A laminar flow is desired from a tank with a well-rounded entrance to a 6-mm-diameter pipe that drains the tank. A container catches 20 L of 20°C water in 4 minutes. Determine the Reynolds number so one can decide if the flow is laminar.
(A) 972
(B) 1220
(C) 1770
(D) 1920
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The "hot shot" thermodynamic engine operating between 40°C and 380°C has an efficiency that is 60% of that of an ideal Carnot engine operating between the same temperatures
If the "hot shot" engine absorbs energy at a rate of 60 kW, at what rate does it exhaust energy? A) 36 kW B) 41 kW C) 57 kW D) 60 kW
An electronic circuit board is the shape of a flat plate 0.3 m × 0.3 m in plan-form and dissipates 15 W. It is placed in operation on an insulated surface in a horizontal position or at an angle of 45 degrees to horizontal, in both cases; it is in still air at 25°C. If the circuit fails above 60°C, determine if the two proposed installations are safe.
GIVEN
• A flat plate with insulated back, horizontal or at an angle of 45 degrees in still air
• Plate size (s × s) = 0.3 m × 0.3m
• Heat generation rate (qG) = 15 W
• Air temperature (T?) = 25°C
• Maximum plate temperature (Ts) = 60°C
FIND
• If the two plate positions are safe
ASSUMPTIONS
• Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 43°C
Thermal expansion coefficient (?) = 0.00316 1/K
Thermal conductivity (k) = 0.0267 W/(m K)
Kinematic viscosity (?) = 17.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A copper wire of length 5.0 m, cross sectional area 6.9 × 10^?6 m2, and Young's modulus 11 × 10^10 N/m2 has a 190-kg load hung on it. What is its increase in length? (g = 9.8 m/s2)
a. 5.0E–3 m b. 1.8E–2 m c. 7.3E–3 m d. 1.2E–2 m e. 2.5E–2 m
Briefly explain why high-mass stars have shorter lifetimes than low-mass stars
What will be an ideal response?