Fluids Viscosity Effect on Non-Isothermal Buoyancy-Driven Exchange Flow in Inclined Pipes

Buoyancy-driven exchange flow is studied experimentally for different Atwood numbers, inclination angles and fluid pairs. The density difference drives the flow, that is achieved through added salinity for isothermal case and temperature difference for the non-isothermal case. Detailed benchmarking experiments were run for isothermal and non-isothermal cases. The degree of flow instability and mixing was found to increase as the inclination angle moves towards vertical, in both isothermal and non-isothermal experiments. The influence of temperature in the non-isothermal experiments caused a significant increase in the flow instability and diffusion. The rate of fluids interpenetration was measured showing an asymmetry from the observed non-isothermal results. The heavy cold finger advances at a faster rate compared to the light hot fluid finger. This phenomenon was quantified for the full range of inclination angles and Atwood numbers. The effect of temperature-viscosity relation on the dynamics of the flow was studied experimentally. Each fluid phase was viscosified separately, maintaining the same density difference. The viscosities were varied by adding Xanthan gum. The effect of viscosity ratio was quantified by measuring the front velocity of the fluid fingers over the full range of inclination angles. Same density difference was maintained in both isothermal and non-isothermal experiments. The fluids interpenetration rate was maximum for intermediate inclination angles and was observed in both isothermal and non-isothermal (without Xanthan gum) cases. The overall observed asymmetry for visosified experiments was found to be less compared to the non-isothermal experiments (without Xanthan gum) at any given Atwood number.