Comparison of Heat Exchanger Designs for Aircraft Thermal ...

1 Comparison of heat Exchanger Designs for Aircraft Thermal Management William Cody Reed Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Aerospace Engineering Pradeep Raj, Co- Chair Michael R. von Spakovsky, Co- Chair Seongim Choi May 5, 2015 Blacksburg, Virginia Keywords: Thermal Management System, Optimization, Aerospace, heat Exchangers, Thermal Storage Comparison of heat Exchanger Designs for Aircraft Thermal Management William Cody Reed Thermal management has become a major concern in the design of current and future more and all electric Aircraft (M/AEA). With ever increasing numbers of on-board heat sources, higher heat loads, limited and even decreasing numbers of heat sinks, integration of advanced intelligence, surveillance and reconnaissance (ISR) and directed energy weapons, requirements for survivability, the use of composite materials, etc.

2 , existing Thermal management systems and their components have been pushed to the limit. To address this issue, more efficient methods of Thermal management must be implemented to ensure that these new M/AEA Aircraft do not overheat and prematurely abort their missions. Crucial to this effort is the need to consider advanced heat Exchanger concepts, comparing their Designs and performance with those of the conventional compact exchangers currently used on-board Aircraft Thermal management systems. As a step in this direction, the work presented in this thesis identifies two promising advanced heat Exchanger concepts, namely, microchannel and phase change heat exchangers. Detailed conceptual design and performance models for these as well as for a conventional plate-fin compact heat Exchanger are developed and their design and performance optimized relative to the criterion of minimum dry weight. Results for these optimizations are presented, comparisons made, conclusions drawn, and recommendations made for future research.

3 These results and comparisons show potential performance benefits for Aircraft Thermal management incorporating microchannel and phase change heat Acknowledgements This thesis would not have been possible without the assistance of many people. I would like to thank both of my advisors, Dr. Pradeep Raj and Dr. Michael von Spakovsky, for giving me the opportunity to work on this project and providing me with guidance and pushing me to do better throughout the entire process. Without you this work would not exist. I would also like to thank Dr. Seongim Choi for serving on my committee and providing assistance when needed. To all of the friends I have made in Blacksburg, thanks for helping in so many ways to allow this work to be completed. Special thanks to the other aerospace graduate students that listened to my ideas and provided distractions when I needed to get away for a while. To Megan, thank you for supporting me through this past year.

4 You always kept me going even while being away and provided a bright spot in many long days. To my parents, Dana and Cathy, and my sister, Molly, I cannot give enough thanks. Your unwavering support and love has allowed me to accomplish all that I have. Without you, I could ve completed only a small piece of what was done. This work is dedicated to you. iv Table of Contents Chapter 1 - Introduction .. 1 Historical Background .. 1 More Electric Aircraft .. 1 Directed Energy .. 2 Problem Description .. 3 Thermal Issues in Modern Aircraft .. 3 Simulation of a Mission .. 4 Thesis Objectives .. 6 Chapter 2 - Literature Review .. 7 Modeling and Analysis of Aircraft Thermal Subsystems .. 7 Aircraft Conceptual Design and Optimization .. 7 Tip-to-Tail Aircraft Modeling .. 9 Aircraft Vehicle Subsystem (AVS) .. 9 Propulsion Subsystem(PS) .. 9 Electrical Subsystems .. 9 Thermal Management Subsystems.

5 10 Fuel Thermal Management Subsystem (FTMS) .. 10 Adaptive Power and TMS (APTMS) .. 10 heat Exchanger Modeling and Simulation .. 11 Plate-Fin heat Exchanger .. 12 heat Exchanger Sizing, Modeling, and Simulation in the Literature .. 13 Advanced heat Exchanger and Thermal Management Technology .. 14 Microchannel heat Exchangers .. 14 Manufacturing Challenges of Microchannel heat Exchangers .. 15 Phase Change Energy Storage .. 16 Chapter 3 - Model 19 Development of the Microchannel heat Exchanger Sizing Algorithm .. 19 Microchannel heat Exchanger Sizing Optimization .. 26 Thermal Energy Storage (TES) Model .. 27 v Chapter 4 - Results .. 30 Microchannel heat Exchanger Model Validation .. 30 Fixed-Fin-Efficiency APTMS PAO-Air Microchannel heat Exchanger .. 32 Accounting for Fin Geometry with a Fixed Fin Efficiency .. 32 Fixed-Fin-Efficiency APTMS heat Exchangers using the New Fin Efficiency-Geometry Constraint.

6 35 Fixed-Fin-Efficiency FTMS PAO-Fuel Microchannel heat Exchanger using New Fin-Efficiency-Geometry Constraint .. 42 Variable-Fin-Efficiency APTMS PAO-Air Microchannel heat 46 Phase Change Materials .. 50 Chapter 5 Conclusions and Recommendations .. 55 Appendix A Microchannel heat Exchanger Sizing Algorithm .. 57 63 vi List of Figures Figure Aircraft Thermal requirements over time .. 3 Figure Tip-to-tail mission profile .. 5 Figure Cost of change in the design process .. 7 Figure Essential Aircraft sub-systems that form the tip-to-tail model .. 11 Figure Plate fin heat Exchanger fin geometries .. 12 Figure Tube-fin versus Plate-fin heat Exchanger .. 13 Figure Comparison of plate fin versus microchannel core volumes .. 15 Figure TES cell schematic .. 17 Figure Example of the discretization scheme for the quasi-2D TES PCM model .. 17 Figure Example of the discretization scheme for the 2D TES PCM model.

7 18 Figure Schematic of a typical counter flow microchannel heat Exchanger .. 19 Figure Iterative sizing process for area .. 22 Figure heat Exchanger thermodynamic system .. 22 Figure TES Thermodynamic System .. 28 Figure APTMS cold side microchannel heat Exchanger actual vs assumed fin efficiency 33 Figure APTMS hot side microchannel heat Exchanger actual vs assumed fin efficiency .. 33 Figure APTMS cold side plate fin heat Exchanger actual vs assumed fin efficiency .. 34 Figure APTMS hot side plate fin heat Exchanger actual vs assumed fin efficiency .. 34 Figure APTMS microchannel heat Exchanger mass with actual vs assumed fin efficiency .. 35 Figure APTMS microchannel heat Exchanger mass percent increase with actual vs assumed fin efficiency .. 35 Figure APTMS heat Exchanger mass versus heat load for a compact plate fin and microchannel heat Exchanger .

8 36 Figure Percent reduction in APTMS heat Exchanger mass for a compact plate fin and a microchannel heat Exchanger .. 36 Figure Cold side hydraulic diameter of a microchannel and compact plate fin heat Exchanger sized for the APTMS tip-to-tail loads .. 37 Figure Hot side hydraulic diameter of a microchannel and compact plate fin heat Exchanger sized for the APTMS tip-to-tail loads .. 38 vii Figure Overall heat Exchanger length for APTMS microchannel vs plate fin heat Exchanger .. 41 Figure APTMS pressure drop for microchannel vs plate-fin heat 42 Figure FTMS heat Exchanger mass versus heat load for a compact plate fin and microchannel heat Exchanger .. 43 Figure Percent reduction in FTMS heat Exchanger mass for a compact plate fin and a microchannel heat Exchanger .. 43 Figure Cold side hydraulic diameter of a microchannel and compact plate fin heat Exchanger sized for the FTMS tip-to-tail 44 Figure Hot side hydraulic diameter of a microchannel and compact plate-fin heat Exchanger sized for the FTMS tip-to-tail 44 Figure Overall heat Exchanger length for APTMS microchannel and plate-fin heat 46 Figure Mass trend of an APTMS microchannel heat Exchanger using both a fixed and variable fin efficiency.

9 47 Figure Mass trend of an APTMS plate fin heat Exchanger using both a fixed and variable fin efficiency .. 47 Figure Microchannel heat Exchanger fin efficiency cold side .. 48 Figure Microchannel heat Exchanger fin efficiency hot side .. 48 Figure Plate-fin heat Exchanger efficiency cold 49 Figure Plate-fin heat Exchanger efficiency hot side .. 49 Figure Temperature profile of a small volume TES cell for pentadecane, hexadecane, and octadecane .. 52 Figure Temperature profile of a medium volume TES cell for pentadecane, hexadecane, and octadecane .. 52 Figure Temperature profile of a large volume TES cell for pentadecane, hexadecane, and octadecane .. 53 viii List of Tables Table Tip-to-tail mission profile in detail .. 5 Table List of TES parameters .. 17 Table Results for the 2D and quasi-2D TES PCM models for a simulation time of 200 sec.

10 18 Table Geometry equations for a microchannel heat Exchanger .. 20 Table Iterative design heat transfer and pressure drop 23 Table Effectiveness-NTU equations .. 23 Table heat Exchanger mass, volume, and area equations .. 24 Table Variable fin-efficiency equations .. 25 Table Equations to determine the wall heat transfer coefficient .. 25 Table Gnielinski correlations for determining turbulent flow Nussult number .. 26 Table Upper and lower bounds for microchannel and plate-fin optimization decision variables .. 27 Table TES cell and working fluid thermodynamic equations .. 28 Table heat transfer model equation for TES cell .. 29 Table Design information for the APTMS PAO-Air heat Exchanger .. 30 Table Design information for FTMS PAO-Air heat Exchanger .. 30 Table Geometry parameters used for model validation .. 31 Table heat Exchanger validation results.