Experimental study on the air-side thermal-flow performance of additively manufactured heat exchangers with novel fin designs

We introduce novel fin designs for finned tube heat exchangers which enhance the conduction heat transfer within the fin and the convective heat transfer along the fin surface simultaneously. Oval tubes with circular plain fins (CPF), circular integrated pin fins (CIPF) and a serrated integrated pin fins (SIPF) were additively manufactured via Selective Laser Melting (SLM) and their heat transfer and flow characteristics studied in a flow channel for different Reynolds number between 1800 and 7800 as well as fin spacing values between 6mm and 16mm. From the experiments an improvement of Nusselt number and a reduction of friction factor was found for all fin designs when fin spacing increases. CIPF showed a higher Nusselt number compared to CPF at all Reynolds numbers and fin spacing values. The highest Nusselt number as well as moderate friction factor values were found for the SIPF design. However, for SIPF the fin efficiency of 30.3% is lowest due to the high heat dissipation along the fin surface. In order to evaluate the thermal and flow performance three parameters were studied: the performance evaluation criterion, the volumetric heat flux density and the global performance. CIPF gives a higher performance evaluation criterion compared to CPF and SIPF performs best compared to the other fin designs. Highest volumetric heat flux density of 2.72kWm³K was achieved with CIPF at lowest fin spacing. Small differences in the global performance criterion between the fin designs and for various fin spacing were observed. The SIPF design is of advantage, if the required surface area, the material cost and the weight of the finned tube heat exchanger are relevant. From the experimental results a heat transfer correlation that includes Nusselt number, Reynolds number, Prandtl number, fin spacing and fin design has been derived.