Mid Sem Ppt_nipun

8/2/2019 Mid Sem Ppt_nipun

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B T P M I D - T E R M P R E S E N TAT I O N

I N D I A N I N S T I T U T E O F T E C H N O L O G Y, D E L H IC H E M I C A L E N G I N E E R I N G D E PA R M E N T

Calibration of dual-tip voidage probes formeasurement of gas hold-up, bubble size

and bubble rise velocity

Presented by:Nipun Agarwal2008CH10067

Indian Institute of Technology, Delhi


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OBJECTIVE

Calibration of dual tip voidage probes by the use of high speed imaging for measurement of thefollowing parameters in dispersed gas-liquid flows:

Gas hold-upBubble size distributionBubble rise velocity


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APPLICATION & IMPORTANCE

Air- lift reactor Gas-liquid stirred tank Slurry bubble column reactor

Industrial applications

Performance of the above reactors depends upon the gashold-up and bubble size distribution- Interfacial areameasurements

Interfacial area measurements are important to determinethe heat and mass transfer rates


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APPLICATION AND IMPORTANCE

Interfacial area affects the extent of reaction as it directly relatesthe amount of gas and liquid in contact at a particular time

Measurement of hydrodynamic variables

Interfacial areameasurements

Heat and mass transferrates Extent of reaction


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TECHNIQUES AVAILABLE

Two Broad categories of division between techniques

IntrusiveTechniques

VoidageProbes

OpticalProbes

Non IntrusiveTechniques

Tomography

ParticleImage

Velocimetry

Voidage probe(top), tomography (left),PIV (right)


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REVIEW OF LITERATURE

1. Buwa and Ranade, 2005 mentions the calibration of voidage probes by high speed imaging and digital image analysis

The study compares the average gas hold-up measured through both techniques

Calculates Phase Discrimination Threshold for the design by

comparing results by both processes Features Column dimensions: 50 cm (height), 5 cm (width), 2 cm (depth) Images recorded (about 100 images) in an interrogation window of

5cm by 5 cm were analyzed to calculate average bubble diameterand hence gas hold up by:

= 3

,6=1 Comparing the gas hold up values by conductivity experimentsand photography resulted in a PDT value of 10% which is beingused for processing data.


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2. Zaruba et al., 2005 in their paper mention great detail on the study of bubble motion in a rectangular bubble column by means of high speedimaging

Bubble Identification Pictures recorded are scaled on a grey scale map varying from 0

(Pure black) to 255 (Pure white). Bubbles as shown in figure below come into the category of lower

grey scale

A brightness threshold ( ) is applied to clear the image fordetection of bubblesScale(image)> Scale (image)= 255 (white background)Scale(image)< Scale (image)= 0 (black foreground)

Actual image(left), Afterapplying threshold (right)


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For calculating velocity of bubbles Centre of mass is assigned to each bubble- centroid of all pixels

that belong to the area (assuming every pixel has same weight)

Bubble path is traced by superimposing of successive frames Plotting the path of center of gravity of all bubbles (keeping some

threshold maximum value for successive frames)

3. Xue et al., 2007 presents a similar study of validation of four point

optical probe with high speed imaging for the gas hold-up, bubble size and bubble rise velocity distribution.

Uses XCAP software by EPIX to directly calculate the bubble rise velocity distribution with bubble sizes.

Compares the data by both methods for comparison


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EXPERIMENTAL SETUP

The setup consists of the following A rectangular column (Width=

5cm, Depth= 2cm and Height=50cm) made of (PMMA)

polymethylmethacrylate Spargers designed specially for

generating a uniform andpatterned flow of bubbles

High Speed imaging camera forphotographic measurements

Probes and signal conditioningsystem for acquiring data

Schematic of the set-up


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KEY HIGHLIGHTS OF THE DESIGN

Rectangular column specially design of theminimum possible thickness

Ensures generation of a 2-D array of bubblesimportant for photographic measurements

Ensures that the bubbles do not overlap

Small spargers designed specifically for the setupto ensure uniform bubble and inline bubbleproduction

An interrogation window of 5 cm x 5 cm forphotographic measurements

Experimental setup


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WHY THE NEED OF STUDY?

When a bubble hits a probe tip, the interaction between the tip and the bubble dents the leading edge of the bubble

This can happen because of following

Properties of liquid: Surface tension, polarity, density

Properties of probe: Material, shape

Therefore to account for the irregularities that may arise in the

measurement due to distortion of bubbles on hitting the probe we needto calibrate the method and validate the measurements obtained by theprobes with that of high speed imaging


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Image Processing Steps

1. Video is broken into images.

2. Appropriate test screen is cut out

3. Photograph is converted to binary

4. Set threshold to distinguish bubblesin the image.

5. Clear the picture of disturbances

6. Analyze the image using ImageJ


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METHODOLGY

There has been validation studies validating the gas hold-up by highspeed imaging but not much has been reported in terms of validationof bubble size and rise velocity measurements

Simultaneous data acquisition by both the voidage probes and by themeans of high speed imaging

Comparing the data of gas hold-up, bubble size and rise velocity distribution generated by both the process

Validating the results and making appropriate changes in theprocessing methodology or probe design as per the requirements


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PRESENT WORK

The column of the required dimension has been acquired Spargers with needle sizes 18, 21 and 23 gauge has been constructed

for experimentation with different bubble sizes

Performed a preliminary experiment recording a test video by a highspeed imaging camera

FUTURE WORK Simultaneous experiments for both the methods and validating the

results with each other

Introducing any changes in the probe configuration or processingmethodology if required for validation


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THANK YOU

Mid Sem Ppt_nipun

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