Hello, cfx family. I use cfx5.5 to simulate the combustion in a furnace, at the same time calculate the coupling heat transfer to the oil in pipe. The first difficulty is the fuel and the fume is ideal gas ,while the oil is liquid .The other is the coupled heat transfer. If I use cfx4.4,there is the same difficulties.

Is it a thermal oil heater you are trying to calculate?

What do you want to know, is it just the heat transfer to the oil? or do you need an exact calculation of the oil flow, with temperature and velocity in discrete points?

Thank you Jan. Yes,I'm trying to calculate a thermal oil furnace. There is gas combustion in the hearth and cold oil flow in the pipe. The fluid(fuel,air and combustion product) in the hearth is gas,while the oil in the pipe is liquid. Is it necessary to calculate a two-phase fluid with combustion? Another difficulty is the mesh of pipe wall with the thickness of 10mm.

You should be able to calculate the system without including an equation for the oil.

But what is important for you? is it to predict the wall heat transfer correctly in the furnace or do you need an exact knowledge about the oil flow.

If it is the wall heat transfer in the boiler then you do not need to include the oil as a fluid, you can calculate the heat tranfer to the fluid by use of standard rules for heat transfer calculations, included as user fortran. I normally do calculations on boiler with steam. In this case is the heat transfer coefficient from the steam very high so I can assume , that the inside temperature in the furnace is equal to the steam temperature.

perfect!I will use fortran to calculate heat transfer to oil.Thanks!

Try with a simple case for a start. Find an example you can calculate by your heat transfer knowledge, you could take a tube with the oil surrounded by hot air for an example. You could also expand it to forced convection. Try to simulate some cases and compare the results. It is much easier to discover mistakes in a well controlled small example.

Good luck Jan