Page 254 - Handbook of Energy Engineering Calculations

− 50 = 900°F (482.2°C). From the steam tables find the saturation
2
temperature of steam at 1200 lb/in (abs) (8273 kPa) as 567.2°F (297.3°C).
Hence the steam will be superheated when it leaves the boiler.

2. Compute the boiler evaporator coolant outlet temperature
Incoming feedwater enters the boiler evaporator section where it is heated by

the NaK before entering the boiler steam section. To provide heat transfer
between the NaK leaving the evaporator section of the boiler and the
incoming boiler feedwater, a temperature difference between the two fluids is

necessary. Assume that the NaK coolant leaves the boiler evaporator section
at a temperature 40°F (22.2°C) higher than the incoming feedwater. With the
incoming feedwater at the saturation temperature, or 567.2°F (297.3°C), the
NaK coolant outlet temperature from the boiler evaporator = 567.2 + 40 =
607.2, say 607°F (319.4°C).

3. Plot the boiler coolant temperature path
Locate the boiler outlet steam state on the h-t diagram, Fig. 2, on the 1200-
2
lb/in (abs) (8273-kPa) pressure curve and the 900°F (482.2°C) temperature
horizontal. From this point, project vertically upward to the 950°F (510°C)
NaK temperature horizontal to locate point 1, the temperature of the NaK
entering the boiler, Fig. 2.
Next, locate the point 1a where the liquid enthalpy line of the h-t diagram,
2
Fig. 2, intersects the 1200-lb/in (abs) (8273-kPa) evaporation enthalpy line.
From point 1a, project vertically upward to 607°F (319.4°C), point 2, the
temperature of the NaK coolant leaving the boiler evaporator section.

Points 1 and 2 are the NaK temperature path in the boiler evaporator and
steam-generating sections. Assuming that the NaK has a constant specific
heat while flowing through the boiler evaporator and steam-generating
sections (a completely valid assumption), draw a straight line between points
1 and 2 and extend it to intersect the 550°F (287.8°C) temperature line at

point 3. Note that point 3 represents the temperature of the NaK entering the
intermediate heat exchanger.

4. Determine the boiler feedwater inlet temperature
Feedwater enters the boiler at a yet unknown temperature. During passage

between the boiler inlet and the evaporator section inlet, the feedwater