HYDRODYNAMIC AND THERMAL EFFECTS OF DRAG AND HEAT TRANSFER COEFFICIENTS UNDER LAMINAR UNSTEADY FLOW CONDITIONS IN POROUS MEDIA

摘要

Solid-fluid thermal interactions during unsteady flow in porous media play an important role in the regenerators and heat exchangers of pulse tube cryocoolers. Pore-level thermal processes in porous media under laminar unsteady flow conditions have recently been investigated and have been shown to produce significantly larger heat transfer coefficients compared to those in steady flow [1]. The objective of this investigation was to study pore-level hydrodynamic and thermal phenomena during pulsating sinusoidal flow through a generic, two-dimensional porous medium by numerical analysis. The investigated porous media are periodic arrays of rectangular cylinders, and are meant to represent tube bundles in micro heat exchangers. Furthermore, an examination of the effects of flow pulsations on the drag and heat transfer coefficients that are encountered in the standard, volume-average energy equations was carried out. Detailed numerical data for the typical 75% porous configuration, with flow pulsation frequencies of 20, 40, and 80 Hz were obtained at mean flow - Reynolds numbers in the range 0-1000. Based on these numerical results, the instantaneous as well as cycle-average drag coefficients and heat transfer coefficients, to be used in the standard unsteady volume- average momentum and energy conservation equations, were derived.