© 2020 Elsevier LtdComprehensive experiments are conducted to analyze complex heat transfer characteristics and flow nature of a flat plate closed loop pulsating heat pipe charged with ternary mixtures. Consecutive channels of the heat pipe have different cross sections. Fluids forming the mixtures are deionized water (W), methanol (M) and pentane (P). Effects of different volume mixing ratios of these fluids (W:M:P = 1:1:1, 1:2:3 and 1:3:2) on thermal performance are evaluated comparatively with pure counterparts. Experimental range also covers other key parameters: filling ratio (30%, 50% and 70%), inclination angle (0° and 90°) and heat input. Flow patterns and bubble-liquid dynamics are examined. Results show that medium filling ratio of 50% presents optimum performance for all mixing ratios. At vertical orientation, ternary mixtures, especially the ones having higher content of pentane or methanol (1:2:3 and 1:3:2), show significantly better thermal characteristics compared to pure fluids. However, heat pipes charged with ternary mixtures are highly dependent on gravity; such that flat plate closed loop pulsating heat pipe having mixtures cannot operate in horizontal position. In usage of ternary mixtures, liquid droplets flowing down through channels are observed; this is called as rewetting phenomenon enhancing thermal performance. Force analysis characterizing thermo-fluid-geometric coupling is conducted.