|Title of Invention||
"AN INSTRUMENTATION SYSTEM FOR MEASUREMENT OF VELOCITY OF SOLID LIQUID AND GASEOUS MATERIALS IN TWO PHASE FLOWS"
|Abstract||An instrumentation system for measurement of velocity of solid, liquid and gaseous materials in two-phase flows, characterised in that the system comprises a measuring unit which is provided with a capacitance sensing probe A, a bandpass amplifier B, a phase-sensitive detector C and an instrumentation amplifier D, such as herein described, and aa interfaced personal computer (PC), such as herewith described, said measuring unit and personal computer being arranged to operate in an inter-connected manner.|
|Full Text||The present invention relates to an instrumentation
solid, liquid and gaseous
system for measurement of velocity of/materials in two-phase
The invention relates more particularly to an instrumentation system for measuring velocity of materials
flowing simultaneously in tv/o phases, such as liquid-gas, gas-
solid, liquid-solid and/through a pipe line of electrical nonconducting material by using two non-intrusive type of capacitance sensing probes disposed outside the pipe line at a specified distance apart, amplifying the A.C. signal output of each sensing probe, detecting the in-phase component of the A.C. output signal of each sensing probe by a phase-sensitive detector to produce a B.C. voltage outout, amplifying the D-d. voltage output of each sensing probe by a low drift instrumentation amplifier having a means for adjustment of the amplification, converting analogue output of each instrumentation amplifier into corresponding digital signal by an A/D converter, calculating the velocity of materials in the statistical cross-correlation technique by a Personal computer (PC) acquiring the digitised signal from each A/D converter, corresponding to the A.C. signal output of each sensing probe.
The measurement of velocity of materials in two-phase flows is a challenging problem. At present no reliable means is available for directly measuring the velocity of materials in two-Phase flows. The industries requiring such measurements depend mostly on indirect methods, such as measurement of loss in weight of materials during the flows, which are of low accuracy.
The object of the present invention is to nrovide a reliable means for direct measurement of the velocity of materials in two-ohase flows as required by different industries, such as, steel plants, oower olante, nuclear plants and chemical olants.
The other object is to provide a means for locating the blockage area in the distributed oioe network of pneumatic material conveying systems.
The invention is described fully and Particularly with reference to the accomoanying drawings in which -
Figure 1 shows the circuit diagram of the measuring unit containing capacitance sensing probe 'A), bandpass amplifier (B), Phase sensitive detector (C) and instrumentation amplifier (D) used in the system;
Figure 2 shows the cross section of a oipe of
electrical non-conducting material fitted with a non-intrusive type sensing capacitor; and
Figure 3 shows an experimental set-up for measuring the velocity of gas bubbles moving in a gas-liquid two-phase
flow through a pipe line.
the measuring unit containing Referring to Fig. 1 tj/the capacitance sensing orobe A
consists of an electrical bridge whose armsare formed by the transformer 5, active capacitor 3 and dummy caoacitor A. The bridge is excited by a sinusoidal voltage source 1 of amplitude 0.2V (t>eak to peak) and frequency 10kHz connected across the orimary of the transformer, one terminal of which is connected to ground. The imba4anc« outout of the bridge is amnlified by an operational amplifier 2 provided within the sensing probe.
which is of tyoe ICL-800? having a high inout impedance and stabilised by capacitance feedback connection. The effect of stray capacitances on the bridge output is comoensated for by connecting relatively small canscitors across the active and dummy capacitors. The transformer is a balanced torroid of ratio 1:1:1 wound on a ferrite core.
The out out A-C. signal of the caoacitance sensing orobe A is supplied at the in out of the band oass amplifier 3 which contains an operational amolifier 6A of type OP-07 connected in feedback configuration to prevent any phase shift of the amplified signal output and acts as a voltage follower.
The phase-sensitive detector C contains two MOSFETS (metal oxide silicon field effect transistors), marked 7, 8, which are connected in common drain and common gate configuration, The signal outnut of the band pass amolifier is supplied to the co'.rjnon drain of the two MOSFETS through an operational amplifier 6B of type OP-0?. The MOSB'ET 7 if of N-type (BS170) and MOSPET 8 is of P-type (BS250).
A square wave generator -) of type LM-393 is provided in the phase-sensitive detector to generate square wave output signal in response to the A.C. signal of 10 KHz frequency supplied at its input from a ratio arm of the transformer 5 for synchronising the ohase-sensitive detector C. The generated square wave signal is supplied to the common gate of the two MOSFETS 7 and 8 through a current limiting resistor 10 of preferred value 1.2 kilo ohm to trigger the MOSFETS. MOSFET 7 conducts during the positive half cycle and MOSFET 8 conducts
uring the negative half cycle of the square wave signal. As a result the wave form of the A-C, signal supplied to the common drains of the MOSFETS oasses through the sources of the MOSFETS in synchronism with the square wave signal to produce a B.C. output voltage at the inout of the low Pass filter 11 which removes the A.C» components of the D.C. output voltage. The D*C. outout voltage of filter 11 is supplied to the input of the instrumentation amplifier D.
The instrumentation amplifier D contains two integrated circuits (1C) 12A, 12B, each being of type AD 624, which are connected in tandem forming respectively the first and second stage of the amolifier. The oreferred gain of the first stage, 1C (12A), is set at 200 and that of the second stage, 1C (12B), is programmable around 9. A low pass fitter 13 is orovided in-between the said first and second stages to eliminate the noise signal of 50 Hz frequency oresent in the j.C- inout voltage of the amolifier. The D.J. voltage obtained at the output of the second stage, 1C (12B), corresponds to capacitance -change of the active capacitor 3 in the corresponding capacitance sensing probe. The gain controls 14 and 15 are provided in the amplifier for calibrating the system in terms of velocity of the moving materials in two phase flows.
The circuit of the measuring unit shown in Fig. 1 is fabricated on a Printed Circuit Board in a compact form to make it suitable lor easy application in the measurement of velocity of moving materials in two phase flows. As already stated, two such measuring units are reauired to be fitted OB a
pipe line at a specified distance apart along the direction of the two ohase flow of materials.
The D,C. analogue outout voltages of the two measuring units are converted into corresponding digital outputs by means of two A/D (analogue to digital) converters interfacing a ^86 based personal computer (PC) operating at a speed upto 33 MHz through the necessary interfacing cards. The A/D converters and PC form an integral oart of the invented instrumentation system. To detect the fluid disturbances which are assumed to retain their identity between the locations of the two measuring points, a software for operation in the statistical cross-corelation mode is adopted. The calibration of the system in terms of the velocity of flow is carried out by means of the PC.
In carrying out exoeriments using the invented system, 12-bit resolution and eight-differential channel A/D cards are used for interfacing the PC. The conversion speed of the cards for a single channel is 60 KHz and the inout voltage required for the cards is _+ 5 volts or _* 10 volts. The response time of the system depends on the conversion time of the A/D cards and the speed of the PC. The maximum sampling speed achieved through the software developed in C language is 30 KHz with two channels, which is also the limiting soeed of the A/D cards. The acquired data is storeo in hard disk for further processing. For PC with clock speed belov; 20 ?4Hz, the data acquisition routine is written in C and assembly languages to achieve a 30 KHz data sampling speed. The data acquisition
routine has the facility to select the sampling soeed based on the expected maximum velocity of the two phase flow.
The signals obtained from the two measuring units are Passed through an 'average subtraction1 routine. The output signals of the average subtraction routine are filtered to reject the noise signal components thereof. The standard deviations of the 'Gaussian window length' are selected according to the sampling speed and the total number of samples tested. The means for automatic adjustment of the Gaussian window length depending upon the sampling speed and total number of samples tested is provided in the software used. The filtered signals are cross-correlated together to estimate the velocity of the two Phase flow.
If x(t) and y(t) reoresent the two signals received from the two capacitance sensing probe? disposed 'upstream1 and 'downstream1 respectively in the two Phase flow under measurement, then the cross-correlation function between the two signals is :
(1) where Rxy (to) is the value of the cross-correlation function when the upstream signal is delayed by a time to, T is the sampling duration of the signals and t if an instant during the sampling period.
Rxy attains its maximum value when to is equal to the transit time tx of the material to flow from the 'upstream probe' to the 'downstream probe*. Hence the flow rate is :
where L is the spacing between the two probes.
The velocity of the two phase flow obtained from relation (2) is stored in a file of the computer and also Played on a monitor. The graphical outputs for different signals can be retrieved as and when required.
Various probe configurations such as strip, ring, parallel plate, double helix are adopted in known capacitance sensors. With a view to attaining an increased capacitance sensitivity and ease of fabrication, the active and dummy capacitors of each probe have been designed by attaching a pair of curved metal plates on the surface of a pipe of an insulating material like perspex/glass and of round cross section.
From the cross section of the pipe containing the capacitor 3 or capacitor 4, shown in Fig. 2, it is found that
the capacitor comprises a hollow pipe section 16 of insulating
glass material such as perspex^/of internal radius R. and external
radius R,,, a screen 18 of electrical conductor such as stainless steel and two curved metal plates 17A, 173 such as of stainless steel placed in diameterically opposite positions on the outside surface of tube 16 each subtending an angle X at the centre of the tube, being glued thereto and wrapped with an insulating material like paper, and a metal screen 18 such as of stainless steel of external radius R, covering the oipe section containing the capacitor Plates. The screen is connected to ground.
The preferred design parameters of the capacitor are :
In a oarticular capacitor, R^ is 10mm R2 is 11mm R-z is 12mm and each of plates 17A, 17B is of curved length 15mm along, the outside circumference of nioe 16, width 10mm along the axis of the oioe 16 and thickness 0.04 mm. The wrapping paoer is of thickness 1mm. The screen is of stainless steel sheet of thickness 0.04mm.
Any initial difference in the active and dummy capacitors is removed by connecting additional caoacitors of relatively small capacitance across the active and dummy caoacitors of a probe.
In the experimental set-uo shown, in Fig. 3 the velocity of gas-liquid flow is measured using the invented system. The set-uo comprises a riser tube 18 through which a mixture of air and water rises from its bottom 19 to its top 20. At the bottom of the riser tube, comorested air from compressor 21 is supplied through control valves 22, 23, and nozzle 25, and water is fed by gravity from reservoir 26. The air-water mixture formed at the outlet of the nozzle being of lower density comnared with water moves uoward to the top 20 of the riser tube and then downward to allow the air to escape into the atmosphere and the water to return to the reservoir 26. The orobe of one measuring unit is disposed in the upstream position 27 and the probe of the other measuring unit is disposed in the downstream position 28.
For determining the velocity of a bubble moving upward through the riser tube, gas slugs in the form of cylindrical bubbles are injected into the compressed air by means of a hypodermic syringe 25.
The velocity of the bubbles in the riser tube is estimated from the empirical relation :
where g is the acceleration clue to gravity (981cm/sec );
d is the internal diameter of the riser tube, which
is 1cm in the set-uo used; and V is the velocity of the bubble in cm/sec.
The velocity estimed from relation (3) is 10.96 cm/sec, which comoares closely with the velocity 9.^3 to 9*63 cm/sec, determined by using the invented system for bubbles of different sizes.
We Claim :-
1. An instrumentation system for measurement of velocity
of solid, liquid and gaseous materials in two-phase flows,
characterised in that the system comprises a measuring unit which
is provided with a capacitance sensing probe A, a bandpass
amplifier B, a phase-sensitive detector C and an instrumentation
amplifier D, such as herein described, and an interfaced personal
computer (PC), such as herewith described, said measuring unit
and personal computer being arranged to operate in an inter
2. The system as claimed in claim 1, wherein the capacitance
sensing probe A contains an electrical bridge formed by a ratio
ana transformer 5, active capacitor 3, dummy capacitor 4 and
operational amplifier 2.
3. The system as claimed in claim 2, wherein the transformer 5 is a balanced torroid of ratio 11:1 wound on a ferrite core*
4. The system as claimed in claim 2, wherein each of active and dummy capacitors 3, 4 is formed by attaching a pair of curved metal, such as stainless steel, plates 17A, 17B of required thickness on the surface of a fluid conveying pipe 16 of electrical insulating material, perspex/glass, and of round cross-section, in diametrically opposite positions by glueing, wrapping the metal plates with paper of thickness 1mm, and covering the pipe section containing the wrapped metal plates with a metal, such as stainless steel plate of thickness 0.04mm acting as a screen and being connected to ground.
5. The system as claimed 1m claim 4, wherein each curved
metal plates 17A, 17B is of curved length 15mm along the outside
circumference of the pipe and width 10mm along the axis of the
pipe and of thickness 0.04mm, and the pipe is of outside radius
11mm and inside radius 10mm.
6. The system as claimed in claim 1, wherein the band pass
amplifier B contains an operational amplifier 6A of type OP-07,
connected in feedback configuration.
7. The system as claimed in claim 1, wherein the phase-
sensitive detector C contains tv/o MOSFBTS (metal oxide silicon
field effect transistors) 7,8 which are connected in common drain
and common gate configuration, MOSFET 7 being of N-type (BS170)
and MOSFET 8 of P-type (BS250); an operational amplifier 6B for
amplifying the signal received from the output of the band pass
amplifier B and applying the amplified output to the common drain
of the two MOSFBTS 7,8; A square wave generator 9 of type LM-393
for generating a square wave output signal in response to the A.C.
signal of 10 KHz frequency supplied at its input from a ratio arm
of transformer 5 and applying the output signal to the common gate
of the two MOSFBTS; and a low pass filter 11 for removing the A. C.
components of the D. C. voltage obtained from the sources of the
two MOSFBTS at the output of the phase-sensitive detector C.
8. The system as claimed in claim 1, wherein the
instrumentation amplifier D contains two integrated circuits (1C)
12A, 12B, each of type AD 624, which are connected in tandem to
form respectively the first and second stage amplifier having a
set gain of 200 and a programmable gain of 9; a low pass filter 13
between the said first and second stages of the amplifier formed by IC's 12A, 12B to eliminate the noise signal; and controls 14, 15 for calibrating the system in terms of velocity of moving materials in two phase flows.
9. The system as claimed in claim 1, wherein the analogue to Digital (A/D) converters used are of 60 KHz conversion speed for a single channel with input voltage + 5 volts or jt 10 volts.
10. The system as claimed in any preceding claim, wherein the personal computer (PC) is 486 based, operating at speed upto 33 MHz, interfaced with a 12-bit resolution and eight-differential channel analogue to digital (A/D) converter and is provided with a software suitable for operation of the PC in the statistical cross-correlation mode.
|Indian Patent Application Number||481/DEL/1997|
|PG Journal Number||13/2009|
|Date of Filing||25-Feb-1997|
|Name of Patentee||STEEL AUTHORITY OF INDIA LTD.|
|Applicant Address||RESEARCH & DEVELOPMENT CENTRE, IRON & STEEL ENTERPRISE, ISPAT BHAWAN,LODI ROAD, NEW DELHI-110003, INDIA.|
|PCT International Classification Number||G01P 5/08|
|PCT International Application Number||N/A|
|PCT International Filing date|