Active Control of Heat and Mass Transfer using Functional Jets Array

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Control of scalar transport and local distribution is of significance for improvement of jet utilized fluid devices. Concepts of an array of jets and feedback control were introduced in order to control thermal fluid features. In the present study, three types of array of jets were investigated, that is, an array of triple parallel 2-dimensional air jets (width 15mm, nozzle spacing 50mm and Reynolds number 4000-8000), a staggered array of seven circular air jets (diameter 13mm, nozzle spacing 17mm and Reynolds number 1700-9500) and two parallel planar impinging water jets (width 10mm, nozzle spacing 36mm and Reynolds number 500-1000). Characteristics of the velocity field were examined in order to design control system by particle image velocimetry (PIV). In the first one, the exits velocity of the three jets were determined with feedback control based on the velocity distribution detected by an array of hot-wire probes in real time. Fluctuation intensity of the averaged velocity distribution was reduced and the system became robust with the recovering time shortened for disturbance. Neural network algorithm was applied to further complicated shape of velocity or concentration profile as a controller. In the second one, the relation between jets mixing and the ratio of the surrounding jets velocity was examined experimentally so that control system to realize the directional shape was achieved, which can rotate the orientation of concentration profile as a time sequential control. In the third one, manipulation of the local shear layers via the synthetic excitation through the fine slits at the nozzle exit was applied in order to control vorticies near the impinging plate. The present feedback control system showed the reduction of wall temperature fluctuation by the modification of vortices changing the pattern and the phase of the excitation.