A printed circuit board (PCB) is cooled by laminar. fully developed airflow in adjoining, parallel-plate channels of length L and separation distance a The channels may be assumed to be of infinite extent in the transverse direction, and the upper and lower surfaces we insulated. The temperature T s of the PCB board is uniform, ¡md airflow with an inlet temperature of T m , i , is driven by a pressure difference Δ p . Calculate the average heat removal rate per unit area ( W/m 2 ) from the PCB.
A printed circuit board (PCB) is cooled by laminar. fully developed airflow in adjoining, parallel-plate channels of length L and separation distance a The channels may be assumed to be of infinite extent in the transverse direction, and the upper and lower surfaces we insulated. The temperature T s of the PCB board is uniform, ¡md airflow with an inlet temperature of T m , i , is driven by a pressure difference Δ p . Calculate the average heat removal rate per unit area ( W/m 2 ) from the PCB.
Solution Summary: The author explains the average heat removal rate per unit area from the PCB. The mass flow rate through the channel is given as, cm=rho
A printed circuit board (PCB) is cooled by laminar. fully developed airflow in adjoining, parallel-plate channels of length L and separation distance a The channels may be assumed to be of infinite extent in the transverse direction, and the upper and lower surfaces we insulated. The temperature
T
s
of the PCB board is uniform, ¡md airflow with an inlet temperature of
T
m
,
i
, is driven by a pressure difference
Δ
p
. Calculate the average heat removal rate per unit area
(
W/m
2
)
from the PCB.
Water flows in a duct having a cross-section of 10x20 mm with a mean bulk diameter of 15.56 deg C. If the duct wall temperature is constant at 60 deg C and fully developed laminar flow prevails.
a.) Calculate the heat transfer coefficient, h in W/m2-deg Cchoices: (405, 305, 151, 252)
b.) What is the thermal conductivity of water at the given temperature, k in W/m-deg Cchoices: (0.604, 0.6, 0.585, 0.595)
c.) Calculate the heat transfer rate per unit length in W/mchoices; (605, 366, 505, 404)
6.64 Consider application of the naphthalene sublimation
technique (Problem 6.63) to a gas turbine blade that is
coated with naphthalene and has a surface area of
A, = 0.05 m².
Airflow
V,T_
- Turbine blade with
naphthalene coating
A., T., P. (T₂)
To determine the average convection heat transfer coef-
ficient for a representative operating condition, an
experiment is performed in which the coated blade is
exposed for 30 min to atmospheric air at the desired
velocity and a temperature of T = 27°C. During the
experiment the surface temperature is T. = 27°C, and at
its conclusion the mass of the blade is reduced by
Am = 8 g. What is the average convection heat transfer
coefficient associated with the operating condition?
A vehicle carrying refrigeration box is moving with a speed of 24 m/s on a road withambient temperature of 323 K. The dimensions of box are 3 m(H) × 4 m (W) × 10 m (L).Assume a wall temperature of 283 K and air flow is parallel to the longest side of the box.Neglecting the heat loss from the front side and backside of the box, calculate heat lossfrom four surfaces. For flow over flat surfaces useNu = 0.036(Re)0.8(Pr)1/3The properties of air at bulk mean temperature are : = 1.165 kg/m3, Pr = 0.701, cp = 1005 J/kg – K, = 16 × 10–6m2/s
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