hw2 - MEEN 315, SECTION 503 PRINCIPLES OF THERMODYNAMICS...

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MEEN 315, SECTION 503 PRINCIPLES OF THERMODYNAMICS Fall 2009 Homework #2 DUE September 15, 2009 1. A spherical balloon holding 35 lb m of air has a diameter of 10ft (like a small hot air balloon). For the air, determine (a) the specific volume in ft 3 /lb m and (b) the weight in lb f . Let g = 31.0 ft/s 2 . Concepts: specific volume, English units Solution: 2. A gas initially at P 1 = 1 bar (i.e., the pressure of the gas at state 1 is 1 bar) and occupying a volume of 1 liter is compressed within a piston-cylinder assembly to a final pressure P 2 = 4 bar. (a) If the relationship between pressure and volume during the compression is polytropic, that is, P v = constant (note that n = 1), determine the volume, in liters, at a pressure of 3 bar. Also, plot the overall process on a graph of pressure versus volume. (b) Repeat for a linear pressure-volume relationship between the same end states. Concepts: Processes, pressure-volume relationships, metric units, graphing NOTE: Both the studied processes in (a) and (b) are important processes in thermodynamics. The first, the polytropic process, is what is typically observed in many real compression and expansion processes (such as what is observed in an internal combustion engine, a steam engine, and many other piston / cylinder type devices). The general polytropic process is written as P v n = constant; in this problem, n = 1. The second, the linear process, is often observed for piston/cylinder arrangements where a linear spring is acting on the face of the piston (see problem 4!!). We will discuss both of these processes in more detail as the semester continues. In case you’re having trouble mathematically working the polytropic process, take note that: P v = constant, which means P 1 v 1 = P 2 v 2
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Solution:
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3. A gas contained within a piston-cylinder assembly undergoes three processes in series: Process 1 – 2: Compression with P v = constant from P 1 = 1 bar, V 1 = 1.0 m 3 to V 2 = 0.2 m 3 . Process 2 – 3: Constant pressure expansion to V
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This note was uploaded on 12/03/2009 for the course MEEN 315 taught by Professor Ramussen during the Spring '07 term at Texas A&M.

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hw2 - MEEN 315, SECTION 503 PRINCIPLES OF THERMODYNAMICS...

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