Electric Motor Thermal Management R&D (Presentation), NREL
Electric Motor Thermal Management R&D
Kevin Bennion Organization: NREL Email: [email protected] Phone: 303-275-4447
Team members/collaborators: Justin Cousineau, Charlie King, Gilbert Moreno, Caitlin Stack (NREL) Tim Burress, Andy Wereszczak (ORNL)
DOE Vehicle Technologies Office Electric Drive Technologies FY15 Kickoff Meeting
Oak Ridge National Laboratory Oak Ridge, Tennessee This presentation does not contain any November 18 – 20, 2014 proprietary or confidential information. NREL/PR-5400-63004 NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. Thermal Management Enables More Efficient and Cost-Effective Motors State of the Art • Water-ethylene glycol stator Stator Cooling Jacket cooling jacket • Automatic transmission fluid (ATF) impingement on motor end windings Stator End Winding
Why Motor Cooling • Current Density Photo Credit: Kevin Bennion, NREL Rotor Stator o Size o Weight o Cost • Material Costs o Magnets o Rare-earth materials o Price variability • Reliability • Efficiency Photo Credit: Kevin Bennion, NREL
DOE APEEM FY15 Kickoff Meeting 2 Passive and Active Cooling
Passive Thermal Stack •Motor geometry •Material thermal properties •Thermal interfaces
Passive Motor Active Thermal Thermal Convective Stack Cooling
Photo Credit: Kevin Bennion, NREL Management
Active Convective Cooling •Cooling location •Heat transfer coefficients •Available coolant •Parasitic power
DOE APEEM FY15 Kickoff Meeting 3 Challenges
Problem Motor Cooling Section View Extracting heat from within the motor to protect the motor and Stator Cooling Jacket Nozzle/Orifice enable high power density Case 6 Stator-Case Challenges ATF Flow Contact 5 1. Orthotropic (direction 1 End Winding dependent) thermal conductivity Stator of lamination stacks Laminations ATF Slot Winding 2 3 4 2. Orthotropic thermal conductivity Impingement of slot windings 3. Orthotropic thermal conductivity Air Gap 1 of end windings 4. Convective heat transfer Rotor Laminations coefficients for ATF cooling Rotor Hub 5. Thermal contact resistance of Shaft stator-case contact ATF Flow 6. Cooling jacket performance Motor Axis
DOE APEEM FY15 Kickoff Meeting 4 Proposed Research Objectives
Motor Cooling Section View Problem Stator Cooling Jacket Case Nozzle/Orifice Stator-Case Contact ATF Flow Core Thermal Capabilities End Winding Stator and Research Tasks Laminations ATF Slot Winding Impingement
Air Gap
Objective Rotor Support broad industry demand Laminations Rotor Hub for data, analysis methods, and Shaft experimental techniques to ATF Flow improve and better understand Motor Axis motor thermal management
DOE APEEM FY15 Kickoff Meeting 5 Research Focus
Automatic Transmission Fluid Heat Transfer
• Measure convective heat transfer coefficients for ATF cooling of end Research windings Photo Credit: Jana Jeffers, NREL Tasks • Measure interface thermal resistances and orthotropic thermal conductivity Material and Thermal of materials Interface Testing
Support broad industry demand for data Objective to improve and better understand motor thermal management Photo Credit: Justin Cousineau, NREL
DOE APEEM FY15 Kickoff Meeting 6 Accomplishments to Date – FY14 Active Cooling
Direct Impingement on Impingement on Motor End Target Surfaces Windings
Measure heat transfer coefficients for ATF cooling of end windings
Photo Credit: Jana Jeffers, NREL Photo Credit: Kevin Bennion, NREL Average Heat Transfer Coefficients • Establish credibility of experiment and data through comparison of plain target surface results to existing correlations in literature • Produce new data for textured surfaces representative of end-winding wire bundles Spatial Mapping of Convective Heat Transfer Coefficient • Jet local convective heat transfer • Large-scale end-winding convective heat transfer mapping
DOE APEEM FY15 Kickoff Meeting 7 ATF Impingement Target Surfaces
• ATF impingement baseline target is plain, polished copper with 600-grit sandpaper • Additional targets mimic wire bundles with insulation (18, 22, and 26 AWG)
Baseline 18 AWG 22 AWG 26 AWG
Radius (wire and insulation), N/A 0.547 0.351 0.226 mm
Total wetted surface area, mm2 126.7 148.2 143.3 139.2
Credit: Gilbert Moreno, NREL 18 AWG 22 AWG 26 AWG
AWG = American Wire Gauge
DOE APEEM FY15 Kickoff Meeting 8 Comparison to Plain Surface Correlations
Comparison of test results to literature correlations on flat target surface
12,000 50°C 70°C
90°C K)
- 10,000 Metzger et al., 1974 (90°C) 2 Ma et al., 1997 (50°C) Ma et al., 1997 (70°C) Ma et al., 1997 (90°C) 8,000 Leland and Pais, 1999 (50°C) Leland and Pais, 1999 (70°C) Leland and Pais, 1999 (90°C)
6,000 coefficient (W/m coefficient
4,000 transfer
2,000 Heat Heat
0 0 2 4 6 8 10 Jet velocity (m/s) ATF fluid properties provided by Ford
DOE APEEM FY15 Kickoff Meeting 9 Spatial Mapping of Heat Transfer
Local convective heat transfer coefficient • Jet impingement heat
d, nozzle transfer coefficients are not diameter Liquid jet uniform over the entire Air cooled surface
Stagnation zone
Wall jet zone • The highest heat transfer Tw coefficients occur at the jet Heated surface impact zone • The rate of decrease in the Heat transfer coefficient heat transfer coefficient is unknown
r / d
DOE APEEM FY15 Kickoff Meeting 10 TLC Experimental Apparatus
• Fabricated a test section to spatially Test article cross-sectional view measure jet impingement heat transfer Foil: heated via joule coefficients on a discrete heat source. heating • Initial tests will be conducted using thermochromic liquid crystals (TLCs), followed by infrared imaging Lexan insulation/support
Teflon insulation/ support ATF inlet vessel Bus bars
Test article bottom view
Bottom side view of heated foil with camera 2-mm-diameter nozzle Test article fixture
DOE APEEM FY15 Kickoff Meeting 11 Accomplishments to Date – FY14 Passive Thermal Stack
Material Effective Thermal Properties for Measurements Motor Design and Simulation
Measure interface thermal resistances and orthotropic thermal conductivity of materials
Photo Credit: Justin Cousineau, NREL Photo Credit: Kevin Bennion, NREL Stacked lamination thermal conductivity • Quantified thermal contact resistance between motor laminations • Supports improved thermal models for motor design and thermal analysis Winding effective thermal properties • Initiated work to measure orthotropic thermal properties • Supports improved thermal models for motor design • Enables analysis to improve thermal properties of motor materials Case-to-stator thermal contact resistance • Developed ability to measure case-to-stator thermal contact resistance
DOE APEEM FY15 Kickoff Meeting 12 Through-Stack Thermal Conductivity
Measured Stack Thermal Lamination-to-Lamination Effective Through-Stack Resistance Thermal Contact Resistance Thermal Conductivity
Force Applied
Hot Plate
Copper Spreader
Thermal Grease Copper Metering Block
Lamination Stack
Thermal Grease Copper Metering Block
Copper Spreader
Cold Plate Photo Credit: Justin Cousineau, NREL
DOE APEEM FY15 Kickoff Meeting 13 Through-Stack Thermal Conductivity
Measured Stack Thermal Lamination-to-Lamination Effective Through-Stack Resistance Thermal Contact Resistance Thermal Conductivity
M19 29 Gauge, 138 kPa Data Force Applied 2500 Data with Systematic Error K/W] - 2000 Weighted Curve Fit Hot Plate
1500 Copper Spreader Thermal Grease Copper Metering Block 1000 Lamination Stack Copper Metering Block 500 Thermal Grease Measured Stack Lamination Measured
Thermal (mm² Resistance Copper Spreader 0 0 2 4 6 8 10 Cold Plate Number of Contacts • Lamination-to-lamination thermal contact resistance calculated from slope of weighted curve fit Error bars represent 95% confidence level 14 DOE APEEM FY15 Kickoff Meeting 14 Through-Stack Thermal Conductivity
Measured Stack Thermal Lamination-to-Lamination Effective Through-Stack Resistance Thermal Contact Resistance Thermal Conductivity 350 300
250 Lamination Lamination - K/W]
- 200 M19 26 Gauge to 150 M19 29 Gauge [mm² HF10 100 Arnon7 - Lamination
Thermal Contact Resistance ThermalResistance Contact 50 0 138 276 414 552 Pressure [kPa] • The lamination-to-lamination thermal contact resistance is affected by the surface topography and contact pressure
Error bars represent 95% confidence level 15 DOE APEEM FY15 Kickoff Meeting 15 Through-Stack Thermal Conductivity
Measured Stack Thermal Lamination-to-Lamination Effective Through-Stack Resistance Thermal Contact Resistance Thermal Conductivity
M19 29 Gauge, 138 kPa Example 3.3 3.1 Effective Through-Stack Thermal Conductivity
2.9 Asymptote ( → ∞)
2.7 𝐿𝐿
Conductivity 𝑁𝑁 2.5 K] - 2.3
[W/m 2.1 1.9 Stack ThermalStack 1.7 1.5
- Through 0 10 20 30 40 50
Number of Laminations (NL) • The effective through-stack thermal conductivity approaches the asymptote within 30–50 laminations
16 DOE APEEM FY15 Kickoff Meeting 16 Through-Stack Thermal Conductivity
Measured Stack Thermal Lamination-to-Lamination Effective Through-Stack Resistance Thermal Contact Resistance Thermal Conductivity
2.2 M19 26 Gauge 2.0 M19 29 Gauge
Thermal Thermal K]
- HF10 1.8 Arnon7 Stack - 1.6 • Asymptotic thermal 1.4 conductivity increases with pressure 1.2 Conductivity[W/m • Asymptotic thermal 1.0 conductivity depends on Asymptotic Through Asymptotic 0.8 inter-lamination thermal contact resistance, 0.6 lamination thermal 0 200 400 600 conductivity, and lamination Pressure [kPa] thickness Error bars represent 95% confidence level 17 DOE APEEM FY15 Kickoff Meeting 17 In-Plane Lamination Thermal Conductivity
M19 29 Gauge Laminations
K]
- 25.0 21.9 21.7 21.8 20.0
15.0
10.0 Photo Credit: Justin Cousineau, NREL • Confirmed in-plane thermal 5.0 conductivity is close to bulk material thermal Plane Thermal Plane Thermal Conductivity [W/m - 0.0
In conductivity Bulk Calculated Measured 3 Material 1 Value 2
1. Based on measured thermal conductivity of similar material 2. Calculated assuming 99% stacking factor 3. Average of measured orthotropic property in setup shown in figure
DOE APEEM FY15 Kickoff Meeting 18 FY15 Tasks to Achieve Key Deliverable
2014 2015 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Publications for End- Deliverable Winding Heat Transfer ATF impingement experiments to measure variation in local convective heat transfer coefficients End-winding spatial mapping of ATF convective heat transfer coefficients on end-winding features
Go/ Select passive No-Go thermal materials Thermal measurements of passive thermal stack for bench-level elements in collaboration with Oak Ridge National testing in Laboratory (ORNL) partnership with • Winding thermal properties ORNL • Contact interfaces • Thermal analysis support in collaboration with ORNL motor research
DOE APEEM FY15 Kickoff Meeting 19 Local ATF Jet Heat Transfer Mapping
Spatially measure jet impingement heat transfer coefficients on a discrete heat source. Bottom view of test article Heated foil temperature distribution 111°C
64°C Thermal-electrical finite element analysis (FEA) reveals edge effects mostly associated with copper bus bars • ∆T across foil 47°C (most of heat loss to copper bars) • 85% of foil heater power dissipated by jet
DOE APEEM FY15 Kickoff Meeting 20 Local ATF Jet Heat Transfer Mapping
Spatially measure jet impingement heat transfer coefficients on a discrete heat source. Bottom view of test article Heated foil temperature distribution Guard heaters 112°C
105°C Use of guard heaters minimize edge effects through the use of guard heaters • ∆T across foil 7°C (heat loss to copper decreased) • 98% of foil heater power dissipated by jet
DOE APEEM FY15 Kickoff Meeting 21 Spatial Mapping of Heat Transfer
Large-scale end-winding convective heat transfer mapping • Map the large-scale spatial distribution of the heat transfer coefficients over motor end windings • Study effects of
o Oil jet placement o ATF free flow over end- winding surfaces Photo Credit: Kevin Bennion, NREL o Jet interactions
DOE APEEM FY15 Kickoff Meeting 22 Spatial Mapping of Heat Transfer
Large-scale end-winding convective heat transfer mapping
Custom heat transfer sensor package in end winding • Target surfaces installed on three surfaces to measure heat transfer coefficients o Outside diameter surface o Inside diameter surface o Axial end surface
Example ATF jets
DOE APEEM FY15 Kickoff Meeting 23 Spatial Mapping of Heat Transfer
Large-scale end-winding convective heat transfer mapping
1. Fluid Jet Geometry ATF jets • Location and 1 orientation of ATF fluid jets • Nozzle type/geometry • System flow rate • Jet velocity • Parasitic power 2. Relative positon between 2 measured heat transfer and jet location • Impact of gravity and free fluid flow • Fluid interactions between jets
DOE APEEM FY15 Kickoff Meeting 24 Passive Thermal Stack
Sample Case-Stator Contact • Case thermal contact resistance Surface for Motor Cooling
o Case surface characteristics • Slot and end-winding effective thermal conductivity • Potting materials for end-winding cooling
Example Interference Fit with Sample Motor End Windings Stator and Cooling Jacket Case
Photo Credits Kevin Bennion, NREL DOE APEEM FY15 Kickoff Meeting 25 Project Summary
Project Duration: FY14–FY16 Overall Objective: Provide data to support broad Industry demand for improving motor thermal management FY14 Focus: Characterized ATF impingement average heat transfer coefficients and completed lamination-to- lamination thermal contact resistance measurements Deliverable: Completed measurement of average convective heat transfer coefficients with ATF and compared results of plain surface data to correlations in the open literature. Completed lamination-to-lamination thermal contact measurements and stack effective thermal conductivity Go/No-Go: Developed test apparatus to measure local impingement heat transfer results with ability to measure local heat transfer coefficients. Developed test hardware design and plan for representative wire bundle geometries FY15 Focus: Spatially map ATF impingement convective heat transfer coefficients and measure passive thermal stack thermal resistances Deliverable: Publish end-winding heat transfer performance data Go/No-Go: In collaboration with ORNL select passive thermal stack materials for bench-level thermal testing FY16 Focus: Confirm convective heat transfer performance on in-situ motor thermal performance tests. Deliverable: Report heat transfer performance and model validation Go/No-Go: Complete in-situ motor thermal tests for ATF cooling Publications: K. Bennion and J. Cousineau, “Sensitivity Analysis of Traction Drive Motor Cooling,” in IEEE Transportation Electrification Conference and Expo (ITEC), 2012, pp. 1–6. DOE APEEM FY15 Kickoff Meeting 26 Technology-to-Market Plan
• This research impacts industry needs because …
o The heat flow, temperature distribution, and fluid dynamics for motor thermal management are complex problems
o Data on cooling convective heat transfer coefficients and heat spreading within the motor are needed to improve motor performance within cost, efficiency, and reliability constraints
• This research is on the path to commercialization because …
o The research is reviewed by and shared with industry experts o The data are used by industry experts in the analysis and design of electric motors
DOE APEEM FY15 Kickoff Meeting 27 Partners/Collaborators
• Industry
o Motor industry suppliers, end users, and researchers – Input on research and test plans – Sharing of experimental data, modeling results, and analysis methods – Companies providing research input, requesting data, or supplying data include: Ford, Chrysler, GM, Tesla, UQM Technologies, Remy, Magna, John Deere, Oshkosh
• Other Government Laboratories
o ORNL – Support from benchmarking activities – Collaboration on motor designs to reduce or eliminate rare-earth materials – Collaboration on materials with improved thermal properties . Potting materials for end windings for improved heat transfer . Slot winding materials
DOE APEEM FY15 Kickoff Meeting 28 Acknowledgments: For more information, contact: Susan Rogers and Steven Boyd Principal Investigator U.S. Department of Energy Kevin Bennion [email protected] Phone: (303)275-4447
Team Members: APEEM Task Leader: Justin Cousineau Sreekant Narumanchi Charlie King [email protected] Gilbert Moreno Phone: (303)275-4062 Caitlin Stack Tim Burress (ORNL) Andy Wereszczak (ORNL)
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.