HVAC · Heat-Transfer · Problem 20PDFSolution in PDF ↓
HVAC · Heat-Transfer · Problem 20
Problem & Solution
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Problem: A clean new domestic hot water heater uses 25 PSI saturated steam to heat 50GPM water from 60 to 130 degrees.
Given: 25 PSI saturated steam to heat 50GPM water from 60 to 130 degrees; 50GPM volume flow rate still entering at 60 degree...
Approach: After a year of operation, the overall filing factor is found to be 0.001 hour foot square degree F per BTU.
Key formula: formula is in the murm but this is the formula that we're going to derive fouling factor
Calc: What will the hot water supply outlet temperature be for the same 50GPM volume flow rate still entering at 60 degrees F but und...
Result: Now realistically on a test problem situation you're not going to be expected to iterate through a problem multiple times but you have to be able t...
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Student questions asked in live office hours about this problem
OH 97: HVAC: Heat Transfer-20
Q: In Heat Transfer 20 (fouled heat exchanger), what prompts you to iterate after initially calculating 103°F as the outlet temperature — wouldn't the fouling factor already account for the changed conditions?
A: The iteration is necessary because the LMTD correction factor F depends on the exit temperatures, which you don't know until after you calculate them — creating a circular dependency. You make an initial guess for the outlet temperature, calculate the heat transfer with F, then check whether the result is consistent with your assumed exit temperature, iterating until they converge.