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Question 1

Define fluid in terms of mechanical behaviour

Answer 1

Both fluids and solids resist normal stresses by deforming however solids deform a limited amount and fluids do so continuously

Question 2

Define stress

Answer 2

Force per unit area

Has two components - shear and normal

Question 3

Define pressure

Answer 3

Normal stress in static fluids

Question 4

Stress equations

Answer 4

σ= F/A
τ= F/A

Question 5

Technique of forming equations by simplifying units

Answer 5

Principle of dimensional homogeneity

Question 6

Coefficient of compressibility

Answer 6

κ = dP/(dρ/ρ) = −dP/(dV/V) = - pressure change/ relative volume change

Question 7

Isothermal compressibility

Answer 7

α = 1/κ for an ideal gas RT = constant and κ=P

Question 8

Reynold’s number equation

Answer 8

Re = ρVL/μ

Question 9

Reynold’s number values

Answer 9

Re < 2400 laminar
2400 < Re < 4000 transitional
4000 < Re turbulent

Question 10

Mach number

Answer 10

Ma =v/c= flow velocity /speed of sound
Ma<1 subsonic
Ma =sonic
1< Ma supersonic
1 << Ma hypersonic

Question 11

Extensive properties

Answer 11

Depend on amount in system (V, E)

Question 12

Intensive properties

Answer 12

Independent of mass in system (T, ρ)

Question 13

Continuum approximation

Answer 13

Atomic nature of matter is neglected, properties can be extrapolated to zero-size regions

Question 14

Dynamic viscosity meaning μ

Answer 14

Resistance to deformation of a fluid from shear stress τ = μ dy/du

Question 15

Viscosity for a newtonian fluid

Answer 15

μ = μ(P,T) strong function of temperature

Question 16

Viscosity of a non-Newtonian fluid

Answer 16

μ = μ(du/dy)

Question 17

Kinematic viscosity

Answer 17

v = μ/ρ ratio of dynamic viscosity and density

Question 18

Examples of non-Newtonian fluids

Answer 18

Shear thinning - colloidal suspensions, polymer solutions (paints)
Shear thickening - water-cornstarch (custard), water-sand
Bingham plastic - toothpaste, mayonaise

Question 19

Surface tension

Answer 19

Intermolecular forces cause gas-liquid phase to act like it’s in tension

Question 20

Capillary effect in tubes

Answer 20

Wetting h= 2σcosφ / ρgR

Non-wetting eg mercury φ>90°

Question 21

Saturation temperature Tsat

Answer 21

Temperature at which a substance changes phase at a given pressure

Question 22

Saturation pressure Psat

Answer 22

Pressure at which a substance changes phase at a given temperature

Question 23

Pv

Answer 23

Pressure of vapour molecules above liquid in equilibrium

Question 24

Caviation

Answer 24

Occurs when P~ Pv

Bubbles form and collapse from low to high pressure causing damage

Question 25

When there is a linear velocity distribution

Answer 25

du/dy = V/h

V is velocity and h is gap