Material Models

Function of Material Models

Material models depict mass and energy flows.

Available Material Models

The following material models are available in TOP-Energy:

Component Template Library and Project Explorer

The Material Models are stored in a separate folder of the same name in the Component template library.

When a new project is started, the material models are already in the Component Library of the project (see following figure).

How Material Models Work

To view and adjust the properties of a material model, drag the material model component from the Component Library to the scheme and open the form by double-clicking on the component (see following slider).

You can change the color of the net in the Network representation form (see the following figure).

The material model component can be removed from the scheme with the <del> key.

If a second material model (e.g., MM_Thermal_Oil) is to be created in parallel to an existing material model, the material model component (e.g., MM_Water) can be copied by drag-and-drop while holding down the <ctrl> key; and the copy then can be adapted (see following figure). For example, density and heat capacity values can be changed.

To assign the appropriate material model to a net, right-click on the pin to open the context menu and select the material model, e.g., MM_Thermal_Oil (see following slider).

For reasons of clarity, the nets (colored connecting lines) of the individual material models can be hidden individually from the scheme.

Material Properties

Some material models have different functions. You can select which function is used for each scheme in the Simulation ribbon in the Material properties group (see figure below).

While the scheme or one of its components is active (  Scheme or component selected in the Project explorer), you can use the split buttons to select whether

Validity

The selection of the material property (e.g., Energy only or Temperature dependent) applies to all nets and components to which the material model is assigned. If there are two separate circles in which the same material model is to be used with different properties (e.g., Energy and Temperature dependent), create a copy of the material model. The drop-down list of the split button for the material properties will then show all material models of this type created on the scheme (see following figure).

Change

When changing from one function of the material model to another, e.g., from material property Temperature dependent to Energy, all input and output data that are no longer needed, e.g., the inlet and outlet temperatures, are deleted. When changing to the opposite direction, these are restored or filled with default values after saving the project. You need to manually restore the connections to the pins.

A warning appears before any data entered are deleted.

MM_Water

The material model MM_Water describes liquid water as an ideal liquid. With this material model you can choose whether the simulation is carried out only on the basis of energy flows or whether the Flow (outlet) and Inlet temperatures are considered in the simulation.

Energy

If only the Energy is considered, the model is smaller and the simulation may run a little faster. If the temperatures are not interesting, this selection is recommended.

Temperature Dependent

When selecting the material property Temperature-dependent, the Flow (outlet) temperature must be specified for all components (e.g., boiler, heat demand). From this, a system of equations is created with which, after optimization, the mass and energy balances are solved and all remaining inlet or mixing temperatures are calculated. In this way, restrictions of the temperatures can be considered, e.g., if temperatures must not fall below a certain value. This is advantageous when heat generators with different temperature levels are connected in series or mixing temperature conditions of heat generators connected in parallel have to be considered.

The input field for the Flow temperature (see following figure) and the corresponding output fields Inlet temperature and Temperature difference of the heat Transfer medium (water) are only displayed for the material property Temperature dependent and not for Energy.

When switching from energy to temperature dependent, the following warning appears, which you can confirm with OK.

Conversely, when switching from Temperature dependent to Energy the following warning appears, which you also can confirm with OK.

MM_Type_of_Fuel

The Fuel material model uses an elementary composition of carbon, hydrogen, sulfur, nitrogen, and oxygen. The Fuel liquid/solid material model additionally considers the proportions of water and ashes in its composition. It is based on the assumption of an ideal liquid or an ideal solid. For the Fuel gaseous and Fuel liquid/solid models, you can choose whether only the Energy or also the Composition is to be considered.

Energy

If Energy is selected, the fuel is only considered as an energy stream. In a boiler, for example, the efficiency with which thermal energy is obtained from fuel energy can be specified. The selection of the material property Energy makes the model smaller, reduces the calculation time, and spares you the specification of the fuel composition, combustion numbers, etc.

If the fuel model Energy is selected, no pins for connecting the Fresh Air component are displayed on the connected technical components, such as Hot Water Boilers or CHP units.

Considering Composition

The Considering composition option takes into account the material composition of the fuel, the specific proportions of carbon, hydrogen, etc. The combustion, e.g., in the boiler and in the gas turbine, is calculated stoichiometrically.

This is an advantage, if, e.g., for a boiler, the energetic information is not given by the ratio of heat output to fuel output, but by the ratio of heat energy to fuel volume flow. Then the information about the density and thus also the composition of the fuel is needed. A combustion calculation is also necessary if, as in tutorial 51, a boiler is connected to an exhaust heat recovery system.

The section Combustion calculation (see following figure) appears only when the Considering composition property is selected.

When switching from Energy to Considering composition, the following warning appears, which you can confirm with OK.

Conversely, when switching from Considering composition to Energy the following warning appears, which you also can confirm with OK.

Further Information

The articles on the special features of the individual material models provide information on the use and properties: Special Features of Cold and Heat, Steam Special Features, etc.

The Alternative property model calculation option can be enabled for some components in the Notes and tooltip → Developer options form to use a different formulation that is more favorable for the steam condition, for example.