ENGR225Spring2014 - Homework 1 (1)

ENGR225Spring2014 - Homework 1 (1) - ENGR 225 Spring 2014...

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ENGR 225 Spring 2014 Homework #1 due by recitation week of 1/20 1. In what forms can energy cross the boundaries of a closed system? 2. What is an adiabatic process? 3. Write out the full first law of thermodynamics equation making sure you have terms that represent energy in/out, heat in/out, work in/out and mass flow energy in/out. 4. On a hot summer day, a student turns his fan on when he leaves his room in the morning. When he returns in the evening, will the room be warmer or cooler than the neighboring rooms? Why? Assume all the doors and windows are kept closed. 5. A classroom that normally contains 40 people is to be air conditioned with window air- conditioning units of 5 kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/hr. There are 10 light bulbs in the room, each with a rating of 100 W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000 kJ/hr. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.
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