Mass flow rate of cooling water in Diffuser

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Discussion Overview

The discussion revolves around calculating the mass flow rate of cooling water in a double-walled diffuser system that handles exhaust gases at high temperatures. Participants explore the necessary parameters and formulas needed for this calculation, focusing on heat exchange principles and specific heat capacities.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • Mayur describes the system and requests a method to calculate the mass flow rate of cooling water.
  • Matt identifies the system as a double shell heat exchanger and lists several critical parameters needed for calculations, including pressures, temperatures, and gas composition.
  • Mayur provides some parameters but expresses uncertainty about the specific heat capacity (Cp) of the exhaust gas.
  • Matt suggests consulting TEMA standards for determining the Cp value and emphasizes its importance for calculations.
  • Max provides an approximate Cp value and requests a general formula that incorporates it.
  • Matt mentions a proprietary method for calculating Cp values and suggests that following TEMA standards could yield accurate results.
  • Max inquires about alternative methods to obtain the Cp value without access to TEMA standards.
  • Matt offers to calculate the Cp value if the components of the flue gas and their volume percentages are provided.

Areas of Agreement / Disagreement

Participants generally agree on the need for specific parameters to perform the calculations, but there is no consensus on how to obtain the specific heat capacity of the exhaust gas, leading to multiple competing views on the best approach.

Contextual Notes

Limitations include the lack of defined inlet and outlet temperatures for the cooling water, uncertainty regarding the phase change of the cooling water, and the need for detailed gas composition data to accurately determine Cp.

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

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

Thanks
Matt
 

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