Interfacial-wave-modulated thermal interaction between tandem heated modules

Abstract

The present study investigates heat transfer behavior under steady and mechanically perturbed free-surface conditions in an open-channel flow using single- and two-heated test module configurations. The perturbation is generated using an Arduino-controlled rack-and-pinion mechanism driven by stepper motors. Heat transfer performance is evaluated using the Nusselt number (Nu), while the effects of imposed wave motion and module spacing are systematically examined. For a single module, Nu increases with increasing power input (Q) under both conditions; however, the relative enhancement decreases from approximately 36% at Q=347 W to 18% at Q=546 W. The influence of wave characteristics is further analyzed over a frequency range of 0.5–0.9 Hz and an amplitude range of 7–41.8 mm, where the variation in Nu remains within nearly 17%, indicating weak sensitivity of heat transfer within the investigated range. Particle image velocimetry analysis reveals that modulation of the separated shear layer and coherent vortical structures enhances near-wall mixing and thermal transport. A two-module investigation is subsequently performed by varying the normalized spacing distance between the modules. Under steady conditions, the upstream module exhibits a nearly invariant Nu, whereas the downstream module shows enhanced heat transfer as spacing increases. Under perturbed conditions, the upstream module exhibits a spacing-dependent modulation in Nu. This modulation is governed by the relative timing between wake convection and the imposed free-surface oscillation, with synchronization producing the heat-transfer maxima and desynchronization producing the minima. In contrast, the downstream module follows trends similar to those under steady conditions, indicating that its thermal transport remains predominantly governed by wake evolution.