quiz2 - 2 MPa and heated The initial volume is 0 0277 m 3...

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MAE110A Thermodynamics Fall Quarter 2007 http://maecourses.ucsd.edu/mae110a Quiz II This is a 50 minute closed-book exam; no notes. Please put your name on the top sheet. Answer all three questions. Explain your working and state any assumptions you have made. 1 (3 points) Circle the correct answer. 1. A pure substance can never freeze. is an ideal gas. is homogeneous and invariable in chemical composition. is often a combination of reacting gases. can only have one phase. 2. For an ideal gas, internal energy depends on pressure alone. the compressibility factor z = 1. the saturation states exist only above 0 C. there are always three independent intensive properties. specific volume is constant. 3. The first law for a control volume states that ˙ m = 0. is only valid if there is no mass flux through the system. relates rate of change of momentum to external forces. is an energy balance (EB). always leads to SSSF problems. 1
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2 (7 points) A container holding 0 . 1 kg of propane is maintained at 0
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Unformatted text preview: . 2 MPa and heated. The initial volume is 0 . 0277 m 3 and the final volume is 0 . 0307 m 3 . (a) What are the initial and final temperatures of the propane? (b) What is the work done by the system? (c) What is the change in internal energy of the system? 2 3 (10 points) A hot water heater operates in steady state. A mass flux ˙ m 1 of cold water enters and is heated by an electrical resistance; ˙ m 2 of hot water leaves the heater. Define a control volume just inside the heater and inlet/outlet sections 1 and 2 respectively. Neglect kinetic and potential energy effects. (a) Is work done on the control volume? (b) If the heater is well insulated, show that h 2 = h 1 + ˙ W in / ˙ m . What are h and ˙ m ? (c) If the water is taken to be incompressible with constant specific heat c and constant specific volume v , find an expression for T 2 in terms of T 1 , c , ˙ W in , v and Q , the volumetric flow rate. 3...
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This note was uploaded on 04/01/2009 for the course MAE mae 110a taught by Professor ? during the Fall '07 term at UCSD.

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quiz2 - 2 MPa and heated The initial volume is 0 0277 m 3...

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