Heat Transfer Across Tube Banks With a Passive Control Vortex Generator in Steady One-Directional and Oscillatory Flows

Abstract

Fluid can flow in one-directional (normal flow) or oscillatory conditions. Fluid flow in some energy system involved oscillatory flow condition. The use of vortex generator has been proven to improve heat transfer in the case of one-directional flow but the impact of vortex generator in oscillatory flow condition is yet unknown. This study focusses on the heat transfer performance across a heated tube banks using a Computational Fluid Dynamics (CFD) model. Two flow conditions were modelled: steady one-directional and oscillatory flow conditions. Two-dimensional CFD models of steady flow and oscillatory flow were solved using the SST k-? turbulence model for two different cases of heated tube banks with and without the vortex generators. The heat transfer performance for both flow conditions were analysed by considering a heat transfer parameter known as Colburn-j factor. Results showed that the use of a vortex generator increased the heat transfer enhancement, regardless of the flow conditions. However, it is also noted that the heat transfer behaviour in a steady flow and an oscillatory flow is not the same, especially with the appearance of secondary flows in the system. The difference is discussed with respect to dimensionless quantity of Colburn j-factor, the non-dimensionless quantity, and the amplitude of temperature field. The result indicates that the heat equation in the steady flow condition is not very suitable to be directly used in oscillatory flow conditions. Appropriate heat equation needs to be properly addressed for situations that involve oscillatory flow motion.

Computational Fluid Dynamics Study of Wake Recovery for Flow Across Hydrokinetic Turbine at Different Depth of Water

“…So, the transient numerical iteration for each timestep of these CFD models will be iterated until the RMS residual reached these values. Similar range of convergence was also reported especially when the model is transient in nature [17,19]. In this study, the average velocity of the solution was also monitored in addition to the monitoring practice of the residual convergence.…”

“…Silva et al, [15] and Kolekar et al, [16] used Shear Stress Transport (SST) k- turbulence model. The SST k- model was reported to be performing well in many flow conditions that involved both the viscid and inviscid flow regions [17][18][19][20]. The theories or formulas for SST k- turbulence model is standard and can be referred to the published documentation [16,19,20].…”

“…The SST k- model was reported to be performing well in many flow conditions that involved both the viscid and inviscid flow regions [17][18][19][20]. The theories or formulas for SST k- turbulence model is standard and can be referred to the published documentation [16,19,20]. Second order UPWIND differencing scheme was used for discretization of equations in CFD models, following the suggestion as stated by Ramayee and Supradeepan [21].…”

A Computational Study of a Passive Flow Device in a Mechanical Heart Valve for the Anatomic Aorta and the Axisymmetric Aorta

“…Improving the mechanical heart valve design could reduce the risk of platelet activation and haemolysis by minimizing turbulent stresses [17,22]. Previous studies have supported the use of passive flow control devices such as vortex generators (VGs) on the leaflet surface to reduce turbulence and platelet activation related to the regurgitated jet [3,23,24]. In terms of the geometry of the VG, its shape and height could be used to overcome the flow separation problem.…”

“…In terms of the geometry of the VG, its shape and height could be used to overcome the flow separation problem. Studies have suggested that VGs can delay and even suppress flow separation by bringing momentum from the free stream into the boundary layer in order to provide and maintain the strong local stream wise adverse pressure gradient [23][24][25]. After all, the impact of VGs on BMHVs and studies concerning how to choose the appropriate VG configuration are still under investigation, especially in terms of heart valve applications.…”