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Water at 20°C enters a 1.91-cm-ID, 57-cm-long tube at a flow rate of 3 gm/s. The tube wall is maintained at 30°C. Determine the water outlet temperature. What error in the water temperature results if natural convection effects are neglected?
GIVEN
• Water flowing through a tube
• Entering water temperature (Tb,in) = 20°C
• Tube inside diameter (D) = 1.91 cm = 0.0191 m
• Tube length (L) = 57 cm = 0.57 m
• Mass flow rate (m) = 3 gm/s = 0.003 kg/s
• Tube wall surface temperature (Ts) = 30°C
FIND
(a) The water outlet temperature (Tb,out)
(b) Percent error in water temperature rise if natural convection is neglected
ASSUMPTIONS
• Steady state
• Tube temperature is uniform and constant
• The tube is horizontal
SKETCH
PROPERTIES AND CONSTANTS
for water at 20°C
Specific heat (c) = 4182 J/(kg K)
Thermal conductivity (k) = 0.597 W/(m K)
Kinematic viscosity (?) = 1.006 × 10–6 m2/s
Prandtl number (Pr) = 7.0
Absolute viscosity (?b) = 993 × 10–6 (Ns)/m2
Thermal expansion coefficient (?) = 2.1 × 10–4 1/K At 30°C ?s = 792 × 10–6 (Ns)/m2
The figure shows a distance vs. time graph of an object with three distinct regions, I, II, and III
?
The object’s velocity is positive in region II.
a.
True
b.
False
Two parallel conductors each of 0.50-m length, separated by 5.0 × 10^-3 m and carrying 3.0 A in the same direction, will experience what type and magnitude of mutual force? (magnetic permeability in empty space µ0 = 4p × 10^-7 T×m/A)
a. attractive, 1.8 × 10^-4 N c. repulsive, 0.60 × 10^-4 N b. repulsive, 1.8 × 10^-4 N d. attractive, 0.06 × 10^-4 N
When a switch is closed, completing an LR series circuit, the time needed for the current to reach one half its maximum value is ____ time constants
a. 0.250 b. 0.500 c. 0.693 d. 1.00 e. 1.44