Thermodynamics Chapter 1: First Law
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Questions and Answers

What is the mathematical statement of the First Law of Thermodynamics?

  • dQ - dW = 0
  • dQ = dW
  • dU = dQ + dW
  • dU = dQ - dW (correct)

    • What is the significance of the corollary to the First Law of Thermodynamics, dU = dQ - dW?

  • It indicates that there exists a property internal energy (U) of the system. (correct)
  • It proves that energy is always destroyed in a system.
  • It states that work done is always equal to heat added.
  • It shows that energy cannot be converted from one form to another.

    • What is the definition of total energy (E) in the context of the First Law of Thermodynamics?

  • The sum of internal energy, kinetic energy, potential energy, electrical energy, magnetic energy, and chemical energy. (correct)
  • The ratio of internal energy to kinetic energy.
  • The sum of internal energy and kinetic energy.
  • The difference between internal energy and kinetic energy.

    • What is the characteristic of a Perpetual Motion Machine of the First Kind (PMM1)?

    <p>It can produce more energy than consumed.</p> Signup and view all the answers

    What is the consequence of the First Law of Thermodynamics for an isolated system?

    <p>The total energy of the system remains constant.</p> Signup and view all the answers

    What is the primary application of the First Law of Thermodynamics?

    <p>All of the above.</p> Signup and view all the answers

    What is the underlying principle of the First Law of Thermodynamics?

    <p>Energy is neither created nor destroyed, only converted.</p> Signup and view all the answers

    What is the significance of the equation §(dQ - dW) = 0?

    <p>It represents the First Law of Thermodynamics.</p> Signup and view all the answers

    What is the consequence of violating the First Law of Thermodynamics?

    <p>It would lead to a perpetual motion machine.</p> Signup and view all the answers

    What is the benefit of understanding the First Law of Thermodynamics?

    <p>It leads to a better understanding of energy conservation and conversion.</p> Signup and view all the answers

    What is the fundamental principle that all processes in the universe comply with?

    <p>The first and second law of thermodynamics</p> Signup and view all the answers

    What is the implication of the first law of thermodynamics on an electric heater that consumes 1KW of electricity?

    <p>It cannot produce more than 1KW of heat</p> Signup and view all the answers

    What is the characteristic of the flow of mass across the boundary separating the system and the surroundings in most practical systems?

    <p>Steady flow</p> Signup and view all the answers

    What is the assumption made in the analysis of the steady flow energy equation?

    <p>The state of fluid at any point remains constant with time</p> Signup and view all the answers

    What is the term for the energy transferred into or out of a system due to fluid flow?

    <p>Flow energy</p> Signup and view all the answers

    What is the specific enthalpy of a fluid defined as?

    <p>u + p/ρ</p> Signup and view all the answers

    What is the term for the energy loss due to heat transfer, friction, etc. in the steady flow energy equation?

    <p>E/m</p> Signup and view all the answers

    What is the force that moves the mass in and out of a control volume of an open system?

    <p>Flow work</p> Signup and view all the answers

    What is the displacement of the piston in the figure shown in the problem?

    <p>L</p> Signup and view all the answers

    What is the expression for the work done by the piston in the figure shown in the problem?

    <p>W = F × L</p> Signup and view all the answers

    What is the primary purpose of applying the SFEE to a throttle valve?

    <p>To analyse the conversion of thermal energy to kinetic energy</p> Signup and view all the answers

    What is the SFEE equation for a boiler?

    <p>m (h2 - h1) = Q</p> Signup and view all the answers

    What type of work is represented by the equation W_flow = p_1V_1 - p_2V_2?

    <p>Flow work</p> Signup and view all the answers

    What is the purpose of applying the SFEE to a pump?

    <p>To evaluate the pump efficiency and calculate the energy added to the fluid</p> Signup and view all the answers

    What is the equation for internal heat transfer during steady flow processes?

    <p>Q_internal = m × cp × (T2 - T1) + W_internal</p> Signup and view all the answers

    What is the SFEE equation for a condenser?

    <p>m (h1 - h2) = Q</p> Signup and view all the answers

    What is the primary purpose of applying the SFEE to a throttle valve?

    <p>To analyse the conversion of thermal energy to kinetic energy</p> Signup and view all the answers

    What type of work is represented by the equation W_shaft = h_2 - h_1?

    <p>Shaft work</p> Signup and view all the answers

    What is the purpose of applying the SFEE to a boiler?

    <p>To analyse the energy transfer in the form of heat</p> Signup and view all the answers

    What is the total work done during a steady flow process?

    <p>W_total = W_flow + W_shaft + W_internal</p> Signup and view all the answers

    What is the primary function of a nozzle?

    <p>To increase the velocity of a fluid at the expense of pressure</p> Signup and view all the answers

    What is the relationship between the inlet and outlet conditions in a diffuser?

    <p>The kinetic energy decreases, and the enthalpy increases</p> Signup and view all the answers

    What is the purpose of the SFEE in turbine design?

    <p>To determine the work output of a turbine</p> Signup and view all the answers

    What is the formula to calculate the turbine efficiency?

    <p>?_t = (W / (m × (h1 - h2))) × 100</p> Signup and view all the answers

    What is the primary function of a heat exchanger?

    <p>To transfer heat energy from one fluid to another</p> Signup and view all the answers

    What is the formula to determine the work input required to compress a fluid in a compressor?

    <p>W = (m × (h2 - h1)) + (V2² - V1²) / 2 + (Z2 - Z1)</p> Signup and view all the answers

    What is the purpose of the SFEE in compressor design?

    <p>To optimize compressor performance, ensuring efficient compression and minimal energy losses</p> Signup and view all the answers

    What is the function of a throttle valve?

    <p>To restrict fluid flow, reducing pressure and temperature</p> Signup and view all the answers

    What is the relationship between the kinetic energy and enthalpy in a nozzle?

    <p>The kinetic energy increases, and the enthalpy decreases</p> Signup and view all the answers

    What is the formula to calculate the flow work or flow energy?

    <p>W = F × L = pA × L</p> Signup and view all the answers

    Study Notes

    First Law of Thermodynamics

    • The first law states that energy is neither created nor destroyed, but can be converted from one form to another.
    • The total energy of the universe is a constant.

    Corollaries to the First Law

    • There exists a property of a closed system called internal energy (U), which changes by the difference between heat supplied and work done.
    • For an isolated system, energy is constant, and neither heat nor work interactions occur.
    • It is impossible to create a perpetual motion machine of the first kind, which would produce useful work without any energy input.

    Steady Flow Energy Equation (SFEE)

    • The SFEE is a fundamental equation that relates the energy changes between the inlet and outlet of a control volume.
    • The SFEE accounts for energy losses due to heat transfer, friction, and other interactions.
    • The SFEE is written as: m (h1 + KE1 + PE1) = m (h2 + KE2 + PE2) + E

    Applications of SFEE

    Nozzles

    • SFEE helps understand the relationship between inlet and outlet conditions.
    • The equation reduces to: h1 + KE1 = h2 + KE2, showing a conversion of thermal energy to kinetic energy.

    Diffusers

    • SFEE helps understand the relationship between inlet and outlet conditions.
    • The equation reduces to: h1 + KE1 = h2 + KE2, showing a conversion of kinetic energy to thermal energy.

    Turbines

    • SFEE helps design and optimize turbine performance.
    • The equation is used to determine the work output (W) of a turbine.

    Compressors

    • SFEE is essential for designing and optimizing compressor performance.
    • The equation is used to determine the work input (W) required to compress a fluid.

    Heat Exchangers

    • SFEE helps analyze the heat transfer process.
    • The equation is: m1 (h1 - h2) = m2 (h3 - h4)

    Throttle Valve

    • SFEE applies to the throttle valve, showing a conversion of thermal energy to kinetic energy.

    Boiler

    • SFEE helps analyze the energy transfer in a boiler.
    • The equation is: m (h2 - h1) = Q

    Condenser

    • SFEE applies to the condenser, showing a conversion of thermal energy to kinetic energy.

    Pump

    • SFEE helps analyze the energy transfer in a pump.
    • The equation is: h1 + p1/ρg + V1²/2g + z1 = h2 + p2/ρg + V2²/2g + z2

    Work Done During Steady Flow Processes

    • Work done during steady flow processes can be categorized into three types: flow work, shaft work, and internal work.
    • The total work done is the sum of these three types of work.

    Heat Transfer During Steady Flow Processes

    • Heat transfer can be categorized into two types: external heat transfer and internal heat transfer.
    • The total heat transfer is the sum of external and internal heat transfer.

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    Test your understanding of the First Law of Thermodynamics, which states that energy cannot be created or destroyed, only converted from one form to another.

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