Abstract: A high speed data acquisition system was used to detectthe pressure and temperature oscillations of the thermally driven two-phaseloop for different operation parameters using methanol as working fluid. Theoscillation time period and the amplitudes are smaller at high heat fluxthan those at low heat flux. It was found that bubbly flow or slug flowexists in the vapor line at low heat flux, while the annular flow exists athigh heat flux. In addition to these, the effect of the relative elevationdifference between the evaporator and the condenser on the operation of thethermally driven two-phase loop was studied. The maximum heat flux ofevaporator was obtained with the pure natural or the forced air convectionof the fin heat sink condenser under the condition of the upper limittemperature of 90^\circC of the heating block. The present study is toprovide guidelines for the design and operation of the miniature electriccooling.