Air-side heat transfer and flow characteristics of additively manufactured finned tubes in staggered arrangement

摘要

Finned tube bundle heat exchangers are used in a variety of applications. Tube bundles with conventional circular plain fins (CPF) as well as new 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 2row and a 3-row configuration under forced convection with Reynolds numbers between 1600 and 6600. For the new SIPF and CIPF design an improved Nusselt number was found compare to the CPF and higher Nusselt number for the 2-row compared to the 3-row configuration. 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 thermal-flow characteristics of the heat transfer surface was evaluated by the performance evaluation criterion. Hence, an enhancement for the SIPF and CIPF compared to the CPF was found for both tube row configurations. The compactness of the heat exchanger was evaluated by the heat flux per volume and temperature difference, 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 thermal-flow characteristics and volumetric heat flux density than the 3-row configuration. For the global performance criterion no clear trend could be determined, since the value 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 lower compared to the CPF. Based on the experimental results an empirical heat transfer correlation was derived, which includes Nusselt number, Reynolds number, fin design, Prandtl number and tube row number.