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Reynolds number dependence of the drag coefficient for laminar flow through electrically-heated photoetched screens


Experiments are performed to measure the drag coefficient of electrically-heated screens. Square-pattern 80 mesh and 100 mesh screens of 50.8 μm-wide wires photoetched from 50.8 μm thick Inconel sheets are examined. Ambient air is passed through these screens at upstream velocities yielding wire-width Reynolds numbers from 2 to 35, and electrical current is passed through the screens to generate heat fluxes from o to 0.17 MW/m2, based on the total screen area. The dependence of the drag coefficient on Reynolds number and heat flux is determined for these two screens by measuring pressure drops across the screens for a variety of conditions in these ranges. In all cases, heating is found to increase the drag coefficient above the unheated value. A correlation relating the heated drag coefficient to the unheated drag coefficient is developed based on the idea that the main effect of heating at these levels is to modify the Reynolds number through modifying the viscosity. This correlation is seen to reproduce the experimental results closely.

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A :

total screen cross sectional area

C :

fitting coefficient, near unity

c D :

heated drag coefficient

c D, 0 :

unheated drag coefficient

C p :

air specific heat at constant pressure

D :

photoetched wire width, sheet thickness

h s :

stagnation point heat-transfer coefficient

k :

air thermal conductivity

M :

distance between adjacent wires

O :

open area fraction

p :

air pressure

Δp :

air pressure drop across screen

Pr :

Prandtl number for air, μc p/k

Q :

total electrical power to screen

R :

radius of curvature at stagnation point

Re D :

wire width Reynolds number, ρUD/μ

T :

air temperature

U :

air speed upstream of screen

γ :

air specific heat ratio

ρ :

air density

μ :

air viscosity

ω :

exponent in temperature power law for viscosity

(⋯) :

quantity (⋯) evaluated at heated screen temperature


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The authors thank John Lewin and Bob Meyer for their assistance in the design and fabrication of the heated screen test facility and Tom Grasser for his help in performing the experiments. This work was performed at Sandia National laboratories, supported by the U.S. Department of Energy under contract number DE-AC04-94AL85000.

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Torczynski, J.R., O'Hern, T.J. Reynolds number dependence of the drag coefficient for laminar flow through electrically-heated photoetched screens. Experiments in Fluids 18, 206–209 (1995).

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