Common mistakes

Introduction

This page summarizes some common mistakes. Please read through these carefully to not make the same mistakes.

CAD preparation

Fluid domain

Almost all cases set up in ColdStream are about CHT problems, meaning that the heat will go through a solid and will be carried away by the coolant. To prepare for such a case, ColdStream expects that the users provide the fluid domain inside the STEP file. You can easily create the fluid domain by performing a boolean cut operation in your CAD environment to fill in the empty space.

❗️

Important

The fluid volume should be 1 connected volume. ColdStream does NOT allow the fluid domain to contain multiple disconnected pieces

Design domain

The design domain is the volume where ColdStream is allowed to create cooling structures. It should be fully inside its parent region (typically the fluid domain). In your CAD environment, the design domain is a separate volume from its parent region. We advise performing a boolean intersect operation to make sure it is fully within its parent region.

❗️

Important

The design domain should always be fully inside its parent region

Initialization file

Similarly to the design domain, the initialization file only contains the solid structures that fully overlap with the design domain, no parts can stick out. We again advise performing a boolean intersect operation.

❗️

Important

The initialization file cannot extend outside the design domain

Case setup

Pressure target when using a fixedFlowRateInlet

When using a fixedFlowRateInlet in ColdStream, you fix the amount of flow entering the domain independent of the pressure drop between in- and outlet. In a standard or custom design case, this means that ColdStream can keep on adding structures to improve the cooling performance. Without a pressure target to keep it in check, ColdStream could go to the trivial solution where it fully fills the design domain with solid material since you have both conduction and convection. The pressure drop will rise to + infinity, since an infinitely high pressure drop is able to push flow through a full solid block. This is of course not realistic

❗️

Important

Include a pressure target when using a fixedFlowRateInlet

Wrong initialization mode

Depending on the initialization mode selected, ColdStream will behave differently:

• When 'only add' is selected, ColdStream cannot change the solid structures of your initial design, it can only add more material around it or create new structures in the channels.
• When 'only remove' is selected, ColdStream can only take away material from your initial design, it will thus never be able to create new structures inside your existing channels
• With 'add and remove', ColdStream can change everything about your initial design

❗️

Important

The initialization modes work best in a specific scenario, depending on the performance of the initial design. Please contact the support team if you doubts about it.

Adding lots of constraints

Constraints give you as a user control over what Pareto optimal solution you would like to achieve. It is thus tempting to add lots of them. Do know that the more constraints you add, the longer it will take to get to the final result. You also risk that the problem becomes infeasible.

❗️

Important

Carefully think about which constraints to include. The more you include, the longer the runtime and the higher the risk of setting up an infeasible problem.