EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER AND PRESSURE DROP CHARACTERISTICS FOR VERTICAL DOWNFLOW USING TRADITIONAL AND 3D-PRINTED MINI TUBES

In this study, an investigation on the influences of different manufacturing techniques on the heat transfer and pressure drop in the developing and fully developed regions of mini-tube under different flow regimes is introduced. The purpose of this research is to experimentally investigate the heat transfer and pressure drop characteristics using 3D-printed tubes and traditional stainless steel tubes in the vertical direction under isothermal and non-isothermal boundary conditions. Experiments are conducted using distilled water (Prandtl numbers varying from 4 and 7) at Reynolds numbers of 800-10000 with heat fluxes between 30 and 500 kW·m-2. Test tubes with inside diameters of 2 mm are used, and the average surface roughness is 1.6 μm and 15.3 μm, respectively. The results are compared with previous studies. It is verified that the heat transfer characteristics are almost the same for the traditional tube and the 3D-printed tube in the laminar region. The average deviation between these two tubes is 7.7%. However, for the turbulent region, the Nusselt numbers of 3D-printed tube in the turbulent region increases by an average of 45% as compared with a traditional tube. The friction factors under heating conditions also increased by an average of 209%. In addition, the 3D-printed tube enters the transition region earlier. The results show that the average critical Reynolds number of a traditional tube and 3D-printed tube is around 2300 and 2000, respectively. Correlations in the turbulent region are developed to predict the friction factors and heat transfer coefficients with good accuracy.