HW3 - measurement in a gas stream The convection...

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CHE 303-Problem Set 3 Due November 2 nd , 2011, 4 PM 1. A straight rectangular fin has a length of 3.5 cm and a square cross-section of 1.4 mm. the thermal conductivity is 55W/m 0 C. The fin is exposed to a convection environment at 20 0 C and h= 500 W/m 2 0 C. What is the heat loss from the fin if the base temperature is 150 0 C? What would be the maximum possible heat lost from the fin if the temperature of the entire fin is the same as the base temperature? 2. Derive a differential equation (do not solve) for the temperature distribution in a straight conical fin. Assume one dimensional heat flow. 3. Problem 5.66 from textbook Use properties at 300K from Appendix A 4. A thermocouple junction, which may be approximated as a sphere, is to be used for temperature
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Unformatted text preview: measurement in a gas stream. The convection coefficient between the junction surface and the gas is h= 400 W/m 2 .K, and the junction thermophysical properties are k= 20 W/m.K, c p = 400 J/kg.K, and = 8500kg/m 3 . Determine the junction diameter needed for the thermocouple to have a time constant of 2 second. If the junction is at 35 o C and is placed in a gas stream that is at 250 o C, how long will it take for the junction to reach 220 o C? Hint: The time constant (or thermal time constant) is defined as a product of resistance and capacitance (as done in class) L t x...
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This note was uploaded on 01/10/2012 for the course CHE 303 taught by Professor Kim during the Fall '09 term at Drexel.

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