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• Multiports act as internal fins and enhances evaporation rate of working fluid. • Reservoirs at the ends supply required quantity of fluid & reduce fluid entrainment. • Reduction in heat transfer and pressure drop irreversibilities of 17 & 48% observed. • Multiport design showed good stability by withstanding 2.7 bar pressure at 90 W. Thermal performance of an air cooled minichannel thermosyphon having multiports (10 ports) with hydraulic diameter of 1.18 mm is investigated. Experiments conducted at different heat loads (10 to 90 W), filling ratios (40, 50 and 60 %), inclination angles (30, 45, 60 and 90°), confluence lengths (0, 5 and 10 mm) and cooling air velocities (0.8, 1, 1.2 and 1.5 m/s) using acetone as working fluid. Results showed a maximum heat dissipation of 90 W with evaporator wall temperature of 72.2 °C at 5 mm confluence length. Multiports act as internal fins and enhance the surface area of the thermosyphon. This improves the boiling and evaporation rate, leading to reduced thermal resistance and wall temperature. An average reduction of 17.1 and 48.2 % are respectively noted in the irreversibilities of heat transfer and pressure drop at optimum condition. Liquid reservoirs at both ends of the thermosyphon overcomes the entrainment problem and supply the required quantity of working fluid and prevents it from reaching dry out condition. Analysis revealed that, the internal flow pattern transition is between Slug and Geyser flow for the tested heat loads. The present experimental findings can be a useful guide for engineering design to satisfy the requirement of cooling in miniaturized electronic devices. [ABSTRACT FROM AUTHOR]