An Experimental Study of Mist/Air Film Cooling with Fan-shaped Holes on an Extended Flat Plate - Part 2: Two-Phase Flow Measurements and Droplet Dynamics

[+] Author and Article Information
Reda Ragab

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, Louisiana, USA

Ting Wang

Energy Conversion and Conservation Center, University of New Orleans, New Orleans, Louisiana, USA

1Corresponding author.

ASME doi:10.1115/1.4037642 History: Received May 19, 2016; Revised June 21, 2017


A Phase Doppler Particle Analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of two layers; a typical coolant film layer (cooling air containing the majority of the droplets) and a wider droplet layer containing droplets outside the film layer. Thanks to the higher inertia possessed by larger droplets (>20 ?m in diameter) at the injection hole, the larger droplets tend to shoot across over the coolant film layer, resulting in a wider droplet layer than the coolant film layer. The wider droplet layer boundaries are detected by measuring the droplet data rate (droplet number per second) distribution, and it is identified by a wedge-shaped enclosure prescribed by the data rate distribution curve. The coolant film layer is prescribed by its core and its upper boundary. The apex of the data rate curve, depicted by the maximum data rate, roughly indicates the core region of the coolant film layer. The upper boundary of the coolant film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses.

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