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What is a Loop Heat Pipe? Introduction

What is a Loop Heat Pipe? Introduction. LED Power, Inc 1731 Kaiser Avenue Irvine, CA 92614. April 2009. www.ledpower.com. Heat Dissipation Development. Small watts. Middle watts. Large watts. Loop Heat Pipe. Fin + Heat Pipe. Heat dissipation fin. Blue ocean. 2003. 2005. 2009.

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What is a Loop Heat Pipe? Introduction

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  1. What is a Loop Heat Pipe? Introduction LED Power, Inc 1731 Kaiser Avenue Irvine, CA 92614 April 2009 www.ledpower.com

  2. Heat Dissipation Development Small watts Middle watts Large watts Loop Heat Pipe Fin + Heat Pipe Heat dissipation fin Blue ocean 2003 2005 2009 Market segment

  3. History of LHP • The LHP creation was a response to the challenge to develop a heat-transfer device operating on the principle of a heat pipe and possessing all its advantages, but at the same time capable of transferring heat for distances up to 1 m and more at different orientations in the gravity field. • Such a device was first invented in 1972 by Yu. Gerasimov and Yu. Maydanik at the Ural Polytechnical Institute. • The first name of the device was “a heat pipe”. Later the names “a heat pipe with separate channels” and “an antigravitational heat pipe” were used. • In 1989, when these devices came into use in space engineering, there appeared a new name “a Loop Heat Pipe”, which is now generally recognized.

  4. What is LHP? • An LHP (loop heat pipe) is a heat-transfer device that utilizes a micro-scale porous or wick structure to achieve remote heat transport with high power. • It uses a closed-loop pipe filled with working fluid to carry heat from the hot dissipative equipment to the cold external radiator/condenser. • LHPs are entirely passive devices – no external mechanical pumps or other power supplies are required.

  5. How Does LHP Work? • It achieves heat transfer by means of a working fluid that travels between an evaporator and a condenser through a hermetic closed-loop pipe. • Heat at the evaporator is transferred to the fluid, generating vapor. The vapor flows to the condenser and condenses into liquid, thereby dissipating the heat to the surroundings. • The evaporator contains a wick made of micro-porous material, which provides a capillary suction force to draw the condensed liquid back to the evaporator, thus completing the cycle.

  6. Loop Heat Pipe Fixtures • (1) Heat transport in long distance, several meters distance. • (2) High power, as high as several hundreds of Watts. • (3) Flexible, bendable connecting pipe. • (4) Anti-gravity operation, maintaining high heat transfer capability in anti-gravity direction. • (5) Passive heat-transfer device, no external power input.

  7. LHP Reliability Test • LHP reliability • Startup stability • Chemical stability • Structure strength • Durability to vibration etc • Reliability test with heating 1hr, non-heating 1 hr(12 cycles per day) at 80W or 120W • at horizontal and different tilted angles • Performance measurement every week

  8. LHP Long-Term Reliability Test • Evaporator thermal resistance: Rhv < 0.1K/W • Overall thermal resistance: Rha - 0.55 K/Wt

  9. Advanced Heat Dissipation Technology Radiator (Upper Housing) Flexible lines LED heat source LHP Evaporator With our technology, LPI can achieve Tj<65°C 100W side view 100W back view Goal is to keep a low LED junction temperature (<85 °C) to maintain 50,000 hr life @ 70%. With our technology, LPI can achieve Tj<65°C Thermal Image

  10. Loop Heat Pipe on 100 Watt LED Street Light

  11. Loop Heat Pipe on 100 Watt LED Street Light • When the light is turned on, the Loop Heat Pipe (LHP) jumps into action. • As shown above, the heat generated by Light Engine is quickly transferred to condenser L1, L2 and L3.

  12. Loop Heat Pipe on 100 Watt LED Street Light • Since the heat is transferred to the case by means of using a Thermal Connector, we can see the temperature of L1, L2 and L3 change rapidly.

  13. Loop Heat Pipe on 100 Watt LED Street Light • After the start-up of LHP, we can feel a noticeable temperature change of entire back surface.

  14. Loop Heat Pipe on 100 Watt LED Street Light • When the heated area is continuously on, the connecter contact area becomes warm. The temperature of L1, L2 and L3 reach the level about 35 ℃.

  15. Loop Heat Pipe on 100 Watt LED Street Light • The temperature of the case and the connecter contact area keep increasing with time. The connecter contact area becomes hot while the other area of the case is warmed up.

  16. Loop Heat Pipe on 100 Watt LED Street Light • About one hour later, heat transfer system reaches the steady state.

  17. Thank you

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