Chapter 7, Problem 7.18CU

Determine the change in exergy in kJ for each of the following processes in the system with 1 kg of steam at 20 bar and 240 °C initially. a) In case the system is heated to double its volume at constant pressure. b) In case of expansion by doubling the system volume isothermally. dead state; T0=20 °C, P0=1 bar

At a pressure of 1 bar, a temperature of 17 °C and a mass flow of 0.3 kg/s, air enters a stable insulated compressor and exits at 3 bar, 147 °C. Determine the power required by the compressor and the exergy destruction in kW. Express the exergy disappearance as a percentage according to the power required by the compressor. Changes in kinetic and potential energy will be neglected. dead state; T0=17 °C, P0=1 bar

An internal combustion engine is a commonly-analyzed thermodynamic system. In a few sentences, describe the flows of energy and matter across the boundaries of a typical engine.

What does the exergy principle state? The exergy of an isolated system can never decreases, but always increases O The exergy of an isolated system can never increases, but always decreases O The exergy of an isolated system can either increases or decreases O None of the above

Which of the following statements best describes the 2nd law of thermodynamics? The total entropy of a a reservoir must stay the same or increase. The change in internal energy for an ideal gas is given as A U=mc _▲T. V Heat energy will always be transferred from a hotter object to a colder object. Around a complete cycle, the net heat and net work additions must sum to zero. O A reversible cyclic engine can convert all the heat input it receives into useful work output.

answer 96,97,98

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…

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

7.27 Figure P7.27 provides steady-state data for the outer wall of a dwelling on a day when the indoor temperature is maintained at 25°C and the outdoor temperature is 35°C. The heat transfer rate through the wall is 1000 W. Determine, in W, the rate of exergy destruction (a) within the wall, and (b) within the enlarged system shown on the figure by the dashed line. Comment. Let T₂ = 35°C. 20.13, 33-56 Indoor Boundary of enlarged- temperature=25°C T=27C T-3C FIGURE PLAT Outdoor temperature=35°C