Experimental characterization of a double tube heat exchanger with different corrugated tubes and shells

The aim of this paper was to study the influence of a double tube heat exchanger (DTHX) on thermo-hydraulic performance, considering 21 different shell-tube configurations including smooth and corrugated inner and outer tubes. In order to emulate the behavior of high-viscosity food-industry fluids, a 60 degrees brix solution of water and sugar was used as the Heat Transfer Fluid (HTF). A total of 504 experimental tests were carried out, varying the flow velocity (Reynolds number) and the shell corrugation parameters (helix pitch P and groove depth d). The results from three different shells, one smooth and two corrugated shells, and seven different inner tubes, one smooth and six corrugated with a groove depth between 0.5 mm and 1.2 mm are presented. The comparison of the three shells with an inner smooth tube shows significant heat transfer rate enhancements using a light groove depth (CC1) in the outer tube of the DTHX, increasing both the average efficiency and the PEC indicator (Performance evaluation criteria) by 5% compared with the smooth shell. No improvements are found when a higher groove depth (CC2) in the outer tube of the DTHX is used. Regarding the results with different inner tubes, the tubes with the highest groove depth in the tested range (between 0.5 and 1.2 mm), CO11 and CO12 (with a groove depth of 1.1 and 1.2 mm, respectively), show the best results, regardless of the type of shell. Corrugated tube CO12 shows the best results in terms of efficiency, with an average increment of 19% compared with the smooth inner tube. Regarding PEC, CO11 shows an average increment of 9% in the analyzed PEC indicator compared with the smooth inner tube.