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.

背景：纳米流体领域的活跃学者一直在尝试通过各种方法（例如功能化和添加表面活性剂）消除纳米流体稳定性的相关挑战。制备稳定的纳米流体后，必须测量其性质，因为这对热系统的设计至关重要。

目的：作者旨在研究含有功能化MWCNT的冷冻润滑油基纳米流体的稳定性和粘度。研究了浓度和温度对粘度的影响。此外，本研究集中于超声处理时间对所制备样品的稳定性和粘度的影响。

方法：制备化学功能化的MWCNT后，将溶液用超声均化器分散，以最大功率超声处理2、4和8小时。在超声处理10分钟后，通过使用数字旋转粘度计调节适当的纺丝速度，对所有样品进行粘度测量。

结果：第一部分探讨了纳米流体作为纳米润滑剂的稳定性，第二部分研究了纳米流体的粘度以及各种参数对其的影响。最后一项涉及通过众所周知的经验相关性对测得的粘度值进行验证。给出了用于验证问题的测量数据。

结论：通过增加超声处理时间，样品具有更高的稳定性。纳米流体的粘度不会随着超声处理时间的增加而变化，直到两个小时或更长时间。最高质量浓度为0.1％时，有效粘度随线性添加纳米管而增加。