TERMODINAMICA QUIMICA IIQ 568

Balance de energía y entropía

Nota: estos problemas fueron tomados del libro “Fundamentals of thermodynamics” de los autores Borgnakke y Sonntag (disponible en bibliteca)

1. In a heat-driven refrigerator with ammonia as the working fluid, a turbine with inlet conditions of 2.0 MPa, 70ºC is used to drive a compressor with inlet saturated vapor at -20 C. The exhausts, both at 1.2 Mpa, are then mixed together. The ratio of the mass flow rate to the turbine to the total exit flow was measured to be 0.62. Can this be true?. Assume the compressor and the turbine are both adiabatic. (P9.96)

2. A flow of 5 kg/s water at 100 kPa, 20ºC should be delivered as steam at 1000 kPa, 350 ºC to some application. We have a heat source at constant 500 ºC. If the process should be reversible, how much heat transfer should we have? (P9.42)

3. A heat-powered portable air compressor consists of three components: (a) an adiabatic compressor, (b) a constant-pressure heater (heat supplied from an outside source); (c) an adiabatic turbine (see Fig below). Ambient air enters the compressor at 100 kPa, 300 K and is compressed to 600 kPa. All of the power from the turbine goes into the compressor, and the turbine exhaust is the supply of the compressed air. If this pressure is required to be 200 kPa, what must the temperature be at the exit of the heater? (P9.43)

4. A large supply line has a steady flow of R-410a at 1000 kPa, 60 ºC. It is used in three different adiabatic devices shown in Fig. below, a throttle (acelerador) flow, an ideal nozzle (tobera) and an ideal turbine. All the exit flows are at 300 kPa. Find the exit temperature and specific entropy generation for each device and the exit velocity of the nozzle. (P9.85)

CA/SS/2012