Chapter 5

Question 1

Transient Conduction aka

Answer 1

None Steady State. Heat transfer process for which the temperature varies with time, aw well as location within a solid.

Question 2

Solution techniques for Transient conduction

Answer 2

Lumped Capacitance Method
Exact Solutions
Finite Difference Method

Question 3

When is transient conduction initiated?

Answer 3

When there is a change in operating conditions such as change in surface convection conditions, surface radiation conditions, surface temperature or heat flux and or internal energy generation.

Question 4

Lumped Capacitance Method Assumptioms

Answer 4

Mass of body much less then liquid.
Assume Temp of liquid doesn’t change
Solid has constant temperature throughout ie no delta t whithin body

Question 5

How many dimension is lumped capacitance method and why?

Answer 5

0 Dimension because temperature is constant regardless of position of the body and only changes with time.

Question 6

Energy Balance Equation for Lumped Capacitance

Answer 6

Ein/Eout= ρVc

Energy from fluid = energy stored or lost from the body

Question 7

Cp

Answer 7

amount of energy needed heat or cool 1 KG of matter 1 degree celsius

Question 8

Cp Units

Answer 8

J/Kg degree (celsius/kelvin)

Question 9

Thermal Time Constant

Answer 9

(1/hAs)(ρVc) or RconvCt

Question 10

Units of Thermal time Constant

Answer 10

Seconds

Question 11

Ct meaning and formula

Answer 11

Lumped Thermal Capasitance of a Solid. (ρVc), and ability of the body to accumulate energy

Question 12

Rt meaning and formula

Answer 12

Resistance to convection heat transfer

Question 13

Units of hAs/(ρVc)

Answer 13

1/s

Question 14

Will the time constant be greater or lower for a higher value of Ct?

Answer 14

Higher because tau=RtCt

Question 15

θ i=

Answer 15

Ti-T∞

Question 16

Q meaning and formula

Answer 16

Total energy transfer up to some time t, (ρVc) θi[1-exp(-t/ταυ]

Question 17

Bi number equation all forms , units and meaning

Answer 17

hl/k, Rcond/Rconv, (Ts1-Ts2/Ts2-Tinf), unitless, provides a measure of the temperature drop in the solid relative to the temp drop of the surface and fluid

Question 18

What will a high number of thermal conductivity do to the Bi number and why?

Answer 18

It will make the Bi number lower because it is in the denominator.

Question 19

What does a high condcutivity (K) mean for temperature distribution in a wall?

Answer 19

It means heat is transferred easily so it should be flat or linear throughout.

Question 20

What does a high Bi number do to the Temperature profile.

Answer 20

Make it less linear and less flat.

Question 21

Bi number formula

Answer 21

Rcond/Rconv=LcH/K

Question 22

What does the Bi number allow us to do?

Answer 22

Use lumped capasitance method

Question 23

Bi number formula in terms of characteristic length

Answer 23

h*Lc/k

Question 24

Fouriers number equation

Answer 24

α*t/(Lc)^2

Question 25

Characteristic Length

Answer 25

Ratio of Volume to surface area

Question 26

What does Fouriers number tell us?

Answer 26

Provides a measure of the relative effectiveness with which solid conducts and stores thermal energy.

Question 27

Thermal Diffusivity equation symbol and meaning

Answer 27

alpha, k/pCp, and is the ratio of conductivity to to heat capacity

Question 28

Basic formula of characteristic length and meaning

Answer 28

V/As, average length of the body

Question 29

What does the Bi number physically represent?

Answer 29

Temperature drop in a solid relative to temperature difference between the solid and fluid.

Question 30

Formula for the Temperature Distribution using Lumped Capacitance Method.

Answer 30

θ/θi=(T-T♾)/(Ti-T♾)=exp(-Bi•Fo)

Question 31

What does Bi*Fo=

Answer 31

hAst/pVc

Question 32

Theta

Answer 32

T-Tinf

Question 33

t*

Answer 33

Unitless Time=FO

Question 34

X*

Answer 34

x/L

Question 35

θ*

Answer 35

Dimensionless Temp