# Governing equations vs Transport equations

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 Register Blogs Members List Search Today's Posts Mark Forums Read July 15, 2019, 08:25 Governing equations vs Transport equations #1 Senior Member   Mandeep Shetty Join Date: Apr 2016 Posts: 179 Rep Power: 8 This is a basic question. But I did not find any explanations for this. How are governing equations, like mass, momentum, energy conservations equations, different from 'Transport equation'?. Is a conservation equation, like energy equation (heat equation), a transport equation for the temperature?   July 15, 2019, 09:49 #2
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Filippo Maria Denaro
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 Originally Posted by granzer This is a basic question. But I did not find any explanations for this. How are governing equations, like mass, momentum, energy conservations equations, different from 'Transport equation'?. Is a conservation equation, like energy equation (heat equation), a transport equation for the temperature?

Transport equation is a general denomination for the advection-diffusion PDE, see https://en.wikipedia.org/wiki/Convec...usion_equation
The equation is not necessarily related to a flow problem, for example they are often referred as to the transport of chemical species (advecion velocity prescribed).

On the other hand, when we use the conservative form of mass, momentum and total energy we could see those as a more complex expression of the simple advection-diffusion equation.

Do not worry if you read in literature some discrepancy   July 15, 2019, 10:19 #3 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,021 Rep Power: 60   The mass, momentum, and energy equations (and many others) in CFD are indeed transport equations. The heat equation is a transport equation for the internal energy (or enthalpy depending on formulation) and an equation of state is usually invoked to write in with temperature as the primitive variable. In general (widespread in non-fluids fields), a governing equation need not be a transport equation and a transport equation need not be a governing equation. A governing equation need not be a conservation either (economics, the stock market, etc...). In fluids, the main governing equations that you play with just happen to be transport equations based on the principles of mass, momentum, and energy conservation laws and they all are referring to the same thing. granzer likes this.  Tags governing equations, navier stokes equation, transport equation Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post AlanLJ STAR-CCM+ 1 January 2, 2016 14:47 LuisAlberto OpenFOAM Programming & Development 5 August 24, 2015 05:33 joel.lehikoinen OpenFOAM Programming & Development 9 October 3, 2013 08:00 David harvey FLUENT 1 January 31, 2004 06:15 123 Main CFD Forum 6 August 10, 1998 09:05

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