Fluid Mechanics

Question 1

What is fluid mechanics?

Answer 1

it is science of pyhsical behaviour of fluids

Question 2

In which parts can man divide fluids?

Answer 2

into Fluid statics and fluid dynamics

Question 3

What’s the difference fluid statics and fluid dynamics?

Answer 3

Fluid statics is considers as resting fluid, while fluid dynamics is moving fluids

Question 4

Why do we have to describe the flow processes of a fluid?

Answer 4

it helps to solve flow problems, designt of components through or around which flow occure and the flow monitoring

Question 5

Which energy can be used to describe fluid movement?

Answer 5

convective energy, where impules and mass transport is related to the movement of matter (fluid)

Question 6

What are properties of fluids?

Answer 6

1. permanent change of the average position of the molecules to one another (Amorphous behaviour)
2. it’s a continuum
3. only compressive forces can be applied (no tensile nor shear forces)
4. continuous deformation under the influence of shear force

Question 7

why do we have continuous deformtion under the influence of shear force?

Answer 7

low shear stresses lead to a change in shape–> movement–>flow

Question 8

why do we have just compressive forces?

Answer 8

because fluid doesn’t have any solid lattices

Question 9

Learn to draw the figure on how to describe the forces between the static and moving plane

Answer 9

do you know how to draw it?

Question 10

Which elements describe in the figure

Answer 10

Static , moving plane and water as the fluid

Question 11

Can you explain when the moving plane moves?

Answer 11

the moving plane is push by a force, creating a velocity gradient, which is proportional to the force

Question 12

How is the shear stress obtained?

know the equation

Answer 12

by diving the force by the area which is proportional to the velocity gradient

Question 13

Defination of viscosity

Answer 13

it is the internal resistance against movement (resistance of growth)

Question 14

what id the Newton’s law of viscosity?

Answer 14

it describe the relation between shear stress and rate of strain, which states that the shear stress is proportinal to the strain rate

Question 15

Is the dynamic viscosity temperature dependent?

Answer 15

it depends on the state of the material.

Question 16

what is the cause of viscosity?

Answer 16

it is the interchange of momentum between layers of fluid moving with different velocities due to the chaotic molecular motion

Question 17

How does the viscosity changes in liquid and gases if temperature is increased?

Answer 17

For liquids, the viscosity descreases, while for gases it increases

Question 18

Why does the viscosity in gases increase with increase of temperature?

Answer 18

in increase of temperature we have collision of molecules with different average velocities, impulse exchnage ad obtaining shear stress

Question 19

Why is the viscosity of gases smaller than in liquid?

Answer 19

due to lower density, less molecular collisions, causes lower viscosity

Question 20

Why is the vicsoity off liquids descreasing with increasing temperature?

Answer 20

with the increase of temperature, one increase the average distance between molecules, which decrease the intermolecular attractive forces.
Addtionally, the increase of T, leads to increase of the kinetic energy of molecues, which causes frequency of place changes

Question 21

why is the vicsoity of gases increasing with increasing temperature?

Answer 21

increase in temperature , leads to an increase in molecular collisions, which increases the viscosity

Question 22

Fluid statics, names the parts

Answer 22

Pressure in static fluid
communication vessels
Buoyance and sedimentation

Question 23

draw the forces which arts in the static fluids

Answer 23

do you know it?

Question 24

How can one describe the pressure forces in static fluids?

Answer 24

surface of volume elemnts is only affected by respective pressure forces of the neighbouring element

Question 25

How can you describe the pressure force in the x-direction?

Answer 25

Know the equation

Question 26

what other forces can affect the centr of the volume element?

Answer 26

Gravity, electrostatic, centrifugal or inertial froces

Question 27

What is the basic low in static fluid?

Answer 27

the sum of all froces is zero

Question 28

what is the general equation for the forces acting in x, y and z direction?

Answer 28

do you know it?

Question 29

Pressure in static fluids is describe as? (know the eqaution

Answer 29

in one dimension (in the z-direction)

Question 30

How does the following formual p(z)=p(o) + pgz results?

Answer 30

in a heavy fluid, one has a hydrostatic pressure distribution. the density of the incompressibilie fluid is constant, leading to a coordinate system changed

Question 31

for what can the hydrostatic pressure can be used?

Answer 31

for U-tube as measuring instrument

Question 32

How is the pressures between two connected water columns?

Answer 32

the hydrostatic pressure is equal in all planes

Question 33

what is the formula for the equilibrium of forces in a U-tube?

Answer 33

p1=P2 +pgh

Question 34

if the pressure differences is to high, what can be done to still obtain a small U-tube?

Answer 34

at high differences, fluid with high density should be used and vice vicel

Question 35

what is the Archimdes's principle?

Answer 35

A body of any shape immersed in a liquid experiences a weight reduction equal to the weight of the displaced liquid

Question 36

what is the buoyance force equation?

Answer 36

F(b)= m(water)*g

Question 37

what do you have to do if you want to know if your tablet will float or sink?

Answer 37

Do a force equilibrium, where the sum of the fg and fb equa zero. if the tablet density is low, it will float, otherwise it will sink

Question 38

what does the kinematics describes?

Answer 38

it describe the movement of a fluid without considerung the forces that cause this movemnet

Question 39

what are the two approcaches used to decriebe the movements?

Answer 39

La grange and the euler

Question 40

the La Grange approach is?

Answer 40

- obersever moves with fluid element - flow variables are each linked to one fluid element - temporal change of the fluid element properties

Question 41

the Euler approach is?

Answer 41

Stationary observer, decribes passing flow Behavior of the constantly changing fluid particles, which pass the defined loctation flo variables are each linked to several fluid elements

Question 42

what is the correlation between La grange and Euler approache?

Answer 42

material (La grangian) change of peroperties (derviation) of a fluid element expressed in Eulerian reference system

Question 43

what are the different lines?

Answer 43

Streamlines and Pathlines

Question 44

what are Stremlines?

Answer 44

it show at a certain time the directional filed of the velocity vector

Question 45

what is the methematical description of the streamlines?

Answer 45

tangents of velocity vectors (v*dx=0)

Question 46

what are Pathlines?

Answer 46

Path on which a fluid elemnt moves with advancing time

Question 47

what is the methematical description of the pathlines?

Answer 47

dx/dt=v(x,t) (like la grande)

Question 48

what happend for a steady flow?

Answer 48

the speed field is indepnedent of time, therefore streamlines is equal to the pathlines

Question 49

what is a stream filament theory?

Answer 49

- a one dimensional stream, where the steamlines form a closed surface flow tube

Question 50

how are the velocity vectors in the stream filament theory?

Answer 50

streamlines are tangents

Question 51

What does a streamlines tangents of velocity vectors means?

Answer 51

no penetration of fluid mass through the outer surface of tube

Question 52

what are other characteritics of the stream filament theory?

Answer 52

change of flow variables small in d-direction in compaerison to chnage in s-direction

Question 53

change of flow variables small in d-direction in compaerison to chnage in s-direction (what does this means)

Answer 53

one diemnsional changes (s-direction) along stream line calculable

Question 54

Why is the stream filament theory interesting for industry?

Answer 54

Flows through pipes and in channels can be treated as a single stream filament using values of two variables averaged over the cross-section

Question 55

what is the continuity equation?

Answer 55

A1w1=A2w2-->V1=V2

Question 56

what is the Bernoulli equation?

Answer 56

Do you know it?

Question 57

When is the Bernoulli equation valid?

Answer 57

Stationary flows incompressible media frictionless fluid no field forces other than gravity

Question 58

How can the Bernoulli equation be used to describe the nozzle for spray drying?

Answer 58

it is used to describe the pressure forces, where if the dynamic pressure increase, the static pressure has to decrease, for the pressure to be constant through out the drying process

Question 59

When does the dynamic pressure ncreases?

Answer 59

when something is flowing, the faster the liquid flows the lower the static pressure, therefore z1 nd z2 i the bernoulli equation are the same

Question 60

When do we used the hydrosataic, Bernoulli and continity equation?

Answer 60

contiunity equation for speed Bernoulli equation for Pressure hydrostatic for the High

Question 61

What are stirred tanks used for?

Answer 61

to reducs complex experiment in the lab, by simulation of stirred systems via numerical fluid dynamic

Question 62

how do you determined P in a stirred specific diagram?

Answer 62

Calculation of Re-number Reading the Ne-number from diagram Calculation of P

Question 63

when is no baffles needed?

Answer 63

when the laminar flow infleunes of the viscosity forces is dominates

Question 64

When is Turbulent reached?

Answer 64

mostly only reached when baffles are used

Question 65

the transition are depends on?

Answer 65

reactor type, hwereby the bafffles reduce the transition area, leading to turbulent flow