The present work experimental and simulation investigations have been carried out to study heat transfer, friction factor characteristics of a plain and twisted square ducts, with and without inserts. The experiments are performed for the airflow rate through the tested duct fitted with inserts for Reynolds number varied from 8000 to 40000. To reduce pressure drop and enhance heat transfer, twisted square duct is newly introduced without previous research available. The investigational work has been carried out and the experimentation is completely based upon design of experiments to get the...