Introduction to Heat Transfer
6th Edition
ISBN: 9780470501962
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
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Chapter 1, Problem 1.79P
(a)
To determine
Rate of heat loss from the duct.
(b)
To determine
The outlet temperature of heated air.
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A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 1500 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe.
a. Determine the enthalpy of incoming vapor = Answer
kJ / kg.
b. Determine the enthalpy of steam coming out = Answer
kJ / kg.
c. Determine the vapor heat change / loss along the flow = Answer
watt.
d. Specify the minimum required insulation thickness = Answer
cm.
Determine the rate of heat loss per unit length (q′), in W/m, and outer surface temperature Ts,2, in K, for the steam pipe with the inner surface temperature fixed at Ts,1=800 K, inner radius r1=0.06 m, and outer radius r2= 0.12. The outer surface is exposed to an airflow (∞T∞=25°C) that maintains a convection coefficient of h=25 W/m2·K and to large surroundings for which ∞Tsur=T∞=25°C. The surface emissivity of calcium silicate is approximately 0.8.
The temperature of a cylindrical tank containing liquid nitrogen is -10 ° C. Tank diameter is 16 cm. The amount of heat lost by convection and radiation from the tank to the environment is 65.5 W / m. Calculate the temperature of the environment where the tank is located: h = 4.35 W / m2K, ∈ = 1.
Chapter 1 Solutions
Introduction to Heat Transfer
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