EXPERIMENTAL STUDY ON SHELL SIDE HEAT TRANSFER PERFORMANCE OF CIRCUMFERENTIAL OVERLAP TRISECTION HELICAL BAFFLE HEAT EXCHANGERS

A set of experiments were conducted on the circumferential overlap trisection helical baffle heat exchangers with inclined angles of 20 degrees, 24 degrees, 28 degrees and 32 degrees single-thread and inclined angle of 32 degrees dual-thread one, and a segmental baffle heat exchanger as a contrast scheme. The cylinder case of the testing heat exchanger is a common shell, while the tube bundle core could be replaced. The shell side heat transfer coefficient h(o) is obtained by subtract tube-side convection thermal resistance and tube wall conduction resistance from the overall heat transfer coefficient K. The curves of shell side heat transfer coefficient h(o), pressure drop Delta p(o), Nusselt number Nu(o), and axial Euler number Eu-z,Eu-o are presented versus axial Reynolds number Re-z,Re-o. A comprehensive perfoiniance index Nu(o)/Eu-z,Eu-o is suggested to demonstrate the integral properties of both heat transfer and flow resistance of different schemes, and the curves of Nu(o)/Eu-z,Eu-o versus Re-z,Re-o of the different schemes are presented. The results show that the scheme with inclined angle 20 degrees performs better than other schemes, and the scheme with inclined angle 24 degrees ranks the second, however the segment scheme ranks the last. The curves of Nu(o)/Eu-z,Eu-o of both schemes with inclined angle 32 degrees of single-thread and dual-thread are almost coincident, even though their heat transfer coefficient and pressure drop curves are quite different. The results indicate also that for the circumferential overlap trisection helical baffle schemes the optimal inclined angle is around 20 degrees instead of around 40 degrees as rated by many literatures for the quadrant helical baffle schemes.