Study Guide 1

Question 1

Heat Transfer

Answer 1

thermal energy in transit due to a spatial temperature difference

Question 2

Heat flux

Answer 2

HT rate in the 1D direction per unit area perpendicular to the direction of transfer: W/m^2

Question 3

Mass Transfer

Answer 3

Movement of mass due to a species/[ ] gradient in the mixture

Question 4

Mass flux

Answer 4

MT rate in the 1D direction per unit area perpendicular to the direction of transfer: kg of A /m^2 s

Question 5

Conduction

Answer 5

HT through a solid material or stagnant fluid: electron movement (HT)

Question 6

Diffusion

Answer 6

MT through a solid material or stagnant fluid: random particle movements

Question 7

Convection (Heat or Mass)

Answer 7

HT or MT between a surface and an adjacent fluid: movement of heat/mass by both conduction/diffusion and advection (bulk fluid motion)

Question 8

Radiation

Answer 8

HT transfer by emission and absorption of incident electromagnetic radiation

Question 9

Thermal conductivity

Answer 9

Transport property that is characteristic of the wall material: k = W/mK

Question 10

Binary diffusion coefficient

Answer 10

D,AB used in Fick’s Law nd is a function of T/P: D,AB = m^2/s

Question 11

Mass diffusivity

Answer 11

Another name for the binary diffusion coefficient

Question 12

Fourier’s law

Answer 12

q” = -k (dT/dz)

Question 13

Fick’s law

Answer 13

j, Az = -D,AB(dpa/dz)

Question 14

Stationary medium approximation

Answer 14

1) small concentration
2) no advection/bulk fluid movement
What allows us to say that j = N for Fick’s Law and Diffusion

Question 15

Newton’s law of cooling

Answer 15

For Convection, q” = h(Ts - T-infinity)

Question 16

Heat transfer coefficient

Answer 16

h = W/m^2 K
Parameter NOT a property: depends on how fast the movement is

Question 17

Mass Transfer coefficient

Answer 17

kc = m/s
Used in the mass equivalent of the Newton’s Law of Cooling Equation (n,a” = kc(ps - p-infinity) where p = density

Question 18

Forced convection

Answer 18

when the flow is caused by external means like a fan, pump, or atmospheric winds

Question 19

Free convection

Answer 19

When the flow is induced by buoyancy forces which are due to density differences caused by temperature variations in the fluid

Question 20

Stefan - Boltzmann law

Answer 20

There is an upper limit to a surface’s emissivity power

Constant: 5.67 x 10^-8 W/m^2 K^4

q” net = Eo(Ts^4 - Tsurr^4)

E = epsilon, o = sigma

0 <= E <= 1

Question 21

Blackbody

Answer 21

Where the surface emissivity is 1:

Eb = q” emitted = oTs^4

Question 22

Gray body

Answer 22

q” rad = EoTs^4 - aG = Eo(Ts^4 - Tsurr^4)

where a = alpha; absorptivity (0-1)

Question 23

Irradiation

Answer 23

The rate at which all such radiation is incident on a unit area of the surface (G)

Question 24

Absorptivity

Answer 24

A surface radiative property based on the opaqueness of a surface:

Opaque: <1

Question 25

Emissivity

Answer 25

(Epsilon): property that provides a measure of how efficiently a surface emits energy relative to a blackbod

Question 26

Opaque surface

Answer 26

Where the absorptivity is <1 and portions of irradiation are reflected

Question 27

Hydrodynamic boundary layer

Answer 27

A region in the fluid through which the velocity varies from zero at the surface to a finite value (u-infinity) associated with the flow

Question 28

Thermal boundary layer

Answer 28

A region of the fluid through which the temperature varies from Ts at y = 0 to T-infinity in the outer flow

Question 29

Sensible energy

Answer 29

The energy that is being transferred (internal thermal energy)

Question 30

Latent energy

Answer 30

Associated with the phase change between the liquid and vapor states of the fluid (convection process)

Question 31

Heat or thermal energy generation

Answer 31

Associated with the conversion from some other form of internal energy to thermal or mechanical energy: it is a volumetric phenomenon (E.g)

Question 32

Thermal energy storage

Answer 32

Est the energy stored in the surface