Question

If the blade efficiency is 80% and the stage efficiency is 60%, what is nozzle efficiency of a DeLaval turbine?

• A. \( 70% \)
• B. \( 75% \)
• C. \( 80% \)
• D. \( 85% \)

Hint:

For an impulse turbine stage, the stage efficiency is the product of nozzle efficiency and blade efficiency. This relationship is crucial for analyzing the performance of such turbines. Remember that efficiencies are often given as percentages but should be used as decimal values in calculations.

Answer 1

The Correct Option is B

Step 1: Understand the efficiencies involved in a steam turbine stage.
In a steam turbine, the overall efficiency of a stage (stage efficiency) is a product of its individual component efficiencies. For a single-stage impulse turbine like a DeLaval turbine, the stage efficiency (\( \eta_{stage} \)) is the product of the nozzle efficiency (\( \eta_{nozzle} \)) and the blade efficiency (\( \eta_{blade} \)). \[ \eta_{stage} = \eta_{nozzle} \times \eta_{blade} \]
Step 2: Identify the given efficiencies.
Blade efficiency \( \eta_{blade} = 80% = 0.80 \).
Stage efficiency \( \eta_{stage} = 60% = 0.60 \).
Step 3: Calculate the nozzle efficiency.
Rearrange the formula from Step 1 to solve for nozzle efficiency: \[ \eta_{nozzle} = \frac{\eta_{stage}}{\eta_{blade}} \] Substitute the given values: \[ \eta_{nozzle} = \frac{0.60}{0.80} \] \[ \eta_{nozzle} = \frac{6}{8} = \frac{3}{4} = 0.75 \] Convert to percentage: \[ \eta_{nozzle} = 0.75 \times 100% = 75% \] The final answer is $\boxed{\text{2}}$.