Pressure Drop and Heat Transfer Characteristics of MWCNT/Heat Transfer Oil Nanofluid Flow inside Microfinned Helical Tubes with Constant Wall Temperature

Abstract

Experiments are performed to investigate the single-phase flow heat transfer augmentation of MWCNT/HT-B oil in both smooth and microfinned helical tubes with constant wall temperature. The tests in laminar regime were carried out in helical tubes with three curvature ratios of 2R/d=25, 30 and 35. Flow Reynolds number varied from 170 to 1800 resulting in laminar flow regime. The effect of some parameters such as the nanoparticles concentration, the dimensionless curvature radius (2R/d) and the Reynolds number on heat transfer was investigated for the laminar flow regime. The weight fraction of nanoparticles in base fluid was less than 0.4%. within the applied range of Reynolds number; results indicated that for smooth helical tube the addition of nanoparticles to the base fluid enhanced heat transfer remarkably. However, compared to the smooth helical tube, the average heat transfer augmentation ratio due to nanoparticle addition for finned tube was small, about 17%. Also, by increasing the weight fraction of nanoparticles in microfinned helical tubes, no substantial changes were observed in the rate of heat transfer enhancement. For the pressure drop, the results show that the pressure drop of nanofluids was slightly higher than the base fluid and increase as the volume concentrations go up.