Abstract
An experimental setup has been designed, assembled and instrumented to perform thermal tests and observations inside a loop heat pipe (LHP). The hysteresis and temperature oscillations phenomena are investigated. The influence of nucleate boiling in the reservoir on the LHP operation and the effect of non-condensable gases are assessed. The links between temperature oscillations and the hydrodynamic behaviour of the LHP are highlighted. Finally, observations through the transparent lines confirm the occurrence of the condensation phenomena in the condenser and in the transport lines that were already observed by other author .
Highlights
Loop Heat Pipes (LHPs) are efficient heat transfer devices based on the passive heat transfer between a heat source and a heat sink, using the capillary pressure to circulate the fluid
We present a first set of experimental data and show the influence of several parameters (non-condensable gases (NCGs), boiling in the reservoir) on the steady-state operation of the system and on the hysteresis that is observed
- At moderate and high heat fluxes, boiling occurs inside the reservoir, inducing a sharp degradation of the system performance and a significant increase of the hysteresis
Summary
Loop Heat Pipes (LHPs) are efficient heat transfer devices based on the passive heat transfer between a heat source and a heat sink, using the capillary pressure to circulate the fluid. Various undesirable LHP behaviours have been experimentally observed after start-up or to the change of power or heat sink temperature, like hysteresis phenomena and oscillations. As explained by Launay and Vallée (2011), three types of temperature oscillation regimes have been reported in the literature: (i) ultra-high frequency temperature oscillations (period less than 1s), caused by the formation of liquid slugs in the condenser or the vapour line, (ii) high frequency low amplitude oscillations (period of few seconds or few minutes) caused by the inability of the vapour front to find a stable position inside the condenser, and (iii) low frequency high temperature oscillations (period of few hours), which may appear in case of large evaporator thermal inertia, low heat loads and cold sink temperatures. The results are systematically compared to other works of the literature to gain some knowledge on the behaviour of the LHP device
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