Watlow Heater Catalog
Reference Data (SI Unit)
Wattage Requirements Kilowatt-Hours to Superheat Steam 1. Plot points on lines P , Q and S . P represents the inlet temperature (and saturation pressure) of the system. Q represents the liquid content of the water vapor. S indicates the outlet temperature minus the saturated temperature. W indicates the heat content of the water vapor. 2. Draw a straight line from P through Q to W . Read W 1 . 3. Draw a straight line from P through S to W . Read W 2 . 4. Required watts = Weight (lbs) of steam/hour x (W 2 -W 1 ) Watt density is critical. Review temperature and velocity prior to heater selection. Example Shown: Q = 90% quality (% R.H.) P = 75 psig S = 320°F
Superheat Steam
450
0 10
400 300
Q
400
20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Gauge Pressure—lbs/in 2 85 90 95 100 100 200 300
150 100
350
300
50
Quality—% R.h.
25
250
10
Saturated Temperature—°F
400
0
210
P
500
600
Heat Content—Watt–hour/lb
700
Degrees of Superheat—°F
800
900
S
°F = °C * 9 / 5 + 32 1 lbs/in 2 (psi) = 6890 Pa 1 Watt-hour/lb = 7929.52 J/kg
W
Note: Reference is based on >80% steam quality at >20 psig.
542
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