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Experiment Instructions

WL 373 Heat Conduction in Gases

and Liquids

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WL 373 HEAT CONDUCTION IN GASES AND LIQUIDS

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Experiment Instructions

This manual must be kept by the unit.

Before operating the unit:

- Read this manual.

- All participants must be instructed on

handling of the unit and, where appropriate,

on the necessary safety precautions.

Version 0.3 Subject to technical alterations

Gases and Fluids

Thermal Conductivity of

und FlssigkeitenWrmeleitung von Gasen

WL 373

Leistung / PowerHeizer/ Heater

Ein/ On

Aus / Off

Leistung / Power Watt

Temperatur 2/ Temperature 2 CTemperatur 1/ Temperature 1 C

123.4 C 123.4 C

123

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Table of Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Intended Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.1 Structure of the Safety Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.2 Safety Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 Unit Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.1 Unit Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.2 Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.3 Operating the Measurement and Control Unit. . . . . . . . . . . . . . . . . . . 6

3.4 Connecting the Heat Exchanger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5 Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.1 Calibrating the Heat Exchanger. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5.1.1 Preparing for the Experiment . . . . . . . . . . . . . . . . . . . . . . . . 10

5.1.2 Performing the Experiment. . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.1.3 Evaluating the Experiment: Calibration Curve . . . . . . . . . . . 11

5.2 Determination of Coefficients of Thermal Conduction. . . . . . . . . . . . 14

5.2.1 Preparing for the Experiment . . . . . . . . . . . . . . . . . . . . . . . . 14

5.2.2 Performing the Experiment. . . . . . . . . . . . . . . . . . . . . . . . . . 155.2.3 Evaluating the Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.1 Working Sheet: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6.2 Symbols and Units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6.3 Table with Coefficients of Thermal Conduction. . . . . . . . . . . . . . . . . 20

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6.4 Technical Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216.5 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

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1 Introduction 1

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1 Introduction

Using the WL 373 Heat Conduction of Gases

and Liquids unit, basic aspects of steady state

thermal conduction in liquid and gaseous materi-

als can be investigated.

The unit is particularly suited to the determination

of the coefficients of thermal conduction of liquid

and gaseous materials.

The unit comprises a double walled cylinder withan integrated heater acting as the heat source,

and the surrounding cylinder acting as the heat

sink. The medium to be investigated is placed in

between in a measurement slot.

The temperatures of the heat source and sink are

measured using thermocouples and transmitted

to a measurement and control unit where the elec-

trical power consumption of the heater is also dis-

played.

The unit is very easy to set up and operate, it is

thus also suitable for student use.

Working sheets included in the appendix to these

instructions ease the evaluation of experiments.

The following topics are covered by the unit:

Steady-state thermal conduction in gases and

liquids

Determination of coefficients of thermal con-

duction

1.1 Intended Use

The unit is to be used only for teaching purposes.

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2 Safety 2

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2 Safety

2.1 Structure of the Safety Instructions

The signal words DANGER, WARNING or CAU-

TION indicate the probability and potential sever-

ity of injury.

An additional symbol indicates the nature of the

hazard or a required action.

Signal word Explanation

Indicates a situation which, if not avoided, will result in deathor serious injury.

Indicates a situation which, if not avoided, may result in deathor serious injury.

Indicates a situation which, if not avoided, may result in minoror moderately serious injury.

NOTICE Indicates a situation which may result in damage to equip-ment, or provides instructions on operation of the equipment.

DANGER

WARNING

CAUTION

Symbol Explanation

Electrical Voltage

Hot Surfaces

Notice

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2.2 Safety Instructions

WARNING

Reaching into the open measurement andcontrol unit can result in electric shocks.

Disconnect from the mains supply before open-ing.

Work should only be performed by qualifiedelectricians.

Protect the measurement and control unitagainst moisture.

WARNING

Risk of burns.

The knurled bolt and the heat exchanger are veryhot.

Leave the unit cool down.

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3 Unit Description 4

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3 Unit Description

3.1 Unit Construction

Fig. 3.1 Unit Construction

Gases and Fluids


und FlssigkeitenWrmeleitung von Gasen

WL 373

Leistung / PowerHeizer / Heater

Ein / On

Aus / Off



123.4 C 123.4 C

123

1 Heat exchanger (1) with internal heater and cooling facility

2 Base

3 Shut-off valves for the cooling flow and the medium to beinvestigated

4 Measurement and control unit with temperature and heaterpower displays

Mains cable (not shown)

1 2 3 4

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3.2 Function

The heat exchanger contains an electrical heater

that acts as the heat source (1), and an annular

cooling slot through which cooling water flows,

this acts as the heat sink (2). This construction

results in the flow of heat from the inside to the

outside.

Between the heat source and the heat sink is an

annular measurement slot (3) of constant width,

the medium to be investigated is contained here.

The medium is inserted in the slot via a connector(see arrow).

The temperature of the heat source is measured

using a thermocouple (4), the temperature of the

cooling water is measured (viewed in the direction

of the flow of heat) immediately behind the mea-

surement slot, also using a thermocouple, and fed

to the measurement and control unit.

Fig. 3.2 Section through the heat exchanger

Cooling water

connection

Cooling waterconnection

2 4 1 3

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To make it easier to clean the slot, the inner cylin-

der can be removed together with the heater. To

do this undo the knurled bolt (5), remove the lid

(6) and the sealing ring, and take out the cylinder

(7). Refit in the reverse order of removal.

NOTICE

Ensure that the sealing ring is correctly seated!

3.3 Operating the Measurement and Control Unit

The displays for the temperature of the heat

source (1) and the heat sink (2), and the heater

power (power consumption) display (3) are fitted

to the front of the measurement and control unit.

The heater power can be regulated up to

max. 140...150W using the potentiator (4).

The heater can be switched on and off using the

power switch (5).

NOTICE

In order to avoid the heater burning out, itswitches off automatically above a temperature of

95C.

The two thermocouples fitted to the heat

exchanger and the cable for the heater are con-

nected to the rear of the measurement and control

unit. The main switch is also to be found here.

Fig. 3.3 Dismantling theHeat exchanger

77 6 5

Fig. 3.4 Front of the measurement and

control unit

Gases and Fluids


und FlssigkeitenWrmeleitung von GasenWL 373

Leistung / PowerHeizer / Heater

Ein / On

Aus / Off



123.4 C 123.4 C

123

1 2

5 4 3

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3.4 Connecting the Heat Exchanger

Connect the heat exchanger to the shut off

valves in accordance with Fig. 3.5

The hoses are fitted with rapid action hose cou-

plings, to release simply pull back the sleeve.

Make the electrical connections in accordance

with Fig. 3.5

NOTICE

Do not reverse the cables for the thermocouples!

Fig. 3.5 Connection of the heat

exchanger on the base andmeasurement and control unit

A/B Unions for the medium to be investi-

gated

Hose size: 6mm

C Cooling water inlet union

Hose size: 13mm

D Cooling water outlet union

Hose size: 6mm

E To the thermocouple/ heater

connector

F To the test unit input

G To the thermocouple/ cooler

connector

A B C D G

F

E

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4 Principles 8

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4 Principles

The medium to be investigated fills the cylindrical

slot completely. The slot is narrow enough to per-

vent the occurrence of convection, the transfer of

heat in the slot is therefore more or less com-

pletely due to thermal conduction.

Due to the constant width of the slot, thermal con-

duction occurs as in a plane wall. Here the

Fourier law is applicable for the amount of heattransferred Q:

(4.1)

This yields the relationship for the heat flow :

(4.2)

with

Head flow through the wall under

investigation

A Wall surface area

T Temperature gradient in the wall

Wall thickness

Coefficient of the thermal conduction

is temperature dependant; in general the meantemperature in the wall is used.

(in W/Km) can be thought of as the energy that

is conducted every second through a 1m thick

wall over an area of 1m2when there is a temper-

ature difference of 1K between the opposite sides

of the wall.

Fig. 4.1 Thermal conduction in a plane

wall

T T1 T2=

Q

Q

T2

T1 Q A

-----------=

Q

Q A T

------------------------=

Q

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5 Experiments

The selection of experiments makes no claims of

completeness but is intended to be used as a

stimulus for your own experiments.

The results shown are intended as a guide only.

Depending on the construction of the individual

components, experimental skills and environmen-

tal conditions, deviations may occur in the experi-

ments. Nevertheless, the laws can be clearly

demonstrated.

5.1 Calibrating the Heat Exchanger

In order to determine the heat losses in the unit,

calibration is necessary.

Air is used as the medium to be investigated

during the calibration process; air is used

because its coefficients of thermal conduction are

well documented (values are given in the Appen-

dix).

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5.1.1 Preparing for the Experiment

Clean the measurement slot to remove any

water or remnants of other media from the slot

(refer to Fig. 3.3, Page 6).

Connect the heat exchanger to the measure-

ment and control unit in accordance with

Fig. 3.1, Page 4 and Fig. 3.5, Page 7 and

switch on the unit.

Open the shut off valves (1) and (2) for themeasurement slot

Make the cooling water connections and set

the flow rate for example to 1ltr/min at shut off

valve (3)

The flow rate for cooling water to be deter-

mined by the help of a stop watch and a meas-

uring tank in accordance to the following

equation (5.1)

(5.1)

V Capacity water [ltr]

t Time [s]

5.1.2 Performing the Experiment

Set the heat power P= 100W

Wait until the temperature values are constant Read and record the temperatures for heater

T1und cooling water T2, as well as the actual

heater power P

Repeat the experiment with heater powers of

P= 80W, 60W, 40W, 20W, 10W

Fig. 5.1 Shut off valves

V

1

2

3

V

V V

t----=

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5.1.3 Evaluating the Experiment: Calibration Curve

If the slot is viewed as a wall, then the Fourier for-

mula can be applied.

With an average slot diameter of dm= 39,6mm

and an effective slot length of l= 126mm, the

heat exchanger surface area A is

(5.2)

The slot width is = 0,4mm.

With the aid of equation Formula (4.1), Page 8 the

heat loss can be determined and the calibration

curve drawn (refer to Fig. 5.2, Page 13):

The coefficient of thermal conduction of air is tem-

perature dependant and is found to be

Calibration values are marked with .

(5.3)

where

T- Mean air temperature in C

(5.4)

T1 Temperature heater

T2 Temperature cooling water

A 0,0396m 0,126m 0,0157m2

= =

0,0242 1 0,003 T+=

TT1 T2+

2

-------------------=

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For the actual heat flow transferred the equationis:

(5.5)

where

Temperature difference

(5.6)

The heat flow loss can be calculated:

(5.7)

Q

A

A T

-------------------------=

T T1 T2=

Q

B P Q

A=

P

in W

T1in C

T2in C

T

inCAir

in W/Km

B

in W

100 90,9 24,4 66,5 0,0284 74,09

90 84,4 23,9 60,5 0,0281 66,8

80 76,1 23,2 52,9 0,0278 57,73

70 69,7 22,8 46,9 0,0276 50,73

60 55,7 21,8 33,9 0,0270 35,94

50 47,5 21,1 26,4 0,0267 27,66

40 40,4 20,4 20,0 0,0264 20,73

30 33,8 19,8 14,0 0,0261 14,37

20 28,2 19,7 8,5 0,0259 8,65

10 22,6 19,3 3,3 0,0257 3,33

0 19,5 19,1 0,4 0,0256 0,40

Tab. 5.1 Calibrating the heat exchanger

Q

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The values measured in this experiment are to be

used only for this special unit.

Every unit has its own calibration values.

Fig. 5.2 Calibration curve

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Tin C

Bin WQ

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5.2 Determination of Coefficients of Thermal Conduction

The experimental sequence is the same as for the

experiment to record the calibration curve, how-

ever water or oil is now used as the medium to be

investigated.

5.2.1 Preparing for the Experiment

It is very important that the measurement slot is

perfectly clean since even small quantities ofimpurities can seriously affect the results. The

measurement slot must therefore be well

cleansed (refer to Fig. 3.3, Page 6)

Connect the heat exchanger to the measure-

ment and control unit in accordance with

Fig. 3.1, Page 4 and Fig. 3.5, Page 7 and

switch on the unit

Make the cooling water connections and set

the flow rate for example to 1ltr/min at shut offvalve (3) (refer to Formula (5.1), Page 10)

Open the shut off valves (1) and (2) for the

measurement slot

Inject the medium to be investigated for exam-

ple with a syringe into socket A until the

medium runs out of socket B and until no air

bubbles to be seen inside transparent connec-

tion hoses

Close the shut off valves (1) and (2)

Lift up the heat exchanger and rotate it to

remove possible air bubbles out of heat

exchanger into transparent connection hoses,

if necessary bleed the system again by open-

ing the shut off valves (1, 2) and refill the sys-

tem with the medium to be investigated

Fig. 5.3 Shut off valves und sockets

V

1

2

3

A B

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The cause of the variations is predominantly small

remnants of air and other measured media in themeasurement slot.

P

in WT1

in CT2

in CT

in CB

in WA

in WAir

in W/KmLiterature

in W/KmVar.in %

100 45,8 24,5 21,3 22,78 77,22 0,092 0,13 29

70 38,4 24,0 14,4 15,04 54,96 0,097 0,13 25

Tab. 5.3 Example measurement results when using oil as the measured medium

Q

Q

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6 Appendix 17

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6 Appendix

6.1 Working Sheet:

Calibration Curve/ Coefficient of Thermal Conduction

ExperimentNo.:

Date:

Medium: Flow rate cooling water in ltr/min:

Remarks:

P

in WT1

in CT2

in CT

in CB

in WA

in WMedium

in W/KmLiterature

in W/Km

Experiment

No.:

Date:

Medium: Flow rate cooling water in ltr/min:

Remarks:

P

in WT1

in CT2

in CT

in CB

in WA

in WMedium

in W/KmLiterature

in W/Km

Q

Q

Q

Q

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6 Appendix 18

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Fig. 6.1 Calibration curve

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Bin WQ

T in C

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6 Appendix 19

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6.2 Symbols and Units

A Heat transfer surface area m2

dm Mean effective diameterof the heat exchanger mm

P Heater power consumption W

Q Heat transferred W

Heat transfer flow rate W/s

B

Heat flow loss W/s

A Actual heat flow transferred W/s

T Mean air temperature C

T2 Temperature cooling water C

T1 Temperature Heater C

T Temperature difference betweenheat source and heat sink C

Flow rate ltr/min

Slot width mm

Coefficient of thermal

conduction W/Km

Q

Q

Q

V

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6 Appendix 20

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6.3 Table with Coefficients of Thermal Conduction

Substance Temperature in C in

Water 0 0,555

Water 20 0,598

Water 60 0,651

Water 100 0,681

Oil 40 0,123

Oil 80 0,120

Tab. 6.1 Coefficients of Thermal Conduction for Some Liquids

W

Km----------

Substance Temperature in C in

Air T 0,0242(1+0,003T)

Carbon dioxide CO2 0 0,0178

Oxygen O2 20 0,026

Steam 100 0,0242

Steam 200 0,0328

Steam 400 0,0551

Tab. 6.2 Coefficients of Thermal Conduction for Some Gases

W

Km----------

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6 Appendix 21

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6.4 Technical Data

Dimensions:

Base plate:

(L x W x H) 250 x 400 x 150 mm

Measurement amplifier:

(W x H x D) 350 x 130 x 250 mm

Power Supply: 230VAC 50 Hz

Alternatives optional, see type plate

Weight: approx. 8 kg

Heat exchanger:

Effec. transfer area 0,0157 m2

Mean Effec. Diameter 39,6 mm

Slot width 0,4 mm

Heater

Max. Power Consumption 160 W

Thermocouples 2 x Type K

Measurement and control unit

Shut down of the heater supply T=95 C

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6.5 Index

C

Calibration curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Coefficient of thermal conduction . . . . . . . . . . . . . . . . . . . . . . . 1, 8, 9, 20Convection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Cooling water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

F

Fourier law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

H

Heat sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Heat source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Heater power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

I

Impurities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

M

Measurement and control unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

P

Plane wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Power consumption, heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

R

Rapid action hose coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

SSymbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

T

Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Thermal conduction in a plane wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Thermocouple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Topics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

wl373e-v0.3

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