HVAC · Thermodynamics · Problem 5PDFSolution in PDF ↓
HVAC · Thermodynamics · Problem 5
Problem & Solution
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Problem: Thermofive water at 400 psi and 700 degrees is in what thermodynamic state.
Given: 400 psi and 700 degrees is in what thermodynamic state; 400 psi; 400 psi is here and the temperature is 700
Approach: We can start with a hunch.
Calc: And now we know the temperature is 700 degrees F and the pressure is 400 psi.
Calc: 400 psi is here and the temperature is 700.
Result: So that means it is superheated vapor and the best answer choice is deep.
Office Hours
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Student questions asked in live office hours about this problem
OH 15: Thermo 5
Q: What thermodynamic state is water at 400 psi and 700°F, and can you provide examples of water in other states like saturated liquid, saturated mixture, and saturated vapor?
A: Water at 400 psi and 700°F is superheated because the saturation temperature at 400 psi is only 444°F, so the actual temperature of 700°F exceeds saturation. To identify states, use steam tables: if T and P match saturation values, you're on the saturation curve (need quality or enthalpy to pinpoint exact location); if T is higher than saturation at that P, you're superheated; if T is lower, you're subcooled.
OH 108: HVAC: Thermo Module #5
Q: What systematic approach or quick decision rules can I use to instantly know whether water is in a mixed saturated or superheated state to avoid wasting time flipping between steam tables on the PE exam?
A: There's no shortcut to instantly knowing the state without memorizing tables, which I don't recommend. Look for clues by evaluating whether temperature and pressure push you toward superheated or compressed liquid—but you'll develop speed only by actually using the steam tables repeatedly, so embrace the process rather than seeking a quick rule.