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# Boiler: Problem with defining initial pressure in pipeline. FLOW+THERMAL SOLUTION

Hello,
I would like to ask you for help concerning opportunities in selling NX FLOW and NX THERMAL SOLVER.

It is about calculation of a boiler with preheating steam.

The situation is a combination of Thermal and Flow. There are 2 flowing media:

1. Combustion fumes with given flow velocity (mass flow) and temperature. Escaping freely into the surrounding environment.

2. Steam that is preheated through a steel pipe from combustion fumes .We know the mass flow of steam which is the same at  the outlet as at the inlet, the initial temperature of the steam and the initial pressure. We want to know the pressure at the outlet – so we can determine the pressure loss and the temperature.

Principle: Combustion fumes in the boiler heat steam through the steel pipe. Change of temperature causes change of volume and velocity of the steam. Mass flow remains the same. Velocity , pressure and temperature at the outlet will change.

Problem: Solver does not enable to enter initialpressure(InitialPressureCondition). We enter the initial pressure of 86 bar, but results of pressure are still calculated from values of  atmospheric pressure and the ambient conditions.

Question: How to enter the initial pressure in the pipeline correctly?? It is possible to enter that such high pressure (86bar) into the ATM P?

I got good result of temperature.

Some result of velocity, it can be bad, becose it depend on pressure.

Result of pressure, out of range enterd pressure (86bars).

Have somebody some advice with using and defining Initial pressure condition???

Tomas Havlicek

CAE product manager

AXIOM TECH - Czech republic

4 REPLIES

## Re: Boiler: Problem with defining initial pressure in pipeline. FLOW+THERMAL SOLUTION

[ Edited ]

Hello Tomas: As I understand it, right now the tube flow is seeing basically ambient pressure.  To obtain a realistic tube pressure you will need to work with the "opening" definition at the tube outlet.  Right now you are probably defaulting to ambient for "external conditions".  Instead, define an "external pressure" for the opening.  If you do not know the pressure there but instead know the pressure at the inlet, then switch the "opening" and inlet flow around so you are now defining an outlet flow at the pipe exit, and external pressure at the pipe inlet.

I might also comment that if the pipe has a significant view of the combustion flames, radiation heat transfer to the pipe will be important too.

## Re: Boiler: Problem with defining initial pressure in pipeline. FLOW+THERMAL SOLUTION

Yes. It really helped. Switch the "opening" to inlet flow.
Thank you Carl.

Radiation: The real problem is that thera are 1000s of small tubes with helix ribbing.

Have anyone an idea how to mesh? Look at the pictures bellow.

Cut of the boiler.

Detail of 2 small pipes.

Is it some chance to do it with 1D flow.??

Supress ribbing and recalculete it with heat transfer coefficient.???

Solution
Solution
Accepted by Ganesh_S (Community Manager)
‎08-26-2015 04:32 AM

## Re: Boiler: Problem with defining initial pressure in pipeline. FLOW+THERMAL SOLUTION

Hi Tomas:  This is a perfect application for NX Advanced Thermal Duct Flow.  These are 1D "pipe" elements that do a good job of calculating heat transfer and pressure drop without all the overhead of running full 3D.  The convection thermal coupling will let you provide the interior HTC, or the software can calculate a smooth wall HTC and you can provide a multiplier for the helical nature of the surface.  There's a good tutorial in the Advanced Thermal class materials.

## Re: Boiler: Problem with defining initial pressure in pipeline. FLOW+THERMAL SOLUTION

Thanks for the tip. Please Can you navigate me for your referd tutorial. In NX documentation isn't any tutorial for 1D ducting.
Thank you