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«A Dissertation Presented to The Academic Faculty by Aravind Sathyanarayana In Partial Fulfillment of the Requirements for the Degree Doctor of ...»

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POOL AND FLOW BOILING OF NOVEL HEAT TRANSFER

FLUIDS FROM NANOSTRUCTURED SURFACES

A Dissertation

Presented to

The Academic Faculty

by

Aravind Sathyanarayana

In Partial Fulfillment

of the Requirements for the Degree

Doctor of Philosophy in the

George W. Woodruff School of Mechanical Engineering

Georgia Institute of Technology

December 2013

Copyright © 2013 by Aravind Sathyanarayana

POOL AND FLOW BOILING OF NOVEL HEAT TRANSFER

FLUIDS FROM NANOSTRUCTURED SURFACES

Approved by:

Dr. Yogendra Joshi, Advisor Dr. Samuel Graham School of Mechanical Engineering School of Mechanical Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Amyn S. Teja Dr. Sushil Bhavnani School of Chemical and Biomolecular School of Mechanical Engineering Engineering Auburn University Georgia Institute of Technology Dr. Mostafa S. Ghiaasiaan School of Mechanical Engineering Georgia Institute of Technology Date Approved: October 8, 2013 To my grandparents, G. Sriramulu Pillai and K. Jambavathi

ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to all the people who have helped me during the course of my doctoral study at Georgia Tech. First and foremost, I would like to thank my PhD advisor, Dr. Yogendra Joshi, for his constant support, guidance as well as for his comments and critiques. He continually stimulated my thinking ability and made me capable of performing independent research. I have had the opportunity to interact with several researchers who visited our lab, present my work at various conferences and I cannot thank him enough for this enriching experience.

This work was performed in collaboration with Dr. Amyn Teja from the School of Chemical and Biomolecular Engineering at Georgia Tech, and I would like to thank him for his guidance in the chemistry aspects of this work. I am also grateful to my PhD committee members Dr. Sushil Bhavnani, Dr. Mostafaa Ghiaasiaan and Dr. Samuel Graham, for their valuable feedback, as well as reviewing the proposal and dissertation.

This work was funded by the Office of Naval Research and I would like to acknowledge their financial support.

I have worked with Dr. Pramod Warrier as a part of this research work, and I would like to acknowledge his help in evaluating the properties of all the fluids and for providing me with the custom fluids in a timely manner. I would specially like to thank Dr. Yunhyeok Im, a visiting scholar in our group, for graciously allowing me to use his pool boiling setup for my research. I have learnt a lot working with him in the lab and I would always cherish those memories. My thanks are also due to Dr. Minami Yoda and Dr. David Hu for letting me borrow the high speed camera for my experiments. I would

–  –  –

measuring dissolved gas percentages.

I extend many thanks to all my colleagues in the Microelectronics and Emerging Technologies Thermal Laboratory (METTL) for their valuable feedback during our group meetings and also for training me on several tools. I would specially like to thank Dr.

Pramod Kumar and Dr. Krishna Kota for their valuable advice during the initial stages of my research. I have had several informal discussions with them over various topics and they have greatly influenced me as a thinker.

I am grateful to all the staff members at the Microelectronics Research Center (MiRC) for their invaluable help and guidance with the micro-fabrication tools and processes in the cleanroom. I would also like to thank Mr. Louis Boulanger in the ME machine shop for machining the test section for flow boiling experiments. My special thanks go to Mrs. Regina Neequaye for her help in ordering all the components required for my research.

I have made a lot of good friends during my stay in Atlanta, and I would like to thank each and every one of them for making me feel at home all these years. Last but not the least, I express my deepest gratitude to my parents, siblings, my uncle Nagaraju’s family and my aunt Usha’s family for their unconditional love and encouragement throughout my life. I would not have been in this position today without their support.

–  –  –

ACKNOWLEDGEMENTS…………………………………………………………….. iv LIST OF TABLES………………………………………………………………………. x LIST OF FIGURES…………………………………………………………………….. xi NOMENCLATURE………………………………………………………………........ xv SUMMARY…………………………………………………………………………..xviii CHAPTER 1: INTRODUCTION

1.1 Motivation

1.2 Heat Transfer Fluid Selection - Approaches

1.2.1 Ad hoc Approach

1.2.2 Enhancing the Properties of Existing Fluids

1.2.3 Computer Aided Molecular Design

1.3 Research Objectives

1.4 Thesis Outline

CHAPTER 2: LITERATURE REVIEW

2.1 Pool Boiling of Mixtures

2.1.1 Pool Boiling of Aqueous and Alcohol Mixtures





2.1.2 Pool Boiling of Dielectric Liquid Mixtures

2.2 Flow Boiling of Mixtures

2.3 Summary

CHAPTER 3: DESIGN OF HEAT TRANSFER FLUIDS

3.1 Computer Aided Molecular Design

3.2 Fluid Property Prediction

–  –  –

3.2.2 Evaluation of Group Contribution Methods

3.3 Constraints on Fluid Properties

3.4 Figure of Merit Analysis

3.5 New Heat Transfer Fluids

3.6 Summary

CHAPTER 4: FLUID PROPERTIES

4.1 Thermophysical Properties Measurement

4.2 Contact Angle

4.3 Vapor Liquid Equilibrium Curves

4.4 Summary

CHAPTER 5: POOL BOILING EXPERIMENTS.

5.1 Experimental Setup

5.2 Test Chip Fabrication

5.3 Experimental Procedure

5.4 Measurement Uncertainty

5.5 Experimental Results

5.5.1 Effect of Enhanced Surface

5.5.2 Pool Boiling of HFE 7200 – Ethoxybutane and HFE 7200 – Methanol Mixtures

5.5.3 Pool Boiling of HFE 7200 – C6H11F3 Mixture

5.5.4 Pool Boiling of HFE 7200 – C4H4F6O Mixture

5.5.5 Pool Boiling of HFE 7200 – C4H5F3O Mixture

5.5.6 Pool Boiling of HFE 7200 – C4H12O2Si Mixture

5.5.7 Pool Boiling of HFE 7200 – C4H11N Mixture

5.6 CHF Prediction for Higher Mixture Concentrations

–  –  –

5.8 Summary

CHAPTER 6: POOL BOILING SIMULATIONS

6.1 Need for Numerical Simulations

6.2 Phase Field Method

6.2.1 Interface Equations

6.2.2 Conservation Equations

6.3 Pool Boiling Model

6.3.1 Computational Model

6.3.2 Boundary Conditions

6.4 Simulation Results

6.4.1 Effect of Grid Size

6.4.2 Simulations using HFE 7200 and C4H4F6O

6.4.3 Possible Reasons for Discrepancy

6.4.4 Effect of Constant ‘C’ on Simulation Results

6.5 Validation with Experimental Results

6.6 Summary

CHAPTER 7: FLOW BOILING EXPERIMENTS

7.1 Experimental Setup

7.2 Microgap Channel Test Section

7.3 Leak Test and Degassing

7.4 Experimental Procedure

7.5 Data Reduction

7.6 Calibration and Measurement Uncertainty

7.7 Experimental Results

–  –  –

7.7.2 Flow Boiling on Unpolished Surface

7.8 Summary

CHAPTER 8: CONCLUSIONS AND FUTURE WORK

8.1 Conclusions

8.2 Recommendations for Future Work

8.2.1 New Fluid Synthesis

8.2.2 Pool Boiling Experiments

8.2.3 Pool Boiling Modeling

8.2.4 Flow Boiling Experiments

REFERENCES

–  –  –

Table 3.1: Screening of compounds for structural feasibility

Table 3.2: Properties of some existing coolants

Table 3.3: FOM correlations

Table 3.4: FOM for HFE 7200, and cut-off values for candidate fluids

Table 3.5: Candidate fluids selected after FOM analysis

Table 4.1: Supplier information for heat transfer fluids

Table 4.2: Thermophysical property measurements of new fluids

Table 4.3: Properties of heat transfer fluids considered for experiments

Table 5.1: Uncertainties in parameters

Table 5.2: CHF predictions

Table 6.1: Boundary conditions and initial conditions for the computational model.

.....91 Table 6.2: Mesh statistics and solution time for grid size dependence study..................96 Table 6.3: Properties of heat transfer fluids considered for simulations

Table 6.4: Mesh statistics and solution time for different fluids

Table 6.5: Comparison between theoretical predictions and simulations for the bubble departure diameter

Table 6.6: Comparison between theoretical predictions and simulations for the bubble departure frequency

Table 7.1: Flow boiling experimental conditions

–  –  –

Figure 3.1: CAMD – FOM approach

Figure 4.1: Contact angle measurement system

Figure 4.2: Instantaneous droplet shape of HFE 7200 on a plain surface

Figure 4.3: Instantaneous droplet shape of C6H11F3 on a plain surface

Figure 4.4: Instantaneous droplet shape of C4H4F6O on a plain surface

Figure 4.5: Instantaneous droplet shape of water on a plain surface

Figure 4.6: Vapor liquid equilibrium curve for mixture of HFE 7200 – ethoxybutane.

..36 Figure 4.7: Vapor liquid equilibrium curve for mixture of HFE 7200 – methanol.........37 Figure 4.8: Vapor liquid equilibrium curve for mixture of HFE 7200 – C6H11F3...........37 Figure 4.9: Vapor liquid equilibrium curve for mixture of HFE 7200 – C4H4F6O.........38 Figure 4.10: Vapor liquid equilibrium curve for mixture of HFE 7200 – C4H5F3O.......38 Figure 4.11: Vapor liquid equilibrium curve for mixture of HFE 7200 – C4H12O2Si.....39 Figure 5.1: Schematic of pool boiling experimental setup

Figure 5.2: Test chip package mounted on the Teflon block

Figure 5.3: Test chip fabrication process

Figure 5.4: Platinum RTD fabricated on the backside of the chip

Figure 5.5: SEM image of Cu nanowire array (height of nanowires - 4 µm).

.................47 Figure 5.6: SEM image of Cu nanowire array (height of nanowires - 20 µm)................47 Figure 5.7: SEM image of CuO hybrid micro-nanostructured surface_1

Figure 5.8: SEM image of CuO hybrid micro-nanostructured surface_2

Figure 5.9: Temperature – resistance calibration curve for Pt RTD

Figure 5.10: Pool boiling of HFE 7200 on a bare chip, Cu groove surface (width – 70 µm and depth - 70 µm), 3 µm tall and 20 µm tall Cu nanowire surfaces.

.............54

–  –  –

Figure 5.12: Pool boiling curves for HFE 7200, 10 vol.

% mixtures of HFE 7200 – ethoxybutane and HFE 7200 – methanol at 10K subcooling on 4 µm nanowire array

Figure 5.13: Pool boiling curves for HFE 7200, 10 vol.

% mixtures of HFE 7200 – ethoxybutane and HFE 7200 – methanol at 20K subcooling on 4 µm nanowire array

Figure 5.14: Pool boiling curves for HFE 7200 at saturation condition on hybrid micro nanostructured surface

Figure 5.15: Pool boiling curves for 7 wt.

% mixture of HFE 7200 – C6H11F3 at saturation condition on hybrid micro-nanostructured surface

Figure 5.16: Pool boiling curves for HFE 7200 at saturation condition on hybrid micronanostructured surface

Figure 5.17: Pool boiling curve for 10 wt.

% mixture of HFE 7200 – C4H4F6O at saturation condition on hybrid micro-nanostructured surface

Figure 5.18: Pool boiling curves for HFE 7200 at saturation condition on hybrid micronanostructured surface

Figure 5.19: Pool boiling curve for 20 wt.

% mixture of HFE 7200 – C4H5F3O at saturation condition on hybrid micro-nanostructured surface

Figure 5.20: Pool boiling curves for HFE 7200 at saturation condition on hybrid micronanostructured surface

Figure 5.21: Pool boiling curves for 10 wt.

% mixture of HFE 7200 – C4H12O2Si at saturation condition on hybrid micro-nanostructured surface

Figure 5.22: Sediments deposited during saturated boiling of 10 wt.

% mixture of C4H11N – HFE 7200 on a) glass walls, and b) test chip

Figure 5.23: CHF prediction for different concentrations of new fluid – HFE 7200 mixtures on an infinite heater

Figure 5.24: CHF prediction for different concentrations of new fluid – HFE 7200 mixtures on a small heater of area 10 x 10 mm2

Figure 5.25: Cavities on a nanowire (200 nm diameter, 20 µm tall) coated surface.

......76 Figure 6.1: Saturated pool boiling of HFE 7200 at 2.

5 W/cm2 (2000 fps)

–  –  –

Figure 6.3: Interface between two immiscible phases, a) Actual interface, and b) Diffuse interface in PFM

Figure 6.4: Computational model with key dimensions

Figure 6.5: Domains occupied by the liquid and vapor phases initially

Figure 6.6: Mesh settings for a) Case 1, and b) Case 2

Figure 6.7: Fluid volume fraction plots before bubble departure for a) Case 1, and b) Case 2

Figure 6.8: Fluid volume fraction plots before bubble departure for a) HFE 7200, and b) C4H4F6O

Figure 6.9: Fluid volume fraction plots before bubble departure for a) C = 0.

005 m/s and

b) C = 0.1 m/s

Figure 6.10: Fluid volume fraction plots before bubble departure for a) q” = 1 W/cm2, b) q” = 4 W/cm2, c) q” = 6 W/cm2, and d) q” = 8 W/cm2



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