TFS · Practice Exam 1 · Problem 40PDFSolution in PDF ↓
TFS · Practice Exam 1 · Problem 40
Problem & Solution
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- Problem: Equal mass flow rates of water and a 5050 glycoil water mixture with specific equipacity of .75 BTU per pound degree Fahrenheit flow on either side of a shell and tube heat exchanger water enters at 9...
- Key values: 75 BTU
- ✅ Answer: D
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Student questions asked in live office hours about this problem
OH 117 · March 30, 2026
Q: Why doesn't the heat exchanger effectiveness formula from the reference handbook work for this problem, and is a solution of water leaving at 51°F and glycol leaving at 90°F valid?
A: The formula does work and those temperatures are valid — the issue was that the student had the hot and cold stream labels swapped. Since glycol has a lower specific heat capacity (0.75 vs. 1.0 for water) and mass flow rates are equal, glycol is C_min and will undergo the larger temperature change, confirming glycol is the cold stream and water is the hot stream.