WO2012105845A1

WO2012105845A1 - Apparatus and method for adaptive control of the working temperature of a cooling object, and the use of a reverse beta configured stirling cycle for the adjustment of the temperature of the cooling object

Info

Publication number: WO2012105845A1
Application number: PCT/NO2012/000013
Authority: WO
Inventors: Phil Teague
Original assignee: Latent As
Priority date: 2011-02-03
Filing date: 2012-01-31
Publication date: 2012-08-09
Also published as: NO20110194A1

Abstract

An apparatus is described, the apparatus comprising a beta-configured Stirling engine (S) located in a housing (2) arranged to be provided in a hot, enveloping environment (1), where a displacer piston (16) constitutes a moveable barrier between a compression chamber (7') and an expansion chamber (7''), and a fluid communication between the compression chamber (7') and the expansion chamber (7'') comprise successively a hot-side heat-exchanger (10), a regenerative heat-exchanger (9) and a cold-side heat-exchanger (8). A method for temperature regulation of a cooling object (5) arranged in a hot environment (1), is also described. Finally an application of a reversed adaptive beta-configured Stirling-cycle for regulation of the temperature on a cooling object (5) located in a hot environment (1) with a temperature exceeding the prescribed operating temperature of the cooling object (5), is described.

Description

APPARATUS AND METHOD FOR ADAPTIVE CONTROL OF THE WORKING TEM^¬ PERATURE OF A COOLING OBJECT, AND THE USE OF A REVERSE BETA CONFIGURED STIRLING CYCLE FOR THE ADJUSTMENT OF THE TEMPERATURE OF THE COOLING OBJECT

The present invention relates to an apparatus and a method for adaptive adjustment of the inter-piston phase of a reverse beta-configured Stirling cycle, and the application of a reverse, adaptive beta-configured Stirling cycle for the adjustment of the temperature of a cooling object provided in a hot environment with a temperature exceeding the stipulated operating temperature of the cooling object.

Current market technology for cooling systems used for maintaining low operating temperature for devices located within a hot environment, for example within downhole or borehole logging and drilling, is strongly dependent on three key principles: either insulation, ablative cooling or active cooling, or a combination of these. All such systems fail, faced with the problem of permanently maintaining a device, such as electronics, at a suitable operating temperature in a hot environment. In the case of insulation the operational lifetime of such a device is minimal, as insulation only acts to retard the influx of heat into the device from the surrounding ambient environment. In this respect the internal temperature of the device will increase until it reaches the ambient temperature as the insulation method is incapable of extracting thermal energy from the device which needs to be kept cool, but is only capable of slowing the rate of thermal energy entering into the device. Ablative cooling refers to a short-term cryogenic method, whereby a vessel (or a Dewar vessel ) containing pre-cooled fluids, such as liquefied petroleum gas, is dispensed at a controlled rate through a conduit thereby absorbing heat, as it expands, and hereby cool the device. Such a method may be regarded as short-term as the duration of the cooling effect is dependent upon the volume of the vessel, i.e. the cooling effect can only be in force as long as there is enough fluid available.

The active cooling method generally relies upon two principles: thermoelectric and refrigeration.

Thermoelectric systems generally use Peltier elements which are able to move thermal energy from the one side of their envelope to the opposite side, with application of an electric voltage, creating quite large differences in temperature from one side to the other. Such systems are most commonly found in PCs, for example, to assist in the cooling of the central processing unit (CPU) . The issue with Peltier elements is that their effective efficiency, i.e. the amount of energy consumed compared to the amount of energy moved between the hot and the cold surfaces, can fall to a very low level, for example an efficiency of less than 2%, when large differences in temperature are needed over the elements. In hot environments, such as exploration- and production- boreholes in oil and gas, the environmental temperatures might be over 200°C. Electronics generally have a maximum operating temperature of 70-80°C (for processing units), and even automotive electronics can only function at temperatures lower than 150°C. In such cases the required difference in temperatures, which a system has to be capable of maintaining to ensure that the temperature of the device is kept below 70°C, might be as high as 130°C. At such great differences in temperature the use of a Peltier-element for transportation of 10 watts of thermal energy away from a device by depositing said thermal energy into a hot environment of for example 175°C, at 2% efficiency, would consume 500 W in the process. In reality, such elements are usually rated for much lower levels of power consumption, such that the effective efficiency loss results in the system failing to maintain the cold end sufficiently cold.

In the example with borehole systems for exploration and oil- and gas-production, where devices such as instruments, mechanical and electronic elements need be maintained at a temperature much lower than the temperature of the surrounding environment, such a power consumption would be impractical, as most power conveyance systems (such as wireline cables) can only carry a maximum of 1000 W, for which the majority of the power is dissipated in the primary systems and not in supporting systems such as cooling.

The refrigeration method usually consists of one single or a series of linked compressor- and cooling element cycles best described as a standard domestic refrigerator. However, such systems do not function well when the hot-end radiator is already hot, as such systems rely on convection to remove excess heat from the cooling element. Additionally the difference in temperature required in order to maintain an

operating temperature for electronics in a hot environment, as depicted above, requires multiple stages of cooling devices, each with a different working fluid. In this respect, standard systems of the freon-type cannot demonstrate the operating temperature necessary for such applications. A further issue is that cooling systems require compressors and a multitude of moving parts, with the reduction in operational reliability and robustness that follows from this.

In recent years, attempts have been made to use free-piston Stirling-engines in hot environments, like exploration and production wells, with limited success. The systems rely upon active driving of the compression piston only. The displacer piston is connected only to a springing system for displacement and resonance. Such systems need to be tuned, so that the whole assembly reciprocates in resonance, whereby the displacer piston oscillates in a harmonic motion out of phase with the harmonic compression piston motion. The compression piston may be oscillated by means of a linear maneuver organ or a combination of a copper coil and a magnet, or by a mechanical arm connection to a rotating disk, as illustrated in the original Stirling-engine. In this respect such beta-cycle free-piston Stirling engines might be highly efficient as only one piston is being driven, with an actual reduction in mechanic and electric load as a result.

The phase relationship between the compression piston and the displacer piston is, however, a function of the resonant frequency of the system, which is a function of the masses of the pistons, the compression conditions and the pressure and temperature of the working fluid. As the temperature of the working fluid rises as a result of a hot external environment, the pressure of the working fluid will also change; the result is a change in the resonant frequency of the system which alters the phase relationship between the pistons. In practice the Carnot cycle's trapezium form decreases and diminishes as the phase angle of the two pistons decreases from the typical 60 degrees and down towards 0 degrees. In this respect, a free-piston Stirling engine becomes less and less efficient as the temperature and pressure of the working flu- id change, furthermore the cycle collapses and the phase relationship descends to a phase angle of zero degrees, which means that there is no bias between the system' s hot and cold sides. The free-piston Stirling engine requires active cool^¬ ing of the hot-side in one way or another.

With an application of the technology in a borehole used for exploration and production, the environment is very hot (> 100 °C) , and active cooling is not available as there is no cold reservoir available in the vicinity of the engine. Under such circumstances a free-piston Stirling engine will not function and will be incapable of transferring thermal energy from a device which needs to be maintained relatively cool, to a hot environment, as for example well fluids.

The invention has for its object to help or to reduce at least one of the disadvantages of prior art, or at least to present a useful alternative to prior art.

This object is obtained in characteristics stated in the following description and patent claims.

An apparatus comprising known and new technology combined in a new application with respect to adaptive control techniques, thermodynamics, harmonic physics and cooling is provided .

The object of the apparatus is to cool one or more objects located within a hot environment, where the objects must be maintained below a given temperature in order to work correctly, but where the ambient temperature is much higher than said temperature.

The description of the apparatus in this script shows a system which can change its function according to environmental conditions, to offer the best possible performance. The apparatus functions through a series of stages where thermal energy is removed from a device which, in a preferred embodiment, is an electronic component that require a low operating temperature, such as for example below 70°C, and that said thermal energy is deposited in a hot, enveloping envi^¬ ronment through a process of an adaptively controlled, high frequency, reversed beta Stirling cycle.

In a first aspect, the invention more specifically relates to an apparatus comprising a beta-configured Stirling engine provided in a housing arranged to be located in a hot, enveloping environment, where a displacer piston constitutes a displaceable barrier between a compression chamber and an expansion chamber, and a fluid communication between the compression chamber and the expansion chamber comprises successively a hot-side heat-exchanger, a regenerative heat- exchanger and a cold-side heat-exchanger, characterized in that

the expansion chamber is in thermal contact with a cool^¬ ing object, and that

to each of a compression piston and the displacer piston is provided an actuator system comprising

a springing system arranged to be capable of maintaining said piston steady in an initial position,

an electromagnet system arranged to be able to move said piston away from its initial position; as

the electromagnetic systems are connected to a control unit comprising means for monitoring temperature on the cooling object and for regulating amplitude and frequency for each of the compression piston and the displacer piston.

The springing system might be constituted of a spring clamped between the compression piston, respectively the displacer piston, and the housing. The springing system might be constituted like a magnet springing system.

For each of the compression piston and the displacer piston at least one positioning sensor might be connected. The posi^¬ tion sensor might be collected from the group consisting of an electronic accelerometer, a Hall-effect sensor and a linear variable differential transducer.

The control unit might be arranged to be able to add a continuous or discontinuous direct voltage with alternating polarity, to a connected compression piston coil, respectively a displacer piston coil.

In a second aspect, the invention relates more specifically to a method for regulation of the temperature on a cooling object provided in a hot environment, wherein the method comprises of the following steps:

to bring the cooling object into thermal contact with an expansion chamber in a beta-configured Stirling engine;

to regulate amplitude and frequency for each of a compression piston and a displacer piston based on gathering of temperature information from the cooling object and pressure- and temperature information from a working fluid; as

the compression piston, respectively the displacer piston, is moved between an initial position and an end position by a control unit adding a direct voltage with alternating polarity to electromagnetic systems connected to the compres^¬ sion piston, respectively the displacer piston, characterized in that the method comprises the further step:

the compression piston, respectively the displacer piston, is moved from an end position and back to an initial position by means of a springing system.

The direct voltage might be continuous or discontinuous. The compression piston, respectively the displacer piston, might be moved from an end position and back to an initial position by means of a springing system.

In a third aspect the invention relates more specifically to use of a reversed, beta-configured Stirling cycle arranged for adaptive, independent regulation of amplitude and frequency for each of the compression piston and a displacer piston, for regulation of the temperature on a cooling object provided in a hot environment with a temperature exceeding the cooling object's prescribed operating temperature.

In the following an example of a preferred embodiment, illustrated in the enclosed drawings, is described, where:

Figure 1 shows the apparatus generally illustrated in a hot environment with a device which is to be cooled, located heat-insulated in a housing;

Figure 2 shows a first step of cycle in the apparatus;

Figure 3 shows a second step of cycle in the apparatus;

Figure 4 shows a third step of cycle in the apparatus;

Figure 5 shows a fourth step of cycle in the apparatus; and

Figure 6 shows a fifth step of cycle in the apparatus.

In the figures (see particularly fig. 1) the numeral 1 indicates a hot environment as, for example, the well fluids within an exploration or production well for oil and gas, which is in thermal contact with a housing 2 containing a beta-configured Stirling engine S, and where there is provided a cooling object 5, which is in thermal contact with an expansion chamber 7'' in the Stirling engine S and which generally in all essentials is surrounded by an insulation cover 6. In a preferred embodiment, the insulation cover 6 is formed out of stiff foam (aerogel) or another material with outstanding heat insulation qualities.

A flow-dynamics chamber 7 is partly enclosed by the insulation cover 6 and is situated with a closed end portion 7a close by the cooling object 5 which is to be kept cooler than the environment 1. The cooling object 5 can be an electronic component requiring low operating temperature. The tempera^¬ ture of the cooling object 5 is monitored by a temperature sensor 22.

Inside the flow dynamics chamber 7 there is provided a cold- side heat-exchanger 8 and a hot-side heat-exchanger 10 with a regenerative heat-exchanger 9 provided in between. The cold- side heat-exchanger 8 is thermally connected to the flow- dynamics chamber 7 which again is thermally connected to the cooling object 5. The insulation cover 6 envelops the cold- side heat-exchanger 8 and the regenerative heat-exchanger 9.

The regenerative heat-exchanger 9 is in a preferred embodiment constituted from a polyamide material formed as a cylindrical coil construction. This can however also be formed out of any other material with a thermal capacity, and be provided in a concentric cylindrical construction.

The regenerative heat-exchanger 9 works like a thermal condenser. In the preferred embodiment it has a very high thermal capacity, very low thermal conductivity parallel to the fluid flow direction, very high thermal conductivity perpendicular to the fluid flow direction, minimal volume and shows low flow resistance on the working fluid.

The heat-exchangers 8, 9, 10 encircle a centre bore which contains an axial displaceable displacer piston 16 with a displacer piston rod 16a protruding up through an opening 7c in an end cover 7b opposite the base end 7a. The displacer piston rod 16a is close to an end portion 16b opposite the displacer piston 16 connected to a first springing system 20 anchored to the housing 2. A first magnet 18a is provided on the end portion 16b of the displacer piston rod 16a. A first positioning sensor 19 is connected to the displacer piston 16 for monitoring of the position of the displacer piston 16.

The displacer piston 16 constitutes a displaceable barrier in the flow-dynamics chamber 7, as said chamber 7 constitutes a compression chamber 7' and an expansion chamber 1' ' which is in fluid communication through the heat-exchangers 8, 9, 10.

A displacer piston coil 18b is arranged inside the housing 2 in an axial distance from the area of movement of the first magnet 18a. The displacer piston coil 18b and the first magnet 18a constitute a first electromagnet system 17.

The displacer piston 16 can by means of the power applied by the effect of the displacer piston coil 18b on the first mag^¬ net 18a, be moved out from an initial position. The displacer piston 16 is pulled towards the initial position of the first springing system 20.

A tubular compression piston 11 encircles a portion of the displacer piston rod 16a and extends by a first end portion 11a into the end cover opening 7c of the flow-dynamics chamber 7. The compression piston 11 is axial displaceable in re^¬ lation to the displacer piston 16 and the end cover 7b. In a second end portion lib, the compression piston 11 is connected to a second springing system 15 which is anchored in the housing 2. A second magnet 14a is arranged at the mid portion 11c of the compression piston 11. A second positioning sensor 12 is connected to the compression piston 11 for monitoring of the position of the compression piston 11. A compression piston coil 14b is arranged inside the housing 2 in an axial distance from the area of movement of the second magnet 14a. The compression piston coil 14b and the second magnet 14a constitute a second magnet system 13.

The compression piston 11 can by means of the power applied by the effect of the compression piston coil 14b on the second magnet 14a, be moved out from an initial position. The compression piston 11 is pulled towards the initial position by the second springing system 15.

The void of the housing 2 is filled with a pressurized working fluid 3, which in a preferred embodiment is helium, although it could be any compressible fluid. A portion 3a of the working fluid 3 is housed by the flow-dynamics chamber 7.

A pressure and temperature sensor 4 arranged for monitoring of the pressure and temperature of the working fluid 3, is provided inside the housing 2.

Both coils 14b, 18b and the sensors 4, 12, 19, 22 are connected to a control unit 21 which is capable of applying a voltage to each coil 14b, 18b, independently, to control displacement, frequency and the phase relationship in the oscillation of the two coils 14b, 18b based on signals from the sensors 4, 12, 19, 22.

Fig. 2 illustrates a first step of cycle where a direct voltage is applied to the compression piston coil 14b so that the compression piston magnet 14a is moved towards and the compression piston 11 is moved completely into the end cover opening 7c of the flow-dynamics chamber 7, such that the portion 3a of the working fluid 3 housed by the compression chamber 7', is compressed and thereby heated by work put into the fluid 3a. Fig. 3 illustrates a second step of cycle where a direct vol^¬ tage, reversed the voltage on the compression piston coil 18b, is applied to the displacer piston coil 14b. The dis- placer piston magnet 18a and the displacer piston 16 are thereby moved towards the end cover 7b such that the heated working fluid 3a is forced through the hot-side heat- exchanger 10, through the regenerative heat-exchanger 9 and through the cold-side heat-exchanger 8 in order to fill the void made available by the displaced displacer piston 16 in the expansion chamber 7''. As the hot working fluid 3a first passes through the hot-side heat-exchanger 10, a major portion of the heat energy is transferred from the working fluid 3a to the hot-side heat-exchanger 10 compared to the cold- side heat-exchanger 8 as the regenerative heat-exchanger 9 absorbs some of the thermal energy in the working fluid 3a. As the hot-side heat-exchanger 10 is thermally connected to the housing 2, heat is transferred from the working fluid 3a to the environment 1 through the housing 2.

Fig. 4 illustrates that in a third step of cycle, a reverse direct voltage is applied to the compression piston coil 14b, such that the compression piston magnet 14a and the compression piston 11 are pulled back such that the working fluid 3a is expanded inside the flow-dynamics chamber 7 and is thereby cooled by removing work from the fluid (reverse work) .

Fig. 5 illustrates that in the fourth step of cycle, a reverse direct voltage is applied to the displacer piston coil 18b, such that the displacer piston magnet 18a and the displacer piston 16 is moved completely into the flow-dynamics chamber 7 such that the cooled working fluid 3a is forced through the cold-side heat-exchanger 8, through the regenerative heat-exchanger 9 and through the hot-side heat-exchanger 10 to fill the void which is made available by the displaced displacer piston 16. Thermal energy is transferred from the cooling object 5 through the wall of the flow-dynamics cham^¬ ber 7 and into the heat-exchanger 8 in a larger part than to the hot-side heat-exchanger 10 as the regenerative heat- exchanger 9 releases stored thermal energy to the through- flowing working fluid 3a. Influx of heat energy from the hot environment 1 to the cooling object 5 is retarded through the use of thermal insulation cover 6.

Fig. 6 illustrates that in a fifth step of cycle, a voltage is applied to the compression piston coil 14b so that the compression piston magnet 14a moves the compression piston 11 completely into the flow-dynamics chamber 7 so that the working fluid 3a is compressed within the flow-dynamics chamber 7 and thereby heated by work put into the fluid.

The cycle steps 1-5 in accordance with the figures 2-6 are thereafter repeated.

In the process thermal energy is extracted from the cooling object 5 and transferred to the environment 1. In this regard the thermal energy is not transferred by the working fluid 3a, but the difference in thermal energy which is maintained between the hot-side heat-exchanger 10 and the cold-side heat-exchanger 8, creates and maintains a flow of thermal energy between the two heat-exchangers 10, 8 along the shell of the flow-dynamics chamber 7.

In the process, thermal energy is extracted from the cooling object 5 and forced into the environment 1. The pistons 11, 16 oscillate with a phase difference of, in a preferred embodiment, 90 degrees (or n/2 radians) at a frequency of more than 20Hz. In the preferred embodiment, one entire cycle is completed within 15 milliseconds. The higher the oscillating frequency, the higher transmission of thermal energy is achieved between the cold-side heat-exchanger 8 and the hot- side heat-exchanger 10. The same can be determined for an increase in piston displacement, as a larger displacement of the compression piston 11 gives a larger compression effect and thereby also increases the heating of the working fluid 3a.

The absolute positions of the pistons 11, 16 are monitored by sensors 12, 19. In the preferred embodiment, these sensors are electronic accelerometers which provide the largest output voltage at maximum accelerations, i.e. when the pistons 11, 16 have reached the maximum displacement position of their oscillation. However, any type of sensor which is capable of, directly or indirectly, resolving the position of the pistons, may be used, like for example a Hall-effect sensor with a magnet or a linear variable differential transducer.

The control unit 21 outputs oscillating waveforms which in the preferred embodiment are sinusoidal, but may be any re- peatable wave form, including time sections without any output. The phase relationship, i.e. the zero-point offset of each wave form, can be controlled by the electronic control unit 21. Sensory data from the displacement sensors 12, 19, the fluid pressure- and temperature sensor 4 and the temperature sensor 22 in the cooling object 5 are fed into the electronic control unit 21. A software algorithm put into the electronic control unit 21 processes the information from these various sensors in order to determine the best possible amplitude of, and the best possible phase relationship between, the pistons 11, 16 in order to maintain a constant, low operating temperature in the cooling object 5. This way the system is adaptive and capable of independently controlling the amplitude of each piston, in addition to the phase relationship between each oscillation cycle of the pistons 11, 16.

When a voltage is applied to a coil 14b, 18b, a magnetic field is created by the movement of electrons through the coil. This exerts a force onto the magnet 14a, 18a causing displacement of the respective piston 11, 16. When the piston 11, 16 is displaced, it puts work into the respective springing system 15, 20 which in the preferred embodiment, is a mechanical spring, although it could be additional magnets placed in opposing directions, thereby creating a magnetic spring. As the piston 11, 16 reaches its end position, the respective springing system 15, 20 is charged with potential energy. At this stage the control unit 21 de-energizes the coil 14b, 18b, and the springing system 15, 20 releases its work and its potential energy by returning the piston 11, 16 back to initial position. Thereafter reverse voltage is applied to the coil 14b, 18b. This exerts a force onto the magnet 14a, 18a causing displacement in the opposite direction, of the respective piston 11, 16. As the piston 11, 16 reaches its opposite end position, the springing system 15, 20 is recharged with new potential energy. At this stage the control unit 21 de-energizes the coil 14b, 18b, and the respective springing system 15, 20 releases its work and its potential energy by returning the piston 11, 16 to its initial position, which describes one oscillation of a piston. By applying electric voltage to the coils 14b, 18b only when they are to be moved from an initial position to an end position, an energy saving is obtained as the coils 14b, 18b do not consume electrical power when they are de-energized, which contributes to approximately 50% of the entire cycle. As a result, the efficiency of the system is doubled as the power consumption is halved. As the temperature of the working fluids 3a rises and the pressure inside the closed housing 2 in- creases as a result thereof, the control unit 21 is capable of adjusting the relative timing of the two pistons 11, 16 to ensure the best possible phase relationship to maximize the parameters of the Carnot cycle.

Current market technology, in the form of traditional engines or free-piston Stirling engines, are incapable of maintaining high temperature differences between the hot and the cold sides of the system, when the environmental temperature (or the hot-side temperature) is considerably higher than normal room temperature. A common solution is to place a large, air- cooled heat-exchanger or fins on the hot-side of the system, and to either rely on air-blowers (fans) or convection from the large surface area of the fins, in order to remove the excess thermal energy from the system. Another solution is to lead cold fluid (i.e. water) over or around the hot-side of the system to remove excess energy. With either system, the engine does not have, if the environmental temperature of the hot-side gets too high, the capacity to "pump" excess energy into the hot environment, and the result is that the cold- side is gets warmer and slowly trends towards the temperature of the hot-side, thereby reducing the difference in temperatures (or delta) of the system as the hot-side becomes hotter .

When it comes to free-piston Stirling engines, the phase relationship between the compression piston 11 and the dis- placer piston 16, is a function of the resonant frequency of the system which is a function of the masses of the pistons 11, 16, the compression ratios, the pressure of the working fluid 3a and the temperature of the working fluid 3a. As the temperature of the working fluid 3a rises as a result of a hot external environment 1, the pressure of the working fluid 3a will also change. The result is a change in the resonant frequency of the system, which alters the phase relationship between the pistons 11, 16. In practice the trapezium form of the Carnot cycle decreases and diminishes, as the phase angle of the two pistons 11, 16 decreases from the typical 60 degrees and down to 0 degrees. In this regard a free-piston Stirling engine becomes less and less efficient as the working fluid changes temperature and pressure; which additionally collapses the cycle and the phase relationship descends to a phase angle of zero degrees, meaning that there is no difference between the hot and cold sides of the system. The free-piston Stirling engine requires some form of active cooling of the hot-side.

By application of the technology within a borehole used for exploration and production, the environment 1 is very hot (> 100°C) , and active cooling is not available as there is no cold reservoir available in the vicinity of the engine. Under this circumstance, a free-piston Stirling engine will not function and will be incapable of transferring thermal energy from a cooling object 5 in need of being maintained relatively cool, to a hot environment 1, such as well fluids.

The apparatus described in this script demonstrates complete control over the compression piston 11 and the position, amplitude, frequency and phase relationship of the displacer piston 16, as it is suitable for adaptive control by electronics and software which can monitor the temperature of the device to be cooled, and thereafter adjust the amplitude and frequency of the system and thereby adjust the power consumption to the cooling requirement. In addition it can monitor the pressure and temperature of the working fluid 3, 3a and adjust the wave-forms of the oscillations and the phase angles in order to give the best thermodynamic efficiency based upon the conditions at that time. A traditional Stirling en- gine with its fixed phase angle and amplitude, and a free- piston Stirling engine with its control over one piston only, is not capable of doing any of this. As a result, the description of the apparatus in this script demonstrates that the system which adaptively can change its function in accordance with environmental conditions, gives the best possible efficiency .

Claims

C l a i m s

Apparatus comprising a beta-configured Stirling engine (S) provided in a housing (2) arranged to be located in a hot, enveloping environment (1) where a displacer piston (16) constitutes a displaceable barrier between a compression chamber (7') and an expansion chamber {!''), and a fluid communication between the compression chamber (7') and the expansion chamber (7'') comprises successively a hot-side heat-exchanger (10), a regenerative heat-exchanger (9) and a cold-side heat- exchanger (8), c h a r a c t e r i z e d i n that the expansion chamber (7'') is in thermal contact with a cooling object (5) , and that

to each of the compression piston (11) and the displacer piston (16) there is assigned an actuator system comprising

a springing system (15,20) arranged to be capable of maintaining said piston (11,16) steady in an initial position,

an electromagnetic system (13,17) arranged to be able to move said piston (11,16) away from its initial position; as

the electromagnetic systems (13,17) are connected to a control unit (21) comprising means (22) for monitoring temperature on the cooling object (5) and for regulating the amplitude and frequency for each of the compression piston (11) and the displacer piston (16).

Apparatus in accordance with claim 1, c h a r a c t e r i z e d i n that the springing system (15, 20) is constituted of a spring which is clamped between the compression piston (11), respectively the displacer piston (16), and the housing

(2).

3. Apparatus in accordance with claim 1, c h a r a c t e r i z e d i n that the springing system (15, 20) is constituted like a magnet springing system.

4. Apparatus in accordance with claim 1, c h a r a c t e r i z e d i n that there to each of the compression piston (11) and the displacer piston (16) is con nected at least one position sensor (12, 19) .

5. Apparatus in accordance with claim 4, c h a r a c t e r i z e d i n that the position sensor (12, 19) is collected from the group consisting of an electronic accelerometer, a Hall-effect sensor and a linear variable differential transducer.

6. Apparatus in accordance with claim 1, c h a r a c t e r i z e d i n that the control unit (21) is arranged to be able to apply a continuous or discontinu ous direct voltage with alternating polarity, to a connected compression piston coil (14b), respectively a displacer piston coil (18b).

7. Method for regulating the temperature on a cooling ob ject (5) provided in a hot environment (1), wherein the method comprises the following steps:

to bring the cooling object (5) into thermal con tact with an expansion chamber (7'') in a beta- configured Stirling engine (S);

to regulate amplitude and frequency for each of compression piston (11) and a displacer piston (16) based on gathering of information about temperature from the cooling object (5) and information about pressure and temperature from a working fluid (3); as the compression piston (11), respectively the displacer piston (16), is moved from an initial posi- tion to an end position by a control unit (21) adding a direct voltage with alternating polarity to electromagnet systems (13,17) connected to the compression piston (11), respectively the displacer piston, c h a r a c t e r i z e d i n that the method comprises the further step:

the compression piston (11), respectively the displacer piston (16), is moved from an end position and back to an initial position by means of a springing system (15, 20).

Method in accordance with claim 7, c h a r a c t e r i z e d i n that the direct voltage is continuous or discontinuous.

Use of a reversed, beta-configured Stirling cycle arranged for adaptive, independent regulation of amplitude and frequency for each of the compression piston (11) and a displacer piston (16), for regulation of the temperature on a cooling object (5) provided in a hot environment (1) with a temperature exceeding the cooling object's (5) prescribed operating temperature