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 (SG-STHX) 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 SG-STHX, 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 fo,CH/fo,SG=0.28.
In order to simplify the manufacture and improve heat transfer performance of shell-and-tube heat exchangers (STHXs), we have invented a combined multiple shell-pass STHX with continuous helical baffles. The novel combined multiple shell-pass STHX with continuous helical baffles (NOVEL STHX) is compared with the conventional STHX with segmental baffles by Computational Fluid Dynamics (CFD) method. The numerical results show that, under the same mass flow rate M and the same overall heat transfer rate Qm in the shell side, the overall pressure drop DP of the NOVEL STHX is lower than that of the STHX with segmental baffles by about 13%. The heat transfer rate Qm of the NOVEL STHX is higher than that of the STHX with segmental baffles by about 6% under the same overall pressure drop DP. The NOVEL STHX might be used to replace the conventional STHX with segmental baffles in industrial applications to save energy, reduce cost and prolong service life.
In order to improve heat transfer performance of conventional segmental baffled shell-and-tube heat exchangers (STHXs), the shell-and-tube heat exchanger with combined helical baffles (CMH-STHX) were invented. In the present study, the CMH-STHX is compared with three other STHXs which were set up with continuous helical baffles (CH-STHX), discontinuous helical baffles (DCH-STHX) and segmental baffles (SG-STHX), by Computational Fluid Dynamics method. The numerical results show that, for the same mass flow rate at the shell side, the overall pressure drop of the CMH-STHX is about 50% and 40% lower than that of SG-STHX and CH-STHX. The heat transfer coefficient of the CMH-STHX is between those of CH-STHX and DCH-STHX and it is 6.3% lower than that of SG-STHX. The heat transfer coefficient under unit pressure drop h/Δp is introduced to evaluate the comprehensive performance of STHXs. The h/Δp of the CMH-STHX is 7.5%, 6.5% and 87.4% higher on average than those of the CH-SHTX, DCH-STHX and SG-STHX. Furthermore, the total heat transfer rate of CMH-STHX is about 25% higher than that of SG-STHX for the same total pressure drop of shell side. Supported by these results, the new heat exchanger (CMH-STHX) may be used to replace the conventional shell-and-tube heat exchanger in industrial applications.
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