Chapter 5, Problem 5.41CU

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…

If a closed system undergoes a process for which S2=S1, the process must be internally reversible. - True or False One of the Carnot principles states that all power cycles operating between the same two thermal reservoirs have the same thermal efficiency. - True or False One statement of the second law of thermodynamics recognizes that the extensive property entropy is produced within systems whenever internal irreversibilities are present. - True or False

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7.25 As shown in Fig. P7.25, a 1-lb metal sphere initially at 2000°R is removed from an oven and quenched by immersing it in a closed tank containing 25 lb of water initially at 500°R. Each substance can be modeled as incompressible. An appropriate constant specific heat for the water is c 1.0 Btu/lb °R, and an appropriate value for the metal is cm = 0.1 Btu/lb oR. Heat transfer from the tank contents can be neglected. Determine the exergy destruction, in Btu. Let To = 77°F. System boundary Metal sphere: Tmi=2000°R m=0.1 Btu/lb R mm= 1 lb Water: Twj=500°R =1.0 Btu/lb R m 25 lb FIGURE P7.25

Multiple choice Questions Question No. 2: When a system is taken from state A to state B through a reversible path 1 and again the system is taken to its initial state A from B through different reversible path 2, then what will be the effect on entropy? a.entropy increasesb.entropy decreasesc. entropy remains constantd. none of the above

Steam at 44 bar and a dryness fraction, x = 0.9 is throttled to a pressure of 12 bar. Calculate thedifference in power output in kilowatts between the following two expansion processes:a) Steam at the initial pressure of 44 bar and x = 0.9 at State 1 is expanded in a turbine to State 3 at 0.12 bar.b) Steam at the reduced pressure of 12 bar after throttling at State 2 is expanded in another turbine to State 4 at the same exhaust pressure of 0.12 bar.The mass flow rate of steam is 8 kg/sec in both cases and the expansion in both turbines can be assumed to be reversible and adiabatic. Sketch both expansion processes on the same T-s diagram using the respective initial and final state points as described above.Explain the reason for the difference in power output.Calculate the mass flow rate of steam for the turbine operating at the throttled/reduced pressure to generate the same output as the turbine operating at the pressure before throttling.NOTE: You are required to number the state…

Two reversible power cycles are arranged in series. The first cycle receives energy by heat transfer from a reservoir at temperature TH and rejects energy to a reservoir at an intermediate temperature T. The second cycle receives the energy rejected by the first cycle from the reservoir at temperature T and rejects energy to a reservoir at temperature TC lower than T. Derive an expression for the intermediate temperature T in terms of TH and TC when,a. The net works of the two power cycles are equalb. The thermal efficiencies of the two power cycles are equal

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A power cycle operating at steady state receives energy by heat transfer at a rate Q at TH = 1800 Kand rejects energy by heat transfer to a cold reservoir at a rate Oc at Tc = 600K. For each of the following cases, determine whether the cycle operates reversibly, operates irreversibly, or is impossible. (a) Qu = (500) kW, Oc = (100) kW %3D (b) Qu = (500)kW, Wey cycle (250)kW, Oc = (200)kW (c) Weycle = (350)kW, Oc = (150)kW (d) On = (500)kw, Oc = (100)kW