Recent advances in visualization of pulsating heat pipes: A review

Owing to the simple structure and excellent heat transfer performance, pulsating heat pipe (PHP) is widely used in different heat management fields. It relies on the mode of vapour-liquid plug oscillation to heat transfer, involving the process of bubble nucleation, growth, coalescence, collapsing, liquid film evapouration and condensation and others. Thus, the complex heat transfer mechanism and a variety of influencing factors make it difficult to predict heat transfer performance of PHP. To further improve the heat transfer mechanism and theory of PHP, a large number of visualization researches were carried out. This paper provides an overview of latest progress in PHP visualization, the visualization studies of PHP with different visualization techniques, operating conditions (filling ratio, gravity condition, heating mode), structural parameters (overall structure, inner diameter, cross-section, channel layout, inner surface) and working fluids (conventional working fluids, modified working fluids) are summarized and prospected, providing a reference for future visualization research.