Optimalisatie methodologieën voor modellen van tweefase loopsystemen met toepassingen in elektronicakoeling

In this work, a physics-based one-dimensional numerical model is proposed to evaluate the performance of passively cooled loop heat pipe (LHP) systems and their operational limits. An in-house setup was built, consisting of an entirely passive LHP with a flat evaporator (1 cm^2) active area) with accurate temperature measurements. Transparent materials are used to facilitate observations. With careful assessment of input power and calibration of heat transfer coefficients for the condenser, the model is validated by comparing the local temperatures in the evaporator and compensation chamber, the two-phase flow lengths in the condenser, and by evaluating the energy balance. The relative discrepancy between predicted and measured operating temperatures remains below 3.5% across all test cases. The validated model is then used to predict the system performance for the experimental setup with low thermal-conductivity casing, examining the effects of varying the coolant charging mass on various operational limits. The numerical results indicate that the LHP studied operates exclusively in fixed conductance mode. At 50% charging ratio, the system achieves the lowest operating temperature. The naturally cooled condenser and compensation chamber can dissipate over 29.9 W when the coolant saturation temperature reaches 100\celsius. As the heat leakage rate from the evaporator to the coolant in the compensation chamber is low, the analysis of the operational limits shows that, for the current LHP and operating conditions, the heat dissipation limit restricts the maximum input power and activates the heat leakage limit. In addition, the heat dissipation capacity and thermal resistance of the condenser are the primary limitations of the operational envelope. The model is further refined to account for more realistic casing material, and is then used to investigate the influence of various design parameters. When a metallic casing is employed, the heat leakage is significantly amplified, with the casing becoming the dominant pathway for heat leakage from the evaporator to the compensation chamber. This results in a pronounced nonlinear segment in all performance curves --corresponding to variable conductance mode-- across various coolant charging masses. For the LHPs studied with copper casing, this variable conductance mode even becomes the dominant operating mode. In this mode, for identical operating conditions and charging mass, the system exhibits a higher operating temperature. The impact of coolant charging mass on the system performance becomes negligible. Reducing the casing thickness, improving the contact at the wick-fin interface, or using low thermal conductive casing material can mitigate the heat leakage and lower the operating temperature. However, material substitution can also lead to extremely high junction temperatures, which may compromise the system reliability. Finally, analysis on the operational envelopes and limits shows that the use of a metallic casing can readily activate the heat leakage limit to the compensation chamber and, at high input powers, the heat leakage limit to the wick --while not triggering the heat dissipation limit. Under these conditions, variations in condenser geometries or cooling intensities have only a minor influence on the LHP performance and its operational envelope. The results indicate that reducing heat leakage through the casing and improving overall system cooling capacity must be addressed in tandem in the LHP design to achieve optimal performance.