Heat transfer performance enhancement in compact heat exchangers by the use of turbulators in the inner side

The improvement on the hot side heat transfer in compact heat exchangers by the use of wavy turbulators with louvers is experimentally investigated. An unmixed cross-flow compact heat exchanger composed of flat tubes with louver fins in the cold side and with tubes in the presence of turbulators in the hot side was used as prototype. Such type of heat exchanger is used in the cooling system of intake air in turbocharged vehicles, therefore both hot and cold fluids are air. Experimental data has been evaluated using the effectiveness-NTU method. A performance evaluation criteria was used to assess the gain in performance by the use of the turbulators relatively to the smooth tube for Reynolds numbers in the range 2588-7045. A factor above 2 was obtained for all Reynolds numbers, demonstrating gain in performance by the use of turbulators. A new correlation for the Nusselt number in terms of the hydraulic diameter based Reynolds number, Prandtl number and geometric parameters has been proposed for the tubes in the presence of turbulators. 93.75% of the data has been correlated within +/- 13% for the Reynolds number in the range 2588-7045.