Abstract: A novel three-dimensional chamber of the deep-sea pH sensor is designed on the basis of gravity currents principle to facilitate online self-correction. The flows are driven by buoyancy differences between the interior and exterior fluids. A stable stratification and efficient displacement develop in this case. There are two water outlets in the chamber. Bottom gravity currents occur when the dense fluid enters through the inlet, displaces the light fluid in the chamber and pushes it out through high level outlet. On the other hand, surface gravity currents occur when the light fluid enters through the inlet, displaces the dense fluid in the chamber and pushes it out through low level outlet. Computationally, the distribution of velocity field and concentration field in the chambers is investigated with the computational fluid dynamics method. Experimentally the performances of the fluid displacement in the chambers are measured through the wine dye and the pH buffer solution displacement experiment and the effect of the Reynolds number and the Atwood number on the displacing efficiency is quantitatively investigated. Both computational and experimental results show that the barrel-shaped chamber of pH sensor (SS-Ι) cannot achieve full displacement, while the triangular prism chamber of pH sensor (SS-ΙΙ) can accomplish better liquid displacement as long as the sea water and buffer solution have different densities.

Key words: Buffer solution, Calibration, Displacement, pH sensor