Steady-state and transient performance of a miniature loop heat pipe

State-of-the-Art Experimental Studies on Loop Heat Pipes

“…Sometimes, the LHP never really reaches a steady-state but instead displays an oscillating behaviors. These oscillating behaviors have been observed for various LHP designs of the literature (see table N) (Rodriguez and Na-Nakornpanom, 2001;Ku, 2003;Ku and Rodriguez, 2003;Mishkinis et al, 2004;Chen et al, 2006;Singh et al, 2008;Celata et al, 2010;Joung et al, 2010b;Li et al, 2010a). Three types of temperature oscillation regimes have been reported in the literature by Ku (2003) and Ku and Rodriguez (2003): i) ultra-high frequency (period of about one second or less) temperature oscillations, ii) high frequency (period of few seconds or minutes) low amplitude oscillations caused by the inability of the vapor front to find a stable position inside the condenser, iii) low frequency (period of about hours) high amplitude oscillations, which may appear for specific conditions as, for example, large evaporator thermal inertia, low heat load and cold sink temperature compared to the ambient one (Rodriguez and Na-Nakornpanom, 2001; Ku, 2003).…”

“…According to the experimental results, it is difficult to predict the shape of the LHP operating curve, because heat leak at the the evaporator/reservoir is strongly influenced by the E/CC design (wall materials and wick characteristics). U-shaped curves have been most often observed for metal capillary wicks, with ammonia as the working fluid (Maydanik, 2004;Chen et al, 2006) and when the temperature difference between the sink and the ambient is large, whereas curves with flattened shapes have been usually observed for low-thermalconductivity wicks with low-pressure working fluids such as methanol, ethanol, or acetone (Boo and Chung, 2004;Riehl and Dutra, 2005).…”

“…The role of the fluid distribution in the E/CC on the LHP startup has been demonstrated from some experimental studies by varying the relative position of the LHP components (the evaporator position relative to the reservoir and the condenser ones) (Boo and Chung, 2004;Chen et al, 2006; In the main cases, the initial distribution of the fluid charge in the E/CC is estimated from the component position. However, the assumption on the fluid charge distribution at the initial state and its role in the start-up seems supported by various visualization methods, which were implemented by different researchers.…”

“…As the type i) is usually assumed to be caused by the formation of liquid slugs in the condenser or the vapor line, types ii) and iii) are typically induced by the original complex couplings of the thermal and hydrodynamic mechanisms involved by the interactions and feedback between the loop components. Chen et al (2006) studied the influence of the cold source temperature and the relative position of the LHP components (the evaporator position relative to the condenser and the reservoir one's) on the characteristics of the high frequency oscillations (type (ii)). Figure 10 shows, for various LHP configurations, the heat flux ranges for which a temperature oscillating behavior is observed (black surface areas on the histograms).…”

Thermal performance of non-metallic two-phase cold plates for humanoid robot cooling

“…Rittidech [5] investigated the heat transfer characteristics of a closed-loop oscillating heat pipe with check valves. Though many conventional studied [6][7][8][9][10][11] have been conducted on twophase heat transport devices, they have been restricted to copper cold plate. The application in robot cooling devices with non-metallic material has not been reported in the literature except for Karng et al [12].…”