Correct Answer - Option 2 : Irreversible
Explanation:
Throttling (Isenthalpic) process:
A throttling process occurs when a fluid flowing through a passage suddenly encounters a restriction in the passage. The restriction could be due to the presence of an almost completely closed valve or due to sudden and large reduction in flow area etc.
The result of this restriction is a sudden drop in the pressure of the fluid as it is forced to flow through the restriction. This is a highly irreversible process and is used to reduce the pressure and temperature of the refrigerant in a refrigeration system.
Since generally, throttling occurs in a small area, it may be considered as an adiabatic process (as the area available for heat transfer is negligibly small) (δQ = 0) also since no external work is done (W = 0).
h1 = h2
Though throttling is an expansion process, it is fundamentally different from expansion taking place in a turbine. The expansion of a fluid in a turbine yields useful work output and can approach a reversible process (e.g. isentropic process), whereas expansion by throttling is highly irreversible.
