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ahmedbadr
- 29
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i want to ask why heat transfer is considered ti be an irreversibility and why in carnot carnot cycle heat addititon is at constant temperature to make this process reversible
Mapes said:My advice is to link irreversibility in your mind not with "energy dissipation" but with "flow in response to a gradient that tends to erase that gradient." There are a couple advantages. First, gradient-induced flow is easy to quantify, by taking the dot product of the flow vector (in this case, heat flow and direction) with the mathematical gradient of the potential (in this case, the temperature). This dot product is actually proportional to the rate of entropy increase. Second, as you've pointed out, it's not easy to visualize "energy dissipation" when a hot object heats a cold object. It's an amorphous term (how is energy dissipated here?). But the gradient-induced flow view encompasses both friction (matter deforms in response to stress gradients, energy moves in response to temperature gradients) and simple heating/cooling. Swapping these descriptions in my mind was a key part of moving from beginner to advanced thermo.
A reversible process is a thermodynamic process that can be reversed by infinitesimal changes to the system, leaving no change in the surroundings. This means that the system can return to its original state without leaving any trace of the previous process.
The Carnot cycle is a theoretical thermodynamic cycle that is used as a benchmark to compare the efficiency of real-life heat engines. It consists of four reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
The efficiency of the Carnot cycle is defined as the ratio of the work output to the heat input. This means that it measures how much of the energy input is converted into useful work, with the rest being dissipated as waste heat.
Reversible processes are important in thermodynamics because they represent the ideal conditions for energy conversion. They serve as a benchmark for the maximum efficiency that can be achieved by real-life processes, and allow for the comparison and analysis of different systems.
No, it is not possible for a real-life process to be truly reversible. This is because all real-life processes involve some degree of irreversibility, such as heat transfer, friction, and other forms of energy dissipation. However, reversible processes serve as a useful theoretical tool for understanding and analyzing real-life systems.