Thermodynamics Study Notes

Questions and Answers

What specific heat value is required to isothermally compress 800 ft 3 of air per minute from 14.7 psia to 120 psia?

2.34 Btu/lb-oR

14.33 KJ/kg-oK

13.23 KJ/kg-oK (correct)

10.76 Btu/lb-oK

At constant pressure of 689.5 kPa, if the volume of air changes from 0.567 m3 to 0.283 m3, what is the change in internal energy?

493.63 KJ

If the initial volume of an ideal gas is compressed to one half its original volume and to twice its original temperature, what happens to the pressure?

Quadruples (correct)

Doubles

Remains constant

Halves

What is the final pressure of an ideal gas heated from 45 psig and 80oF to 130 oF in a closed container?

To be determined Signup and view all the answers

In a Carnot engine that requires 35 KJ/sec from the hot source and produces 15 kW of power with a sink temperature of 26oC, what is the temperature of the hot source?

250.18 Signup and view all the answers

If a Carnot engine receives 130 Btu of heat from a hot reservoir at 700 oF and rejects 49 Btu of heat, what is the temperature of the cold reservoir?

-22.7 oF Signup and view all the answers

What is the maximum thermal efficiency possible for a power cycle operating between 1200 oF and 225 oF?

58% Signup and view all the answers

For an Otto cycle with a clearance volume of 7% producing 300 kW of power, what is the amount of heat rejected?

152 KW Signup and view all the answers

A closed vessel containing air at 160 KN/m2 gauge pressure and 30oC heated at constant volume to 60oC with atmospheric pressure at 759 mm Hg, what is the final gauge pressure?

185.8 Signup and view all the answers

An air standard engine with a compression ratio of 20 and a cut-off ratio of 5, intake air pressure 100 kPa and temperature 27oC, find the work done per kg of air.

2166 Signup and view all the answers

Steam enters a throttling calorimeter at a pressure of 1.03 MPa. The calorimeter downstream pressure and temperature are 0.100 MPa and 125°C respectively. What is the percentage moisture of the supply steam?

2.62 Signup and view all the answers

A vessel of 0.058 m³ capacity is divided equally by a rigid conducting diaphragm. Initially, both halves contain air at pressures of 137.8 kPa and 413.4 kPa, and temperatures of 27°C and 177°C, respectively. What is the increase of entropy of the system in kJ/°C?

0.00173 Signup and view all the answers

Using steam table, find the enthalpy of steam at kPa if its specific volume is 0.3598 m³/kg.

1625.86 KJ/kg Signup and view all the answers

A throttling calorimeter is connected to the desuperheated steam line supplying steam to the auxiliary feed pump on a ship. The line pressure measures 2.5 MPa. What is the increase of entropy of the system in kJ/°C?

6.6 KJ/kg-°K Signup and view all the answers

Steam enters an isothermal compressor at 400°C and 100 kPa. The exit pressure is 10 MPa. Determine the change of enthalpy.

182 KJ/kg Signup and view all the answers

Steam turbine in Rankine cycle has an exhaust enthalpy of 2650 KJ/kg and delivers 0.8 kg/sec of steam. Determine the heat rejected from the condenser if enthalpy at exit is 200 KJ/kg.

1960 KW Signup and view all the answers

What is the mass flow rate of ground water in a geothermal power plant if it is 1,500,000 kg/hr and the quality after throttling is 30%?

87.5 MW Signup and view all the answers

In a geothermal power plant, if the enthalpy of ground water is 700 KJ/kg, enthalpy at turbine inlet is 2,750 KJ/kg, and enthalpy of hot water in flash tank is 500 KJ/kg, what is the mass of steam flow entering the turbine if mass flow of ground water is 45 kg/sec?

4.27 kg/sec Signup and view all the answers

What is the mass of cooling water required for a geothermal power plant if the turbine brake power is 1000 KW, the condenser outlet has an enthalpy of 210 KJ/kg, and the temperature rise of cooling water in condenser is 8 0C?

46 kg/sec Signup and view all the answers

In a 12 MW geothermal power plant with a mass flow of steam entering the turbine as 26 kg/sec and ground water enthalpy of 650 KJ/kg, what is the overall efficiency of the plant?

15.4% Signup and view all the answers

For a 16,000 KW geothermal plant with generator efficiency and turbine efficiency of 90% and 80%, respectively, and quality after throttling of 20%, how many wells are required to produce if the change in enthalpy at the entrance and exit of turbine is 500 KJ/kg?

4 wells Signup and view all the answers

In a geothermal power plant drawing pressurized water from a well at 20 Mpa and 300 0C, and producing steam water mixture in the separator before entering the turbine, what is the overall plant efficiency if the turbine efficiency is 85% at a rated power output of 10 MW?

7.29% Signup and view all the answers

In a flashed steam geothermal power plant located where underground hot water is available as saturated liquid at 700 Kpa and flashed steam enters the turbine at 500 Kpa, determine the power produced in KW if the flow rate from the well is 29.6 kg/sec.

430.13 kg/s Signup and view all the answers

In an ideal Reheat cycle, what is the cycle efficiency when the steam is throttled condition at 8 Mpa and 480 degrees Celsius, then reheated to 2 Mpa and 460 degrees Celsius?

38.3% Signup and view all the answers

For a reheat steam cycle with specified throttle and reheat pressures and temperatures, what is the cycle thermal efficiency?

34.46% Signup and view all the answers

For a steam turbine before condensation and extraction for feedwater heating in an ideal regenerative cycle, what is the thermal efficiency?

44.14% Signup and view all the answers

In a steam turbine that receives steam and condenses it, with specific enthalpies, what is the water flow rate in kg/s as it passes through the condenser and heats up?

523 Signup and view all the answers

For an open feedwater heater in a steam plant, determine the mass flow rate of the subcooled liquid given the steam flow rate and properties.

2.725 Signup and view all the answers

In an adiabatic process of steam expansion in a turbine, what is the effectiveness percentage from the initial to final conditions?

80 Signup and view all the answers

Calculate the cogeneration efficiency in percent for a steam plant given specific steam properties and extracted flow rates.

No exact answer in the choices Signup and view all the answers

What is the exit temperature of water in a heat exchanger used to cool gas, when water is supplied at a specific rate and temperature?

48 Signup and view all the answers

If the pump work in a Rankine cycle is given, and the water density at the pump entrance pressure is known, what is the pressure at the turbine entrance?

14.47 Mpa Signup and view all the answers

For a Rankine cycle with turbine work and pump work values, what is the efficiency of the cycle given the generated heat by the generator?

35.25% Signup and view all the answers

The density of air entering the engine is 1.176 kg/m^3 and has a volume flow rate of 0.375 m^3/sec. If the air fuel ratio is 21, what is the mass flow rate of fuel?

0.02 kg/sec Signup and view all the answers

A diesel engine develops a torque of 5 KN-m at 1800 rpm. If the brake thermal efficiency is 31%, what is the heat generated by the fuel?

3040.25 KW Signup and view all the answers

In a diesel engine, if the fuel is injected at 6.5% of the stroke and the clearance volume is 10% of the stroke, what is the cut-off ratio?

1.65 Signup and view all the answers

A 373 KW (500 Hp) internal combustion engine has a brake mean effective pressure of 551.5 Kpa at full load. What is the friction power if mechanical efficiency is 85%?

88.23 hp Signup and view all the answers

In a 4-stroke diesel engine with specific parameters, calculate the indicated mean effective pressure in Kpa if mechanical efficiency is 89%.

450.8 kpa Signup and view all the answers

For a 305 mm x 457 mm four-stroke single acting diesel engine rated at 150 KW at 260 rpm, calculate the brake thermal efficiency.

31.53% Signup and view all the answers

Calculate the thermal efficiency for a four-stroke, 8 cylinder Diesel engine with specific dimensions, speed, and fuel consumption data.

35.27% Signup and view all the answers

Determine the brake thermal efficiency for a 6 cylinder diesel engine based on specific test data.

31.13% Signup and view all the answers

Find the capacity (gpm) required for jacket water in a certain diesel engine with given specifications.

242 Signup and view all the answers

Calculate the volume of air in m3/hr with air at 600F and 14.7 psia pressure if boiler efficiency is 70% and FE = 1.10.

212,830 Signup and view all the answers

Calculate the weight in metric tons of coal needed for 24 hours operation at rated capacity if boiler efficiency is 70% and FE = 1.10.

503.443 Signup and view all the answers

How many hours will the coal in the bunker run the boilers if the heating value of coal is 7590 Kcal/kg?

230.8 Signup and view all the answers

Calculate the number of tons of coal fired per hour for a gross efficiency of 85%.

4.89 Signup and view all the answers

Determine the total number of hours to consume the available fuel with a water tube boiler capacity of 1000 kg/hr of steam, factor of evaporation of 1.3, and heating value of fuel of 18,400 Kcal/kg.

853.26 Signup and view all the answers

Calculate the fore coal at an average rate of 4,800 kg/hr and boiler efficiency of 85% to ensure the generation of 50,000 kj/hr of saturated steam.

29,977 Signup and view all the answers

Compute the developed boiler horsepower for a boiler operating at 11 kg/cm2 and other given conditions.

3462.56 Signup and view all the answers

Calculate the overall thermal efficiency of the steam boiler generating specified steam conditions with given fuel properties.

82.78 Signup and view all the answers

Determine the brake power of a steam engine with specified steam conditions and efficiency.

48 Signup and view all the answers

Calculate the brake power of a steam engine with specified steam conditions, consumption, and efficiency.

84 Signup and view all the answers

Determine the indicated power of a steam engine with specified engine dimensions and pressure.

99 Signup and view all the answers

Find the indicated horsepower developed in the cylinder of a steam engine with specified dimensions and pressure.

122.7 Signup and view all the answers

Calculate the indicated engine efficiency based on specified steam conditions, consumption, and mechanical efficiency.

66.74 Signup and view all the answers

Calculate the thermal efficiency of an equivalent Rankine engine with specified steam conditions and consumption.

15.59 Signup and view all the answers

Determine the brake thermal efficiency of a steam engine with specified dimensions, steam conditions, and factors.

14.66 Signup and view all the answers

Find the power generated by an industrial power plant given steam conditions, rates, efficiencies, and losses.

1,556.50 Signup and view all the answers

Calculate the turbine work received by a steam turbine under specified steam conditions and efficiencies.

117 Signup and view all the answers

Determine the quality at exhaust for a steam turbine under specific inlet and exhaust conditions.

91.69 Signup and view all the answers

Calculate the hourly steam consumption of a steam turbine at 60% of rated load based on given equations.

19,200 Signup and view all the answers

Calculate the power output from a turbine receiving specified steam conditions and losing heat.

4375 Signup and view all the answers

What is the pressure 8,000 ft (2000m) below the surface of the ocean? Neglect the compressibility factor, SI units.

20.1 Signup and view all the answers

What temperature does water freeze at on the Kelvin scale?

273 Signup and view all the answers

What are the SI units of temperature?

oK Signup and view all the answers

Steam with an enthalpy of 800 kcal/kg enters a nozzle at a velocity of 80 m/sec. Find the velocity of the steam at the exit of the nozzle if its enthalpy is reduced to 750 kcal/kg. Assuming the nozzle is horizontal and disregarding heat losses. Take g(9.81) m/sec and J = 427 kg-m/kcal.

652.14 m/s Signup and view all the answers

A volume of 450 cc of air is measured at a pressure of 740 mm HG absolute and a temperature of 20°C. What is the volume in cc at 760 mm HG abs. and 0°C?

408.25 Signup and view all the answers

Assuming compression is according to the law PV = constant. Calculate the initial volume of gas at a pressure of 2 bar which will occupy a volume of 6 cubic meters when it is compressed to a pressure of 42 bar.

126 m³ Signup and view all the answers

How much heat, in KJ, must be transferred to 20kg of air to increase the temperature from 20 degrees C to 280 degrees C if the pressure is maintained constant?

5200 Signup and view all the answers

If air is at pressure, p, of 3200 lb/ft² and at a temperature, T, of 800 °R, what is the specific volume, v?

13.3 ft³/lb Signup and view all the answers

The mass of air in the room 3m x 5m x 20m is known to be 350 kg. Find its density.

1.167 kg/m³ Signup and view all the answers

A transportation company specializes in the shipment of pressurized gaseous materials. An order is received for 100 liters of a particular gas at STP (32°F and 1 atm). What minimum volume tank is necessary to transport the gas at 80°F and a maximum pressure of 8 atm?

14 liters Signup and view all the answers

A bicycle has a volume of 600 cm³. It is inflated with carbon dioxide to a pressure of 80 psi at 20°C. How many grams of carbon dioxide are contained in the tire?

5.98 g Signup and view all the answers

An ideal gas at 0.60 atm and 87°C occupies 0.450 liters. How many moles are in the sample? (Given: R = 0.0821 atm/mole K)

0.0091 mole Signup and view all the answers

Air compressed in a diesel engine from an initial pressure of 13 psia and a temperature of 120°F to one twelfth of its original volume. Calculate the final temperature assuming compression to be adiabatic.

1107 Signup and view all the answers

Calculate the gas constant in J/kg°K.

272 Signup and view all the answers

Calculate the specific gravity if the molecular weight of air is 28.97 kg/kg-mol.

1.055 Signup and view all the answers

Calculate the specific heat for the gas in KJ/kg - °K.

0.992 Signup and view all the answers

Determine the theoretical weight of Oxygen in lb/lb of coal.

2.274 Signup and view all the answers

What is the excess air in percent?

26.67% Signup and view all the answers

Determine the air-fuel ratio for complete combustion on molal basis.

1.233 Signup and view all the answers

Calculate the theoretical air needed for the complete combustion of ethane C2H6 for 20 kg fuel.

320.32 kg Signup and view all the answers

Determine the volumetric (molal) analysis of CO2 in the production of combustion.

8.66% Signup and view all the answers

Determine the percent excess air in combustion analysis from Orsat readings.

10.52% Signup and view all the answers

Determine the actual air – fuel in kg air per kg fuel.

17.13 Signup and view all the answers

What mass of liquid oxygen is required to completely burn 1000kg of liquid butane, C4H10 on a rocket ship?

3586 Signup and view all the answers

What is the percentage of CO on a mass basis?

1.9% Signup and view all the answers

What is the percent theoretical air for a known combustion process with fuel and combustion gas composition?

111 Signup and view all the answers

Find the reserve over peak load for a 50 MW power plant with given load characteristics.

5 MW Signup and view all the answers

What is the daily average load for a power plant that produces 280,000 KW-hrs of energy daily?

20 MW Signup and view all the answers

Determine the annual capacity factor of a 100 MW power plant given the energy produced annually.

50% Signup and view all the answers

How many hours did a power plant operate in a year with given use factor and factor?

7709 hrs Signup and view all the answers

What is the thermal efficiency of a Rankine cycle given the steam turbine conditions?

25.55% Signup and view all the answers

Determine the pump work in KJ per kg for an ideal Rankine cycle with specified steam conditions.

4.17 Signup and view all the answers

Calculate the net thermal efficiency of a thermal power plant given power generation and auxiliary power needs.

36.15% Signup and view all the answers

Find the thermal efficiency of an ideal Rankine cycle based on given steam conditions.

27.55% Signup and view all the answers

Calculate the thermal efficiency of a Rankine cycle under specific conditions of operation.

34.24% Signup and view all the answers

Calculate the Mtons of fuel oil/bunker fuel required per 24 hours for a steam generating plant.

515 Signup and view all the answers

Calculate the incremental heat rate of electricity generation in a cogeneration system.

22,504 KJ/KW-hr Signup and view all the answers

Find the net station efficiency of a coal-fired power plant given operational and efficiency details.

33% Signup and view all the answers

Determine the pump work in KJ/kg for a superheat steam Rankine cycle with specific inlet conditions and efficiency factors.

27.3 Signup and view all the answers

Calculate the cogeneration efficiency of a system given steam and heating conditions.

69 Signup and view all the answers

Study Notes

Thermodynamics Study Notes

Pressure and Temperature

At 8,000 ft (2,000 m) below the surface of the ocean, the pressure is approximately 20.1 MPa (neglecting compressibility factor).
The freezing point of water on the Kelvin scale is 273 K.
The SI unit of temperature is Kelvin (K).
1 torr is equivalent to 1/760 atm.

Standard Temperature and Pressure

The standard temperature in the US is Fahrenheit (°F).
The atmospheric pressure is 101.3 kPa (or 1 atm) at sea level.

Energy and Work

The internal energy of a system can be calculated using the specific enthalpy and specific volume.
The power output of a steam turbine can be calculated using the enthalpy and velocity of the steam.
The heat loss from a compressor can be calculated using the enthalpy and velocity of the air.

Ideal Gas Law

The ideal gas law is PV = nRT, where P is pressure, V is volume, n is moles of gas, R is the gas constant, and T is temperature.
The ideal gas law can be used to calculate the volume, pressure, or temperature of an ideal gas.

Compression and Expansion

Compression ratio is the ratio of the initial volume to the final volume.
The compression ratio of an Otto cycle is 6:1.
The final pressure and temperature of a gas can be calculated using the compression ratio and the ideal gas law.

Specific Volume and Density

The specific volume of a gas is the volume of the gas per unit mass.
The density of a gas is the mass of the gas per unit volume.
The specific volume and density of air can be calculated using the ideal gas law.

Heat Transfer

The heat transfer rate can be calculated using the specific heat and temperature change.
The heat transfer rate can be used to calculate the final temperature of a system.

Polytropic Process

A polytropic process is a process where the pressure and volume of a gas change.
The polytropic index (n) can be calculated using the initial and final states of the gas.

These notes cover key concepts in thermodynamics, including pressure, temperature, energy, and ideal gas laws. They also touch on compression and expansion, specific volume and density, heat transfer, and polytropic processes.### Thermodynamics and Heat Transfer

The compression ratio of an ideal Otto cycle is 6:1, with initial conditions of 101.3 kpa and 20°C.
The final pressure and temperature at the end of adiabatic compression are 1244.5 kpa and 599.96°K.
Ammonia weighing 22 kgs is confirmed inside a cylinder equipped with a piston, with an initial pressure of 413 kpa and 38°C.
The amount of work done by the fluid in KJ is 667.
The average Cp value in KJ/kg-K of a gas is 1.044, with 522 KJ/kg of heat necessary to raise the temperature from 300°K to 800°K.

Carnot Cycle and Efficiency

The maximum thermal efficiency possible for a power cycle operating between 1200°F and 225°F is 57.40%.
The Carnot cycle efficiency in percent is 67.56%, with a temperature limit of 1370°C and 260°C.
The thermal efficiency of a particular engine operating on an ideal cycle is 35%.

Air Standard Cycles

The air-standard efficiency of an engine operating on the diesel cycle with a clearance of 8% is 60.02%.
The compression ratio and thermal efficiency of an air standard Otto cycle are 0.55 and 47.89%, respectively.
The cycle efficiency of an air standard diesel cycle is 65.98%, with a compression ratio of 16 and a cut-off ratio of 2.

Heat Engines and Pumps

The brake engine efficiency of a diesel engine operating on a 4-stroke cycle is 63.5%.
The heat rate of a diesel engine is 11315.6 KJ/KW-hr brake, with a compression ratio of 13 and a cut-off ratio of 2.
The thermal efficiency of a heat engine (Carnot cycle) is 13.25%, with an intake and exhaust temperature of 157°C and 100°C, respectively.

Thermodynamic Properties

The enthalpy of 100 psi and 97% quality is 1161 Btu/lb, with hf = 298.55 Btu/lb and hfg = 889.119 Btu/lb.
The entropy of a mixture of steam and water at 1.3 Mpa is 4 KJ/kg-K, with sf = 2.2515, sg = 6.4953, hf = 514.93, and hfg = 1972.7.
The enthalpy of steam at 500 kpa is 1625.86 KJ/kg, with a specific volume of 0.3598 m3/kg.

Steam Tables and Properties

The enthalpy of steam at 827.4 kpa and 171.6°C is 2010.7 KJ/kg, with hfg = 2779.25 KJ/kg.
The temperature and pressure of a throttling calorimeter are 115.6°C and 0.100 Mpa, respectively, with h = 2726.6 KJ/kg.
The enthalpy of steam at 160 psia is 1423.70 KJ, with an initial temperature of 40°C and a final temperature of 600°F.

Steam Systems and Processes

The rate of heat transfer in a steady flow system boiler is 372000 Kcal/hr, with an inlet temperature of 40°C and an outlet temperature of 600°F.
The moisture content of steam leaving a boiler is 3.08%, with a pressure of 827.4 kpa and a temperature of 171.6°C.
The increase in entropy of a system in a throttling calorimeter is 0.00173 KJ/°C, with an initial pressure of 137.8 kpa and a final pressure of 101.4 kpa.### Combustion and Fuels
Equation to calculate the total energy required to raise the temperature of a given amount of water: heat losses and energy applied are considered
Example: 1000 KWH with 25% heat losses, answer is 1333 KWH

Diesel Power Plant

Fuel consumption and its effects on the plant's operation
Example: 30 kg iron in a container with 14.33 kg water, initial temperature of 439oK, change in entropy (Cp = 0.4 KJ/kgoK) = -6.6 KJ/oK
Fuel rate calculation: example 650 liters of fuel at 26 oC in 24 hours with 28 oAPI, answer is 23.83 kg/hr
Heating value of fuel: example, fuel density of 892.74 kg/m3 at 15.67oC, answer is 44,900 KJ/kg
Ultimate analysis of coal: example, C = 69%, N2 = 5%, etc., heating value of fuel = 26,961.45 KJ/kg

Cost of Fuel

Cost of fuel per day: example, 650 Bhp diesel engine, fuel consumption is 0.65 lb/Bhp-hr, cost of fuel is P7.95 per liter, answer is P42,070.45
Cost of fuel to produce one Kwh: example, 250 gallons of fuel at 80°F, produced 2700 KW-Hrs, answer is P1,043/KW-h

Overall Thermal Efficiency

Overall thermal efficiency calculation: example, diesel electric plant, consumed 680 liters of diesel fuel at 26.6°C in 24 hrs, produced 1,980KW-hrs, answer is 26.47%
Example, boiler design, flue gas exit temperature above the dew point, answer is 39°C

Air-Fuel Ratio

Air-fuel ratio calculation: example, complete combustion of ethane C2H6, answer is 320.32 kg
Example, fuel oil C12H26, burned with 50% excess air, answer is 17.13 kg air per kg fuel

Steam Cycle

Thermal efficiency of the cycle: example, Rankine cycle, steam enters the turbine at 2.5 Mpa, condenser of 50 Kpa, answer is 25.55%
Pump work calculation: example, ideal Rankine cycle, steam throttle condition is 4.10 Mpa and 440 0C, answer is 4.17 KJ/kg
Net thermal efficiency: example, thermal power plant generates 5 MW, has 300 kW power needed for auxiliaries, answer is 36.15%
Thermal efficiency of the cycle: example, ideal Rankine cycle, steam throttle condition is 4.10 Mpa and 440 0C, answer is 27.55%

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Review key concepts in thermodynamics, including pressure, temperature, and standard units, ideal for students preparing for exams or seeking to deepen their understanding of the subject.