analysis of air-to-air rotary energy wheels

269 Pages·2006·1.41 MB·English

ANALYSIS OF AIR-TO-AIR ROTARY ENERGY WHEELS

A dissertation presented to
the faculty of
the Russ College of Engineering and Technology
of Ohio University

In partial fulfillment
of the requirements for the degree
Doctor of Philosophy

Abdulmajeed S. Al-Ghamdi
June 2006
© 2006
Abdulmajeed S. Al-Ghamdi
All Rights Reserved
This dissertation entitled
ANALYSIS OF AIR-TO-AIR ROTARY ENERGY WHEELS

by
ABDULMAJEED S. AL-GHAMDI

has been approved for
the Department of Mechanical Engineering
and the Russ College of Engineering and Technology by

Khairul Alam
Moss Professor of Mechanical Engineering

Dennis Irwin
Dean, Russ College of Engineering and Technology
ABSTRACT
Al-GHAMDI, ABDULMAJEED S., Ph.D., June 2006. Integrated Engineering

ANALYSIS OF AIR-TO-AIR ROTARY ENERGY WHEELS (269 pp.)

Director of Dissertation: Khairul Alam
Integration of the energy recovery ventilator (ERV) with a traditional HVAC
system has gained recent attention because of the potential for energy savings. The
energy recovery ventilator selected for this research employs a rotary air-to-air energy
wheel with a porous matrix as the heat and moisture transfer medium. The wheel is
symmetrical and balanced, operating with counter-flow pattern. The primary goal of this
research is to develop a mathematical and numerical model to predict the effectiveness of
this energy wheel.
Three models were developed for the energy recovery ventilator (ERV)
containing a porous exchange matrix: a sensible model, a condensation model, and an
enthalpy model. The sensible model describes the heat transfer in a rotary wheel with a
non-desiccant porous matrix. Two energy conservation equations were used to model this
ERV. The condensation model describes the heat and mass transfer due to condensation
and evaporation in a rotary wheel designed with non-desiccant porous matrix. The
enthalpy model describes the heat and mass transfer in a rotary wheel using a desiccant
porous media matrix in which adsorption and desorption can take place. Both the
condensation and enthalpy models can be mathematically represented by two energy
conservation equations with four basic thermodynamic relationships, and two mass
conservation equations.
A non-dimensional representation for each model was derived and solved using
the finite difference method with the integral-based method formulation scheme. The
study examined the effect of wheel design parameters such as: rotational speed, number
of transfer units, heat capacity, and porosity of the matrix. Operating parameters such as
volume flow rate, inlet air temperatures and humidity ratios were studied, and the
numerical results are compared with experimental results. Experimental data of
effectiveness obtained from a commercial unit are found to be consistent with the
numerical results.

Approved:
Khairul Alam
Moss Professor of Mechanical Engineering
ACKNOWLEDGMENTS
First of all, I would like to thank almighty God for helping and guiding me during
my life and through my study and research. Then, I would like to express my sincere
gratitude and appreciation to my adviser Professor M. K. Alam. Thank you for providing
ideas, guidance, assistance, and editing throughout this research. I especially thank him
for his thoughtful insights not only in scientific research but also in life issues.
I would like to extend my sincere appreciation to my Ph.D. committee members,
Professor H. Pasic, Professor D. Gulino, Professor L. Herman, and Professor N. Pavel,
for supporting and encouraging me to finish this work successfully.
Special thanks go to my wife, Fattmah, for all her patience, understanding,
support, and love. I also wish to thank my family and friends for their support and
encouragement.
Finally, I would like to acknowledge the help of Stirling Technology, Inc. for
letting me use their experimental facility to conduct the experimental works required for
my research. Thanks also go to their mechanical engineer, Jason Morosko.
vii

TABLE OF CONTENTS

ABSTRACT………………………………..………………………………………….…iv

ACKNOWLEDGMENTS………………...…………………………………………….vi

LIST OF TABLES……………………………………………...……………………….xi

LIST OF FIGURES…………………………………………...……………………….xiii

NOMENCLATURE…………………………………………...………………………xix

1. INTRODUCTION…..……………………………………………………………….1

1.1 Background……………………………………………..…………………….…1
1.2 Rotary Air-to-Air Energy Wheels…………………………………………….…3
1.2.1 Principles of Operations…………………………………........................3
1.2.2 Classification……………………………………………….....................5
1.2.3 Typical Wheel….………………………...……………….......................6
1.2.4 Application……………………………………………………………..7
1.3 Review of Analysis of ERVs ………………………………………………….11
1.3.1 Non-Desiccant Wheels…………………………………………………11
1.3.1.1 Sensible Wheels……….……………………………………..12
1.3.1.2 Condensation Wheels………………………………………...15
1.3.2 Desiccant Wheels………………………………………………………16
1.3.2.1 Sorption Wheels…………………..………………………..17
1.3.2.2 Enthalpy Wheels……………………………………………..18
1.4 Research Objectives……………………………………………………………23
1.5 Scope of Research……………………………………………………………...24
1.6 Overview of Thesis…………………………………………………………….26

2. THEORETICAL BACKGROUND……………………………………….………27

2.1 Energy Wheel Models………………………………………………………….27
2.1.1 Sensible Wheel: Willmott’s Model…………………………………….28
2.1.2 Desiccant Wheel: Maclaine-Cross’s Model……………………………37
2.1.3 Enthalpy Wheel: Simonsons’s Model………………………………..41
2.1.4 Discussion of Models…………………………………………………..45
2.2 Effectiveness Correlations.…………………………………………………….46
2.2.1 The ε-NTU Method…….…...………………………………………....46
2.3 Performance Criteria…………………………………………………………...50
viii

2.4 Desiccants Overview…………………………………………………………..53
2.4.1 Desiccant Isotherms…………………………………………………....53
2.4.2 Desiccant Materials…………………………………………………….54
2.4.3 Desiccant General Sorption Curve……………………………………..56
2.4.4 Desiccant Isotherm Model……………………………………………..57
2.5 Thermodynamics Relationships………………………………………………..62
2.5.1 Properties of Moist Air………………………………………………...62
2.5.2 Properties of Matrix……………………………………………………66

3. MODELING OF ROTARY ENERGY WHEELS……………………………….68

3.1 Model Description.…………………………………………………………….68
3.1.1 Coordinates System and Nomenclature………………………………..69
3.1.2 Surface Geometrical Properties………………………………………..71
3.1.3 Dimensionless Parameters……………………………………………..73
3.2 Assumptions……………………………………………………………………75
3.3 Heat Transfer Model (Sensible Wheel Model)………………………………...77
3.3.1 Governing Equations…………………………………………………..77
3.3.2 Dimensionless Representation..………………………………………..81
3.3.3 Effectiveness Correlation for Limiting Cases……………………….....86
3.3.4 Finite Difference Equations.…………………………………………...92
3.4 Heat and Mass Transfer Model (Condensation Model)………………………102
3.4.1 Governing Equations…………………………………………………102
3.4.2 Modeling of Condensation and Evaporation…………………………116
3.4.3 Dimensionless Representation..………………………………………118
3.4.4 Finite Difference Equations.…………...……………………………..124
3.4.5 Control Criteria for Condensation Model Computer Program……….128
3.5 Heat and Mass Transfer Model (Enthalpy Model)…………………………...129
3.5.1 Governing Equations…………………………………………………129
3.5.2 Dimensionless Representation..……………………………………....134
3.5.3 Finite Difference Equations.…………………………...……………..136
3.5.4 Modeling Mass Transfer in the Enthalpy Wheel...…………………...140
3.6 Computer Codes………………………………………………………………142
3.6.1 Structure of Computer Programs………….………………………….142
3.6.2 Convergence and Stability..…………………………………………..145

4. MODELING RESULTS…………………………………………………………..147

4.1 Energy Wheel Characteristics and Boundary Conditions…………………….148
4.1.1 Energy Wheel…………………………………………………………148
4.1.2 Boundary Conditions…………………………………………………152
4.2 Sensible Wheel Model………………………………………………………..153
ix

4.2.1 Temperatures Profiles………………………………………………...154
4.2.2 Effect of Volume Flow Rate Q& on the Wheel Effectiveness………163
4.2.3 Effect of Rotational Speed Ω on the Wheel Effectiveness………165
4.2.4 Influence of NTU on the Effectiveness of Wheel…………………...167
4.2.5 Influence of Porosity ϕ on the Effectiveness of Wheel..…………….169
4.2.6 Summary……………………………………………………………...173
4.3 Condensation Wheel Model .............................................................................174
4.3.1 Heating Mode Where the Condensation Might Take Place…………..174
4.3.2 Comparing the Sensible Effectiveness with Sensible Model
Effectiveness………………………………………………………….177
4.3.3 Effect of the Rotational Speed Ω on the Effectiveness.……………..179
4.3.4 Influence of the Inlet Conditions on the Wheel Performance……….182
4.3.5 Summary……………………………………………………………...184
4.4 Enthalpy Wheel Model……………………………………………………….185
4.4.1 Enthalpy Wheel Behavior…………………………………………….185
4.4.2 Effect of the Volume Flow Rate Q& on the Effectiveness..…………...192
4.4.3 Effect of the Rotational Speed Ω on the Effectiveness….…………..195
4.4.4 Effect of the Porosity ϕ on the Effectiveness of Wheel.…………….197
4.4.5 Effect of the Number of Transfer Unit NTU and Lewis Number Le on
the effectiveness………………………………………………………200
4.4.6 Effect of the Isotherm Shape on the Effectiveness..……………….....204
4.4.7 Effect of the Supply Humidity on the Effectiveness.………………...207
4.4.8 Summary……………………………………………………………...208

5. EXPERIMENTAL DATA AND COMPARISON WITH THE ENTHALPY
MODEL……………………………………………………………………………211

5.1 Description of the Experimental Facility……………………………………..212
5.1.1 Experimental Setup…………………………………………………...212
5.1.2 RecoupAerator………………………………………………………..214
5.1.3 Air Flow Measurement……………………………………………….216
5.1.4 Temeprature and Humidity Measurement……………………………217
5.1.5 Pressure Measurement………………………………………………..217
5.1.6 Data Acquisition and Dasylab………………………………………..217
5.2 Energy Wheel Under Investigation (RecoupAerator)………………………...219
5.3 Operation Conditions…………………………………………………………220
5.4 Experimental Results and Comparison with the Enthalpy Model..…………..222
5.4.1 Winter Tests…………………………………………………………..222
5.4.2 Summer Tests…………………………………………………………225
5.5 Summary……………………………………………………………………...228
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6. RESEARCH SUMMARY, CONCLUSIONS, AND FUTURE WORK…....….229

6.1 Summary……………………………………………………………………...229
6.2 Conclusions…………………………………………………………………...231
6.3 Future Work..…………………………………………………………………233

REFERENCES……………………………………………………………………….235