Surface air temperature is generally measured at 4 ft. above the ground because
What will be an ideal response?
inaccurate readings might occur if placed too close to the ground
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Estimate the mass diffusivity of methane into air at 300 K, assuming ideal gas behavior.
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Calculate the Nusselt number and the convection heat transfer coefficient for water at a bulk temperature of 32°C flowing at a velocity of 1.5 m/s through a 2.54-cm-ID duct with a wall temperature of 43°C. Use the Gnielinski correlation and two other correlations given in te text and cmpare the results.
GIVEN
• Water flowing through a duct
• Bulk water temperature (Tb) = 32°C
• Water velocity (V) = 1.5 m/s
• Inside diameter of duct (D) = 2.54 cm = 0.0254 m
• Duct wall surface temperature (Ts) = 43°C
FIND Use three different methods to find (a) The Nusselt number (NuD)
(b) The convective heat transfer coefficient (hc)
ASSUMPTIONS
• Steady state
• Fully developed, incompressible flow
SKETCH
PROPERTIES AND CONSTANTS
for water at a reference temperature equal to the bulk temperature (Tref = 32°C)
Thermal conductivity (k) = 0.619 W/(m K)
Kinematic viscosity (?) = 0.773 × 10–6 m2/s
Prandtl number (Prb) = 5.16
Absolute viscosity (?b) = 763 × 10–6 (Ns)/m2
Prandtl number at surface temperatue(Prs) = 4.06 At the surface temperature of 43°C:
Absolute viscosity (?s) = 626.3 × 10–6 (Ns)/m2
Heavy-water molecules have a mass number of
A) 18. B) 3. C) 12. D) 10. E) 20.
Originally 2.00 mol of gas are at standard temperature and pressure If the temperature changes to 47.0°C and the pressure decreases to half of what it was, how many liters do the two moles now occupy? (1 atm = 101 kPa, R = 8.31 J/mol ? K)
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