Thermal performance of automotive radiators made of plastic and stainless steel microtubes

The thermal performance of low-temperature radiators constructed from staggered banks of stainless steel microtubes (SST unit) and polymeric fibers (PF unit, polyamide 612) was investigated in air cross-flow conditions. Tests were performed in a calorimetric wind tunnel according to automotive standards with air velocities of 2–10 m/s and coolant flow rates of 6–60 l/min. Experimental results demonstrated that airside pressure drops for SST and PF radiators are nearly identical, with a difference of approximately 1%, showing that tube material did not influence airside pressure drops. Regardless of the 50-time difference in thermal conductivity between stainless steel (12 W/(m·K)) and polyamide (0.24 W/(m·K)), the heat transfer rate of the PF radiator was, on average, only 7% lower than ST, with smaller deviations observed at lower air velocities. The Gaddis and Gnielinski model showed good prediction, with average discrepancies of 3% for heat transfer rate, 7% for overall and airside heat transfer coefficients, and 5% for pressure drops. The results confirm that, when middle buffers are used, polymeric hollow-fiber radiators can be a viable lightweight alternative to metals for low-to-moderate airflow applications (2-10 m/s air speed).