Practice Problem - Reynolds Number

All right, hi everybody. So let's go ahead and solve a question that is fairly fast in finding the Reynolds number. And in this problem, I will also illustrate you how to read charts that is given at the back of the fluid mechanics section of the FE Reference Manual. Okay, and this particular question is asking me on I have a water at 90 degree C, this, it is flowing with a mean velocity of 0.1 meter per second in a 10 centimeter diameter pipe. The Reynolds number is closest to which of these four selections. First thing is, what I'm showing you in here is not going to be given to you at the side of the question. Okay, this is actually part of the FE Reference Manual, and in the tenth edition, that is at page 198. Okay, so you will be flipping to that and you will be reading the numbers for the 90 degree C that is listed over here. Okay, but before that, we need to know what is the definition of Reynolds number. So the Reynolds number definition is given to you on page 181 of the reference manual, or you might as well memorize this. This is not a very difficult thing to memorize. It is rho, V, D, over the dynamic viscosity. Or, I'm just literally copy-pasting from the reference manual. I have this as the kinematic viscosity. So this is the kinematic viscosity, this is the dynamic viscosity. Okay, so obviously you will get the same value, right? But what I'm gonna do is, I'm gonna take a little bit of a shortcut and use this one, because then I know my velocity, 0.1 meter per second. This is 0.1 meters as well, 10 centimeters, right? And I simply go ahead and read the kinematic viscosity, plug it in, and see what happens. Okay, that's the approach that I'm gonna take. So on here, then. Let's go ahead and the velocity is 0.1 meter per second, the diameter is 0.1 meters, 10 centimeters, divided by—that's kind of hard to read—so I'm gonna zoom in in here. So it is 1, 2, 3, 4, 5, 6, 7. Okay, so it is 3.26 times 10 to the minus 7 meters square per second. That is the unit of kinematic viscosity. Actually, it's given here as well, right, right here. So then you simply go ahead and punch this into your calculator, and you will be getting yourself 30,674. What's the unit? Unitless, right, there is no unit. So that is almost 30,500 or 600, and when I look at the choices that I'm given, I just get myself Part C is the answer. Thank you for watching this video.