NUMERICAL MODELING OF THREE-DIMENSIONAL HEAT TRANSFER AND FLUID FLOWTHROUGH INTERRUPTED PLATES USING UNIT CELL SCALE

Abstract

Interrupted-plate heat exchangers are used as regenerators for absorbing and releasing thermal energy such as in a Compressed Air Energy Storage (CAES) system in which the exchanger absorbs energy to cool the air being compressed or liberates energy to heat the air upon expansion. The exchanger consists of layers of thin plates in stacked arrays. In a given layer, the plates are parallel to one another and parallel to the exchanger axis. Each successive layer is rotated to have its plates be perpendicular to those of the layer below but still parallel to the exchanger axis. As flow passes from one layer to the next, new thermal boundary layers develop, beneficial to effective heat transfer. The interrupted-plate heat exchanger can also be seen as a porous medium. As such, it demonstrates strong anisotropic behavior when flow approaches the plates in a direction other than axially. Thus, pressure drops and heat transfer coefficients are dependent upon the attack angle. Mathematical models for anisotropic pressure drop and heat transfer behavior are proposed based on numerical calculations on a Representative Elementary Volume (REV), the unit cell model of the interrupted-plate medium. The anisotropic pressure drop is modeled by the traditionally used Darcy and inertial terms, with the addition of another term representing mixing effects. Heat transfer between the fluid and the plates is formulated in terms of Nusselt number vs. Reynolds number and approach angle of the mean flow. These models are used when solving, on the scale of the heat exchanger application, the volume-averaged Navier-Stokes equations that treat the exchanger region as a continuum. The analysis of the heat exchanger is used for design and optimization of the medium.