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physics
thermodynamics

Thermodynamics for Engineers 1st edition Kenneth A. Kroos, Merle C. Potter - Solutions

Infiltration in a house in the winter where T = - 25° C occurs even when there is no wind due to the difference in the air density between the inside and outside of a house. For an inside temperature of 22° C, the density difference is nearest: (A) 0.207 kg/m3 (B) 0.224 kg/m3 (C) 0.241 kg/m3 (D)
Estimate the value of the Cp of steam at 400° C and 4 MPa: (A) 2.6 kg (B) 2.4 kg (C) 2.2 kg (D) 2.0 kg
Estimate the percent error if the Cp value is used from Table B-2 to find the change in enthalpy of steam that has a temperature change from 200° C to 600° C at 200 kPa: (A) 2 4% (B) 2 6% (C) 2 8% (D) 2 10%
The enthalpy change of 10 kg of ice initially at - 20°C when heated to 200°C at atmospheric pressure is nearest: (A) 9900 kJ (B) 9100 kJ (C) 8300 kJ (D) 6400 kJ
What is the pressure in kPa inside a container if it holds water that is just beginning to boil at a) 140°C, b) 200°C, c) 320°C?
Estimate the temperature of the water in a container if the water is on the verge of boiling at a pressure of a) 12 psia, b) 28 psia, c) 50 psia.
A group of engineers wish to know their elevation when they reach the apex on their mountain climb. They forgot their elevation-measuring device, but they have a thermometer and their thermo book. They build a campfire and boil a pot of water. The water is noted to boil at 90° C. What is their
A mountain climber reaches an elevation ofa) 12,000 ft,b) 20,000 ft,c) 32,000 ft on the mountain of Fig. 2.29. At what temperature will water just boil at the selected elevation?Figure 2.29
A container holds 1 ft3 of liquid water and 5 ft3 of water vapor at 200° F. Calculate the quality of this saturated mixture.
The 4 kg of saturated liquid water in Fig. 2.30 are completely vaporized at a constant pressure of 200 kPa. Determine the volume of the water at state 1 and at state 2.Figure 2.30
Saturated liquid water is contained in a volume of 400 cm3. Heat is added at a constant pressure of 400 kPa until the water is completely vaporized. What is the final volume?
A vessel contains 10 kg of water with a quality of 0.85 at a pressure of a) 140 kPa, b) 200 kPa, c) 2 MPa. Determine the volume of liquid and the volume of vapor. What is the temperature of the mixture?
Ten kilograms of saturated mixture are held in the container of Fig. 2.31 at 40°C and a quality of 0.6. What is the volume of liquid, the volume of vapor, and the pressure of the mixture?Figure 2.31
We want to boil water in a cylinder that maintains a constant pressure of a) 70 psia, b) 150 psia, c) 400 psia. To what temperature do we need to heat the water to make this happen?
The height of Mount Everest is nearly 9000 m. Water would boil at that height at a temperature nearest: (A) 65° C (B) 70° C (C) 75° C (D) 80° C
A 5-m3 container holds water that has a quality of 0.7 at a) 120° C, b) 240° C, c) 370° C. What are the pressure and the mass of water in the container?
A constant-pressure, piston-cylinder device contains 0.5 kg of saturated liquid water at 50°C. Heat is added to the water until it becomes a saturated vapor. What is the initial volume of the water? What is the final volume of the water?
A rigid container holds water at the critical point. The container is cooled until the pressure reaches a) 2 MPa, b) 1200 kPa, c) 400 kPa. Determine the final quality of the water.
Water with a quality of 0.1 is contained in the rigid volume of Fig. 2.32 at 200 kPa. It is heated until the temperature reachesa) 140°C,b) 180°C,c) 210°C. Calculate the quality of the water and the pressure at the final state.Figure 2.32
Four kilograms of water at 25°C are heated at constant pressure, as in Fig. 2.31, until it is saturated liquid at 120°C. Approximate its change in volume.
Two kilograms of water are contained in a piston-cylinder arrangement at 20°C and 5 MPa. It is heated at constant pressure until the temperature reaches 200°C. Calculate its change in volume using i) Table C-4 ii) Table C-1. What do you conclude?
Two kilograms of saturated liquid water at 200 kPa are heated until the pressure and temperature reach 2 MPa and 400°C, respectively. Calculate the change in volume.
A container holds 10 kg of water at 130° C with a quality of 0.4. What is the pressure in the container? What is the volume of the container? What is the volume of the liquid phase?
A 70-ft3 container holds 10 lbm of water at i) 50 psia, ii) 62 psia, iii) 100 psia. What is the state of the water?
Saturated water vapor is held in a container at 200°C. What is the pressure in the container? If the volume of the container is increased by a) 50%, b) 100%, c) 200%, holding the temperature constant, estimate the final pressure.
A 10-ft3 container holds water at 40 psia and 400°F. How much water is in the container?
A container holds 8 kg of water at a pressure of 5 MPa. Calculate the volume of the container if the temperature is a) -5°C, b) 20°C, c) 400°C, d) 800°C.
A mass of 0.02 kg of saturated water vapor is contained in the cylinder of Fig. 2.33. The spring with spring constant K = 60 kN/m just touches the top of the frictionless 160-kg piston. Heat is added until the spring compressesa) 6 cm,b) 10 cm,c) 15 cm. Estimate the final temperature of the steam.
A mass of 0.02 kg of steam with x1 = 0.8 is contained in the cylinder of Fig. 2.33. The spring with spring constant K = 60 kN/m just touches the top of the frictionless 160-kg piston. Heat is added until the temperature reaches 800°C. Estimate the final pressure of the steam. A trial-and-error
The spring of Problem 2.43 is 2 cm above the top of the piston. All other quantities are the same as stated in the problem. Calculate the final temperature for part (a).
Use the steam tables in the Appendix and make a plot to scale of a) a T-v diagram showing a constant-pressure line at 400 kPa, b) a P-v diagram showing a constant-temperature line at 200°C. Include a point in the subcooled region and a point in the superheated region. Observe the distortions of
Water at a pressure of 250 psia has a quality of 0.4. Determine the temperature, the average internal energy, and the average enthalpy for this mixture. Use the steam tables.
Superheated water exists at 1.86 MPa and 420°C. Determine its specific enthalpy using: i) The steam tables in the appendix (a double interpolation is needed) ii) The IRC Calculator iii) The equation h = u + Pv by using u and v from the IRC Calculator Are all the answers acceptable?
Ten pounds of saturated water vapor at 300°F are cooled at constant temperature to a saturated liquid. What is the change in pressure? The change in the total internal energy? The change in total enthalpy? Does ΔH = ΔU + Δ(PV)? a) Use the steam tables b) The IRC Calculator.
Water is maintained at a constant temperature of 200° C, while the specific volume changes from 0.002 m3 /kg to 0.2 m3 /kg. Select the diagram that best represents this process.(A)(B) (C) (D)
Saturated water vapor is compressed from 200°C to 2 MPa and 600°C. Determine the change in specific volume and enthalpy. a) Use the steam tables b) The IRC Calculator.
Four kilograms of water at 20°C are heated at constant pressure of 200 kPa to 400°C. Determine the change in density, internal energy, and enthalpy. a) Use the steam tables b) The IRC Calculator.
Twenty kilograms of water are heated at constant pressure from 300°C and 0.6 MPa to 400°C. Calculate the change in enthalpy. a) Use the steam tables b) The IRC Calculator.
Determine the change in internal energy and enthalpy of water at 100°F and 500 psia if the temperature increases to 500°F while the pressure in Fig. 2.34 is held constant. Usea) The steam tablesb) The IRC Calculator.Figure 2.34
How much energy is needed to increase the temperature of 10 kg of ice from - 20°C to 20°C at atmospheric pressure?
Estimate the amount of energy required to sublimate the 4 kg of water contained in the frozen clothes in a northern state which are at - 20°C. See Fig. 2.35.Figure 2.35
A 0.05-m3 container contains 50 kg of R134a. If the pressure is a) 2.5 MPa b) 240 kPa, what is the state of the refrigerant?
A 10-ft3 container contains 100 lbm of R134a at -20°F. What is the state of the refrigerant?
A constant-pressure, piston-cylinder device contains 100 kg R134a at -12°C and 200 kPa. If the refrigerant is heated at constant pressure until the temperature reaches 60°C, determine: i) The change in volume ii) The change in total internal energy iii) The change in total enthalpy
A flow of saturated liquid R134a at 80°F passes through a throttle where the pressure drops to 10 psia. If the enthalpy remains constant as the refrigerant passes through the throttle of Fig. 2.36, determine the temperature and the quality of the flow exiting the valve.Figure 2.36
Two kilograms of water occupy 80 000 cm3 at 200° C. Its quality is nearest: (A) 0.175 (B) 0.211 (C) 0.287 (D) 0.314
Ammonia is compressed from -40°C and a quality of 0.95 to 400 kPa and 40°C. Calculate the change in specific enthalpy of the refrigerant.
A spherical balloon contains 0.1 kg of air at 120 kPa and 20°C. If the temperature of the air is increased to 35°C and the pressure remains the same, determine the initial and final volume of the sphere.
A spherical 24-in.-diameter balloon contains helium at 72°F. What is the mass of helium in the balloon assuming the pressure is approximately 14.7 psia? Approximate the diameter of the balloon at an elevation of 5000 ft, as shown in Fig. 2.37. (Assume the pressure difference across the balloon
The atmosphere of Mars is composed of carbon dioxide at 1 kPa and - 60°C. Determine the specific volume of the atmosphere.
A 5-m3 -rigid container holds 0.2 kg of air at 300 K. How much air at 300 K must be added to the container to bring the pressure to 500 kPa?
Ten pounds of air at 14.7 psia and 80°F are compressed so that the final volume is one-fourth the initial volume and the pressure is 40 psia. Determine the final temperature of the air.
An enclosed football stadium is maintained at 100 kPa and 20°C. If its volume is 2 × 106 m3, estimate the weight of the air.
Fill in the missing properties in the following table if the air occupies a 10-m3 volume.
Fill in the missing properties in the following table if the air occupies a 30-ft3 volume.
The volume occupied by 20 kg of water at 300° C and 10 MPa is nearest:(A) 0.028 m3(B) 0.088 m3(C) 0.22 m3(D) 0.36 m3
The air in a house is maintained at 72°F. The air outside the house is at - 20°F. What is the difference in the density of the air between the inside and the outside of the house? There are always small passages where air can infiltrate into or from a house even if extreme care is taken to
The tires on an automobile are inflated to 35 psi in New York, where the temperature is -10°F. The auto is driven to Arizona, where the temperature on the blacktop is 160°F. Estimate the pressure in the tires assuming the volume does not change.
The golfer in Fig. 2.39 on a very humid day states that the ball doesn't travel as far because of the heavy air. If the air were less humid at the same pressure and location, would the ball have traveled further? Explain, referring to the ideal-gas law and the fact that the drag FD on the golf ball
Nitrogen exists at 4 MPa and 130 K. Approximate the specific volume using i) The ideal-gas law ii) The compressibility factor from Fig. 2.23.
Ten kilograms of air occupies 1 m3 of space at - 40°C. Calculate and compare the pressure using the: i) Ideal-gas law ii) Van der Waals equation iii) Beattie-Bridgeman equation iv) Z -factor (see Appendix H) v) IRC Calculator
Estimate the pressure of nitrogen at -80°F and v = 0.6 ft3 /lbm using the: i) Ideal-gas law ii) Van der Waals equation iii) Z -factor (see Appendix H)
The pressure and temperature are measured in a tank containing air to be 60 kPa and 2 80 8 C, respectively. Determine the specific volume using the: i) Ideal-gas law ii) Van der Waals equation iii) Z -factor (see Appendix H) iv) IRC Calculator
Calculate the internal energy change and the enthalpy change if the temperature changes from 20°C to 450°C for each of the following, assumed to an ideal gas with constant specific heats: a) Air b) Nitrogen c) Hydrogen d) Propane e) Steam
Steam is assumed to be an ideal gas. Determine the enthalpy change if state 1 is saturated vapor at 30 8 C and state 2 is at 150 8 C and 200 kPa. i) Assume constant specific heats. ii) Use the steam tables. iii) Use the IRC Calculator.
Nitrogen is heated from 20°C to 500°C. Calculate the change in the internal energy and enthalpy. Use: i) Constant specific heats from Table B-2 ii) The ideal-gas table in Appendix F iii) The average specific heat from Table B-5 iv) Equation 2.30
Superheated steam is contained in a rigid volume at 400 8 C and 4 MPa. Energy is released from the steam, resulting in a decreased pressure. The pressure that will cause the steam to just begin to condense is nearest: (A) 2.4 MPa (B) 2.6 MPa (C) 2.8 MPa (D) 3.0 MPa
Twenty pounds of air at 25°F is heated to 1000°F. Determine the change in internal energy and enthalpy. Use: i) Constant specific heats from Table B-2 ii) The ideal-gas table in Appendix F iii) The specific heat at the average temperature from Table B-6 iv) Equation 2.30 v) The IRC Calculator
Estimate the specific heat Cp of steam at 1.6 MPa and 400°C using i) Backward differences, ii) Forward differences, iii) Central differences, iv) Table B-2. Which is the most accurate?
Estimate the specific heat Cp of steam at: a) 0.2 MPa and 400°C b) 1.8 MPa and 400°C c) 7 MPa and 400°C
Estimate the specific heat Cp of steam at: a) 40 psia and 600 ° F b) 140 psia and 600°F c) 600 psia and 600°F
One hundred pounds of water at atmospheric pressure are heated from 60°F to 200°F. What is the enthalpy change? The internal energy change? Why is the difference between the internal energy change and the enthalpy change so small?
If the enthalpy of 5 kg of mercury at 25°C is raised 200 kJ, determine the final temperature of the mercury.
The temperature of 10 kg of ice at - 20°C is raised to 50°C, displayed by Fig. 2.40. Determine the enthalpy change.a) Assume Cp,ice = 2.1 kJ/kg·°C.b) Use Cp,ice = 2.1 1 0.0069 T kJ/kg·°C.Figure 2.40
A 3-L cylinder holds 2 L of steam and 1 L of liquid at 200° C. The quality is nearest: (A) 1.8% (B) 2.2% (C) 2.6% (D) 3.2%
Approximate the heat transfer rate through a 0.8-m by 2-m double-pane window if a convective layer on a vertical pane of glass can be approximated as having an R-factor of 1 m2∙°C/W. The resistivity of the air layer between the panes can be approximated as R = 0.4 m2∙°C/W. The temperature
Two kilograms of water at 20°C are heated at a constant pressure of 100 kPa until the water is saturated steam. The work is nearest: (A) 190 kJ (B) 280 kJ (C) 320 kJ (D) 340 kJ
A conference room with dimensions 4 m by 10 m by 20 m is filled with 100 conference attendees. The air-conditioning system fails, resulting in an increasing temperature. There are 50 100-watt light bulbs, and each person emits approximately 400 Btu/hr (0.117 kJ/s). Assuming a constant pressure, in
The air in a rigid 8-m3 container is at 200 kPa and 60°C. It is heated to 400°C. The heat transfer is nearest: (A) 4100 kJ (B) 2410 kJ (C) 1660 kJ (D) 260 kJ
The 4 kg of air, shown in Fig. 3.34, are heated at constant temperature from 200°C and 600 kPa until the pressure is 4 MPa. The heat transfer demanded by this process is nearest:(A) - 830 kJ(B) - 930 kJ(C) - 1030 kJ(D) - 1130 kJFigure 3.34
A constant pressure of 200 kPa is applied to a 1-m-diameter vertical cylinder in a frictionless piston-cylinder device that is open at the top. Calculate the mass of the piston and the work needed to move the piston 5 m in the vertical direction.
Pressure is related to volume by the relationship PV1.2 = Const, where P is in kPa and V is in m3. Determine the work required to compress an ideal gas from 0.8 m3 to 4000 cm3 if the initial pressure is 140 kPa.
Ten pounds of oxygen are compressed from 20 psia and 50°F in a process governed by the equation PV n = const, where the pressure is in psfa and the volume is in ft3. The final temperature in this process is 100°F. Calculate the work done if a) n = 1.4, b) n = 1.8, c) n = 2.
Air is compressed in the cylinder of Fig. 3.37 such that PV = const, where the pressure is in psfa and the volume is in ft3. The initial pressure and temperature are 40 psia and 200°F, respectively. If the volume changes from 1000 in3 to 100 in3, calculate the work required.Figure 3.37
A balloon is filled with air from an initial radius of 1.2 m until it reaches a radius of 4 m. The pressure is related to the radius by P(r) = 120 - 2(r - 1.2)2 kPa. Calculate the work. (The surface area of a sphere is 4 πr2.)
A gas is allowed to expand in an experimental process where the pressure is measured and the volume is determined. The data is listed below. Estimate the work done during this process.
Pressure is measured at several positions in an experiment. The volume at each position is determined. The results of the experiment are presented in the list that follows. Estimate the work performed by the process.
The air in the cylinder of Fig. 3.39 is initially at 300 kPa. Heat is added until the pressure increases to 900 kPa. Determine the work done by the air on the frictionless piston.Figure 3.39
A paddle wheel rotates at 200 rpm in a substance. Determine the power transmitted by the shaft and the work it inputs into the substance in 20 minutes if it requires 4 N ∙ m to rotate the wheel.
The 400-N weight in Fig. 3.40 is falling at the constant rate of 40 mm/s. The shaft transmits a torque of 2 N ˆ™ m. How much work does the paddle wheel do on the fluid in 20 seconds? What is the rotational speed, in rpm, of the shaft during that time period?Figure 3.40
The 12-V battery of Fig. 3.41 powers the 10-ohm resistance for 3 minutes. The work from the battery inputs energy into the air. How much erengy is added to the air?Figure 3.41
A 1.2 m by 2.4 m window has an R-factor of 2m2 ∙ K/W. If the average outside and inside temperatures are -20°C and 22°C, respectively, how much heat is lost in one day? Estimate how much energy would be lost if there were 20 such windows in a house.
The average temperature of the human body is 98.6°F. Calculate the maximum rate of heat transfer per unit area by radiation from the human body in a room that is at 50°F. What is the percent increase in the heat transfer rate if you are running a fever with a temperature of 102°F?
A 1-m-diameter spherical satellite is traveling in intergalactic space where the surrounding temperature is 0 K. If the satellite has a surface temperature of -50°C, estimate the rate of heat loss by radiation from the satellite.
A rigid container holds 4 kg of water at 20°C. If 200 kJ of heat is added to this system, what will be the final temperature? How much work is done in this process?
The radiator on a car engine removes 20 kW of heat from the engine. If the temperature of the radiator remains constant and no work is done on the coolant, how much heat is being developed by the engine?
A power plant generates 100 MW of heat in the boiler and rejects 75 MW of heat to the surroundings, as sketched in Fig. 3.43. How much work is being produced?Figure 3.43
A system undergoes a four-process cycle. Several quantities for the various processes are listed in the following table. Determine the missing entries. All quantities are in kJ.
Consider that the quantities listed in the table of Problem 3.50 have Btu's. Determine the missing entries.
Ice cubes at -20°C, each occupying a volume of 10 mL, are added to the insulated container of Fig. 3.44 that contains one liter of water at 20°C. Estimate the final temperature, or the mass of ice that melts, after equilibrium is reached if the number of ice cubes isa) 10,b) 25,c)

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