The COP of vapor-compression refrigeration cycles improves when the refrigerant is subcooled before it enters the throttling valve. Can the refrigerant be subcooled indefinitely to maximize this effect, or is there a lower limit? Explain.
> A biology professor notices a speck on a student's lab report and pulls out her magnifying lens to investigate. Holding the lens close to her eye, she is surprised to find Pelomyxa palustris, the largest known species of amoeba. (a) When observed withou
> If the magnetic force due to Earth's field were the only force on the ion, what would the smallest possible radius of its trajectory be?
> A magnifying glass can focus sunlight enough to heat up paper or dry grass and start a fire. A magnifying glass with a diameter of 4.0 cm has a focal length of 6.0 cm. (a) Using information found in Appendix B, estimate the size of the image of the Sun
> What is the greatest possible magnetic force on the sodium ion due to Earth's field?
> (a) For a converging lens with a focal length of 3.50 cm, find the object distance that will result in an inverted image with an image distance of 5.00 cm. Use a ray diagram to verify your calculations. (b) Is the image real or virtual? (c) What is the
> Suppose some 238U2+ ions are present in the beam. They have the same mass m as the 238U+ ions but twice the charge (+2e). (a) With what speed do the 238U2+ ions emerge from the accelerating plates, assuming 238U+ ions emerge with speed v? (b) Sketch th
> Starting with Fig. 23.39, perform all the algebraic steps to obtain the mirror equation in the form of Eq. (23-22).
> Find the point of no return for an airport runway of 1.50 mi in length if a jet plane can speed up at 10.0 ft/s2 and slow down at 7.00 ft/s2. The point of no return is the point where the pilot can no longer abort the takeoff without running out of runwa
> Find the mass of the 238U+ ions in terms of v, B, D, and universal constants.
> Show that when rays parallel to the principal axis reflect from a concave mirror, the reflected rays all pass through the focal point at a distance R/2 from the vertex. Assume that the angles of incidence are small. [Hint: Follow the similar derivation f
> Suppose some 235U+ ions are present in the beam. They have the same charge as the 238U+ ions but a smaller mass (approximately 0.987 37m). (a) With what speed do the 235U+ ions emerge from the accelerating plates, assuming 238U+ ions emerge with speed v
> Derive the magnification equation, m = h′/h = −q/p, for a convex mirror. Draw a ray diagram as part of the solution.
> The uniform magnetic field in the velocity selector is directed out of the page and has magnitude B. (a) What should the magnitude and direction of the electric field in the selector be to allow ions with speed v to pass straight through? (b) Sketch th
> In a subway station, a convex mirror allows the attendant to view activity on the platform. A woman 1.64 m tall is standing 4.5 m from the mirror. The image formed of the woman is 0.500 m tall. (a) What is the radius of curvature of the mirror? (b) The
> The accelerating plates have area A and are a distance d apart. (a) What should the charges on the plates be so the ions emerge at speed v, ignoring their initial kinetic energies? Indicate which plate is positive and which negative. (b) Sketch the ele
> A concave mirror has a radius of curvature of 5.0 m. An object, initially 2.0 m in front of the mirror, is moved back until it is 6.0 m from the mirror. Describe how the image location changes.
> An engineer wants to design a toy racetrack using an electromagnetic rail gun (see Problem 122) to accelerate a car of mass 40 g starting from rest. The horizontal rails are to be 1.0 m long and 2.0 cm apart. The magnetic field in the rail gun is to be 0
> The right-side rearview mirror of Mike's car says that objects in the mirror are closer than they appear. Mike decides to do an experiment to determine the focal length of this mirror. He holds a plane mirror next to the rearview mirror and views an obje
> The neutrons produced in fission reactors have a wide range of kinetic energies. After the neutrons make several collisions with atoms, they give up their excess kinetic energy and are left with the same average kinetic energy as the atoms, which is / .
> A baryon with charge 0 composed of up and/or strange quarks and/or antiquarks.
> Explain how these quantities differ: distance traveled, displacement, and displacement magnitude.
> Reconsider Prob. 9–162. Using appropriate software, investigate the effect of varying the compressor isentropic efficiency over the range 60 to 100 percent. Plot the power input to the compressor and the electric power saved by using a heat pump rather t
> A heat pump using refrigerant-134a heats a house by using underground water at 8°C as the heat source. The house is losing heat at a rate of 60,000 kJ/h. The refrigerant enters the compressor at 280 kPa and 0°C, and it leaves at 1 MPa and 60°C. The refri
> A pump is used to transport water to a higher reservoir. If the water temperature is 20°C, determine the lowest pressure that can exist in the pump without cavitation.
> A heat pump that operates on the ideal vapor compression cycle with refrigerant-134a is used to heat a house and maintain it at 75°F by using underground water at 50°F as the heat source. The house is losing heat at a rate of 80,000 Btu/h. The evaporator
> The pressure on the suction side of pumps is typically low, and the surfaces on that side of the pump are susceptible to cavitation, especially at high fluid temperatures. If the minimum pressure on the suction side of a water pump is 0.70 psia absolute,
> Refrigerant-134a enters the condenser of a residential heat pump at 800 kPa and 50°C at a rate of 0.022 kg/s and leaves at 750 kPa subcooled by 3°C. The refrigerant enters the compressor at 200 kPa superheated by 4°C. Det
> What is cavitation? What causes it?
> An air-standard cycle with variable specific heats is executed in a closed system and is composed of the following four processes: 1-2 v = constant heat addition from 14.7 psia and 80°F in the amount of 300 Btu/lbm 2-3 P = constant heat addition to 3200
> Define internal, external, and open-channel flows.
> A heat pump operates on the ideal vapor-compression refrigeration cycle and uses refrigerant 134a as the working fluid. The condenser operates at 1000 kPa and the evaporator at 200 kPa. Determine this system’s COP and the rate of heat supplied to the eva
> The temperature of the lubricating oil in an automobile engine is measured as 150°F. What is the temperature of this oil in °C?
> What is a water-source heat pump? How does the COP of a water-source heat pump system compare to that of an air-source system?
> Do you think a heat pump system will be more cost-effective in New York or in Miami? Why?
> An actual refrigerator operates on the vapor-compression refrigeration cycle with refrigerant-22 as the working fluid. The refrigerant evaporates at −15°C and condenses at 40°C. The isentropic efficiency of the compressor is 83 percent. The refrigerant i
> The manufacturer of an air conditioner claims a seasonal energy efficiency ratio (SEER) of 16 (Btu/h)/W for one of its units. This unit operates on the normal vapor-compression refrigeration cycle and uses refrigerant-22 as the working fluid. This SEER i
> A commercial refrigerator with refrigerant-134a as the working fluid is used to keep the refrigerated space at −30°C by rejecting its waste heat to cooling water that enters the condenser at 18°C at a rate of 0.25
> A refrigerator uses refrigerant-134a as the working fluid and operates on the vapor-compression refrigeration cycle. The evaporator and condenser pressures are 200 kPa and 1400 kPa, respectively. The isentropic efficiency of the compressor is 88 percent.
> Repeat Prob. 9–151E using appropriate software if ammonia is used in place of refrigerant-134a. Data from Prob. 9-151: A refrigerator uses refrigerant-134a as its working fluid and operates on the ideal vapor compression refrigeration cycle. The refrige
> A refrigerator uses refrigerant-134a as its working fluid and operates on the ideal vapor compression refrigeration cycle. The refrigerant evaporates at 5°F and condenses at 180 psia. This unit serves a 45,000 Btu/h cooling load. Determine the mass flow
> An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 800 kPa and the evaporator at −20°C. Determine this system’s COP and the amount of powe
> Repeat Prob. 9–14 using constant specific heats at room Temperature. Data from Prob. 9-14: An air-standard cycle with variable specific heats is executed in a closed system with 0.003 kg of air and consists of the following three processes: 1-2 v = cons
> The temperature of a system drops by 45°F during a cooling process. Express this drop in temperature in K, R, and °C.
> A refrigerator uses refrigerant-134a as the working fluid and operates on the ideal vapor compression refrigeration cycle except for the compression process. The refrigerant enters the evaporator at 120 kPa with a quality of 34 percent and leaves the com
> A refrigerator operates on the ideal vapor-compression refrigeration cycle and uses refrigerant 134a as the working fluid. The condenser operates at 300 psia and the evaporator at 20°F. If an adiabatic, reversible expansion device were available and used
> An ideal vapor-compression refrigeration cycle using refrigerant-134a as the working fluid is used to cool a brine solution to −5°C. This solution is pumped to various buildings for the purpose of air conditioning. The refrigerant evaporates at −10°C wit
> An air conditioner using refrigerant-134a as the working fluid and operating on the ideal vapor compression refrigeration cycle is to maintain a space at 22°C while operating its condenser at 1000 kPa. Determine the COP of the system when a temperature d
> An ice-making machine operates on the ideal vapor-compression cycle, using refrigerant-134a. The refrigerant enters the compressor as saturated vapor at 20 psia and leaves the condenser as saturated liquid at 80 psia. Water enters the ice machine at 55°F
> A 10-kW cooling load is to be served by operating an ideal vapor-compression refrigeration cycle with its evaporator at 400 kPa and its condenser at 800 kPa. Calculate the refrigerant mass flow rate and the compressor power requirement when refrigerant-1
> It is proposed to use water instead of refrigerant-134a as the working fluid in air-conditioning applications where the minimum temperature never falls below the freezing point. Would you support this proposal? Explain.
> Consider two vapor-compression refrigeration cycles. The refrigerant enters the throttling valve as a saturated liquid at 30°C in one cycle and as subcooled liquid at 30°C in the other one. The evaporator pressure for both cycles is the same. Which cycle
> Does the area enclosed by the cycle on a T-s diagram represent the net work input for the reversed Carnot cycle? How about for the ideal vapor-compression refrigeration cycle?
> A large fraction of the thermal energy generated in the engine of a car is rejected to the air by the radiator through the circulating water. Should the radiator be analyzed as a closed system or as an open system? Explain.
> An air-standard cycle with variable specific heats is executed in a closed system with 0.003 kg of air and consists of the following three processes: 1-2 v = constant heat addition from 95 kPa and 17°C to 380 kPa 2-3 Isentropic expansion to 95 kPa 3-1 P
> In a refrigeration system, would you recommend condensing the refrigerant-134a at a pressure of 0.7 or 1.0 MPa if heat is to be rejected to a cooling medium at 15°C? Why?
> Why is the throttling valve not replaced by an isentropic turbine in the ideal vapor-compression refrigeration cycle?
> Does the ideal vapor-compression refrigeration cycle involve any internal irreversibilities?
> Refrigerant-134a enters the condenser of a steady-flow Carnot refrigerator as a saturated vapor at 90 psia, and it leaves with a quality of 0.05. The heat absorption from the refrigerated space takes place at a pressure of 30 psia. Show the cycle on a T-
> A steady-flow Carnot refrigeration cycle uses refrigerant-134a as the working fluid. The refrigerant changes from saturated vapor to saturated liquid at 60°C in the condenser as it rejects heat. The evaporator pressure is 180 kPa. Show the cycle on a T-s
> Why is the reversed Carnot cycle executed within the saturation dome not a realistic model for refrigeration cycles?
> Why do we study the reversed Carnot cycle even though it is not a realistic model for refrigeration cycles?
> Repeat Prob. 9–131 assuming both the pump and the turbine are isentropic. Data from Prob. 9-131: Consider a steam power plant that operates on a reheat Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa a
> Consider a steam power plant that operates on a reheat Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 500°C and the low-pressure turbine at 1 MPa and 500°C. Steam leaves the condenser as a saturate
> The temperature of a system rises by 130°C during a heating process. Express this rise in temperature in kelvins.
> A steam power plant operates on an ideal reheat Rankine cycle between the pressure limits of 15 MPa and 10 kPa. The mass flow rate of steam through the cycle is 12 kg/s. Steam enters both stages of the turbine at 500°C. If the moisture content of the ste
> An air-standard cycle is executed within a closed piston–cylinder system and consists of three processes as follows: 1-2 V = constant heat addition from 100 kPa and 27°C to 850 kPa 2-3 Isothermal expansion until V3 = 7V2 3-1 P = constant heat rejection t
> An ideal reheat Rankine cycle with water as the working fluid operates the inlet of the high pressure turbine at 8000 kPa and 450°C, the inlet of the low-pressure turbine at 500 kPa and 500°C, and the condenser at 10 kPa. Determine the mass flow rate thr
> Steam enters the high-pressure turbine of a steam power plant that operates on the ideal reheat Rankine cycle at 800 psia and 900°F and leaves as saturated vapor. Steam is then reheated to 800°F before it expands to a pressure of 1 psia. Heat is transfer
> An ideal reheat Rankine cycle with water as the working fluid operates the boiler at 15,000 kPa, the reheater at 2000 kPa, and the condenser at 100 kPa. The temperature is 450°C at the entrance of the high-pressure and low-pressure turbines. The mass flo
> Reconsider Prob. 9–125. How much does the thermal efficiency of the cycle change when the temperature at the entrance to the low-pressure turbine is increased to 550°C? Data from Prob. 9-125: Consider a steam power plant that operates on the ideal rehea
> Consider a steam power plant that operates on the ideal reheat Rankine cycle. The plant maintains the boiler at 17.5 MPa, the reheater at 2 MPa, and the condenser at 50 kPa. The temperature is 550°C at the entrance of the high-pressure turbine, and 300°C
> Consider a simple ideal Rankine cycle and an ideal Rankine cycle with three reheat stages. Both cycles operate between the same pressure limits. The maximum temperature is 700°C in the simple cycle and 450°C in the reheat cycle. Which cycle do you think
> How do the following quantities change when a simple ideal Rankine cycle is modified with reheating? Assume the mass flow rate is maintained the same.
> Is there an optimal pressure for reheating the steam of a Rankine cycle? Explain.
> Steam enters a heat exchanger at 300 K. What is the temperature of this steam in °F?
> Show the ideal Rankine cycle with three stages of reheating on a T-s diagram. Assume the turbine inlet temperature is the same for all stages. How does the cycle efficiency vary with the number of reheat stages?
> A binary geothermal power plant uses geothermal water at 160°C as the heat source. The plant operates on the simple Rankine cycle with isobutane as the working fluid. Heat is transferred to the cycle by a heat exchanger in which geothermal liq
> Can any ideal gas power cycle have a thermal efficiency greater than 55 percent when using thermal energy reservoirs at 627°C and 17°C?
> The net work output and the thermal efficiency for the Carnot and the simple ideal Rankine cycles with steam as the working fluid are to be calculated and compared. Steam enters the turbine in both cases at 5 MPa as a saturated vapor, and the condenser
> Reconsider Prob. 9–117. Using appropriate software, determine how much the thermal efficiency of the cycle would change if there were a 50 kPa pressure drop across the boiler. Data from Prob. 9-117: A simple Rankine cycle uses water as the working fluid
> A simple Rankine cycle uses water as the working fluid. The boiler operates at 6000 kPa and the condenser at 50 kPa. At the entrance to the turbine, the temperature is 450°C. The isentropic efficiency of the turbine is 94 percent, pressure and pump loss
> Reconsider Prob. 9–115E. How much error is caused in the thermal efficiency if the power required by the pump were completely neglected? Data from Prob. 9-115: A steam Rankine cycle operates between the pressure limits of 1500 psia in the boiler and 2 p
> A steam Rankine cycle operates between the pressure limits of 1500 psia in the boiler and 2 psia in the condenser. The turbine inlet temperature is 800°F. The turbine isentropic efficiency is 90 percent, the pump losses are negligible, and the cycle is s
> Reconsider Prob. 9–113. Irreversibilities in the turbine cause the steam quality at the outlet of the turbine to be 70 percent. Determine the isentropic efficiency of the turbine and the thermal efficiency of the cycle.
> A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 15 MPa in the boiler and 100 kPa in the condenser. Saturated steam enters the turbine. Determine the work produced by the turbine, the heat transferred i
> Consider a system whose temperature is 18°C. Express this temperature in R, K, and °F.
> Repeat Prob. 9–111 assuming an isentropic efficiency of 85 percent for both the turbine and the pump. Data from Prob. 9-111: Consider a 210-MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C
> Consider a 210-MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C and is cooled in the condenser at a pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and
> Consider a solar-pond power plant that operates on a simple ideal Rankine cycle with refrigerant 134a as the working fluid. The refrigerant enters the turbine as a saturated vapor at 1.4 MPa and leaves at 0.7 MPa. The mass flow rate of the refrigerant is
> What is the difference between the clearance volume and the displacement volume of reciprocating engines?
> A simple ideal Rankine cycle which uses water as the working fluid operates its condenser at 40°C and its boiler at 250°C. Calculate the work produced by the turbine, the heat supplied in the boiler, and the thermal efficiency of th
> A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 4 MPa in the boiler and 20 kPa in the condenser and a turbine inlet temperature of 700°C. The boiler is sized to provide a steam flow of 50 kg/s. Determi
> A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 3 MPa in the boiler and 30 kPa in the condenser. If the quality at the exit of the turbine cannot be less than 85 percent, what is the maximum thermal ef
> Is it possible to maintain a pressure of 10 kPa in a condenser that is being cooled by river water entering at 20°C?
> The entropy of steam increases in actual steam turbines as a result of irreversibility. In an effort to control entropy increase, it is proposed to cool the steam in the turbine by running cooling water around the turbine casing. It is argued that this w
> Compare the pressures at the inlet and the exit of the boiler for (a) actual and (b) ideal cycles.
> Consider two closed systems A and B. System A contains 3000 kJ of thermal energy at 20°C, whereas system B contains 200 kJ of thermal energy at 50°C. Now the systems are brought into contact with each other. Determine the direction of any heat transfer b
> How do actual vapor power cycles differ from idealized ones?
> Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. What is the effect of superheating the steam to a higher temperature on;
> Consider a simple ideal Rankine cycle with fixed turbine inlet temperature and condenser pressure. What is the effect of increasing the boiler pressure on;
