Mass transfer coefficient in small chamber with air flow control unit

Using the newly developed airflow control unit (ACU), chamber performance was examined through measuring the air velocity (v_a) near the specimen surface and mass transfer coefficient (MTC). v_a and its distribution depending on fan revolutions were examined over nine points at a distance of 10mm from the specimen surface. MTC was investigated by tests with using filter papers and water vapor in the chamber installed with ACU. For MTC tests, seven conditions of fan revolution were set at less than 700rpm, and loading factor 0.11 m²/m³ was adopted to avoid saturating of humidity in the chamber instead of 2.2 m²/m³ of usual emission test. As the results, vadistributions were even and in a small deviation. When v_a ranges from 0.10 to 0.27 m/s, tested MTC were in 17.4 to 22.0m/h, while the values of JIS and previous studies in much lower levels. Chamber-tested MTCs should be much lower than those of theoretical calculation, because the given Q/A would make the potential of mass transfer decreased at the chamber test but theoretical calculation have the assumption of infinite Q. There, theoretical MTC depending on v_a were recalculated using the properties of dry and wet air. CFD simulations provided that steady state appeared at over L=0.44 m²/m³ at v_a = 0.1m/s and the MCT was 15.3m/h, which was close to the result of the chamber test at 300 rpm (much less than 0.1m/s), because the limited ventilation rate in the chamber test restrained the vapor transfer and consequently MTC. It was cleared that tested MTC always showed the higher values than JIS and theoretical ones, and could become close to other ones by compensation considering the velocity boundary layer and the loading factor.