In this paper, a novel ultra-thin flat heat pipe (UFHP) with an active steam chamber of 76 × 46 × 0.2 mm 3 is successfully designed, fabricated and tested. The innovation point of the UFHP is its thinner thickness with only 0.65 mm total thickness which can reduce the space for heat dissipation in electronic devices and accommodate its increasingly compact structure. Another innovation point is the design of supporting pillars. It is etched in the UFHP to avoid the ultra-thin chamber deformation and can also supply vertical channels for liquid reflux. Thermal performance is assessed and results reveal that the optimal operating power of the UFHP is 7.1-13.7 W at different tilt angles and liquid filling rates. When the filling rate is 1.05 and the tilt angle is 90 degrees, it has the best performance, and the minimum average thermal resistance is 1.15 °C W −1 with the input power varying from 7.1 to13.7 W. When the input power is 15.9 W and the evaporator temperature is 60 °C, the heat transfer performance of the vertically placed UFHP is perfect and with a thermal conductivity of 800 W m −1 K −1 . This research is of great significance for the production of UFHP with ultra-thin thickness and good heat transfer performance.

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This paper investigates the effect of silver nanofluid on a flat-plate pulsating heat pipe (FP-PHP). The simulation was performed using FLUENT 15.0 software, for which a three-dimensional model having a microchannel structure in the condensation section was developed. The developed model adopted the volume of fluid (VOF) method to track the internal vapor-liquid interface of the FP-PHP and to observe the state of the two-phase flow. The result revealed the evident presence of various types of bubble flows, including dispersed bubble flows, slug flows, annular flows, and column flows in the evaporation section. Trends in thermal resistance variation during simulation were studied by changing the volume fraction, liquid filling rate, and heating power. The thermal resistance of the FP-PHP containing silver nanofluid was lower and the FP-PHP exhibited stable state when the heating power reached 120 W. The optimal volume fraction of silver nanofluid was 1%, and the FP-PHP containing sliver nanofluid exhibited increased heat transfer efficiency.

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