Question: Run-around coil heat recovery systems

AI Thread Summary
The discussion revolves around calculating the mass flow rate of exhaust gases from a gas-fired furnace using the given air-fuel ratio (AFR) and the properties of air and fuel. The user seeks clarification on how to derive the mass flow of the exhaust gases, noting that they have the AFR in volume but lack the density of the exhaust gases. It is suggested that the mass flow rate of the exhaust gases can be determined by calculating the combined mass flows of air and fuel entering the furnace. By using the known densities of air and fuel, the user can calculate the individual mass flows and subsequently derive the mass flow of the exhaust gases. The conversation emphasizes the importance of understanding the relationship between volume ratios and mass flow rates in thermal systems.
Lord Dark
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hey guys ,, how are you all ??

guys , I've got the following problem , Air enters a gas-fired furnace at 20deg at a mass flow rate of 0.2kg/s and is burned with an air-fuel ratio by folume of 12. the gases leave the furnace at 350deg. A run-around coil system is installed to recover some of the energy of the exhaust gases in order to preheat the air entering the furnace. Calculate :

1- the required mass flow rate of the 2nd fluid.
.
.
.etc .

my problem is i don't know how to get the mass flow of the gas exiting , i have the AFR = 12 in volume , how to use it to get the gas out of the furnace ? they gave me the density of the air and the fuel only not the gas out .. should i get it density too ?
 
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The mass rate out is the same as the combined mass flows in of the fuel and air. You know the the density of the air you can work out the volume of air which from the ratio you can work out the volume of fuel. You know the density of the fuel so you can work out the mass flow of the fuel.
 

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