# fluid machanics Definition and Topics - 45 Discussions

No Wikipedia entry exists for this tag
1. ### Comparetto type Air Cleaner/Filter: What causes its increased airflow?

Typical box fan+air filter setups use axial consumer-grade fans designed for providing maximum air flow at low power consumption. These fans do not provide sufficient air flow at the high static pressure requirements typical of air filters. The air filters DIYers use are high Merv(e.g Merv 13)...
2. ### I What is a free surface?

I’m currently studying Fluid Mechanics, during an analysis I came across this We now consider an example that combines centrifugal force and gravity: a liquid in a drum (centrifuge) rotates with constant angular velocity ##\omega## about a vertical axis. The centrifugal force per unit of...
3. ### Three doubts in a paragraph on the equilibrium of Incompressible fluids

These are the images from Sommerfeld’s Lectures on Theoretical Physics, Vol 2 chapter 2, section 6, Equilibrium of Incompressible Fluids. Image 1 Image 2 Doubt 1 : What does it mean for a force to act on a fluid volume? Force acts on a point, force may act on a surface but I’m unable to...
4. ### (Fluid mechanics) How to find the flow rate of a gas from a vessel

I am working on a project where I have to calculate various results relating to the motion of a water bottle rocket being launched. I am currently stuck on trying to find how long the thrust period of the rocket is. The model for the rocket is as follows: It is a 2L (0.002m3 bottle filled with...
5. ### Flow Rate (Q) of Viscous Flow between Two Plates

I know how to derive the formula, but I have no idea how to actually use this. Where it says ##50~cm## wide, I'm not sure if that's in the x-direction or the z-direction. ##W##, the width in the equation, is in the z-direction. ##\mu## can be calculated, but I'm not sure what the pressure...
6. ### Trouble with fluid thermodynamics and nuclear thermal rockets

Summary:: In need of help determining the exhaust velocity of a rocket nozzle given temperature and propellant molar mass Greetings and salutations! My name is Robert DeVries, world builder extraordinaire. I have come with questions in search of answers. So for the last few days I've been...
7. ### Impeller analysis help

Hello there, im trying to analyze an impeller i found at home (small one) so i can find the torque-speed graph. The thing is that i get stuck in an equation with 3 unknowns instead of 2 and i dont know what else to assume. My approach is as follows: I take the usual equation: ## M = \dot{m} (...
8. ### Fluid Mechanics: Flow rate required to achieve a constant height

Some thoughts that I've had on the question are saying the volume flow rate (##Q##) in, must equal the volume flow rate out. If that's the case, then: ##Q_{in} = Q_{out}## ##A_1V_1=A_2V_2## But... no areas have been given. And height doesn't enter this equation at all. Then I thought it...
9. ### Thrust on an triagular lamina emersed in a liquid.

I feel there is a really obvious flaw in my logic but i cant pin it down So i have to find the thrust on the lamina which is basically force of bauyancy F(bouyancy)= Vρg Now volume of the triangular lamina is its rea into its hieght. v = Ah hence F = Ahρg some information i feel i didnt...
10. ### I want to understand this equation - Fluid Mechanics

Hi all! I have started reading Fluid Mechanics at my own pace (no university study) and really I would like to grasp the ideas behind it. So I have Fluid Mechanics by Cengel - 4th edition. At page 45 the coefficient of compressibility or bulk modulus of elasticity (κ) is introduced. ##κ =...
11. ### Energy equation for fluid mechanics

Homework Statement Water is supplied at 4.50 m3/s and 415 kPa (abs) to a hydraulic turbine through a 1.0-m inside diameter inlet pipe as indicated in the figure. The turbine discharge pipe has a 1.2-m inside diameter. The static pressure at section (2), 3 m below the turbine inlet, is 25 cm Hg...
12. ### Splash mechanics on Mars

They found an underground lake on Mars last week! Given that the lake exists and is actually liquid (and has a surface), two obvious questions come to mind: 1. Will I be able to beet my earthly current record in bouncing a pebble there? 2. If I release a pebble from a given height here and...
13. ### Injector pressure drop in a liquid rocket engine

Hello everybody, I hope you are doing fine. I'm currently designing an injector for a hydrogen peroxide - ethanol engine, and the following formula is confusing me: Q = Cd * A * sqrt( 2 * dP / rho); where Cd is the discharge coefficient, A the total area, dP the pressure drop, and rho the...
14. ### Relationship between volumetric flow rate and pressure

Hello everybody, This is my first post. I've been working on a liquid rocket engine for a while, but I have never gotten to work on its feed system (fluid mechanics), until recently. We are using a very simple pressure fed system, and its main goal is to deliver the propellants at a specific...
15. ### Control volume, Fluid mechanics

Homework Statement I have a situation as illustrated by the image above, where the red box illustrates the CV. The pressure on the left side of CV is P1, while the pressure on the right side of CV is P2. Here I´ve directed the pressure forces acting inwards on CV. The problem arises with...
16. ### Rising of a liquid during rotataion in a cylinder

Homework Statement [/B] A 25-cm-diameter, 100-cm-high cylindrical container, (as shown), is partially filled with 75-cm-high liquid (density = 900 kg/m3). Determine the rotational speed at which the liquid will start spilling. Calculate the gauge pressure at the centre of the bottom of the tank...
17. ### Area of common surface of two bubbles

What will be the area of common surface of two identical bubbles of radius R , i know there common surface will be flat as the radius of curvature of comman surface will tends to Infinity , but how do i relate with area of flat surface I tried to use Energy = Surface tension * area And then...
18. ### Mathematica Solve Perturbation problem with mathematica

u'(1-epsilon(u')^2)=-y uo(1)=0 u1(1)=0 I need solve this problem with mathematica.
19. ### Difficuilt and/or interesting problems in fluid mechanics

Homework Statement Can anyone please give me hard and interesting problems regarding fluid mechanics problems such as hydrostatic and air prssure bouyance force and Bernoullis equation(Bernoullis equation problems only for liquids)? I tried looking for them but the ones I found were quite...
20. ### A hollow sphere sinks some fraction f in water..

Homework Statement When completely hollow. To what fraction of volume should water be poured into it so that it is just enough to cause the sphere to sink. [/B] Homework Equations Archemedes : Buoyant fource equals weight of water displaced The Attempt at a Solution Let's first find the...
21. ### Why must we use integral to find the resultant force?

Homework Statement Hydrostatic force on a plane surface ex: Hydrostatic force on a gate: Homework Equations The Attempt at a Solution why cant we just use the formula in the red box above for problem 3.57? instead I have to use integral I am confused, how does this gate different from a...
22. B

### Finding torque in rotating cylinder (viscosity )

Homework Statement Homework Equations τ= η* (dv/dy) The Attempt at a Solution so dA= 2π* r * dr T = ∫ τ * r * dA T = ∫((0.01* r* 2*π * 450 /60)/(5*10^-3) ) * r * 2π* r *dr = (592.1762)*(r^4/4) T = 0.11 Nm is this correct?
23. D

### E-Balance for Jet Ejector

I am working on problem that has to deal with a jet ejector. For the life of me, I cannot figure out the E-Balance equation for it. Below is a cut away image of the ejector. The fluid is the same so using the ideal gas law I do not think should be included. Any help is greatly appreciated...
24. ### Mean section method

Homework Statement I have problem of obtaining the cross sectional area . Homework Equations The Attempt at a Solution Taking section 2-3 as an example , my working is [ (3.3 +4.8) / 2 ]* 5 = 20.25 , but the ans provided is 29.28 , how to get the 29.28 ?
25. ### Surface runoff

Homework Statement In my book , i was told that when the drainage of surface is high then the surface runoff will be low . However , i dont think it's correct . Homework Equations The Attempt at a Solution Definiton : Runoff can be described as the part of the water cycle that flows over...
26. ### Flow thru a channel constriction

Homework Statement When a part of the channel is constricted , why will the Emin = Eo ? Homework Equations The Attempt at a Solution I just have the figure showing in case 1 and case 2, Emin = Eo without any explanation ... Can someone explain about it ? I tried to search many online...
27. ### Possible Air Conditioning System?

Hello everyone! Summer is coming and instead of buying a $200-$400 air conditioner, I'd figure I could try a DIY version. I came up with a schematic (attached below) and how I think it would work. I feel like I'm missing something blatantly obvious that will make it not feasible. Wondering if...
28. ### Best hydraulic section

Homework Statement Determine the depth of the flow of channel if the best hydraulic channel is needd for composite channel in figure to convey flow rate of 6.5(m^3/s) , Manning coefficient n on bed slope are 0.015 and 0.0015 respectively . Homework Equations The Attempt at a Solution I...
29. ### Does entropy increase behind surface tension?

Is there any entropic gain when the surface of a liquid is minimised? Per example, molecules "enjoy" maximum entropy when they are at the interior. Is this valid?
30. ### Should I learn fluid mechanics or thermodynamics

I am graduate student from structural mechanics of solids and need to learn 1 course from fluids and thermal group which includes fluid mechanics or thermodynamics+heat transfer. I am unsure which one would be better to learn, especially which would be helpful in future for solid mechanics. Can...