Which of the following is comprised of the answers to the who, when, and where questions?
What will be an ideal response?
Distribution
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Free Fall: Abby throws a ball straight up and times it. She sees that the ball goes by the top of a flagpole after 0.50 s and reaches the level of the top of the pole after a total elapsed time of 4.1 s. What was the speed of the ball at launch? Neglect air resistance.
A. 11 m/s B. 23 m/s C. 34 m/s D. 45 m/s E. 48 m/s
Molecular Speeds: The molecular weight of nitrogen, N2, is 28 g/mol. What is the rms speed of nitrogen molecules in a cooler at 8.0°C? The Boltzmann constant is 1.38 × 10-23 J/K and NA = 6.022 × 1023 molecules/mol.
A. 450 m/s B. 500 m/s C. 550 m/s D. 600 m/s E. 650 m/s
The resultant of a 40-N force at right angles to a 30-N force is
A) 30 N. B) 40 N. C) 50 N. D) greater than 50 N.
A long, heated, cylindrical steel rod is removed from a heat treatment furnace and has to be cooled to complete the process. If the surface temperature of the rod is at 150°C and the cooling fluid temperature is maintained at 25°C, what is the minimum diameter of the rod to produce turbulent natural convection heat transfer if it is held in a horizontal position in (a) air and (b) water? Also, determine the initial heat transfer rate by natural convection from a 10-cm diameter rod in each of the two fluids.
GIVEN
• Long heated cylindrical steel rod, cooled by natural convection.
• Surface temperature of rod (Ts=1500C
• Fluid temperature (T?) = 250C
FIND
(a) Minimum diameter of rod to produce turbulent natural convection in (i) Air (ii) water
(b) Initial heat transfer rate by natural convection from 10 cm diameter rod in each fluids.
ASSUMPTIONS
• Radiation is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 87.5°C
Thermal expansion coefficient (?) = 0.00277 1/K
Thermal conductivity (k) = 0.0298 W/(m K)
Kinematic viscosity (?) = 22.55 × 10–6 m2/s
Prandtl number (Pr) = 0.71
for water at the mean temperature of 87.5°C
Thermal expansion coefficient (?) = 0.000678 1/K
Thermal conductivity (k) = 0.6765 W/(m K)
Kinematic viscosity (?) = 0.33 × 10–6 m2/s
Prandtl number (Pr) = 67.8