Third Year Sem 2 Theory

Question 1

What is Dry Bulb Temperature?

Answer 1

The ambient air temperature. It is called “Dry Bulb” because the air temperature is indicated by a thermometer not affected by the moisture of the air. (Normal Temp of air)

Question 2

What is the Wet Bulb Temp?

Answer 2

The adiabatic saturation temperature. The Wet Bulb temperature is always between the Dry Bulb temperature and the Dew Point

Question 3

What is the Dew Point?

Answer 3

The Dew Point is the temperature at which water vapor starts to condense out of the air.

T.dp = Tsat@pv

Question 4

What is the absolute / specific humidity?

Answer 4

Ratio of vapor mass/ dry air mass

Also w = 0.622 (Pv/Pa) or = 0.622(Pv/P-Pv)

Question 5

What is relative Humidity?

Answer 5

Ratio of Mass of vapor / Mass of maximum moisture hold of air

O/ = Pv/Pg

Question 6

What is theNusselt Number?

Answer 6

Indicated the improvement in convective heat transfer from a surface relative to conduction heat transfer.

Question 7

What is the Prandtle Number?

Answer 7

Indicated relative magnitude of thermal to momentum diffusion. Also provides property dependence of fluid

Question 8

What is the Reynolds Number?

Answer 8

Ratio of Inertia to Viscous effects. Also shows turbulent and mixing ability.

Question 9

What is the Grashof Number?

Answer 9

It is the natural convention equivalent of the Re number and the flows ability to mix.

Question 10

What are the three modes of heat transfer? Explain them!

Answer 10

Conduction - spontaneous from hot-cold wherever temp gradient
Convection - Transfer due to fluid motion
Radiation - Electromagnetic waves between separated surfaces

Question 11

What is Fourier Law?

Answer 11

The rate of heat flowing in a given direction is proportional to the temp gradient in that direction and the area normal to the direction.
Q=-KA dT/dx

Question 12

What’s the difference between natural and forced convection?

Answer 12

Natural (free) is when induces by buoyancy forces

Forced caused by external forces (fans or pumps etc)

Question 13

What are the three things that happen to Radiation?

Answer 13

Absorbed (alpha), Transmitted (tauo), Reflected (rho)

Question 14

What is a black body?

Answer 14

One which completely absorbs radiation! alpha = 1

Question 15

Will shiny things have a high or low emissivity?

Answer 15

lower

Question 16

What is Irradiation?

Answer 16

G is the combined total of radiation.

example alpha = G.absorbed rad / Incident Radiation (G)

Note: Alpha + Tauo + Rho = 1

Question 17

What is an opaque body?

Answer 17

Tuao = 0 (transmitted radiation = 0)

Question 18

What affects fin temp distribution and rate of decrease?

Answer 18

Its controlled by the convective heat loss relative to the conduction heat transfer. h and P determine the convective loss and K and A determine the conduction transfer.

Question 19

Explain the basic principle and its limitations upon which ideal gas mixtures are treated to allow calculation of properties and application to the energy conservation equations.

Answer 19

Mixtures assumed independent and dont interact at molecular level. Mass/energy can simply add. Limitations as gas behaves non-ideal at high densities with low temp or high pressure.

Question 20

What’s Daltons Law?

Answer 20

Pressure of a gas mixture is equal to the sum of pressures if each gas existed alone at the mixture temp and volume.

Question 21

What’s Amagats Law?

Answer 21

Volume of a gas mixture is equal to the sum of volumes if each gas existed alone at the mixture temp and pressure.

Question 22

What is the Rayliegh Number?

Answer 22

Product of Grashofand Prandtle