Mod-01 Lec-06 Viscosity (Contd.) and Surface Tension

Introduction to Fluid Mechanics and Fluid Engineering by Prof. S. Chakraborty,Department of Mechanical Engineering,IIT Kharagpur.For more details on NPTEL visit nptel.ac.in

[@anantharam4695]

omg..its the great Suman Chakroborthy sir...King of Fluids....

[@mdsaifansari6123]

Circle and Ellipse. The professor is awesome.

[@tahsinengin9388]

I think some corrections are in place for the first M expression. You have integrated du expression by assuming M is constant, which is essentially not. This type of analysis could give good approximation when the gap between two cylinders is narrow. It can be as good as a linear velocity variation accross the gap. For a better approach, we can assume a laminar flow in annular gap of two long cylinders, and solve N-S equation for an expression of the tangential velocity component of flow. Then we can find the tangential velocity gradient on the surface of the inner cylinder. This will give us the torque needed to maintaing the motion.

[@gautamjha3988]

if we treat enclosed fluid as solid and for constant angular velocity input torque must be constant .EXPLAINATION IS BELOW although after overcoming the resistance offered by viscosity ,FOR the fluid and shaft SYSTEM to be rotated at constant angular velocity constant input torque is required and also it is possible only when torque transmit at each layer of fluid is same. any further correction is welcomed.

[@tahsinengin9388]

@@gautamjha3988 This is not a solid body, and as I said a year ago :-)), this analysis is only valid when the gap is relatively very narrow.

[@gautamjha3988]

@@tahsinengin9388 continuum mechnics gives us freedom to treat fluid as a bulk thats why according to me we can treat as a solid body.do u have any doubt about this?

[@TahsinEngin-Akademi]

@@gautamjha3988 Total torque is certainly constant, but local torque varies across the gap as a function of radial coordinate. Therefore I have doubt about your comments, not about the continuum mechanics.

[@firozkhan_2002]

From the first lecture itself I'm observing that u are constantly pointing out things and suggesting advanced level solutions. Plz remember that this course is for UG 3rd sem students, that too this is the beginning of the course (Module 1). Prof is very well aware of the solutions u have, and even he can give very complex and technically advanced solutions for the same problems, but since this is a basic module hence all sorts of technical complexities are avoided for the better understanding of the beginner level students.

[@hurshsingh4913]

Awesome content delivery

[@pranav9339]

At 17:38, for the thin film approximation, Can we apply limit R2 -> R1 because size of shaft is always constant. We can adjust size of bearing (R2). By this I guess we could get even better approximation function for infinisimal gap.

[@Azzu974]

At interface molecule pulls downwards but bottom molecules pushes outwards then the molecules sustain at same point

[@sunainam7119]

Surface tension is tangential to surface. But two tangents can be drawn at a point on surface. Can anyone plz tell which tangent do we consider?

[@46sayakdash612]

In the direction of motion

[@arkitkabir6950]

If we assume the flow is newtonian then what is difference in first question solved in video by considering narrow gap and without considering narrow gap? If profile isn't linear then how can we use the assumption of newtonian fluid?

[@kaustavroy8971]

Newtonian fluid means at a given temperature viscosity coefficient remains constant or in other words shear stress is linear to strain rate... So it does not mean that newtonian fluids will always have a linear profile!!!!! For newtonian fluid flow through pipes inlaminar condition, the velocity profile is parabolic....For small gap we can approximate the flow to have a linear profile.

[@kanakbhatia7495]

How and why is M taken constant in first example

[@sudeepmenon17]

why is there a requirement to assume a narrow gap, when we already assumed the fluid to be newtonian ?? Newtonian fluid itself implies that the stress should linearly vary with strain??

[@anmolrattan1828]

With the narrow gap, one can assume velocity profile is linear.

[@roshithmittakolu1885]

we are assuming rate of shear strain to be linear in narrow gap. But in the newtonian fluid law we actually dont know the variation of rate of shear strain that can be anything it can also vary with y direction So according to shear strain profile shear stress profile will vary i.e if parabolic variation of shear strain mean parabolic variation of shear stress.

[@user-cd5op5ti2k]

see the lecture again. when you define shear stress, when 'dely' and delt tends to zero, then its velocity profile could be linear in newtonian fluid. so narrow gap assumption is needed.

[@gautamjha3988]

@@user-cd5op5ti2k dely and delt zero doesnot tell that velocity profile is linear ,it only tells that for small angular deformation corresponding to small time interval rate of shear strain = velocity gradient ,so i dont think ur logic is correct

[@user-nf6lm8lc9l]

I want to draw a circle, it becomes an ellipse. Whenever I want to draw an ellipse, it becomes a circle.

[@pradeepchandra1734]

I WONDER WHAT THAT BLUE DRESS GIRL DOES NOW...? HAHA