Applied Thermodynamics(heat rejec on)
Note 1: Heat Addi on and Rejec on Defini ons
Heat addi on and rejec on refer to the transfer of heat energy into or out of a thermodynamic
system. When heat is added to a system, the system's internal energy increases, leading to an
increase in temperature. Conversely, when heat is rejected from a system, the system's internal
energy decreases, leading to a decrease in temperature.
For example, consider a pot of water on a stove. When the stove is turned on, heat is added to the
pot of water, increasing its internal energy and temperature. If the pot is removed from the stove,
heat is rejected from the pot of water, decreasing its internal energy and temperature.
Note 2: Heat Transfer Modes
Heat can be transferred in three different modes: conduc on, convec on, and radia on. Conduc on
is the transfer of heat energy through a solid material due to the collision of par cles. Convec on is
the transfer of heat energy through a fluid medium due to the movement of the fluid. Radia on is
the transfer of heat energy through electromagne c waves.
For example, consider a hot plate on a stove. When the stove is turned on, heat is conducted from
the stove element to the hot plate, increasing its temperature. The hot plate then transfers heat to
the surrounding air through convec on, and the surrounding objects through radia on.
Note 3: Heat Addi on and Rejec on Processes in Thermodynamic Cycles
Heat addi on and rejec on processes play a cri cal role in thermodynamic cycles. A thermodynamic
cycle is a series of processes that a thermodynamic system undergoes, ending up in its ini al state. In
a thermodynamic cycle, heat is added to the system in some parts of the cycle and rejected from the
system in other parts of the cycle.
For example, consider a power cycle. In a power cycle, heat is added to the system (usually a gas) in a
high-temperature part of the cycle, and then the gas expands, doing work. A er that, the gas is
cooled down, and heat is rejected to the surroundings. The cycle repeats, and power is generated.
Note 4: Heat Addi on and Rejec on Processes in Refrigera on Systems
Heat addi on and rejec on processes are also crucial in refrigera on systems. A refrigera on system
is a device that cools a space or object by removing heat from it and rejec ng it to the surroundings.
The refrigera on cycle consists of four processes: heat rejec on, compression, heat addi on, and
expansion.
For example, consider a refrigerator. The refrigerator uses a refrigerant that circulates through the
system, absorbing heat from the food inside the refrigerator and rejec ng it to the surroundings.
During the heat rejec on process, the refrigerant is cooled down by the condenser, and then the
high-pressure refrigerant enters the expansion valve, where its pressure drops, and it cools further.
The cold refrigerant then enters the evaporator and absorbs heat from the food inside the
refrigerator. The cycle repeats, and the food stays cool.
Note 1: Heat Addi on and Rejec on Defini ons
Heat addi on and rejec on refer to the transfer of heat energy into or out of a thermodynamic
system. When heat is added to a system, the system's internal energy increases, leading to an
increase in temperature. Conversely, when heat is rejected from a system, the system's internal
energy decreases, leading to a decrease in temperature.
For example, consider a pot of water on a stove. When the stove is turned on, heat is added to the
pot of water, increasing its internal energy and temperature. If the pot is removed from the stove,
heat is rejected from the pot of water, decreasing its internal energy and temperature.
Note 2: Heat Transfer Modes
Heat can be transferred in three different modes: conduc on, convec on, and radia on. Conduc on
is the transfer of heat energy through a solid material due to the collision of par cles. Convec on is
the transfer of heat energy through a fluid medium due to the movement of the fluid. Radia on is
the transfer of heat energy through electromagne c waves.
For example, consider a hot plate on a stove. When the stove is turned on, heat is conducted from
the stove element to the hot plate, increasing its temperature. The hot plate then transfers heat to
the surrounding air through convec on, and the surrounding objects through radia on.
Note 3: Heat Addi on and Rejec on Processes in Thermodynamic Cycles
Heat addi on and rejec on processes play a cri cal role in thermodynamic cycles. A thermodynamic
cycle is a series of processes that a thermodynamic system undergoes, ending up in its ini al state. In
a thermodynamic cycle, heat is added to the system in some parts of the cycle and rejected from the
system in other parts of the cycle.
For example, consider a power cycle. In a power cycle, heat is added to the system (usually a gas) in a
high-temperature part of the cycle, and then the gas expands, doing work. A er that, the gas is
cooled down, and heat is rejected to the surroundings. The cycle repeats, and power is generated.
Note 4: Heat Addi on and Rejec on Processes in Refrigera on Systems
Heat addi on and rejec on processes are also crucial in refrigera on systems. A refrigera on system
is a device that cools a space or object by removing heat from it and rejec ng it to the surroundings.
The refrigera on cycle consists of four processes: heat rejec on, compression, heat addi on, and
expansion.
For example, consider a refrigerator. The refrigerator uses a refrigerant that circulates through the
system, absorbing heat from the food inside the refrigerator and rejec ng it to the surroundings.
During the heat rejec on process, the refrigerant is cooled down by the condenser, and then the
high-pressure refrigerant enters the expansion valve, where its pressure drops, and it cools further.
The cold refrigerant then enters the evaporator and absorbs heat from the food inside the
refrigerator. The cycle repeats, and the food stays cool.
