What is equipment model

The constituent parts of an equipment model are:

Variables/Properties

Types of variables:

Input
Output
State

The constituent parts of a variable are:

a value (single or multidimensional)
a unit of measure (uom)
data type (real, integer, boolean, reference, etc)
valid ranges (optional)
default value (optional)
description

The constituent parts of a unit of measure are:

type (mass flow, etc)
multiplier and
bias

For instance, temperature is available both in Fahrenheit and Celsius degrees and the conversion is F = 1.8*C +32. The multiplier is 1.8 and the bias term is 32. Also, the default uom for a given uom type, is marked with a multiplier of 1 and a bias of 0.

Set of equations/algorithms and constraints

Only the fundamental equipment models, which are not specified as aggregates of other models, are specified directly by their transfer function Y=F(X). The constraints are related not only to laws of nature (water below freezing point is not liquid any more) but with constraints posed by individual process units. For example there may be a maximum capacity for a given equipment block.

All these can be incorporated in the generic mathematical expression Y=F(X), where X, Y are respectively arrays of input and output variables to an equipment block.

Derived models also have constraints, not only those that are inherited from its constituent parts, but also new constraints that involve one or more unit operations.

Interface

The interface of an equipment model specifies the inputs and outputs of that model.

The entry/exit points of the interface are the only means of connecting to/from the equipment model when using it in constructing another model (either equipment or process area). Every input and output of the interface has the following properties:

declared functionality (a description of its normal usage)
normal composition

The input/output attribute is relative to the flow of the species through it.

for a positive flow – into the equipment, it is an input.
for a negative flow – out of the equipment, it is an output.

Symbol

Each instance has a graphical representation. There are a set of symbols available to choose from, in the parent Model of the Instance. One symbol is the default, which is assigned to the Model Instance when the Instance is created, and it can be changed with other symbol from the list of symbols of Instance’s Model. The symbol can be represented by: an image; a set of basic graphical shape objects( e.g. line, rectangle, circle, ellipse, text etc ).