Chapter 5, Problem 5.38CU

As shown in the figure below, two reversible cycles arranged in series each produce the same net work, Wcycle. The first cycle receives energy QH by heat transfer from a hot reservoir at TH-1000°R and rejects energy Q by heat transfer to a reservoir at an intermediate temperature, T. The second cycle receives energy Q by heat transfer from the reservoir at temperature T and rejects energy Qc by heat transfer to a reservoir at Te - 500°R. All energy transfers are positive in the directions of the arrows. Determine: Hot reservoir at TH lH R1 Reservoir Q at T 20 R2 lc Cold reservoir at Tc We cycle W Wcycle (a) the intermediate temperature T, in °R, and the thermal efficiency for each of the two power cycles. (b) the thermal efficiency of a single reversible power cycle operating between hot and cold reservoirs at 1000°R and 500°R, respectively. Also, determine the ratio of the network developed by the single cycle to the network developed by each of the two cycles, Wcycle-

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

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…

Air enters a nozzle operating at steady-state at 800°R, with a negligible velocity, and exits with a velocity of 1500 ft/s. Heat transfer occurs from the nozzle to the surroundings at a rate of 10 Btu per lbm of air flowing. Determine the temperature at the exit, °R. Assume: o air is an ideal gas, variable specific heats, and o potential energy effects are negligible.

One kilogram of water in a piston- cylinder assembly undergoes the two internally reversible T processes in series shown in Fig. P6.94. For each process, determine, in kJ, the heat transfer and the work. 2 1 s = constant p = constant P₁ = 0.1 Mpa T₁ = 100°C 3 ▲ Figure P6.94 P3 = 1.0 Mpa T3 = 400°C S

Air in a closed piston-cylinder arrangement is expanded from the initial pressure of 9 bar and initial volume of 0.023 m to the final state of p = 3 bar. A polytropic relation of pV^1.27 = constant was followed between pressure and volume for the process. The specific internal energy at the initial and final states are 160 and 97 kJ/kg, respectively. The mass of the air is 0.3 kg. Neglecting the effect of kinetic and potential energy, determine the heat transfer, in kJ.

As shown in the figure below, two reversible cycles arranged in series each produce the same net work, Weycle. The first cycle receives energy QH by heat transfer from a hot reservoir at TH = 1500°R and rejects energy Q by heat transfer to a reservoir at an intermediate temperature, T. The second cycle receives energy Q by heat transfer from the reservoir at temperature T and rejects energy Qc by heat transfer to a reservoir at Tc = 500°R. All energy transfers are positive in the directions of the arrows. Hot reservoir at T RI W. cycle Reservoir at T R2 Wcycle Cold reservoir at Te Determine: (a) the intermediate temperature T, in °R, and the thermal efficiency for each of the two power cycles. (b) the thermal efficiency of a single reversible power cycle operating between hot and cold reservoirs at 1500°R and 500°R, respectively. Also, determine the ratio of the net work developed by the single cycle to the net work developed by each of the two cycles, Woycle-

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

A 60-lb aluminum bar, initially at T₂ = 150°F, is placed in a tank together with 190 lb of liquid water, initially at Tw= 70°F, and allowed to achieve thermal equilibrium. The aluminum bar and water can be modeled as incompressible with specific heats c₂ = 0.216 Btu/lb.ºR and cw = 0.998 Btu/lb.°R, respectively. Consider the aluminum bar and water as the system and ignore heat transfer between the system and its surroundings. Determine the final temperature Tf, in °F, and the amount of entropy produced within the tank, in Btu/°R.