Chapter 7, Problem 7.11CU

Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x, = 0.5 undergo the two different processes 7.33 described below. In each case, the mixture is brought from the initial state to a saturated vapor state, while the volume remains constant. For each process, determine the change in exergy of the water, the net amounts of exergy transfer by work and heat, and the amount of exergy destruction, each in kJ. Let To = 300 K, Po =1 bar, and ignore the effects of motion and gravity. Comment on the difference between the exergy destruction values. a. The process is brought about adiabatically by stirring the mixture with a paddle wheel. Answer b. The process is brought about by heat transfer from a thermal reservoir at 610 K. The temperature of the water at the location where the heat transfer occurs is 610 K Answer

7.36 At steady state, hot gaseous products of combustion from a gas turbine cool from 3000°F to 250°F as they flow through a pipe. Owing to negligible fluid friction, the flow occurs at nearly constant pressure. Applying the ideal gas model with ₂ = 0.3 Btu/lb/ºR, determine the exergy transfer accompanying heat transfer from the gas, in Btu per lb of gas flowing. Let T. = 80°F and ignore the effects of motion and gravity. -568.43

1. The first law of thermodynamics discussesa. Thermal equilibriumb. Energy conservationc. Direction of heat flowd. Entropy is zero at absolute zero temperature 2. A tank contains 1 kg mass gas whose density is 700 kg/m3. The pressure is increased from 1 bar to 3 bar. The approximate specific boundary work of the system isa. Cannot be find since some data is missingb. 285 kJ/kgc. 0 kJ/kgd. 0.285 kJ/kg 3. The nozzle is a device in whicha. Area decreases b. Area increasesc. Velocity decreases d. Velocity increases 4. Choose the correct statement/s with respect to entropy change during a processa. Entropy increases with increase in pressure at constant temperatureb. Entropy increases with increase in temperature at constant pressurec. Entropy can be kept constant by systematically increase both pressure and temperatured. Entropy can not be changed 5. The isentropic process is also called asa. Adiabatic processb. Irreversible adiabatic processc. Reversible adiabatic processd. Reversible…