Chapter 7, Problem 7.33P

Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x1= 0.3 undergo the two different processes 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 = 300K, 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. 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.

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

Steam at a pressure of 21 bar and a dryness fraction of 0.9 occupies a volume of 0.427 m' in a cylinder behind a piston is allowed to expand reversibly to a pressure of 7 bar according to the relationship, PV1.25 = Constant. Sketch the process on the p-v diagram and calculate the work and heat transfers in kJ. %3D