What if critical velocity ration is less than one?
Answers
How to Calculate Critical Velocity
Updated March 13, 2018
By Jonathan Marker
Critical velocity is the speed and direction at which the flow of a liquid through a tube changes from smooth, or "laminar," to turbulent. Calculating critical velocity depends on multiple variables, but it is the Reynolds number that characterizes the flow of the liquid through a tube as either laminar or turbulent. The Reynolds number is a dimensionless variable, meaning it has no units attached to it.
Calculating Critical Velocity
If you wanted to find the critical velocity for water moving through a section of pipe, we'll start out by using the basic formula for calculating critical velocity: Vcrit = (Nr_µ) / (D_ρ). In this equation, Vcrit represents critical velocity, Nr represents the Reynolds number, µ (mu) represents the coefficient of viscosity (i.e., the resistance to flow) for a given liquid, D represents the inner diameter of the pipe, and ρ (rho) represents the density of the given liquid. The µ (mu) variable is measured in meters-squared per second and the density of the given liquid is measured in kilograms per meter-squared.
Say you have a two meter-long section of pipe with an inner diameter of 0.03 meters, and you want to know the critical velocity of water passing through that section of pipe at a velocity of 0.25 meters per second, represented by V. Although µ varies with temperature, its typical value is 0.00000114 meters-square per second, so we will use this value in this example. The density, or ρ, of water is one kilogram per cubic meter.
If the Reynold's number is not given, you can calculate it using the formula: Nr = ρ_V_D/µ. Laminar flow is represented by a Reynold's number of less than 2,320, and turbulent flow is represented by a Reynold's number of greater than 4,000.
Plug in the values for each of the variables of the Reynold's number equation. After plugging in the values, the Reynold's number is 6,579. Because it is greater than 4,000, the flow is considered turbulent.
Now plug in the values to the critical velocity equation, and you should get: Vcrit = (6,579_0.000000114 meters/second-squared) / (0.03 meters_1 kilogram/cubic meter) = 0.025 meters/second.
References
About the Author
Did you find this page helpful?
Related Articles
How to Determine Specific Gravity
How to Calculate Water Flow Through a Pipe Based on Pressure
How to Convert Differential Pressure to Flow
How to Convert CV to GPM
How to Find Partial Pressures
How to Calculate Orifice Size
How to Calculate Pressure From Flow Rate
From the WebPowered by
What Happens When a Man Grows a Beard, According to Science
Dangerous Food Trends You Should Absolutely Never Try
Extinct Creatures That Would Wreck the Earth If They Were Alive
The American Hermit Who Fled the US 50 Years Ago
You Should Never Put a Lemon in Your Drink. Here's Why
Study Reveals After You Die, Your Brain Knows You're Dead
The FOIA Reveals Everything the FBI Knows About Bigfoot
This Is the Oldest Family on Earth
How to Determine Specific Gravity
Updated April 24, 2017
By John Brennan
Specific gravity is the ratio of the density of a substance to the density of water at a given pressure and temperature. Specific gravity is typically measured at 4 degrees Celsius (39.2 degrees Fahrenheit), unless otherwise indicated. According to SIMetric, the density of water at 4 degrees Celsius and standard atmospheric pressure is 62.4 pounds per cubic foot.
Determining specific gravity is a simple two-step process that starts with calculating the density of the substance you want to test. Note that specific gravity is only applicable to liquids and solids, because gases have a variable density.
Measure out 25 milliliters (1.526 cubic inches) of the liquid you intend to test, using the graduated cylinder.
Place the cup on the scale and measure its weight. Next, add the 25 milliliters of liquid from the graduated cylinder to the cup and weigh the cup again. The difference between the weight of the cup with and without the liquid is the weight of the liquid.
Divide the weight of the liquid by the volume of the liquid to find its density. Density is measured in units of mass per volume (i.e., how many grams or pounds of the substance fit into a specific volume). The density of water, for example, is 1 gram per milliliter, or 62.4 pounds per cubic foot.
Divide the density of the liquid by the density of water to find the specific gravity. In other words, specific gravity equals the density of the liquid divided by 62.4 pounds per cubic foot (if you are using imperial units) or 1 gram per milliliter (if you are using metric