This model describes the cylindrical drum of a drum boiler, without assuming thermodynamic equilibrium between the liquid and vapour holdups. Connectors are provided for feedwater inlet, steam outlet, downcomer outlet, riser inlet, and blowdown outlet.

The model is based on dynamic mass and energy balance equations of the liquid volume and vapour volume inside the drum. Mass and energy tranfer between the two phases is provided by bulk condensation and surface condensation of the vapour phase, and by bulk boiling of the liquid phase. Additional energy transfer can take place at the surface if the steam is superheated.

The riser flowrate is separated before entering the drum, at the vapour pressure. The (saturated) liquid fraction goes into the liquid volume; the (wet) vapour fraction goes into the vapour volume, vith a steam quality depending on the liquid/vapour density ratio and on the avr parameter.

The enthalpy of the liquid going to the downcomer is computed by assuming that a fraction of the total mass flowrate (afd) comes directly from the feedwater inlet. The pressure at the downcomer connector is equal to the vapour pressure plus the liquid head.

The metal wall dynamics is taken into account, assuming uniform temperature. Heat transfer takes place between the metal wall and the liquid phase, vapour phase, and external atmosphere, the corresponding heat transfer coefficients being gl, gv, and gext.

The drum level is referenced to the centreline.

The start values of drum pressure, liquid specific enthalpy, vapour specific enthalpy, and metal wall temperature can be specified by setting the parameters pstart, hlstart, hvstart, Tmstart

Modelling options

The following options are available to specify the orientation of the cylindrical drum:


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