Steam-side film coefficient (rule of thumb): For preliminary design under ordinary conditions, a reasonable steam-side heat transfer coefficient is about ________ kcal/hr·m²·°C.

Introduction:
When sizing condensers or reboilers quickly, engineers often use a steam-side film coefficient based on condensation of saturated steam on clean surfaces with good drainage. This provides an order-of-magnitude estimate for overall heat-transfer coefficients before detailed calculations and vendor data are available.

Given Data / Assumptions:

• Condensing steam on the shell or tube side under ordinary conditions.
• Clean surfaces; reasonably good condensate drainage; non-condensables minimal.
• Coefficient expressed in kcal/hr·m²·°C (engineering units as stated).

Concept / Approach:
Film condensation coefficients for saturated steam on metallic surfaces typically fall in the several thousand to more than ten thousand kcal/hr·m²·°C range depending on orientation, surface condition, and condensate behavior. A common rule-of-thumb value used for preliminary design is approximately 7000–8000 kcal/hr·m²·°C, with 7500 being a representative number.

Step-by-Step Solution:
Select an estimate consistent with ordinary, clean conditions.Use the mid-range rule-of-thumb ≈ 7500 kcal/hr·m²·°C.Adopt 7500 as the design placeholder pending detailed checks.

Verification / Alternative check:
Textbook examples and vendor literature show similar magnitudes for film condensation, with adjustments for orientation, non-condensables, and flooding.

Why Other Options Are Wrong:

• 1250 or 2500: Too low for clean condensing steam films; might reflect gas-side coefficients.
• 15000: Possible in special cases but high for ordinary conditions.
• 500: Far too low.

Common Pitfalls:
Ignoring the significant impact of non-condensables, condensate flooding, and surface condition, which can lower the effective coefficient substantially.

Final Answer:
7500