are common to the continuous flow devices (ECET, ECCHP) and the piston-in-cylinder 5 devices (BEE, BDE). In summary, all four devices preferably employ the expansion-based thermodynamic cycle. Energy transfer from or to the air mass is preferably accomplished using evaporation or condensation, which are processes that are rapid and involve significant amounts of energy in the form of latent heat. For the heat pumps, the 10 continuous flow device (ECCHP) collects droplets through swirl and centrifugal force, whereas the piston-in-cylinder device (BDE) collects droplets by passage of air through cyclone collectors mounted in a secondary piston. The energy source for the ECET and BEE heat engines is preferably heat energy in the inlet air. Some of this energy can be converted to mechanical or electrical power, 15 and the exhaust air stream is cooler than it would be due to evaporation alone, thus giving an additional benefit. The energy source for the ECCHP and BDE heat pumps is preferably the latent heat of water vapour in air, in addition to mechanical power supplied to the extraction fan or piston respectively. The heat pumps preferably operate with a high coefficient of performance. 20 A number of distinct advantages are available to at least preferred embodiments of the invention: low capital and maintenance costs due to the simple design and few moving parts; the devices do not need fossil fuels or other machinery or engines (except for the energy required to complete the thermodynamic cycles for the heat pumps); there are no 25 atmospheric emissions (except possibly those associated with the energy required to WO 2007/118282 PCT/AU2007/000498 16 complete the thermodynamic cycles for the heat pumps); the heat engines (ECET, BEE) can run on a renewable energy supply such as passive solar heating; the heat pumps (ECCHP, BDE) can use renewable energy inputs; the efficiency of the heat engines (ECET, BEE) increases with pre-heating of the inlet air, such as can be cheaply s accomplished by various methods, especially passive solar collectors; the devices preferably do not contain components operating at high temperature, as is common with most other engines; the heat engines (ECET, BEE) produce power and a cool exhaust from water and the heat energy in hot dry air; the heat pumps (ECCHP, BDE) can produce chilled distilled water and a warm dry exhaust from power and moist cool air; 10 and all the devices would be almost silent and have low visual impact. Although the inventions have been described with reference to specific embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in other forms.

Claims

1. A heat engine which includes: an inlet duct to receive an air stream containing hot dry air; a turbine operatively associated with said inlet duct, said turbine in use extracts 5 energy from an inlet air stream as said air stream flows through said inlet duct to reduce the pressure of said air stream in said duct; a low-pressure evaporator extending from an outlet end of said inlet duct and operable to evaporate water injected into said air stream under conditions of reduced air pressure; 10 means to inject water droplets into said air stream in said low-pressure evaporator; an outlet duct extending from said low-pressure evaporator; and a fan operatively associated with said outlet duct and operable to extract air from said low-pressure evaporator. is

2. A heat engine according to claim 1, wherein said injection means includes a plurality of spray nozzles.

3. A heat engine which includes: a cylinder of constant cross section having a chamber to receive an air stream containing hot dry air; 20 a plurality of inlet valves through which said air stream can flow .into said chamber; a piston within said cylinder and movable relative thereto to alter the volume of said chamber and a pressure of the air stream; means to inject water droplets into said chamber under conditions of expanded 25 chamber volume and reduced air pressure; a plurality of outlet valves through which said air can exit said chamber; and means including a power take-off mechanism to cause reciprocating motion of said piston.

4. A heat engine according to claim 3, wherein said injection means 30 includes a plurality of spray nozzles. AMENDED SHEE IPENAU 18

5. A heat pump which includes: an inlet.duct to receive an air stream containing moist air; a turbine operatively associated with said inlet duct, said turbine in use extracts energy from an inlet air stream as said air stream flows through said inlet duct to reduce 5 the pressure of said air stream in said duct; means to inject seed water droplets into said air stream prior to said turbine; a low-pressure condenser extending from an outlet end of said inlet duct and operable to condense water vapour contained in said air stream under conditions of reduced air pressure; 10 means to collect water droplets in said air stream prior to removal of said air stream from said low-pressure condenser; an outlet duct extending from said low-pressure condenser; and a fan operatively associated with said outlet duct and operable to extract air from said low-pressure condenser. is

6. A heat pump according to claim 5 wherein said collection means includes a plurality of cyclones to collect water droplets condensed on said means under conditions of reduced pressure.

7. A heat pump according to claim 5, wherein including means to impart a swirl velocity upon said air stream causing the air stream in said low-pressure condenser 20 to swirl.

8. A heat pump according to claim 7, wherein said swirl means includes a plurality of vanes.

9. A heat pump according to any one of claims 5 to 8, wherein injection means includes a plurality of spray nozzles. 25

10. A heat pump according to any one of claims 5 to 9, wherein said low pressure condenser includes apertures to aid in the collection of condensed water from walls of said low-pressure condenser.

11. A heat pump which includes: a cylinder of constant cross section having a chamber to receive an air stream of 30 moist air; a plurality of inlet valves through which said air stream can flow into said chamber; a piston within said cylinder and movable relative thereto to alter a volume of said chamber and a pressure of the air stream; AMENDED SHEET 19 means to inject seed water droplets into said chamber prior to an increase in said volume; means communicating with said chamber to collect microscopic water droplets condensed in said chamber under conditions of reduced pressure prior to a reduction in 5 said volume; a plurality of outlet valves through which said air can exit said chamber; and means including a power supply mechanism to cause reciprocating motion of said piston relative to said cylinder to alter said volume.

12. A heat pump according to claim 11, wherein said outlet valves are 10 operable with said piston.

13. A heat pump according to claim 11 or claim 12, wherein said piston is a primary piston.

14. A heat pump according to any one of claims 11 to 13, wherein said injection means includes a plurality of spray nozzles. is

15. A heat pump according to any one of claims 11 to 14, wherein said collection means includes a plurality of cyclones mounted in a secondary piston.

16. A heat pump according to claim 15, wherein including attachment means to attach the primary piston to the secondary piston.

17. A heat pump according to claim 16, wherein said primary and 20 secondary pistons are attached together during an expansion cycle. AMENDED SHEET