CFD analysis of heat transfer enhancement by wall mounted flexible flow modulators in a channel with pulsatile flow.

The aim of the present study is to explore heat transfer and pressure drop characteristics in a pulsating channel flow due to wall-mounted flexible flow modulators (FFM). Cold air in pulsating fashion is forced to enter through the channel having isothermally heated top and bottom walls with one/multiple FFMs mounted on them. The dynamic conditions of pulsating inflow are characterized by Reynolds number, non-dimensional pulsation frequency and amplitude. Applying the Galerkin finite element method in an Arbitrary Lagrangian-Eulerian (ALE) framework, the present unsteady problem has been solved. Flexibility (10-4 ≤ Ca ≤ 10-7), orientation angle (60° ≤ Î¸ ≤ 120°), and location of FFM(s) have been considered in this study to find out the best-case scenario for heat transfer enhancement. The system characteristics have been analyzed by vorticity contours and isotherms. Heat transfer performance has been evaluated in terms of Nusselt number variations and pressure drop across the channel. Besides, power spectrum analysis of thermal field oscillation along with that of the FFM's motion induced by pulsating inflow has been performed. The present study reveals that single FFM having flexibility of Ca = 10-5 and an orientation angle of θ = 90° offers the best-case scenario for heat transfer enhancement.

Thin film liquid-vapor phase change phenomena over nano-porous substrates: A molecular dynamics perspective.

Surfaces with nano-pores have significant effect in enhancing heat transfer during phase change process. In this study, Molecular dynamics simulations have been performed to investigate thin film evaporation over different nano-porous substrate. The molecular system consists of argon as the working fluid and Platinum as the solid substrate. To study the effect of the nano-pores in phase change process, the nano-porous substrates had been structured with four different hexagonal porosity with three different heights. The structures of the hexagonal nano-pore were characterized through variation of void fraction as well as height to arm thickness ratio. Qualitative heat transfer performance has been characterized by closely monitoring the temporal variation of temperature and pressure, net evaporation number, wall heat flux of the system for all cases under consideration. The quantitative characterization of heat and mass transfer performance has been done by calculating the average heat flux and evaporative mass flux. Diffusion coefficient of argon is also evaluated to illustrate the effect of these nano-porous substrate in enhancing the movement of argon atoms thus heat transfer. It has been found that the presence of hexagonal nano-porous substrates significantly increases heat transfer performance. Structures with lower void fraction offers better enhancement of heat flux and other transport characteristics. Increment in nano-pores height also significantly enhances heat transfer. Present study clearly points out the noteworthy role associated with nano-porous substrate in modulating heat transfer characteristics during liquid-vapor phase change phenomena both from qualitative and quantitative perspectives.