valve energy losses

[tc7]

I am looking for a basic explanation of the energy loss due to pressure drop through a valve or orifice. I understand the drop in static pressure is accompanied by a increase in velocity head and these can be summed up to determine the total energy lost across the valve. But! most references seem to simply state these losses result in fluid temperature rise and leave it at that. My question is why is there a temp rise? is it simply a matter of fluid turbulence causing molecules to crash into each other? or is there a better theory that I am missing?
Thanks for any thoughts or referrals on this.
Tom

 

[quark]

You are right. Increased velocity cuases increase in momentum and energy is lost due to increased collisions and this results in temperature rise.

 

[owlscreech]

Also it is the result of viscous shear: the velocity of fluids are not the same throughout the flow stream. Therefore there is relative movement of infinitesimal layers of fluid against each other. Relative movement means friction because of the same collision effect you spoke of earlier, only in the context of the helter-skelter movement of molecules in turbulant flow. This effect becomes dominant with very low Reynolds numbers, i.e. laminar flow.