In a turbine, the fluid expands almost

ANS:C - adiabatically

In a turbine, the fluid expands almost adiabatically. A turbine is a device that converts the energy of a moving fluid (liquid or gas) into mechanical energy by allowing the fluid to flow over blades mounted on a rotor. In many practical cases, the expansion of the fluid through the turbine occurs rapidly and without significant heat exchange with the surroundings. This type of process is known as adiabatic expansion. In an adiabatic process, there is no heat exchange between the system (the fluid passing through the turbine) and its surroundings. As the fluid expands through the turbine blades, it does work on the turbine, causing the rotor to spin and produce mechanical energy. Since there is no heat exchange, the temperature of the fluid typically changes, leading to an adiabatic temperature change. Therefore, the fluid expands almost adiabatically in a turbine.