Background: Active scholars in the nanofluid field have continuously attempted to remove
the associated challenge of the stability of nanofluids via various approaches, such as functionalization
and adding a surfactant. After preparing a stable nanofluid, one must measure the properties,
as this is vital in the design of thermal systems.
Objective: Authors aimed to investigate the stability and viscosity of refrigeration lubrication oilbased
nanofluids containing functionalized MWCNTs. The effects of concentration and temperature
on viscosity were studied. Furthermore, the present study focused on the effect of sonication time on
the stability and viscosity of the prepared samples.
Methods: After the preparation of chemically functionalized MWCNTs, solutions were dispersed
with an ultrasonic homogenizer for 2, 4 and 8 hours sonication at maximum power. Viscosity measurements
for all samples were made 10 minutes after sonication by adjusting the proper spinning
velocity using a digital rotary viscometer.
Results: The first part deals with the stability of the nanofluid as a nanolubricant, and the second one
investigates the viscosity of the nanofluid and the effects of various parameters on it. The last one is
related to the validation of the measured viscosity values by means of well-known empirical correlations.
The measured data are given for validation issues.
Conclusion: The samples will have higher stability by increasing the time of sonication. The viscosity
of a nanofluid does not change with the increase of sonication time to two hours and higher. Up to
mass concentration of 0.1%, the effective viscosity increases with adding nanotubes linearly.