Laminar fluid flow and mass transfer in a standard field and laboratory emission cell

摘要

The field and laboratory emission cell (FLEC) is becoming a standard method of characterizing pollutant emissions from building materials. Based on this method, the material and the inner surface of the FLEC cap form a cone-shaped cavity. The airflow is distributed radially inward over the test surface through a slit in a circular-shaped channel at the perimeter of the chamber. After mass transfer, the air is exhausted through an outlet in the center. Usually, emission rate profiles are obtained using such cells. However, the local convective mass transfer coefficients are now needed. In this study, laminar fluid flow and mass transfer in a standard FLEC are investigated. The velocity field and moisture profiles are obtained by solving Navier-Stokes equations numerically. The whole geometry, including the air inlet and outlet, channel, air slit, and emission space, are included in the numerical modeling domain. The mean convective mass transfer coefficients are calculated and compared with the experimental data. In the test, distilled water is used in the FLEC lower chamber to substitute the emission surface. Mass transfer data are obtained by calculating humidity differences between the inlet and outlet of a gas stream flowing through the FLEC. The study concentrates on assessing the variations of velocity and humidity profiles, as well as convective mass transfer coefficients, in the cell.