Hello I’ d like to have your thoughts about any temperature variation when a fluid passes through a narrower part of a tube, a subject quite rarely discussed.. Can we start with « perfect Bernoulli conditions »and an incompressible fluid having only translational energy,. flowing theough a perfectly insulated tube. When the fluid passes through the restriction, we can assume I believe that an average molecule’s total energy is unchanged. Although the energy is more concentrated along the direction of the tube,can we assume that energy exchange with the walls of the narrower part of the tube will be unchanged ? And that there will be no temperature change ? Now the fluid is hotter than the surrounding air and the tube is not insulated. When the fluid passes through the narrower part of the tube, can we assume that as collisions of molecules against the walls of the tube are less frequent, that energy transfer from the hot fluid to the colder wall will be reduced and that therfore the walls of the narrower part of the tube will be colder ?