# Flows

Purpose: The job of flows is to fill and drain accumulations. The unfilled arrow head on the flow pipe indicates the direction of positive flow.

Selection and Placement:

- Select the flow icon by clicking once on the icon in the Building Block palette. Note that the default flow type is the uniflow, which flows in one direction only. To select a biflow from the drop-down palette, click and hold the flow icon, and select the bi-directional flow.

- Move the mouse to the desired starting location on the page.

- Click-and-hold.

- Drag the cursor to the place where the flow will end. Release the click. As you drag, the flow will follow your cursor movement.

Selection and Placement Notes:

- To bend a flow pipe, depress the shift key and change the direction of mouse movement as you drag the flow. Each time you depress the shift key, a 90 degree bend will be put in the flow pipe.

- To draw an outflow from a stock, be sure to start with the cursor inside of the stock. If you are not within the boundary of the stock when you begin dragging, your flow will be drawn with a cloud at its source.

- To draw an inflow to a stock, make sure that your cursor makes contact with the stock before you release your click. The stock will turn gray on contact to let you know to release your click. If you release the click prematurely, a cloud will appear at the destination end of the flow pipe.

- To replace a cloud with a stock, select the stock with the Hand tool. Drag the stock over the cloud. When the cursor (the tip of the index finger on the hand) is directly atop the cloud, the cloud will turn gray. Release your click, and the flow will be connected to the stock. The cloud will disappear.

Surface Operations: Figure 4-14 details surface operations which may be performed on a flow.

Figure 4-14 Surface Operations on Flows

Mapping Dialog Operations: When you open a flow in the Mapping mode, you'll enter its Mapping dialog. Figure 4-15 details the operations within this dialog.

Figure 4-15 Flow Dialog - Mapping Mode

Flow Mapping Dialog Notes:

- Uniflow vs. Biflow: Uniflow means that the flow will flow in one direction only. With uniflows, the flow volume will take on non-negative values only. On the other hand, biflows can take on any value. If you specify a flow as a biflow, a second, shaded arrowhead will appear on the flow to point the direction of negative flow. It is not possible to have a biflow connected to a conveyor, queue, or oven. Note that you can select uniflows or biflows directly from the drop-down list in the building block palette.

- Unit Conversion: When the flow is conserved (i.e., it connects two stocks), the unit conversion check box is enabled. Unit conversion enables you to convert the units of measure for the flow, as material moves through the flow pipe. Unit conversion is useful in modeling processes such as assembly processes which transform raw materials into finished goods, or chemical processes which involve molecular transformations. When you specify a flow as unit converted, a shaded half-circle will appear in the flow regulator on the diagram to indicate that unit conversion is taking place.

Modeling Dialog Operations: In the modeling mode, the flow dialog sports additional controls, as described in Figure 4-16.

Figure 4-16 Flow Dialog - Modeling Mode

Flow Modeling Dialog Notes:

- Required Inputs: The Required Inputs list contains a list of all inputs which have been connected to the flow using connectors. Anything in the Required Inputs list must be used in the equation definition for the flow.

- Unit Conversion: When Unit conversion has been checked, an additional field will appear in the flow dialog. As shown in Figure 4-17, the inflow multiplier can be a number. Alternately, it can be some model variable which appears in the Required Inputs list. What comes out of the upstream stock will be multiplied by the inflow multiplier, and then added to the downstream stock. When the model runs, the software will report the values for the flow, before unit conversion has taken place.

Figure 4-17 Flow Dialog - Unit Conversion