Chapter 5, Problem 5.25CU

The thermal efficiency of a reversible power cycle operating between hot and cold reservoirs is 50%. Evaluate the coefficient of performance of: (a) a reversible refrigeration cycle operating between the same two reservoirs. (b) a reversible heat pump cycle operating between the same two reservoirs.

As shown in the figure, a reversible power cycle R and an irreversible power cycle I operate between the same hot and cold thermal reservoir. Cycle I has a thermal efficiency equal to one-third of the thermal efficiency of cycle R. (b) If each cycle develops the same net work, determine which cycle (i) receives greater energy by heat transfer from the hot reservoir, (ii) discharges greater energy by heat transfer to the cold reservoir. WR R Hot reservoir m Qc=QH-WR l'c=QH-W₁ Cold reservoir W₁

A heat pump cycle is used to maintain the interior of a building at 25°C. At steady state, the heat pump receives energy by heat transfer from well water at 9°C and discharges energy by heat transfer to the building at a rate of 120,000 kJ/h. Over a period of 14 days, an electric meter records that 1500 kW · h of electricity is provided to the heat pump.Determine:(a) the amount of energy that the heat pump receives over the 14-day period from the well water by heat transfer, in kJ.(b) the heat pump’s coefficient of performance.(c) the coefficient of performance of a reversible heat pump cycle operating between hot and cold reservoirs at 25°C and 9°C.

A power cycle operates between two thermal reservoirs at 1200 K and 400 K, respectively. For each of the three cases below, determine: (i) The net power produced by the cycle, in kW; (ii) The thermal efficiency; and (iii) Use the Clausius inequality and comparisons to the thermal efficiency of a reversible cycle operating between the given temperatures to determine whether the cycle operates in a reversible or irreversible manner, or is impossible. case |  QH(kJ/s)   | QL(kJ/s)   A    |   600           | 400   B    |   600          |   0   C    |   600          |  200

Second-law efficiency is a measure of the performance of a device relative to its performance under reversible conditions.

(b) A heat engine with a thermal efficiency of 40 percent rejects 1000 kJ/kg of heat. Determine the amount of heat it receives.

A heat engine, operating between reservoirs at temperatures of 372 deg C and 17 deg C, performs 3.2 kJ of net work, and rejects 13.1 kJ of heat. What is the actual thermal efficiency (%)?

An inventor claims to have developed a refrigerator that at steady state requires a net power input of 1.1 horsepower to remove 12,000 Btu/h of energy by heat transfer from the freezer compartment at -30°F and discharge energy by heat transfer to a kitchen at 70°F. Evaluate this claim.   This claim is a) impossible b) possible

Q3/ A heat pump cycle operating between two reservoirs receives energy Q2 from a cold reservoir at T2 = 250K and rejects energy Qı to a hot reservoir at T1 = 300K. For each of the following cases determine whether the cycle operates reversibly, irreversibly or is impossible. (a) Q2 =300KJ , W = 400 KJ (b) Q2 = 2000KJ , Q1 = 2200KJ (c) Q1 = 3000KJ , W= 500KJ (d) W = 400 KJ , COP =6 %3D