Theory

Question 1

Define the Nusselt Number

Answer 1

A measure of the total convective transfer to the conductive heat transfer.

Question 2

Define the Reynolds Number

Answer 2

A measure of inertial forces to viscous forces.

Question 3

Define the Grashof Number

Answer 3

A measure of the buoyancy forces over viscous forces.

Question 4

Define the Prandtl Number

Answer 4

A measure of the rate of viscous diffusivity to the rate of thermal diffusivity.

Question 5

Is Jason a fanny?

Answer 5

Yes.

Question 6

What is the simplification of the radiation equation for a small convex object in a large enclosure?

Answer 6

Q=A1 E1 Sigma (T1^4 - T2^4)

Question 7

What is the simplification of the radiation equation for parallel planes?

Answer 7

Q=(A Sigma (T1^4 - T2^4))/((1/E1)+(1/E2)-1)

Question 8

What is the simplification of the radiation equation for concentric cylinders.

Answer 8

Q=(A1 Sigma (T1^4 - T2^4))/((1/E1) +(1-E2/E2)x(r1/r2))

Question 9

Explain what geometrical or thermal aspects determine the temperature profile along a fin.

Answer 9

A larger surface area of a fin will increase transfer rate. A material with a greater heat transfer coefficient, h, will increase heat transfer also (e.g a aluminium fin is much more effective than a glass or wooden one).

Question 10

Explain term ‘fin effectiveness’.

Answer 10

The ratio of the overall fin heat transfer of fins over the heat transfer that would exist without fins being present.

Question 11

Explain term ‘fin efficiency’..

Answer 11

The ratio of the overall fin heat transfer ratio to the heat transfer if the entire surface of the fin was at the base temperature.

Question 12

What is the formula for calculating LMTD?

Answer 12

LMTD=((Delta Tb)-(Delta Ta))/ln(Tb/Ta)

Question 13

Explain the basic principle and its limitations upon ideal gas mixtures.

Answer 13

The basic principle is that each component of the mixture is independent of any other component. Mass and energy of each component can be added together to give total mass and total energy.

Question 14

Define Dalton’s law.

Answer 14

Daltons law: The pressure of a gas mixture is equal to the sum of the pressures each gas would exert if it existed alone at the mixture temperature and volume .

Question 15

Define Amagat law:

Answer 15

Amagat law: The volume of a mixture is equal to the sum off the volume each gas would occupy if it existed alone at the mixture temperature and pressure

Question 16

Define absolute humidity.

Answer 16

Ratio of mass of water vapour to the mass of dry air.

Question 17

Define relative humidity.

Answer 17

Mass of water vapour as a fraction of maximum possible at mixture temperature.

Question 18

Define dew point.

Answer 18

Temperature at which vapour starts to condense at constant pressure cooling. It is equal to saturation temperature at vapour pressure.

Question 19

Define air enthalpy.

Answer 19

Total enthalpy of mixture due to dry air and vapour.

Question 20

Define the concept of a compressibility factor.

Answer 20

Z is a measurement of how close a gas or mixture of gasses behaves like an idea gas. An idea gas has a compressibility factor of 1 and anything less than this becomes increasingly less ideal.

Question 21

Explain why ideal gas assumptions can be used for both air and water vapour for air conditioning applications

Answer 21

In air conditioning applications water vapour/air mixtures only contain about 1% of water vapour. This means that given air conditioning applications are generally at atmospheric pressure the water vapour pressure will