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 ?