If we use 67 W of power to heat 148 g of water, how long will it take to raise the temperature of the water from 15°C to 25°C? The specific heat of water is 4190 J/kg ? K
A) 93 s
B) 5.3 s
C) 22 s
D) 114 h
Answer: A
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An aniline-alcohol solution is flowing at a velocity of 3 m/s through a long, 2.5 cm-ID thin-wall tube. Steam is condensing at atmospheric pressure, on the outer surface of the tube, and the tube-wall temperature is 100°C. The tube is clean, and there is no thermal resistance due to a scale deposit on the inner surface. Using the physical properties tabulated below, estimate the heat transfer coefficient between the fluid and the pipe using and compare the results. Assume that the bulk temperature of the aniline solution is 20°C and neglect entrance effects.
GIVEN
• An aniline-alcohol solution flowing through a thin-walled tube
• Tube is clean with no scaling on inner surface
• Velocity (V) =3 m/s
• Inside diameter of tube (D) = 2.5 cm = 0.025 m
• Tube wall surface temperature (Ts) = 100°C
• Solution has the properties listed above
• Solution bulk temperature (Tb)= 20°C FIND
• The heat transfer coefficient ( ch ) using: (a) Equation (7.61) (b) Equation (7.66)
ASSUMPTIONS
• Steady state
• Entrance effects are negligible
• Thermal resistance of the tube is negligible
• Tube wall temperature is constant and uniform
• Fully developed flow
SKETCH
PROPERTIES AND CONSTANTS
The density of water ? 1000 kg/m3