Basics

Up to 10 WT cells are available, virtually any interconnection is possible, each inlet of the two "sides" of each WT can be fed from up to 6 inflows.

Tip: If 6 inflows are not sufficient, a "functionless" heat exchanger can be interposed, with each side increasing the possible inflows by a factor of 6. The mixing temperatures are obtained by linear averaging weighted by the "mass flow". In terms of the method, this "mass flow" physically represents a "water value flow" (mass flow times spec. heat capacity), which means that mergers of material flows of different substances can also be included in the process. However, in the case of noticeable heat shading during mixing, this must be taken into account by installing an auxiliary heat exchanger with supply or removal of the appropriate heat flow.

After starting the NETWORK chapter, a menu with 3 options appears, the first two of which contain the coupled design of heat exchangers in the network, but offer only limited editing options.

Both for the network design with coupled heat exchanger design, as well as for general investigations on WT networks, the 3rd option (=without WT design) is started with. For a later coupled heat exchanger design, however, the specified mass flow unit "kg/s" must not be changed in order to avoid subsequent error messages and corrections.

In the first two options, deletion is deactivated to ensure consistent numbering of the WT in the network and in the "outer" network. The first WT layout is done in the 2nd option (First layout). First select "Load network" in the "Form" under "File", then select the WT one after the other (double-click) and start WT recalculation. The menu "Basic data input" of WTS appears. During the calculation, a file name for the currently calculated WT must be entered.

A final editing can be done in the first option. After starting, a list appears in which, to the left of the number of the WT assigned in the network, the name of the file belonging to it is to be entered, which must exist. In this option, if necessary, new target efficiencies can also be specified, which causes a redesign of the WT in question.

In the two options with heat exchanger design, each heat exchanger can or must be assigned a type (default is "without evaporation or condensation"). For this purpose, "Set heat exchanger type" is activated in the network under Options. Double-click on a heat exchanger symbol to enter the exchanger type.

For each WT in the network must be specified:

Both efficiencies, as well as the inflow as relative mass flow to both WT sides (sum of up to 6 possible inflows = 1).

The inflow can be a medium with a known temperature (specify medium number with prefix "M"), or it can come from another WT (specify WT number and side). In the network mode, this information is determined automatically from the circuit diagram.

New file, Load file, Save, Save as, Check, Calculate, Network, Recalculate WT, Paste WT, Copy WT, Delete WT, Append WT, Network on

Change input field with image keys, change input column with [Ctrl ->] or [Ctrl <-], overwrite mode is default, change to insert with Insert key.

In the form, the inflow flows appear only as "relative mass flows", whose sum must be one for each side of a WT. In the network, the mass flows can be entered either as "absolute mass flows" or as "water value flows" (the displayed unit "kg/s" can be exchanged for any unit of your choice in the network, options menu "Set mass flow unit").

If the unit is to represent a water value current, select "J/Ks" as the unit or "w" as the identifier for it.

The consistency of the entries is rigorously checked automatically before calculation (balances for WT, nodes and total network, for the mass flow unit "J/Ks" or "w" also efficiency check).

The data of the editor form and the network image are mutually mapped to each other when switching over. It is recommended to start a new project with the network design (network mode).

Here the form supports the basic functions (like calculating.. ), the efficiencies of the heat exchangers, the temperatures of the media inlets and a project identification can or must be entered here.

In the form under "Options" it is possible to switch from "Network on" to the form mode (with the answer for "yes"), from which the network is no longer accessible. In the form mode, only calculations can be made, the necessary entries of the data for the "circuit" (inflow and rel. mass flow) must be made manually.

In addition, an "intermediate mode" can be set (answer for "no"), but in this case, for example, entered circuit data is automatically saved over when returning from the network.

Insert a node by pressing the left mouse button and dragging the mouse. What type of node is drawn must be selected in the menu beforehand: There are 3 types of heat exchanger symbols (horizontal, vertical and cross rectangles). The "Side 1" is yellow and the "Side 2" of each heat exchanger symbol is filled in blue.

Furthermore, there are symbols for medium inlet (orange) and for outlet (filled in gray). A symbol for pipe nodes (green) facilitates the creation of clear circuits.

Pipe symbols are drawn (after selection in the menu) by clicking the origin node from the then visible central square to the destination node. Afterwards, this still straight line can be clicked and reshaped (dragged) by means of the then visible black square.

The size of the symbols cannot be changed. Moving (move) is always possible except in pipeline mode.

With the option "align" in the menu, everything is aligned again to "grid places" after shifts (then compensate for errors that become visible and select "align" again in the menu). By moving the mouse to the symbols and double-clicking, an input window appears with an explanation of the data input that is then possible. The input of mass flow or water value flow data is only possible in this way and only in the network (because more data is required for the description of the entire network than for the pure network calculation in the form mode).

In the network, the check of the mass flow balance can be requested under "Help". When returning to the form, such a balance is also carried out within the network analysis, as well as the preparation of the network data for the calculation. When returning to the network, the temperature results are written on the pipe symbols.

Under "Options" you will find the option to enter the mass flows again instead (the temperatures of the heat exchangers can still be viewed under "Help").

Under "Edit", the "select all" menu can be used to either "adjust" the entire image (which may be necessary several times during the creation of a network: move the mouse pointer to one of the selected symbols, press the left mouse button and drag), or to delete the entire image content.

The "select mode" should work similarly, after which a rectangle can be drawn with the mouse. When releasing the left mouse button, the nodes within the rectangle are selected. Currently, the nodes selected in this way cannot be moved together, but they can be deleted.

When combining different media, noticeable heat tints can occur which require a correction of the mixing temperatures. This correction can be approximated without iteration using an auxiliary heat exchanger (not a real heat exchanger) and an auxiliary medium:

Let DT be the heating of the water value flow w1 of the mixture flow on side 1 of the auxiliary heat exchanger to be simulated. Then select the inlet temperature of the auxiliary medium on side 2 of the auxiliary heat exchanger approximated to "w1 temperature + DT/P1", the water value flow w2 = w1, and for the efficiencies P1 and P2 the same small value, such as 0.01.

In the network, names and/or designations (up to approx. 55 characters) can be assigned to the automatically consecutively numbered heat exchangers under "Help", option "Note WT designation". This assignment is retained during all editing operations (deletion of heat exchangers, etc.).

Here, in particular, auxiliary WT can also be marked and thus distinguished from structurally designed WT.

The option "Note ME designation" can be used to characterize the media entries in the same way.

Checked

1.     Are the used medium inlet temperatures available?

2.     Are the inflows all realized with respect to heat exchanger outlets?

3.     Are the efficiencies available and are they all between > zero and < one?

4.     Are the rMp_x between zero and one?

5.     Are the inflow sums equal to one?

6.     Are both WT sides connected in each case?

7.     Are there at least 2 different media entries?

8.     Are the requested inlet temperatures different?

The tests are usually sufficient to identify a heat exchanger network that cannot be calculated.

For "Calculate", the following types of errors, which are only to be considered as potential errors (warnings), are tolerated: 2, 5, 13, 15 and 16.

Where the displayed error occurs is indicated at the end of each error line.

Error type 1:             Medium index too large

Error type 2:             Warning: Should inlet temperature really be zero?

Error type 3:             Mass flow specification missing

Fault type 4:             Inflow from non-existent WT required

Error type 5:             Note: WT feeds itself

Fault type 6:             Inflow side of the feeding WT unknown

Error type 7:             Mass flow "out of range

Error type 8:             No mass flow or total mass flow > 1 on page 1

Error type 9:             Total mass flow too small on page 1

Error type 10:          No mass flow or total mass flow > 1 on page 2

Error type 11:          Total mass flow too small on page 2

Error type 12:          Efficiency "out of range" for side 1 or 2

Error type 13:          Warning: Should only one inlet temperature <> zero?

Error type 14:          Inlet temperatures are all zero

Error type 15:          Warning: There are equal inlet temperatures <> zero

Error type 16:          Warning: The inlet temperatures requested by WT are the same