Zimparov V.Bonev P.Angelov M.Hristov J.2024-07-102024-07-102024-07-102024-07-102022-01-010354-983610.2298/TSCI211206060ZSCOPUS_ID:85135534789https://rlib.uctm.edu/handle/123456789/734Five wire-coil inserts with fixed wire diameter and different pitches, fitted inside a round tube have been experimentally studied in a transitional and low turbulent flow. Water was used as a working fluid at a wide range of flow conditions: 103 < Re < 104 and 3.9 < Pr < 10.0. The geometrical parameters of the inserts are: e/Di = 0.070, and p/e = 6.7, 9.0, 10.0, 12.5, and 15.0. The variation of the friction factor and heat transfer coefficients have been obtained and compared with those of the smooth pipe. Performance evaluation criteria for the cases FG-1a, FG-2a, and VG-2a have been used to evaluate the maximum and real benefit that can be obtained. The greatest benefit can be achieved with the pitch of the wire-coil insert p/e = 10.0.enArticle