When considering a 28 W/cm2 high heat flux application (250W IC at 30x30mm) with a fairly aggressive heat sink thermal resistance target below 0.2 oC/W (50 oC delta-T), heat sink solutions using two-phase devices are a likely option. But, choosing among a standard heat pipe, direct contact heat pipe, or vapor chamber solution requires a bit more analysis.
Here are 3 possible two-phase configurations: heat pipes embedded in an aluminum base, direct contact machined heat pipes, and a vapor chamber (direct contact) – Figure 1.
As shown in Table 1, the standard heat pipe solution has a delta-T above ambient of 53.9 oC (0.216 oC/W) with a baseline cost of 1X. By spending and additional 10% on this solution (cost of 1.1X), a solution where machined heat pipes make direct contact with the heat source results in an 8.5% improvement to the delta-T; down to 49.3 oC which equals a thermal resistance of 0.197 oC/W.
If a further reduction to delta-T is needed, a move to a direct contact vapor chamber reduces thermal resistance to 0.155 oC/W or 38.7 oC. The cost adder for this configuration is on the order of 15% from the standard heat pipe design.
Click here for the full analysis showing an additional 2 configurations
