Heat transfer from R134a/oil boiling flow in pipe: Internal helical fin and hybrid nanoparticles

The present study investigates experimentally heat transfer of the forced convection boiling of a R134a/nano oil mixture in a horizontally-aligned tube with an aluminum helical fin. The effects of various parameters including refrigerant mass flow, vapor quality, star-shaped fin, oil concentration and volume fraction of nanoparticles are studied. SiO2-TiO2 nanoparticles are synthesized by applying both ultra-sound irradiation and sol-gel methods. Morphology and size of nanostructures are portrayed through the exact use of scanning electron microscopy, while the phase of the product is investigated by an X-ray diffraction pattern (XRD). The findings indicate that as the mass flow enhances, the heat transfer coefficient rises. The heat transfer coefficient and pressure drop have increased by using a helical fin. Regarding the oil-refrigerant mixture, the heat transfer coefficient augments at low vapor quality and reduces at high vapor quality. By adding nanoparticles, heat transfer increases, but a decreasing trend in heat transfer is observed from a certain vapor quality. The highest percentage of increase in heat transfer at a mass velocity of 380 kg/m2.s is for the case with a fin and a mixture of R134a/nano oil, and this amount is equal to 89%. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study experimentally investigates the heat transfer of forced convection boiling of a R134a/nano oil mixture in a horizontally-aligned tube with an aluminum helical fin. The findings show that increasing mass flow enhances heat transfer coefficient, while adding nanoparticles can increase heat transfer, but a decreasing trend is observed at a certain vapor quality.