Parallel flow of atmospheric air over a flat plate of length L = 3 m is disrupted by an array of stationary rods placed in the flow path over the plate. Laboratory measurements of the local convection coefficient at the surface of the plate are made for a prescribed value of V and T s > T ∞ . The results are correlated by an expression of the form h x = 0.7 + 13.6 x − 3.4 x 2 , where h x has units of W/m 2 ⋅ K and x is in meters. Evaluate the average convection coefficient h ¯ L for the entire plate and the ratio h ¯ L / h L at the trailing edge.
Parallel flow of atmospheric air over a flat plate of length L = 3 m is disrupted by an array of stationary rods placed in the flow path over the plate. Laboratory measurements of the local convection coefficient at the surface of the plate are made for a prescribed value of V and T s > T ∞ . The results are correlated by an expression of the form h x = 0.7 + 13.6 x − 3.4 x 2 , where h x has units of W/m 2 ⋅ K and x is in meters. Evaluate the average convection coefficient h ¯ L for the entire plate and the ratio h ¯ L / h L at the trailing edge.
Parallel flow of atmospheric air over a flat plate of length
L
=
3
m
is disrupted by an array of stationary rods placed in the flow path over the plate.
Laboratory measurements of the local convection coefficient at the surface of the plate are made for a prescribed value of V and
T
s
>
T
∞
.
The results are correlated by an expression of the form
h
x
=
0.7
+
13.6
x
−
3.4
x
2
,
where
h
x
has units of
W/m
2
⋅
K
and x is in meters. Evaluate the average convection coefficient
h
¯
L
for the entire plate and the ratio
h
¯
L
/
h
L
at the trailing edge.
To good approximation, the thermal conductivity k of a gasdepends only on the density ρ ,mean free path l , gas constant R , and absolute temperatureT . For air at 20 8 C and 1 atm, k ≈0.026 W/(m.K) and l ≈6.5 E-8 m. Use this information to determine k for hydrogenat 20 ° C and 1 atm if l ≈ 1.2 E-7 m.
2
Q1. Convection heat transfer coefficient does not depend on geometric parameters of the
system (True/False)
Q2. Forced convective heat transfer coefficient depends on type of flow (True/False)
Q3. Increase in thermal conductivity increases the Nusselt Number (True/False)
Q4. If the Nusselt number (Nu) is unity, the heat transfer is purely by convection (True/False)
Q5. The thickness of the thermal boundary layer increases in the direction of flow (True/False)
Q6. Increase in film thickness.
convective heat transfer coefficient.
Q7. The relative thickness of hydrodynamic and thermal boundary is better described
dimensioniess number.
Q8. In forced convection, the
heat
transfer
coefficient strongly depends
on.
.dimensionless number.
09. Fin increase the heat transfer rates by increasing
Q10. Thermal conductivity of the fin should be
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