Second-law thermodynamic comparison and maximal velocity ratio design of shell-and-tube heat exchangers with continuous helical baffles

Shell-and-tube heat exchangers (STHXs) have been widely used in many industrial processes. In the present paper, flow and heat transfer characteristics of the shell-and-tube heat exchanger with continuous helical baffles (CH-STHX) and segmental baffles (SGSTHX) were experimentally studied. In the experiments, these STHXs shared the same tube bundle, shell geometrical structures, different baffle arrangement, and number of heat exchange tubes. Experimental results suggested that the CH-STHX can increase the heat transfer rate by 7-12% than the SG-STHX for the same mass flow rate although its effective heat transfer area had 4% decrease. The heat transfer coefficient and pressure drop of the CH-STHX also had 43-53% and 64-72% increase than those of the SGSTHX, respectively. Based on second-law thermodynamic comparisons in which the quality of energy are evaluated by the entropy generation number and exergy losses, the CH-STHX decreased the entropy generation number and exergy losses by 30% and 68% on average than the SG-STHX for the same Reynolds number. The analysis from nondimensional correlations for Nusselt number and friction factor also revealed that if the maximal velocity ratio R >2.4, the heat transfer coefficient of CH-STHX was higher than that of SG-STHX, and the corresponding friction factor ratio kept at constant f_o,CH/f_o,SG = 0.28.