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Thermodynamic System, Surrounding and Boundary:
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A system is defined as a quantity of matter or region in space chosen for the thermodynamic study. the mass or region outside the system is called the surroundings.

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the real or imaginary surface that separates the system from its surroundings is called boundary. the boundary of a system can be fixed or movable. mathematically speaking, the boundary has zero thickness and thus it can neither contain any mass nor occupy any volume in space.

system+ surrounding= universe.

enter image description here 1. Control Mass Mass is fixed by its quantity & identity. No mass can enter or leave the system. but the energy in the form of heat or work can cross-boundary. volume may change.

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No mass transfer ex: the mass of gas or vapour contained in an engine cylinder. enter image description here

2.Control Volume. Matter, as well as energy(heat, work), can cross-system boundary. The boundary of an open system is called control surface & they can be real, imaginary. enter image description here enter image description here

ex: most of engg. devices

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3. Isolated System

No interaction between system &surrounding. fixed mass & energy. No mass or energy. Transfer across the system boundary.

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ex: Thermo flask, the universe, etc.

Other examples of a closed system: lead-acid battery, weight on pre. cooker, refrigerator when its door is closed, a coil spring in an automobile, electric bulb, the air in football in play, a satellite orbiting earth.

Other examples of the open system: turbines, compressors, heat exchangers, nozzles, diffusers, open cycle gas turbine power plant, Tc engine, A window Ac, pressure cooker, a domestic water pump, ceiling fan, boiler, etc.

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