problem to find mass flow rate from pressurized tank

tauhoi

hi all, i have problem with getting the right equation here. Actually the objective here is to find a mass flow rate of air discharged from a pressurized tank. this is my project and after studying all the seems so called related equation in term of thermodynamic, i've got no idea. for me, i got stuck in the energy balace equation at last and then trying to figure out in the internet and found so many unfamiliar equations. Please help and teach me.