A manufacturing facility has a production line to fill its air conditioning systems with liquid refrigerant-134a. A throttling valve is used to reduce the pressure of refrigerant-134a before filling. If the throttling valve is replaced by a turbine, which can generate power, how mach can this turbine save in electricity cost?

What is known:

• Refrigerant-134a is at 0.3 MPa after throttling.
• Refrigerant-134a is at -4^oC and 1 MPa before throttling.
• The mass flow rate of refrigerant-134a is 200 kg/s.

• Determine the maximum power that the turbine can produce.
• If the turbine operates 8,760 hr/yr, and electricity costs the facility $0.08/kWh, how much can the turbine save per year?

• Take the turbine as a system. This is a control volume.
• Assume the turbine is adiabatic and the process is reversible. That gives,
  S₁ = S₂