GB2484157A

GB2484157A - Multiple stage diffused ejector pump and heat pump

Info

Publication number: GB2484157A
Application number: GB1101760.5A
Authority: GB
Inventors: Kenneth William Patterson Drysdale
Original assignee: Theodoma Ltd
Current assignee: Theodoma Ltd
Priority date: 2010-10-01
Filing date: 2011-02-02
Publication date: 2012-04-04
Also published as: GB201101760D0

Abstract

A multiple stage ejector pump comprises a suction inlet 10, an outlet 11, and a plurality of series connected subÂassemblies 2, 3, 4, each comprising a motive fluid inlet 7, a nozzle 8 and a mixing chamber 9. For each sub-assembly nozzle inlet is in fluid communication with the motive fluid inlet and a nozzle outlet is in fluid communication with the respective mixing chamber. The ejector pump further comprises a fluid output diffuser 5 in fluid communication with an outlet from the downstream most assembly. The ejector pump is used in a heat pump (e.g. CO2 based) assembly for collecting waste and solar ground source heat as a heat source for the main circuit and for heating motive fluid (Fig. 3) drawn from the main circuit. There may be a turbogenerator output.

Description

HEAT PUMP APPARATUS

Technical Field

The present invention relates generally to thermodynamic power cycles and heat pump cycles, and to systems and apparatus for use in generating power and/or pumping heat. The invention relates in particular, but not exclusively, to systems which create a refrigeration and/or heating effect with minimum energy waste.

Background

Air conditioning is almost universally present in hotels, apartment blocks and other multi story buildings around the world. The energy required to power such systems represents a significant cost.

Many such air conditioning plants operate on a standard vapour compression refrigeration cycle. A working fluid enters a compressor as a vapour, and is pumped to a condenser, where it loses heat and condenses to a liquid. The liquid working fluid is forced through an expansion mechanism such as a throttle valve or a capillary tube, where it is expanded and becomes a cold, liquid/vapour mixture. The liquid vapour mixture travels to an evaporator where it is heated to become a vapour, and then travels back to the condenser. The heat absorbed by the working fluid in the evaporator provides the desired cooling effect.

In most large scale operations the evaporator is used to cool a heat transfer fluid, usually water based, which is then pumped to satellite heat exchangers in the areas which require cooling.

The heat absorbed by the condenser is also transferred to a heat transfer fluid, again typically water based. The heat absorbed is rejected to the environment by a cooling tower or other suitable heat rejection device.

The performance of such air conditioning systems is measured by dividing the rate of heat absorption by the evaporator by the power required to run the compressor. This ratio is called the Coefficient of Performance or COP.

Many refrigeration systems can be reversed, so that the condenser acts an evaporator, and the evaporator as a condenser. In this configuration the system can be used for heating, and may be referred to as a "heat pump".

Whether a given system is referred to as a heat pump or a refrigeration system can be regarded as a matter of whether it is the heating aspect or the cooling aspect which is required. Accordingly the terms "heat pump", "refrigeration system" and air conditioning system" are used interchangeably herein. In some cases the term "heat pump" is used where both the heating and the cooling effect of the system are useful.

Some refrigeration systems of the prior art use ejector pumps to provide at least a portion of the required compression of the working fluid.

Summary

According to a first aspect of the invention there is provided a multiple stage ejector pump for a heat pump circuit, the ejector pump comprises a suction inlet and an outlet, the ejector pump further comprising a plurality of subassemblies, each sub-assembly comprising a motive fluid inlet, a nozzle and a mixing chamber, and the sub-assemblies connected in series so as to cumulatively increase fluid flow rate within the ejector pump, for each sub-assembly an inlet of the respective nozzle is in fluid communication with the motive fluid inlet, and an outlet of each respective nozzle is in fluid communication with the respective mixing chamber, and the ejector pump further comprising a diffuser from which ftuid is output from the ejector pump, and the diffuser is in fluid communication with an outlet from the downstream-most sub-assembly.

The term fluid' includes both liquid and vapour/gas phases, either singularly or in combination, such as Co2 (R?44), R410a and R134a, for

example.

The ejector pump may advantageously be installed into an existing heat pump circuit to replace a conventional compressor. In such an arrangement there may be no need to remove the compressor, rather the ejector pump could be installed, leaving the compressor in situ, and a valve arrangement ensuring that the working fluid is diverted through the ejector pump.

Preferably the sub-assemblies are connected directly to one another in series.

Preferably, the diffuser is the sole diffuser of the ejector pump, and no diffuser is provided between sub-assemblies.

Preferably the motive inlets and the suction inlets are arranged such that the force vectors of the fluid from those inlets are substantially aligned along a common axis.

Preferably the diffuser comprises a feedback outlet arranged to allow a proportion of fluid passing through the pump to be fed back into the pump.

A second aspect of the invention relates to a fluid circuit comprising the ejector pump of the first aspect of the invention.

One embodiment of the invention may be viewed as novel cooling system comprising a hybrid combination of a heat pump and multi-stage ejector pump. The ejector pump employs positive energy feedback within itself and uses the heat pump plus waste and or solar heat sources as the driving means to each of its stages.

In one preferred embodiment of a thermodynamic cycle the heat pump and the ejector pump draw heat from a common heat load with the refrigerant working fluid entering a common suction input at the ejector, after having been passed through an expansion valve and flashed to vapor in an evaporator.

In another preferred embodiment the heat pump draws heat from the final suction chamber of the ejector and returns its output to the multiple motive inputs of the ejector.

In one embodiment a branch of the vapor flow is passed to the heat pump comprising normal components and pipe work as would be found in any standard system.

The ejector pump preferably comprises multiple stages contained within a common enclosure comprising nozzles, mixing chambers and a single diffuser section. Preferably there is also a novel positioning of the motive inputs and common suction input, which are in line within the same plane, instead of the suction line being orientated at ninety degrees to the motive input and mixing chamber, as is normally the case in ejector design. Multiple nozzles and mixing chambers allow multiple motive inputs within an ejector design with a single diffuser. The multiple inputs advantageously provide an increased entrainment force being the vector sum of all the entrainment forces. The increased entrainment force results in a higher than normal mass flow rate of refrigerant through the common heat load with increased cooling power and a higher than normal COP. Furthermore, the multiple mixing chambers enable the ejector design to be optimized for both entrainment ratio and compression ratio. As the area ratio between the mixing chamber diameter and nozzle throat increases, so does the entrainment ratio, but this is at the expense of compression ratio between the ejector output and its suction input. The multiple mixing chambers enable multiple nozzles to be used in series resulting in multiple entrainment forces acting together, as well as making provision for multiple area ratios. For example, in an ejector which has three nozzles and three mixing chambers the first two area ratios can be optimized for entrainment and the last for compression ratio. The alignment of the motive inputs and common suction input along a common axis provides a means of efficiently implementing the above mentioned key design strategy of the high COP system.

Another aspect of the invention relates to a power generation and/or heat pump cycle comprising the ejector pump of the first aspect of the invention.

One embodiment of the invention comprises a heat pump circuit comprising a heat exchanger in thermal communication with a solar heat collection means, and a heat exchanger in thermal communication with the solar heat collection means, and the heat exchanger providing a heat supply to an ejector pump of the circuit.

One or more of the embodiments of the invention may comprise a ground installed heat exchanger arrangement for a power generation/heat pump cycle, the arrangement comprising a solar heat collection medium, the solar heat collection medium arranged to be exposed to solar radiation, a first heat exchanger in thermal communication with the solar heat collection medium and the arrangement further comprising a second heat exchanger in thermal communication with the ground.

The heat exchangers arc preferably thermally isolated from each other.

The first heat exchanger preferably serves as an evaporator for a working fluid and the second heat exchanger preferably serves as a condenser for the working fluid.

The first heat exchanger is preferably located above the second heat exchanger.

The solar heat collection medium may comprise a biodegradable material such as wood chippings and/or grass cuttings.

According to another aspect of the invention there is provided a method of power generation and/or heat pumping comprising use of the ejector pump of the first aspect of the invention.

Brief description of the drawings

Various embodiments of the invention will now be described by way of example only, with reference to the following drawings in which: Figure 1 is longitudinal cross-section of a multiple-stage ejector pump, Figure 2 is a schematic representation of a heat pump circuit, Figure 3 is a schematic representation of a further heat pump circuit, Figure 3a is a schematic representation of a turbogenerator for use with the circuit of Figure 3, Figure 4 is a cross-sectional view of ground installed heat exchange matrices forming part of the heat pump circuit of Figure 3, Figure 5 is a schematic diagram of cooling system/heat pump and the ground installed matrices of Figure 4, Figure 6 is a schematic diagram of a heat conversion system, Figure 7 shows a cooling cycle on a pressure versus enthalpy plot, Figure 8 shows a carbon dioxide energy conversion circuit, Figure 9 shows a further carbon dioxide energy conversion circuit, Figure 10 shows a carbon dioxide power generation cycle, Figure 11 is a table of data logging results, Figure 12 is a schematic diagram of a power generation system, Figure 13 is a schematic diagram of a further power generation system, Figure 14 is a Pressure-Enthalpy diagram, and Figure 15 is a schematic diagram of a conventional air conditioning system powered by a power generation system of Figure 12 or Figure 13.

Detailed Description

With reference to Figure 1, there is shown a multiple stage ejector pump, of overall general tubular form and comprising a fluid suction inlet 10 and a fluid outlet 11. The pump 1 comprises three sub-assemblies 2, 3, and 4. Each sub-assembly essentially relates to a respective stage. Each sub-assembly essentially comprises a motive nozzle 8, a motive fluid inlet 7 and a mixing chamber 9. Like, or substantially alike, features are designated with corresponding reference numerals. The three sub-assemblies are connected directly in series.

Each nozzle 8 is of tapered profile, tapering in a downstream direction.

The nozzle is positioned substantially centrally of the inner volume of the tubular body of each sub-assembly, defined by an inner surface 15. Thus an annular space 16, of varying diameter, is defined between an outer surface of the nozzle and the inner surface of the tubular body, which annular space arranged to allow fluid to pass therethrough.

Each respective mixing chamber 9 is located downstream of an outlet end of each nozzle. Each mixing chamber comprises a portion of substantially constant cross-section. It will be noted that the tapered volume at the end of each mixing chamber is arranged to ensure that the supersonic wave of fluid is broken before reaching the next sub-assembly.

Each motive fluid inlet 7 is located in a respective side wall portion of the internal space of the pump. In use, motive fluid is fed to each nozzle by way of a respective conduit 17 (of which only one is shown).

The ejector pump 1 further comprises a diffuser 5 which is located at the downstream-most end of the pump. The diffuser defines a space, the cross-sectional area of which increases in a downstream direction. An endmost portion of the diffuser corresponds to the outlet 11 of the pump 1.

The diffuser 5 is provided with an outlet 19. A compressor (not shown in Figure 1, but shown in Figure 2) draws a proportion of the fluid passing through the outlet 19 and feeds said fluid back into ejector pump by way of the motive inlets 7.

It should be noted that in the embodiment shown in Figure 1, the dimensions shown are relative to the diameter of the throat of the nozzle.

In use, the overall operation of the ejector pump within a heat pump circuit is as follows. The fluid is fed back into the pump 1 through the motive fluid inlets at relatively high pressure. The motive fluid is accelerated by the respective nozzle, thereby creating a low pressure zone, therefore causing down stream fluid to be drawn through the annular space around the nozzle and through the pump (and originally through the suction inlet 10).

Reference is made to Figure 2 which shows the ejection pump 1 in situ in a heat pump circuit 30. The circuit comprises a receiver 31 which stores refrigerant 32. Downstream of the receiver there is provided a pump 33 controlled by a variable speed drive 34. Downstream of the pump 33 there is a controllable valve 34. The outlet from the valve 34 is urged through a heat exchanger 35. On exiting the heat exchanger 35 the fluid is drawn into the ejector pump 1. Attention is drawn to the presence of a compressor 36 which effects the positive feedback described above. On being output from the diffuser 5, the fluid inputs to the heat exchanger 37. On exiting the heat exchanger 37 is in part determined by a controllable throttle valve 38.

In a variant embodiment, shown at 39, and as an alternative to using the positive feedback arrangement described above, the motive fluid is sourced directly from the receiver 31, through a valve 39a, a heat exchanger 39b and a compressor 39c.

There are multiple important advantages to the embodiments described above which will now be described.

It will be appreciated that by careful selection of the ratio of the cross-sectional area of the nozzle throat to the cross-sectional area of the mixing chamber, one can determine the extent of entrainment or compression at each stage of the pump. It can be seen that for the stages corresponding to the sub-assemblies 2 and 3, the area ratio is the same, whereas, the last stage the cross-sectional area of the mixing chamber is smaller and so the area ratio is different.

Because the pump includes only one single diffuser, located at the end of the pump, the overall length dimension is smaller as compared to if each sub-assembly had its own respective diffuser. This results in the advantages of reducing the overall length of the pump, which is an important consideration when space available for installation is limited.

It also has the advantage of reducing losses as the fluid passes through a shorter length.

Perhaps most advantageously, the ejector pump 1 creates a multiplication in the COP of a standard heat pump by using its high pressure output, plus any available waste and or solar heat to drive the motive inputs of a multi-stage ejector pump. Positive heat feedback and internal summing of the entrainment forces within the ejector pump increases the mass flow rate within a common evaporator resulting in an increase of cooling power to the heat load.

Each of the ejector's motive inputs are connected to the high pressure output of the heat pump(s) compressor(s), and or any of the available waste/solar heat sources which provide the motive drive to each of the stages.

The working fluid at each motive input is high enthalpy, energy rich, refrigerant vapor which acquires a high velocity as it passes through the motive nozzles. The high velocity working fluid causes a drop in pressure in the mixing chamber of each ejector stage which increases the suction force in the ejector's common suction line. The resultant suction forces are thus summed within a common enclosure.

The increased force in the common suction line results in an increase in the mass flow rate of the refrigerant in the common evaporator. This in turn results in a non linear increase in cooling power with a minimal increase in electrical input to the system.

Furthermore, and as mentioned above, the multiple mixing chambers enable the ejector design to be optimized for both entrainment and compression ratio. Referring to Perry's Chemical Engineers Handbook it can be seen from the relevant design graphs that as the area ratio between the mixing chamber diameter nozzle throat increases so does the entrainment ratio, but this is at the expense of compression ratio between the ejector output and its suction input. The multiple mixing chambers enable multiple nozzles to be used in series resulting in multiple entrainment forces acting together, as well as making provision for multiple area ratios. For example, in an ejector which has three nozzles and three mixing chambers the first two area ratios can be optimized for entrainment ratio and the last for compression ratio. The alignment of the motive inputs and common suction input along a common axis provides a means of efficiently implementing the above mentioned key design strategy of the high COP system. Each successive sub-assembly being arranged in series results in a cumulative increase in fluid flow rate with each sub-assembly.

These combined effects advantageously result in a cooling system with an extraordinarily high COP.

The following mathematical proof demonstrates the high COP which can be obtained using the ejector pump 1, as applied to the data logging results shown in Figure 11 (which were obtained from a circuit similar to that shown in Figure 3). Let:

iii: = mass flow rate in each motive input of the multi-stage ejector th, = mass flow rate entrained in each stage of the multi-stage ejector = total mass flow rate after the nth stage of the multi-stage ejector = a function defining motive mass flow rate = a function defining entrained mass flow rate e = entrainment ratio per stage = compounded entrainment ratio after the nth stage = change in enthalpy within the evaporator P = electrical input power Pf = electrical input power factor = total heat removed by cooling evaporator P = electrical input power to vaporize the ejector inputs QT = net heat removed by evaporator COP = coefficient of performance of system (electrical heating inputs removed) COPR = coefficient of performance of system (all electrical inputs generated within the system boundary) Considering the functions acting at the various inputs and outputs -IflT = + (1) i/a = fth (2) = (3) = (?il + ihj" (4) kF= th(1 + i.)n (5) = fl ( ±.e) (6) ne n(n-1)e2 n(n-1)(n-2)e3 1T1T m[1 + + 2! + 3! (7) from results:- hnwx = 445-and h:mtn = 21O-thus [hincLx -hm:in] = 235 kJ/kg from results average total motive heat input = 14.83 kW given n = 3 thus average heat per motive input = 14.83/3 = 4.94 kW 4 * thus ri = = 0.021 kg/s from results T = 0.2 kg/s from (6) and results = n (1 t (8) = 6m7/th 1) (9) e, = e, = 8.52 = 0.2 kg/s

-

Q= ur.j (10) = :r [kinacT-h.rntr] (11) = 0.2 kg/s x (445 -210) kJ/kg = 47 kW QT =Q11-P (12) from results P1, = 2.1 kW Pf = 0.79 COP = QT/(PxPf) (13) COP = (47 -14.83)/(2.1 x 0.79) (14) COP = 32.17/1.66 COP = 19.39 If waste or solar heat available to flash ejector motive inputs then QT=Qn thus COPR = 47/(1.66) = 28.31 Various examples of thermodynamic circuits which advantageously include the ejector pump 1 will now be described.

Figure 3 shows a heat pump circuit 50, which is somewhat similar to that shown in Figure 2 (and like reference numerals are used for the same or similar components). The circuit 50 includes three ground installed heat exchanger matrices 60, 61 and 62, each arranged to carry the working fluid. As best shown in Figure 4, the matrices are located at respective levels in the ground. Each matrix comprises a length of heat conductive conduit (such as copper tubing) arranged in serpentine or convoluted fashion. An uppermost layer 63 comprises an infrared membrane, below which there is provided a void 64. The membrane 63 allows heat to enter the void 64, but substantially prevents heat from escaping therefrom. Underlying the void 64 there is provided a layer compost material 65, for example comprising wood chippings and/or grass cuttings. The solar heat is transmitted through the membrane and heats the compost 65, causing it to decompose, and in so doing creates a heat store. The heat stored by the compost causes temperatures of up to around 35 degrees Celsius to achieved. The matrix 60 is in thermal communication with the compost layer 65. Below the matrix 60, the matrix 61 is located; the matrices 60 and 61 have a spaced-apart relationship by way of a layer of moist sand. Immediately below the matrix 61, the matrix 62 is located, and the matrices 61 and 62, vertically spaced-apart by virtue of a layer of moist sand 6?.

Immediately below the matrix 62, there is provided a layer of moist sand 68, and a rain water drain 69.

Returning to Figure 3, on exiting the receiver 31 at a pressure of around 4.5 bar, and having passed through the filter/dryer 45, the fluid bifurcates into two flows-one to provide a motive input to the ejector pump 1 and the other to provide a suction input to the ejector pump. A pump 33 pumps the working fluid towards and through the matrix 60, the working fluid exiting the pump at a pressure of around 7 bar and a temperature of 14 degrees Celsius. On passing through the matrix 60, the working fluid is heated from the compost layer 65. The heated working fluid is then further heated by way of the heat exchanger 52 which imparts waste heat to the working fluid. On exiting the heat exchanger 52, at a temperature of around 56 degrees Celsius, and at a pressure of around 7 bar, the working fluid is then fed into the motive inlets of the ejector pump 1. In relation to the working fluid which forms the suction flow, it is first cooled by passing through a sub-cooler receiver 46, in which the fluid therein is subjected to the effect of a sub-cooler device, such as a compressor based sub-cooler 47. The cooled working fluid exits the receiver at a pressure of around 2 bar and a temperature of around -10 degrees Celsius, and then passes through a feedback controlled expansion valve 34, exiting the expansion valve at a pressure of around 1 bar and a temperature of around -20 degrees Celsius, before passing through the matrix 61, through which it receives heat from the ground. A feedback control 34a is used to monitor the fluid exiting the heat exchanger 61, and issue a control signal to the valve 34.

On exiting the ejector pump 1, at a pressure of around 10 bar and a temperature of around 54 degrees Celsius, the working fluid passes through the matrix 62, which serves as a condenser, and yields heat to the ground. The fluid leaves the matrix 62 at a pressure of around bar and a temperature of around 35 degrees Celsius, and then passes through the heat exchanger 37, which serves as a sub-cooler. The fluid leaves the heat exchanger 37 at a pressure of around 10 bar and a temperature of around 18 degrees Celsius. The fluid then passes through a valve 48, exiting the valve at a pressure of around 4.5 bar, and a temperature of around 14 degrees Celsius.

Figure 5 shows a block diagram of the overall system.

As alluded to in Figure 3a, the matrix 62 could be replaced by a turbogenerator 80, comprising a turbine, which is arranged to convert heat in the fluid exciting from the ejector pump 1, into electricity.

Because of the high COP of the ejector pump 1, electricity generated by the turbogenerator 80 is generated at high efficiency. As illustrated in 1? Figure 6, the arrangement of the heat pump and the turbogenerator and the heat reservoir, such as ground heat or heat from the sea, or other low-grade heat, results in generation of electricity to power the heat pump and provide an electricity supply to an electricity grid. It is also to be noted that waste heat from the turbogenerator is fed to the heat pump.

The turbogenerator 80 preferably comprises a turbine chamber and a turbine, wherein the motive force of the pressurized working fluid causes the turbine to rotate, and the turbine connected to an electrical generator such that when the turbine is rotated, the electrical generator generates electricity.

Reference is now made to Figure 7 which is a pressure-enthalpy plot showing the cooling cycle implemented by the circuit 50 which illustrates in particular an important advantage of sub-cooling the fluid of the suction input in a liquid state. A typical cooling cycle which includes use of a conventional compressor, without the presence of the ejector pump 1, would follow the path A-B-C-E-A. (It will be appreciated that initially, during start-up, it would follow the path B-C-F-G-B.) However, the circuit 50 in fact follows the path A-B-C-D-A. The cycle passes from C to D, instead of from C to E, because the deceleration caused by the diffuser of the ejector pump is transferred into pressure.

Because of the shorter cooling cycle path, a condenser of smaller dimensions is advantageously required, and so advantageously a more compact compressor can be used. Moreover, it will be appreciated that we arc able to lower the lowest temperature by 10 to 20 degrees Celsius in a very energy efficient manner.

The circuit 50 advantageously uses stored solar heat, waste heat and the heat of the ground, and combines with the high COP ejector pump 1 to result in a high-efficiency heat pump cycle. It is to be noted that in the event that no waste heat is available, the pump 33 is relocated as shown in broken lines, at 33a, and the motive energy input to the ejector pump is derived from heat output from the sub-cooler, as shown at 4?a.

Figure 8 shows a circuit 90 in which the working fluid is carbon dioxide.

The circuit 90 is thermally connected to the circuit 50 by way of a heat exchanger 91 which transfers heat from the output of the ejector pump 1 to the circuit 90. The circuit 90 comprises a carbon dioxide receiver 92.

The receiver 92 is connected to two carbon dioxide vessels, one for containment of carbon dioxide in liquid form and the other for containment of carbon dioxide in vapour form. Downstream of the receiver 92 there is provided a filter/dryer 93 and a pump 94. The pump 94 pumps liquid carbon dioxide from the receiver 92 towards the heat exchanger 91 where the working fluid receives heat. The working fluid exits the heat exchanger 91 at a pressure of around 40 bar and a temperature of around 30 degrees Celsius, and thereafter then reaches a superheater heat exchanger 95 where it receives further heat from a waste heat source. The vapourised working fluid exits the heat exchanger 95 at a temperature of around 60 degrees Celsius and a pressure of around 40 bar. The vapourised working fluid then drives a turbogenerator 96, the rotational output of which is then converted into electricity, rectified and inverted at 9? to provide a useable electricity supply. Working fluid exits the turbogcnerator 96 at a temperature of around 15 degrees Celsius and a pressure of around 20 bar, which is then subjected to a condenser heat exchanger 98, and the condensed working fluid then returns to the receiver 92 at a temperature of around 7 degrees Celsius and a pressure of around 20 bar.

Reference is now made to Figure 9 which shows a further embodiment in which a circuit 100 comprises a turbogenerator which is driven from a low temperature heat source at typically 10°C to 15°C using carbon dioxide as the working fluid. Carbon dioxide is a natural substance and as such has many advantages over synthetic compounds such as CFCs and HCFCs normally used in cooling/heating/organic Rankin cycle applications as well as having good heat absorption properties at tow temperatures. The turbogenerator could provide the energy to drive a number of useful processes such as highly efficient heating/cooling systems, electric cars, electrolysis of water to produce hydrogen as a fuel, to name but a few applications, thus enabling the conversion of low grade waste heat to useful power at temperatures of around 30°C and below. The possible operating temperature range is well within that of solar thermal heat collectors which would be capable of operating for significant periods each day for most of the year round in a large number of countries worldwide.

The thermodynamic cycle realised by the circuit 100 comprises a high temperature carbon dioxide reservoir 101 heated from a high COP heat pump 102 via a first heat exchanger 103 operating from a latent heat source at say 0°C to 30°C and a pressure of 40 bar to 50 bar. In the embodiment shown the latent heat source is the heat withdrawn from a cooling load 110, which load is cooled by a carbon dioxide cooler 111.

The circuit 100 further comprises a low temperature turbogencrator 104, a low temperature carbon dioxide reservoir 106 being cooled by a second high COP heat pump 105 to a temperature of typically -15°C to -20°C via a second heat exchanger (not illustrated) and operating at a pressure of 19 bar to 22 bar. Working fluid passing from the receiver 101 to the turbogenerator 104 is subjected to a pump 112 and is superheated by way of a heat exchanger 113, which uses a heat output from the heat pump 102. The second heat pump 105 dumps its heat output back into the high temperature reservoir 101 via a third heat exchanger (not illustrated) located within or associated with the high temperature reservoir 101. It is envisaged that in one preferred embodiment the heat exchangers form an integral part of the two reservoirs. In a second preferred embodiment the heat exchangers may be optionally located outside the two reservoirs. The two reservoirs also form a high pressure/low pressure path to allow the working fluid to pass through the turbogenerator 104 and thus produce useful power from the temperature and pressure differentials thus created.

It will be appreciated that each of the heat pumps 102 and 105 comprises an ejector pump 1.

Some of the advantages of using carbon dioxide as the working fluid are as follows: It is a naturally occurring substance It has good thermodynamic properties for power generation at low temperatures It supports a minimal component design, is oil free and environmentally friendly Carbon dioxide based systems can support power generation for sustained periods Carbon dioxide in a closed system has no adverse environmental impact Carbon dioxide systems operating with solar thermal heat collectors are a source of renewable energy Carbon dioxide power generation systems could significantly unload the national grid and save fossil fuel.

Figure 10 shows carbon dioxide cycle which is an implementation of the circuit 100.

Reference is now made to Figure 12 which shows a Co2 power generation circuit which comprises an ejector pump 100, a superheater heat exchanger 102 (essentially of the same form as heat exchanger 61 shown in Figure 3, being ground installed and drawing heat from stored solar-derived energy), a turbogenerator 103, which comprises an integrated turbine and a generator, and the circuit further comprises two feedback conduits 105. Pressure relief outlets 119 are provided connected to the heat exchanger 102.

The pump 100 is of similar form to the ejector pump 1, save that each sub-assembly comprises two, longitudinally coincident nozzles 108, provided in a respective common mixing chamber. The motive inlets to the nozzles arc fed by way the feedback conduits 105, each conduit connected to a respective set of nozzles. Each feedback conduit is connected to an output from the heat exchanger 102, taking a proportion of the vapour flowing towards the turbine. Each conduit 105 comprises a receiver 115 and a non-return valve 116. Each receiver 115 is connected to two Co2 vessels (not illustrated), one containing liquid Co2 and the other containing Co2 in vapour form. A mixer then combines the Co2 from the vessels and feeds the same into the (respective) receiver. Non-return valves 125 and 126 are provided at the inlet and at the outlet, respectively, of the ejector pump 100.

The output from the turbogencrator 103 is connected to a rectifier 110, the output from the rectifier is output to a battery pack 111, the electrical power from the battery pack is output to a DC/AC converter 112, and the output from the converter is fed to mains interface equipment 113.

In use, the circuit operates as follows. A start-up operation is required to bring about an initial flow of fluid within the circuit. A compressor 120 is operated to cause a pressure differential between the downstream most mixing chamber of the pump and an inlet to the heat exchanger 102. A supply of Co2 from the receivers 115 is caused to enter the motive inlets of the nozzles. In turn, a flow of Co2 through the ejector pump 100 is brought about (at which point the compressor 120 can be deactivated) in which the ejector creates a suction force at its input end and a rise in pressure at its output end. The rise in pressure is transmitted to the turbogenerator via the heat exchanger 102. The heat exchanger 102 heats the Co2 vapour to around 30 to 50 degrees centigrade. The vapour output from the heat exchanger 102 causes the turbogenerator 103 to turn, so generating electricity (as will be described further below). The turbogenerator 103 produces a pressure drop at its output of around 20 bar to a pressure of around 20 Bar, -20 degrees centigrade and 760 kJ/kg. The ejector pump 100 draws in the vapour exhaust from the turbogenerator, and by compression occurring within the pump, produces an output of approximately 40 bar, 0 degrees centigrade at around 740 kJ/kg. The heat exchanger 102 then re-heats the vapour to be input to the turbogenerator 103 to around 780 kJ/kg to 800 kJ/kg.

The electricity generated by the turbogenerator 103 is first rectified by the rectifier 110. The output from the rectifier 110 is then used to charge a rechargeable battery pack 111. the electrical output from the battery pack 111 is then fed to a Dc to AC converter and then to three-phase mains interface equipment 113 for connection to an electricity grid. In order to reduce the duty cycle of the turbogenerator the ejector pump 100 is deactivated when the stored charge in the battery pack 111 reach a sufficient level. This is achieved by way of a voltage comparator (not illustrated) which, when the predetermined level is reached, activates a solenoid valve (not illustrated) in each of the feedback conduits to prevent fluid from flowing to the motive inputs. When the voltage comparator senses that stored charge has fallen below a predetermined level, the valves in the feedback conduits 105 are re-opened, so allowing the ejector pump 100 to re-commence driving the turbogenerator 103.

In the embodiment shown, the turbogenerator 103 comprises oil-bearings.

Accordingly, an oil-vapour separator (not illustrated) is provided to receive and separate the oil from the vapour from the sump of the turbogenerator 103. The oil is fed back into the turbogenerator and the vapour is fed to a low pressure vapour output of the turbogenerator. It will be appreciated that in an alternative embodiment gas bearings are provided instead of oil bearings (and advantageously gas bearings having a greater longevity as compared to oil bearings).

A heat exchanger 130 is provided to transfer heat to a water cooling circuit comprising a water pump 131 and a heat rejector 132. this allows heat to be taken out of the vapour circuit should the circuit need to be shut down.

The circuit shown in Figure 12 may be viewed as a vapour driven heat engine which operates in the superheat region of a Ph graph, and rejects no heat apart from that required to operate the turbogenerator 103 making it extremely efficient at around 80%. Because there is no need to return the vapour to a liquid, no liquid pump is required. Further, no condenser is required. Operating solely in the vapour phase means that no energy is expended in effecting phase transitions between liquid and vapour, and according differs from a Rankin cycle.

Reference is made to Figure 13 which shows a simplified representation of a further embodiment of a Co2 vapour driven heat engine circuit comprising the ejector pump 1, a Co2 receiver 140, the heat exchanger 102, and the turbogenerator 103. The battery pack, rectifier, and mains conversion components are omitted for simplicity. In use, the receiver 140 is charged to around 40 bar using a mixture of Co2 liquid and Co2 vapour via a Co2 mixer. Cold Co2 liquid at around 40 bar, 0 degrees celsius is forced into the heat exchanger 102 and super-heated to around 30 to 50 degrees celsius, at around 780 to 800 kJ/kg. With reference to the Ph diagram of Figure 14, once the initial charge in the receiver is flashed to vapour, transitions between points A to B to C in the superheat region, the heat exchanger 102 only has to replace the heat lost in the turbogenerator and the ejector pump. Heat is lost between points A to B and B to C and gained between points C to A. Although not illustrated in Figure 12 or Figure 13, there is provided a pressure relief valve immediately upstream of the inlet to the turbogenerator.

It will be appreciated that either of the circuits shown in Figure 12 and Figure 13 could be converted to cooling system by the addition of a condenser. It will further be appreciated that an integrated Co2 based high COP cooling/power generation system can be envisaged, in which power is generated from rejected heat.

Reference is made to Figure 15 which illustrates how the power generation system of Figure 12 or 13 could be used to power the compressor of a convention refrigeration system. The conventional refrigeration system comprises a compressor 200, a heat aeeepter 201, and a sub-system 202, and a heat rejector 203. A plate heat exchanger 204 is included on a heat outlet of the sub-system 202, upstream of the heat rejector. The exchanger 204 transfers heat to a water circuit which includes a water pump 210 and an expansion vessel 211. Heal from the heated water is transferred to a heat exchanger of the power generation system, shown generally at 220. Generated electrical output from the system is fed to a changeover switch 230. The changeover switch receives an electrical input from a mains supply 240.

The switch 230 is arranged to determine when the electrical power from the system 220 reaches a predetermined level, at which point the switch 230 is operative to cause the electrical power from the system 220 to power the compressor, in place of power from the mains supply 240.

Should the switch subsequently determine that the electrical power from the system falls below the predetermined level, the switch causes the power supply to the compressor to revert to the mains supply 240.

Advantageously, the implementation shown in Figure 15 is achieved without needing to compromise the integrity of the conventional system, and so minimising the risk of voiding the warranty conditions of the conventional system by the inclusion of the power generation system.

It will appreciated that the various embodiments described above not only make use of heat that would otherwise be wasted, for example heat exhausted from a turbine, but that use of also made of renewable energy sources, such as solar power. This conversion into useful energy is effected extremely efficiently by way of the high COP ejector pump 1.

Claims

CLAIMS1. A multiple stage ejector pump for a fluid circuit, the ejector pump comprising a suction inlet and an outlet, the ejector pump further comprising a plurality of subassemblies, each sub-assembly comprising a motive fluid inlet, a nozzle and a mixing chamber, and the sub-assemblies connected in series so as to cumulatively increase fluid flow rate within the ejector pump, for each sub-assembly an inlet of the respective nozzle is in fluid communication with the motive fluid inlet, and an outlet of each respective nozzle is in fluid communication with the respective mixing chamber, and the ejector pump further comprising a diffuser from which fluid is output from the ejector pump, and the diffuser is in fluid communication with an outlet from the downstream most assembly.
2. An ejector pump as claimed in claim 1 in which the sub-assemblies are connected directly to one another in series.
3. An ejector pump as claimed in claim 1 or claim 2 in which the diffuser is the sole diffuser of the ejector pump, and no other diffuser is provided between sub-assemblies.
4. An ejector pump as claimed in any preceding claim in which the motive inlets and the suction inlets are arranged such that the force vectors of the fluid from those inlets are substantially aligned along a common axis.
5. An ejector pump as claimed in any preceding claim in which the diffuser comprises a feedback outlet arranged to allow a proportion of fluid passing through the pump to be fed back into the ejector pump. 2?
6. An ejector pump of any preceding claim which comprises at least two sub-assemblies.
7. An ejector pump as claimed in claim 6 which comprises three sub-assemblies
8. An ejector pump as claimed in any preceding claim in which each sub-assembly comprises at least two nozzles.
9. An ejector pump as claimed in claim 8 in which the nozzles in each sub-assembly are located at substantially the same longitudinal position in a respective common mixing chamber.
10. A fluid circuit comprising the ejector pump of any of claims 1 to 9.
11. A fluid circuit as claimed in claim 10 which comprises a heat exchanger arranged to cause transfer of heat to the fluid of the circuit from at least one of a solar energy source, a waste heat source and a latent heat source.
12. A fluid circuit as claimed in claim 10 or in claim 11 arranged to effect a heat pump cycle.
13. A fluid circuit as claimed in any of claims 10 to 12 arranged to effect power generation cycle.
14. A fluid circuit as claimed in any of claims 10 to 13 arranged to cause the fluid to remain in a vapour state around the circuit.
15. A fluid circuit as claimed in claim 14 in which the fluid is a refrigerant fluid.
16. A fluid circuit as claimed in claim 15 in which the fluid is Co2.1?. A fluid circuit as claimed in any of claims 10 to 16 which comprises a turbine arranged to be driven by the flow of fluid in the circuit.18. A fluid circuit as claimed in claim 1? which comprises a heat exchanger between an outlet of the ejector pump and the inlet to the turbine, the heat exchanger arranged to heat the fluid flowing towards the turbine inlet.19. A fluid circuit as claimed in claim 17 or claim 18, in which fluid exiting the turbine arranged to be input into an inlet of the ejector pump.20. A power generation and/or heat pump cycle comprising the ejector pump of any of claims 1 to 9.21. A cycle of claim 20 comprising a turbogenerator, and wherein heat exhausted by the turbogenerator is transferred to an inlet of the ejector pump.22. A cycle of claim 20 or claim 21 which includes a heat exchanger for transferring heat from a latent, solar or waste heat source to heat fluid to be used to drive the turbogenerator.23. A method of power generation and/or heat pumping comprising use of the ejector pump of any of claims 1 to 9.24. An ejector pump substantially as herein described, with reference to the accompanying drawings.25. A fluid circuit substantially as herein described, with reference to the accompanying drawings.26. A method of power generation and/or heat pumping substantially as herein described, with reference to the accompanying drawings.