The present work investigates the role of contact angle hysteresis at the liquid-liquid-solid interface (LLS) on the rod climbing effect of two immiscible Newtonian liquids using experimental and numerical approaches. Experiments revealed that the final steady state contact angle, θw at the LLS interface varies with the rod rotation speed, ω. For the present system, θw changes from ∼69◦ to ∼83◦ when the state of the rod is changed from static condition to rotating at 3.3 Hz. With further increase in ω, the θw exceeds 90◦ which cannot be observed experimentally. It is inferred from the simulations that the input value of θw saturates and attains a constant value of ∼120◦ for ω > 5 Hz. Using numerical simulations, we demonstrate that this contact angle hysteresis must be considered for the correct prediction of the Newtonian rod climbing effect. Using the appropriate values of the contact angle in the boundary condition, an excellent quantitative match between the experiments and simulations is obtained in terms of- the climbing height, the threshold rod rotation speed for onset of climbing, and the shape of liquid-liquid interface. This resolves the discrepancy between the experiments and simulations in the existing literature where a constant value of the contact angle has been used for all speeds of rod rotation.

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The choice of heat transfer fluids(HTF) significantly dictates the thermal efficiency of the solar power plant. Presently, molten salt is widely used choice owing to its phase, low cost and non-toxic nature. Along with other alternatives like liquid metals, multiphase fluids, these HTFs are limited to peak operating temperatures ranging from 300-550°C. With the introduction of Dense Particle Suspensions (DPS) as an HTF, the highest operating temperatures in a Solar thermal power plant can reach up to 700°C, offering considerable scope for improving thermal efficiency. Due to the higher average specific heat as compared to the alternatives, CO2 is a promising working fluid in the considered range of moderately high operating temperatures. The cost of the components and size of the power block makes the transcritical CO2 cycle an attractive alternative. The present work analyses the theoretical efficiency of the proposed cycle, with the peak operating temperature ranging from 550°C to 700°C. The effects of the variation in the lower operating pressure and the condensation temperature have also been analysed. It is observed that thermodynamic efficiencies as high as 40% can be reached at the maximum operating temperature. The optimum combination of the lower operating pressure and the condensation temperature is also noted.