Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Reexamination Certificate
2002-11-29
2004-04-13
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
Reexamination Certificate
active
06718834
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a carbon nanotube—based liquid flow sensing device. The present invention also relates to a method for measuring the flow of a liquid using carbon nanotube. More particularly, the present invention relates to a method for measuring the velocity of a liquid along the flow thereof as a function of the current/voltage generated in carbon nanotube due to the flow of the liquid along the surface thereof. In another application, the present invention also relates to a device for the conversion of energy comprising using at least one carbon nanotube and also to a method for the conversion of kinetic energy of a liquid flow into electrical energy using one or more carbon nanotubes.
BACKGROUND OF THE INVENTION
The measurement of liquid velocity along the direction of flow is of significant importance in several applications. For example, an accurate determination of velocity of ocean or river tides along the direction of the flow is important in predicting tidal patterns, potential weather fluctuations, etc. Other areas where such liquid velocity determination along the flow are of importance include medical applications such as in cardiac and renal therapeutics.
Several methods are known in the art for the measurement of liquid velocity along its flow. For example, one method of low speed flow field velocity determination comprises particle imaging velocimetry, which comprises suspending colloidal particles in the liquid. A fast charge coupled device is provided across the planar cross section of the flow in order to image the colloidal particles. The small seed colloidal particles are illuminated using a laser light sheet. The charge coupled device camera electronically records the light scattered from the particles. Analysis of the image obtained enables determination of the particle separation, and thereby the velocity of the particles.
However, this method has several disadvantages. The primary disadvantage is the underlying assumption that the movement of all the colloidal particles assume the direction of the flow. This is not necessarily true in the case of large sized particles or in the case of very low velocities. Thus, the application of this method is limited to velocities of greater than 0.02 m/s. It is thus, also important in this method, to ensure that the particle size is small enough to ensure that the particle follows the flow of the liquid but at the same time is large enough to effectively scatter light. The equipment required (lasers, CCD cameras) is also large in size. Another disadvantage is that the method is dependant entirely on image analysis and thereby on the analysis algorithms. Since the particle imaging velocimetry method measures the velocity of the colloidal particles and there is no direct digital signal corresponding to the liquid velocity, the flow velocity of pure liquid cannot be measured. The method also is not appropriate for systems where optical access is absent and for liquids that are turbid.
Another method known in the prior art for liquid velocity measurement is Doppler velocimetry which comprises measurement of the Doppler shift of scattered light from micron sized particles suspended in the liquid. The method relies on the fluctuation in the intensity of scattered light received from colloidal particles entrained in a liquid when passing through the intersection of two laser beams. The Doppler shift between the incident and the scattered light is equal to the frequency of the fluctuation of intensity which is therefore proportional to the component of particle velocity lying in the plane of the two laser beams and perpendicular to their bisector. However, this method also suffers from several disadvantages. The method is operable where the particle velocities are greater than 0.001 m/sec. This method also requires large and expensive equipment such as a plurality of lasers and digital counters. Another significant disadvantage of this method is that it is restricted to a single point measurement with the data obtained being completely dependant on the particle arrival in the measuring volume and not on user requirements. Particle velocity and its derivatives differ in vortex cores and across shocks. Similar to particle imaging velocimetry, this method also requires that the particle size be small enough to flow along the liquid flow path easily but large enough to produce the required signal above the noise threshold. This method also does not work in systems where optical access to the liquid flow path at the measurement volume is absent. Signal level depends on the detector solid angle. As a result while the Mie scattering intensity is substantially better in the forward direction, it is difficult to set up forward receiving optics which remain aligned to the moving measurement volume. Greater noise at higher speed with radio frequency interference is possible. Again, similar to the PIV method, the flow velocity of unseeded liquids cannot be measured since there is no direct digital signal corresponding to the liquid velocity. This method is appropriate only for liquids containing colloidal particles and not for clear liquids.
Another known method to measure fluid velocity comprises the measurement of heat transfer change using a electrically heated sensor such as a wire or a thin film maintained at a constant predetermined temperature using an electronic control circuit. The heat sensor is exposed to the fluid whose velocity measurement is to be taken. The fluid flowing past the sensor cools the heat sensor which is compensated by the an increased current flow from the electronic control circuit. Thus, the flow velocity of the fluid can be measured as a function of the compensating current imparted to the heat by the electronic control circuit. However, in this method a slight variation in the temperature, pressure or composition of the fluid under study can result in erroneous readings. In order to maintain a relatively accurate measurement from the heat sensor, it is also necessary to provide complicated compensating electronics for constantly calibrating the sensor against any change in environmental parameters. In addition, even such compensating electronics can be subject to error. The sensor generally is operable at fluid velocities of greater than 0.01 m/s and not for very low velocities. At low velocities, the convection currents in the liquid cause a malfunction in the sensor.
Another method of liquid velocity measurement comprises calculating the velocity of the liquid flow as a function of vortices created downstream in the liquid using a bluff body or a shedder bar. The vortices are counted using piezoelectric sensors or ultrasonic sensors. This method is useful for measuring only flow rates greater than 0.001 L/s. The method focuses on measuring volumetric flow rates and not directly measuring flow velocities. Thus while useful for small flow rates, the device is not appropriate for liquids with high viscosity.
It is also known to calculate flow liquid velocity in high viscosity liquids using a plurality of pairs of piezo-resistive pressure sensors across an integrated fluid restriction in order to measure the differential pressure. However, while this device is operable at flow rates of the rate of a few &mgr;L/s, the volumetric flow rates and not flow velocities are measured. Also, this method is suitable for measurement of small flow rates only.
Yet another method for the measurement of flow velocities comprises the use of rotary flow meters which work on an arrangement of turbine wheels. The motion of the liquid through the turbine, otherwise called the rotor wheel, causes the turbine to rotate. The rotational frequency of the rotor wheel depends on the velocity of the liquid and is measured using either an electro-optical system or by electronically sensing the square wave pulse generated by magnets embedded in the turbine vanes. The size of the sensor arrangement is also to the order of 50 cm
3
. The rotary flow meter is suitable for use in cooling systems ir
Ghosh Shankar
Sood Ajay Kumar
Indian Institute of Science
Lefkowitz Edward
Nixon & Vanderhye P.C.
Thompson Jewel V.
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