Shahid Chamran University of AhvazJournal of Applied and Computational Mechanics2383-45366420201001Experimental Study of the Heat Transfer Enhancement in Concentric Tubes With Spherical and Pyramidal Protrusions8018121475410.22055/jacm.2019.30122.1686ENAfrasyabKhanDepartment for Management of Science and Technology Development, Ton Duc Thang University (TDTU), Ho Chi Minh City, VietnamFaculty of Civil Engineering, Ton Duc Thang University (TDTU), Ho Chi Minh City, Vietnam0000-0001-9230-202XJournal Article20190629In the current research project, the thermal performance of a series of newly designed mixers has been investigated. Each mixer has two concentric cylinders comprising two annular slot flow channels around a solid cylindrical rod at the center. In each mixer, the first cylinder around the central solid rod has either spherical or pyramidal protrusions throughout the outer surface. It has been observed that with varying mass flow rate of cold and hot water (1 kg/m<sup>3</sup>-sec to 5 kg/m<sup>3</sup>-sec), 17% increase in rate of heat transfer for cold water & 73% for hot water has been observed with a variation in mass flow rate of 1-3 kg/m<sup>3</sup>-sec with all combination of angles of holes in spherical protrusions. In the case of pyramidal protrusions, the rate of heat transfer has been raised from 16% for cold water & 88% for hot water at varying a mass flow rate of 1-3 kg/m<sup>3</sup>-sec in all combinations of angles of the top vortex in each protrusion. The effect of imparting the centrifugal force has raised the rates of heat transfer in the range of 24-36% at varying rpm from 60-180 rpm of the central cylinder, with the highest with 120 rpm. A comparison of the heat transfer rates reveals that with increasing the mass flow rates, rpm, angle of the holes in spherical protrusions and angle of the traversed angle at the top corner of each pyramidal protrusion didnâ€™t contribute linearly in terms of rising in the rate of heat transfer.https://jacm.scu.ac.ir/article_14754_8076515f3999bfa864026a1086a92840.pdf