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In a practical heat engine, heat is generated by burning a fuel, work is extracted from this heat resulting in the working fluid cooling, and heat is then rejected at the lower temperature. As you must know, in an internal combustion engine heat is rejected both in the engine cooling system and the exhaust.
In a power plant, using water/steam as the working fluid in a closed cycle, there are four phases in the cycle: 1. Water is pumped at high pressure into a steam raising unit (boiler) 2. Heat from the fuel, be it coal, oil, gas, or nuclear, is added to the water causing it to become steam 3. the steam is expanded through a turbine doing work, that is driving the generator 4. the steam is condensed back to water using external cooling water. This is called the Rankine cycle. At stage 4 heat is being rejected into the external cooling water, and this heat is lost. It is minimised by running the condenser under vacuum so that steam at less than 100 celsius can still do work, and the final turbine discharge temperature is as low as 30C. Theoretically the efficiency of such a cycle is maximised by making the steam to the turbine as hot as material constraints allows, and the condenser vacuum as low as the local cooling water temperature will allow. The maximum practical efficiency of such a plant is about 42 percent, meaning that 58 percent of the heat from the fuel is rejected. For a PWR nuclear plant the steam temperature is much lower and the cycle efficiency is less, more like 30 percent.
I hope this enables you to see why in a practical heat engine there must be heat rejection. There are several entries in Wikipedia for further reading, see 'Heat Engines' first.
What else can I help you with?
Is heat rejection the same as heat dissipation?
No, heat rejection and heat dissipation are not the same. Heat rejection refers to the process of transferring heat from one place to another, such as releasing heat from a system into the surroundings. Heat dissipation, on the other hand, is the dispersion of heat within a system to lower its temperature.
What is heat rejection?
Heat rejection is the process of transferring heat energy from a system or material to its surroundings. This can occur through various mechanisms such as conduction, convection, and radiation, and is commonly used in cooling systems to dissipate excess heat. Heat rejection is essential in maintaining optimal operating conditions for many systems and devices.
What is the minimum number of stages that a steady state thermodynamic heat engine or heat pump can have?
If it only has 2 stages it really isn't an engine. It is possible to describe a heat engine/heat pump with 3 stages, but calculating the changes in thermodynamic properties, work, and heat in each stage can be difficult with only 3 stages. It is also extremely difficult to build an actual pump or engine that only uses 3 stages - you always seem to wind up with one that really has 4 stages with one of them being a very short stage between 2 of the 3 you meant to have. For all practical purposes, you will have at least 4 stages in a heat engine or heat pump.
What is the relationship between isentropic enthalpy and thermodynamic processes?
Isentropic enthalpy is a measure of energy in a system that remains constant during an isentropic process, which is a thermodynamic process where there is no change in entropy. In thermodynamic processes, isentropic enthalpy helps to analyze the energy changes that occur without considering any heat transfer or work done.
How can heat do work in a thermodynamic system?
Heat can do work in a thermodynamic system by transferring energy to the system, causing the system to expand and perform mechanical work. This process is governed by the first law of thermodynamics, which states that energy cannot be created or destroyed, only transferred or converted.
A quantity that gives the direction of a thermodynamic process is?
specific heat
Is heat a thermodynamic function?
what is heat a thermodynamic function
Is heat rejection the same as heat dissipation?
No, heat rejection and heat dissipation are not the same. Heat rejection refers to the process of transferring heat from one place to another, such as releasing heat from a system into the surroundings. Heat dissipation, on the other hand, is the dispersion of heat within a system to lower its temperature.
What is heat rejection?
Heat rejection is the process of transferring heat energy from a system or material to its surroundings. This can occur through various mechanisms such as conduction, convection, and radiation, and is commonly used in cooling systems to dissipate excess heat. Heat rejection is essential in maintaining optimal operating conditions for many systems and devices.
What is the minimum number of stages that a steady state thermodynamic heat engine or heat pump can have?
If it only has 2 stages it really isn't an engine. It is possible to describe a heat engine/heat pump with 3 stages, but calculating the changes in thermodynamic properties, work, and heat in each stage can be difficult with only 3 stages. It is also extremely difficult to build an actual pump or engine that only uses 3 stages - you always seem to wind up with one that really has 4 stages with one of them being a very short stage between 2 of the 3 you meant to have. For all practical purposes, you will have at least 4 stages in a heat engine or heat pump.
How do you solve Lenoir cycle?
To solve the Lenoir cycle, you need to analyze the thermodynamic processes involved, which include isentropic compression, constant pressure heat addition, isentropic expansion, and constant pressure heat rejection. Use the ideal gas law and thermodynamic equations to calculate the efficiency, work output, and heat transfer for each process. You can also utilize the equations for specific heat capacities and the properties of the working fluid to derive the necessary parameters. Finally, apply the first and second laws of thermodynamics to ensure the cycle adheres to energy conservation principles.
What is the relationship between isentropic enthalpy and thermodynamic processes?
Isentropic enthalpy is a measure of energy in a system that remains constant during an isentropic process, which is a thermodynamic process where there is no change in entropy. In thermodynamic processes, isentropic enthalpy helps to analyze the energy changes that occur without considering any heat transfer or work done.
How can heat do work in a thermodynamic system?
Heat can do work in a thermodynamic system by transferring energy to the system, causing the system to expand and perform mechanical work. This process is governed by the first law of thermodynamics, which states that energy cannot be created or destroyed, only transferred or converted.
Can you put the word thermodynamic is a sentence?
yes the word "thermodynamic" can be called a sentence. "THERMO" means heat and "DYNAMICS means motion or movement. -Thermodynamic refers to the study of heat and temperature and their relation to energy and work.
What does an isothermal PV diagram illustrate about a thermodynamic process?
An isothermal PV diagram illustrates a thermodynamic process where the temperature remains constant.
What does the adiabatic process graph illustrate about the relationship between temperature and pressure in a thermodynamic system?
The adiabatic process graph shows that as temperature increases, pressure also increases in a thermodynamic system. This relationship is due to the fact that in an adiabatic process, no heat is exchanged with the surroundings, so changes in temperature directly affect pressure.
What is an adiabat?
An adiabatic process is a thermodynamic process, there is no gain or loss of heat.
