Transient and conjugate heat and mass transfer in hexagonal ducts with adsorbent walls

Honeycomb type adsorbent beds, either in the form of cycling adsorbent beds, or in the form of rotary wheels, are increasingly used in air purification, dehumidification, and energy recovery, etc. The temporal behaviors of operation require a dynamic analysis of the heat and mass transfer in the elementary ducts in the wheels or beds. In this paper, the transient heat and mass transfer in the honeycomb adsorbent ducts of hexagonal cross sections are studied both numerically and experimentally. The transient equations governing the momentum, energy and mass conservation in the air stream and in the porous solid walls are solved simultaneously as a conjugate problem. The velocity, temperature, humidity and water content contours in the ducts are obtained. The effects of operating time and solid wall thickness on the air side convective heat and mass transfer coefficients are analyzed. Different from traditional steady-state heat transfer tubes, the effects of wall thickness are disclosed here. The Nusselt and Sherwood numbers for the fully developed (both axially and temporally) hexagonal ducts with various wall thickness ratios are obtained. They provide guidelines for future component design and performance optimization of adsorption systems. (C) 2015 Elsevier Ltd. All rights reserved.