Heat loads produced by electronics inside a mobile device are increasing as more computing power is packed into them. During the design phase of a product, these loads have to be taken into account. Simulations provides a way to try different designs more quickly, and built-in optimization tools help to find the most suitable solution.
Vapor chambers are thin heat spreaders that offer very high spreading capabilities without adding too much thickness to a low profile device. They work by evaporating water to steam, which transfers heat away from a heat source to the cooler regions of the chamber. This means that to simulate a vapor chamber correctly it would require simulating phase changes and rapid mass flows in very thin volume. This would consume a lot of computing time, which makes it unusable in detailed simulation in the system level models. Therefore, a simpler model has to be developed. A few of these exist, but they were considered to be too complex for the current application. The goal of this thesis was to develop a behavioral model, which would model the vapor chamber as one domain in the CFD simulation model.
Experimental data was taken as the basis of the behavioral model. The measurements were done with a 0.6 mm vapor chamber and a 3 mm copper reference sample. The experimental setup was replicated into a commercial CFD simulation software and the model was tuned to match with the calibration sample. Then, using the tuned model, the thin vapor chamber was simulated by assuming various thermal conductivity values.
Data from the simulations were compared to the experiments by using RMSE minimization. It produced a function that described how the vapor chamber’s effective conductivity changes with temperature. To use the algorithm built into the CFD software, a linear approximation was applied to the function. The linearization provided parameters that enabled to create a temperature dependent material model that was used in the one cuboid behavioral model of the vapor chamber
