Building a Closed-Loop Liquid Cooling Simulation in Simcenter FLOEFD: Challenges and Solutions

In thermal simulations, liquid cooling is often used to manage heat dissipation in high-performance electronics. While open-loop cooling systems can be simulated using "Fluid Subdomains" with assigned velocity inlet and pressure outlet boundary conditions, achieving a closed-loop system requires additional considerations. This article explores the challenges in modeling a closed-loop liquid cooling system and provides solutions for ensuring stability and accurate thermal performance.

Challenges in Creating a Closed-Loop Model

A common challenge in transitioning from an open-loop to a closed-loop system is ensuring continuity between the inlet and outlet. The goal is to simulate an external pump that maintains a constant fluid flow rate while ensuring that the temperature of the fluid entering the inlet matches that of the fluid exiting the outlet.

Approaches to Achieving a Closed-Loop System

Two primary methods can be used to maintain the same inlet temperature as the outlet temperature:

1. Using a Surface Goal for Temperature

• A surface goal is defined for the temperature at the outlet.
• The inlet temperature is then set to match this value using formula dependency.

2. Using an Internal Fan to Link Inlet and Outlet

• An internal fan is defined with a characteristic curve containing only one point at the required flow rate (with an arbitrary pressure drop).
• The outlet is designated as the surface where fluid enters the fan, and the inlet is where the fluid exits.

The internal fan method is generally preferred as it directly links the inlet and outlet, but it may introduce instability in the simulation. In such cases, a goal-dependent boundary condition can be used instead, which decouples the inlet from the outlet and improves stability.

Addressing Implementation Issues

One challenge that arose during implementation was that the surface goal temperature did not appear as an available option in the inlet boundary condition settings. Additionally, the simulation was being run in a steady-state mode, which further complicated parameter dependency.

Solution: Creating a Parameter for Goal Dependency

• A parameter must first be created and assigned to the goal value representing the outlet temperature.
• This parameter can then be used for the boundary condition at the inlet.

However, a common issue encountered was that the parameter did not appear in the formula definition for the inlet boundary condition, leading to errors when manually entering it.

Resolution and Further Resources

To resolve this, it is important to correctly define the parameter within the software’s settings. More details on how to create and use parameters can be found in Siemens' documentation:
Siemens Help Documentation.

Conclusion

Building a closed-loop liquid cooling simulation requires careful consideration of temperature continuity and stability. While the internal fan method is generally preferred, using a goal-dependent boundary condition can provide a more stable alternative in cases where simulation instability occurs. Properly defining parameters within the software is crucial to ensuring accurate boundary condition assignments.

By following these approaches, a closed-loop liquid cooling system can be successfully modeled, leading to more accurate thermal simulations and better cooling system designs.