Abstract. Recent and constant demands for greater power densities and smaller sizes of electronic systems have stimulated the growth of new designs of different passive heat transfer methods such as heat pipes. Particularly, Oscillating Heat Pipes (OHPs) are relatively novel devices, capable of removing high heat rates over long and short distances with not much temperature drop. Its heat transfer mechanism relies on a self-oscillating motion of a two-phase flow of a working fluid circulating through meandering channels. This study concentrates on the design, building and assembling a test rig in order to analyse the flow pattern of deionised water through a 5 turns Flat Plate Oscillating Hat Pipe under different heat inputs, which was made in the School of Engineering and Materials Science of the Queen Mary University of London by two PhD students. The filling ratio of the water is 40%. Furthermore an experimental study on the OHP thermal performance is carried out in order to examine the effects of different surface wet conditions: super hydrophilic, hydrophilic and cleaned brass. It is demonstrated the formation of liquid slugs and vapour plugs of the water along the channels. The experimental results showed that the hydrophilic surface tend to be more energy efficient. The heat transfer performance of the superhydrophilic and hydrophilic is higher than brass by 5-12% and 15-20% respectively