Mass center equivalent rectangle model for universal correlation of hydrothermal features of helical baffle heat exchangers

Abstract The prediction using a universal correlation of the shell side Nusselt number with the Reynolds number for helical baffle heat exchangers (HBHXs) has been in vain, because of the impropriate formula of the cross-section area of helical channel or the flow velocity. The shell side friction factor is of similar situation. A new model of mass center equivalent rectangle (MCER) is proposed to calculate the cross-sectional area of the helical flow channel of the HBHX with the hypothesis that the parameters on the mass center cylinder can represent the mean values of the spiral channel. Taking helix pitch as hypotenuse and two sides of the right triangle are along the mass center equivalent helix angle and its normal direction, and the latter and the radius of the shell are postulated to be the two edges of the windward rectangle. The flow cross-section area of the helical channel is the rectangle area subtracting the total ellipse area of the tubes in the rectangle area. The verification of the model is quite satisfactory for quadrant HBHXs by both the heat exchanger design software HTRI and the existing experimental results in a master thesis with the deviations of ho·Pro−1/3 ~ Reo are respectively within +17% to −10% and ±18%. The verification of the model is also satisfied with experimental results of a trisection circumferential overlap HBHX. The coefficients in the correlation formulas especially for the friction factor need be further consummated relating to the helical baffle type and baffle connection style of the HBHXs.