Homework #6

Name:_______________________________ Çengel & Boles, 7th Ed. July 25, 2013

ME 305 Thermodynamics II Homework #6

Woodbury Summer 2013

These problems are due Monday, July 29. 1.

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A mixture of 5 kg of H2 and 4kg of O2 in a piston-cylinder in a polytropic process with n=1.6. The temperature increases from 40C to 250C. Assume constant specific heats. a) What is the heat transfer for this process (kJ)? b) What is the entropy change for this process (kJ/K)? A gas mixture of 10% CO2, 20% H2O, and 70% N2 on a molar basis is initially at 1500K and is cooled in a constant pressure process at 100kPa to 600K. Assume variable specific heats. a) Compute the heat loss per kg of mixture. b) What is the dew point temperature of this mixture? A room contains moist air at 30C and 102 kPa. The partial pressure of the vapor is 1.5kPa. Determine: a) the relative humidity b) the humidity ratio c) the dew point temperature Moist air at 28C, 100kPa, and 50% relative humidity flows in a duct and is cooled at constant pressure to 20C. Determine a) the heat transfer (kJ/kg-air) b) the relative humidity at the exit An air conditioning system has a spray section followed by a reheater. Moist air at 32C and φ=77% enters (state 1) and passes through the water spray, leaving the spray section (state 2) saturated with water. The moist air is then heated to 25C and φ=45% (state3) with no moisture change. a) what is the temperature at state 2? b) what is the change in moisture in the overall process, in kg-H20/kg-air?