Mass transport from a flat plate and cylinder in a strong, high temperature, oscillating flow field.

Abstract

The mass transfer enhancement from two liquid surfaces placed inside a strong, high temperature, oscillating flow field was investigated. The device used for creating this flow field was a "Helmholtz type" pulse combustor. These devices operate in resonance with velocity oscillation amplitudes typically ranging between 20 and 100 m/s, frequencies between 50 and 200 Hz, and tailpipe gas-phase temperatures between 700-1500 K. To quantify the mass transport enhancement under various operating conditions, and to model a realistic drying application, attention is focused on the evaporation rates from two different surfaces: a cylindrical surface placed transverse to the tailpipe flow and a flat plate surface placed against the tailpipe wall. The mass transfer enhancements from both surfaces were investigated by examining their time-average evaporation rates and surrounding flow field properties. The flow field properties were determined using Laser Doppler Velocimetry and Laser Schlieren. Both the velocity data and schlieren video indicate that the momentum transport (and therefore heat or mass transport) is non-quasi-steady. Over the range and combination of operating conditions studied, the results show mass transfer enhancements approaching 100% for both the cylinder and flat plate. The mass transfer rates are strongly affected by the pressure amplitude, weakly affected by the mean flow Reynolds number, and insignificantly affected by the frequency. The enhancements are attributed to increased turbulence and significant non-quasi-steady flow behavior over the transport surfaces.