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The indicator diagram is used to calculate the work done and the power produced in an engine cylinder [2] or used in a compressor cylinder. The indicator diagram was developed by James Watt and his employee John Southern to help understand how to improve the efficiency of steam engines. [3]
The diagram enables calculation of the work performed and thus can provide a measure of the power produced by the engine. [ 4 ] To exactly calculate the work done by the system it is necessary to calculate the integral of the pressure with respect to volume.
Expansion of working fluid takes place isentropically and work is done by the system on the piston. The volume ratio V 4 / V 3 {\displaystyle V_{4}/V_{3}} is called the "isentropic expansion ratio". (For the Otto cycle is the same as the compression ratio V 1 / V 2 {\displaystyle V_{1}/V_{2}} ).
Thermodynamic work is one of the principal kinds of process by which a thermodynamic system can interact with and transfer energy to its surroundings. This results in externally measurable macroscopic forces on the system's surroundings, which can cause mechanical work, to lift a weight, for example, [1] or cause changes in electromagnetic, [2] [3] [4] or gravitational [5] variables.
The net work equals the area inside because it is (a) the Riemann sum of work done on the substance due to expansion, minus (b) the work done to re-compress. Because the net variation in state properties during a thermodynamic cycle is zero, it forms a closed loop on a P-V diagram.
In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol ) is a thermodynamic potential that can be used to calculate the maximum amount of work, other than pressure–volume work, that may be performed by a thermodynamically closed system at constant temperature and pressure.
In power engineering, the power-flow study, or load-flow study, is a numerical analysis of the flow of electric power in an interconnected system. A power-flow study usually uses simplified notations such as a one-line diagram and per-unit system, and focuses on various aspects of AC power parameters, such as Voltage, voltage angles, real power and reactive power.
This article uses the physics sign convention for work, where positive work is work done by the system. Using this convention, by the first law of thermodynamics, The yellow area represents the work done = + where W is work, U is internal energy, and Q is heat. [1] Pressure-volume work by the closed system is defined as: