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Eighth International Congress of Fluid Dynamics and Propulsion (ICFDP8-EG-113)
ICFDP
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An experimental investigation was conducted to analyze the effect of an oblique multi circular air jets impingement on the flow fields and drying rates from a flat surface. The spent air was exhausted freely from the target surface. The je- to- jet spacing (S/D = 2.5, 3.5, 4.5 and 5.5), the jet exit-to-impingement plate distances (offset ratio H/D = 2, 4 and 6) and jet inclination angles (jet axis with impingement plate) (θ = 90o, 80o, 70o and 60o) have been investigated. An aerodynamic investigation was conducted for such reattachment flow fields. For the present experimental tests, two types of techniques were utilized to study the dominant structures of such flow type. The first quantitative technique is to measure the pressure distribution along the solid impinging flat plate. The second qualitative technique is a flow visualization one in which the flat plate is coated with colored tempera powder plus kerosene mixture, while a digital camera is used to capture the visualized flow pattern due to impingement on the flat plate. Air flow through the suggested multiple jets was used as the drying media. A porous media flat plate is used as a target surface for the drying process in mass transfer experiments. For homogenous wet texture, such flat plate was uniformly sprayed with the distilled water. In the present study, the Reynolds number at the jet exit was 28,000.
The results show that the surface pressure distribution and the drying rates are dependent on S/D, H/D and parameters. For the normal multiple jets, the Cp profile has two peaks along the impingement line, one at the impingement point of each jet and the other occurs midway between adjacent jets owing to the collision of the spreading flows from adjacent impinged jets. The peak of Cp due interactions decreases with the increasing jet-to-jet spacing S/D. For an oblique multiple jets, the peak of pressure coefficient due to the impingement of each jet is less than the value with the normal jet ( = 90o). For an oblique multiple jets, the location of the peak of Cp is displaced somewhat from the intersection of the geometric axis of the jet with the plate surface and moves away from symmetry as the inclination angle decreases. The location of the peak of pressure coefficient region appears to fall between 0 and 4D away from the geometrical impinging point of the normal jets. For the normal and an oblique multiple jets the maximum drying rate is obtained at the relatively large jet exit-to-plate spacing H/D = 6 and the rate of drying is minimum at small jet exit-to-plate spacing H/D = 4. The main contribution of this study is the optimum situation for the jet-to-jet spacing (S/D = 3.5), the inclination angle ( = 60o) and the jet exit-to-plate distance (H/D = 6) is the optimum case which satisfy the largest drying rates beside the uniform pressure distributions along the drying plane.
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