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Air-side thermal and flow performance study of additively manufactured tube bundle heat exchangers with novel fin design

Unger, S.; Beyer, M.; Pietruske, H.; Szalinski, L.; Hampel, U.

Finned tube bundle heat exchangers are used in a variety of applications with the plain circular fin being the most common design. In the present investigation we proposed two novel heat exchanger designs integrated pins, which improve the heat conduction from the fin base to the fin tip as well as the convective heat transfer along the fin surface. Tubes with conventional circular plain fins (CPF) as well as novel circular integrated pin fins (CIPF) and serrated integrated pin fins (SIPF) were additively generated by a Selective Laser Melting (SLM) process. They were tested in a flow channel in a 2-row and a 3-row configuration under forced convection with Reynolds numbers between 1600 and 6600. For the new SIPF and CIPF designed we found an improved Nusselt number compare to the CPF and higher Nusselt number for the 2-row compared to the 3-row configuration. From the analysis of the single tube rows it was found that the Nusselt number is highest for the first row and reduces downstream. The friction factor was lowest for the SIPF at all Reynolds number and the CIPF gave lower friction factor compared to CPF for Reynolds numbers up to approximately Re=4000. Furthermore, the performance of the heat transfer surface was evaluated by the performance evaluation criterion. Hence, an enhancement of 72.6 % and 33.6 % for the 2-row configuration as well as 63.4 % and 29.1 % for the 3-row configuration for the SIPF and CIPF compared to the CPF was found. The compactness of the heat exchanger was evaluated by the volumetric heat flux density, which was greatest for the CIPF followed by the SIPF and lowest for the conventional CPF design. In general the 2-row heat exchanger configuration reached greater performance and volumetric heat flux density than the 3-row configuration. The global performance criterion strongly depends on the flow conditions. Thus, the SIPF heat exchanger performs best at lower and intermediate Reynolds numbers up to Re=5000 and the CPF design is best at higher Reynolds numbers. Eventually, the surface area and the volume of the heat exchanger with SIPF are 30.7 % and 6.9 % lower compared to the conventional heat exchanger. Based on the experimental results an empirical heat transfer correlation was derived, which includes Nusselt number, Reynolds number, Prandtl number, fin design and tube row number.

Keywords: Novel heat exchanger designs; Heat transfer; Friction factor; Thermal-flow performance; Additive Manufacturing; Integrated pin fin

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Permalink: https://www.hzdr.de/publications/Publ-30842
Publ.-Id: 30842