Humidifier (complex)
File: humidifier complex.doc
Last edition: 2003-03-20/MK
Author: Lars Halling
History: 96-03-01/HN First released version
96-10-04/MK Updated to Menta 1.20
97-09-01/MK Updated to Menta 3.0
98-12-16/MK New file namne.
2003-03-20/MK Updated to Menta 4.0
Description
Model of humidifier (injection of saturated steam with temperature 100°C). The dynamics of the model is a simple first order system.
We use the (dry bulb) temperature and the relative humidity to define the state of the moist air entering the humidifier. Internally these properties are recalculated to enthalpy and humidity ratio using psychrometric relations. The state of the moist air leaving the humidifier may now be calculated in terms of enthalpy and humidity ratio simply by adding the contribution from the steam. Finally we convert back to temperature and relative humidity. The mass of steam injected into the air stream is assumed to be proportional to the control signal. Maximum steam injection (qmax) is achieved when uc = 100%. The nominal values for qmax and qair are selected to give 0.01 kg steam / kg air when uc = 100%.
REFERENCES:
ASHRAE. (1993):"1993 ASHRAE HANDBOOK, FUNDAMENTALS," SI-edition. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc, Atlanta.
Inputs
(Real) %RH before Humidifier. (FiA)
(Real) Temp. before Humidifier, °C. (TA)
(Real) Control signal, % (Uc)
Outputs
(Real) Temp. after Humidifier, °C. (TB)
(Real) %RH after Humidifier. (FiB)
Constants
(Real) qair = air flow through humidifier (m³/s). Nominal value = 5.0 m³/s.
(Real) qmax = maximum steam flow (kg/s). Nominal value = 0.06 kg/s.
(Real) Patm = atmospheric pressure (Pa) = 101315 Pa.
(Real) rho = density of air (kg/m³) = 1.2 kg/m³, at P = 101315Pa and 20°C.
(1993 ASHRAE HANDBOOK, FUNDAMENTALS).
(Real) c8-c13 = constants in calculation of saturation pressure, see (1993 ASHRAE HANDBOOK, FUNDAMENTALS).
(Real) hs = specific enthalpy for saturated steam at 100°C = 2675.4 kJ/kg
(1993 ASHRAE HANDBOOK, FUNDAMENTALS).