I did some basic calculations on isotropic heat loss in a circular tube. I don't have the knowledge to model it in detail but I don't think this is correct.
You can set tube height to something tiny like 5mm. It takes a fraction of a second to fill that.
As someone who's printed a lot, on fast printers you have to set a minimum layer time because it takes up to 20 seconds for the layer below to solidify, cool to below the glass transition. Plastic is a bad conductor so heat loss through the walls probably isn't as bad as you'd think
I own a 3D pen and I use it to repair and tweak prints. Sometimes I use it to fill small cavities with material. The surrounding area usually doesn’t enjoy the heat, but PLA definitely can be injected to a degree. Maybe not to fill thin channels in the infill, but to fill a few strategically placed and shaped voids, yes.
You can set tube height to something tiny like 5mm. It takes a fraction of a second to fill that.
As someone who's printed a lot, on fast printers you have to set a minimum layer time because it takes up to 20 seconds for the layer below to solidify, cool to below the glass transition. Plastic is a bad conductor so heat loss through the walls probably isn't as bad as you'd think