High-performance grooved heat pipe modelling requires improved knowledge of flow behavior inside grooves. Even if this flow is usually laminar, a free surface governed by capillarity leads to many difficulties when calculating the mean friction factor of grooves. in the present study, an experimental bench has been developed in order to visualize the liquid-vapor interface channels of four different axially grooved heat pipes. Subsequent experimentation, which is associated with image processing programs, allows for measurement of liquid height and meniscus radius evolution in a groove along the heat pipe axis. As regards laminar flow inside the grooves typically used in heat pipes, the mean fiction factor has been measured.