Chapter 9 - Conjugate Heat Transfer in Plate-Fin and Tube Heat Exchangers

Abstract

Plate-fin and tube heat exchangers are extensively used in air conditioning and the petro-chemical industries. Previous studies were mainly purely experimental and case-specific. In this chapter, fluid flow and conjugate heat transfer in a typical representative duct in a plate-fin and tube heat exchanger are investigated. The representative duct selected is surrounded by two neighboring columns of tubes at half the fin pitch. The unsteady behavior of fluid flow and heat transfer in the exchanger duct in transitional flow regime is studied. A large eddy simulation technique (LES) is used to perform a detailed investigation of the temporal oscillations of streamwise, spanwise and normal velocity components in the exchanger duct and their effects on conjugate heat transfer between fins and fluid. Temperature fields, pressure drops, and fin efficiencies are calculated. Temporal variations of instantaneous velocity show that, contrary to the vortex shedding in a bare tube bank, the flow in the exchanger bundle is more like a duct flow, with steady vortexes formed behind each tube. A frequency spectrum analysis of velocity fluctuations further proves that vortex shedding is not the dominant mechanism for momentum and heat transfer. Rather, tube-induced oscillations are the dominant factor. The focus of the study is on the instability and transitional behavior of fluid flow in the exchanger. It is shown that the flow in the exchanger is more like a duct flow than a flow across a bare tube bank.