Fundamentals of Heat and Mass Transfer
7th Edition
ISBN: 9780470917855
Author: Bergman, Theodore L./
Publisher: John Wiley & Sons Inc
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Chapter 3, Problem 3.59P
A 0.20-m-diameter. thin-walled steel pipe is used to transport saturated steam at a pressure of 20 bars in a room for which the air temperature is 25°C and the convection heat transfer coefficient at the outer surface of the pipe is
- What is the heat loss per unit length from the bare pipe (no insulation)? Estimate the heat loss per unit length if a 50-mrn-thick layer of insulation (magnesia, 85%) is added. The steel and magnesia may each be assumed to have an emmissivity of 0.8, and the steam-side convection resistance may be neglected.
- The costs associated with generating the steam and installing the insulation are known to be $100/m and of pipe length, respectively. If the steam line is to operate 7500 h/yr. how many years are needed to pay back the initial investment in insulation?
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Steel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to delivering steam with a pressure of 600 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 10 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible).
a. Hourly heat loss ... (kj / hr)b. temperature between insulation layers ... (° C.)
One vessel having a carbon-steel wall of thickness 5 mm
carrying
saturated steam and water at 423K. The vessel is insulated with magnesia of
thickness 50 mm. If the ambient air temperature is 321 K, determine the heat
loss from the vessel.
Given:
i. thermal conductivity of carbon steel is 52 W/m.K
ii. thermal conductivity of magnesia is 0.5 W/m.K
iii. surface coefficient of insulation surface is 3 W/m2.K
Steel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 800 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 10 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible).
a. Heat loss per hour. = AnswerkJ / hr.
b. Temperature between insulation layers. = Answer ° C.
Chapter 3 Solutions
Fundamentals of Heat and Mass Transfer
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