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Natural convection heat transfer performance of additively manufactured tube bundle heat exchangers with novel fin design

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

In many applications finned tube bundles are commonly used for heating or cooling purpose. Hence, the natural convection heat transfer from finned heat exchanger configurations with novel design in a chimney was experimentally studied. These novel fin designs use integrated pins to enhance the heat conduction from the fin base to the fin tip as well as the convective heat transfer along the fin surface. Oval 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 and installed at the bottom of a 6.5 m long chimney. All heat exchanger designs were tested in a 2-row and 3-row configuration with Rayleigh numbers between 25,000 and 120,000. We found the average Nusselt number of SIPF to be higher and the Nusselt number of the CIPF to be lower compared to the CPF. Furthermore, the 2-row configuration achieved greater Nusselt number compared to the 3-row configuration for all heat exchanger designs. The analysis of the individual tube rows showed highest Nusselt numbers at the first tube row and the lowest at the last tube row for both configurations. However, for the SIPF the difference between the first and second tube row is smaller compared to the CPF and CIPF. In order to evaluate the compactness of the heat exchanger, the volumetric heat flux density was applied. Similar to Nusselt number the volumetric heat flux density enhanced for the SIPF and reduced for the CIPF compared to the conventional design. Also the 2-row configuration reaches greater thermal performance compared to the 3-row configuration. Additionally, the surface area and the volume of the heat exchanger material are 30.7 % and 6.9 % lower for the SIPF compared to the CPF. The experimental outcome was used to develop an empirical heat transfer correlation between Nusselt number, Rayleigh number, fin design and tube row number.

Keywords: Novel heat exchanger designs; Natural convection; Heat transfer performance; Additive Manufacturing; Integrated pin fin

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Publ.-Id: 31008