Contents lists available at ScienceDirect International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt Magnetohydrodynamics forced convection of nanofluid in multi-layered U-shaped vented cavity with a porous region considering wall corrugation effects Fatih Selimefendigil a, ⁎ , Hakan F. Öztop b a Department of Mechanical Engineering, Celal Bayar University, 45140 Manisa, Turkey b Department of Mechanical Engineering, Technology Faculty, Fırat University, 23119 Elazığ, Turkey ARTICLEINFO Keywords: Porous layer U-shaped vented cavity Corrugation Convection Finite volume method Nanofluid ABSTRACT Magnetohydrodynamics forced convection of CNT-water nanofluid in a layered U-shaped vented cavity invol- ving a porous region is investigated under the impact of wall corrugation. The numerical study is performed by using the finite volume method. Impacts of Reynolds number (between 100 and 1000), Hartmann number (between 0 and 50), Darcy number (between 10 -4 and 5 × 10 -2 ), porous layer height (between 0.1H and 0.5H),height(between0and0.5H)andnumberoftriangularwaves(between1and16)andcurvature(between 0.01H and 0.2H) at the U-turn of the vented cavity on the convective heat transfer features are examined. The flow field and heat transfer are affected by variations in the Reynolds number, magnetic field strength and permeability of the porous medium. The average Nusselt number increases significantly with higher magnetic field strength and at Hartmann number of 50, the amount of enhancement is 112% while the impact is reverse for highest value of Darcy number of the porous compound. The corrugation of the bottom wall which is a triangular wave was found to be used as an effective tool for fluid flow and heat transfer features. The average heat transfer rate reduces with higher number of corrugation waves (68.2% reduction) while it first increases thenreduceswithhigherheightofthecorrugation.ThecurvatureoftheneckintheU-shapedcavityreducedthe heat transfer rate which is 15.5% at the highest value. 1. Introduction Convection in vented cavities plays an important role in a variety of thermal engineering configurations such an in HVAC applications, electronic cooling, MEMs, food processing, in some chemical en- gineering systems and many others [1,2]. Even though there are many studies related to vented cavities considering various location of ports in forced and mixed convection configurations [3,4], there are a few studies with the U-shaped geometry. This geometry is particular in- terest to some special type heat exchangers used in ground water en- ergy extraction. Over the years, many studies are performed for the application of different active and passive heat transfer methods in heat transfer devices [5–8] and particularly for convective heat transfer in cavities [9–11]. An extensive review is made for the use of different turbulators in heat transfer devices in ref. [12]. Impact of extended surfaces, corrugated tubes and various swirl flow devices used in heat exchangers on the thermal performance enhancements are discussed in detail. Corrugation of the surfaces is employed in many convection studies as passive heat transfer enhancement. Selimefendigil and Oztop [13] examined the natural convection for the impact of wall corruga- tion effects in a square cavity with ferrofluids. It was observed that the wall corrugation results in heat transfer enhancement which is affected by the location of magnetic dipole source. A review study is presented in ref. [14] for the advancements and applications of convective heat transfer with corrugation effects. Laminar and turbulent flow regimes were covered with a emphasis for the corrugated tubes applicable in a variety of engineering applications. In the current work, nanoparticles are used with magnetic field ef- fects. Nanofluid technology is related to adding nano-sized particles in thebasefluidwhichisusedasheattransferfluidinvariousapplications from thermal management to thermal energy storage [15–22].Overthe years, many advanced techniques are developed for nanofluids simu- lation in heat transfer considering various nanoparticles and different physical mechanisms. Advanced models for nanofluids are offered and successful implementation of nanofluid technology for convective heat transfer applications are performed [23–30]. In this work, use of highly https://doi.org/10.1016/j.icheatmasstransfer.2020.104551 ⁎ Corresponding author. E-mail address: fatih.selimefendigil@cbu.edu.tr (F. Selimefendigil). International Communications in Heat and Mass Transfer 113 (2020) 104551 0735-1933/ © 2020 Elsevier Ltd. All rights reserved. T