Numerical study of microwave cancer therapy for liver tissue using bioheat model

Abstract

Rotating cylinder flows are very important in aerodynamics and in engineering structures. Confined channel flow also has a wide range of applications including particles migration through veins, droplet dynamics and so on. The present study demonstrates a numerical investigation of forced convection heat transfer over a rotating hot circular cylinder vertically placed at the central axis of a confined horizontal channel for laminar and turbulent flow. The turbulent flow is investigated based on Reynolds Averaged Navier-Stokes (RANS) equations using the Shear Stress Transport (SST) model. Fully developed flow of air at ambient temperature is considered at the channel inlet for both laminar and turbulent flow cases, whereas the surface of the channel is kept insulated. The cylinder is rotating either in clockwise or counter-clockwise direction with a constant angular speed. The speed ratio, defined as the ratio between the cylinder’s circumferential speed to the free stream speed, is varied along with the free stream speed. The governing mass, momentum and energy equations in non-dimensional form are solved numerically using Galerkin finite element method. For simultaneously solving those equations, segregated solution approach is applied, where multiple systems that depend on one another are solved separately in segregated steps. The modelling is performed in a steady and incompressible fluid flow. Parametric simulation is carried out over a range of mean flow Reynolds number based on the mean velocity of the working fluid within the range of 40 ≤ Re ≤ 2000 for laminar flow and 3000 ≤ Re ≤ 107 for turbulent flow. The variation of blockage ratio (β ) is considered as 0.05, 0.1 and 0.2, whereas the rotational Reynolds number of the cylinder based on the peripheral velocity of the cylinder is set at Rec = 4, 10, 20 and 30. The numerical results are visualized in terms of streamline plots, pressure contours and isosurface plots of thermal field. The distributions of coefficient of drag, coefficient of lift and average Nusselt number of the hot cylinder surface as a function of Reynolds number reveal a number of interesting observations from the present findings. From this study, it is found that rotational direction of the cylinder has negligible effect on thermal or flow fields and thus it doesn’t affect the drag or lift coefficients and average Nusselt number. Although, the rotational speed of the cylinder has a significant influence on thermal or flow fields, it also doesn’t affect any of the performance parameters. However, the downstream vorticity is greatly influenced by both the free stream velocity and the blockage ratio. Drag coefficients are higher for smallest cylinder both in laminar and turbulent flow whereas Lift coefficients are higher for laminar zone but no regular pattern is found for turbulent flow. For laminar flow, Nu is greater for smallest cylinder but opposite for the case of turbulent flow. It is also found that the changes in Re and β significantly affect both the aerodynamic and the thermal performance of the confined channel. Drag coefficient decreases with the increase of Reynolds number while Lift coefficient approaches to zero for higher Reynolds number for laminar flow but for turbulent flow it shows arbitrary value around zero. And, Nu increases with the increase of Reynolds number up to a certain range in turbulent zone, after that following a decreasing pattern, it remains almost constant.