The four fundamental forces in nature are the strong, weak, electromagnetic, and gravitational interactions
a. True
b. False
Indicate whether the statement is true or false
True
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What is the leading hypothesis for Venus’s lack of water?
A. Venus formed closer to the Sun and accreted very little water. B. Its water is locked away in the crust. C. Its water molecules were broken apart, and hydrogen was lost to space.
The most luminous quasars can give off ________ times more light than our own Galaxy
Fill in the blank(s) with correct word
For a particular process where a fluid is being heated in a 2 inch (5.08 cm) diameter tube, the Nusselt number is predicted to be 45. If the fluid has a thermal conductivity of 1.5 Btu/hr·ft·ºF (2.6 W/mK) what is the predicted convective heat transfer coefficient?
What will be an ideal response?
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