Patent Application
20130133347
Embodiments of the present invention are related generally to the field of cooling systems and, more particularly, to a system and method for compression of fluids.
Compressors are typically used in systems and appliances that require fluids to be compressed and obtain high pressure. Such a need is felt in systems that follow a thermodynamic refrigeration cycle, for example, but not limited to, refrigerators, air conditioners, automotive cooling systems, and power plant cooling systems. Compressors are employed in such systems to compress the coolant and maintain a desired temperature in the system.
Compressors commonly utilize a piston that compresses fluids entering a hollow cylinder, called compression chamber, in the compressor body. The piston moves linearly back and forth to compress the fluid to create the high pressure fluid required to carry out the cooling operations in the system. The piston is displaced from an original position and kept in motion whenever the requirement for compressing fluids arises. Several configurations exist where the piston is set in motion to ensure fluids are compressed.
In an exemplary configuration, piezoelectric materials have been used as actuators to initiate displacement of pistons in the compressors. The piezoelectric material is provided with an excitation signal that causes the material to expand or contract. Generally, the piezoelectric material is coupled with the piston in such a way that the piston is displaced back and forth in the compression chamber, when the piezoelectric material experiences a change in shape and/or form.
Although the piezoelectric material causes displacement that may be desirable to compress fluids, the amount of displacement is dependent on several parameters including an excitation signal provided to the material. For high pressure requirements in a compression cycle in systems that require intensive cooling at a fast rate, a significant amount of energy is consumed by the excitation signal to be provided to the piezoelectric material. Moreover, piezoelectric material alone, even when provided with sufficient excitation signal, cannot provide both force and displacement to achieve the high pressure requirements at a fast rate.
Accordingly, there is a need for an improved system and method that provides for energy efficiency in driving the piston in the compression chamber of the fluid compressor.
In accordance with an embodiment of the invention, a system for controlling temperature of an enclosed space is provided. The system includes a fluid compressor to increase pressure of a coolant fluid. The fluid compressor includes a compression chamber having an inlet for the coolant fluid and an outlet for the compressed coolant fluid. Further, the fluid compressor includes a piston disposed within the compression chamber. The piston within the compression chamber is displaced using a driving system. The driving system includes a piezoelectric actuator coupled to the piston to cause lateral displacement of the piston in the compression chamber in response to an excitation signal. The driving system also includes an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston to enhance the displacement of the piston caused by the piezoelectric actuator. One end of the amplifying element is fixed to a base of the fluid compressor and the piezoelectric actuator is disposed between the amplifying element and the piston. Furthermore, the system to control temperature includes a condenser operatively coupled to the fluid compressor, to remove a portion of the heat contained in the compressed high temperature coolant fluid. The system also includes an expansion valve to reduce pressure of the compressed coolant fluid entering from the condenser and further reduce the temperature of the compressed coolant fluid. An evaporator to control temperature of the enclosed space by drawing heat from the enclosed space through the coolant fluid from the expansion valve is also included in the system.
In accordance with another embodiment of the invention, a system to compress fluids is provided. The system includes a driving system to displace a piston back and forth in a compression chamber. The driving system includes a piezoelectric actuator that causes a displacement of the piston in the compression chamber. The piston is disposed on top of the piezoelectric actuator. Further, the driving system includes an amplifying element that is coupled to the piezoelectric actuator to enhance the displacement caused by the piezoelectric actuator. The amplifying element is disposed in such a way that the piezoelectric actuator is placed on a top end of the amplifying element and an opposite end of the amplifying element is mechanically coupled with a base of the fluid compressor.
In accordance with another embodiment of the invention, a method for compressing fluids in a fluid compressor is provided. The method for compressing fluid includes displacing a piezoelectric actuator from its initial position with an excitation signal. The piezoelectric actuator is disposed below a piston of the fluid compressor that is configured to displace back and forth in a compression chamber of the fluid compressor. Further, the method includes amplifying the displacement of the piston by a degree of at least seven using an amplifying element. The amplifying element is disposed in such a way that the piezoelectric actuator is disposed on a top end of the amplifying element and an opposite end of the amplifying element is mechanically coupled with a base of the fluid compressor.
The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which:
While embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
As discussed in detail below, embodiments of the invention include a driving system for compression of fluids. Aspects of the present technique reduce energy consumption of compressors used to compress fluids. The system further provides for displacement of a piston in the fluid compressor at resonant frequency, thus achieving compression at a fast and efficient rate. The system as per the present technique includes a piezoelectric actuator and an amplifying element. The piezoelectric actuator is coupled to the piston to cause lateral displacement of the piston in the compression chamber in response to an excitation signal. The system further includes an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston to enhance the displacement of the piston caused by the piezoelectric actuator. The amplifying element is disposed in such a way that one end of the amplifying element is fixed to a base of the fluid compressor and the piezoelectric actuator is disposed between the amplifying element and the piston. The present technique is described in greater detail in the foregoing paragraphs with the help of accompanied drawings.
In the illustrated embodiment, the system 100 includes a fan 110 that blows the warm air 112 from the atmosphere on the coolant liquid in the evaporator 108. Further, according to certain embodiments of the present invention, the condenser 104 includes coiled tubes 118 to carry the compressed coolant fluid. According to another embodiment of the present invention, the evaporator 108 also includes coiled tubes 116 to carry the coolant fluid in and out of the enclosed space.
In another embodiment, the system 100 includes an excitation sub-system (not shown) that provides an excitation signal to the piezoelectric actuator in the fluid compressor 102. The system 100 also includes a feedback controller to control at least one of frequency and amplitude of the excitation signal provided to the piezoelectric actuator. The feedback controller includes at least one of a pressure sensor, a temperature sensor, and a stroke sensor that sense at least one of pressure of the coolant fluid in the compression chamber, temperature of the coolant fluid in the compression chamber, and a stroke of the piston within the compression chamber respectively. The feedback controller provides a feedback to the excitation sub-system based on the information obtained from at least one of the sensors to provide excitation signal that displaces the piezoelectric actuator appropriately to achieve efficient performance.
According to one embodiment of the present invention, the piezoelectric actuator 206 is fixed with the amplifying element 208 using at least one of nuts, bolts, rivets, or any known adhesive material. According to another embodiment of the present invention, the amplifying element 208 is fixed with the base 214 of the fluid compressor 102 using at least one of nuts, bolts, rivets, or any known adhesive material.
In one embodiment, the fluid compressor 102 includes an excitation sub-system configured to provide the excitation signal to the piezoelectric actuator 206. The excitation signal provided by the excitation sub-system is an electric signal that causes a displacement in the piezoelectric actuators. When the excitation signal is transmitted to the piezoelectric actuator 206, the piezoelectric actuator 206 expands or contracts depending on a phase of the excitation signal and causes the piston 204 to move. The movement of the piezoelectric actuator 206 causes the amplifying element 208 to stretch or expand. The change in shape of the amplifying element 208 caused by the piezoelectric actuator 206 causes an enhancement in the displacement of the piston 204. The displaced piston 204 then causes the fluid entering the compression chamber 202 through the inlet 210 to compress. The compressed fluid finally exits the compression chamber 202 through the outlet 212 and is supplied to a system utilizing the fluid compressor 102. According to one embodiment of the present invention, the displacement of the piston 204 is enhanced when the aforementioned operation occurs at resonance. To achieve resonance, the fluid compressor 102 has to be provided excitation signal that has a frequency close to a resonant frequency of the fluid compressor 102. The resonant frequency of the fluid compressor 102 is typically dependent on operating conditions, fluid pressure, and fluid temperature. In another embodiment, the fluid compressor 102 includes a feedback controller coupled to the excitation sub-system to ensure that the fluid compressor 102 operates in a resonant frequency with change in the operating conditions of the fluid compressor 102. The feedback controller is described in greater detail in conjunction with
In yet another embodiment, the amplifying element 208 is a coiled spring. The coiled spring has a spring stiffness associated with it, which signifies an amount of change in shape the coiled spring can accommodate. The amount of displacement enhanced by the amplified element 108 varies according to, among other factors, the spring stiffness. When a coiled spring is used as an amplifying element, it is placed in such a way that it is parallel to the direction of the movement of the piston. According to another embodiment of the present technique, the amplifying element 208 is a pre-buckled beam.
The piezoelectric actuator 206, according to one embodiment of the present technique, is a piezoelectric stack actuator. Piezoelectric stack actuators are commercially available in the market and are constructed using piezoelectric materials that convert applied electrical energy to mechanical energy and cause movement. Some examples of commercially available piezoelectric stack actuators include, but are not limited to, Piezomechanik GmBH manufactured PSt/150/14 . . . VS20 series piezoelectric stack actuators, PSt/150/20 . . . VS25 series actuators, PSt/150/7 . . . VS12 series actuators, and other similar piezoelectric stack actuators manufactured by other actuator manufacturers like Noliac®, and CEDRAT Technologies. The piezoelectric actuator 206, according to another embodiment of the present technique, is an amplified piezoelectric actuator that is commercially available in the market. Examples of Amplified piezoelectric actuators include, but are not limited to, APA®, XL series manufactured by CEDRAT Technologies. Alternatively, any piezoelectric material that converts electrical energy to mechanical energy, like Quartz, Topaz, Langasite, Sodium Tungstate, and that can be used to construct a stack of piezoelectric actuator can be used in the fluid compressor 102 as described in the present technique.
In yet another embodiment, the amplifying element 208 and the piezoelectric actuator 206 are selected based on a set of requirements that include, but are not limited to, degree of compression expected, volume of fluid in the compression chamber 202 per cycle, and time taken by the fluid compressor 102 to compress the fluid. In certain situations, a plurality of piezoelectric actuators along with plurality of amplifying elements can be stacked in parallel to cause displacement of the piston in the compression chamber 202.
The monitored fluid pressure and fluid temperature of the fluid in the compression chamber 202 are analyzed to determine a change in frequency or amplitude of the excitation signal provided to the piezoelectric actuator 206 in such a way that the piston 204 provides maximum strokes and/or the driving system operates in a frequency that is a resonant frequency of the piezoelectric actuator 206.
An output of the sensor 404 is used to determine at least one of fluid pressure, fluid temperature, and a piston stroke. The output of the sensor 404 is then split in two separate signals using a filter 406. One branch of the output of the sensor 404 is used to compute an amplitude of the displacement of the piston 204 in the compression chamber 202 by first converting the signal to a DC voltage signal through the converter 410. The second branch from the sensor 404 is fed to the PLL detector 408 to determine a frequency at which the piston 204 is being displaced in the compression chamber 202. The processor 412 determines a change that is required in an amplitude and/or frequency of the excitation signal provided by the excitation sub-system 402. The processor 412 is further configured to control the excitation subsystem in such a way that the excitation signal makes the piston 204 displace at resonant frequency.
Further for experimental testing of the fluid compressor 102, a spring with a stiffness of 1.2×105 N/m and a piezoelectric actuator with a constant of 4×106 N/m were selected. The experimental set-up results were compared against a performance of a fluid compressor using only the piezoelectric actuator with the same constant. It was observed that with varying amplitude of excitation signal; the displacement in the fluid compressor as described in the present technique was greater than displacement achieved by using only the piezoelectric actuator. For example, for a voltage of 40V using only the aforementioned piezoelectric actuator a displacement of 2.9 μm is achieved, whereas using the driving system of the fluid compressor 102 described in the present technique a displacement of 74.5 μm is achieved for a voltage of 40V. Similarly for an excitation signal of 120V usage of only the piezoelectric actuator provides a displacement of 42.7 μm whereas the driving system of the fluid compressor 102 of the present technique provides for a displacement of 326 μm. The degree of displacement amplification observed for various amplifying element stiffness has been observed to be at least 7.0.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The systems and methods illustrated are not limited to the specific embodiments described herein, but rather, components of the system may be utilized independently and separately from other components described herein. Further, steps described in the method may be utilized independently and separately from other steps described herein.
While only certain features of embodiments of the invention have been illustrated and described herein, many modifications and changes will occur by those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as they fall within the true spirit of embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 4061/CHE/2011 | Nov 2011 | IN | national |
