Water and saline fluid mechanics

In summary, the speaker has a system that pumps water/saline and is trying to determine the relative flow rate, pressure, and velocity in different tubes. They are unsure if they have enough information and may need to hook up a pressure gauge to the outflow to calculate the head drop. Another person suggests using the Hagen-Poiseuille equation and taking into account any non-ideal effects in the system. The speaker may need to use real data and equipment to accurately determine the fluid properties.
  • #1
illogical_Eric
1
0
Hey Guys,
i have a system that I'm pumping with water/ saline. as illustrated below.

At the inflow i hooked up a pressure gage to my pump and read 120mmHg (closed system), and at the outflow I am reading 400ml/min ( I did this by disconnecting the system and timed filling a beaker). I'm trying to work out what the relative flow rate,pressure and velocity of the water/saline will be in the 6mm ID and 10mm ID tubes respectively.

Do i have enough information to do this? I think i need to hook my pressure gage up to the outflow and calculate the head drop across the system, but I'm not so sure.
Thanks for any help, i didn't take any fluid mechanics modules in college.
Eric
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  • #3
Not enough information. At bare minimum you would to provide the lengths of the five sections. From there you may be able to draw on the available engineering data for the fluid and types of pipe, plug the data for each section into the Hagen–Poiseuille equation to get the effective resistances, and then do something analogous to a KVL/KCL analysis (that layout looks similar to a Wheatstone Bridge). That's assuming you ignore the Bernoulli effect around the ends of the 3mm section, which would complicate the math horrendously. (disclaimer: I haven't studied fluid mechanics either).

It sounds like this is not just an academic theoretical question. And since no one in the real-world would devise such a strange layout for simply moving fluid from point A to point B, I'm inclined to suspect that the fluid if doing something along the way, such as passing through valves or heat exchangers, which would change the situation significantly.

Even if you were to compile all of the basic data, the non-ideal effects from whatever-the-fluid-is-doing-along-the-way would likely swamp the accuracy of any simple mathematical model. It's not worth trying to figure it out from base principles.

At this point I would proclaim, "Ahh, @#$% it," and just go out and buy some https://www.amazon.com/b?node=3206433011&tag=pfamazon01-20 and pressure gauges and whack them in where I needed real, reliable data. I wouldn't be confident in anything else, anyway. And it sounds like this may be important (your use of the word "saline" rather than "salt water" or "sea water" is a clue...).

Fluid velocity is simple: AvgVelocity = FlowRate / CrossSectionalArea. Just keep you units consistent.
 
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Related to Water and saline fluid mechanics

1. What is the difference between water and saline fluid?

Water and saline fluid have different chemical compositions. Water is composed of two hydrogen atoms and one oxygen atom, while saline fluid contains additional sodium and chloride ions. This difference in composition affects their physical and chemical properties, such as density and viscosity.

2. How does the presence of salt affect the behavior of water in fluid mechanics?

The presence of salt in water increases its density and decreases its viscosity, making it more difficult to compress and flow. This can affect the way water moves in a fluid system, as well as its ability to dissolve and transport other substances.

3. How is the movement of water and saline fluid affected by temperature?

Both water and saline fluid have different densities and viscosities at different temperatures. As temperature increases, the molecules in these fluids gain more energy and move more quickly, causing them to spread apart and decrease in density. This can affect the overall flow and behavior of water and saline fluid in a system.

4. Can saline fluid mix with water in a fluid system?

Yes, saline fluid can mix with water in a fluid system. Due to the difference in density and viscosity, the two fluids may not mix evenly and may form layers or currents. However, the presence of salt can also cause water to dissolve and mix with other substances more easily.

5. How does the movement of water and saline fluid impact marine life?

The movement of water and saline fluid can have a significant impact on marine life. Changes in temperature, salinity, and other physical properties of these fluids can affect the behavior and distribution of marine organisms. High concentrations of salt can also be harmful to some species, while others have adapted to thrive in saline environments.

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