Heat transfer characteristics of Taylor vortex flow with shear-thinning fluids

Pioneered by Taylor in the early twentieth century, Taylor vortex flow has attracted significant research attention in the past few decades. This can be attributed to its vast applications in different chemical processes such as decomposition of biopolymers that requires heating and cooling operations. Generally, the flow between coaxial cylinders comprising of an inner rotating cylinder has been severally investigated thus leading to the discovering of several features associated with Taylor vortex flow. Reynolds number has been largely used in the characterization of flow regimes for investigation of Taylor vortices characterization. However, successful application of the Taylor vortex flow systems in various processes requires the knowledge of Taylor vortex flow under a non-isothermal field.

Presently, several studies on the heat transfer characteristics of Taylor vortex flow are mainly based on the Newtonian fluids. This involves evaluation of the heat transfer coefficients under different operational conditions using different equations correlating the Nusselt number and Reynolds number. For example, researchers have revealed that the increase in the relative buoyancy results in a series of secondary flow regimes induced by classical Taylor vortices. Unfortunately, most of the studies under non-isothermal field are limited to Newtonian fluid systems. Therefore, investigation of heat transfer characteristics of non-Newtonian fluids is highly desirable as they are too important in chemical industries. This should, however, take into consideration the property and influence of shear-thinning phenomenon on the heat transfer characteristic of the Taylor vortex flow.

To investigate the effects of shear-thinning property on the heat transfer characteristics of Taylor vortex flow based on effective Reynolds number, Dr. Hayato Masuda and Professor Makoto Shimoyamada from the University of Shizuoka together with Professor Naoto Ohmura from Kobe University designed an empirical correlation equation between the effective Reynolds number and the Nusselt number in the fluid systems. Specifically, the local distribution of physical properties of non-Newtonian fluid i.e. viscosity, velocity and temperature were determined and compared to those of Newtonian fluids. The fluid flow and the heat transfer were investigated through numerical simulation in a Carreau model by changing the parameter values from 1 to 0.3. The main objective was to accurately reflect the shear-thinning effects. The research work is currently published International Journal of Heat and Mass Transfer.

The flow condition in the experiment was limited to laminar Taylor vortex flow region to enable measurements of the physical properties that are normally difficult to measure experimentally. A decrease in the shear-thinning property resulted in an increase in the local Nusselt number and a corresponding decrease in the temperature and the thickness of the boundary layer. On the other hand, the correlation between the effective Reynolds number and global Nusselt number revealed that the increase in the shear-thinning property led to larger sizes of Taylor vortices. For instance, a global Nusselt number was evaluated within ±10% error for parameter values of 1, 0.7 and 0.5 and ±20% for the parameter value of 0.3. Altogether, the Japanese scientists successfully provided in their study the essential information that will advance understanding of the heat transfer characteristic of Taylor vortex flow with shear-thinning fluids.