Abstract: Heat dissipation performance can seriously affect the long-term operation of junction box’s power system for seafloor observation network. The dissipation mechanism of heat generated by electrical thermal sources in sealed pressure chamber is analyzed, and its main impact factor is deduced, based on the heat conduction theory. Filling oil in chamber might greatly improve the heat dissipation performance is concluded and validated by simulations on gas and oil medium through Fluent, respectively. But problem of over-pressure that is harmful to electrical components is induced due to oil thermal expansion. A gas-liquid coexistence method by leaving an appropriate proportion of gas volume in oil is presented and theoretically analyzed based on Clapeyron theorem to alleviate the pressure. In order to validate the proposal, tests are carried out on the scenarios of 0%, 2%, 5% and 10% gas volume. Theoretical analysis and test results show that：filling the chamber with de-electrical oil could improve the heat dissipation performance, but over-pressure phenomena is induced; gas-liquid coexistence method could alleviate the oil pressure, for 25# transformer oil, a gas volume of more than 8.8% could suppress the increased pressure less than 0.1 MPa. Gas-liquid coexistence method is applied on the power supply of a prototype of seafloor observation network. Results from the laboratory test are consistent with theoretical analysis.

Key words: Gas-liquid coexistence, Heat dissipation, Power converter, Seafloor observation network