Capillarity enhancement of micro heat pipes using grooves with variable apex angle

Abstract

We present a novel methodology to enhance the capillarity and thus the heat transfer capacity of a polygonal micro heat pipe by axially varying the apex angle of grooves. To analyse the effect of axial variation of apex angle on thermal performance of micro heat pipes, we use a quasi-one-dimensional mathematical model that takes into account the axial variation of apex angle. We analyse micro heat pipes with linear variation of apex angle and uniform apex angle. Numerical results of our model show that a linear increase in the apex angle from the evaporator to the condenser section can increase the heat transport capacity of the micro heat pipe by more than 55% compared to micro heat pipe with uniform apex angle. We describe how the axial variation in apex angle leads to enhanced capillarity in a micro heat pipe. We show that axial variation of apex angle redistributes the liquid mass from the condenser section of the micro heat pipe to the evaporator section resulting in a reduction of liquid pressure drop. Lastly, we mathematically optimise the axial variation of apex angle to obtain 100% enhancement in the maximum heat transport capacity in comparison to micro heat pipe with uniform apex angle.