|Title of Invention||
CARBON NANOTUBE FLOW SENSOR AND ENERGY CONVERSION DEVICE
|Abstract||A method of near net shape forming of ceramidceramic compolite meolben by plasma spraying compriling the steps of feeding ceramic i powder into the plasma gun of a phlsma Ipraying apparatus by uling an inert ~rrier gas; spraying the resulting molten ceramic on to a substrate of a shape necessary to produce the shape of the laid member, the lurface of the said substrate heing knurled; and stripping off the plasma sprayed ceramic body from the substrate by means such as controlled leaching with acid or by cryogenic treatment.|
|Full Text||FIELD OF INVENTION
This invention relates to Carbon Nanotube Flow Sensor and Energy Conversion Device. Furtlier this invention relates to the field of flov\/ sensors. More particularly this invention relates to Carbon Nanotube as flow sensors, further this invention relates to the carbon Nanotubes as energy conversion devices.
PRESENT STATE OF ART
The present flow sensors are basically based on the following technology:
i) Particle imaging veloclmetry (PIV): In this technique colloidal particles are suspended in the liquid, and are imaged using fast Charge Coupled Device (CCD). PIV measures the velocity of particles entrained in a flowing fluid across a planar cross section of the flow. A laser light sheet is used to illuminate the small seed colloidal particles. A Charge Coupled Device (CCD) camera is used to electronically record the light scattered from the particles. The image is analyzed to determine the particle separation, and hence the velocity of the particles, which are assumed to follow the path of the flow.
ii) Doppler velocimetry : In this technique the flow velocity is measured from the ng Doppler shift of the scattered light from micron-sized particles suspended in the liquid. As the suspended particles entrained in a fluid pass through the intersection of two laser beams, the scattered light received from the particles fluctuates in intensity. The frequency of this fluctuation is equivalent to the Doppler shift between the incident and scattered light, and is thus proportional to the component of particle velocity, which lies in the plane of the two laser beams and is perpendicular to their bisector.
iii) Thermal Anenometry : A thermal anemometer measures fluid velocity by sensing changes in heat transfer from a small, electrically-heated sensor (wire or thin film) exposed to the fluid under study. The heated sensor is held at a constant temperature using an electronic control circuit. The cooling effect resulting from the fluid flowing past the sensor is compensated for by increasing the current flow to the sensor.
Iv) Vortex flow meters: A bluff body or shedder bar in the flow generates a street of vortices downstream. The Vortex Flow meter measures the flow by counting the number of vortices by ultrasonic/ piezoelectric sensors
v) The measurement of the differential pressure signal across an integrated fluidic restriction.: The flow rate measurement is done by measuring the differential pressure by two piezo-resistive pressure sensors, signal across an integrated fluidic restriction.
vi) Rotary Flow Meter : It works on the turbine wheels arrangement: The motion of the liquid through the turbine (commonly called the rotor wheel) causes the turbine to rotate. The rotational frequency of the turbine which depends upon the velocity of the liquid is measured either by an Electro-optical system or by electronically sensing the square wave pulse generated by magnets embedded in the vanes of the turbine.
The table below gives the comparative study of various types of the existing flow sensors :
It can be noted that all the existing flow sensors only the Rotary Flow Meter is an energy conversion device. It converts the mechanical energy of the liquid flow motion to electrical signal (current). However the device has a large size (-50 cm^) and operates at fairly high flow rates (: L/ ).
This invention overcomes the drawbacks in the present flow sensors and energy conversion devices by its very small size whereby it will be able to work in biological systems, not requiring external driving power as it can self-generate electrical signals, by having fast response and high sensitivity, capability to measure low velocities, being economical in construction and also because it causes only a small perturbation to the liquid motion during its operation. Further advantages of this invention over the present devices can be understood from the detailed description of the invention herein.
OBJECTS OF THE INVENTION
The primary object of this invention is to construct novel sensors for measuring the flow velocity of liquids, which can also be used as an energy conversion device.
It is another object of the invention to invent and design a flow sensor, which requires no external driving power, but can self generate an electrical signal (current).
It is another object of the invention to invent and design a flow sensor having fast response, electrical output (current), high sensitivity and capability to measure low velocities.
It is another object of the invention to invent and design a flow sensor, which requires no seeding of the liquid with colloidal particles
It is another object of the invention to design and construct a novel flow sensor device, which is economical in construction and efficient in operation and a substitute for traditional flow measuring devices.
it is another object of the invention to invent and design a flow sensor, which can work in biological systems.
It is another object of the invention to design a small device, which by the virtue of its small size and simplicity in construction causes very small perturbation to the liquid motion.
It is also another object of the invention to design a device, which results in considerable saving of cost.
Further object of the invention will be clear from the following description:
DETAILED DESCRIPITON OF THE INVENTION
The device proposed uses Carbon Nanotubes as the sensing material. These carbon Nanotubes are fullerene-related structures which can be thought of a shell(s) of rolled graphite sheet with a diameter of about one to two nm and a length in the order of several microns. Since the ratio of the length to the diameter of these materials is very large (: 1 ), they behave effectively as one dimensional systems. These nanotubes are of two types. Single Wall Carbon Nanotubes, and Multi Wall Carbon Nanotubes. Single Wall Carbon Nanotubes consists of a single
shell. Multi Wall carbon Nanotubes is made up of multiple concentric shells. It might also be said that the Single Wall Carbon Nanotubes exists in the form of a bundle. The bundles have a hexagonal lattice with a single- Single Wall Carbon Nanotube existing on the lattice points
We use the one-dimensional nature of the Carbon Nanotubes to detect flow motion. When a liquid flows over these nanotubes, the momenta of the liquid molecules are imparted to the charge carriers in the Nanotubes. This can cause either via phonons or via Coulombic interactions. Since Nanotubes are effectively one-dimensional system, there are only two directions along which these charge carriers can scatter i.e. either along the flow or opposite to the flow. The electrons have a preferential scattering along the direction of the flow. This causes the system to develop a current dependent on the velocity of the flow. Thus the proposed device made out of Single Wall Carbon Nanotubes produces electrical signals in response to liquid flow over it
It is also shown that Multi Wall Carbon Nanotubes can also be used, though with lower sensitivities. The sensitivity of the Multi-wall carbon Nanotubes is less than that of Single Wall Carbon Nanotubes approximately by a factor of 10.
BRIEF DESCRIPTION OF THE DIAGRAMS
Fig.1 shows the Construction of the device:
A thin layer (A) of the Nanotubes (Single wall / multi wall) is sandwiched between two metal electrodes ( B ,C ).
The metal electrodes (B, C) are used to provide ohmic contacts to the Nanotubes (A).
A thin layer of insulating varnish Is coated on the surface of the metal electrodes (B, C) exposed to the liquid environment (X1 X2 X3 X4 (dimensions are arbitrary)) to prevent electrical contact between the metal electrodes and the surrounding liquid.
The whole assembly is built on an insulating material base (D) of PTFE (= poly-tetrafluoroethylene).
Electrical contacts are taken out from the metal electrodes (B, C) using enameled copper wires (E). Thickness of the wires (E) is 10 microns. The using enameled copper wires (E) are used to export the current developed in the sensor to the current meter (F). The current meter (F) is placed outside the liquid environment.
The arrows marked by W indicates the direction of the flow velocity of the liquid.
Figure 2 shows characteristic curve of the flow sensor : The liquid used for the experiment is double distilled water. The current (I) developed by the sensor (plotted along the ordinate) with velocity (V) (plotted along the abscissa). The current plotted on the ordinate is in the units of microamperes while the velocity of water is plotted in the abscissa in the units of cm/sec. It is observed that the current developed in the sensor has a logarithmic dependence on the velocity of the liquid. The phenomenological relation relating the current (I) to the velocity (V) of the liquid is found to be: I=a log(/?V+l where a and (3 are constants , the values of which depend on the nature of the liquid.
It may further be mentioned that the sensor works for all liquids. However it was found that the sensitivity of the sensor was larger for polar liquids (water) as compared to non-polar liquids (e.g. methanol, propanol, etc)
Only the component of the velocity of the liquid along with the length of the nanotubes contribute to the generation of current by the sensor, this sensor is a deterministic indicator of the flow direction. Moreover the high sensitivity of the device at low velocities -10-5-10-3 cm/sec is enormously advantageous over available devices which work at much higher velocities. The response time of this device is less than 0.02 sec. The device by virtue of its small size and simplicity in construction causes very small perturbation to the liquid motion.
The figure shows a matrix (3x3) Snm( n=1,2,3: m = 1,2,3) of thin layer of carbon nanotubes (Single Wall / Multi wall) (A) is sandwiched between two metal electrodes ( B ,C ).
The individual elements of the matrix Snm is connected by enameled copper wires (E). Which provide path for electrical currents.
The metal electrodes (B,C) are used to provide ohmic contacts to the nanotubes (A).
A thin layer of insulating varnish is coated on the surface of the metal electrodes (B, C) exposed to the liquid environment to prevent electrical contact between the metal electrodes and the surrounding liquid.
The whole assembly is built on an insulating material base (D) of PTFE (= polytetrafluoroethylene).
The dimensions of all the matrix elements Snm i.e the Carbon Nanotube and the metal electrodes are same as that shown in Fig 1.
The entire assembly is suspended in a moving liquid environment
Linear combination of these sensors in series will form voltage source. The parallel combination of the devices will form current source.
For a typical 3x3-matrix energy conversion device the current developed across X&Y is about 50 microamperes and 10mV for liquid (water) velocities of 0.0001 cm/sec.
This energy conversion device works for all liquids. However the electrical signals (current/voltage) generated is larger for polar liquids (water) in comparison to non-polar liquids (alcohol)
Though the size of the prototype design of the device as shown in Figure 1 is ~ 1mm^. It is possible to fabricate this device at micron size i.e. size of a single Carbon Nanotube. The fabrication of the energy conversion device can be done on a single silicon wafer to increase the dimension of the matrix for giving larger magnitudes of current and voltages.
SALIENT FEATURES OF THE INVENTION
1. The device is a fast response, low velocity flow sensor having electrical output, which can be fabricated at mm dimensions, and possibly upto micron sizes.
2. The flow sensors can also be vised as an energy conversion device allowing it to be used as a voltage or a current source
3. The design generates considerable cost savings with its simple installation and energy efficient design, providing a viable alternative to traditional flow measuring devices.
4. The device works in small liquid volumes, in optically inaccessible places, and has a high sensitivity at low velocities. More over the sensing material (Carbon Nanotubes) is a carbon based compound and is bio compatible. Thus device can be used to measure flow velocities in biological systems/environments for e.g. blood.
1. A flow sensing device useful for measurement of liquid flow velocities along the direction of the liquid flow and irrespective of a nature of the liquid, said device comprising at least one carbon nanotube, said at least one carbon nonatube being arranged between at least two conducting elements, the two conducting elements connecting the least one carbon nanotube to an electricity measurement device for measuring electricity generated as a function of a rate of flow of the liquid.
2. A device as claimed in claim 1, wherein the carbon nanotube is a single wall type carbon nanotube.
3. A device as claimed in claim 1, wherein the carbon nanotube is a multiwall type carbon nanotube.
4. A device as claimed in claim 1, wherein the electricity measurement device comprises an ammeter to measure a current generated across opposite ends of said at least one carbon nanotube or a voltmeter to measure a potential difference across the opposite ends of the at least one carbon nanotube.
5. A device as claimed in claim 1, wherein the flow sensing device further comprises of a plurality of carbon nanotubes all connected in series or parallel with a single one of the two conducting elements each being provided at the respective extreme ends of the plurality of carbon nanotubes.
6. A device as claimed in claim 5, wherein the plurality of carbon nanotubes are connected in series so as to measure a potential difference generated across the ends of the plurality of carbon nanotubes,
A device as claimed in claim 5, wherein the plurality of nanotubes are connected in parallel to each other so as to enable determination of current generated across two ohmic contacts formed by the respective conducting elements at the ends thereof.
A device as claimed in claim 1, wherein the flow-sensing device further comprises a protective insulating coating to prevent electrical contact with the liquid.
A device as claimed as claimed in 1, wherein the flow sensing device is provided on a insulated base.
A device as claimed in claim 1, wherein the conducting elements each comprise of a wire.
A device as claimed in claim 1, wherein the conducting elements each comprises of an electrode.
A device as claimed in claim 1, wherein the conducting elements each comprises of a combination of wire connected to an electrode.
A device as claimed in claim 1, wherein the liquid whose flow velocity is determined is flowing water.
A device as claimed in claim 1, wherein the liquid is a biological fluid.
A device as claimed in claim 1, wherein the biological fluid is blood.
A flow-sensing device useful for measurement of liquid flow velocities as hereby substantially described with respect of the accompanying drawings.
|Indian Patent Application Number||466/MAS/2001|
|PG Journal Number||20/2006|
|Date of Filing||13-Jun-2001|
|Name of Patentee||M/S. INDIAN INSTITUTE OF SCIENCE|
|Applicant Address||BANGALORE 560 012|
|PCT International Classification Number||G01P 5/00|
|PCT International Application Number||N/A|
|PCT International Filing date|