Flow and Thermal Characteristics of Condensing Steam in a Single Horizontal Mini-Channel of a Multiport Cylinder Dryer

摘要

In papermaking processes it is well known that the dryer uses the greatest amount of energy and has costly components compared with other devices. These dryers thus offer outstanding opportunities for energy savings and cost reduction. Recently, Argonne National Laboratory developed the concept of a multiport cylinder dryer in which the steam flows through "ports," or longitudinally oriented mini-channels, which are close to the cylinder-dryer surface. It was reported that the innovative design minimized the condensate layer thickness and increased the dryer shell's surface temperature. However, no systematically obtained experimental data are available. In this study we conducted experiments to investigate the flow and thermal characteristics of condensing steam in a single horizontal mini-channel, which represents a part of a multiport cylinder dryer. Based on the results, the flow pattern through a single horizontal mini-channel is presented. Also, we observed that the condensing heat transfer coefficient in the single horizontal mini-channel was about seven times higher than that of a conventional dryer with spoiler bars. Finally, the effects of the steam mass flux, system pressure, and aspect ratio of the mini-channel on the average condensing heat transfer coefficients as well as the pressure drops are presented.