Originally Posted by stompk
So, when the baggage handler on the tarmac can see his breath, and the cars in the unloading zone have visible exhaust, what is your reason for jets on the taxi-way not having visible exhaust? What I hear you saying is the jet exhaust is so much hotter. Condensation occurs from the difference between exhaust temp (breath, jet exhaust) and ambient temperature. Therefore jets on the ground should show visible exhaust, like a car, when it's 20f and below, if the world worked as the way you suggest with your pseudo-science.
I've already described the process. In the case of the plane the exhaust is moving at hundreds of feet per second, and mixing into a VERY much larger column of air. I've only seen that process take place personally in local conditions of driving rain. In normal conditions the air is insufficiently humid to support the condensing mist, which evaporates away. If your visible breath lasts for a brief period of time, then how much more brief (and further away from the onlooker) may the transition from invisible to visible and back again be for a jet exhaust which is so much quicker?
The jet exhaust is a violent mixer... ...that's the difference. But it is not the only mixer.
In the case of contrails, the aircraft's WAKE VORTEX gathers up the jet trails in counter-rotating spirals. These large vortices may entwine and form VORTEX RINGS. The downward-falling pendules of a massive persistent contrail form from these vortex motions. The whole process is described here:
... without a trace of pseudoscience