a) Working fluid : For working of cyclic process (i.e. whose initial and final state is same) to receive and reject heat, some working fluid is required, which absorbs and rejects heat to produce work of expansion, e.g. Working fluid in petrol enfiine is a mixture of air and petrol. In case of steam turbine, working fluid is steam while in case of gas turbine, working fluid is gas.
(b) Heat source and heat sink : According to 2nd law of thermodynamics, for working
of heat engine, at least two thermal reservoirs are required. Working fluid will
receive heat from heat source and rejects heat to heat sink.
(c) Arrangement to get work output: To get work of expansion, some arrangement is
required for circulation of fluid. It may be piston and cylinder as in case of I.C.
or it may be rotating shaft and casing as in case of turbine.