help .i am designing a shell and tube heat exchanger but the velocity on the shell side is high ,exceeding the limit for gasses under a range of pressures .Even after increasing passes the velocity reduces but is still high . Iam designing for a gas-gas system.Should i use another type heat exchanger design or there's something else i can do .The hot fluid contains Co2 ,N2 and O2 gasses while the cold fluid contains air(02 and N2)