Patent Application
20110252812
The invention generally relates to refrigeration, and more specifically, to a travelling wave thermoacoustic piezoelectric refrigerator for performing refrigeration utilizing travelling acoustic waves.
Nowadays thermoacoustic engines are commonly used as heat pumps or refrigerators. The thermoacoustic refrigerators utilize energy associated with thermoacoustic waves for refrigeration process.
In existing technologies, usually thermoacoustic refrigerators utilize energy associated with the thermoacoustic waves to transfer heat from a lower temperature end to a higher temperature end. Such thermoacoustic refrigerators use transducers as acoustic drivers for utilizing the acoustic energy. Further, the thermoacoustic refrigerators use a hot heat exchanger and a cold heat exchanger. A porous structure may be configured between the hot heat exchanger and the cold heat exchanger. The porous structure is made up of one or more of metal foils, a metal mesh, a sheet of a foamed metal, and sheets of filter paper. Additionally, the thermoacoustic refrigerators may include one or more moving parts and moving masses to generate the thermoacoustic waves. These one or more moving parts and moving masses require sliding seal mechanisms for their operation. The thermoacoustic waves may be generated within the thermoacosutic refrigerators using mechanism used for generating sonic waves. The thermoacoustic waves thus generated are utilized to trigger the heat from the lower temperature end to the higher temperature end.
Further, a free piston mechanism may be used to reduce complexities in using the one or more moving parts and moving masses in the thermoacoustic refrigerators to generate the thermoacoustic waves. The free piston mechanism in the thermoacoustic refrigerators utilizes gas springs to generate thermoacoustic waves. The gas springs in the thermoacoustic refrigerators work similar to mechanical pistons, thereby, partially eliminating the need of sliding seal mechanisms. However, the use of moving masses in the thermoacoustic refrigerators is still required in such thermoacoustic refrigerators.
Therefore, there is a need for a system for efficiently performing refrigeration process using thermoacoustic energy.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.
Before describing in detail embodiments that are in accordance with the invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a travelling wave thermoacoustic piezoelectric refrigerator. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
Generally speaking, pursuant to various embodiments, the invention provides a travelling wave thermoacoustic piezoelectric refrigerator. The travelling wave thermoacoustic piezoelectric refrigerator includes a housing having two ends. The two ends of the housing are connected using an inertance component. The housing includes a first portion and a second portion. Additionally, the housing includes a compressible fluid. Further, the travelling wave thermoacoustic piezoelectric refrigerator includes a porous stack. The porous stack is positioned between the first portion and the second portion within the housing. The first portion includes a cold heat exchanger. The cold heat exchanger is positioned near to an end of the porous stack. The second portion includes a hot heat exchanger. The hot heat exchanger is positioned near to an end of the porous stack opposite to the end of the porous stack near to the cold heat exchanger. Further, the travelling wave thermoacoustic piezoelectric refrigerator includes a resonator. The resonator includes an end connected to the second portion of the housing. The travelling wave thermoacoustic piezoelectric refrigerator also includes a piezoelectric bimorph. The piezoelectric bimorph is positioned at an end of the resonator opposite to the end of the resonator connected to the second portion. The piezoelectric bimorph is configured to oscillate upon receiving energy from an external energy source. The piezoelectric bimorph oscillates to resonate with the resonator. The resonance generates acoustic energy within the resonator. Further, the acoustic energy thus generated triggers travelling acoustic waves within the housing. The travelling acoustic waves traverses between the first portion and the second portion through the porous stack and the inertance component. The traversal of the travelling acoustic waves enables the compressible fluid to transfer heat from the cold heat exchanger to the hot heat exchanger.
Referring to figures and in particular to
Travelling wave thermoacoustic piezoelectric refrigerator 100 further includes a porous stack 112. Porous stack 112 may include, but are not limited to, one or more of metal foils, a metal mesh, a sheet of a foamed metal, and a sheet of filter paper. Porous stack 112 is positioned between first portion 108 and second portion 110 within housing 102. First portion 108 includes a cold heat exchanger 114. Cold heat exchanger 114 is positioned near to an end of porous stack 112. Additionally, second portion 110 includes a hot heat exchanger 116. Hot heat exchanger 116 is positioned near to an end of porous stack 112 opposite to the end of porous stack 112 near to cold heat exchanger 114. For example, porous stack 112 is positioned between cold heat exchanger 114 and hot heat exchanger 116 within housing 102.
Further, travelling wave thermoacoustic piezoelectric refrigerator 100 includes a resonator 118. Resonator 118 includes an end connected to second portion 110 of housing 102. A configuration of resonator 118 may be one of a straight configuration and an optimally shaped configuration. In an embodiment, resonator 118 may be optimally shaped to have a tapered configuration. A cross-sectional shape associated with resonator 118 may be one of a circle, a square, a rectangle, and a polygon. For example, in a scenario, resonator 118 with a tapered configuration may have a cross-sectional shape of a circle.
Travelling wave thermoacoustic piezoelectric refrigerator 100 includes a piezoelectric bimorph 120. Piezoelectric bimorph 120 is positioned at an end of resonator 118 opposite to the end of resonator 118 connected to second portion 110. Piezoelectric bimorph 120 oscillates upon receiving energy from an external energy source. The external energy source may include one of, but not limited to, electrical energy and solar energy. Piezoelectric bimorph 120 may be oscillated by an existing system known in the art. The existing system may be capable of utilizing the external energy source to oscillate piezoelectric bimorph 120. Thus, the amount of oscillation of piezoelectric bimorph 120 may be based on the amount of energy supplied by the external energy source. For example, a frequency of oscillation of piezoelectric bimorph 120 may be increased by increasing the amount of energy supplied to piezoelectric bimorph 120.
Upon receiving the energy from the external energy source, piezoelectric bimorph 120 oscillates to resonate with resonator 118. The resonance within resonator 118 generates acoustic energy within resonator 118. For example, piezoelectric bimorph 120 oscillates to generate an acoustic wave within resonator 118. The acoustic wave thus generated resonates with resonator 118 to generate acoustic energy.
The acoustic energy within resonator 118 triggers travelling acoustic waves within housing 102. The travelling acoustic waves traverse between first portion 108 and second portion 110 through porous stack 112 and inertance component 104. For example, in an instance, travelling acoustic waves may be generated in a housing of a travelling wave thermoacoustic piezoelectric refrigerator. The travelling acoustic waves may travel between a first portion and a second portion of the housing through a porous stack and an inertance component inside the housing. The travelling waves may be generated based on movement of one or more fluid parcels of a compressible fluid within the housing. The movement of the one or more fluid parcels may be triggered by acoustic energy generated due to the resonance in a resonator of the travelling wave thermoacoustic piezoelectric refrigerator.
In an embodiment, temperature of compressible fluid 106 may be varied to trigger the travelling acoustic waves within housing 102. The temperature of compressible fluid 106 may be varied by varying the temperature of surrounding of travelling wave thermoacoustic piezoelectric refrigerator 100. For example, in order to trigger the travelling acoustic waves, the temperature of surrounding is increased. This increase in temperature of the surrounding heats housing 102 thereby heating compressible fluid 106 for generating travelling acoustic waves based on resonance within resonator 118. The travelling acoustic waves thus generated traverse between first portion 108 and second portion 110.
Further, in an embodiment, first portion 108 may facilitate acoustic compliance for the travelling acoustic waves within housing 102. Due to the acoustic compliance the travelling acoustic waves entering first portion 108 increases the pressure inside first portion 108. The travelling acoustic waves travel through first portion 108 until the pressure inside first portion 108 reaches a threshold capacitance pressure. After reaching the threshold capacitance pressure, the travelling acoustic waves travel through first portion 108 until the pressure of the travelling acoustic waves remains higher than the threshold capacitance pressure. In other words, travelling acoustic waves may not travel through first portion 108 when the pressure of the travelling acoustic waves is less than the threshold capacitance pressure.
In another embodiment, inertance component 104 may facilitate acoustic inertance for the travelling acoustic waves within housing 102. Due to the acoustic inertance, the travelling acoustic waves entering inertance component 104 increases the pressure inside inertance component 104. The travelling acoustic waves travel through inertance component 104 once the pressure inside inertance component 104 reaches a threshold inertance pressure. In other words, until the pressure inside inertance component 104 is less than the threshold inertance pressure the travelling acoustic waves may not be able to travel through inertance component 104.
Thus, first portion 108 and inertance component 104 may provide a positive feedback to the travelling acoustic waves. This positive feedback may increase frequency associated with the travelling acoustic waves. This is explained in detail in conjunction with
Further, the traversal of the travelling acoustic waves between first portion 108 and second portion 110 enables compressible fluid 106 to transfer heat from cold heat exchanger 114 to hot heat exchanger 116. In order to transfer the heat from cold heat exchanger 114 to hot heat exchanger 116, compressible fluid 106 traverses between cold heat exchanger 114 and hot heat exchanger 116 within porous stack 112 based on the travelling acoustic waves. This results in cyclic transformation of compressible fluid 106 within porous stack 112. The cyclic transformation includes compression, heating, expansion, and cooling of one or more of fluid parcels of compressible fluid 106 within porous stack 112. A cyclic transformation of the one or more fluid parcels inside a porous stack within a travelling wave thermoacoustic piezoelectric refrigerator is explained in detail in conjunction with
In an embodiment, the travelling acoustic waves generated within housing 102 may be varied by varying the energy supplied by the external energy source to piezoelectric bimorph 120. The travelling acoustic waves thus generated enables compressible fluid 106 to transfer heat from cold heat exchanger 114 to hot heat exchanger 116. For example, in an instance, the temperature level of cold heat exchanger 114 may start increasing, thereby resulting in a need to cool cold heat exchanger 114. This increase in temperature of cold heat exchanger 114 may also result in slow down of refrigeration process. To decrease the temperature of cold heat exchanger 114, travelling acoustic waves of high intensity need to be generated. The high intensity travelling acoustic waves may be generated by increasing the energy supplied by the external energy source to piezoelectric bimorph 120. This high intensity travelling acoustic waves facilitates in transfer of heat from cold heat exchanger 114 to hot heat exchanger 116 thereby accelerating the refrigeration process.
In another embodiment, the energy supplied by the external energy source to piezoelectric bimorph 120 may be varied based on a threshold oscillation frequency of piezoelectric bimorph 120 for triggering the travelling acoustic waves within housing 102. The threshold oscillation frequency is associated with a resonating frequency of resonator 118. For example, the threshold oscillation frequency indicates a frequency associated with resonator 118 for generating first harmonic resonance within resonator 118. However, it will be apparent to a person skilled in the art that the threshold oscillation frequency of the resonator may indicate a frequency for generating resonance of any harmonic level within the resonator.
In still another embodiment, temperature associated with hot heat exchanger 116 may be varied to generate the travelling acoustic waves within housing 102. For example, the temperature level of hot heat exchanger 116 may increase upon receiving heat from cold heat exchanger 114. This may result in heat transfer from hot heat exchanger 116 to one or more fluid parcels of compressible fluid 106 near hot heat exchanger 116. When the one or more fluid parcels travel towards cold heat exchanger 114, heat may traverse from hot heat exchanger 116 to cold heat exchanger 114. To decrease the traversal of heat from hot heat exchanger 116 to cold heat exchanger 114, temperature within hot heat exchanger 116 may be decreased. The decrease in temperature of hot heat exchanger 116 reduces temperature difference between hot heat exchanger 116 and cold heat exchanger 114. This may in turn reduce a need of high intensity travelling acoustic waves to transfer heat from cold heat exchanger 114 to hot heat exchanger 116.
In an embodiment, temperature associated with cold heat exchanger 114 may be varied to generate the travelling acoustic waves within housing 102. For example, the temperature level of cold heat exchanger 114 may start increasing. As a result, cold heat exchanger 114 may need to be cooled. This increase in temperature of cold heat exchanger 114 may also result in slow down of refrigeration process. Further, this may also result in a need of travelling acoustic waves of high intensity to transfer heat from cold heat exchanger 114 to hot heat exchanger 116. Thus, for triggering the refrigeration process, the temperature within cold heat exchanger 114 is decreased. This may reduce the need of high intensity travelling acoustic waves for transferring heat from cold heat exchanger 114 to hot heat exchanger 116.
Travelling wave thermoacoustic piezoelectric refrigerator 100 uses piezoelectric bimorph 118 and includes fixed parts for the refrigeration process. The use of such fixed parts eliminates the need of sliding seal mechanisms. Referring back to acoustic compliance and acoustic inertance of travelling wave thermoacoustic piezoelectric refrigerator 100, the acoustic compliance and the acoustic inertance provide positive feedback to the travelling acoustic waves. This increases the intensity of the travelling acoustic waves generated in housing 102. Moreover, this also reduces the need of high frequency oscillation of piezoelectric bimorph 120 to create high intensity travelling acoustic waves within housing 102.
Referring now to
Further, the travelling acoustic waves travel between a first portion such as, first portion 108 and a second portion such as, second portion 110 through porous stack 202 and an inertance component 208 such as, inertance component 104. Inertance component 208 facilitates acoustic inertance for the travelling acoustic waves. Additionally, the first portion acts as a compliance 210 inside the housing. Compliance 210 facilitates acoustic compliance for the travelling acoustic waves. The travelling acoustic waves generated inside the housing travel through compliance 210 and inertance component 208 forming a loop inside the housing.
In an instance, porous stack 202, compliance 210, and inertance component 208 form a closed circuit. The closed circuit may have compliance 210 as capacitance and inertance component 208 as inductance. Compliance 210 and inertance component 208 are tuned such that the velocity and the pressure of the travelling acoustic waves are in phase. Further, compliance 210 and inertance component 208 provide a positive feedback to the travelling acoustic waves. The positive feedback provided to the travelling acoustic waves is similar to a positive feedback provided by a capacitance and an inductance serially connected in the closed circuit. The positive feedback increases the frequency of the travelling acoustic waves. Additionally, compliance 210 and inertance component 208 reduce impedance of the travelling acoustic waves. Thereafter, the travelling acoustic waves with increased frequency and reduced impedance enables the compressible fluid to transfer heat from cold end 204 of porous stack 202 to hot end 206 of porous stack 202.
Referring now to
The cyclic transformation of fluid parcel 300 takes place upon creation of travelling acoustic waves within a housing such as, housing 102. The travelling acoustic waves are created due to resonance between oscillations of a piezoelectric bimorph such as, piezoelectric bimorph 120 and a resonator such as, resonator 118. The resonance generates acoustic energy within the resonator. The acoustic energy thus generated triggers generation of the travelling acoustic waves within the housing. This is explained in detail in conjunction with
Due to the travelling acoustic waves, fluid parcel 300 traverses between a cold heat exchanger such as, cold heat exchanger 114 and a hot heat exchanger such as, hot heat exchanger 116 through the porous stack such as, porous stack 112 of the travelling wave thermoacoustic piezoelectric refrigerator. While fluid parcel 400 traverses, fluid parcel 400 receives heat energy from neighborhood walls of the porous stack such as, a wall 304 and a wall 306 of the porous stack. The travelling acoustic waves enable fluid parcel 300 present near the hot heat exchanger to travel from the hot heat exchanger towards the cold heat exchanger at stage 308. Simultaneously, fluid parcel 300 is compressed during the travel from the cold heat exchanger to the hot heat exchanger at stage 308. Moreover, temperature of fluid parcel 300 is decreased because of the compression. This decrease in temperature of fluid parcel 300 and compression of fluid parcel 300 is indicated by stage 308 as shown in P-V diagram 302. As indicated by stage 308 in P-V diagram 302, pressure increases during this stage and a volume associated with fluid parcel 300 decreases. Towards the end of stage 308, temperature of fluid parcel 300 is lower as compared to temperature of wall 304 and wall 306 of the porous stack near fluid parcel 300. Thereafter, at stage 310, fluid parcel 300 receives heat from one or more of the cold heat exchanger, wall 404 and wall 406. This heating of fluid parcel 300 is indicated by stage 310 as shown in P-V diagram 402. As indicated by stage 310 in P-V diagram 302, pressure increases during this stage and a volume associated with fluid parcel 300 initially reduce and then increases. Towards the end of stage 310, fluid parcel 300 starts travelling towards the hot heat exchanger from the cold heat exchanger.
Thereafter at stage 312, while traveling towards the hot heat exchanger, fluid parcel 300 expands because of heating. Moreover, temperature of fluid parcel 300 is increased because of the compression. This increase in temperature of fluid parcel 300 and expansion of fluid parcel 300 is indicated by stage 312 as shown in P-V diagram 302. As indicated by stage 312 in P-V diagram 302, pressure decreases during this stage and a volume associated with fluid parcel 300 increases. Towards the end of stage 312, temperature of fluid parcel 300 is higher as compared to temperature of wall 304 and wall 306 of the porous stack near fluid parcel 300. At stage 314, fluid parcel 300 releases heat to one or more of the hot heat exchanger, wall 304 and wall 306 near fluid parcel 300. This result in gradual decrease in volume of fluid parcel 300 based on cooling of fluid parcel 300. The cooling of fluid parcel 300 and decrease in volume of fluid parcel 300 is indicated by stage 314 as shown in P-V diagram 302. As indicated by stage 314 in P-V diagram 302, pressure decreases during this stage and a volume associated with fluid parcel 300 initially increases and then decreases. Thereafter, towards the end of stage 314, fluid parcel 300 starts travelling towards the cold heat exchanger from the hot heat exchanger similar to stage 308. Thus, resulting in the cyclic transformation of fluid parcel 300 inside the porous stack within the travelling wave thermoacoustic piezoelectric refrigerator. This cyclic transformation of one or more fluid parcels within the porous stack contributes to the refrigeration process. This is explained in detail in conjunction with
Various embodiments of the invention provide a travelling wave thermoacoustic piezoelectric refrigerator for performing refrigeration. The travelling wave thermoacoustic piezoelectric refrigerator uses a piezoelectric bimorph. As a result, the frequency of oscillation of the piezoelectric bimorph is easily controlled to trigger the refrigeration process. Further, the travelling wave thermoacoustic piezoelectric refrigerator uses piezoelectric bimorph along with fixed parts thereby eliminating the need of sliding seal mechanisms or any moving parts. Moreover, acoustic compliance and acoustic inertance of the travelling wave thermoacoustic piezoelectric refrigerator provide positive feedback to the travelling acoustic waves. This increases the intensity of the travelling acoustic waves generated in the housing thereby reducing the amount of energy required to oscillate the piezoelectric bimorph.
Those skilled in the art will realize that the above recognized advantages and other advantages described herein are merely exemplary and are not meant to be a complete rendering of all of the advantages of the various embodiments of the invention.
In the foregoing specification, specific embodiments of the invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
