PIPE-FLO does not perform heat transfer calculations, nor does it have a specific tool for modeling both sides of a heat exchanger in one device. However, a user can employ the existing PIPE-FLO tools, the component tool and the X-Link plug-in, to achieve this functionality.

In the example system below, 90°F light oil needs to be cooled to 60°F at a flow rate of 500 gpm through a shell and tube heat exchanger. 50°F cooling water is available, but it cannot be discharged at temperature higher 70°F. The initial guess for flow rate on the cooling side is 200 gpm. Using PIPE-FLO and X-Link, the hydraulic resistances and flow rate for the cooling water can be found for the counter flow heat exchanger in the following model:

The shell and tube sides of the heat exchanger will be modeled separately using the component tool. With one Flow vs. dP point for each side, a second order resistance curve can be generated for the two components. In this example, the shell side has 5 psi dP at 500 gpm and the tube side has 4 psi at 200 gpm.

The pressure drops in the heat exchanger can now be calculated. The dP at the Shell Side reports as slightly higher than the 5 psi entered on the curve since flow is mass balanced and 500 gpm of 60°F Oil is equivalent to 507.1 gpm of 90°F oil.

The following relationship will be used to determine the required flow rate of the cooling water through the tube side of the heat exchanger required to meet the specified conditions:

This can be rearranged to directly solve for the mass flow rate through the cold (tube) side.

X-Link can now be employed to import the necessary data points into Excel, where the calculations can be made and the resulting flow rate returned. The fill column tool can be used to quickly retrieve information for several items from PIPE-FLO. In this case, it is used to retrieve the names of the fluid zones in the system.

Once the names are imported, standard cell references and fill techniques work well to generate the rest of the data. The functions and codes for X-Link can be found in the PIPE-FLO help files or downloaded as a pdf from the "Pull PIPE-FLO data into Excel using X-link" knowledgebase article. The link can be found in the related articles section at teh bottom of the page.

Fluid densities, temperatures and flow rates at the control valves are imported and used to calculate mass flow rates for use in the heat transfer equation. The initial cooling water flow rate at CV02 is included on the table for indication of the current setting.

 

The required mass flow of water is calculated in Excel and rounded to the desired PIPE-FLO input precision. X-link will assign values to PIPE-FLO at the maximum precision, so it is best to round these values in Excel where necessary.

Finally, the new volumetric flow rate for the 50°F water through CV02 is returned to PIPE-FLO using the pfeAssign function.





Returning to PIPE-FLO, the system model now reflects the change in flow rate at CV02 and the new dP at the tube side is calculated.