Contents lists available at ScienceDirect International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt Experimental investigation of mixed convection on an oscillating vertical flat plate Selma Akcay a, ⁎ , Unal Akdag b , Hakan Palancioglu b a Institute of Science and Technology, Aksaray University, 68100 Aksaray, Turkey b Department of Mechanical Engineering, Aksaray University, 68100 Aksaray, Turkey ARTICLE INFO Keywords: Oscillation Vertical plate Mixed convection Heat transfer enhancement ABSTRACT This study experimentally investigates the mixed-convection heat transfer on a moving vertical flat plate. The setup comprises a hanger–pulley system above a transparent volume in which the experimental model moves; a flywheel-motor assembly, which generates the oscillation movement; a power supply; and a datalogger. The experimental model comprises two copper plates on which the thermocouples are placed and Kapton heaters between the plates. For the study, heat flux was applied to the plate surface (q”) and the Womersley number (Wo) and dimensionless oscillation amplitude (Ao) were varied; the effects of these parameters on mixed-con- vection heat transfer were analyzed. The experiments were performed for four different values of Ao and five different oscillation frequencies with three different heat fluxes. The results show that heat-transfer performance is significantly affected by Ao, Wo, and heat flux applied to the plate surface. We observed that heat-transfer performance increases with the increase of both the Wo number and the dimensionless oscillation amplitude for all heat fluxes tested. The obtained results are presented as a function of dimensionless numbers. We also compare experimental results with other researchers' prior-published studies. 1. Introduction External flows on flat surfaces have an important role in heat- transfer applications. Due to the high-velocity flows in these applica- tions, forced-convection effects have been increasingly usually in- vestigated [1,2]. Buoyant forces are generally neglected when ex- amining fluid flow on heated horizontal surfaces. However, for vertical or inclined surfaces, buoyant forces have a strong influence on the flow area and thus cannot be ignored. Because heat transfer on a vertical plate with constant temperature or heat flux is common in industrial applications, mass and heat transfer on these plates are also important aspects to be studied. The condition where natural and forced con- vection occur together is called mixed convection. In the forced case, depending on the direction of the forces, the lifting forces can improve or deteriorate the heat-transfer rate. Consequently, all passive or active heat-transfer applications that improve natural or forced convection can also improve mixed-convection heat transfer. Modifications such as the use of fins to increase surface area, the addition of various turbu- lators into the flow, electric- or magnetic-field applications, the addi- tion of nano-sized particles to the basic fluid, the use of basic fluid under supercritical conditions, the use of vibrating fluid, or the use of continuous moving plates improve heat transfer with natural, forced, or mixed convection [3–12]. The velocity and temperature distributions on moving surfaces can affect the heat-transfer rate on the surface. Lifting effects within the boundary layer have been investigated by many researchers for continuously moving horizontal [13,14], vertical [15–19], and oblique surfaces [20–23]. Oscillatory flows are known to cause higher heat and mass transfer. Oscillating movement is achieved either by fluid vibration around a fixed object or by vibration of a solid body in any fluid. Although fluid vibration around a fixed object requires more energy, the same goal is achieved in both approaches. Oscillating flows are widely used in compact high-performance heat exchangers, piston engines, chemical reactors, pulsating burners, high-performance stirling engines, cryo- genic refrigeration, and in various applications in the aerospace in- dustry and military fields [24–28]. Having numerically examined the effect of periodic oscillations on time-dependent mixed convection from a vertical plate, Saeid [29] re- ported that the cycle-average Nu number decreased with increasing oscillation amplitude and frequency for fixed Pr and Ri numbers. Goma and Taweel [30] analyzed the effect of oscillations on natural- and forced-convection heat transfer on vertical surfaces with constant temperature and reported that surface oscillations improved heat transfer. Anilkumar [31] examined the natural convection of time- https://doi.org/10.1016/j.icheatmasstransfer.2020.104528 ⁎ Corresponding author. E-mail addresses: selma.352@hotmail.com (S. Akcay), uakdag@gmail.com (U. Akdag), hakanpalancioglu@aksaray.edu.tr (H. Palancioglu). International Communications in Heat and Mass Transfer 113 (2020) 104528 0735-1933/ © 2020 Elsevier Ltd. All rights reserved. T