Thermodynamics — Engineering Board Exam Reviewer

200 free Thermodynamics practice questions for the Philippine Engineering Board Exam, each with the correct answer and a worked solution.

Air at 101.325 kPa and 25 °C has a relative humidity of 60%. If the saturation pressure at 25 °C is 3.169 kPa, what is the partial…
A two-stage air compressor with perfect intercooling compresses air from 100 kPa to 900 kPa. For minimum total work, what should the…
An air-standard Otto cycle has a compression ratio of 10. At the start of compression the air is at 300 K, and the maximum cycle…
Two kilograms of air is heated at constant pressure from 300 K to 600 K. What is the change in internal energy? (cp = 1.0 kJ/kg· K, R =…
A 2 kW electric heater operates for how long to consume 1 kWh of energy?
Water flows at 2 m3/s from a reservoir 50 m above a hydraulic turbine. If the turbine-generator efficiency is 90%, what is the electrical…
Water flows at 0.1 L/s through a shower heater and its temperature rises by 15 °C. Assuming all electrical energy goes into the water…
Air at 500 kPa and 1 m3 expands isentropically in a closed system to 100 kPa. What is the work done by the air? (k = 1.4)
Air at 500 kPa and 1 m3 expands isentropically to 100 kPa. What is the final volume? (k = 1.4)
Two kilograms of air is heated from 300 K to 450 K. What is the change in enthalpy? (cp = 1.0062 kJ/kg· K)
Two kilograms of air occupy 1 m3 at 400 kPa. What is the temperature of the air? (R = 0.287 kJ/kg· K)
What is the pressure of 10 kg of air in a 2 m3 tank at 300 K? (R = 0.287 kJ/kg· K)
When 1 kg of saturated liquid water at 100 °C and 101.325 kPa is vaporized, h fg = 2257 kJ/kg and the boundary work is about 169.4 kJ…
One kilogram of saturated liquid water at 100 °C is completely vaporized at a constant pressure of 101.325 kPa. If vf = 0.001043 m3/kg and…
The Orsat apparatus is used to analyze:
If 120% theoretical air is supplied for combustion, the percent excess air is:
Excess air in combustion is the air supplied in addition to the:
What is the theoretical air–fuel ratio by mass for complete combustion of octane ( C8H18)? (Mair = 28.97)
What is the theoretical (stoichiometric) air–fuel ratio by mass for the complete combustion of methane ( CH4)? (Air: 21% O2, 79% N2 by…
A material with very low thermal conductivity used to reduce heat transfer is called a/an:
The dimensionless number that represents the ratio of convective to conductive heat transfer at a fluid boundary is the:
Which of the following materials has the highest thermal conductivity?
In a counterflow heat exchanger, the hot fluid cools from 150 °C to 90 °C while the cold fluid is heated from 30 °C to 70 °C. What is the…
A pipe is covered with insulation (k = 0.05 W/m· K) with inner radius 5 cm and outer radius 10 cm. If the temperature difference across…
Using Wien's displacement law ( max T = 2898 m· K), at what wavelength is the emission of the sun (T 5800 K) at a maximum?
If the absolute temperature of a blackbody is doubled, the rate of radiation it emits increases by a factor of:
A small surface ( = 0.8, A = 0.5 m2) at 400 K is surrounded by large walls at 300 K. What is the net radiation heat transfer from the…
What is the rate of radiation emitted by a 1 m2 blackbody surface at 500 K? ( = 5.67 × 10-8 W/m2· K4)
A composite wall consists of 10 cm of material (k = 0.5 W/m· K) and 5 cm of insulation (k = 0.05 W/m· K). If the temperature difference…
A plane wall 0.2 m thick with a thermal conductivity of 0.8 W/m· K has an area of 10 m2. If the temperature difference across it is 25 °C…
The Sensible Heat Ratio (SHR) in air conditioning is the ratio of:
The lowest temperature to which water can theoretically be cooled in an evaporative cooling tower is the:
Water enters a cooling tower at 40 °C and leaves at 30 °C. The entering air has a wet-bulb temperature of 25 °C. What are the range and…
Moist air at 101.325 kPa has a vapor partial pressure of 2 kPa. What is the humidity ratio?
Subcooling the refrigerant liquid leaving the condenser in a vapor-compression system:
In an absorption refrigeration system, the compressor of a vapor-compression system is replaced by:
Which refrigerant is widely used in large industrial plants such as ice plants and cold storage due to its high latent heat, though it is…
A refrigeration system removes 50 kW of heat. What is its capacity in tons of refrigeration?
In a vapor-compression refrigeration cycle, h at evaporator exit = 390 kJ/kg, h at compressor exit = 425 kJ/kg, and h at condenser exit =…
A vapor-compression refrigeration system has a refrigerating effect of 140 kJ/kg. What refrigerant mass flow rate is needed for a capacity…
In a vapor-compression refrigeration cycle, h at evaporator exit = 390 kJ/kg, h at compressor exit = 425 kJ/kg, and h at condenser exit =…
A cogeneration plant is one that:
In a steam power plant, the component that converts the thermal energy of steam into mechanical work is the:
Which of the following increases the thermal efficiency of a Rankine cycle?
Air enters a compressor at 300 K and is compressed with a pressure ratio of 8. The actual exit temperature is 590 K. What is the…
A steam power plant has a net work of 992 kJ per kg of steam. What is its steam rate?
In an ideal Rankine cycle, the turbine inlet enthalpy is 3200 kJ/kg, turbine exit enthalpy is 2200 kJ/kg, the pump inlet enthalpy is 192…
A regenerator in a gas turbine plant is most effective when:
For an ideal Brayton cycle with minimum temperature 300 K and maximum temperature 1200 K, what pressure ratio gives the maximum net work?…
For an ideal Brayton cycle with compressor inlet at 300 K, pressure ratio 8, and turbine inlet at 1300 K, what is the back work ratio? (k…
An ideal Brayton cycle has a compressor inlet temperature of 300 K, a pressure ratio of 8, and a turbine inlet temperature of 1300 K. What…
An engine produces 1.2 kJ of net work per cycle with a displacement volume of 0.002 m3. What is the mean effective pressure?
In an air-standard Otto cycle, the temperature after compression is 700 K and after heat addition is 1800 K. What is the heat added per…
In an ideal Diesel cycle, the temperature at the start of heat addition is 900 K and at the end of heat addition is 1800 K. What is the…
An ideal Diesel cycle has a compression ratio of 18 and a cutoff ratio of 2. What is its thermal efficiency? (k = 1.4)
An ideal Otto cycle has an efficiency of 55%. What is its compression ratio? (k = 1.4)
What is the air-standard efficiency of an Otto cycle with a compression ratio of 10? (k = 1.4)
What is the thermal efficiency of an ideal Otto cycle with a compression ratio of 8? (k = 1.4)
In the wet (two-phase) region, which pair of properties is NOT independent and therefore cannot fix the state?
The degree of superheat of steam at 1 MPa and 250 °C, if the saturation temperature at 1 MPa is 179.9 °C, is:
A tank contains a liquid-vapor mixture of water at 100 kPa with a specific volume of 0.5 m3/kg. If vf = 0.001043 m3/kg and vg = 1.694…
A 0.5 m3 rigid tank contains saturated water vapor at 1 MPa (vg = 0.1944 m3/kg). What is the mass of the vapor?
Steam from a 1 MPa line is throttled in a calorimeter to 100 kPa, where its enthalpy is found to be 2716 kJ/kg. At 1 MPa, hf = 762.8 kJ/kg…
A wet steam mixture at 200 kPa has a quality of 0.8. If vf = 0.001061 m3/kg and vg = 0.8857 m3/kg, what is its specific volume?
Steam at 1 MPa has a quality of 90%. If hf = 762.81 kJ/kg and h fg = 2015.3 kJ/kg, what is its enthalpy?
Wet steam at 100 kPa has an enthalpy of 2000 kJ/kg. If hf = 417.46 kJ/kg and h fg = 2258.0 kJ/kg, what is its quality?
Two Carnot engines operate in series between 1000 K and 300 K. If both engines produce equal work, what is the intermediate temperature?
Two Carnot engines operate in series. The first receives heat at 1000 K and the second rejects heat at 300 K. If both engines have equal…
1000 kJ of heat is available from a reservoir at 1000 K. If the environment is at 300 K, what is the maximum work (exergy) obtainable from…
An actual heat engine has a thermal efficiency of 30%, while a Carnot engine between the same reservoirs has an efficiency of 50%. What is…
A 10-ton refrigeration unit has a refrigerating capacity of approximately:
A refrigerator removes heat from a cold space at 5 kW with a COP of 2.5. How much heat is rejected to the surroundings?
A refrigerator removes heat from a cold space at 5 kW with a COP of 2.5. What is the power input required?
A Carnot heat pump extracts heat from outside air at 270 K and delivers heat to a house at 300 K. What is its COP?
An inventor claims that an engine operating between 500 K and 250 K has a thermal efficiency of 60%. The claim is:
A Carnot engine has an efficiency of 40% and rejects heat to a sink at 300 K. What is the source temperature?
A Carnot engine receives 1000 kJ of heat from a source at 600 K and rejects heat to a sink at 300 K. How much work does it produce?
What is the maximum possible efficiency of a heat engine operating between 800 K and 300 K?
1000 kJ of heat is transferred directly from a reservoir at 600 K to a reservoir at 300 K. What is the total entropy generated?
Air changes from 100 kPa, 300 K to 500 kPa, 500 K. What is the change in specific entropy? (cp = 1.0 kJ/kg· K, R = 0.287 kJ/kg· K)
One kilogram of air expands isothermally to three times its initial volume. What is the change in entropy? (R = 0.287 kJ/kg· K)
One kilogram of water is heated from 300 K to 350 K. What is its change in entropy? (c = 4.187 kJ/kg· K)
A system receives 500 kJ of heat reversibly at a constant temperature of 400 K. What is its change in entropy?
One kilogram of air is heated at constant pressure from 300 K to 600 K. What is the change in entropy? (cp = 1.0 kJ/kg· K)
For the same pressure ratio and initial state, which compression process requires the LEAST work in a steady-flow compressor?
In a constant-pressure process of a closed system, the heat transferred is equal to the change in:
In a constant-volume process, the heat transferred is equal to the change in:
In an isothermal process of an ideal gas, the heat added is equal to:
One kilogram of air is compressed polytropically (n = 1.3) from 300 K to 400 K. What is the heat transfer? (cv = 0.7186 kJ/kg· K, k = 1.4)
A gas is compressed from 100 kPa and 1 m3 to 800 kPa and 0.2 m3. What is the polytropic exponent n of the process?
A gas at 100 kPa and 1 m3 is compressed polytropically (n = 1.3) to 0.5 m3. What is the work done on the gas?
One kilogram of air at 300 K is compressed isentropically in a closed system (piston-cylinder) with a pressure ratio of 8. What is the…
Air at 100 kPa is compressed isentropically to one-tenth of its original volume. What is the final pressure? (k = 1.4)
Air at 300 K is compressed isentropically with a pressure ratio of 8. What is the final temperature? (k = 1.4)
A 0.5 m3 rigid tank contains air at 400 kPa and 300 K. The tank is heated and a relief valve releases air so that the remaining air is at…
A gas mixture contains 2 kg of N2 (M = 28) and 1 kg of O2 (M = 32) at a total pressure of 300 kPa. What is the partial pressure of N2?
Air consists of approximately 79% N2 and 21% O2 by mole. What is its apparent molecular weight? (M N2 = 28, M O2 = 32)
How many kilomoles are there in 5 kg of carbon dioxide (M = 44 kg/kmol)?
For air with R = 0.287 kJ/kg· K and k = 1.4, what is the value of cp?
A gas has a specific gas constant of 0.2598 kJ/kg· K. What is its molecular weight?
What is the specific gas constant of a gas with a molecular weight of 28 kg/kmol (e.g., nitrogen)?
A gas in a rigid container is at 200 kPa and 300 K. If it is heated to 450 K, what is its final pressure?
A gas occupies 2 m3 at 300 K. If it is heated at constant pressure to 450 K, what is its final volume?
A gas occupies 3 m3 at 100 kPa. If it is compressed isothermally to 1 m3, what is its final pressure?
What is the mass of air in a 2 m3 tank at 500 kPa absolute and 300 K? (R = 0.287 kJ/kg· K)
A boiler produces 10 kg/s of steam, with an enthalpy rise of 2500 kJ/kg. It burns 0.8 kg/s of fuel with a heating value of 40,000 kJ/kg…
An engine with a brake thermal efficiency of 30% develops 100 kW. If the heating value of the fuel is 44,000 kJ/kg, what is the fuel…
A power plant has a thermal efficiency of 40% and a net output of 500 MW. What is the rate of heat input?
Water is pumped from 100 kPa to 5100 kPa at a rate of 10 kg/s. Assuming incompressible flow with v = 0.001 m3/kg, what is the ideal pump…
A steam condenser must remove 5000 kW of heat. If the cooling water temperature rise is limited to 10 °C, what is the required mass flow…
Steam enters an adiabatic nozzle at 30 m/s with h = 3200 kJ/kg and leaves with h = 2900 kJ/kg. What is the exit velocity?
Steam flows through an adiabatic nozzle with an enthalpy drop of 200 kJ/kg. If the inlet velocity is negligible, what is the exit velocity?
Air flows steadily through a compressor at 2 kg/s. Its temperature rises from 300 K to 450 K. Neglecting heat transfer and…
Steam enters a turbine at 5 kg/s with an enthalpy of 3000 kJ/kg and leaves with 2400 kJ/kg. Neglecting heat loss and changes in kinetic…
Three kilograms of air is heated at constant pressure from 300 K to 400 K. How much heat is added? (cp = 1.0 kJ/kg· K)
Two kilograms of air is heated in a rigid tank from 300 K to 500 K. How much heat is added? (cv = 0.7186 kJ/kg· K)
One kilogram of air at 300 K is compressed isothermally from 100 kPa to 500 kPa. What is the magnitude of the work required? (R = 0.287…
A gas expands at a constant pressure of 200 kPa from 0.5 m3 to 1.5 m3. How much work is done by the gas?
A paddle wheel does 200 kJ of work on a gas in a rigid tank while 50 kJ of heat is lost to the surroundings. What is the change in…
A closed system rejects 50 kJ of heat while 80 kJ of work is done ON the system. What is the change in internal energy?
A 1000-kg car moves at 25 m/s. What is its kinetic energy?
A body of mass 10 kg is raised vertically by 50 m. What is the increase in its potential energy? (g = 9.81 m/s2)
An electric water heater rated at 3 kW heats 50 liters of water from 15 °C to 60 °C. Assuming no heat losses, how long will it take? ( = 1…
How much heat is required to change 1 kg of water at 20 °C into saturated steam at 100 °C and atmospheric pressure? (c = 4.187 kJ/kg· K, h…
A 0.5-kg copper block (c = 0.385 kJ/kg· K) at 200 °C is dropped into 2 kg of water (c = 4.187 kJ/kg· K) at 25 °C in an insulated…
How much heat is required to convert 2 kg of ice at −10 °C into water at 20 °C? (cice = 2.09 kJ/kg· K, h if = 335 kJ/kg, cwater = 4.187…
How much heat is required to melt 2 kg of ice at 0 °C into water at 0 °C? (latent heat of fusion = 335 kJ/kg)
How much heat is needed to raise the temperature of 5 kg of water from 20 °C to 80 ° C? (c = 4.187 kJ/kg· K)
How many psi is equal to 1 standard atmosphere?
An automobile tire has a gauge pressure of 200 kPa at 25 °C. After driving, the temperature of the air rises to 50 °C. Assuming constant…
What is the gauge pressure at a depth of 10 m below the free surface of fresh water? ( = 1000 kg/m3, g = 9.81 m/s2)
A vacuum gauge connected to a condenser reads 30 kPa. If the atmospheric pressure is 101 kPa, the absolute pressure in the condenser is:
A pressure gauge on a tank reads 250 kPa. If the atmospheric pressure is 101.325 kPa, what is the absolute pressure in the tank?
Convert 68 °F to kelvin.
Convert 300 K to degrees Rankine.
Convert 25 °C to degrees Fahrenheit.
In a steady-flow device, the energy required to push fluid into or out of a control volume (Pv) is called:
The amount of heat required to change 1 kg of saturated liquid water at 100 °C into saturated vapor at 100 °C (1 atm) is approximately:
For a saturated liquid, the quality x is:
The Gibbs free energy is defined as:
The maximum useful work obtainable from a system as it comes to equilibrium with its environment is called:
A thermocouple measures temperature based on the:
The heating value of a solid or liquid fuel is usually determined using a:
The scientist who introduced the term 'entropy' was:
The thermal efficiency of a heat engine is defined as:
The Clausius inequality states that for any cycle:
The free (unrestrained) expansion of an ideal gas into a vacuum in an insulated rigid vessel results in:
Intercooling between stages of a multistage air compressor:
Reheating in a Rankine cycle is primarily done to:
The function of the condenser in a steam power plant is to:
A nozzle is a device that:
For a polytropic process PVn = C, which value of n corresponds to an isothermal process of an ideal gas?
On a T–s diagram, the area under a reversible process curve represents:
The Mollier diagram is a plot of:
As the pressure on water increases, its saturation (boiling) temperature:
Steam whose temperature is higher than the saturation temperature corresponding to its pressure is called:
The SI unit of thermal conductivity is:
The value of the Stefan–Boltzmann constant is approximately:
Heat transfer by convection is governed by:
On a psychrometric chart, sensible heating or cooling of air is represented by a:
Relative humidity is defined as the ratio of:
The temperature of air measured by an ordinary thermometer exposed to air (shielded from radiation) is called the:
The coefficient of performance (COP) of a refrigerator is defined as:
One ton of refrigeration (TR) is equal to approximately:
In a vapor-compression refrigeration system, the refrigerant absorbs heat from the refrigerated space in the:
In the dual (limited-pressure) cycle, heat is added:
The Stirling cycle consists of:
The Brayton cycle is the ideal cycle for:
The Otto cycle is the ideal cycle for:
The Carnot cycle consists of:
A perpetual motion machine of the second kind (PMM2) violates the:
The Clausius statement of the second law says that:
The Kelvin–Planck statement of the second law says it is impossible for a device operating in a cycle to:
The law stating that the total pressure of a gas mixture equals the sum of the partial pressures of its components is:
The value of the universal gas constant R is approximately:
Gay-Lussac's law states that for a fixed mass of gas at constant volume:
Boyle's law states that for a fixed mass of gas at constant temperature:
For an ideal gas, the difference between cp and cv is equal to:
The ratio of specific heats k = cp/cv for air at room temperature is approximately:
The amount of heat required to raise the temperature of a unit mass of a substance by one degree is called:
The heat required to change the phase of a substance without a change in temperature is called:
The direct change of phase from solid to vapor is called:
The state at which saturated liquid and saturated vapor states become identical is called the:
On the Fahrenheit scale, the normal freezing and boiling points of water are:
At what temperature do the Celsius and Fahrenheit scales read the same value?
The instrument used to measure atmospheric pressure is the:
Standard atmospheric pressure is equal to:
One calorie (cal) is approximately equal to:
One British thermal unit (BTU) is approximately equal to:
The SI unit of energy is the:
Enthalpy is defined as:
A process that takes place at constant volume is called:
A reversible adiabatic process is also called:
A process that takes place infinitely slowly so that the system remains infinitesimally close to equilibrium at all times is called:
Heat and work are classified as:
Which of the following is an extensive property?
A system in which both mass and energy may cross the boundary is called a/an:
A system in which mass does NOT cross the boundary but energy may cross is called a/an:
The First Law of Thermodynamics is essentially a statement of the principle of:
Thermodynamics is the branch of science that deals with: