Experimental optimization of capillary structures for loop heat pipes and heat switches

Loop Heat Pipes (LHP) and Heat Pipes (HP) are used in the thermal management of electronic devices with high-density heat dissipation. In these two-phase thermal devices, the key component is the capillary structure (CS) that pumps the working fluid using the capillary forces generated by the meniscus, which is formed due to evaporation. The performance of the LHP and the HP depends greatly on the internal structure and external configurations of the CS. However, there is not enough experimental and theoretical data on the optimization of the capillary structures of evaporators. The “inverted meniscus” scheme is the usual configuration for Loop Heat Pipes (LHP) but not for Heat Pipes (HP), which use the “classical” scheme. This paper presents the results of extensive experimental investigations on the optimization of the physical and geometrical parameters of the flat CS including thickness, configuration and size of vapor grooves, for different CS materials and working fluids. Additionally, the paper presents a comparative study between the “classical” and the “inverted meniscus” schemes of vaporization. Based on the obtained results, two examples of evaporators have been designed and evaluated.