EBSILON®Professional Online Documentation
If you do the identification of a component property (e.g. efficiency or k*A for a heat-exchanger), you can use the calculated reference polynomial for improving the calculation of the component. This applies to all components, which
Normally, in the off-design mode, the efficiency or the k*A is calculated from the corresponding nominal value and from one or more characteristic lines. This determines the behaviour of the component and the missing results for the outlet lines can be calculated.
If you want to identify a component, you have to use a different off-design calculation mode, where you can specify the outlet values. The efficiency or the k*A is calculated in this case. Such a calculation mode is called "Identification Mode" for the component. For instance, for the feed water preheater, FSPEC = Outlet temperature T2 is specified. In this mode, T2 is used as given from outside and k*A is calculated. For the steam turbine, either FCHR = Power specification or FCHR = H2 given (the corresponding ETAI is then calculated).
To use an adaptation polynomial, you must
In the mode FADAPT = "Replace", the part load behaviour of the component is determined by the adaptation polynomial, without considering the characteristic lines. In the mode FADAPT = "Correct", the adaptation polynomial is considered as a correction factor to the characteristic lines. See the corresponding component description for details.
The transfer of the polynomial determined by EbsIdent to the adaptation polynomial sheet must be done manually. You find the polynomial determined by EbsIdent at the end of the corresponding log file. You may use the Windows clipboard (Ctrl+C / Ctrl+V) to copy the text, but you have to do certain modification to the text of the polynomial. The reason is that the adaptation polynomial is not evaluated by EbsScript, but instead by the EBSILON®Professionalcalculation kernel itself. Therefore, certain restrictions have to be considered:
o Addition,
o Subtraction,
o Multiplication,
o Division,
o Power (which can be written here by ^, e.g. 2^3 = 8, or by the EbsScript notation "pow (2,3)")
o The mathematical function abs, acos, asin, atan, ceil, cos, exp, floor, log, log10, max, min, sin , sqrt, tan (for details see EbsScript functions)
o The conditional "?" (the expression x ? y : z is evaluated to y, if x != 0, else to z )
o You may refer to the values of the lines connected to the corresponding component by the attribute name:
o p (pressure),
o t (temperature),
o h (enthalpy),
o m (mass flow),
o v (specific volume) or
o i (Index value),
followed by the number of connection. For instance, m1 is the inlet mass flow on line 1, t4 is the temperature on line 4.
The attribute „i” makes a cross-reference to any line in the cycle possible. For this have to place an index value (component 45) on the designated line and set the FTYP of this component to the value (e.g. pressure or temperature) that should be applied in the polynomial. Thereafter a number must be entered in this component 45 under FIND (higher than 0, e.g. 4711). This number also has to be written in the polynomial after “i” (e.g. i4711). This way a reference to this line value is created in the polynomial.
The application of the names q (performance / heat flow) and VM (volume flow) in the polynomial is not possible. These attributes have to be represented as product (q = m*h and respectively vim = v*m).
Generally, you should be aware that adaptation polynomials that cause a large deviation from the standard behaviour of a component, can have a negative influence on the convergence behaviour. The software assumes that you use these polynomials for a small correction only.
During the identification process, you are calculating the components in an identification mode (see last section). If it is possible for you to use the identification mode permanently, you can compare the resulting value (e.g. for the efficiency or k*A) from the calculation of your model with the corresponding value of the polynomial. In this case, you can evaluate the polynomial with EbsScript. The ratio between the result of the model calculation and the result of the polynomial is called quality factor.
EbsScript offers a convenient function to calculate quality factors automatically:
qualityFactors (index, result);
The"index" is an integer variable that refers to the id of the identification item in your EbsIdent configuration. The"Result" is a real value containing the resulting quality factors.
If you use this function, you do not have to perform any manual specifications for adaptation polynomials. The function "qualityFactors" automatically considers the polynomial in the way they are stored in the ".ref" files.