EML 3100 S10 T2 packet

# EML 3100 S10 T2 packet - Test #2 Elements of Thermo EML...

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Test #2 Elements of Thermo EML 3007 October 27, 2009 Open book (class text only), open notes (prepared by you, class site downloads). 2 hours. Problem 1 (40). An ideal steam Rankine cycle with superheat operates with a condenser temperature of 20 C. It is well known that increasing the cycle pressure ratio will increase the cycle efficiency; here you are to estimate how sensitive the effect is. To do that: a) calculate the cycle efficiency when the pump discharge pressure is 10 MPa. Also determine the maximum cycle temperature. b) calculate the cycle efficiency when the pump discharge pressure is 12.5 MPa. Also determine the maximum cycle temperature. c) Calculate the change in efficiency per change in maximum temperature. That is, find " # " T max d) Taking the maximum temperature and condenser temperature as the external reservoir temperatures, find the Carnot efficiency for the two cases. For which case is the actual efficiency a greater percentage of the Carnot efficiency? Problem 2 (30). A rigid container is divided in half by a partition. One half of the volume contains air at 5 atm and 300K, while the other half is a vacuum. The partition is suddenly removed, allowing the air to occupy the entire container, and the system is allowed to reach equilibrium with negligible heat transfer. a) Taking the air as a perfect gas, find its change in temperature. b) Find the change in entropy of the air. Problem 3 (30). Humid air in the atmosphere rises as it encounters mountains, causing rain or snow via the decrease in pressure at higher altitude. a) If air is initially at 0.5 atm and 290 K, how far must the pressure drop before freezing temperatures occurs? b) Now consider the water vapor in the air. The concept of partial pressure is such that the total pressure is sum of the partial pressures of the water vapor and the dry air. For condensation to begin under the conditions of part a, what would the partial pressure of the water vapor be? What would be the ratio of water partial pressure to total pressure (this, by the way, would be the mole fraction of water).

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Test #2 Elements of Thermo EML 3007 March 19, 2009 Open book (class text only plus printout of chap. 23, the pdf), open notes (prepared by you, class site downloads). 2 hours. Problem 1 (50). A simple Rankine cycle with superheat (the turbine inlet is superheated) operates with water as the working fluid. The condenser pressure is 75 kPa and the boiler pressure is 3 MPa. The cycle is ideal except that the turbine efficiency is 93%, and the turbine exit quality is not 100%. The turbine inlet temperature is 350 °C. a)
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## This note was uploaded on 09/06/2011 for the course EML 3100 taught by Professor Sherif during the Spring '08 term at University of Florida.

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EML 3100 S10 T2 packet - Test #2 Elements of Thermo EML...

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