Condenser mixture of gases — computing total condenser pressure from partial pressures In a steam condenser, the partial pressures are: steam = 0.06 bar and air = 0.007 bar. What is the total condenser pressure?

Introduction / Context:
Exhaust spaces in condensers often contain a mixture of saturated steam and non-condensable gases (air, dissolved gases released from feedwater). Understanding how partial pressures combine to determine the total back pressure is key to evaluating condenser performance and turbine/engine efficiency.

Given Data / Assumptions:

• Steam partial pressure p_steam = 0.06 bar.
• Air partial pressure p_air = 0.007 bar.
• Ideal-gas behavior for the gas mixture; total pressure equals sum of partial pressures.

Concept / Approach:
Dalton’s law of partial pressures states that the total pressure of a mixture of non-reacting gases equals the sum of the partial pressures exerted by each component. In a condenser, saturated steam coexists with air; the absolute back pressure is the sum of their partial pressures. Lowering the air content (via effective air extraction) reduces the total back pressure and improves plant efficiency.

Step-by-Step Solution:
Write total pressure: p_total = p_steam + p_air.Insert values: p_total = 0.06 + 0.007.Compute: p_total = 0.067 bar.Therefore, the condenser pressure is 0.067 bar.

Verification / Alternative check:
At p_steam = 0.06 bar, the saturation temperature is around 36–37°C. The small additional air partial pressure raises total back pressure slightly, matching practical observations.

Why Other Options Are Wrong:

• 0.06 or 0.007 bar: each ignores the other constituent.
• 0.053 bar: subtracts instead of adding.
• 0.600 bar: off by an order of magnitude.

Common Pitfalls:
Confusing gauge with absolute pressure, or forgetting that even a small air partial pressure materially increases total back pressure.

Final Answer:
0.067 bar