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

摘要

A set of experiments were conducted on the circumferential overlap Bisection helical baffle heat exchangers with inclined angles of 20°, 24°, 28° and 32° single-thread and inclined angle of 32° 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 Ap_o, Nusselt number Mi_o, and axial Euler number Eu_(z,o) are presented versus axial Reynolds number Re_(z,o) A comprehensive performance index Nu_o/Eu_(z,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,o) versus Re_(z,o) of the different schemes are presented. The results show that the scheme with inclined angle 20° performs better than other schemes, and the scheme with inclined angle 24° ranks the second, however the segment scheme ranks the last. The curves of Nu_o/Eu_(z,o) of both schemes with inclined angle 32° 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° instead of around 40° as rated by many literatures for the quadrant helical baffle schemes.