Optimization of thermoacoustic apparatus based on operating condition and selected user input

The present disclosure relates to thermoacoustic devices, and more specifically to electrical control systems that optimize the operation of thermoacoustic devices such as thermoacoustic refrigerators or thermoacoustic heat engines.

The pulse tube refrigerator is typical of a traveling wave thermoacoustic refrigerator. In such devices, acoustic waves travel through the gas. The pressure and velocity vibrations of the gas are approximately in phase in some area of the device. Therefore, these devices are commonly referred to as traveling wave devices.

Sound sources, such as electromechanical transducers with movable pistons, generate sound energy that vibrates within a sealed containment device that contains compressed gas. Acoustic energy is a "hot" heat exchanger, regenerative heat exchanger or "regenerator" that is commonly connected to a heat reservoir at ambient temperature via a first heat exchanger, such as a heat exchange fluid. And, through another heat exchanger, such as a heat exchange fluid, passes through a "cold" heat exchanger connected to a heat load cooled by the refrigerating machine. Usually, the low temperature heat exchanger is followed by another tube called a "pulse tube", followed by the last ambient temperature heat exchanger, the "ambient" heat exchanger, and the "ambient" heat exchange. The vessel isolates the low temperature heat exchanger, thereby helping to reduce the parasitic heat load on the chiller. "High temperature" heat exchangers and "ambient" heat exchangers are often at the same temperature. After the "ambient" heat exchanger is an orifice combined with an acoustic load, often an inertia and compliance that dissipates the sound energy. As used herein, "heat exchanger (heat)" "Exchange)" is considered to mean a device that exchanges heat between the gas inside a thermoacoustic device and an outer fluid such as a stream of air.

In the steady state, a temperature gradient is established in the regenerator in the direction from the high temperature heat exchanger to the low temperature heat exchanger (when considered as a vector, the gradient is in the opposite direction). Ideally, heat is transferred almost isothermally between the gas and the heat storage material (often a porous metal or ceramic material or mesh). Due to the traveling wave acoustic phase matching, the gas in the regenerator undergoes almost a Stirling cycle. Thus, for the acoustic energy consumed, maximum heat can be transferred from the cold heat exchanger to the hot heat exchanger.

In loop-type traveling wave thermoacoustic chiller devices of the type known in the art, the acoustic load is the back of the electromechanical converter, with some of the acoustic energy that would normally be dissipated within the load. It is replaced by an acoustic section that delivers to, thereby reducing the input power required for a given cooling power and thus increasing the efficiency of the device. In another configuration, "excess" acoustic power is delivered to the back of the electromechanical transducer of the second thermoacoustic refrigerator, and its load is "excessive" to the back of the first electromechanical driver. It is similarly replaced by an acoustic section that delivers acoustic power in a closed loop. Similarly, three or more thermoacoustic chiller units can be connected from output to input within a closed loop. In another device known in the art, "excess" acoustic power is delivered to the front of the electromechanical transducer.

Similarly, a traveling wave thermoacoustic heat engine is a device that converts heat into work. In this device, heat is applied in a "hot" heat exchanger that is kept at a high temperature. The "cold" heat exchanger and the "ambient" heat exchanger are maintained at ambient or cold temperature. The vibrating sound energy in the containment device is converted into electrical energy by a power transducer, such as an electromagnetic transducer.

Temperatures in thermoacoustic coolers and heat engines are rarely constant, but are functions of ambient conditions, thermal availability, user settings, and so on. When operating at a given power and frequency, the efficiency of thermoacoustic chillers fluctuates with temperature, high temperature, low temperature, and ambient heat exchanger temperature. Similarly, when operating at a given power and under a given load, the efficiency of a thermoacoustic heat engine fluctuates with the temperature of the heat exchanger. This effect is particularly significant in the case of loop refrigerators or engines. The reason is that these systems are resonant systems, where the resonant frequency affects the acoustic gain inside the regenerator, the load in the case of an engine, the temperature of the ambient environment in which the device operates, and some heat exchangers. This is because it partially depends on the operating temperature such as the temperature of. As the temperature changes, the resonant frequency changes and therefore the optimum operating frequency. For pulse tube chillers and similar devices, as the temperature changes, the phase alignment of the acoustic power within the region of the regenerator changes, presumably reducing the effectiveness of the heat storage, thereby reducing the efficiency of the device. Therefore, there is a need in the art for devices and methods that control the operational aspects of thermoacoustic devices so as to optimize their efficiency as a function of operating conditions such as temperature, humidity and the like.

<p> Accordingly, the present disclosure provides electrical control of thermoacoustic refrigerator frequency and / or input power to optimize its efficiency as a function of operating temperature, ambient temperature, humidity, and selected user input. And methods. The present disclosure also covers systems and methods that provide electrical control of the load impedance of a thermoacoustic heat engine to optimize its efficiency as a function of operating temperature, ambient temperature, humidity, and selected user input. And.</p>

<p> The thermoacoustic refrigerator includes a nearly hollow, sealed body containing working gas. A heat storage device, a first heat exchanger, and a second heat exchanger are arranged in the main body. Sound energy from the electromechanical driver is sent into the body. Each heat exchanger measures the temperature of the heat exchange fluid, if present, in close proximity to the heat exchanger inside the body and / or outside the body and / or during the operation of the thermoacoustic device. A temperature sensor may be provided. An ambient temperature sensor may also be provided to measure the temperature within the ambient area of the device where heat is dissipated. An additional temperature sensor may be provided to measure the temperature of the space to be cooled. Humidity sensors may also be provided to measure relative or absolute humidity in the ambient area where heat is excluded and / or in the space to be cooled. The controller receives data from various sensors, which are usually measured at multiple times, and provides control signals based on these signals and user input. The control signal is provided to the variable frequency driver, which drives the electromechanical driver according to the control signal. Thus, the operation of the thermoacoustic device is at least partially controlled as a function of heat exchanger temperature, ambient temperature, and ambient humidity. The operation of the thermoacoustic device can then be optimized during use (eg, with minimal drive power requirements).</p><p> Further, the acoustic power in the main body may be converted into electrical energy, and the state of this conversion may also be factored into a control signal. Further, the transducers for measuring the acoustic pressure and the gas flow velocity may be arranged inside the main body, and the outputs of these sensors may be factorized into control signals. In some embodiments, the past state of the system may be incorporated into the control algorithm. For example, whether a temperature signal increases or decreases may be factored into a control signal as an additional input.</p><p> In some embodiments, the controller may be a memory containing a look-up table, in which independent variables such as ambient temperature and humidity and user-defined operating parameters such as cold setting points and other operating parameters are present. , Frequency and drive current are matched, thereby determining the control signal from the look-up table. In other embodiments, dependent variables such as heat exchanger temperature, internal pressure, and internal gas flow rate, and / or past states of any independent or dependent variable are also looked up to determine the control signal. It may be referenced in the table. In still other embodiments, logic or digital or analog circuit elements may be used to determine operating parameters, including drive frequency and power. This logic may include the ability to switch between several look-up tables with different combinations of input variables depending on the current device state and past device state.</p><p> In embodiments with multiple acoustic transducers, the controller may determine independent drive power and electrical phase for each transducer.</p><p> The operation of the thermoacoustic heat engine is essentially the one described above, in the absence of an electromechanical driver. Rather, an acoustic energy converter is provided within the body. The impedance of the load connected to the sound energy converter partially controls the operating state of the thermoacoustic heat engine. The control signal (at least partially determined from the various operating temperatures) determines the impedance of the load, thereby controlling the efficiency of operation of the thermoacoustic heat engine.</p><p> The above is a summary of some of the unique aspects, features and advantages of the present disclosure. However, this summary is not exhaustive. As such, these other aspects, features, and advantages of the present disclosure will become more apparent in the light of the claims provided herein, from the detailed description and accompanying drawings below. There will be.</p>

<figref num="1">FIG. 3 is a ruptured view of a thermoacoustic refrigerator according to a first embodiment of the present disclosure, which includes operating temperature, ambient temperature and humidity, and control circuit elements that optimize efficiency as a function of selected user input.</figref><figref num="2">FIG. 2 is a break view of a thermoacoustic refrigerator according to a second embodiment of the present disclosure, which includes operating temperature, ambient temperature and humidity, and control circuit elements that optimize efficiency as a function of selected user input.</figref><figref num="3">FIG. 3 is a break view of a thermoacoustic refrigerator according to a third embodiment of the present disclosure, which includes operating temperature, ambient temperature and humidity, and control circuit elements that optimize efficiency as a function of selected user input.</figref><figref num="4">FIG. 5 is a cut-off view of a thermoacoustic heat engine according to a first embodiment of the present disclosure, which includes operating temperature, ambient temperature and humidity, and control circuit elements that optimize efficiency as a function of selected user input.</figref><figref num="5">It is a schematic diagram of the type of load control circuit which may be deployed in the thermoacoustic heat engine of the type shown in FIG.</figref><figref num="6">FIG. 2 is a cut-off view of a thermoacoustic heat engine according to a second embodiment of the present disclosure, which includes operating temperature, ambient temperature and humidity, and control circuit elements that optimize efficiency as a function of selected user input.</figref><figref num="7">FIG. 5 is a schematic diagram of a power combiner circuit of a type that may be deployed in a thermoacoustic heat engine of the type shown in FIG.</figref>

FIG. 1 is a ruptured view of a thermoacoustic chiller 70 that includes control circuit elements that optimize efficiency as a function of operating temperature, ambient temperature and humidity, and selected user input. Although the description relating to FIGS. 1 and 1 is focused on the refrigerator, the description herein is similar to heat pumps, heat engines, and other forms of thermoacoustic devices, as further described herein. It will be understood that this is the case.

The thermoacoustic refrigerator 70 includes a substantially tubular body 72. The material from which the body 72 is constructed may vary depending on the application of the present invention. However, the body 72 (actually all bodies described herein) should generally be thermally and acoustically insulating and capable of withstanding the pressurization of at least some atmospheres. Is. An exemplary material for the body 72 includes stainless steel or iron-nickel-chromium alloy.

A heat storage device 74 is arranged in the main body 72. The heat storage 74 (actually all heat storages described herein) provides a relatively high thermal mass and a large surface area of interaction with the gas, but offers a variety of materials and low acoustic damping. It may be constructed from any of the structural arrangement configurations. Wire mesh or screen, open cell material, random fiber mesh or screen, or other materials and arrangement configurations as understood by those skilled in the art may be employed. The density of the materials that make up the regenerator 74 may be constant, or the area of interaction between the gas and the wall and the acoustic impedance are adjusted for optimum efficiency over the longitudinal dimensions of the regenerator 74. It may vary along the longitudinal axis so that it does. The details of the regenerative device design are usually known in the art and are therefore not further described herein.

Adjacent to each lateral end of the regenerator 74, there are first and second heat exchangers 76, 78, respectively. The heat exchangers 76, 78 (actually all heat exchangers described herein) are among the various material and structural arrangement configurations that provide relatively high heat transfer efficiency from the body 72 to the transfer medium. It may be constructed from any of the above. In one embodiment, the heat exchangers 76, 78 may be one or more tubes that hold the fluid to be heated or cooled inside. The heat exchangers 76, 78 are formed from a material and, during the operation of the refrigerator, the heat energy (for heating or cooling) between the fluid in the heat exchangers 76, 78 and the gas in the body 72. Is made and arranged in a size that efficiently transmits. To increase heat transfer, the surface areas of heat exchangers 76, 78 may be increased using fins or other structures well known in the art. Tubes 77, 79, which are connected to heat exchangers 76, 78, respectively, allow fluid to be transferred from / to and from / to heat exchangers 76, 78 from an external heat reservoir or load of heat storage 74. The details of the heat exchanger are usually known in the art and are therefore not further described herein.

Optionally, the third heat exchanger 80 may be disposed within one end of the body 72, for example, such that the heat exchanger 78 is located between the heat exchanger 80 and the heat storage 74. Good. The third heat exchanger 80 is formed from a material and is efficient in heat energy (for heating or cooling) between the fluid in the heat exchanger and the gas in the body 72 during the operation of the refrigerator. It may have the same configuration as the first and second heat exchangers 76, 78, such as one or more tubes that are sized and arranged to transmit. The tube 81 allows fluid transfer from / to and from / to the third heat exchanger 80 from the heat reservoir or load external to the heat storage device 74.

The electromechanical driver 82 (eg, acoustic wave source) is located in the body 72 in close proximity to the first heat exchanger 76. Many different types of devices may function as electromechanical drivers 82, such as the well-known movable coil, piezoelectric, electrostatic, ribbon, or other forms of loudspeakers. Very efficient, frequency tuned and frequency stable speaker designs are preferred so that the cooling efficiency of the chiller is maximized.

A variable frequency driver (VFD) 84 is connected to an electromechanical driver 82. The VFD84 is capable of driving the electromechanical driver 82 at the desired frequency and amplitude with very high conversion efficiency. The acoustic load 73, such as an orifice, forms part of the body 72 in close proximity to the second or third heat exchangers 78, 80 and dissipates the sound energy.

First, a gas such as helium is sealed inside the housing 72. The oscillating power from the VFD84 is provided to the electromechanical driver 82, which produces acoustic vibrations in the gas. With the proper selection of dimensions and the proper material selection for the housing 72 and the heat exchanger 74 and the use of the proper gas, the proper Stirling cycle is started in the area of the heat exchanger 74 and once the system reaches steady state, the first A temperature gradient is established within the regenerator 74 so that the 1 heat exchanger 76, the "hot" heat exchanger, is at a relatively higher temperature than the 2nd heat exchanger 78, the "low temperature" heat exchanger. ..

The Sterling cycle is a constant volume cooling of gas that eliminates heat to the heat storage when the gas moves from the high temperature heat exchanger to the low temperature heat exchanger, isothermal expansion of the gas, and high temperature heat exchange from the low temperature heat exchanger. It consists of constant volume heating of the gas that receives the heat from the heat exchanger when the gas moves in the direction of the vessel, and subsequent isothermal compression of the gas. At the time of isothermal compression, the gas is in the initial state and the process , Repeat itself. In this way, heat is transferred from the low temperature heat exchanger to the high temperature heat exchanger. The heat storage device 74 helps to store thermal energy and significantly improves energy conversion efficiency.

Several sensors are employed to take into account the various systems and ambient temperatures when determining the frequency and / or amplitude at which the VFD84 drives the electromechanical driver 82. These sensors can generally be divided into two types. The two types are the type that detects quantities that are almost unrelated to the operating state of the device, such as ambient temperature and humidity, and the internal pressure amplitude, gas flow rate, gas temperature, heat exchanger temperature, and temperature of the space to be cooled. It is a type that detects an amount that depends to some extent or almost depends on the operating state of the device.

According to the embodiment shown in FIG. 1, these sensors are a thermocouple 89 that measures the temperature inside the main body 72 close to the heat exchanger 76, and a thermocouple that measures the temperature of the heat exchange fluid in the heat exchanger 76. Thermocouple 91 to measure the temperature inside the main body 72 close to the heat exchanger 78, thermocouple 90 to measure the temperature of the heat exchange fluid in the heat exchanger 78, main body 72 close to the heat exchanger 80 It takes the form of a thermocouple such as a thermocouple 93 that measures the temperature inside the heat exchanger 80 and a thermocouple 92 that measures the temperature of the heat exchange fluid inside the heat exchanger 80. The use of thermocouples as temperature sensors is merely an example, and any type of temperature sensor may be used. Further, the ambient temperature sensor 94 such as a thermocouple, a thermometer, etc. can be used, for example, as an ambient temperature in a space where heat is removed by a refrigerator, an ambient temperature in a space close to an intake port of the device, or an external temperature. It is arranged close to the main body 72 in order to measure and the like. That is, this space may be physically close to the thermoacoustic chiller 70, or may be heat, such as outside a building to be cooled or in an adjacent room (if the thermoacoustic chiller 70 is a room cooler). It may be physically separated from the acoustic refrigerator 70. Therefore, in one embodiment, the temperature sensor 94 is close to the thermoacoustic chiller 70, and in another embodiment, the temperature sensor 94 is in the room to be cooled, but not necessarily close to the thermoacoustic chiller 70. However, in yet another embodiment, the temperature sensor 94 does not have to be somewhere near the thermoacoustic refrigerator 70. Here, the present inventors distinguish between the ambient temperature and the temperature inside the space to be cooled. The temperature inside the space to be cooled depends on the operation of the device (ie, the device cools it), while the ambient temperature does not depend on the operation of the device. Thus, conceptually, the operation of the thermoacoustic chiller 70 can be partly a function of "outside" temperature, rather than just a function of the temperature of the room to be cooled.

Further, the hygrometer (humidity sensor) 96 may be arranged close to the main body 72 in order to measure the ambient humidity in the space where heat is removed by the refrigerator. The hygrometer 96 or additional hygrometer may also be arranged to measure absolute or relative ambient humidity, as described above for the temperature sensor 94. Although various thermocouples, thermometers, and hygrometers have been disclosed and shown in FIG. 1, it should be noted that many of these elements are optional, and the inventors of the present invention have performed the minimum. It is proposed that the form comprises a single thermometer, a thermocouple, or a similar sensor 89. The single thermometer, thermocouple, or similar sensor is the temperature in the area of the body 72, outside the thermoacoustic device, and the area in which the thermoacoustic device operates in one of the heat exchangers. It is possible to measure the temperature of. Further, additional thermocouples, thermometers, humidity sensors, and other sensors such as pressure sensors and flow rate sensors may be provided in various combinations without departing from the spirit and scope of the present disclosure.

Thermocouples 86, 88, 90, and 92, thermometer 94, and hygrometer 96 (and other sensor devices) are each connected to provide a data signal to controller 98. Controller 98 uses various temperature, humidity, and other measurements to generate control signals to control the VFD84, which is an electromechanical driver to optimize efficiency or cooling power. Control (change) 82 frequencies and input power, current, and / or voltage. The controller 98 may periodically sample various variables during the operation of the thermoacoustic refrigerator 70, and the periodic control updated to the VFD 84 to compensate for changes in operating and ambient conditions. A signal may be provided, thereby maintaining optimum or selected efficiency. Therefore, the controller 98 can generate a control signal at least partially from a plurality of temperature data signals, and the operation of the electromechanical driver 82 based on the control signal is optimized for the thermoacoustic refrigerator 70. Signals are acquired at various times during the operation of the thermoacoustic refrigerator 70 to provide operational efficiency. Alternatively, temperatures from thermocouples 86, 88, 90, and 92, thermometer 94, and hygrometer 96 (and other sensor devices) are provided to controller 98 at predetermined intervals during the operation of the thermoacoustic refrigerator 70. Other mechanisms may be provided as such.

Further input to controller 98 may be adjustable user parameter 99. Such user input parameters may include the desired cooling power, maximum power consumption, desired cooling temperature, etc. for the thermoacoustic refrigerator 70.

According to one embodiment, the controller 98 comprises logic programmed to change the frequency and / or power of the electromechanical driver 82 according to a look-up table that includes a mapping from ambient temperature to frequency and power. For example, as the ambient temperature increases, the power can remain constant and the frequency can be increased. In one particular modeled example, the temperature of the low temperature heat exchanger 78 (measured by thermocouple 90) is 299.8 K, and the high temperature and ambient heat exchange (measured by thermocouples 88 and 92, respectively). When the temperatures of the instruments 76 and 80 are both 308.2K, the optimum frequency for the input power of 12.9 watts was found to be 60Hz. However, as the temperature of the high temperature and ambient heat exchangers 76, 80 increases to 318.2K, the optimum frequency for an input power of 12.9 watts increases to 61.2Hz. Maintaining power requires increasing the input current from the VFD84 from 1.14 amps to 1.18 amps. The look-up table elements that correspond to this map are shown in Table 1.<tables num="1"><img file="JP2011237165A_D0001.tif" /></tables>

In one embodiment, the controller may be implemented by an embedded microprocessor and an analog-to-digital converter and a digital-to-analog converter. In another embodiment, a fully analog solution consisting of a combination of VFD and transistor amplifiers and electronic components may be used. In yet another embodiment, a combination of analog logic and digital logic may be used. As is well known to control system design experts, a feedback control system, i.e. a control system that uses input variables that depend on the operating state of the device, and a control system that has a memory of the system's past state is a condition. Steady state operation may be achieved only underneath. Under other conditions, the control system may oscillate between different states, i.e. fail to "capture" or "lock" to the desired state. .. Therefore, in embodiments where the controller of the system described herein uses dependent or historical variables as inputs, logic and control that is more involved than the lookup table is required to ensure steady-state operation. There is a possibility that For example, if the initial state of the system exceeds the device's capture range, the control system will only use the independent variable as it approaches its user-defined setpoint, and thus will use a combination of the independent and dependent variables. It may be designed to switch to.

As a further example, some variables, such as pressure amplitude, respond to changes in operating parameters relatively quickly, while other variables, such as the temperature of the space to be cooled, have a relatively long time delay (lag). Respond to changes in operating parameters. To prevent vibration, the controller should respond to changes in the temperature of the space to be cooled more slowly than to changes in pressure amplitude.

As a further example, consider a device having a look-up table in Table 1. This look-up table may not have inputs for all combinations of heat exchanger temperatures. In these cases, the controller turns on the refrigerator at a default frequency and power, eventually reaching a set in the look-up table, at which point the device is "locked". It may have logic that will be set and the controller will start using the lookup table to specify the operating parameters.

In general, the techniques for designing such controllers are well known to experts in feedback control system design.

Optimal frequencies and power will vary from thermoacoustic device to thermoacoustic device. They will also vary depending on user preferences such as cooling power. In one embodiment, the controller 98 is designed for a particular thermoacoustic device (eg, a particular dimension, material, etc.). In another embodiment, the controller 98 can be configured for use with multiple devices. For example, the lookup table is stored in rewritable memory such as flash memory and can be reprogrammed for each device. The look-up table does not need to be fixed for a given unit, but can be modified as the units move to different rooms, different conditions, and so on. In various other embodiments, the controller may be interchangeable between devices of the same type (eg, the same cooling power), the controller may be between different types of devices (eg, 1kW and 10kW units). Can be interchangeable with and / or existing devices can be modified to have sensors and controllers.

In another embodiment, controller 98 uses a feedback loop to optimize efficiency and power. Some detected parameters, such as external temperature and humidity and user settings including temperature setting points, are independent of controller output. Other parameters such as the internal temperature, internal pressure, and flow rate of the heat exchangers 76, 78, 80 will change as the frequency and power of the VFD84 change. Therefore, in the feedback embodiment, additional sensors such as pressure and flow velocity sensors (not shown) located within the body 72 and a measure of the state of the VFD84 (indicated by the dotted line connecting the VFD84 to the controller 98) are employed. To. The "feedback" system takes advantage of these latter values. Only "feedforward" systems make use of the former.

Feedforward systems are universally stable, while feedback systems may not be universally stable. Therefore, a control system with feedback may suggest a more complex process. For example, in one embodiment, the system is started using only feedforward type (ie, independent) inputs. When the system reaches steady state, it implements a feedback system.

FIG. 2 is a broken view of a second embodiment of the thermoacoustic refrigerator 100 that includes control circuit elements that optimize efficiency as a function of operating temperature, ambient temperature and humidity, and selected user input. The thermoacoustic refrigerator 100 includes a substantially tubular body 102. A refrigerator 104 is arranged in the main body 102.

Adjacent to each lateral end of the refrigerator 104 are first and second heat exchangers 106 and 108, respectively. The heat exchangers 106, 108 may be constructed from any of a variety of materials and structural arrangement configurations that provide relatively high heat transfer efficiency from within the body 102 to the transfer medium. In one embodiment, the heat exchangers 106, 108 may be one or more tubes that hold the fluid to be heated or cooled inside. The heat exchangers 106, 108 are formed from a material and, during the operation of the refrigerator, the heat energy (for heating or cooling) between the fluid in the heat exchangers 106, 108 and the gas in the body 102. Is made and arranged in a size that efficiently transmits. To increase heat transfer, the surface areas of heat exchangers 106, 108 may be increased using fins or other structures well known in the art. Tubes 110, 112 allow fluid transfer from / to and from heat exchangers 106, 108 / from an external heat reservoir or load of the heat storage device 110.

Optionally, the third heat exchanger 114 may be disposed within one end of the body 102, for example, such that the heat exchanger 108 is located between the heat exchanger 114 and the heat storage device 104. Good. The third heat exchanger 114 is formed from a material and is efficient in heat energy (for heating or cooling) between the fluid in the heat exchanger and the gas in the body 102 during the operation of the refrigerator. It may have a configuration similar to that of the first and second heat exchangers 106, 108, such as one or more tubes that are sized and arranged to transmit. Tube 116 allows the transfer of fluid from / to / from the heat reservoir or load external to the heat storage device 100 and / from / to the third heat exchanger 114.

The electromechanical driver 120 (for example, an acoustic wave source) is arranged at the first longitudinal end of the main body 102, and the acoustic converter 122 faces the electromechanical driver 120 centering on the heat storage device 104 and faces the main body 102. It is arranged at the second longitudinal end of the. Many different types of devices may function as electromechanical drivers 82, such as the well-known movable coil, piezoelectric, electrostatic, ribbon, or other forms of loudspeakers. Very efficient, compact, frequency tuned and frequency stable speaker designs are preferred so that the cooling efficiency of the chiller is maximized.

Similarly, many different types of devices may serve the function of the acoustic converter 122. Well-known electrostatic, electromagnetic, piezoelectric, or other forms of microphones or pressure transducers form the acoustic converter 122. In addition, gas springs, compliance elements, inertial elements, or other acoustic elements may be employed to enhance the functionality of the converter 122. Again, efficiency is a preferred attribute of the acoustic converter 122 such that the cooling efficiency of the regenerator is maximized.

The variable frequency driver (VFD) 126 is connected as an input to the combiner 128 (of the type known in the art). The VFD126 is capable of driving the electromechanical driver 120 at the desired frequency and amplitude with very high conversion efficiency. The output of combiner 128 is the impedance circuit Z₁Form an input to. Impedance circuit Z₁Outputs form an input to the sound source 120. Second impedance circuit Z₂The output of is connected as an input to combiner 128. The output from the acoustic converter 122 is the impedance circuit Z.₂Provided as an input to. Impedance circuit Z₁, Z₂The role of is to match the system impedance to efficiently drive the electromechanical driver 120 at the desired frequency and phase. Phase delay circuit φ_(W)May also be employed to achieve the desired phase alignment, as is well known in the art.

During operation, the oscillating power from the VFD 126 is provided to the electromechanical driver 82, which produces acoustic vibrations in a gas such as helium sealed within the housing 102. With the proper selection of dimensions and the proper material selection for the housing 102 and the heat exchanger 104 and the use of the proper gas, the proper Stirling cycle is started in the region of the heat exchanger 74 and once the system reaches steady state, the first A temperature gradient is established within the regenerator 104 so that the heat exchanger 106 of 1 and the "hot" heat exchanger are at a relatively higher temperature than the second heat exchanger 108 and "cold" heat exchanger. .. The heat storage device 104 stores heat energy and helps to significantly improve the energy conversion efficiency.

Several sensing devices (again, device operating conditions such as ambient temperature and humidity) to take into account various systems and ambient temperatures when determining the frequency and / or amplitude at which the VFD126 drives the electromechanical driver 120. Detection devices that detect quantities that are largely unrelated to, and detections that detect quantities that are somewhat or nearly dependent on the operating state of the device, such as internal pressure amplitude, gas flow rate, heat exchanger temperature, and temperature of the space to be cooled. Device) is adopted. In the embodiment of FIG. 2, the sensors are a thermocouple 140 that measures the temperature inside the body 102 close to the heat exchanger 106, a thermocouple 142 that measures the temperature of the heat exchange fluid in the heat exchanger 106, and a heat exchange. Thermocouple 144 to measure the temperature of the heat exchange fluid in the vessel 108, thermocouple 145 to measure the temperature inside the main body 102 close to the heat exchanger 108, and the temperature of the heat exchange fluid in the heat exchanger 114 Thermocouples such as the thermocouple 146 and the thermocouple 147 that measures the temperature inside the body 102 close to the heat exchanger 114. Again, the use of thermocouples as temperature sensors is merely an example, and any type of temperature sensor may be used.

A temperature sensor 148, such as a thermometer or thermocouple, is arranged to measure the ambient temperature in the space from which heat is removed by the refrigerator. Further, a hygrometer (humidity sensor) 150 may be arranged to measure the ambient humidity in the space where heat is removed by the refrigerator. Although various thermocouples, thermometers, and hygrometers have been disclosed and shown in FIG. 1, it should be noted that many of these elements are optional, and the smallest embodiment is a single. It is equipped with a thermocouple, a thermometer, or other sensor. In addition, additional temperature-related sensors such as additional thermocouples, thermometers, and internal pressure sensors may be provided in various combinations without departing from the spirit and scope of the present disclosure.

Thermocouples 104, 142, 144, and 146, a thermometer 148, and a hygrometer 150 (and other sensor devices) are each connected to provide a data signal to the controller 152. The controller 152 uses various temperature, humidity, and other measurements to generate control signals to control the VFD126, which is an electromechanical driver to optimize efficiency or cooling power. Control (change) 120 frequencies and input power, current, and / or voltage. Controller 152 also has a phase (φ_(W)) And impedance (z₁And z₂) May be controlled.

Further input to controller 152 may be adjustable user parameter 154. Such user input parameters may include the desired cooling power, maximum power consumption, desired cooling temperature, etc. for the thermoacoustic refrigerator 100.

According to one embodiment, the controller 152 comprises logic programmed to change the frequency and / or power of the electromechanical driver 120 according to a look-up table that includes a mapping from ambient temperature to frequency and power. For example, as the ambient temperature increases, the power can remain constant and the frequency can be increased. In one embodiment, the look-up table can be implemented by an embedded microprocessor and an analog-to-digital converter and a digital-to-analog converter. In another embodiment, a fully analog solution consisting of a combination of VFD and transistor amplifiers and electronic components may be used. In yet another embodiment, a combination of analog logic and digital logic may be used.

Optimal frequencies and power will vary from thermoacoustic device to thermoacoustic device. They will also vary depending on user preferences such as cooling power. Thus, the user may provide control over various inputs 154 to the controller 152, for example, via a software interface (not shown).

In the feedback embodiment, additional sensors such as pressure and flow velocity sensors (not shown) located within the body 102, a measure of the state of the VFD126, and / or a measure of the output of the converter 122 are employed.

It will be appreciated that the arrangement configuration described above can be extended to other configurations of thermoacoustic refrigerators. Figure 3 shows an example of such an alternative. The thermoacoustic refrigerator 200 shown in FIG. 3 is a closed loop device having a cooling stage connected in series. Briefly, such a system comprises two or more cooling stages 202a, 202b, wherein the cooling stages 202a, 202b are essentially arranged as described above, electromechanical drivers 204a, 204b, first. Includes heat exchangers 206a, 206b, regenerators 208a, 208b, second heat exchangers 210a, 210b, and an optional third heat exchanger 212a, 212b. Each stage 202a, 202b is further connected to the back side of the electromechanical driver of the next stage acoustic transmission lines 214a, 214b (in one embodiment, channels through which acoustic waves may travel). Is).

According to the embodiment shown in FIG. 3, thermocouples 222a, 224a, and 226a are provided to measure the temperature of the heat exchange fluid in the heat exchangers 206a, 210a, and 212a, respectively. Thermocouples 221a, 223a, and 225a are provided to measure temperatures close to the heat exchangers 206a, 210a, and 212a, respectively. Similarly, thermocouples 222b, 224b, and 226b are provided to measure the temperature of the heat exchange fluids in the heat exchangers 206b, 210b, and 212b, respectively. Thermocouples 221b, 223b, and 225b are then provided to measure temperatures close to the heat exchangers 206b, 210b, and 212b, respectively.

In addition, a thermometer 228 is provided to measure the ambient temperature in the space where heat is removed by the refrigerator. A hygrometer (humidity sensor) 230 is provided to measure the ambient humidity in the space where heat is removed by the refrigerator. Once again, temperature and humidity checks at various locations have been proposed here, but many checks are optional and many different combinations and additional measures are possible and envisioned herein.

The thermocouple, thermometer 228, and hygrometer 230 (and other sensor devices) each provide data to controller 232. Controller 232 uses various temperature, humidity, and other measurements to generate control signals to control VFD234a, 234b, which VFD234a, 234b to optimize efficiency or cooling power. Controls (changes) the frequency, relative phase, and input power, current, and / or voltage provided to the electromechanical drivers 204a, 204b, and / or the relative phase of the driver's current and / or voltage. Note that controller 232 can control VFD234a, 234b independently, thereby compensating for differences in materials, dimensions, location, and other variables between stages 202a and 202b. Should be.

Further input to controller 232 may be adjustable user input parameter 236. Such user input parameters may include desired cooling power, maximum power consumption, desired cooling temperature, etc. for the thermoacoustic refrigerator 200.

As mentioned above, in one embodiment, the controller 232 follows the frequency and / or power and / of the electromechanical drivers 204a, 204b according to a lookup table containing a temperature-to-frequency, power, and phase mapping for each stage. Alternatively, it has logic programmed to change the current phase (and optionally reprogrammable). In another embodiment, for each stage 202a, 202b, a fully analog solution consisting of a combination of VFD and transistor amplifiers and electronic components may be used. In yet another embodiment, a combination of analog logic and digital logic may be used.

In addition, optional inputs to controller 232 are feedback from VDF234a, 234b and data from additional sensors such as pressure and flow velocity sensors (not shown) located within body 201. A feedback loop may be used to further optimize the efficiency and / or power usage of the thermoacoustic chiller 200 and provide operational stability, as described above.

Although the above description has been from the perspective of optimized control of the thermoacoustic refrigerator, the general principles disclosed herein may be similarly applied to thermoacoustic heat engines. FIG. 4 is a cross-sectional view of an embodiment of a thermoacoustic heat engine 300 incorporating these general principles. Many elements of the thermoacoustic heat engine 300, well known, simply include a hollow, loop-sealed body structure 302 in which a regenerator 304 is located. The regenerator is a first heat exchanger 306 (generally a "cold" exchanger) at the first end of the regenerator and a second heat exchanger 308 (generally a "hot" exchange) at the opposite end of the regenerator. Close to the vessel). The third heat exchanger 310, which has a near ambient temperature, may be present at any option. A resonator 312 in the form of an extension of the hollow body structure 302 is provided. The main body structure 302 is filled with a pressurized gas. A temperature difference occurs before and after the heat storage 304, that is, between the low temperature heat exchanger 306 and the high temperature heat exchanger 308, exposing the gas to local heat transfer. Sound energy in the form of pressure waves within the area of the regenerator exposes the gas to local and periodic compression and expansion. Under favorable acoustic conditions, the gas effectively undergoes a proper Stirling cycle within the regenerator 304.

In order to reduce the fluid resistance loss, it is desirable to have a large acoustic impedance in the regenerator 304. Therefore, one family of known thermoacoustic heat engines uses acoustic resonators and / or acoustic feedback networks 314 to achieve this high impedance. However, these networks are not tunable during use and do not consider the operating conditions of the heat engine to optimize operation.

Therefore, the embodiment shown in FIG. 4 comprises a variable acoustic impedance such as the electromechanical converter 316, which comprises the efficiency and operation of the thermoacoustic heat engine 300, for example by modifying the resonant frequency of the device. Impedance adjustment (load) for optimizing may be provided. In essence, the controllable portion of the pressure wave energy within the body 302 may be converted to electrical energy by the electromechanical transducer 316, depending on various systems and ambient temperatures and operating conditions.

Several temperature sensors are employed to take into account the various systems and ambient temperatures when determining the operation of the electromechanical transducer 316 for frequency and impedance regulation. According to the embodiment shown in FIG. 4, these sensors take the form of thermocouples such as thermocouples 322, 324, and 326 that measure the temperature of the heat exchange fluid in the heat exchangers 306, 308, and 310. .. In addition, thermocouples 321, 323, and 325 are provided to measure the temperature inside the body 302 in close proximity to the heat exchangers 306, 308, and 310.

In addition, a thermometer 328 is provided to measure the ambient temperature in the space where heat is removed by the refrigerator. Further, a hygrometer (humidity sensor) 330 is provided to measure the ambient humidity in the space where heat is removed by the refrigerator. Once again, temperature and humidity checks at various locations have been proposed here, but many checks are optional and many different combinations and additions are possible and envisioned herein.

Thermocouples, thermometers 328, and hygrometers 330 (as well as other sensor devices) are connected to provide data to controller 332. The controller 332 uses various temperature, humidity, and other measurements to generate control signals to control the load control circuit 324, which is connected to the electromechanical transducer 316 and is described in more detail below. .. The load control circuit 324 controls (alters) the load presented by the electromechanical transducer 316 and therefore adjusts the impedance within the thermoacoustic heat engine 300 to optimize heating efficiency.

Further input to controller 332 may be adjustable user input parameter 336. Such user input parameters may include the desired heating, efficiency index, etc. for the thermoacoustic heat engine 300.

As mentioned above, in one embodiment, the controller 332 is programmed (and optionally reprogrammable) to control the load control circuit 334 according to a look-up table that includes a temperature-to-load mapping. ) With logic. In another embodiment, an analog solution consisting of a load control circuit 334 and a combination of transistor amplifiers and electronic components may be used. In yet another embodiment, a combination of analog logic and digital logic may be used.

FIG. 5 shows an example of a load control circuit 334 of a type that may be used in the thermoacoustic heat engine 300 of FIG. In the embodiment shown in FIG. 5, a variable tap transformer circuit under the control of controller 332 is shown. Many other circuit devices, such as varicap circuits, may be employed without departing from the spirit and scope of the present disclosure. The electromechanical transducer 316 is attached to the load control circuit 334._n, T_nConnected at. At least a portion of the power attenuated by the electromechanical transducer 316 is u_n, V_nAvailable for use in the output of the load control circuit 334, u_n, V_nThe system 350 to which the is connected will partially affect the impedance of the electromechanical transducer 316. Therefore, in one embodiment, the feedback signal is provided from the system 350 back to the controller 332, just as the controller 332 provides the optimized control signal to the load control circuit 334.

It will be appreciated that the arrangement configuration described above can be extended to other configurations of thermoacoustic heat engines. FIG. 6 shows an example of such an alternative, in this case the two-stage loop heat engine 500. Briefly, such a system comprises a housing 502 divided into approximately two heating stages 504a, 504b (although three or more stages are within the scope of this disclosure). Each stage 504a, 504b is arranged and operated consistently with the previous description, first heat exchangers 506a, 506b, regenerators 508a, 508b, second heat exchangers 510a, 510b, and options. Third heat exchangers 512a and 512b are arranged. Similarly, electromechanical converters 514a and 514b are arranged in each stage. Each stage 504a, 504b further has acoustic transmission lines 516a, 516b connected in series behind the electromechanical transducer of the next stage (in one embodiment, acoustic waves may travel through it). It has a channel).

According to the embodiment shown in FIG. 6, the thermocouples 520a and 520b are provided to measure the temperature of the heat exchange fluid in the heat exchangers 506a and 506b, respectively, and the thermocouples 522a and 522b are the heat exchangers 510a. , 510b are provided to measure the temperature of the heat exchange fluid, respectively, and optionally, thermocouples 524a and 524b are provided to measure the temperature of the heat exchange fluid in the heat exchangers 512a and 512b, respectively. .. In addition, thermocouples 519a, 521a, and 523a are provided to measure the temperature inside the body 501 in close proximity to the heat exchangers 506a, 510a, and 512a, respectively. Furthermore, thermocouples 519b, 521b, and 523b are provided to measure the temperature inside the body 501 in close proximity to the heat exchangers 506b, 510b, and 512b, respectively.

The thermometer 528 is provided in close proximity to the thermoacoustic heat engine 500 to measure the ambient temperature in the space where heat is removed by the heat engine. Further, the hygrometer (humidity sensor) 530 may be provided in close proximity to the thermoacoustic heat engine 500 to measure the ambient humidity in the space where heat is removed by the heat engine. Once again, temperature and humidity checks at various locations have been proposed here, but many checks are optional and many different combinations are possible and envisioned herein. The present inventors propose that the minimum embodiment includes thermocouples 518a and 518b. Additional thermocouples, thermometers, humidity sensors, and other temperature-related sensors such as pressure sensors may be provided in various combinations without departing from the spirit and scope of the present disclosure.

The thermocouple, thermometer 528, and hygrometer 230 (and other sensor devices) are each connected to provide data to controller 532. Controller 532 uses various temperature, humidity, and other measurements to control load control circuits (not shown) connected to taps s, t of electromechanical transducers 514a, 514b, respectively. Generate a control signal. Controller 532 is capable of independently controlling each load control circuit for independent load adjustment of electromechanical transducers 514a, 514b, thereby the material, dimensions, between stages 504a and 504b. It should be noted that differences in location and other variables are compensated.

Further input to controller 532 may be adjustable user input parameter 534. Such user input parameters may include the desired heat consumption, output power, etc. for the thermoacoustic heat engine 500.

As mentioned above, in one embodiment, the controller 532 is programmed to control the load control circuitry for electromechanical transducers 514a, 514b according to a look-up table containing temperature-to-load mapping for each stage. Has (and optionally reprogrammable) logic. In another embodiment, an analog solution consisting of a load control circuit and a combination of transistor amplifiers and electronic components may be used. In yet another embodiment, a combination of analog logic and digital logic may be used.

Again, at least some of the power attenuated by the electromechanical transducers 514a, 514b may be used to perform useful work. In the case of an n-stage thermoacoustic heat engine, there may be as many as n electromechanical transducers to provide this power. The outputs from these electromechanical transducers are coupled by the combiner circuit 352 shown in FIG. 7 to provide a single output pair x, y for connecting to a system performing work (not shown). Similarly, as described above, the system to which x and y are connected will partially affect the frequency and impedance of the electromechanical transducer in the n-stage heat engine. Therefore, in one embodiment, the feedback signal is sent from the system to the controller (controller 532 in FIG. 6) so that the optimized control signal is provided to various load control circuits (such as the load control circuit 334 in FIG. 5). Etc.) provided to return.

The limitations of the scope of claims are intended to define the boundaries of the present disclosure including and up to these limitations. To further emphasize this, the term "substantially" may be used from time to time herein in connection with the limitations of the claims (although considerations for modification and imperfections are not included. , Not limited to the restrictions used with the term). Although it is difficult to define the limitations of the disclosure itself as strictly as possible, the inventors have described the term as "to a large extent" and "as practical as it is." It is intended to be interpreted as "as nearly as practicable", "within technical limitations", etc.