Understanding Carnot's Cycle & Reversible Processes

In summary: Carnot cycle is necessary in order to have a net work output and complete the cycle. The isothermal processes ensure that heat flow occurs with minimal temperature differences, while the adiabatic processes allow for a decrease in temperature before the next isothermal process begins, resulting in a net work output. This combination of processes is essential for the efficiency of a Carnot cycle. In summary, in order to have a complete and efficient Carnot cycle, both reversible isothermal and reversible adiabatic processes must be used. This allows for minimal temperature differences and a decrease in temperature before the next process begins, resulting in a net work output.
  • #1
anigeo
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Why is it so that along with reversible isothermic processes , reversible adiabatic processes must be taken up to complete carnot's cycle?
 
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  • #2
anigeo said:
Why is it so that along with reversible isothermic processes , reversible adiabatic processes must be taken up to complete carnot's cycle?
There are two things that are required of a Carnot cycle:

1. In order to be reversible, heat flow must only occur where there is an infinitessimal temperature difference between the system and the reservoirs. So all heat flow must be isothermal.

2. In order to make it a complete cycle, the isothermal expansion must be followed by some kind of compression.

If there was an isothermal compression that started at the end point of the isothermal expansion, there would be no net work done. The compression has to require less work to accomplish than the work that is done on the isothermal expansion. This means the temperature has to decrease before the compression can begin. Since heat flow has to occur with an infinitessimal temperature difference, there can be no heatflow as the temperature decreases. So the temperature reducing expansion has to be adiabatic. Thus an adiabatic expansion has to be inserted after the isothermal expansion so that the compression can begin at a lower temperature and require less work to get back to the original state.

Following the adiabatic expansion, isothermal compression begins and is then followed by an adiabatic compression so the first part of the next cycle, the isothermal expansion, can occur at the temperature of the hot reservoir - higher temperature.

AM
 

1. What is Carnot's cycle and why is it important in thermodynamics?

Carnot's cycle is a theoretical thermodynamic cycle that describes the most efficient way to convert heat into work. It is important in thermodynamics because it provides a benchmark for the maximum efficiency that any heat engine can achieve.

2. How does Carnot's cycle work?

Carnot's cycle consists of four reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. In each process, the system either absorbs or releases heat while doing work, resulting in a net conversion of heat into work.

3. What is a reversible process?

A reversible process is a thermodynamic process that can be undone by exactly reversing each step. This means that the system and its surroundings return to their original states, and no energy is lost or wasted. Reversible processes are idealized and do not occur in real-world systems, but they provide important theoretical insights into the behavior of thermodynamic systems.

4. How does Carnot's cycle relate to the second law of thermodynamics?

Carnot's cycle is based on the second law of thermodynamics, which states that heat always flows spontaneously from a hot object to a cold object. Carnot's cycle demonstrates that the maximum efficiency of a heat engine is dependent on the temperature difference between the hot and cold reservoirs.

5. What are some real-world applications of Carnot's cycle?

Carnot's cycle is used to understand and design various heat engines, such as steam turbines and internal combustion engines. It also plays a role in the design of refrigeration and heat pump systems. In addition, Carnot's cycle is the basis for the concept of thermodynamic efficiency, which is important in many industrial processes.

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