DESC:Field of Invention
The present invention relates to the development of instrumentation to identify two phase flow regime. In particular, the present invention discloses a single LED Photodiode pair to determine two phase flow regime and two LED and single photodiode to characterize the two phase flow regime length and flow regime velocity.

Background of the Invention
A phase may be a solid or liquid or a gas often described as the three states of matter. The study of two phase flows especially those of gas-liquid are of immense significance in a variety of industrial relevance. Typical examples are heat exchangers, refrigeration systems, fluid separation and electronic cooling. Flow through pipes of small diameters of the order of 2-4 mm is also attaining importance. There exists a boundary which distinguishes the micro flows from macro flows which is yet to be clearly understood. The effects are explained based on the effects of gravity, surface tension and viscosities.

There have been a number of studies to determine the properties of such flows. The characteristics of air-water two-phase flow in small diameter vertical tubes was studied by Mishima and Hibiki [1]. John and Srinivas [2] scrutinized the consequence of tube diameter and shape on flow regime transitions in small hydraulic tube diameters for two-phase flow. Venkatesan et al. [3], studied the effect of diameters on various flow regimes and presented a flow map for pipes of mini channel diameters. The study gave a clear explanation of differences in the types of flow regime observed when the diameter of the pipe is less than 2mm. A variety of intrusive as well as non intrusive techniques have been designed in the past for determining properties like the flow regime, volume fraction and two phase flow velocity. Methods based on X-ray or Gamma-ray extinction can be used for measuring the gas to liquid volume ratio. Kumar et al. used Gamma ray tomography to measure the void fraction [4]. Ikeda et al. [5] used X ray to characterize the two phase flows. These methods necessitate some sophisticated instrumentation techniques. An electrical non-intrusive sensor for computing the mean permittivity of two-phase mixtures is dealt with capacitance sensors [6-10]. This method is reasonably accurate and non-invasive in comparison with the erstwhile techniques. The major disadvantage of this method is that the results are pragmatic in determining the flow regime only after some progressive computations, since data is made available only for void fractions. Some explicit analysis has to be carried out to acquire the results from this technique. This necessitates the requirement to develop an optical sensor where the results can be validated with human visualisations.

Attempts were made to use the technique of digital image processing to study the two phase flows [12-16]. This method gave a different stance to the problem of flow regime identification. On the contrary the complexity of measurement of two phase velocity and removal of noise stressed the need for advancement in the field of flow measurements. Optical measurement technique using the concept of illumination of flow channel was patented by in Delville et al. [17]. The method uses at least two detectors and the time lag involved in receiving the sensor output was used to calculate the flow regime velocity and length. However it was not possible to the calculate the nature of two phase flow regime with this as the method involved the capturing of difference in current magnitude between the two detectors.

Thus it can been seen that though different two phase flow regime measurement techniques have been proposed, the complexities involved in them and the inherent difficulty in identifying the two phase flow regime necessitates development of simple yet precise technique. The proposed technique uses LED and single photodiode accompanied by the use of Volatage Frequency distribution to identify the two phase flow regime.

Summary of the Invention
Accordingly, the present invention in one embodiment provides a method for assisting determination of a two-phase flow regime through at least one light-emitter detector pair, said method comprising the steps of:
illuminating a flow-channel carrying a two-phase material through at least one light-emitter; and
detecting a light beam reflected/refracted by said material using at least one light detector, wherein said detection includes recording a voltage produced by said light detector through a data acquisition system.

In other embodiment, the present invention provides method for determining a two-phase flow regime through at least one light-emitter detector pair, the method comprising:
illuminating a flow-channel carrying a two-phase material through at least one light-emitter; and
detecting a light beam reflected/refracted by said material using at least one light detector, wherein said detection includes recording a voltage produced by said light detector through a data acquisition system.to determine the flow-regime of said material within the flow-channel;
determining a time scope and a frequency-distribution variation in terms of said voltage through said data acquisition system; and
analysing at least one of said determined time scope, and said frequency-distribution variation to determine the flow-regime of said material within the flow-channel.

In another embodiment, the present invention provides an apparatus for assisting determination of a two-phase flow regime through at least one light-emitter detector pair, the apparatus comprising:
at least one light emitter for illuminating a flow-channel carrying a two-phase material;
at least one light detector for detecting a reflected/refracted light beam from said two-phase material; and
a data acquisition means for recording a voltage produced by said light detector.

In yet another embodiment, the present invention provides a method for determining a two-phase velocity, the method comprising:
illuminating a transparent conduit carrying a two phase material with a first light source and a second light source, the first and the second light sources being spaced apart from each other by a known distance;
detecting a first light beam and a second light beam using a light detector, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from an interface between the first material and the second material and the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the interface between the first material and the second material;
determining a time difference between the detection of the first light beam and the detection of the second light beam; and
determining a velocity of flow of the first material through the transparent conduit based on the time difference.

In still another embodiment, the present invention provides an apparatus for determining two-phase velocity, the apparatus comprising
a first light source;
a second light source placed at a known distance from the first light source, the first light source and the second light source being adapted to illuminate the transparent conduit carrying the two phase material;
a light detector adapted to detect a first light beam and a second light beam, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from an interface between the first material and the second material and the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the interface between the first material and the second material; and
one or more modules for determining:
a time difference between the detection of the first light beam and the detection of the second light beam; and
a velocity of flow of the first material through the transparent conduit based on the time difference.

In further embodiment, the present invention provides a method for determining a length of at least one phase flowing through a transparent conduit, said method comprising the steps of:
illuminating the transparent conduit carrying a two phase material with a first light source and a second light source, the first and the second light sources being spaced apart from each other by a known distance;
detecting a first light beam, a second light beam and a third light beam using a light detector, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a first interface between the first material and the second material, the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the first interface between the first material and the second material, and the third light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a second interface between the first material and the second material;
determining a first time difference between the detection of the first light beam and the detection of the second light beam;
determining a velocity of flow of the first material through the transparent conduit based on the first time difference;
determining a second time difference between the detection of the first light beam and the detection of the third light beam; and
determining a length of a first material flowing through a transparent conduit based on the second time difference and the velocity of flow of the first material.

In still another embodiment, the present invention provides an apparatus determining a length of at least one phase flowing through a transparent conduit, said device comprising:
a first light source;
a second light source placed at a known distance from the first light source, the first light source and the second light source being adapted to illuminate the transparent conduit carrying the two phase material;
a light detector adapted to detect a first light beam, a second light beam and a third light beam, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a first interface between the first material and the second material, the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the first interface between the first material and the second material, and the third light beam corresponds to a reflection/refraction of the light produced by the first light source or the second light source and emanating from a second interface between the first material and the second material;
one or more modules configured for determining:
a time difference between the detection of the first light beam and the detection of the second light beam;
a velocity of flow of the first material through the transparent conduit based on the time difference;
a second time difference between the detection of the first light beam and the detection of the third light beam; and
a length of a first material flowing through a transparent conduit based on the second time difference and the velocity of flow of the first material.

To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended figures. It is appreciated that these figures depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying figures.

Brief Description of Figures:
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying figures in which like characters represent like parts throughout the drawings, wherein:
Figure 1 shows a flow chart corresponding to a first embodiment of the invention;
Figure 2 shows another flow chart corresponding to a second embodiment of the invention;
Figure 3 shows a detailed internal construction of the system in accordance with the first and second embodiments of the present invention;
Figure 4 shows a flow chart corresponding to a third embodiment of the invention;
Figure 5 shows a detailed internal construction of the system in accordance with the third embodiment of the present invention;
Figure 6 shows a flow chart corresponding to a fourth embodiment of the invention;
Figure 7 shows a detailed internal construction of the system in accordance with the fourth embodiment of the present invention;
Figure. 8 ilustrates a principle of detection in designed optical sensor;
Figure. 9 illustrates an exemplary emitter circuit;
Figure. 10. illustrates an exemplary receiver circuit;
Figure. 11 illustrates an exemplary schematic diagram of the experiment conducted to deletine the two-phase flow regime ;
Figure. 12 illustrates Bubbly flows based two-phase flow regime;
Figure. 13 illustrates a time scope for bubbly flows based flow-regime;
Figure. 14 illustrates a frequency distribution for bubbly flow based flow-regime;
Figure. 15 illustrates slug flows based flow-regime;
Figure. 16 illustrates a time scope for slug flows based flow regime;
Figure. 17 illustrates a frequency distribution for slug flows;
Figure. 18 illustrates slug annular flows based flow-regime;
Figure. 19 illustrates a time scope for slug annular flows based flow-regime;
Figure. 20 illustrates a frequency distribution for slug annular flows;
Figure 21 illustrates stratified flows based flow-regime;
Figure 22 illustrates a time scope for the Stratified flows;
Figure 23 illustrates a frequency distribution for the Stratified flows;
Figure 24 illustrates wavy stratified flows based flow regime;
Figure 25 illustrates a time scope for the wavy stratified flows;
Figure 26 illustrates a frequency distribution for Wavy stratified flows;
Figure 27 illustrates measurement of Slug velocity as a part of deletermination of two-phase velocity;
Figure 28 illustrates measurement of the Slug Velocity-time scope;
Figure 29 illustrates measurement of Slug length as a part of deleternination of length of one of the phase in a two-phase liquid; and
Figure 30. Illustrates measurement of the Slug length-time scope;

Further, skilled artisans will appreciate that elements in the figures are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the figures with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

Detailed Description:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the figures and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present invention will be described below in detail with reference to the accompanying figures.

Figure 1 illustrates a method for assisting determination of a two-phase flow regime through at least one light-emitter detector pair, in accordance with a first embodiment of the present invention. The method comprises illuminating (step 102) a flow-channel carrying a two-phase material through at least one light-emitter; and detecting (step 104) a light beam reflected/refracted by said material using at least one light detector. The detection includes recording a voltage produced by said light detector through a data acquisition system.

Figure 2 illustrates a method for determining a two-phase flow regime through at least one light-emitter detector pair, in accordance with a second embodiment of the present subject matter. The method comprises illuminating (step 202) a flow-channel carrying a two-phase material through at least one light-emitter; detecting (step 204) a light beam reflected/refracted by said material using at least one light detector, wherein said detection includes recording a voltage produced by said light detector through a data acquisition system; determining (step 206) a time scope and a frequency-distribution variation in terms of said voltage through said data acquisition system; and analysing (step 208) at least one of said determined time scope, and said frequency-distribution variation to determine the flow-regime of said material within the flow-channel.

Figure 3 shows a detailed internal construction of an apparatus (300) in accordance with the first and second embodiments of the present invention. The apparatus (300) comprises: at least one light emitter (302) for executing the steps 102 and 202, and at least one light detector (304) and a data acquisition system (306) for executing the steps 104 and 204. Further, the apparatus (300) comprises other modules (308) for executing the steps 206 and 208.

In another aspect of the invention, the modules (308) for determining the time scope, frequency distribution, and the flow-regime of the two-phase material can be a single integrated module.

Figure 4 illustrates a method for determining a two-phase velocity in accordance with a third embodiment of the invention. The method comprises the steps of: illuminating (step 402) the transparent conduit carrying the two phase material with a light source; detecting (step 404) a first light beam and a second light beam using a light detector, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from an interface between the first material and the second material and the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the interface between the first material and the second material; determining (step 406) a time scope and a frequency distribution of the voltage thus produced by the light detector; and analysing (step 408) the time scope and the frequency distribution to determine a type of flow of the two-phase material inside the transparent conduit.

Figure 5 shows a detailed internal construction of an apparatus (500) in accordance with the third embodiment of the present invention. The apparatus comprises a first light source (502) and a second light source (504) placed at a known distance from the first light source, wherein the first light source and the second light source being adapted to perform the step 402. A light detector (506) is adapted to discharge the step 404. Further, one or more modules (508) are configured for discharging the steps 406 and 408.

In an aspect of the invention, the modules (508) for determining a time difference between the detection of the first light beam and the detection of the second light beam and the module for determining a velocity of flow of the first material can be a single circuit.

Figure 6 illustrates a method for determining a length of at least one phase flowing through a transparent conduit, in accordance with a fourth embodiment of the present invention. The method comprises the steps of: illuminating (step 602) the transparent conduit carrying a two phase material with a first light source and a second light source, the first and the second light sources being spaced apart from each other by a known distance; detecting (step 604) a first light beam, a second light beam and a third light beam using a light detector, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a first interface between the first material and the second material, the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the first interface between the first material and the second material, and the third light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a second interface between the first material and the second material; determining (step 606) a first time difference between the detection of the first light beam and the detection of the second light beam; determining (step 608) a velocity of flow of the first material through the transparent conduit based on the first time difference; determining (step 610) a second time difference between the detection of the first light beam and the detection of the third light beam; and determining (step 612) a length of a first material flowing through a transparent conduit based on the second time difference and the velocity of flow of the first material.

In an implementation, the third light beam as depicted in step 604 corresponds to a reflection/refraction of the light produced by the second light source and emanates from a second interface between the first material and the second material;

Fig. 7 illustrates an apparatus (700) for determining a length of at least one phase flowing through a transparent conduit, in accordance with a fourth embodiment of the present subject matter. The apparatus (700) comprises a first light source (702) and a second light source (704) placed at a known distance from the first light source (702), wherein these first and second light sources are equivalent to the light sources (502, 504) and configured to execute the step 602, which is analogous to the step 402. A light detector (706) is analogous to the light detector (506) and is adapted to execute the step 604, which is equivalent to the step 504. Further, one or more modules (708) are configured to execute the steps 608, 610 and 612.

In an aspect of the invention, two or more of (a) the module for determining a time difference between the detection of the first light beam and the detection of the second light beam, (b) the module for determining a velocity of flow of the first material, (c) the module for determining a second time difference between the detection of the first light beam and the detection of the third light beam, and (d) the module for determining a length of a first material flowing through a transparent conduit can be an integrated module.

Fig 8 illustrates an outline of the overall sensing principle followed behind the claimed subject matter. An optical sensor consists of two main components-emitter (302, 502, 602, 604, 702, 704) and receiver (304, 504, 606, 706). A light emitting diode (LED) of high wavelength (red colour around 700 nm) is used as the emitter (302, 502, 602, 604, 702, 704). Red colour was used since the sensitivity of a photodiode is maximum in this range of wavelength.

Fig 9 shows the emitter circuit (302, 502, 602, 604, 702, 704) used. The photodiode in Fig. 10 acts as a receiver (304, 504, 606, 706). Light from the LED falls on the photodiode and produces an output voltage. The maximum output voltage across the photodiode is obtained at complete darkness and the minimum is obtained at the closest proximity.

The underlying principle of operation of the designed optical sensor is that when light travels across a boundary between two different media, its speed changes. This can be visualised from Huygen’s principle using a wavefront model. The extent to which a light ray bends can be indicated by the term optical density or refractive index. There are 3 types of interfaces encountered in the present experiment in which the light beam travels.
Air Glass interface
Glass liquid interface
Liquid Gas interface.

The velocity of the wavefront decreases as the light moves to an optically denser medium and the refracted angle is lesser than the incident angle. From Fig. 8 it can be understood that if the capillary tube is filled with air, the refraction angle is greater than when filled with water. So the intensity of light that falls on the photo diode is more in the case of larger volume of water in turn giving a low voltage output. The case is just the opposite for larger volume of air. The number of photons or the light rays falling on the photodiode is directly dependent on the parameters like lateral displacement d and the emitter ray incident angle ?1.

Taking an infinitesimal area of the curved glass tube to be rectangular in cross section, from laws of refraction
d=hsin?_1 (1-(cos?_1)/v((??-n?_1^2 sin^2 ?_1+n?_2^2)/(n_1^2 ))) (1)

where h is the thickness of the glass slab, n1 and n2 are the first and second medium respectively. Considering identical procedures for all the mentioned interfaces, total lateral displacement of the incident light radiation can be calculated. Using Eqn. 1 and snell’s law of refraction it can be stated that
d=?¦d_i (2)

where i is the number of the interfaces. Computing the lateral displacement and incident angle using the above method, the positioning of the sensor elements can be approximated. In the present analysis the angle of incidence of the light emitting diode with respect to the normal is kept at 45º.

Fig. 11(a) illustrates an experimental set-up as is fabricated for faciliating flow of adiabatic air–water mixtures in round horizontal tubes. The pipe diameter is kept constant at 3.4 mm for which the flow map is available in literature [3]. The pipe diameter is verified by image enhancement and using distance transform. The pumping of water is carried out by a water pump. Air is pumped using an air pump at a pressure slightly above the atmospheric pressure. Both the liquid and gas streams flows separately through rotameters before entering the T-section. The flow is controlled by individual flow control valves. The test section is made of borosilicate smooth glass material with inner diameter 3.420 mm. The wall contact angle of water is approximately taken as 0º. Temperature of water stored is in the range of 27–28 ºC.

Further, a circuit (306) for data-acquisition to draw the time scope is shown as a part of present Fig. 11 (b). The voltage drop across the photodiode is connected to the National instruments traditional data acquisition system ( NI-4350) and the time scope was seen and recorded in Microsoft Excel with 60 Hz frequency for further analysis with higher accuracy.

As a part of the aforesaid data-acquisition, the recorded data is sampled for a particular time interval based on the type of flow regime and the graph of variation in voltage with time is drawn. This is referred as the time scope. The voltages are read and the frequency of voltage is plotted against the read-value of voltage. A frequency distribution table is made that displays the frequency of various values of voltages in a sample. Each entry in the table would contain the frequency or count the voltage within a particular interval pertaining to different two phase flow regimes. A graph is plotted between the frequency and the voltage.

Fig. 12 depicts identification of Bubbly flow regime for a two-phase liquid. Bubbly flow is visualized as spherical or non-spherical elements of different lengths. Gas is dispersed in the form of bubbles in the liquid which is the continuous phase. Bubbles tend to stay on top surface of tube due to buoyancy. At high liquid and moderate gas velocities, spherical bubbles are observed and with further increase in gas velocity, the length of the bubble reduces and the frequency with which the bubbles appear increases. The bubbly flow is characterized by spherical or non-spherical bubbles which may be equal to or less than the channel diameter. In mini channels it is of the order of a few mm.

While, Fig. 12 shows the bubbly flow captured using the camera, Fig. 13 shows the time scope recorded using DAQ. The time scope shown is obtained for voltage amplitude of 3.8 V. (0.15 V calibrated for liquid flow). Fig 14 shows the plot of voltage frequency distribution curve for a bubbly flow. The single peak in the frequency distribution is similar to the results of Costigan and Whalley [18]. The single peak around 0.6 V indicates that the relative amount of water is much high compare to that of air. A smaller peak at high voltage indicates relatively small volume of air.

Fig. 15 pertains to identification of Slug flow regime. Slug type flow is obtained for low liquid superficial velocity and high gaseous superficial velocity. Individual bubbles may undergo coalescence or it may be due to elongated bubbles where a bubble is formed whose diameter is greater than that of the tube called as slug. Slug flow regime is characterized by a bullet shaped slug having a sharp nose at front and hardened tail. The elongated bubble is formed because of restriction due to tube diameter leading to compression. The slug flow is shown in Fig. 15. The time scope for slug flow shown in Fig. 16 has a flat region at high voltage indicating a high void fraction indicating slug flow pattern. Further processing of the optical signal is carried out on the real time data by plotting the Frequency distribution curve as shown in Fig 17. The two peaks at 0.15 V and at 3.8 V indicate the slug flow regime having a higher void fraction over discontinuous bubbly regime considering the same area.

Fig. 18 depicts identification of slug annular flow regime. In the slug-annular pattern, the liquid rises in the form of wave as shown in Fig. 18. The dip in voltage as shown in Fig.19 indicates sudden rise in liquid at proximate location to the photodiode. Some authors have mentioned the flow as serpentine type flow. The time scope indication in Fig. 19 is a clear representation of the liquid rise. The Frequency distribution curve of the slug annular flow is shown in Fig 20. The small distributions near 2.5 V show the liquid level rise. The high frequencies aroung 3.8 V indicates the distribution of air.

Fig. 21 illustrates identification of stratified flow regime. The complete separation of the liquid and gaseous phases characterizes the stratified flow. In stratified smooth the interface between two phases is without any fluctuation. Fig. 21 indicates a stratified-smooth flow regime. Fig 22 shows the time scope for the flow corresponding to Fig. 21. Fig 23 is a frequency distribution curve plot for stratified smooth flow regime. The approximate straight line in both these graphs indicates the complete separation of air-liquid flow observed in the sensor.

Fig. 24 shows the stratified wavy flow. Fig. 25 shows the time scope corresponding to stratified wavy flow. Majority of the datapoints are at high voltage. The dip in voltage is an indication of the interfacial waves. The wave corresponding to the maximum dip in graph is shown in Fig 24. The Frequency distribution curve is similar to the slug annular flow except that the wavy structure is indicated by the curve in the encircled part in the plot in Fig 26.

Fig. 27 illustrates measurement of two phase flow regime velocity and length, as executed by thje modules 508 and 708. Two LED’s or the two light sources (502, 504 or 707, 704) are kept to faciliate calculation of the slug length and slug velocity. Two LED’s are kept closer to each other at a distance d. As the slug passes the two LED’s, two peaks are obtained. The position at which the two peaks are obtained is shown in Fig. 27. The direction of flow is from left to right. Peak A in Fig. 28 corresponds to the time at which the light from LED A (502, 702) strikes the front end of the slug. Peak B corresponds to the time at which the light from LED B (504, 704) strikes the front end of the slug. So the time between Peak A and Peak B is the time required by the slug to cross the distance d. So the distance d when divided by the time between peak values indicates the velocity of the flow regime. The second LED is switched off after the slug velocity is measured. As the flow regime passes through one of the optical sensor, there are two peak voltage values indicating the front and rear air-water interface in the same sensor. Peak D is with reference to the slug hitting the front end and Peak E is with reference to the slug hitting the rear end as shown in Fig. 29. The time between the peaks (D and E) in graph shown in Fig. 30 gives the time taken by a single slug or bubble to cross the sensor. Knowing the velocity from the above method, the flow regime length can be identified.

Validation and reproducibility
The flow regime, velocities and length are also determined from high speed videometry and the results are compared in table 1 and table 2. It can be seen that the results from the present measurement technique are in close agreement with videometry results thus validating the present measurement technique. The same trend was confirmed for 4-5 times and hence the reproducibility factor was also confirmed.

Table 1. Measurement of velocity
S.NO TIME:
PHOTODIODE A (s) TIME:
PHOTODIODE B (s) CALCULATED VELOCITY(m/s) VELOCITY
(FROM VIDEO delay) (m/s)
a) 8.1 19.2 0.005 0.0045
b) 1.6 3.4 0.0275 0.0225
c) 0.8 6.0 0.01 0.0154

Table. 2. Measurement of Slug length
S.no Time lag between the 2 sensors Velocity Time lag from time scope for single graph Bubble /slug length Validation using image Processing
1 6s 0.83 cm/s 3s 24.9mm 25 mm
2 10s 0.5 cm/s 4s 20 mm 20 mm
3 8s 0.625cm/s 2s 12.5 mm 12.5 mm

Overall, the present invention is at least directed towards the development of a single LED-photodiode pair based two phase flow regime identification. The following are the special features.
Simpler design using a single LED-photodiode pair
Measurement technique is suitable in all transparent tubes
Applicable to two fluids which have differences in refractive index
Faster response and real time flow regime identification
Able to determine two phase flow regime velocity and length using two LEDs and single photodiode
Flow regimes identified includes- slug, bubbly, stratified, stratified wavy, annular and slug annular

While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The figures and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible.

References
[1] Mishima, K., and T. Hibiki. "Some characteristics of air-water two-phase flow in small diameter vertical tubes." International Journal of Multiphase Flow 22.4 (1996): 703-712.
[2] Coleman, John W., and Srinivas Garimella. "Characterization of two-phase flow patterns in small diameter round and rectangular tubes." International Journal of Heat and Mass Transfer 42.15 (1999): 2869-2881.
[3] Venkatesan, M., Sarit K. Das, and A. R. Balakrishnan. "Effect of diameter on two-phase pressure drop in narrow tubes." Experimental Thermal and Fluid Science 35.3 (2011): 531-541.
[4] Kumar, Sailesh B., Davood Moslemian, and Milorad P. Dudukovic. "A ?-ray tomographic scanner for imaging voidage distribution in two-phase flow systems." Flow Measurement and Instrumentation 6.1 (1995): 61-73.
[5] Ikeda, Takashi, Koichi Kotani, Yuichiro Maeda, and Hideki Kohno "Preliminary study on application of X-ray CT scanner to measurement of void fractions in steady state two-phase flows." Journal of Nuclear Science and Technology 20.1 (1983): 1-12.
[6] Warsito, W., and L-S. Fan. "Measurement of real-time flow structures in gas–liquid and gas–liquid–solid flow systems using electrical capacitance tomography (ECT)." Chemical Engineering Science 56.21 (2001): 6455-6462.
[7] X. Liu, X. Qiang, H. Qiao, G. Ma, J. Xiong, Zh. Qiao, A theoretical model for a capacitance tool and its application to production logging, Flow Meas. Instrum. 9 (4) (1998) 249–257.
[8] J. Tollefsen, E.A. Hammer, Capacitance sensor design for reducing errors in phase concentration measurements, Flow Meas.Instrum. 9 (1) (1998) 25–32.
[9] T. Loser, R. Wajman, D. Mewes, Electrical capacitance tomography: image reconstruction along electrical field lines, Meas.Sci. Technol. 12 (8) (2001) 1083–1091.
[10] Jaworek, A., A. Krupa, and M. Trela. "Capacitance sensor for void fraction measurement in water/steam flows." Flow Measurement and Instrumentation15.5 (2004): 317-324.
[11] Li, Hao, and Michael G. Olsen. "MicroPIV measurements of turbulent flow in square microchannels with hydraulic diameters from 200µm to 640µm."International journal of heat and fluid flow 27.1 (2006): 123-134.
[12] Hassan, Y. A., T. K. Blanchat, C. H. Seeley, and R. E. Canaan. "Simultaneous velocity measurements of both components of a two-phase flow using particle image velocimetry." International Journal of Multiphase Flow 18.3 (1992): 371-395.
[13] Lecuona, A., P. A. Sosa, P. A. Rodriguez, and R. I. Zequeira. "Volumetric characterization of dispersed two-phase flows by digital image analysis." Measurement Science and Technology 11.8 (2000): 1152.
[14] Lindken, R., and W. Merzkirch. "A novel PIV technique for measurements in multiphase flows and its application to two-phase bubbly flows." Experiments in fluids 33.6 (2002): 814-825.
[15] Zhai, Lei, Shouping Dong, and Honglian Ma. "Recent methods and applications on image edge detection." Education Technology and Training, 2008. International Workshop on Geoscience and Remote Sensing. ETT and GRS 2008. International Workshop on. Vol. 1. IEEE, 2008.
[16] Haralick, Robert M., Stanley R. Sternberg, and Xinhua Zhuang. "Image analysis using mathematical morphology." Pattern Analysis and Machine Intelligence, IEEE Transactions on 4 (1987): 532-550.
[17] Delville, Jean-Pierre, Joël Plantard, Sébastien Cassagnere, and Matthieu Robert de Saint Vincent. "Measuring device for characterizing two-phase flows." U.S. Patent 8,743,350, issued June 3, 2014.
[18] Costigan, G., and P. B. Whalley. "Slug flow regime identification from dynamic void fraction measurements in vertical air-water flows." International Journal of Multiphase Flow 23.2 (1997): 263-282.
,CLAIMS:We claim:
1. A method for assisting determination of a two-phase flow regime through at least one light-emitter detector pair, said method comprising the steps of:
illuminating (step 102) a flow-channel carrying a two-phase material through at least one light-emitter; and
detecting (step 104) a light beam reflected/refracted by said material using at least one light detector, wherein said detection includes recording a voltage produced by said light detector through a data acquisition system.
2. The method as claimed in claim 1, further comprising:
determining a time scope and a frequency-distribution variation in terms of said voltage through said data acquisition system; and
analysing at least one of:
said determined time scope; and
said frequency-distribution variation;
to determine the flow-regime of said material within the flow-channel.
3. A method for determining a two-phase flow regime through at least one light-emitter detector pair, the method comprising:
illuminating (step 202) a flow-channel carrying a two-phase material through at least one light-emitter;
detecting (step 204) a light beam reflected/refracted by said material using at least one light detector, wherein said detection includes recording a voltage produced by said light detector through a data acquisition system;
determining (step 206) a time scope and a frequency-distribution variation in terms of said voltage through said data acquisition system; and
analysing (step 208) at least one of said determined time scope, and said frequency-distribution variation to determine the flow-regime of said material within the flow-channel.
4. An apparatus (300) for assisting determination of a two-phase flow regime through at least one light-emitter detector pair, the apparatus comprising:
at least one light emitter (302) for illuminating a flow-channel carrying a two-phase material; and
at least one light detector (304) for detecting a reflected/refracted light beam from said two-phase material; and
a data acquisition means (306) for recording a voltage produced by said light detector.
5. The apparatus (300) as claimed in claim 4, wherein said data acquisition means (306) comprises one or more modules (308) for at least one of:
determination of a time scope and a frequency-distribution variation associated with said voltage through said data acquisition means (306); and
analysis of a time scope and a frequency-distribution variation determined in terms of said voltage to further determine the flow-regime of said material within the flow-channel.
6. A method for determining a two-phase velocity, the method comprising:
illuminating (step 402) a transparent conduit carrying a two phase material with a first light source and a second light source, the first and the second light sources being spaced apart from each other by a known distance;
detecting (step 404) a first light beam and a second light beam using a light detector, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from an interface between the first material and the second material and the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the interface between the first material and the second material;
determining (step 406) a time difference between the detection of the first light beam and the detection of the second light beam; and
determining (step 408) a velocity of flow of the first material through the transparent conduit based on the time difference.
7. An apparatus (500) for determining two-phase velocity, the apparatus comprising
a first light source (502);
a second light source (504) placed at a known distance from the first light source, the first light source and the second light source being adapted to illuminate the transparent conduit carrying the two phase material;
a light detector (506) adapted to detect a first light beam and a second light beam, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from an interface between the first material and the second material and the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the interface between the first material and the second material; and
one or more modules (508) for determining:
a time difference between the detection of the first light beam and the detection of the second light beam; and
a velocity of flow of the first material through the transparent conduit based on the time difference.
8. A method for determining a length of at least one phase flowing through a transparent conduit, said method comprising the steps of:
illuminating (step 602) the transparent conduit carrying a two phase material with a first light source and a second light source, the first and the second light sources being spaced apart from each other by a known distance;
detecting (step 604) a first light beam, a second light beam and a third light beam using a light detector, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a first interface between the first material and the second material, the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the first interface between the first material and the second material, and the third light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a second interface between the first material and the second material;
determining (step 606) a first time difference between the detection of the first light beam and the detection of the second light beam;
determining (step 608) a velocity of flow of the first material through the transparent conduit based on the first time difference;
determining (step 610) a second time difference between the detection of the first light beam and the detection of the third light beam; and
determining (step 612) a length of a first material flowing through a transparent conduit based on the second time difference and the velocity of flow of the first material.
9. The method as claimed in claim 8, wherein said third light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from a second interface between the first material and the second material;
10. An apparatus (700) for determining a length of at least one phase flowing through a transparent conduit, said apparatus comprising:
a first light source (702);
a second light source (704) placed at a known distance from the first light source, the first light source and the second light source being adapted to illuminate the transparent conduit carrying the two phase material;
a light detector (706) adapted to detect a first light beam, a second light beam and a third light beam, wherein the first light beam corresponds to a reflection/refraction of the light produced by the first light source and emanating from a first interface between the first material and the second material, the second light beam corresponds to a reflection/refraction of the light produced by the second light source and emanating from the first interface between the first material and the second material, and the third light beam corresponds to a reflection/refraction of the light produced by the first light source or the second light source and emanating from a second interface between the first material and the second material; and
one or more modules (708) configured for determining:
a time difference between the detection of the first light beam and the detection of the second light beam;
a velocity of flow of the first material through the transparent conduit based on the time difference;
a second time difference between the detection of the first light beam and the detection of the third light beam; and
a length of a first material flowing through a transparent conduit based on the second time difference and the velocity of flow of the first material.