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Midterm32007Solution

# Midterm32007Solution - ENGR 225 December 3 2007 Name_Key...

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ENGR 225 Name ______Key______________ December 3, 2007 Please Check One Recitation: 8:30___; 10:00 ___; 1:15___ Short answer (2 pts. Each, for T/F and multiple choice circle the best answer of the choices given , fill in the blank must be completed with a meaningful word or phrase) 1. The expression below represent a balance of _ mechanical _ energy for 1-D incompressible steady flow ˙ m P 1 " + # 1 V 1 2 2 + gz 1 \$ % & ( ) + ˙ W pump = ˙ m P 2 " + # 2 V 2 2 2 + gz 2 \$ % & ( ) + ˙ W turbine + ˙ E mech , loss 2. T F The expression given in Q. 1 can also be written as P 1 " g + # 1 V 1 2 2 g + z 1 + h pump = P 2 " g + # 2 V 2 2 2 g + z 2 + h turbine , e + h L 3. The symbol ‘h’ in the expression given in Q. 2 represents a) enthalpy b) head c) height d) none of the above 4. For internal flow of velocity, V, in a pipe of length L and diameter D , h L = f L D + K L " # \$ % & ( V 2 2 g therefore ˙ E mech , loss = ˙ mgh L = ˙ mg f L D + K L " # \$ % & ( V 2 2 g ___________________ 5. T F Depending on what you are trying to learn, different choices for points 1 & 2 are made when applying the expressions given in Q.1 and Q.2 to a given situation. 6. When there are minor losses for flow in a pipe a) K L values must be determined b) it is equivalent to a longer pipe c) mechanical energy is being converted to heat d) all of the above e) none of the above 7. The friction factor, f, can be well approximated from the __ Moody ____ chart or the Haaland relation 1 f " # 1.8log 6.9 Re + \$ / D 3.7 % & ( ) * 1.11 + , - . / 0 8. T F For external flows, there are two net forces, drag and lift, that operate in two different directions that are 90 0 apart. 9. Drag coefficients depend on 10. A thermos bottle is a device that is designed to have a high thermal resistance for heat flow due any of the _____ three ________ ( give a number ) modes of heat transfer. 11. T F Convection is a complex process that is often analyzed using a heat transfer coefficient that is not a property of the fluid, but is an experimentally determined parameter whose value depends on all the variables influencing convection such as the surface geometry, the nature of the fluid motion, the properties of the fluid, and the bulk fluid velocity.

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12. A valid expression for heat flow by radiation is 4 \$ T surr 4 ( ) 2 + T surr 2 ( ) T surf + T surr ( ) T surf \$ T surr ( ) 13. The thermal conductivity of an aluminum window frame is roughly ___ 100 _____ times larger than the thermal conductivity of the glass that the window is made from. 14. T F In the expression, " T " t = # " 2 T " x 2 the symbol α refers to kinetic energy correction.
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