Homework3_Solution

# Homework3_Solution - Solve problem 1.34 Change the...

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BAEN-366 SPRING/09 Homework #3 Read Chapter 1 Page 13 – 32 Answer the following questions 1) What is “energy storage” Give an example. Energy storage is the amount of energy being kept in a system over a time interval. Example: All the carbohydrates we ingest, they will remain in our body unless we use them as energy source. 2) What is energy generation? Give an example. It’s the energy that is converted from one form into thermal energy. Example: A heater that used electrical energy to generate heat. 3) What is the difference between application of conservation of energy over a time and at an instant of time ? Application at an instant of time deals with energy and it is measured in joules, while application over a time deals with energy rates and it’s expressed in J/s.

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Unformatted text preview: Solve problem 1.34 Change the following: • SS temperature of 80°C • Ambient temperature of 30°C • D = 70 mm • L = 270 mm Solution a) i) Resistor as the control volume. SS → E ST = 0 W No energy flows in → E IN = 0 W E G = V*I = (24 V)*(6 A) = 144 W Since E IN and E ST are cero, then: E OUT = E G → E OUT = 144 W ii) System as the control volume. E IN = E G = 0 W E OUT = V*I = (24 V)*(6 A) = 144 W E ST = - E OUT → E ST = - 144 W b) Eg = q * V → q = Eg V V = (π D 2 ) * L 4 q = 4 (144 W) = 1.39 x 10 5 W/m 3 π (0.07m 2 ) (0.27m) c) E OUT = q conv = h A (Ts – T∞) A = πDL + 2 (π D 2 ) = π (0.07m) (0.27m) + 2 (π (0.07m) 2 ) = 0.0671 m 2 4 4 144W * (80 - 30)C 0.0671 m 2 h = 42.9 W/m 2 K...
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Homework3_Solution - Solve problem 1.34 Change the...

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