Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO 2 nanofluid with slug flow regime

This paper studied the heat transfer characteristics of the upward vertical two-phase flow of air and water/SiO 2 nanofluid under constant heat flux conditions with a slug flow regime. An experimental setup has been erected. The test section included a vertical copper pipe with an 11 mm inner diameter and a 1.6 m length. The concentration range of nano-SiO 2 in the nanofluids was reported as 0.1–0.5 mass%. Also, 0.5 mass% of sodium dodecyl sulfate (SDS) was added to the base fluid as a surfactant in all of the tests. In order to control the slug flow regime according to the Beggs and Brill flow pattern map in the vertical pipe, liquid Reynolds numbers were controlled from 2100 to 9600 and gas Reynolds numbers were 820 to 1650. The results indicated higher heat transfer coefficient (HTC) and Nusselt numbers of air/aqueous nanosilica nanofluids relative to the two-phase flow of air/water with the same regime. In two-phase flows with maximum Reynolds numbers, the upmost HTC was obtained at 0.5 mass% of nanosilica. The simulation results presented an average relative error less than 10%, which indicates that the experimental and simulation results are in good agreement. Graphical abstract