rheology

Question 1

what is a newtonian fluid

Answer 1

the rate of flow of the fluid (y) is directly propionate to the applied stress

Question 2

what is the equation for relative viscosity

Answer 2

nr = n/no

nr = relative viscosity
n = the viscosity of solution
no = relative to the solvent

Question 3

what is the equation for specific viscosity

Answer 3

nsp = nr -1

Question 4

what is the equation for reduced viscosity or the viscosity number

Answer 4

k= nsp/ c

k = reduced viscosity
nsp = specific viscosity
c = mass concerntrattion of solution (g/cm^3)

Question 5

how do you determine the viscosity of a newtonian fluid

Answer 5

glass capillary viscometers
- where the time taken for the fluid to pass through the dashed line is measure. then using the HAGEN - POISEUILLE EQUATION
- disadvantages are that it is time consuming, can not be automated and no control of shear

falling sphere viscometer
-the viscosity it’s measured through STOKES LAW where it is rearranged to make n the subject

Rotational viscometers
- the viscosity is measured by measuring the torque and turning speed - this can be easily measured at different rates

Question 6

what are some examples of newtonian fluids

Answer 6

water

ethanol

Question 7

what are non newtonian fluids

Answer 7

the viscosity of the fluid is dependant on the shear, the shear stress and the shear rate

Question 8

what are the types of newtonian fluids

Answer 8

1. plastic bingham flow
2. psuedoplstic
3. dilantancy

Question 9

what is plastic bingham flow

Answer 9

• a bingham plastic does not flow until. field stress is applied
  for example plastic

Question 10

what is pseudo plastic

Answer 10

• this is when shear thinking occurs - the viscosity reduced

the viscosity reduces with added sheer

the gradient is curved and then plato’s near the need

when low sheer - the polymer chains re tangled and are ,ore viscous

when there is high shear the polymer chains are untangled and it is less viscous

and example is polymer gels

Question 11

what is dilatancy

Answer 11

• shear thickening

the gradient (which is viscosity) is low then rises
the viscosity increases with added shear

when there is low shear the particles are dispersed a

when there is high shear the particles are forced l together making it more viscous

an example is concerntrated suspension such as corn starch

Question 12

what is the power law

Answer 12

• it is able to tell us whether a fluid is newtonian, psuedoplastic, dilatancy

if the flow of behaviour index (n) is

1= newtonian fluid
1 or more = psuedoplastic
1 or less = dilatancy

Question 13

what is time dependant behaviour

Answer 13

• the flow of some materials is dependant on the time
  teh changes i the structure of the material may not occur immediately

Question 14

what are the w different types of rheomsteer testing

Answer 14

• flow - to measure high shear, in single direction
• creep - to measure shear in a single push and in a single direction - this is for low shear
• oscillatory - to measure shear, this is in both directions - back and fourth at low shear rate

Question 15

what is the difference between spring and dash[ot

Answer 15

• spring - this is when maximum force is applied making sure that it is below the specific yield point - so that no bonds are broken, it will experience stress and once that strain is gone it will immediately return to its original position
• dashpot - when strain is applied it will not return to its original position and will rather stay in teh position that it originally was in

Question 16

what is viscoelasticity

Answer 16

this is when some fluids for example polymer gels behave like both spring and dashpot so when strain is applied they may return it it’s original position but with will have lost some energy