Fluids, W2

Question 1

Causes of viscosity in gases and liquids.

Answer 1

G- molecular interchange due to lack of rigid constraints, weak cohesive forces. Incr with temp.
L-shear stress from molecular interchange, cohesive forces, decr with temp, incr with high pressure.

Question 2

Kinematic viscosity

Answer 2

v=μ/ρ (viscosity/ fluid density). (ms^2/s).

Question 3

Rise and fall of a liquid in a narrow tube due to surface tension.

Answer 3

Forces- atmospheric pressure is equal outside and inside the tube. Upward pull balanced by weight of liquid column.Convex Hg- liquid does not wet the tube, concave (water): liquid wets the tube.

Question 4

Hydraulic lift

Answer 4

Works on pascals principle: pressure applied to a confined fluid is transmitted equally to all directions.

Question 5

Vapour pressure

Answer 5

Pressure exerted by a vapour in equilibrium with its liquid phase at a given temperature. Molecules in constant movement have enough energy to escape liquids surface and become vapour.
Confined space vapour molecules= liquid.
Incr temp means incr vapour pressure.
Liquid BOILS when vapour pressure= external pressure.

Question 6

Cavitation

Answer 6

When bubbles form in a liquid due to pressure drag, low pressure zone. They collapse when subjected to a higher pressure zone and form again due to energy transfer.

Question 7

Define Compressibility and Bulk modulus

Answer 7

C:
The ability of a substance to decrease its volume under increased pressure, (1/Pa).
BM: a measure of a substance’s resistance to compression. K= -V (dP/ dV). Change in pressure over change in volume.
Gases; high compressible, low K.
Liquids; less compressible, high K.
Solids; incompressible, very high K.
K= δp/-δV/V= δp/δρ/ρ

Question 8

Coefficient of compressibility β

Answer 8

β= -1/V (δV/δp) takes place at a constant temperature.