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When real fluid flows in a pipe due to fluid's viscosity pressure energy of fluid is converted to heat. What I don't quite understand is the mechanism in which this happens. When heat is created it inreases average kinetic energy of molecules in a fluid shouldn't that inrease fluid pressure since pressure of a fluid is connected to the average kinetic energy of its molecules. More energy they have they can transfer more momentum on pipe during collision and thus bigger pressure. I think I don't quite understand what pressure of a fluid is as term in Bernoulli's equation, what causes it. Any constructive answer is appreciated.

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"Viscous Heating" is a bit of a misnomer. When viscous deformational work is done on a fluid, the mechanical energy is converted, not into heat, but into internal energy. Of course, for a gas, the internal energy increase is accompanied by a temperature increase, but the pressure does not have to increase if the specific volume increases. In the case of a nearly incompressible liquid, changing the temperature does not need to directly affect the pressure.

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