Title of Invention

AN APPARATUS FOR MEASURING FLOW RATE OF A CONDUCTING LIQUID IN A PIPELINE.

Abstract

Measurement of the volume flow rate of a liquid flowing through a pipe line was made by using instruments such as obstruction type, target type, vortex typ, coriolis force type and apparatus employing electromagnetic flow measurement technique. Most of these conventional instruments are costly, power intensive and require close surveillance. The present invention provides an instrument which overcomes the above shortcomings and relates to an apparatus for measuring flow rate of a conducting liquid in a pipeline comprising - e) a plurality of electrodes A,B,C, and D made of metal or alloy chemically inert to the flowing liquid mounted on the flow head and connected to an A.C. power source (E); (f) recesses with close tolerance and situated diametrically opposite to each other for insertion of the said electrodes; (g) a signal conditioner (F) to amplify, rectify and filter the A.C. signal obtained from step (a); (h) a lineariser (G) which linearises the output of the signal conditioner and display the flowrate of the liquid in liter/minute as well gives rise to an output which linearly varies with flowrate, characterised in that the electrodes are held in place by terminal screws (1) connected to metallic probes (2) mounted on flow tube (3), which carry flanges (4) at predetermined locations.

Full Text

The present invention relates to an apparatus for measuring flow rate of a conducting fluid through a pipeline More particularly this invention pertains to a system for flow measurement of a conducting liquid by using plurality of electrodes attached to a pipeline through which the liquid flows. These electrodes are usually placed in a pipeline at diametrical distance apart from each other. Previously, for measuring the volume flow rate for a liquid different types of measuring instruments were used such as, for instance obstruction type, target type, vortex type, coriolis force type and so on. However for conducting liquid flow measurement, electromagnetic flow measurement technique has been found to be much more easier and less costly in comparison to the other flow measuring instruments stated earlier. Tn this technique, an intense magnetic field is produced in selected region of a flow tube by means of two coils excited from an AC or a DC source. Two sensing electrodes are placed in diametrically opposite positions inside the tube in physical contact with the flowing liquid. The magnetic field induces an e.m.f. in the liquid between the electrodes which is directly proportional to the flow. Most of the conventional equipment are costly, power intensive and require close surveillance. The principal object of the present invention is to provide an apparatus for measuring rate of flow of a conducting liquid which does not require any excitation coil, A further object of this invention is to provide an apparatus capable of generating signals, which are easily readable. A still further object of this invention is to provide an apparatus that is cost effective and can be made from indigenously available raw materials and electronic components. Another object of this invention is to provide an apparatus, which is compact and can be easily transported to work site, the only requirement being the availability or proximity of an A.C. power source. The foregoing objects are achieved by the present invention pertaining to an apparatus for measuring flow rate of a conducting liquid in a pipeline comprising in combination- (a) A flow head consisting of a uniform pipe section made of insulating material like fiber glass, PVC, hard plastic, nylon etc. fitted with end flanges; (b) a plurality of electrodes made of metals or alloys chemically inert to the flowing liquid mounted on the flow head made of insulating material and connected to a stabilised sinusoidal AC. source with constant amplitude and frequency and (c) a signal conditioner with a linearisation unit. The subject of invention relates to an apparatus, for measuring flow rate of a conducting liquid in a pipeline comprising - (a) a plurality of electrodes A,B,C and D made of metal or alloy chemically inert to the flowing liquid mounted on the flow head and connected to an AC. power source (E); (b) recesses with close tolerance and situated diametrically opposite to each other for insertion of the said electrodes ; (c) a signal conditioner (F) to amplify, rectify and filter the AC. signal obtained from step (a); (d) a lineariser (G) which linearises the output of the signal conditioner and display the flowrate of the liquid in liter/minute as well gives rise to an output which linearly varies with flowrate, characterised in that the electrodes are held in place by terminal screws (l) connected to metallic probes (2) mounted on flow tube (3), which carry flanges (4) at predetermined locations. The apparatus of this invention employs two pairs of identical metal electrodes inserted into the selected zone of the flow head which are in physical contact with the flowing liquid in such a way that they cause no obstruction to the flow. The electrodes are placed in the same horizontal axial plane of the horizontal pipe with each pair in diametrically opposite locations. The distance between the pairs along the pipeline is equal to the diameter of the pipe. The system of electrodes is excited by an AC, source and the output voltage has been found to be linearly related with flow under streamline condition and has a small non-linear zone under turbulent condition. This output voltage may be concerted to a DC. voltage signal by using a conventional signal conditioner. The non-linear zone is linearised by using a conventional linearisation unit.. The experimental data have been found to substantially conform to the theoretical equations discussed hereafter. THEORETICAL CONSIDERATIONS: The measurement of volume flow rate of a conducting liquid is generally done in the process industries by using electromagnetic flow meters since this technique is very simple compared to the other methods. There are other techniques of this flow measurement like absorption type, turbine type, coriolis force type, target type, vortex type, etc. But for the conducting liquid flow measurement, the electromagnetic flow measurement technique is much easier and less costly compared to the other measurements. In this technique an intense magnetic field is produced in the selected region of the flow tube by means of two coils excited from an AC. or a DC. source. Two sensing electrodes are placed on the diametrically opposite positions inside the tube in contact with the flowing liquid. The flowing liquid induces an e.m.f between the electrodes which is directly proportional to the flow. In the present instance, a novel technique of measurement of flow of a conducting liquid has been described. In this technique no excitation coil is required. This technique consists of four metal electrodes inserted into the selected zone of the flow which are always in contact with the liquid and produce no obstruction to the liquid flow. This electrode system is excited from an AC source with constant amplitude and frequency and the output signal has been found to be linearly related with the liquid flow under streamline condition along with a small non-linear zone at turbulent condition. This output voltage has been converted into a D.C. signal in the range 1-5 volts by using a signal conditioner and the non-linear zone is linearised by a linearisation unit. The design of the flow head and the calibration data before and after linearisation are reported here as an example. The experimental data are almost found to conform to the theoritical equations. When two metal electrodes are immersed in a conducting liquid the polarisation effect at each electrode produces an electric double layer at the metal liquid interface across which there exists a difference in potential along with a polarisation impedance. If a very small value of sinusoidal voltage signal be applied across the electrodes then this ac voltage signal is superimposed with the half cell potential at each electrode and accordingly the flow of ions from one electrode to the other occurs. The electric current due to this flow ions may be opposed by the DC. polarisation impedance and the ohmic impedance of the liquid between the two electrodes. Again if there is a flow of liquid from one electrode to the other then the flow of a liquid element along with the ions may be opposed by the viscous effect of the liquid produced by the velocity gradient. Hence the net impedance between the electrodes defined as the ratio of the supply voltage to the current may be assumed to be dependent on the electrode polarisation effect, ohomic effect and the velocity gradient of the liquid. The D.C. polarisation effect non-linearly depends on the electric current density and frequency of excitation and ohmic effect may be assumed constant for a particular system. When a liquid flows through a pipe line there exists a velocity gradient across the cross section of the pipe line which depends on the flow rate of the liquid if the polarisation effect and ohmic effect are assumed to be constant. In the present application the effect of four electrodes inserted into a conducting liquid flowing through the pipe line with proper insulation at the diametrically opposite positions has been studied. Since an impedance is always found to exist between any two of these electrodes, the four electrodes may be assumed to be equivalent to four lumped impedances as shown in Fig. 1 of the accompanying drawings. When a conducting liquid flows through the horizontal pipe under the streamline condition it may be assumed to have no component of its velocity along any diameter since it is perpendicular to the length of the pipe line. Hence the lumped parameter impedance Z1, between the diametrically opposite electrodes A & C and Z3 between the similar electrodes B & D may remain constant but the effective lumped impedance Z2 between A & B or Z4 between C& D tends to change due to the velocity gradient among the liquid layers between the electrodes. Hence if any two diagonally opposite electrodes be supplied from a very small value sinusoidal stabilised AC. source then the output across the other two electrodes may change due to the flow of the conducting liquid following the Wheatstone"s bridge network principle. So for a small value of supply voltage Vs at a fixed frequency applied between B and C and for a very high input impedance of the measuring circuit the bridge output voltage signal Vo between A & D may be given by Vo=VS(Z2Z4 -Z1Z3)./(Z1+Z4)(Z2 + Z3) (1) For a very small value of AC. voltage VS and for the identical electrodes Z1 - Z3 and Z2 - Z4. Let at any flow rate Qo of the liquid Z1 - Z3 = ZC , Z2 = Z4 =ZO and at any other flow rate Q slightly different from Qo the value of ZO changes to Zq. Hence the Taylor series expansion of Zq may be given by ZQ = ZO +(dZq/dQ)Qo ?Q + (d2ZQ/dQ2)Qo ? Q2 +.......... (2) where AQ = Q - Qo Let (dZq/dQ)Qo= µ and (d2ZQ/dQ2)Qo = b Hence Zq = ZO + µ ?Q + b ?Q2 +............... (3) Under streamline conditions, the value of b and the co- efficients of higher order terms may be assumed to be very small. Hence for a very small change (?Q) of flow rate, Zq may be given by Zq = ZO + µ ?Q (4) Hence putting Z1 — Z3 = ZC and Z2 = Z4 = Zq in equation no. (1) the bridge output voltage for a liquid flowrate Q is given by Vo = VS[(Zq-Zc)/(Zc + Zq)] (5) From the equation nos (4) and (5) we get Vo = VS[(ZO+ µ ?Q-ZC)/(ZC +ZO+ µ ?Q)] or Vo = VS[(ZO+ µ ?Q -ZC)/(ZC + ZO )(1+ µ ?Q)(ZC + ZO) Or, Vo = VS[(ZO+ µ ?Q -ZC)/(ZC + ZO )][(1+ µ ?Q)(ZC + ZO)]-1 Or, VO = VS[(ZO+ µ ?Q -ZC)/(ZC+ZO)][(1- µ ?Q(ZC + ZO)] [ since µ ?Q/( Zq + Zq) « 1] Or, VO = VS{l/(ZC+ZO )}[(ZO+ µ ?Q -ZC)/(ZC+ZO)][(1- µ ?Q(ZC + ZO)] Or VO = VS{l/(ZC + ZO )}[( ZO-ZC)+ µ ?Q -ZC)/(ZO+ZC)] µ ?Q(ZC + ZO)} - µ2 ?Q2/( ZC + ZO)] VO = {1/ (ZC +ZO )} [ (ZO - ZC) +{2ZC / ( ZO+ ZC)} µ ?Q ] VS - [µ2 ?q2 / (ZC+ZO)2] VS or VO = K1+K2 ?Q + K3 ?Q2 (6) where K1 =[ (ZO - ZC) / (ZO + ZC)] VS (7) K2 = [2µ ZC /(ZO + ZC)2]VS (8) K3= [µ 2/(ZC+ZO)2]VS (9) Under the streamline conditions, the term K3 = [µ2 / (Zc+ZO)2]VS may be assumed to be very small and hence for a very small change ?Q of flow rate, the equation no. (6) may be written as VO = K1 + K2 ?Q or VO=K1+K2(Q-QO) (11) Hence the bridge output voltage is linearly related with the incremental change in flow rate under the stream line condition. Under no flow condition Qq - 0 and for electrode separation along the pipe line equal to the pipe diameter, Zo = Zc , Hence K1 = 0 and the equation no. (11) is reduced to VO = K2Q (12) Thus the bridge output voltage is linearly related with flow rate when the flow rate is very small and streamline. Under the turbulent condition, the equation no. (3) may be given as Zq-Zq +µ ?Q +b ?Q2 Hence from equation (5) the bridge output voltage is given by Vo = VS[(Zq-Zc)/(Zc+Zq)] Or, VO = [(ZO + µ ?Q +b ?Q2 -Zc)/(ZO + µ ?Q + b ?Q2 +ZC)]Vs (13) So under turbulent condition, the bridge output voltage may be non linearly related with the incremental change of flow rate. But Zq+ Zq » µ ?Q + b ?Q2 for very small of ?Q.. So the bridge output voltage under turbulent condition may be given from equation no. (13) by the following equation. vo = [(Zo-zc +µ ?Q +b ?Q2 )/[(ZO + Zc) [1+(µ ?Q + b ?Q2 )./(zO+zc ) ] vS Or VO = VS[(Zo-Zc + µ ?Q +b ?Q2)/(ZO + ZC)]+(µ ?Q +b ?Q2 )./(Zo+Zc ) ]-1 Or, VO = VS[(ZO-Zc + µ ?Q +b ?Q2)/(ZO + Zc)][1-(µ ?Q +b ?Q2)./(ZO+Zc ) ] [ Since ZO+Zc » µ ?Q +b ?Q2] Or, VO = VS{1/(ZO + ZC)}[(ZO-ZC + µ ?Q + b ?Q2 )][1-(µ ?Q + b ?Q2)./(Zo+Zc)] Or, VO = VS { 1/ (ZO + ZC ) } [(ZO - ZC + µ ?Q + b ?Q2)] [ 1- (µ ?Q + b ?Q2 )./ (ZO+ ZC )] Or, Vo = VS{1/(ZO + ZC)}[(ZO-ZC +µ ?Q + b ?Q2) - (ZO-ZC)(µ ?Q + b ?Q2)./(ZO+ZC)-(µ ?Q + b ?Q2)2/(ZO+ZC)] or, VO = Vs{1/(Zo + Zc)}[(Zo-ZC + µ ?Q + b ?Q2) (ZO -ZC) µ ?Q /(ZO+ZC) - (ZO-ZC) b ?Q2)./(ZO+ZC) - µ2 ?Q2 /(ZO+ ZC )-2 µb ?Q3 /(ZO+ Zc ) b2 ?Q4 /(Zo+ Zc )] Or, VO = VS{1/(ZO + ZC)}[(ZO - ZC + µ ?Q{l-(ZO-ZC)/(ZO+ZC)} + [b { 1 - ( ZO - ZC) /(ZO+ ZC )} -µ2/(ZO+ ZC )]?Q2 - 2 µb ?Q3 /(ZO+ ZC )-b2 ?Q4) /(ZO+ ZC )] Or, VO = VS [{ZO- ZC )/(ZO+ ZC)] +[{2µZC/(ZO+ ZC)2}VS]?Q + [{(2ZCb- µ2)/(ZO+ ZC)2}VS]?Q2 - [{2µ b/( ZO+ ZC)2 } Vs ]?Q3 -[{b2 /(ZO + ZC)2}VS]?Q4 Or, VO = K1+K2?Q +K3 ?Q2-K4?Q3- K5 ?Q4 (14) where K1 =[ (ZO - ZC) / (ZO + ZC)] VS K2 = [2µZC/(Zo + ZC)2]VS K3 = [(2ZC b - µ2 ) / (ZO + ZC )2 ] VS (15) K4 =[2µb/(ZO+ ZC)2]VS (16) K5 =[b2/(ZO+Zc)2]VS (17) Since µ and b are small so K4 and K5 may be negligible and hence the above equation no. (14) may be written as VO = K2 + K2 ?Q + K3 ? Q2 (18) Hence the relation between the bridge output voltage and the incremental change of flow rate may be assumed to be parabolic under some conditions of turbulent flow. Starting from an initial flow rate Qo, if the flow rate be changed by a small value to Q in the turbulent region then the above (18) is reduced to Vo = K1 + K2 (Q-Qo) + K3 (Q- Qo) 2 (19) In the drawings accompanying this specification, the following figures have been used to illustrate the invention. Fig. 1 shows a cross- sectional view of the flow head of the flow meter with lumped parameter equivalent impedances Z1, Z2, Z3 & Z4 between four electrodes, wherein 1 denotes terminal screw, 2denotes metallic probe, 3 denotes flow tube and 4 denotes flange; Fig.2 shows a conventional block diagram of the signal conditioner and lineariser; Fig.3 shows a flow sheet diagram illustrating the deployment of the apparatus of the subject invention, Fig.4 is the experimental graph showing the calibration characteristic of the flow transducer The present invention will be further described by means of the following example, which is given by way of illustration and not by way of limitation. EXAMPLE The design of the flow head is very simple as shown in Fig.2 of the drawings. It involves only the selection of the electrode material that should be chemically inert to the flowing liquid. In the present design, the flow rate of water through a one-inch pipeline has been measured. The electrode material is selected to be stainless steel. Since the outside and inside diameters of the pipe are 25mm and 20 mm respectively so the length of each electrode is selected to be 15 mm with 2 mm insertion depth. The diameter of each electrode is selected to be 4 mm. These selections are made so that the obstruction to the flow is minimum. Each electrode is covered with PVC sleeve and is fitted with a 2-mm terminal screw, Each electrode is then mounted on the flow head along its line of symmetry through a proper hole so that the electrode may be inserted with tight fitting condition and there is no water leakage at the operating pressure. The small gap, if any, is sealed with Araldite. The length of the flow head is selected to be one meter with flange connections at both ends of internal diameter exactly equal to that of the pipe line. The flow head is connected with the pipe line through insulating gasket of Teflon sheet. The lumped parameter bridge circuit formed by the four electrodes as shown in Fig.(l), is supplied from a stabilised sinusoidal oscillator at 5V, 1000 Hz. Any two diagonal electrodes are taken as the bridge supply nodal points and the other two diagonal electrodes as the bridge output nodal points. The bridge output voltage signal is converted into 1-5 Volt dc signal by the signal conditioner. This signal is linearised by using the conventional lineariser unit as shown in the block diagram. The experiment is performed using tap water with the experimental set up as shown in Fig.4 of the drawings. The flow through the pipe line is increased in small steps and in each step the signal conditioner output and the lineariser output are noted in both increasing and decreasing modes. The static calibration graphs obtained from the experiment for the signal conditioner output and lineariser output are as shown in Fig.4 of the drawings. DISCUSSIONS The repeatability and reproducibility of the experimental data in the increasing and decreasing modes were found to be satisfactory.The calibration graph shown in Fig.5 of the drawing reveals that the nature of the graph is linear over large portion of the operating zone. The non-linearity may be due to the turbulence effect of flow The nature of the graph appears to follow the theoretically derived equations (II) and (18). The technique is very simple and requires no magnetic excitation field coils as in the case of an electromagnetic flow meter and hence it is very low cost. From the foregoing it may be seen that the invented apparatus and its mode of operation are quite simple and requires no magnetic excitation field coils as in the case of an electromagnetic flow meter. This renders the apparatus versatile, easy to operate and cost effective. Additional modifications and improvements of the present invention may also be apparent to those skilled in the art. Thus the particular combination of parts described and illustrated herein is intended to represent only one embodiment of present invention and is not intended to serve as limitations of alternative devices within the spirit and scope of the invention. I claim: 1. An apparatus for measuring flow rate of a conducting liquid in a pipeline comprising - (a) a plurality of electrodes A,B,C and D made of metal or alloy chemically inert to the flowing liquid mounted on the flow head and connected to an A.C. power source (E); (b) recesses with close tolerance and situated diametrically opposite to each other for insertion of the said electrodes; (c) a signal conditioner (F) to amplify, rectify and filter the A.C. signal obtained from step (a); (d) a lineariser (G) which linearises the output of the signal conditioner and display the flowrate of the liquid in liter/minute as well gives rise to an output which linearly varies with flowrate, characterised in that the electrodes are held in place by terminal screws(1) connected to metallic probes (2) mounted on flow tube(3), which carry flanges (4) at predetermined locations. 2. An apparatus as claimed in Claim 1, wherein the electrodes are made of stainless steel. 3. An apparatus as claimed in Claims 1 and 27 wherein each electrode is mounted on the flow head along its line of symmetry through recesses provided in the flow head. 4. An apparatus as claimed in claims 1 to 3, wherein flange connections are provided at both ends of the flow head having internal diameter exactly equal to that of the pipe line. 5. An apparatus for measuring flow rate of a conducting liquid in a pipe line, substantially as herein before described with particular reference to the accompanying drawings. Measurement of the volume flow rate of a liquid flowing through a pipe line was made by using instruments such as obstruction type, target type, vortex type, coriolis force type and apparatus employing electromagnetic flow measurement technique. Most of these conventional instruments are costly, power intensive and require close surveillance. The present invention provides an instrument which overcomes the above shortcomings and relates to an apparatus, for measuring flow rate of a conducting liquid in a pipeline comprising - (e)a plurality of electrodes A,B,C and D made of metal or alloy chemically inert to the flowing liquid mounted on the flow head and connected to an A.C. power source (E); (f) recesses with close tolerance and situated diametrically opposite to each other for insertion of the said electrodes ; (g) a signal conditioner (F) to amplify, rectify and filter the A.C. signal obtained from step (a); (h) a lineariser (G) which linearises the output of the signal conditioner and display the flowrate of the liquid in liter/minute as well gives rise to an output which linearly varies with flowrate, characterised in that the electrodes are held in place by terminal screws(1) connected to metallic probes (2) mounted on flow tube(3), which carry flanges (4) at predetermined locations.

Documents:

00536-kol-2004-abstract.pdf

00536-kol-2004-claims.pdf

00536-kol-2004-correspondence.pdf

00536-kol-2004-description (complete).pdf

00536-kol-2004-description (provisional).pdf

00536-kol-2004-drawings.pdf

00536-kol-2004-form 1.pdf

00536-kol-2004-form 18.pdf

00536-kol-2004-form 2.pdf

00536-kol-2004-form 3.pdf

00536-kol-2004-form 5.pdf

00536-kol-2004-letter patent.pdf

00536-kol-2004-pa.pdf

00536-kol-2004-reply f.e.r.pdf

536-KOL-2004-CORRESPONDENCE-1.1.pdf

536-KOL-2004-CORRESPONDENCE.pdf

536-KOL-2004-FORM 27.pdf