Why does turbulent mixing result in a reduction of pressure and an increase in temperature?

Question

For example, if i have a horizontal orifice plate in a tube and i'm pushing flow through it, there will be significant turbulent mixing downstream of the orifice plate. E.g. https://www.youtube.com/watch?v=KbTnJwaVUcQ&feature=youtu.be

This turbulent mixing will reduce the static pressure of the flow i believe, resulting in an increase in temperature due to conservation of energy. But i can't fully grasp this idea conceptually.

I think i struggle to conceptualize static pressure and temperature as being inversely proportional i.e. in my head an increase in temperature means particles are moving about more and if particles are moving about more they would exert a larger pressure in a confined box, so why does the pressure reduce in a flow when the temperature is increasing?

Answer 1

Piping systems that contain orifice plates are normally "open", meaning that they are practically never blocked in while full of liquid. This means that when turbulence results in fluid friction with a small amount of consequent heating, the liquid is free to expand slightly. As this expansion occurs, the liquid is flowing down its associated pipe due to a pressure gradient, meaning that the pressure is decreasing in the direction of flow. Thus, it is a normal operating condition for the liquid to heat slightly as the liquid pressure drops.