Thermodynamics Concepts Quiz
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Questions and Answers

What will happen to the volume of a confined gas if the pressure is tripled at constant temperature?

  • The volume will be reduced to one-third of its original value (correct)
  • The volume will be tripled
  • The volume will remain unchanged
  • The volume is constant

What is the pressure of 750 mmHg in kilopascals (kPa)?

  • 90 kPa
  • 103 kPa
  • 100 kPa (correct)
  • 110 kPa

If a gas with an unknown volume expands to a container of 10 m³ at 500 mmHg, what is the unknown volume if the initial pressure is 1 atmosphere?

  • 6.75 m³
  • 5.67 m³
  • 6.58 m³ (correct)
  • 7.65 m³

What is the density of an iron block that weighs 5 Newtons and has a volume of 200 cm³?

<p>2549 kg/m³ (A)</p> Signup and view all the answers

Determine the air-standard efficiency of an engine operating on the diesel cycle with a clearance of 6% and suction pressure of 99.87 kPa.

<p>62.11% (B)</p> Signup and view all the answers

For an Otto cycle with a compression ratio of 8, what is the calculated pressure during compression?

<p>18.38 (B)</p> Signup and view all the answers

In a Carnot cycle connected in series, what is the work output of cycle C if heat added to cycle A is 1000 kW?

<p>111.44 kW (A)</p> Signup and view all the answers

What is the mass of water vapor contained in a 150m³ room at 100 kPa, 23°C and 40% relative humidity?

<p>1.9342 kg (D)</p> Signup and view all the answers

If air is compressed adiabatically from 30°C to 100°C and the mass of air is 5 kg, what is the change in entropy?

<p>0 kJ/K (C)</p> Signup and view all the answers

How many hours will the available coal run the boilers if one boiler produces 1591 kg of steam per hour and the other produces 1364 kg?

<p>230.80 hrs (A)</p> Signup and view all the answers

What is the efficiency of the boiler if the heating value of the fuel is 40,000 kJ/kg and the factor of evaporation is 1.10?

<p>62.70% (A)</p> Signup and view all the answers

What is the rate of evaporation for a water tube boiler with a factor of evaporation of 1.10 and a heating surface area of 250 m²?

<p>7,817.16 kg/hr (C)</p> Signup and view all the answers

What is the particulate discharged per million BTU of heat input to the furnace based on the given data?

<p>12 lb/10^6 BTU (A)</p> Signup and view all the answers

How high should the chimney be if the gas density is 0.75 kg/m³ and the driving pressure is 0.25 kPa?

<p>63.7 m (A)</p> Signup and view all the answers

What is the total number of hours to consume the available fuel based on a boiler capacity of 1000 kg/hr?

<p>853.36 hrs (A)</p> Signup and view all the answers

What is the specific evaporation if the factor of evaporation is 1.10 and the actual evaporation is known to be 10?

<p>95.2 (D)</p> Signup and view all the answers

What is the net power produced by the ideal standard Brayton cycle described, given the conditions stated?

<p>529.76 kW (B)</p> Signup and view all the answers

What is the overall efficiency of a 12 MW geothermal power plant with steam entering the turbine at the given mass flow and quality?

<p>9.6 % (A)</p> Signup and view all the answers

How many wells are required for a 16,000 KW geothermal plant with specified efficiencies and quality after throttling?

<p>4 wells (A)</p> Signup and view all the answers

What is the calculated penstock diameter for a Pelton type turbine given the head and friction loss data?

<p>1,355.73 mm (A)</p> Signup and view all the answers

What is the secondary power that a 9,000 KW hydro-electric plant could deliver upon receiving 110,000 KW-hrs for that day?

<p>80,080 KW-hrs (A)</p> Signup and view all the answers

What is the power output in KW from a Pelton type turbine installed below a gate with certain friction loss?

<p>34,452 (C)</p> Signup and view all the answers

How many identical turbines operating at 139.0 rpm with specified efficiency and flow are needed for a head of 1200 ft?

<p>3 turbines (C)</p> Signup and view all the answers

What is the diameter of the chimney for gas entering at 8 m/sec with a mass of 50,000 kg/hr?

<p>1.81 m (A)</p> Signup and view all the answers

Determine the diameter of a chimney for a coal-fired steam boiler using 3000 kg of coal per hour.

<p>1.91 m (B)</p> Signup and view all the answers

What is the appropriate diameter for a stack with flue gases entering at a rate of 5.0 kg/sec and a driving pressure of 0.20 kPa?

<p>0.95 m (D)</p> Signup and view all the answers

Calculate the intercooler pressure between the first and second stage of a 10-stage air compressor compressing from 100 kPa to 800 kPa.

<p>123.11 kPa (C)</p> Signup and view all the answers

What is the intercooler pressure between the second and third stage in a 3-stage air compressor compressing from 100 kPa to 700 kPa?

<p>365.88 kPa (A)</p> Signup and view all the answers

What is the suction pressure if the discharge pressure of an air compressor is 5 times the suction pressure and the work is 19.57 kW?

<p>98 kPa (A)</p> Signup and view all the answers

What is the cost of the fuel to produce one KW-hr for a diesel electric plant that consumed 240 gallons and produced 3930 KW-hr?

<p>P6.87 (C)</p> Signup and view all the answers

How much air is consumed by a turbo-charged, 16-cylinder, Vee-type diesel engine at rated load and speed?

<p>3,000 kg/hr per cylinder (B)</p> Signup and view all the answers

In a cascade refrigeration cycle, what is the typical temperature threshold for cooling objects?

<p>-56C (B)</p> Signup and view all the answers

Which type of refrigerant control is specifically designed to maintain a pressure difference while the compressor operates?

<p>Thermostatic expansion valve (A)</p> Signup and view all the answers

What is the approximate percentage reduction in compressor power consumption for every 3C drop in inlet air temperature?

<p>1% (C)</p> Signup and view all the answers

What modern method is utilized to detect air compressor leaks?

<p>Acoustic leak detector (C)</p> Signup and view all the answers

For foundation of stacks, the maximum pressure on the soil is derived from the weight and what additional factor?

<p>Wind movement (B)</p> Signup and view all the answers

When considering multistage compression in an ideal Brayton cycle, how does the back work ratio typically behave?

<p>Decrease (A)</p> Signup and view all the answers

What is the atmospheric pressure if a vacuum pump can lift water at a temperature of 20℃ and pressure of 2.34 KPa?

<p>159.30 (C)</p> Signup and view all the answers

When installing a foundation bolt for an engine, the inside diameter of the surrounding pipe sleeve should be at least how many times the diameter of the anchor bolt?

<p>3 times (C)</p> Signup and view all the answers

What is the diameter of the impeller of the pump if each impeller diameter developed a head of 38 ft?

<p>3.71 inches (A)</p> Signup and view all the answers

What is the horsepower of the engine when it is making 300 rpm with an average pressure of 120 psi?

<p>171.4 Hp (C)</p> Signup and view all the answers

How much work is done if the heat transferred out of the system is 150 kJ/kg and internal energy decreases by 400 kJ/kg?

<p>250 kJ/kg (C)</p> Signup and view all the answers

What is the power produced by an engine with a thermal efficiency of 50% and heat transferred at a rate of $10^6$ kJ/hr?

<p>138 MW (D)</p> Signup and view all the answers

How many calories are absorbed each second by the boiler if the steam engine delivers 8 Hp and operates at 30% efficiency of a Carnot engine?

<p>12.7 kCal/s (C)</p> Signup and view all the answers

What is the indicated mean effective pressure of an engine with a brake mean effective pressure of 750 kPa and 80% mechanical efficiency?

<p>136 psi (A)</p> Signup and view all the answers

Determine the diameter of the stud bolt required to fasten down the cylinder head of a 203 mm x 304 mm gas engine, given the explosion pressure of 31 kg/sq.cm.

<p>38.1 mm (B)</p> Signup and view all the answers

What is the pitch of a single threaded trapezoidal metric thread used as a translation screw?

<p>4 mm (D)</p> Signup and view all the answers

Flashcards

Mass of water vapor in a room

The amount of water vapor present in a 150 m³ room with specified conditions of pressure, temperature, and relative humidity.

Boiler capacity

The rate at which a boiler produces steam, typically measured in kilograms per hour

Factor of evaporation

A ratio representing the actual evaporation rate and the theoretical evaporation rate.

Boiler rating

The percentage of a boiler's maximum possible output.

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Boiler efficiency

The percentage of fuel energy converted into steam energy.

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Heating surface area

The area of a boiler where heat is transferred to water to produce steam.

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Particulate discharge

The amount of solid particles emitted from a boiler per unit of heat input to the furnace.

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Chimney Height

The vertical distance from the boiler to the top of the chimney, affecting the draft of the gases.

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Gas volume change with pressure

At constant temperature, if the pressure of a confined gas triples, its volume decreases to one-third its original value.

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750 mmHg to KN/m^2

750 mmHg is approximately 100 KN/m^2.

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Temperature conversion from Rankine to Celsius

To convert temperature from Rankine (degR) to Celsius (degC), the formula is given (T°C) = T°R/1.8 - 459.67 .

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Gas expansion calculation

If a gas expands from one container to another at constant temperature, the product of initial volume and pressure equals the product of final volume and pressure.

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Density of iron block

Density is mass divided by volume. A 5 Newton iron block with a volume of 200 cm^3 has a density of approximately 2549 kg/m^3

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Diesel cycle efficiency

The air-standard efficiency of a diesel cycle depends on the clearance, injection timing, and the heat capacity ratio (k).

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Otto cycle compression pressure

The pressure during compression in an Otto cycle with a compression ratio of 8 depends on the initial conditions.

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Entropy change in adiabatic compression

The change in entropy when air is compressed adiabatically from 30°C to 100°C for a mass of 5 kg is approximately zero (0) when considering the ideal air model under the simplified process model.

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Chimney Diameter Calculation

Determining the diameter of a chimney for a given gas flow rate, temperature, pressure, and gas constant.

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Coal-Fired Boiler Chimney Diameter

Calculating chimney diameter for a steam boiler using coal, considering air for combustion, flue gas properties, and allowable gas velocity.

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Power Plant Stack Diameter

Calculating the diameter of a stack for a power plant, given flue gas properties (rate, temperature, composition), driving pressure, and ambient conditions.

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Intercooler Pressure (Air Compressor)

Determining the pressure at an intercooler stage in a multi-stage air compressor, to maintain efficiency and prevent excessive temperature rise during compression.

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Air Compressor Suction Pressure

Calculating the suction pressure of an air compressor given the discharge pressure, volume flow rate, and compressor work, considering the compression process.

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Fuel Cost per kWh

Calculating the cost of fuel consumed per kilowatt-hour (kWh) of energy produced by a power plant, given fuel consumption, fuel price, and energy produced.

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Air Consumption (Diesel Engine)

Calculating the amount of air consumed per hour by a specific number of cylinders in a turbocharged diesel engine at a given load and speed.

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Compressor Stages and Intercooler Location

Understanding the placement of intercoolers in multi-stage air compressors for improved efficiency; typically placed between stages in order to reduce temperature rise and increase the volumetric efficiency.

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Cascade refrigeration cycle

A refrigeration cycle used for extremely low-temperature applications.

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Refrigerant control - pressure difference

Automatic expansion valve controls refrigerant flow based on pressure differences.

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Compressor power consumption vs. inlet air temp

Lowering inlet air temperature by 3°C decreases compressor power consumption by approximately 2%.

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Air compressor leak detection

Modern methods use air leak detectors for pinpoint accuracy.

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Maximum pressure on stack foundation

The maximum pressure from soil weight and wind loads for a stable stack foundation.

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Foundation bolt pipe sleeve diameter

Pipe sleeve inside diameter should be at least 3 times the anchor bolt diameter.

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Multistage Brayton cycle back work ratio

Back work ratio decreases with multistage compression.

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Submersible pump power calculation

Calculating power for a pump involves factors including flow rate, lift height, and pump installation depth.

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Brayton cycle net power

The usable power output of an ideal Brayton cycle, calculated with given input conditions of mass flow rate, initial pressure, temperature and final temperature.

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Geothermal power plant efficiency

The ratio of usable power output to the total energy input from steam, considering factors like quality after throttling and initial ground water enthalpy.

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Geothermal plant wells

The number of wells needed to deliver a needed steam flow rate considering the flow rate of each well, generator, and turbine efficiency and enthalpy change across the turbine.

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Pelton turbine penstock diameter

The diameter of the pipe (penstock) delivering water to a Pelton turbine, based on head, friction loss, length of pipe, and the coefficient of friction.

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Hydroelectric plant secondary power

The extra power a hydro-electric plant could generate beyond its primary output given its overall efficiency and energy delivered to the customer.

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Hydroelectric plant power output

The power output of a hydro power plant, calculated using the plant's overall efficiency and the power delivered to the customers.

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Turbine count based on specific conditions

The number of turbines needed, based on desired power output, head, flow rate and turbine specific speed.

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Turbine Selection based on power output

Calculation of the number of identical turbines required to achieve a desired power output considering flow rate and head

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Drawdown

The vertical distance that the water level in a well drops when the pump is running at its rated capacity.

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Discharge Head

The total height that the pump can lift water, including the height of the water column and any frictional losses in the piping system.

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Impeller

The rotating part of a pump that creates pressure by transferring energy to the fluid.

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Indicated Mean Effective Pressure

The average pressure exerted on the piston of an engine during a complete cycle, calculated theoretically using pressure readings.

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Brake Mean Effective Pressure

The average pressure exerted on the piston of an engine during a complete cycle, measured experimentally using a brake dynamometer.

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Mechanical Efficiency

The ratio of the power output of an engine to the power input, representing how much power is lost due to friction and other mechanical losses.

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Thermal Efficiency

The ratio of the work output of a heat engine to the heat input, representing how much heat energy is converted into useful work.

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Carnot Engine

A theoretical heat engine that operates on an idealized reversible cycle and achieves the highest possible efficiency between two given temperatures.

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Study Notes

Thermodynamics 1

  • Pressure and Volume Relationship (Constant Temperature): If pressure triples at constant temperature, volume reduces to one-third its original value.
  • Pressure Conversion: 750 mmHg equals approximately 100 KN/m².
  • Temperature Conversion: 620°R equals approximately 71.11°C.
  • Gas Volume Calculation: Unknown volume can be determined if volume, pressure and temperature are known, and the initial container is allowed to expand to another container.
  • Density Calculation: The density of an iron block weighing 5 Newton and having a volume of 200 cm³ is approximately 2549 kg/m³.

Thermodynamics 2

  • Diesel Cycle Efficiency: Air-standard efficiency of a diesel engine with 6% clearance, operating at 99.87 kPa suction pressure, with 7% stroke fuel injection, and k = 1.4 is approximately 62.11%.
  • Otto Cycle Compression Ratio: An otto cycle with a compression ratio of 8 will have a different compression pressure.
  • Carnot Cycle Work Output: A Carnot cycle with a 1000 kW heat input to the first part of the series will have a different work output depending on the operation.
  • Adiabatic Air Compression: A change in entropy is calculated during an adiabatic compression of air from 30°C to 100°C for 5 kg of air.
  • Internal Energy Change (Tank): A decrease in internal energy calculation is given.
  • Heat Transfer: Stefan-Boltzmann constant is discussed for power/unit area.
  • Heat Loss Calculation: Heat loss per hour through 1 sq ft of 18-inch thick furnace wall, given inside wall temp and thermal conductivity, can be calculated.
  • Water Temperature Change: Calculations for heat exchanger with 55,000 gallons of water are given.

Heat Transfer

  • Heat Transfer Operations: Common operations using the power/unit area Stefan-Boltzmann constant for a black body radiation are given in the text.
  • Wall Temperature Calculation: Calculation is available for the outside surface temperature of a wall given its heat loss per hour through 1 sq ft.
  • Water Temperature Calculation: An example calculation for the entrance water temperature of 55,000 gallons of water through a heat exchanger at a given exit temperature is given.

Combustion

  • Fuel Consumption and Storage: Calculations involving a cylindrical fuel storage tank are shown.

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Thermodynamics Past Paper PDF

Description

Test your knowledge on key concepts in thermodynamics, including pressure and volume relationships, temperature conversions, and cycle efficiencies. This quiz covers essential principles such as the Diesel and Otto cycles, along with various calculations related to gas laws and densities.

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