Flashcards in Conduction Deck (16):

1

## Types of conduction

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1) steady state conduction

2) unsteady state conduction

2

## Steady state conduction

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No accumulation of heat

Q constant throughout

3

## Unsteady conduction

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Heat gets accumulated

Heat generation and heat consumption

Parabolic type of profiles

4

## Thermal conductivity

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Independent of temperature gradient except porous solids where radiation can affect

Dependent on temperature

Usually an average k value from both the temperatures are used

5

## Thermal conductivity of metals

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Decreases with increase in temperature since the mean free path for the free electrons to move reduces because of particle vibration

Decreases with impurities example alloys have less conductivity than pure metals

6

## Thermal conductivity of liquids

### Decreases with temperature except water which reaches a maximum

7

## Thermal conductivity of gases

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Incresases with increase in temperature

Proportional to square of T for mono atomic gases

Decreases with increase in molecular weight

8

## Resistance

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Length/ conductivity * area

K/W

Conductance

9

##
Log mean area of cylinder

Log mean radius of cylinder

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Geometric mean area of sphere

Geometric mean radius of sphere

10

## Unsteady state Heat conduction

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Heat generation

Heat consumption

11

## Dimensional number associated with unsteady state heat transfer

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Biot number

Fourier number

12

## Biot number

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Conductive resistance of solid/ convective resistance of fluid

hL/k

13

## Bi < 0.1

### Lumped system

14

## Bi > 0.1

### Distributed system

15

## Fourier number

### Conduction rate/ storage rate

16