Density and Viscosity

Question 1

What are the boiling, melting and critical temperatures of oxygen?

Answer 1

Boiling point: -183 C
Melting: - 219 C
Critical temp: -118

Question 2

What is the critical pressure of oxygen?

Answer 2

50 bar

Question 3

What is saturated vapour pressure (SVP) of oxygen at 20 C?

Answer 3

1.4 bar

Question 4

What are the boiling, melting and critical temperatures of nitrous oxide?

Answer 4

Boiling point: -88 C
Melting: - 91 C
Critical temp: 36.5 C

Question 5

What is the critical pressure of nitrous oxide?

Answer 5

72 bar

Question 6

What is saturated vapour pressure (SVP) of nitrous oxide at 20 C?

Answer 6

50.8 bar

Question 7

What are the boiling, melting and critical temperatures of carbon dioxide?

Answer 7

Boiling point: -79 C
Melting: - 57 C
Critical temp: 30 C

Question 8

What is the critical pressure of carbon dioxide?

Answer 8

73 bar

Question 9

What is saturated vapour pressure (SVP) of carbon dioxide at 20 C?

Answer 9

57 bar

Question 10

What are the boiling, melting and critical temperatures of helium?

Answer 10

Boiling point: -269 C
Melting: - 272 C
Critical temp: - 268 C

Question 11

What is the critical pressure of helium?

Answer 11

2.3 bar

Question 12

Regarding the density of a gaseous substance (true or false):

Density is mass per unit volume measured in kg.m

Answer 12

False. Density is measured in kg/m3.

Question 13

Regarding the density of a gaseous substance (true or false):

A decrease in pressure increases density

Answer 13

False. Increasing pressure leads to an increase in density.

Question 14

Regarding the density of a gaseous substance (true or false):

An increase in temperature increases the kinetic energy of the molecules within gas and therefore increases the density

Answer 14

False. Decreasing temperature leads to an increase in density.

Question 15

Regarding the density of a gaseous substance (true or false):

Density has a more marked effect on turbulent flow than viscosity does

Answer 15

True

Question 16

Regarding the density of a gaseous substance (true or false):

Density has a more marked effect than viscosity on the flow at the base of a rotameter

Answer 16

False. The base of a rotameter has a narrow orifice around the bobbin causing laminar flow, which is more markedly affected by viscosity than density.

Question 17

Regarding the viscosity of a gaseous substance (true or false):

Viscosity is directly proportional to laminar flow

Answer 17

False. Viscosity is inversely proportional to laminar flow.

Question 18

Regarding the viscosity of a gaseous substance (true or false):

The viscosity of honey is greater than that of water

Answer 18

True.

Question 19

Regarding the viscosity of a gaseous substance (true or false):

An increase in temperature increases viscosity

Answer 19

False. Increasing temperature decreases viscosity, the ability of the substance to resist flow.

Question 20

Regarding the viscosity of a gaseous substance (true or false):

An increase in pressure leads to an increase in viscosity

Answer 20

True

Question 21

Regarding the viscosity of a gaseous substance (true or false):

A fluid with higher viscosity improves laminar flow, given fixed tube length and radius and pressure gradient

Answer 21

False. Increasing viscosity reduces laminar flow.

Question 22

Regarding flowmeters (true or false):

A pneumotachograph is an example of a fixed orifice, variable pressure device

Answer 22

True

Question 23

Regarding flowmeters (true or false):

A rotameter relies on the constant pressure drop supporting the weight of the bobbin

Answer 23

True

Question 24

Regarding flowmeters (true or false):

A Wright’s Respirometer is used to measure flow

Answer 24

False. A Wright’s Respirometer is used to measure volume; only with the addition of a timing device can it measure flow.

Question 24

Regarding flowmeters (true or false): A peak expiratory flowmeter is an example of a constant pressure variable orifice device

Answer 24

True

Question 25

Regarding flowmeters (true or false): A Bourdon gauge can be used to calculate flow if a timing device is also used

Answer 25

False. A Bourdon aneroid gauge is used to measure pressure.

Question 26

Which of the following best describes the effect of changes on flow measurement near the top of a rotameter? A. An increase in gas density causes the bobbin to rotate less B. A decrease in viscosity leads to an increase in laminar flow C. The pressure difference across a rotameter bobbin is constant D. An increase in gas temperature decreases the density of the gas and increases flow E. The flow measurement should be read from the top of the bobbin

Answer 26

D. This statement is the best fit because it describes the effect of a change in gas density on the more turbulent flow found at the top of a rotameter. A. Incorrect. An increase in density reduces flow and, therefore, causes the bobbin to rotate less. However, the rotation of the bobbin does not affect the measurement of flow. B. Incorrect. Decreased viscosity causes an increase in laminar flow, but laminar flow is found mostly at the base of the rotameter where the orifice is small. C. Incorrect. The pressure difference across the bobbin, with the weight of the bobbin pressing down and gas pressure pushing up, is constant and will not affect changes in flow measurement. E. Incorrect. The flow measurement should be read from the top of a flat-topped bobbin and from the middle of a spherical bobbin, neither of which affects changes in flow measurement at the top of a rotameter.

Question 27

The boiling point of oxygen is: A. -183 C B. -88 C C. -269 C

Answer 27

A. Correct. B. Incorrect. -88C is the boiling point of nitrous oxide. C. Incorrect. -269C is the boiling point of helium.

Question 28

The critical temperature of nitrous oxide is: A. 72C B. 30C C. 36.5C

Answer 28

A. Incorrect. 72 bar is the critical pressure of nitrous oxide. B. Incorrect. This is the critical temperature of carbon dioxide. It is similar to the critical temperature of nitrous oxide which is why they can both be condensed to liquids. C. Correct.

Question 29

What will happen to the flow if the temperature is increased in laminar flow? A. The flow will increase B. The flow will decrease C. The flow will remain the same

Answer 29

A. The flow will increase Laminar flow is affected by the factors in the Hagen-Poiseuille equation: Laminar flow = ∆Pr4∏/8lη Where ∆P is the pressure difference from the start of the flow to the end; r is the radius of the tube; l is the length of the tube and η (Greek symbol Eta) is the fluid viscosity. Temperature reduces viscosity and hence increases flow.

Question 30

What will happen to the flow if the pressure gradient is increased in laminar flow? A. The flow will increase B. The flow will decrease C. The flow will remain the same

Answer 30

A. The flow will increase Laminar flow is affected by the factors in the Hagen-Poiseuille equation: Laminar flow = ∆Pr4∏/8lη Where ∆P is the pressure difference from the start of the flow to the end; r is the radius of the tube; l is the length of the tube and η (Greek symbol Eta) is the fluid viscosity. A pressure gradient increase describes a variation in pressure applied to the flow of fluid and is not the same as consistent pressure increase. Adding a pressure bag to a litre of fluid increases the rate of flow; this is an increased pressure gradient.

Question 31

What will happen to the flow if the viscosity is reduced in laminar flow? A. The flow will increase B. The flow will decrease C. The flow will remain the same

Answer 31

A. The flow will increase Laminar flow is affected by the factors in the Hagen-Poiseuille equation: Laminar flow = ∆Pr4∏/8lη Where ∆P is the pressure difference from the start of the flow to the end; r is the radius of the tube; l is the length of the tube and η (Greek symbol Eta) is the fluid viscosity.

Question 32

What will happen to the flow if the temperature is increased in turbulent flow? A. The flow will increase B. The flow will decrease C. The flow will remain the same

Answer 32

A. The flow will increase Turbulent flow is proportional to r2 and √∆P and inversely proportional to length of the tube and density of the fluid. Temperature reduces density and therefore increases flow.

Question 33

What will happen to the flow if the pressure gradient is increased in turbulent flow? A. The flow will increase B. The flow will decrease C. The flow will remain the same

Answer 33

A. The flow will increase Turbulent flow is proportional to r2 and √∆P and inversely proportional to length of the tube and density of the fluid. Increasing the pressure gradient increases turbulent flow but not as much as laminar flow, because the streamlining is lost.