TFS · Heat Transfer · Problem 2PDFSolution in PDF ↓
TFS · Heat Transfer · Problem 2
Problem & Solution
Video Synthesis
Topic: Psychrometrics — A skylight is comprised of two layers of half-inch thick laminated glass with a 1-inch air gap with a thermal resistance R equals 0.5 in between.
Method: The inside and outside film coefficients are 1.5 and 2 respectively.
Key values: 6, Btu per hour per foot squared, 12 feet over K is the same thing, 1 foot over 12k equals 2
Reference: search the reference handbook for second metric chart, find that p
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Student questions asked in live office hours about this problem
OH 107
Q: Why does the maximum heat flux in this skylight problem equal the internal film coefficient times the temperature difference between inside air and dew point temperature?
A: The maximum heat flux is limited by when the inside glass surface cools to the dew point temperature—if it gets any colder, the air at that surface will saturate and condensation occurs, which becomes a constraint. As inside air contacts the cold glass surface, it cools at constant humidity ratio (moving left on the psychrometric chart), so relative humidity increases until reaching saturation at the dew point.