HVAC · Practice-Exam-2 · Problem 63PDFSolution in PDF ↓
HVAC · Practice-Exam-2 · Problem 63
Problem & Solution
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Topic: Pipe flow / fluid mechanics — 50 degree water enters a steam boiler with a capacity of 200 boiler horsepower.
Method: The boiler has an operating pressure of 10 psi g.
Key values: 33,470 BTU per hour per boiler HP and that equals 6 million 694, ,000 BTU per hour, 5,861 pounds per hour and we want GPM so we
Reference: look up in the reference handbook search measurement relationships
✅ Answer: A
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Student questions asked in live office hours about this problem
OH 122 · June 8, 2026
Q: In a boiler problem, why is standard liquid water density used to convert mass flow rate to volume flow rate, rather than accounting for the density change as water transitions from saturated liquid to saturated vapor?
A: The density calculation applies only to the entering condition (subcooled liquid), not the mixed saturated state after heating. Since the system is steady flow, mass flow rate is constant throughout, so working backwards to find the inlet volume flow rate only requires the inlet density. At 10 psiG, liquid water behaves as essentially incompressible, so standard water density is appropriate.