HEAT+MASS TRANSFER-ACCESS >CUSTOM<
5th Edition
ISBN: 9781260168440
Author: CENGEL
Publisher: MCG CUSTOM
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Textbook Question
Chapter 2, Problem 30P
Consider a medium in which the heat conduction equation is given in its simplest form as
- Is heat transfer steady or transient?
- Is heat transfer one- two-, or three-dimensional?
- Is there heat generation in the medium?
- Is the thermal conductivity of the medium constant or variable?
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A 300-ft-long section of a steam pipe whose outer diameter is 4 in passes through an open space at 50°F. The average temperature of the outer surface of the pipe is measured to be 280°F, and the average heat transfer coefficient on that surface is determined to be 6 Btu/h·ft2·°F. Determine (a) the rate of heat loss from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace having an efficiency of 86 percent, and the price of natural gas is $1.10/therm (1 therm = 100,000 Btu).
Heat is transferred steadily through a 0.2-m-thick, 8 m × 4 m wall at a rate of 2.4 kW. The inner and outer surface temperatures of the wall are measured to be 15°C and 5°C. The average thermal conductivity of the wall is
(a) 0.002 W/m·°C (b) 0.75 W/m·°C (c) 1.0 W/m·°C
(d) 1.5 W/m·°C (e) 3.0 W/m·°C
Water flows through a pipe at an average temperature of T∞ = 70°C. The inner and outer radii of the pipe are r1 = 6 cm and r2 = 6.5 cm, respectively. The outer surface of the pipe is wrapped with a thin electric heater that consumes 300 W per m length of the pipe. The exposed surface of the heater is heavily insulated so that all heat generated in the heater is transferred to the pipe. Heat is transferred from the inner surface of the pipe to the water by convection with a heat transfer coefficient of h = 85 W/m2·K. Assuming constant thermal conductivity and one-dimensional heat transfer, express the mathematical formulation (the differential equation and the boundary conditions) of the heat conduction in the pipe during steady operation. Do not solve.
Chapter 2 Solutions
HEAT+MASS TRANSFER-ACCESS >CUSTOM<
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