Cooling of LED headlamp in automotive by heat pipes

This article introduces the paper "Cooling of LED headlamp in automotive by heat pipes".

1. Overview:

  • Title: Cooling of LED headlamp in automotive by heat pipes
  • Authors: Randeep Singh, Masataka Mochizuki, Tadao Yamada, Tien Nguyen
  • Year of Publication: 2020
  • Journal/Conference of Publication: Applied Thermal Engineering
  • Keywords: Passive cooling, Flexible heat pipe, Hinge heat pipe, Piezo fan, Lighting, Automotive thermal management

2. Research Background:

  • Social/Academic Context of the Research Topic: Automotive headlamps are transitioning from halogen/xenon to LEDs. LEDs offer twice the luminous efficacy, 10-15 times longer lifespan, and improved styling compared to halogen lamps. Unlike halogen lamps, LEDs require temperature control to maintain monochromaticity, luminous intensity, and longevity.
  • Limitations of Existing Research: Traditional aluminum die-cast heat sinks used for LED cooling solutions are thermally inefficient, structurally heavy, and space-intensive.
  • Necessity of Research: Research is needed on heat pipe-based cooling systems for various LED headlamp designs and styles, capable of handling thermal performance up to 20W per module.

3. Research Objectives and Research Questions:

  • Research Objective: To propose, design, and characterize heat pipe-based cooling systems for different designs and styles of LED headlamps and thermal capability of up to 20 W/per-module.
  • Core Research Question: Can heat pipe-based cooling systems provide a more efficient and lighter alternative to die-cast heat sinks for LED headlamps?
  • Research Hypothesis: Heat pipe-based cooling systems can offer higher thermal performance and lighter weight compared to die-cast heat sinks for LED headlamps.

4. Research Methodology:

  • Research Design: Design and characterization of heat pipe cooling systems for various LED headlamp designs and styles.
  • Data Collection Method: Characterization of steady-state thermal performance (operating temperature and thermal resistance), temperature measurement using T-type thermocouples (accuracy +/- 0.1 °C), heat load provision using thermal simulators (current and voltage accuracy +/-0.01 A or V).
  • Analysis Method: Thermal resistance analysis, comparison of different cooling solutions.
  • Research Subjects and Scope: Various heat pipe designs including high-performance cylindrical/flattened copper-water heat pipes for low/high beam cooling, hinge heat pipes for adaptive headlamps with swivel function cooling, and flexible heat pipes for remotely mounted heat sinks.

5. Key Research Findings:

  • Core Findings: Heat pipe heat sinks provide "40-50% lighter" weight and "2-3 times higher thermal capability" compared to die-cast heat sinks. Heat pipe merits include "ultra-thin form factor, higher degrees of freedom and higher design tolerance."
  • Statistical/Qualitative Analysis Results:
  • Heat pipe heat sinks maintained LED package temperature below 80°C at a 25°C ambient temperature.
  • The total thermal resistance from the LED junction to ambient air for the hinge heat pipe assembly was "6.89 °C/W".
  • Piezo fan cooling reduced the source temperature by "7.6 °C" and increased the enclosure air temperature by "3.7 °C".
  • Data Interpretation: Heat pipes drastically improve heat dissipation capability and enable better space utilization and passive cooling.
  • Figure List:
    • Fig. 1. Heat load output by different lamp types.
    • Fig. 2. Heat output versus device length for different automotive electronic/electric systems.
    • Fig. 3. LED package for automotive headlamp.
    • Fig. 4. Schematic of LED package with thermal module (top), and system thermal resistance network (bottom).
    • Fig. 5a. Cooling module design for automotive headlamp.
    • Fig. 5b. Heat pipe heat sink for cooling high beam LED package inside head-lamp.
    • Fig. 6. Heat pipe heat sink for headlamp high beam cooling.
    • Fig. 7. Thermal test on LED headlamp with heat pipe based cooling of high beam.
    • Fig. 8. Breakdown thermal resistance for different components from LED junction to ambient air.
    • Fig. 9. Hinge heat pipe assembly.
    • Fig. 10. Hinge heat pipe assembly for cooling LED package with swivel function.
    • Fig. 11. Flexible heat pipe.
    • Fig. 12. Heat pipe assembly with frame as heat sink.
    • Fig. 13. Heat pipe assembly for cooling fog light LED package in headlamp.
    • Fig. 14. Heat pipe heat sink for low beam LED package cooling.
    • Fig. 15. Axial fan installed inside headlamp for forced convection cooling.
    • Fig. 16. Round type Piezo fan.
    • Fig. 17. Velocity profile of round piezo fan.
    • Fig. 18. Cooling enhancement for LED headlamp using piezo fan.
Fig. 1. Heat load output by different lamp types.
Fig. 1. Heat load output by different lamp types.
Fig. 2. Heat output versus device length for different automotive electronic/ electric systems.
Fig. 2. Heat output versus device length for different automotive electronic/ electric systems.
Fig. 3. LED package for automotive headlamp
Fig. 3. LED package for automotive headlamp
Fig. 4. Schematic of LED package with thermal module (top), and system thermal resistance network (bottom).
Fig. 4. Schematic of LED package with thermal module (top), and system thermal resistance network (bottom).
Fig. 5a. Cooling module design for automotive headlamp.
Fig. 5a. Cooling module design for automotive headlamp.
Fig. 5b. Heat pipe heat sink for cooling high beam LED package inside headlamp.
Fig. 5b. Heat pipe heat sink for cooling high beam LED package inside headlamp.
Fig. 13. Heat pipe assembly for cooling fog light LED package in headlamp
Fig. 13. Heat pipe assembly for cooling fog light LED package in headlamp
Fig. 14. Heat pipe heat sink for low beam LED package cooling
Fig. 14. Heat pipe heat sink for low beam LED package cooling
Fig. 15. Axial fan installed inside headlamp for forced convection cooling.
Fig. 15. Axial fan installed inside headlamp for forced convection cooling.
Fig. 15. Axial fan installed inside headlamp for forced convection cooling.
Fig. 15. Axial fan installed inside headlamp for forced convection cooling.

6. Conclusion and Discussion:

  • Summary of Key Results: Heat pipe cooling solutions for LED headlamps are lighter and offer higher thermal performance than die-cast heat sinks. Various heat pipe designs (cylindrical, flattened, hinge, flexible) were developed and tested.
  • Academic Significance of the Research: Demonstrated the effectiveness of heat pipes for LED headlamp cooling and provided design options for various headlamp styles.
  • Practical Implications: Heat pipe technology offers a viable solution for efficient and compact cooling of next-generation LED headlamps, enabling passive cooling and better space utilization.
  • Limitations of the Research: The paper does not explicitly mention limitations.

8. References:

[1] US Department of Energy, Energy Efficiency of LEDs, PNNL-SA-94206, March 2013, Available: http://energy.gov/eere/ssl/downloads/energy-efficiency-leds.
[2] OSRAM GmBH, Viewed: 27 March 2016, Available: http://www.osram-os.com/osram_os/en/index.jsp.
[3] R. Singh, M. Mochizuki, Y. Saito, T. Yamada, T. Nguyen, Ti Nguyen, Heat pipes applications in cooling automotive electronics, Heat Pipe Sci. Technol. An Int. J. 6 (3) (2015) 1-13.
[4] M. Mochizuki, Y. Saito, K. Mashiko, T. Raay, R. Singh, High power heat removal by heat pipes & two phase heat transfer for electric vehicle, 53rd Japan Heat Transfer Symposium, (2016).
[5] B. Orr, A. Akbarzadeh, M. Mochizuki, R. Singh, A review of car waste heat recovery systems utilising thermoelectric generators and heat pipes, Appl. Therm. Eng. (2016), https://doi.org/10.1016/j.applthermaleng.2015.10.081.
[6] R. Singh, M. Mochizuki, Y. Saito, T. Yamada, T. Nguyen, Ti Nguyen, A. Akbarzadeh, Loop heat pipe applications in automotive thermal control, Proc. 17th International Heat

9. Copyright:

This material is based on the paper: [Original Paper Title] by [Paper Author].
This material is a summary based on the above paper, and unauthorized use for commercial purposes is prohibited.
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