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Capillary Limit in a Loop Heat Pipe with a Single Evaporator
ISSN: 0148-7191, e-ISSN: 2688-3627
Published July 15, 2002 by SAE International in United States
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This paper describes a study on the capillary limit of a loop heat pipe (LHP) at low powers. The slow thermal response of the loop at low powers makes it possible to observe interactions among various components after the capillary limit is exceeded. The capillary limit at low powers is achieved by imposing an additional pressure drop on the vapor line through the use of a metering valve. A differential pressure transducer is also used to measure the pressure drop across the evaporator and the compensation chamber (CC). Test results show that when the capillary limit is exceeded, vapor will penetrate the primary wick, resulting in an increase of the CC temperature. Because the evaporator can tolerate vapor bubbles, the LHP will continue to function and may reach a new steady state at a higher operating temperature. Thus, the LHP will exhibit a graceful degradation in performance rather than a complete failure. The loop can recover from degraded performance due to previous vapor penetration by reducing the heat load without the need of a re-start. Moreover, the ground test results show that the fluid inventory and the relative tilt between the evaporator and the CC have profound effects on the loop operating temperature due to their effects on the vapor content inside the evaporator core. The operating temperature in turn affects the wick’s capillary capability and the total pressure drop. This makes the concept of the LHP heat transport limit somewhat ambiguous.
CitationKu, J., Ottenstein, L., Rogers, P., and Cheung, K., "Capillary Limit in a Loop Heat Pipe with a Single Evaporator," SAE Technical Paper 2002-01-2502, 2002, https://doi.org/10.4271/2002-01-2502.
- Maidanik, Y. F., et al., “Heat Transfer Apparatus,”United States Patent No. 4515209, 1985.
- Ku, J., “Operating Characteristics of Loop Heat Pipes,” SAE Paper No. 1999-01-2007, 1999.
- Cheung, M., Hoang, T., Ku, J., and Kaya, T., “Thermal Performance and Operational Characteristics of Loop Heat Pipe (NRL LHP),” SAE Paper No. 981813, 1998.
- Kaya, T., and Ku, J., “Investigation of the Temperature Hysteresis Phenomenon of a Loop Heat Pipe,” 1999 National Heat Transfer Conference, Albuquerque, New Mexico, August 15- 17, 1999.
- Ku, J., Ottenstein, L., Kaya, T., Kobel, M., and Rogers, P., “Temperature Oscillations in Loop Heat Pipe Operation,” STAIF 2001, American Institute of Physics, Albuquerque, New Mexico,February 11-142001
- Wolf, D., and Bienert, W., “Investigation of Temperature Control Characteristics of Loop Heat Pipe,” SAE Paper No.941576, 1994.
- Ku, J., Ottenstein, L., Rogers, P., and Cheung, K., “Low Power Operation in a Loop Heat Pipe,” SAE Paper 2001-01-1992, 2001.
- Kaya, T., and Ku, J., “Performance Characteristics of a Terrestrial Loop Heat Pipe,”AIAA paper No. 2000-0966, 38th Aerospace Sciences Meeting and Exhibit,, January 10-132000, Reno, Nevada.