Physics Help Forum First law over constricting pipe section

 Oct 8th 2018, 03:38 AM #1 Junior Member   Join Date: Oct 2018 Posts: 1 First law over constricting pipe section So i am trying to get a sense of the change in internal energy for a fluid that flows through a constricting pipe ($\displaystyle d_{out}  Oct 8th 2018, 11:14 AM #2 Senior Member Join Date: Jun 2016 Location: England Posts: 703 Please clarify your naming conventions. I don't want to have to look up the first law and work out what is what. __________________ ~\o/~  Oct 9th 2018, 04:00 AM #3 Junior Member Join Date: Sep 2014 Location: Brasília, DF - Brazil Posts: 28 You forgot the gravitational energy and since your fluid is incompressible:$\displaystyle U_{in}\approx U_{out}\$. It is possible to describe the Bernoulli equation by means of the first law of thermodynamics. __________________ Work on: General thermal systems Cryogenics Micro-drop fluid mechanics