Experimental Studies of Vertical Mixing in an Open Channel Raceway for Algae Biofuel Production

124 Pages·2016·5.11 MB·English

by  Ram Sudheer Voleti

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All Graduate Theses and Dissertations Graduate Studies
8-2012
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Ram Sudheer Voleti
Utah State University
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EXPERIMENTAL STUDIES OF VERTICAL MIXING IN AN OPEN CHANNEL
RACEWAY FOR ALGAE BIOFUEL PRODUCTION

by

Ram Sudheer Voleti
A thesis submitted in partial fulfillment
of the requirements for the degree
of
MASTER OF SCIENCE
in
Mechanical Engineering
Approved:

Dr. Byard D. Wood Dr. Clair J. Batty
Major Professor Committee Member

Dr. Leijun Li Dr. Barton L. Smith
Committee Member Committee Member

Dr. Mark R. McLellan
Vice President for Research and
Dean of the School of Graduate Studies

UTAH STATE UNIVERSITY
Logan, Utah
2012
ii

Copyright © Ram Sudheer Voleti 2012
All Rights Reserved
iii

ABSTRACT
Experimental Studies of Vertical Mixing in an Open Channel
Raceway for Algae Biofuel Production
by
Ram Sudheer Voleti, Master of Science
Utah State University, 2012
Major Professor: Dr. Byard D. Wood
Department: Mechanical and Aerospace Engineering
Turbulent mixing plays an important role in the distribution of sunlight, carbon
dioxide, and nutrients for algae in the raceway ponds. For large-scale raceway ponds the
choice of mixing technology still needs to be evaluated in order to prevent algae
sedimentation and to enhance light utilization efficiency. In open ponds, mixing the algae
culture is of great significance in terms of input energy costs and particularly
productivity. A very small amount of research has been performed previously using
different vortex generators in the algal raceway ponds, but the quantification of mixing
depth relationships is not defined well. By accepting the premise from the literature
review that mixing increases algal production, delta wings were selected to study mixing
characteristics in the raceway. The main objective of this research was to study algae-
raceway hydrodynamics with an emphasis on increasing vertical mixing.
iv

A clear acrylic raceway was designed and constructed for flow visualization
studies. Experimental investigations were performed to quantify the vertical mixing with
and without delta wings in a lab-scale raceway at approximately the same power input to
the paddle wheel. Velocity vector profiles and turbulence parameters were measured
using an Acoustic Doppler Velocimeter (ADV) at various locations along the entire
length of the raceway. The results indicated that the addition of delta wings increases the
vertical mixing intensity or circulation of algae cells over the raceway depth. Vortices
were observed in the raceway up to a distance of around 3 m downstream of the delta
wing. This sort of systematic vertical mixing plays an important role to produce the
flashing light effect (light-dark cycles) on algae mass culture. In addition, turbulence
dissipation rates were evaluated to compare them with the published literature and to
estimate the microscales using the Kolmogorov hypothesis. Also, an energy model was
developed to operate the paddlewheel-driven raceway with the delta wing.
(123 pages)
v

PUBLIC ABSTRACT
Experimental Studies of Vertical Mixing in an Open Channel
Raceway for Algae Biofuel Production
by
Ram Sudheer Voleti, Master of Science
Utah State University, 2012
Major Professor: Dr. Byard D. Wood
Department: Mechanical and Aerospace Engineering
The USU BioEnergy Center has been successful in developing algae feedstocks
for renewable biofuels and bioproducts. The concept is to utilize and maximize algae
feedstocks for liquid transportation fuels, biomass for burning and digestion, and high
value co-products. It is theorized that increasing the mixing in open and closed algal
production systems improves the productivity of the algae culture. A raceway cultivation
system was chosen to examine the phenomena of mixing. Vertical mixing will provide
more uniform exposure to sunlight for all of the algae in the raceway. The main focus of
this research was to increase vertical mixing. Delta wing vortex generator was selected as
a viable source of creating vertical mixing. A series of experiments were carried out to
study the mixing characteristics in a lab-scale raceway that was designed specifically for
raceway hydrodynamics. Finally, the results were discussed and appropriate conclusions
drawn.
vi

ACKNOWLEDGMENTS
I would like to express my highest regards and gratitude to my major professor
and supervisor, Dr. Byard Wood, who continues to provide encouragement, guidance,
support, and advice. I will be forever indebted to him for believing in me right from the
beginning of my career as a research assistant at USU. I am thankful to Dr. Barton Smith
for his class lectures, help, and input during the progress of my research. I would like to
thank my committee members, Dr. Clair Batty, Dr. Leijun Li, and Dr. Barton Smith, for
extending their service and support.
I am thankful to all the current and past Raceway Hydraulics Research Group
members, including Aaron, Blake, Dan, Garrett, Jayson, Justin, and Pete, for the support
given by them during my research. Also, I would like to thank all the people who were
involved directly or indirectly and helped in the construction of the clear acrylic raceway
at USU Algae Energy Systems lab. I feel grateful to the USU BioEnergy Center and the
US Department of Energy (Grant Number DE-EE0003114) for all the financial support.
Finally, I am thankful to my wonderful family, teachers, relatives, and friends for
their love and support, and for all the confidence and trust they put in me.
Ram Sudheer Voleti
vii

CONTENTS
Page
ABSTRACT ................................................................................................................... iii
PUBLIC ABSTRACT .................................................................................................... v
ACKNOWLEDGMENTS ............................................................................................. vi
LIST OF TABLES ......................................................................................................... ix
LIST OF FIGURES ........................................................................................................ x
ACRONYMS ............................................................................................................... xiv
NOMENCLATURE ..................................................................................................... xv
CHAPTER
1. INTRODUCTION .......................................................................................... 1
2. OBJECTIVES ................................................................................................. 4
3. LITERATURE REVIEW ............................................................................... 5
3.1. Effects of Turbulence on Algae Growth ............................................... 5
3.2. Mixing in Algal Raceway Ponds ........................................................ 10
4. APPROACH AND PROCEDURE ............................................................... 13
4.1. Experimental Setup ............................................................................. 13
4.1.1. Raceway Description ............................................................. 14
4.1.2. Delta Wing Setup ................................................................... 15
4.2. Preliminary Experiments..................................................................... 16
4.3. Acoustic Doppler Velocimeter Measurements ................................... 17
4.3.1. ADV Description and Principle of Operation ........................ 17
4.3.2. Sampling Frequency and Time .............................................. 21
4.3.3. Section-wise Grid Measurements .......................................... 24
viii

4.4. Data Analysis ...................................................................................... 27
4.4.1. Data Post Processing .............................................................. 27
4.4.2. Measurement Uncertainty Analysis ....................................... 30
4.4.3. Estimation of Turbulence Parameters .................................... 32
4.4.4. Estimation of Turbulence Dissipation Rates .......................... 33
4.5. Comparison of ADV and PIV Measurements .................................... 36
4.6. Power Measurements and Raceway Energy Model ............................ 37
5. EXPERIMENTAL RESULTS AND DISCUSSION ................................... 39
5.1. Comparison of ADV Data with PIV Data .......................................... 39
5.2. Velocity Vector Profiles ..................................................................... 40
5.2.1. Experiment Set 1 .................................................................... 41
5.2.2. Experiment Set 2 .................................................................... 43
5.2.3. Experiment Set 3 .................................................................... 60
5.3. Quantification of Vertical Mixing ...................................................... 70
5.3.1. Vertical Mixing Index Results ............................................... 70
5.3.2. Turbulence Dissipation Rates and Scales .............................. 73
6. CONCLUSIONS AND RECOMMENDATIONS ....................................... 80
REFERENCES ............................................................................................................. 82
APPENDICES .............................................................................................................. 86
A. RACEWAY ENERGY MODEL ................................................................. 87
B. ADV-PIV CONTOUR PLOTS .................................................................... 94
C. COPYRIGHT PERMISSION .................................................................... 104
ix

LIST OF TABLES
Table Page
4-1. Technical specifications of the MicroADV [23] .................................................. 21
4-2. Power consumption by the paddle wheel at different conditions ......................... 38
5-1. Data obtained by ADV and PIV at 1.07 m downstream of the delta wing
in the raceway ....................................................................................................... 40
5-2. Data obtained by ADV and PIV without delta wing in the raceway .................... 40
5-3. Comparison of maximum vertical velocities for experiment set 1 ....................... 42
5-4. Comparison of maximum vertical velocities for experiment set 2 ....................... 52
5-5. Comparison of maximum vertical velocities for experiment set 3 ....................... 61
5-6. Averaged turbulence dissipation rates and Kolmogorov length scales for
experiment set 1 .................................................................................................... 77
5-7. Averaged turbulence dissipation rates and Kolmogorov length scales for
experiment set 2 .................................................................................................... 78
5-8. Comparison between the turbulence dissipation rates reported in the
literature and the present studies ........................................................................... 79