GB2175050A - Apparatus for converting heat energy into mechanical and/or electrical energy - Google Patents

Abstract

Apparatus (2) for converting heat energy into mechanical and/or electrical energy, which apparatus (2) comprises a fluid operated motor (4) having a high pressure input side (6) and a low pressure output side (8), oscillator means (10) which is connected to the high pressure side of the motor and which is for causing a working fluid in the oscillator means to oscillate in pressure, and valve means (36) for reintroducing working fluid from the low pressure side of the motor back into the oscillator means at periods when the oscillating pressure of the working fluid in the oscillator means is less than the pressure at the low pressure output side of the motor. The fluid in the oscillator means receives heat in heat exchangers (14, 16, 18, 20). <IMAGE>

Description

SPECIFICATION Apparatus for converting heat energy into mechanical and/or electrical energy This invention relates to apparatus for converting heat energy into mechanical and/or electrical energy.

Heat energy can be converted directly into electrical energy by various known forms of cells or thermopiles, but in general the efficiency of such devices is very low and typically of the order of 5%. In an attempt to achieve higher efficiencies, it is usual to use indirect conversion processes which operate on more favourable cycles. For example, heat energy can be employed to raise the temperature of water until steam is formed, the steam then being used in a steam engine such as a turbine to produce mechanical shaft work. This mechanical work can be converted to electrical energy, for example by means of a generator or an alternator, or the mechanical energy can be used directly if so required.Although relatively high efficiencies can be obtained in this way, using indirect conversion processes, there is the disadvantage that the input heat energy must be at a relatively high temperature in order that the temperature of the water may be raised sufficiently to form steam. In general, the lower the temperature of the input heat energy, the more difficult becomes the conversion process, and of course if the temperature of the input heat energy is below the boiling point of water, an indirect conversion process as described above becomes impossible. Although the problem can at times be solved by using a different fluid besides water, such solutions are extremely expensive and in general not practical.

In my United Kingdom Patent No.1538884, I have described and claimed apparatus for converting heat energy into mechanical and/or electrical energy. This apparatus as described in Patent No.1538884 enables the heat energy to be converted into mechanical and/or electrical energy in a relatively efficient way.

It is an aim of the present invention to provide apparatus for converting heat energy into mechanical and/or electrical energy, which apparatus operates on the general principles taught in Patent No.1538884 but which apparatus can be more simply constructed than the apparatus described in Patent No.1538884.

More specifically, the apparatus described in Patent No. 1 538884 requires the use of means such for example as a fly wheel for storing kinetic energy whereas the present invention uses the kinetic energy stored in an oscillating working fluid as an essential constituent of the apparatus. Furthermore, in the apparatus described in Patent No.1538884 the working fluid is only heated in a heat exchanger and it is not also heated whilst it is in first and second chambers. The apparatus of the present invention aims to improve on this by enabling all the working fluid to be heated so that a greater pressure rise can be obtained than in the apparatus described in Patent No.1538884, other conditions being equal.

Still further, the apparatus of Patent No.1538884 is such that the pressure difference across the machine/motor varies throughout the cycle of oscillation and it is a further aim of the present invention to enable the apparatus of the present invention to use a motor in which the pressure difference across the motor is substantially constant.

Accordingly, this invention provides apparatus for converting heat energy into mechanical and/or electrical energy, which apparatus comprises a fluid operated motor having a high pressure input side and a low pressure output side, oscillator means which is connected to the high pressure side of the motor and which is for causing a working fluid in the oscillator means to oscillate in pressure, and valve means for reintroducing working fluid from the low pressure side of the motor back into the oscillator means at periods when the oscillating pressure of the working fluid in the oscillator means is less than the pressure at the low pressure output side of the motor; The apparatus of the present invention will normally operate on a closed circuit in a push/pull mode. The valve means will be effective to operate in synchronism with the pressure oscillations in the working fluid.The pressure oscillations will preferably be resonant oscillations.

The oscillator means may comprise an electro dynamic or mechanical exciter for providing and maintaining the pressure oscillation of the working fluid.

The working fluid is preferably a liquid. It is to be appreciated however that the working fluid may be a gas or a vapour. Mixtures of liquids, gases and vapours may also be employed. When the working fluid is a liquid, it is preferably oil but other liquids such as water or refrigerants such as dichlorodifluoromethane may be employed.

The valve means may be operated by a variable speed motor, or from the main output shaft of the fluid operated motor.

The valve means is preferably a rotary valve, in which case the rotary valve is advantageously operated by a variable speed motor in the form of a variable speed d.c. motor or a synchronous a.c. motor, or from the main output shaft of the fluid operated motor.

The oscillator means will be normally constructed to include a heat exchange arrangement whereby heat energy can be supplied to the apparatus to heat the working fluid and to cause a required pressure rise in the working fluid.

The heat exchange arrangement may comprise pipework receiving heated fluid, for example heated water.

The heated fluid may be provided from a heat pump operating from a heat sink such for example as the atmosphere, a sea, the ground, or any large mass which has been heated by the sun or any other source of heat.

It is a well known characteristic of the heat pump that the amount of heat energy that can be extracted is greater than the energy that is required to be supplied to the shaft of the heat pump, by a ratio known as the coefficient of performance of the heat pump. This ratio is always greater than one and can be as high as ten, in a suitably designed system.

The heat energy is available from the heat pump at a temperature above that of the heat sink from which the energy has to come, and it is this heat energy which is supplied to the heat exchange arrangement.

An embodiment of the invention will now be described solely by way of example and reference to the accompanying drawings in which: Figure 1 shows apparatus for converting heat energy into mechanical and/or electrical energy; and Figure 2 illustrates a working liquid pressure cycle.

Referring now to Fig. 1, there is shown schematically apparatus 2 for converting heat energy into mechanical and/or electrical energy. The apparatus 2 comprises a fluid operated motor in the form of a hydraulic motor 4. The hydraulic motor 4 has a high pressure input side 6 and a low pressure output side 8.

The apparatus 2 further comprises oscillator means 10 which is connected via conduit 12 to the high pressure side 6 of the hydraulic motor 4. The oscillator means 10 comprises four heat exchange sections 14,16,18,20 and an electro dynamic exciter 22. The heat exchange sections 14,16,18,20 will include heat exchange coils, and oil inside a closed circuit including the heat exchange sections 14,16,18,20 will be oscillating at oscillating pressures.

The electro dynamic exciter 22 is provided with an oscillating piston 23. The electro dynamic exciter 22 will be effective to maintain the pressure oscillations and the pressure will oscillate as shown in Fig. 2. In Fig. 2, there is shown a pressure wave form 24 together with a high pressure line 26 and a low pressure line 28. The pressure wave form 24 goes below the low pressure line 28 over the shaded area 30. When the oil pressure at end A of the heat exchange sections 14,16,18,20 is equivalent to the low pressure shown in the shaded area 30, then oil from the low pressure side 8 of the hydraulic motor 4 can be introduced into the high pressure input side 6 of the apparatus 2 because the low pressure output side 8 will effectively be at the pres sure indicated by the low pressure line 28 which will effectively be higher than the pressure representated by the shaded area 30.

The hydraulic fluid in the form of the oil is reintroduced into the circuit of the apparatus 2 on the high pressure input side 6 of the hydraulic motor 4 via conduits 32,34. It will be seen that the conduit 34 communicates with the heat exchange sections 14,18 as shown.

Since the oil can only be introduced from the low pressure output side 8 of the hydraulic motor 4 over limited periods in each operating cycle of the apparatus 2 (i.e. when the oil pressure corresponds to the shaded area 30 shown in Fig. 2) it will be apparent that valve means is required for reintroducing the working fluid in the form of the oil from the low pressure output side 8 of the hydraulic motor 4 back into the oscillator means 10 at the appropriate periods when the oscillating pressure of the oil in the oscillator means 10 is less than the pressure at the low pressure output side 8 of the hydraulic motor 4. The valve means illustrated in Fig. 1 is a rotary valve 36 which is driven by a motor 38 via line 40. The motor 38 is a variable speed d.c.

motor or a synchronous a.c. motor, or alternatively the valve could be driven by the main mechanical output shaft 54.

The oscillator means 10 requires heat energy to heat the oil in the heat exchange sections 14,16,18,20. The flow of this medium is indicated by the arrowed line 42. The heating medium is advantageously water but it can be any other heating medium. The water is advantageously heated from a heat pump operating from any sink of heat energy such for example as the atmosphere, a sea, the ground, or any large mass which has been heated by the sun or any other source of heat.

A conduit 44 connects the hydraulic motor 4 to an accumulator 46, the accumulator 46 being required to maintain constant low pressure at the low pressure output side 8 of the hydraulic motor 4.

Fig. 1 shows also a pump 48, a motor 50 for the pump 48 and an oil reservoir 52. The pump 48, the motor 50 and the oil reservoir 52 are required to replenish drain flow from the hydraulic motor 4.

In order to avoid loss of heat from the oscillator means 10, the oscillator means 10 is thermally isolated with appropriate cladding material (not shown).

The hydraulic motor 4 is provided with a mechanical output shaft 54 as shown. This shaft 54 can be used to provide mechanical work directly or it can be used to rotate an electrical generator for the purpose of generating electricity.

The apparatus 2 operates such that all the oil in the oscillator means 10 is heated and this is effective to give a good pressure rise and possibly better than the pressure rise described in Patent No.1538884. The oscillation of energy is between the pressure energy and kinetic energy of oil flow in the coils of the heat exchange sections 14,16,18,20. This oscillation of energy is such that a flywheel is not essential to the design of the apparatus 2 although, if desired, a flywheel may be employed. The pressure difference across the hydraulic motor 4 is substantially constant.

It will be appreciated that during use of the apparatus 2, the rotary valve 36 will open at just the required period in the operating cycle of the apparatus 2 (this period corresponding to the shaded area 30 shown in Fig. 2) to allow oil to be reintroduced along line 34 back into the otherwise closed circuit including the oscillator means 10. In effect, a pulse of oil will flow from the low pressure output side 8 of the hydraulic motor 4 into the high pressure circuit as represented by the high pressure input side 6 of the hydraulic motor 4.

However, because the closed circuit will be operating in a push/pull arrangement, when end A of the circuit goes to a low pressure, the end B of the circuit will go to a higher pressure and thus the average pressure on the high pressure side of the apparatus 2 will be maintained at the required level. This means that oil does not have to be pumped from low pressure to high pressure and it will instead just flow each time the pressure oscillations at the high pressure side of the circuit reach the required pressure minimum as indicated by the shaded area 30 in Fig. 2. The electro dynamic or other type of exciter 22 employed should be effective to drive the resonant hydraulic circuit which has a relatively high "Q", where "Q" represents the ratio of oscillating energy to input energy.The exciter 22 provides an oscillating pressure input to replace losses in the resonant circuit.

The resonant oscillation of oil in the heat exchanger coils in the heat exchange sections 14,16,18,20 are effected to improve heat transfer between the heat source and the oil.

Oil will be oscillating backwards and forwards in the coils, picking up heat on each cycle.

The peak flows will be much higher than the steady flow through the hydraulic motor 4 so that, even at low motor speeds, the heat transfer can be effective, maintaining the high pressure and available torque. Even if the efficiency of the engine part of the system is comparatively low, and will only provide part of the input power required by-the heat pump, the results will still be valuable.

For example, if the heat pump has a coefficient of performance equal to three (a present typical value) and part of the heat output is reconverted back into mechanical energy in the engine with an efficiency of, for example, 20%, then the effective coefficient of performance would be increased considerably. Thus, suppose the heat pump requires one kW input to give three kW of heat output, then, if the engine produces 0.6 kW of mechanical energy, which is used to help drive the heat pump, the net heat output would be 2.4 kW and the net mechanical input will be 0.4 kW, giving an overall coefficient of performance of 2.4/0.4=6.0. Thus the technique of feeding back some of the heat, converted into mechanical energy, into the heat pump is valuable even if there is no net output.

It is to be appreciated that the embodiment of the invention described above has been given by way of example only and that modifications may be effected. Thus, for example, a different type of valve to the rotary valve 36 may be employed. Similarly, a different type of oscillator means 10 may be employed. The rotary valve 36 could be designed to supply oil in pulses to both ends of the resonant oil circuit, i.e. ends A and B in Fig. 1, since both of these ends will have periods of low pressure.

Claims (7)

1. Apparatus for converting heat energy into mechanical and/or electrical energy, which apparatus comprises a fluid operated motor having a high pressure input side and a low pressure output side, oscillator means which is connected to the high pressure side of the motor and which is for causing a working fluid in the oscillator means to oscillate in pressure, and valve means for reintroducing working fluid from the low pressure side of the motor back into the oscillator means at periods when the oscillating pressure of the working fluid in the oscillator means is less than the pressure at the low pressure output side of the motor.

2. Apparatus according to claim 1 in which the oscillator means comprises an electro dynamic or mechanical exciter for providing and maintaining the pressure oscillation of the working fluid.

3. Apparatus according to claim 1 or claim 2 in which the valve means is operated by a variable speed motor, or from the main output shaft of the fluid operated motor.

4. Apparatus according to any one of the preceding claims in which the valve means is a rotary valve.

5. Apparatus according to any one of the preceding claims in which the oscillator means is constructed to include a heat exchange arrangement whereby heat energy can be supplied to the apparatus to heat the working fluid and to cause a required pressure rise in the working fluid.

6. Apparatus according to claim 5 in which the heat exchange arrangement comprises pipe work receiving heated fluid.

7. Apparatus for converting heat energy into mechanical and/or electrical energy, substantially as herein described with reference to the accompanying drawings.