Forced Convection in Turbulent Flow

2013 ◽  
pp. 241-308
Keyword(s):  
Turbulent Flow ◽  
Forced Convection

Multi-Fidelity Analysis of Acoustic Streaming in Forced Convection Heat Transfer

2019 ◽  
Author(s):  
Tapish Agarwal ◽  
Iman Rahbari ◽  
Jorge Saavedra ◽  
Guillermo Paniagua ◽  
Beni Cukurel
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Forced Convection ◽  
Parameter Space ◽  
Thermal Boundary Layer ◽  
Acoustic Streaming ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Wave Disturbances

Abstract The behavioral characteristics of thermal boundary layer dictate the relative efficiency of forced convection heat transfer. This research effort is related to the detailed analysis of the temporal evolution of thermal boundary layer under periodic excitations. In presence of oscillations, a distinct thin Stokes layer is formed inside the attached boundary layer, which interacts nonlinearly with the mean flow in the near wall region. This interaction leads to modification of temporally averaged flow fields, commonly known as acoustic streaming. As a result, the aero-thermal wall gradients are modified leading to significant changes in wall shear stress and heat flux. However, the small spatial scales and the inherent unsteady nature of streaming has presented challenges for prior numerical investigations, preventing the identification of optimal parameters. In order to address this void in numerical framework, the development of a three-tier numerical approach is presented. As a first layer of fidelity, a laminar model is developed for fluctuations and streaming flow calculations in laminar flows subjected to travelling wave disturbances. This technique is an extension of the Lin’s method to traveling wave disturbances of various speeds (absent of previously employed assumptions), along with inclusion of energy equation. With low computational cost, this level of abstraction is intended to identify the broad parameter space that yield desirable heat transfer alterations. At the next level of fidelity, 2D U-RANS simulations are conducted across both laminar and turbulent flow regimes. This is geared towards extending the parameter space obtained from laminar model to turbulent flow conditions. As the third level of fidelity, temporally and spatially resolved DNS simulations are conducted to simulate the application relevant compressible flow environment. The exemplary findings indicate that in certain parameter space, both enhancement and reduction in heat transfer can be obtained through acoustic streaming. Moreover, the extent of heat transfer modulations is greater than alterations in wall shear, thereby surpassing Reynolds analogy.

Enhanced Heat Transfer Through the Use of Nanofluids in Forced Convection

2004 ◽  
Author(s):  
Daniel J. Faulkner ◽  
David R. Rector ◽  
Justin J. Davidson ◽  
Reza Shekarriz
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Forced Convection ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Enhanced Heat Transfer ◽  
Low Reynolds Numbers ◽  
Turbulent Flow Regime

Much attention has been paid in recent years to the use of nanoparticle suspensions for enhanced heat transfer. The majority of this work has focused on the thermal conductivity of these nanofluids, which can be as much as 2.5 times higher than that of the plain base fluid. The present work moves beyond measurements of non-flowing liquids, to explore the role that nanofluids can play in enhancing convective heat transfer within microscale channels. A unique pseudo-turbulent flow regime is postulated, which simulates turbulent behavior at very low Reynolds numbers, in what are nominally laminar flows. The resulting fluid mixing has the potential to raise the average convective heat transfer coefficient within the channel. Numerical modeling, using the lattice Boltzmann method, confirms the existence of the pseudo-turbulent flow regime. Finally, experimental results are presented which demonstrate a significant heat transfer enhancement when using nanofluids in forced convection. The current results are especially relevant to microchannel heatsinks, where the low Reynolds numbers impose limitations on the maximum Nusselt number achievable.

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