Mass flow rate of cooling water in Diffuser

[Max_sky]

Hello Everyone,
I am Mayur
I am working on a system, in the system there is one diffuser through which exhaust gases at 3000K are flowing at a rate of 170Kg/s. The material of diffuser is Stainless Steel. The diffuser is double walled type with cooling water flowing between the walls.
I need to find the mass flow rate of cooling water to keep the system cool.

Can anyone give me the formula or some methood to calculate the mass flow rate..

Thanx

 

[CFDFEAGURU]

Hello,

What you have is a double shell heat exchanger (or double shell radiant recuperator) with flue gas inlet temperature of 3000 K (2540 F). That is extremely hot.

More information is needed to begin any type of calculation.

1. What is the pressure of the cooling water and the flue gas?
2. What is the inlet temperature of the cooling water?
3. What is the maximum allowable exit temperature of the cooling water?
4. Is the cooling water allowed to change phase to steam?
5. What is the outlet temperature of the flue gas? If you don't know this value then knowing the inlet and outlet temperature of the cooling water will be sufficient.
6. What is the flue gas stream compose of? CO, CO2, H20, ... I am sure it is a combination of them, so what are the percentages (volume or weight % of each component?)

7. What is the Specific Heat of constant pressure, Cp, of the flue gas?

Thanks
Matt

 

[Max_sky]

Thanx Matt

The pressure of the Exhaust gas in 4 bar max, the shell thickness is 36mm, flow of the exhaust gas is for not more than 200Sec, we have to decide the inlet an outlet temperature of the cooling water.
the purpose of cooling is to protect the shell from heat and not to cool the exhaust.
About the exhaust gas it's a misture of SO2, H2O, CO CO2,...etc in very indefinite proportion.
I could not figure out the Cp for the gas.

Let me no if the data is sufficient...

Thanx

 

[CFDFEAGURU]

Hi Max,

You will need to know the Cp value for the gas stream. See the TEMA (Tubular Exchange Manufacturers Association) standards. In there is a method of how to obtain this value.

Thanks
Matt

 

[Max_sky]

Hey Matt

The Cp value for the exhaust gas is approx 1.318 KJ/Kg/K. this value may change, so if you can give me some general formula in terms of cp it will be better for me.

Thanx
Max

 

[CFDFEAGURU]

... so if you can give me some general formula in terms of cp ...

My company uses a proprietary method of calculating the Cp values for gas mixtures, but I checked it against the method in the TEMA standards and the results are in close agreement for the mixtures that I checked. So if you follow the method in the TEMA standards you should be able to calculate an accurate Cp value. Do you have access to the TEMA standards?

Thanks
Matt

 

[Max_sky]

No i don't have access to TEMA Standards. Is there any other way i can to get the Cp value...??

Thanx
Max

 

[CFDFEAGURU]

I can calculate it for you. What are the components of the flue gas and each of their volume percents?

Thanks
Matt