What is the first law of thermodynamics and its significance?
ANSWER: The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. It signifies the principle of energy conservation, which is crucial for analyzing energy ...
Fundamentals of Engineering Thermodynamics With
worked Examples A+
What is the first law of thermodynamics and its significance?
ANSWER: The first law of thermodynamics states that energy cannot be created or destroyed,
only transferred or converted from one form to another. It signifies the principle of energy
conservation, which is crucial for analyzing energy flows in thermodynamic systems.
Explain the concept of enthalpy and its application in thermodynamics.
ANSWER: Enthalpy is the total heat content of a system, defined as the sum of its internal
energy and the product of pressure and volume. It is used to calculate the heat transfer in
processes occurring at constant pressure, such as in heating and cooling applications.
What is the difference between an open system and a closed system in thermodynamics?
ANSWER: An open system allows both mass and energy to cross its boundaries, such as a steam
turbine, while a closed system permits only energy transfer, like a sealed piston-cylinder device.
Define specific heat capacity and its importance in thermodynamic processes.
ANSWER: Specific heat capacity is the amount of heat required to raise the temperature of a unit
mass of a substance by one degree Celsius or Kelvin. It is essential for calculating the heat
exchange in heating, cooling, or phase change processes.
What is the second law of thermodynamics, and how does it apply to energy systems?
ANSWER: The second law of thermodynamics states that energy transformations are not 100%
efficient, and some energy is always dispersed as unusable heat. It explains the direction of
energy transfer and the concept of entropy in energy systems.
How is the Carnot cycle the basis for understanding thermodynamic efficiency?
ANSWER: The Carnot cycle represents an idealized thermodynamic cycle that operates between
two temperatures, providing the maximum possible efficiency for a heat engine. It sets a
benchmark for evaluating real-world systems.
Describe the four stages of a Carnot vapor refrigeration cycle.
ANSWER: The Carnot vapor refrigeration cycle consists of:
1. Isentropic compression: The refrigerant is compressed, increasing its pressure and
temperature while entropy remains constant.
2. Isothermal heat rejection: The refrigerant rejects heat to the surroundings at a constant
high temperature, condensing into a liquid.
3. Isentropic expansion: The refrigerant expands, reducing its pressure and temperature
while maintaining constant entropy.
, 4. Isothermal heat absorption: The refrigerant absorbs heat from the low-temperature space,
evaporating back into a vapor.
Provide an example of a Carnot vapor refrigeration cycle in operation.
ANSWER: Consider a Carnot refrigeration cycle operating between a freezer at -20°C and an
ambient environment at 30°C. The refrigerant absorbs heat from the freezer space during
isothermal heat absorption, keeping the freezer cold, and rejects heat to the ambient environment
during isothermal heat rejection, completing the cycle.
What is entropy, and why is it important in thermodynamic analysis?
ANSWER: Entropy is a measure of the disorder or randomness of a system. It is crucial for
determining the feasibility of thermodynamic processes and analyzing energy losses due to
irreversibilities.
How does the concept of reversibility apply to thermodynamic systems?
ANSWER: A reversible process is an idealized process that occurs without any entropy
generation or energy dissipation. Reversibility helps define the maximum efficiency of
thermodynamic systems and serves as a reference for real-world processes.
Explain the concept of thermal efficiency and its calculation for a heat engine.
ANSWER: Thermal efficiency is the ratio of the work output of a heat engine to the heat input. It
is calculated as the difference between the heat added and heat rejected divided by the heat
added.
What factors influence the performance of a vapor compression refrigeration system compared to
a Carnot refrigeration cycle?
ANSWER: Factors include the irreversibilities in real-world components, non-ideal refrigerant
behavior, frictional losses, and heat transfer limitations. Unlike the Carnot cycle, real systems
cannot achieve maximum efficiency due to these practical constraints.
What is the role of a compressor in a refrigeration cycle?
ANSWER: The compressor increases the pressure and temperature of the refrigerant, enabling it
to reject heat to the surroundings and cycle back to the evaporator for heat absorption.
WORKED EXAMPLE>
A Carnot vapor refrigeration cycle operates between thermal reservoirs at 44 °C°C and 3030 °C°C. The
working fluid is saturated vapor at the end of the compression process and saturated liquid at the
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