HW04_Sol

# HW04_Sol - 4 Air goes through a polytropic process from 125...

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ME 3513 – Thermodynamics I Solutions to Homework Assignment # 4 – Work and Heat Due: 09/22/2004 to discuss in class 1. An ideal gas goes through an expansion process where the volume doubles. Which process will lead to the larger work output: an isothermal process or a polytropic process with n = 1.25? 2. A constant pressure piston cylinder contains 0.2 kg water as saturated vapor at 400 kPa. It is now cooled so the water occupies half the original volume. Find the work in the process.

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3. A piston/cylinder has 5 m of liquid 20oC water on top of the piston (m = 0) with cross- sectional area of 0.1 m2, see Fig. P2.57. Air is let in under the piston that rises and pushes the water out over the top edge. Find the necessary work to push all the water out and plot the process in a P-V diagram.

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Unformatted text preview: 4. Air goes through a polytropic process from 125 kPa, 325 K to 300 kPa and 500 K. Find the polytropic exponent n and the specific work in the process. 5. A cylinder containing 1 kg of ammonia has an externally loaded piston. Initially the ammonia is at 2 MPa, 180 ° C and is now cooled to saturated vapor at 40 ° C, and then further cooled to 20 ° C, at which point the quality is 50%. Find the total work for the process, assuming a piecewise linear variation of P versus V . 6. A pot of steel, conductivity 50 W/m K, with a 5 mm thick bottom is filled with 15 ° C liquid water. The pot has a diameter of 20 cm and is now placed on an electric stove that delivers 250 W as heat transfer. Find the temperature on the outer pot bottom surface assuming the inner surface is at 15 ° C....
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HW04_Sol - 4 Air goes through a polytropic process from 125...

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