## Fluids

#### Gauge Pressure vs Operating pressure

• cehangir
Subscriber

Hi,

I am working on combustion at high pressure. the model I want has operating pressure of 6 atm.

For the boundary conditions for inlet and outlet in ANSYS FLUENT, pressure is shown as supersonic/gauge pressure. Should I be inputting 6 atm or should i input 5 atm (since Pgauge = Pabs - Patm)

It is a simple question so I hope someone can clarify it to me

Regards

Ceh

• DrAmine
Ansys Employee

The supersonic/gauge pressure will be used by Fluent if the flow on entry is supersonic (3D case you need to give 5 boundary information as 0 information is provided from the domain) or if you want to initialize from it. You need to input the total pressure on your inflow boundary. Please check the Fluent User'S Guide when it talks about the Pressure Inlet Boundary Condition.

Every single pressure input in Fluent is a relative / gauge pressure input: relative to the operating pressure you provide. So If you have Total pressure = 6 atm Operating pressure is 5 atm then I will set the Total pressure at pressure inlet to 1 atm.

• EngineerMech
Subscriber

hello,

I have related question please, what if I have inlet pressure=75bar  for fluid1(co2) and inlet pressure=4bar  for fluid2(water-ethylene glycol) in a contour flow heat exchanger, so please what is the best boundary condition set for inlet and outlet

thanks

• BSabrina
Subscriber
Hi Sir

Kind regards
• DrAmine
Ansys Employee

Pressure Inlet for both. Operating Condition pressure is only a shift pressure. It just helps to reduce round-off. Quite relevant if incompressible EOS is used or very low Mach number compressible flows.

• BSabrina
Subscriber

Hi Sir,

I have a question for you please... is the Operating pressure (for example equal 1 atm) should be lower than gauge pressure!!! I read this, but some articles put the gauge pressure equal zero!!! Do you have an answer for that please Sir?

Kind regards

• DrAmine
Ansys Employee

If you set operating pressure than for the flow configuration where its by far larger than the gauge pressure. The documentation clearly explains when providing an operating pressure is a must and where it is desired.

• VidushiUCT
Subscriber

Do you mean to say if anyone wants to model an operating pressure of 6atm in a reactor, he will put the value of 5atm in the operating condition section in fluent?