In which component is the energy balance described by q = h2 - h1?

In which component is the energy balance described by q = h2 - h1?

• A. Boiler
• B. Turbine
• C. Condenser
• D. Pump

Answer: (A)

When a steady-flow device has negligible shaft work, the first-law energy balance simplifies to q = h2 − h1, where h is specific enthalpy. In a boiler the fluid undergoes a large enthalpy rise as it is heated from liquid water (state 1) to steam (state 2) with little or no mechanical work being done by the system. That means the heat added to the fluid equals the enthalpy change, so q = h2 − h1 is positive and represents the heat transfer into the fluid. In other components, work is exchanged: turbines produce shaft work and have q ≈ 0, condensers remove heat (q < 0), and pumps involve small heat transfer with enthalpy changes tied more to pumping work than heat input. Hence the boiler is the component where the energy balance takes the form q = h2 − h1.

When a steady-flow device has negligible shaft work, the first-law energy balance simplifies to q = h2 − h1, where h is specific enthalpy. In a boiler the fluid undergoes a large enthalpy rise as it is heated from liquid water (state 1) to steam (state 2) with little or no mechanical work being done by the system. That means the heat added to the fluid equals the enthalpy change, so q = h2 − h1 is positive and represents the heat transfer into the fluid. In other components, work is exchanged: turbines produce shaft work and have q ≈ 0, condensers remove heat (q < 0), and pumps involve small heat transfer with enthalpy changes tied more to pumping work than heat input. Hence the boiler is the component where the energy balance takes the form q = h2 − h1.