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An isothermal process is a type of thermodynamic process in which the temperature T of a system remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and a change in the system occurs slowly enough to allow the system to be continuously adjusted to the temperature of the reservoir through heat exchange (see quasi-equilibrium).
The PV diagram is a particularly useful visualization of a quasi-static process, because the area under the curve of a process is the amount of work done by the system during that process. Thus work is considered to be a process variable , as its exact value depends on the particular path taken between the start and end points of the process.
This Process Path is a straight horizontal line from state one to state two on a P-V diagram. Figure 2. It is often valuable to calculate the work done in a process. The work done in a process is the area beneath the process path on a P-V diagram. Figure 2 If the process is isobaric, then the work done on the piston
Isothermal : The process is at a constant temperature during that part of the cycle (=, =). Energy transfer is considered as heat removed from or work done by the system. Energy transfer is considered as heat removed from or work done by the system.
Working fluids are often categorized on the basis of the shape of their T–s diagram. An isentropic process is depicted as a vertical line on a T–s diagram, whereas an isothermal process is a horizontal line. [2] Example T–s diagram for a thermodynamic cycle taking place between a hot reservoir (T H) and a cold reservoir (T C).
Isothermal transformation diagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic scale). They are generated from percentage transformation-vs time measurements, and are useful for understanding the transformations of an alloy steel at elevated temperatures.
A diagram of a generic thermodynamic system An important concept in thermodynamics is the thermodynamic system , which is a precisely defined region of the universe under study. Everything in the universe except the system is called the surroundings .
The definition of = allows us to rewrite this as d F = − S d T − p d V . {\displaystyle \mathrm {d} F=-S\,\mathrm {d} T-p\,\mathrm {d} V.} Because F is a thermodynamic function of state , this relation is also valid for a process (without electrical work or composition change) that is not reversible.