Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN: 9781305387102
Author: Kreith, Frank; Manglik, Raj M.
Publisher: Cengage Learning
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Oxy-acetylene torches can be used to cut or weld metal .Oxygen and acetylene are fed from separate compressed gas cylinders through pressure regulators to the torch where they are mixed and combusted .To estimate the amount of metal that can be cut or welded per unit volume of gas, the composition of the gases produced by combustion and heat produced by the combustion reaction must be determined .For this problem:
Define a closed system that can be used to calculate the heat produced
Define an open system that can be used to calculate the heat produced
List at least two intensive variables that are important in calculation
List at least two extensive variables that are important in the calculation
A child opens the door of the freezer that is turned off, to observe its operation. If the ambient temperature is 30°, what will be the behavior of the internal temperature of the freezer when it is opened and why?
a. does not change, since there is no material between the environment and the interior of the freezer for heat exchange
b. is increasing, because the convection between the environment and the air inside the refrigerator does not transfer heat from the outside to the center
c. does not change, since there is no contact between the surface of the meat and the external environment
d. increases, because sunlight falls on the meat, increasing the energy.
Then, when turning on the freezer again, it is observed that the back of the freezer gradually warms up, and remains warm during the operation of the machine. The amount of thermal energy emitted by the freezer must be:
a. equal to 0; the heating is due to a problem with the freezer
b. Less than the energy drawn from inside the…
Two inches of urethane foam will reduce heat loss close to 1000% when applied to a 2-inch diameter uninsulated steel pipe. Assume the pipe wall thickness is 0.25-inches, the pipe interior convective heat loss (hi) is 500 BTU/hr-ft2-oF, and the pipe outside convective heat loss ho 20 BTU/hr-ft2-oF, k steel is 25 BTU/hr-ft-oF, and k insulaton is 0.023 BTU/hr-ft-oF. (hint - calculate heat loss with and without insulation.
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