7 replies to this topic

[panagiotis]

Hello everyone,
Have you ever calculated the temperature rise of fluid due to friction of the pipe?

I would approach by applying an energy balance between two points of the pipe.

Do you have anything further to share with me?

I already searched in my favourite search engine! ????

[latexman]

If the fluid is gas/vapor (you did not say), the solution is well known and well documented as adiabatic compressible flow.

[panagiotis]

Thank you Latexman for your answer. Indeed I forgot to mention that I am referring to gas. I will search it then as adiabatic compressible flow.

[panagiotis]

Well by a quick searching I can't really find something that can really answer my question!

[latexman]

Then you are not looking hard enough. There is lots of information. Look in your university thermo text. Look in Perry’s. Look in Crane Technical Paper No. 410. Look in Darby’s book. Look in White’s book. Look in Shapiro’s book. Use Search on this website! Or https://gprivate.com/62g1z

[snickster]

Depends on the type of flow.

 

In liquid flow in a completely insulated pipe where flow is completely adiabatic (no heat to or out of the pipe) temperature will remain same based on conservation of energy.

 

For gas flow it will depend on type of flow such as the more common:

 

1) Gas flow from high pressure tank to low pressure tank though piping by quickly opening a block valve

 

In this case there is flow and friction until the tanks pressure equalize.With totally insulated system no heat is transfered into or out of the system.  However this is still a constant enthapy process where:

 

dH = 0  = Cp (dT)  So even with friction the temperature and enthalpy remains the same

 

What has changed is that the entropy has increased  and the available energy of the higher pressure state is lost since no work had been done when it could have been.

 

2) Adiabatic frictional flow in completly insulated pipe where no heat in or out is transferred like water case above (Fanno Flow)

 

Same as liquid flow above.  In any case with or without friction if the velocity is to increase (increae in kinetic energy) without any heat input to the system it must come from the internal enthaply so the temperature must drop.

 

With friction and no incease in velocity then it will be a constant enthalpy process where Cp(T2-T1)=0=Co  Where CoTo is the stagnation enthalpy (total engergy of system when not in motion) but this is not possible unless pipe diameter is continually increase to maintain same velocity,

 

When compressible flows with friction the pressure will drop, density will decrease and velocity will increase.  The only energy available to increase the velocity is the energy already in the gas with no heat transfer into the system.  This comes from the gas enthapy:

 

dH=Cp (dT) = V²/2g     And total energy of system is H + V²/2g = U + PV + V²/2g  = CoTo the stagnation enthalpy

 

3)  Isothermal flow - this assumes a constant tempererature based on assuming enough heat transfer occures into the pipe to maintain a constant temperature (heat into pipe =  V²/2g ) without having to come from its own internal enthalpy - this is a common assumption for the common and well used isothermal equations for calculation of piping gas flow pressure drop which gives reasonable results in most cases and is more simple to use.  

Edited by snickster, 17 December 2022 - 09:20 PM.

[breizh]

Hi,

Consider this paper to support your work. Many more using my favorite friend.

Good luck.

Breizh 

[panagiotis]

Thank you all for your reply!!
I will have a deeper look on what you sent me!