experimental research on heat transfer of water in tubes with conical ring inserts in transient regime

forced convective of water in horizontal tubes with conical tube inserts has been studied experimentally. the transient flow regime has been used for the tests. experimental results are validated with existing well established correlation. the turbulators were placed in two different arrangements: converging conical ring, referred to as cr array and diverging conical ring, dr array. two correlations for the nusselt number based on the experiment are introduced for practical use. it is found that the insertion of turbulators has enhanced the nusselt number for the dr arrangement up to 521%, and for the cr arrangement up to 355%, although using the turbulators cause a significant increase in pressure drop.