Introduction

I am in the process of describing an empirical science that is in existence and the next major thing to describe is the way that we deal with the flow of fluids in pipes. This cannot be done without the use of the property viscosity.

 

I have said that this is a personal text that lays out my view of this subject and here I am writing for any one who uses engineering science and is a bit more curious than most. You may not always agree with what I say but you are free to ignore it and I have found that what follows works for me. Viscosity has always troubled me because I learnt about it through Poiseuille and laminar flow as if this is the main application and then without more ado it was used in every conceivable type of flow. Subsequently, however I thought about it, there seemed to be no obvious justification for this extension of its use and yet it worked extremely well. With the rise of the internet I looked for explanations but I have never seen any satisfying explanation. The question that I now need to answer is, why is viscosity a property and therefore universal in its application and what does it quantify? In the event the question was in the front of my mind for many days before I could put together all that I know in some satisfactory way. Keep in mind that all we need as engineers is an explanation that lets us think about engineering applications without making silly mistakes of principle.

 

I think that people do not spend enough time just looking at water on the move. Water is the liquid that we see most often although no one else that I know ever bothers to look at it carefully even when they have an opportunity. When I first started looking at flowing water I could make little sense of it, mostly because my degree course was not a suitable preparation. Sometimes I could see no sense because I did not know the shape of the surfaces that affected the flow because they were obscured by the murky water. Year on year I learnt more and more observations fitted together and now I can often understand what is happening and why.