Init Macro, UDF, Initial Temperature CFD Simulation

Description

In this project, we performed a numerical simulation using ANSYS Fluent software’s User-Defined Function (UDF). For this CFD product, we used Init Macro to write UDF programming. We considered a simple double-pipe heat exchanger.

The heat exchanger is a device for heat transfer between cold and hot sides. Hot water flows in the inner pipe, and cold water in the outer pipe. Heat transfer leads to heating the outer tube and cooling the inner tube.

First, we modeled the geometry in 3D with Design Modeler software., Then, we meshed the model with ANSYS Meshing software. Meshing is Structured, and 147,200 cells are created. Finally, we numerically simulated the current model based on the CFD method by ANSYS Fluent software.

Methodology (UDF)

In this project, initialization must be done with high accuracy to improve the quality and accuracy of heat transfer. In the initialization, the cold and hot sides must be defined.

But there is a problem. You can only initialize a fixed temperature value for the entire model domain, While you need to initialize two different temperatures for two different parts of the domain. In these cases, you can use the patch method.

First, create a region within the model domain and then define a different temperature for the new region using the patch method. But we can do it in another way. We can create a region in the model by defining a function regarding spatial coordinates and the desired temperature for that region.

So, we used a User-Defined function (UDF) to initialize fluid temperature. We must use the Init Macro (DEFINE_INIT macro) for this UDF.

Conclusion (UDF)

After completing the calculation, we will review the results. We checked the results using several temperature contours in different cross-sections of the model domain. First, we obtained the contours after initialization (before starting the simulation run process).

The contours showed that the temperature in the inner tube of the heat exchanger is different from the temperature in the outer tube of the heat exchanger. We conclude that we have defined the UDF correctly, and this UDF has been correctly applied to the model.

After ensuring the UDF works correctly, we start the final solution process. Then, we examine the temperature contours. The results show that the heat transfer occurs correctly inside the heat exchanger.