Page 86 - DJJ20063- Thermodynamics 1
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DJJ20063- Thermodynamics 1
3.2.2 Explain non-flow energy equation
In a close system, although energy may be transferred across the boundary in the form of
work energy and heat energy, the working fluid itself never crosses the boundary. Any
process undergone by a close system is referred to as non-flow process.
The equation for non-flow process is given as follows:
U1 + Q = U2 + W
or, U2 – U1 = Q –W
In words, this equation states that in a non-flow process, the change in the internal
energy of the fluid is equal to the nett amount of heat energy supplied to the fluid minus
the nett amount of work energy flowing from the fluid.
This equation is known as the non-flow energy equation, and it will now be shown how
this may apply to the various non-flow processes.
3.2.3 Determine the properties for constant pressure, constant volume,
isothermal, adiabatic and polytrophic process for ideal gas.
a) Constant temperature (Isothermal) process (pV = C)
If the change in temperature during a process is very small then that process may be
approximated as an isothermal process. For example, the slow expansion or compression
of fluid in a cylinder, which is perfectly cooled by water may be analysed, assuming that
the temperature remains constant.
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