Understanding Viscometry (Rheometery): Defining Viscosity and Apparent Viscosity
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- Опубліковано 6 жов 2024
- This video demonstrates the Cone-and-Plate method of measuring absolute viscosity of liquids. What are viscosity, viscometry and rheometry? Find out answer to these in this video.
Viscosity is the property of a fluid by which it resists motion/deformation in shear. High viscous fluid will require higher force to shear it. The shearing stress (N/mm^2 or Newton per meter square) also depends upon the speed with which we are deforming (in shear) the fluid and the thickness of the fluid within which shearing is taking place. Shear rate is given as the velocity of shearing (v) divided by the fluid thickness (h), that is, v/h and it has the unit of s^-1 (per second). Viscosity is given as the ratio of the shear stress to shear rate. This is also known as the Newton's Law of viscosity. The viscosity measured by this principle is known as the dynamic or absolute viscosity. The units of this viscosity is Pascal second. Viscosity of a fluid is highly dependent on the prevailing temperature and pressure. There are relationships that can be used to find viscosity at different temperatures and pressures if viscosity at normal temperature pressure is known along with some constants of the equations.
The method that I have used in this video is known as the Cone-and-Plate viscometry. The machine was built by Anton Paar company. In the method, the torque (N-m) to rotate the cone at a fixed speed is measured and then we can use a formula to obtain viscosity at that shear rate. If the liquid is non-Newtonian then this viscosity will be the apparent viscosity because it will change if you change the shear rate.
Rheology is the study of flow properties of complex fluids which are mostly non-Newtonian in nature. Rheometers are basically viscometers for these complex fluids.
In this video you will find data and plot of viscosity as a function of the shear rate for two liquids, the synthetic engine oil and olive oil.
There were a lot of concepts related to rheology I was struggling to piece together. Thank you for making this so clear.
This helped me a lot! Starting my bachelors thesis next week 😅 thank you
Good luck!!
I am here for the same reason haha
Which topic ?
Thanks for the informative video, I learned something new today about what a rheometer is used for. It is used for to measure the force required to shear a liquid.
You are right. Using the proper theory, the rheometer can be used to find out the viscosity of the liquid such as a lubricating oil that you put in your car.
Very informative video.
Sir how to do rheology of viscus paste.
Thanks for asking.
For pastes, extrusion based rheology can be used. Normal rheometer can not be used due to the problem of wall slip. Squeeze film test can also be used. This paper may help: www.sciencedirect.com/science/article/abs/pii/S0377025796015467
For paste we model as yield + Non-Newtonian or power law, for example, Herschel Bulkley model.👍
@@engineeringmaterials-tribo5142 sir i am a PhD research scholar working on a viscus ceramic paste struggling to analyse some of my sample but I cant find any rheometer system. will you help me sir.
@@debu326 I do not have such rheometer. Try extrusion or squeeze film compression methods of measuring. That is what I can say. There are many published such works in this field. My old research was in this field. You can check my old publications here. scholar.google.com/citations?user=aybvKicAAAAJ&hl=en
I am sorry I can not help much. Best wishes 👍
Very informative. For viscosity values shown in the table, should we exclude the measurement at point 1 as it gives a totally different value from points 2 to 20?
time 23:55. Yes you have pointed out an important aspect of the data collection. Often the initial couple data may be totally different and need to be omitted. Also, every test must be repeated at the same set of conditions three times, at least.
Thanks for the video prof. I am recently starting a Master Thesis on Rheologie examination using very high shear rates, i am wondering the career prospects in the field, Will I be satisfied on this aspect ?
It depends which department you are in. Rheological studies are generally carried out for polymers, lubricants etc. If you have conducted your research well then you should definitely try in similar kind of companies. You will need broad domain knowledge of the department you are in.
Is it possible to find viscosity of existing bituminous layer of any road?
If yes, please elaborate !!
The bituminous layer is highly viscous at normal temperatures but a higher temperatures it flows. This company makes instruments for bitumen at high temperature. For a very viscous liquid we can also use the capillary flow method (Saybolt) to measure kinematic viscosity.
Dear Prof, have you run it for thermoplastic polymer?
You can only run thermoplastic polymer when it is in melt form. This machine is not suitable for that purpose. We can measure viscosity of standard oils.
Are engine oil and olive oil Newtonian fluids under all conditions of temperature? I would imagine that engine oil has some n-paraffin fractions that could form wax at certain temperatures, as is the case with diesel and some other distillate fuels.
Was the Excel spreadsheet obtained directly from the viscometer software or some of the parameters were calculated from measured data?
Thanks. Both oil will turn very viscous at lower temperatures with non-Newtonian behaviour.
Excel is directly obtained from the machine with columns of stress and strain rate data. So, it is easy to plot them and obtain viscosity.
Hello Sir, Is this RheolabQC or different?
Anton Paar rheometer
@@engineeringmaterials-tribo5142 which model?
Thank you very much Sir. But i would like to know about that how the viscosity of yogurt is tested.
If the yoghurt is easily flowable then the rheometer described in this video can be used. For yoghurt that does not flow like a fluid then perhaps you should conduct compression test, just like we do for cheese.
@@engineeringmaterials-tribo5142 . Thank you very much Sir. Now my mind is almost cleared.
why UA-cam thought that this lecturer is speaking Hindi, while he spoke English. lol
May be because I uploaded the video in India.