A fuel mixer configured to provide a fuel-air mixture to a combustor of an engine. The fuel mixer may include a mixer body having a mixer outer wall, a center body, an annular passageway defined between the mixer outer wall and the center body, and a fuel tube assembly placed circumferentially about the mixer body. The fuel tube assembly may include at least one fuel channel for injecting a fuel flow into the annular passageway. The fuel tube assembly may be configured to cool a boundary layer flow present in the annular passageway. The fuel tube assembly may be configured to cool the mixer outer wall, the center body, or both the mixer outer wall and the center body. Heat from the mixer outer wall, the center body, or both the mixer outer wall and the center body, may pass to the fuel flow in the fuel tube assembly.