Experimental investigation of liquid viscosity's effect on the flow behaviour and void fraction in a small diameter bubble column: How much do we know?

The viscosities of heavy oils and bitumen are significantly above those of water and light crude oil and are found in the oil and gas, polymer, metallurgical, and process industries. Unfortunately, little research attention has been given to the void fraction, and the behaviours of such flows as bubbles rise over them in bubble columns. How the liquid viscosity influences the behaviour of these flows and void fraction were examined using the electrical capacitance tomography (ECT), level swell technique and visual technique with a high-speed camera. It was found that: an excellent agreement was achieved within ±10% for comparison between the obtained void fraction using both techniques for all the liquid viscosities considered. In contradiction to previous findings, an increase in liquid viscosity provokes a corresponding increase in the void fraction, yet the influence is seen to reverse for gas superficial velocities beyond 0.25 m/s. In concordance with Mori et al. (1999)'s observations, a liquid viscosity increment brings about a corresponding decrease in the bubble frequency. The Taylor bubble's rise velocity was heavily dependent on the liquid viscosity range, whereby increases in liquid viscosity bring about a rise in the flow distribution coefficient. The bubble drift velocity, on the contrary, reduces with increasing liquid viscosity.