Liquid Controls SP4000 - Manual (Page 26)

23
SP4000 Flow Computer
3.11 Steam Net Heat
Measurements:
A flowmeter measures the actual volume flow in a steam line. A temperature and a
pressure sensor are installed to measure temperature and/or pressure. All measurements
are made on the steam side of a heat exchanger.
Calculations:
• Density, mass flow and net heat flow are calculated using the steam tables stored in
the flow computer. The net heat is defined as the difference between the heat of the
steam and the heat of the condensate. For simplification it is assumed that the
condensate (water) has a temperature which corresponds to the temperature of
saturated steam at the pressure measured upstream of the heat exchanger.
• Saturated steam requires either a pressure or temperature measurement with the
other variable calculated using the saturated steam curve.
• Optional steam trap monitoring using compensation input.
Input Variables:
Superheated Steam: Flow, temperature and pressure
Saturated Steam: Flow, temperature or pressure
Output Results:
• Display Results
Heat, Mass or Volume Flow Rate, Resettable Total, Non-Resettable Total,
Temperature, Pressure, Density, (optional: peak demand, demand last hour,
time/date stamp)
• Analog Output
Heat, Mass or Volume Flow Rate, Temperature, Pressure, Density, Peak
Demand, Demand Last Hour
• Pulse Output
Heat, Mass or Volume Total
• Relay Outputs
Heat, Mass or Volume Flow Rate , Total, Pressure, Temperature Alarms, Peak
Demand, Demand Last Hour
Applications:
Monitoring the thermal energy which can be extracted by a heat exchanger taking into
account the thermal energy remaining in the returned condensate. For simplification it is
assumed that the condensate (water) has a temperature which corresponds to the
temperature of saturated steam at the pressure measured upstream of the heat exchanger.
STEAM NET HEAT
Net Heat Flow
Net Heat Flow = Volume flow • density (T, p) • [E
D
(T, p)– E
W
(T
S(p)
)]
E
D
= Specific enthalpy of steam
E
w
= Specific enthalpy of water
T
S(p)
= Calculated condensation temperature
(= saturated steam temperature for supply pressure)
Calculations
Steam Net Heat
Illustration
Flowmeter Temperature
Transmitter
PRINT
5
0 –
TIME
CLEAR
•
MENU
ENTER HELP
TEMP
4
PRE 1
3
RATE
2
TOTAL
1
GRAND
6
SCROLL
7
PRE 2
8
DENS
9
Pressure
Transmitter
Water
Steam
*
* or Steam Trap Monitor