52
(iii)
INDEX
Pa~e
SAFETY IN THE USE OF EQUIPMENT
General Safety Rules
6
2
THE THERMAL RADIATION UNIT
Introduction
Receipt of Equipment
Description
Installation Requirements
6
8
8
9
Commissioning
9."
10.'.,
EXPERIMENTS: 22,
Radiometer Data Sheet
1. Inverse Square Law for HeatTo show that the intensity of radiation on a surface is inverselyproportional to the square of the distance of the surface from theradiation source.
24.
2. Stefan-Boltzmann LawTo show that the intensity of radiation varies as the fourth powerof the source temperature.
3. EmissivityITo determine the emissivity of different surfaces (polished, silveranodised, matt black).
4. Emissivity IITo demonstrate how the emissivity of radiating surfaces inproximity to each other will affect the surface temperatures andthe heat emitted.
. 27
29
32
5. Kirchoff's LawTo detennine the validity of Kirchoff's Law which states that theemissivity of a grey surface is equal to its absorptivity of radiation'received from another surface when in a condition of thermalequilibrium.
6. Area FactorsTo demonstrate that the exchange of radiant energy from onesurface to another is dependent upon their intertOIinectinggeometry, i.e. a function of the amount that each surface can'see' of the other.
34
"
36
7. InverseSquareLawfor Light .To show that the illuminance of a surface is inversely proportional .to the square of the distance of the surface from the light ~urce.
8. Lambert's Cosine Law
To show that the energy radiated in any direction at an angle witha surface is equal to the normal radiation multiplied by the cosineof the angle between the direction of radiation and the normal tothe surface.
39
42
~..
(iv)
Page
9. Lambert'sLaw of Absorption '
To show that light passing through non-opaque matter is reducedin intensity in proportion to the thickness and absorptivity of thematerial.
45
DIAGRAMS:
RCCB Installation 48
rransform~r~o~~~~n~91~V,_~i!S2~___, 7 -~ ~-~~-c ~ _. -- _~9._- --.
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GENERAL SAFETY RULES
1. FollowRelevantInstructions
(a) Before attempting to install, commission or operate equipment, all relevantsuppliers/manufacturers insnuctions and local regulations should' be understood andimplemented. "
(b) It is irresponsible and dangerous to misuse equipment or ignore instructions, regulations orwarnings. '
(c) Do not exceed specified maximum operating conditions (e.g. temperature, pressure, speed,, etc.).
,- ~-- .~," ...', of-. '"--- -..
"
2. Installation- ,--"." '.
(a) Use lifting tackle where possible to install heavy equipment Where manual lifting isnecessary beware of strained backs and crushed toes. Get help from an assistant if necessary.
Wear safety shoes where appropriate. .~,:_.
..,,' "'.
- ',.
(b) Extreme care should be exercised to avoid damage to the equipment during handling andunpacking. When using slings ,to lift equipment, ensure that the slings are attached'.'tostructural framework and do not foul adjacent pipework, glassware,etc. Whenusing fork lifttrucks, position the forks beneath structural framework ensuring that the forks do not fouladjacent pipework, glassware, etc. Damage may go unseen during commissioningcreating apotential hazard to subsequent operators.- -
(c) Where special foundations are required follow the insnuctions providedand do not improvise.Locare heavy equipment at low level.
(d) Equipment involving inflammable or corrosive liquids should be sited in a containment areaor bund with a capacity of 50% greater than the maximum equipment contents. .
(e) Ensure that all services are compatible with the equipment and that independent isolators arealways provided and labelled. Use reliable connections in all instances, do not improvise.
(0 Ensure that all equipment is reliably earthed and connecred to an electrical supply at the correctvoltage. The electrical supply must incorporate an Earth Leakage Circuit Breaker (ELeB) orResidual Current Circuit Breaker (RCCB) to protect the operator from severe electric shockin the eventof misuseor accident. /
(g) Potential hazards should always be the first consideration when deciding on a suitable locationfor equipment Leave sufficient space between equipment and between walls and equipment
3. Commissioning
.. (a) Ensure that equipment is commissioned and checked by a compe~ent member-of staff beforepennitting students to operate it. '
4. OR,eration
(a) Ensure ~t students are fully aware of the potential hazards when operatingequipment.
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3
(b) Students should be supervised by a competent member of staff at all times when in thelaboratory. No one should operate equipment alone. Do not leave eqUipment runningunattended.
(c) Do not allow students to derive their own experimental procedures unless they are competentto do so.
(d) Serious injury can result from touching apparentlystationaryequipmentwhen using astroboscopeto 'freeze'rotarymotion. .
S. Maintenance-~_-~__n~.-
(a) Badlymai~Uilit~d-;quipmentiia potenn81nazard~EnsUrethata competentmemberof staff -
is responsible for organising maintenance and repairs on a planned basis.
(b) Do not permit faulty equipment to be operated. Ensure that repairs are carried out competentlyand checked before students are permitted to operate the equipment .
6. UsinllElectricitv
(a) At least once each month, check that ELCB's (RCCB's) are operating correctly by pressingthe 1EST button. The circuit breaker must trip. w.!1enthe button is pressed (failure to tripmeans that the operator is not protected and a repair must be effected by a competentelectrician before the equipment or electrical supply is used):
(b) Electricity is the commonest cause of accidents in the laboratory. EIisure that all members ofstaff and students respect it -
(c) Ensure that the electrical supply has been disconnected from the equipment before attemptingrepairsor adjustments. '
(d) Water and electricity are not compatible and can cause serious injury if they come into contactNever operate portable electrical appliances adjacent to equipment involving water unless someform of constraint or barrier is incorporated to prevent accidental contact.
(e) Always disconnect equipment from the electrical supply when not in use:'
/
7. AvoidinllFires or Explosion
(a) Ensure that the laboratory is provided with adequate flre extinguishers appropriate to thepotential hazards.
(b) Where inflammable liquids are used, smoking must be forbidden. Notices should be displayedto enforce this.
..(c) Beware since f1ne powders or dust can spontaneously ignite under certain conditions. Empty
" vessels having contained inflammable liquids can contain vapour and explode if ignited.
(d) Bulk quantities of inflammable liquids should be stored outside ttle laboratory in accordancewith local regulations.
(e) Storage tanks on equipment should not be overfilled. All spillages Shbuld be immediatelycleaned up, carefully disposing of any contaminated cloths, etc. Beware of slippery floors.
'."?
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4
<0 When liquids giving off inflammable vapours are handled in the laboratory, the area shouldbe ventilated by an explosion-proof extraction system. Vents on the equipment should beconnected to the extraction system. . .
(g) Students should not be allowed to prepare mixtures for analysis or other purpose withoutcompetent supervision.
8. Handling-Poisons, Corrosiveor ToxicMaterials
(a) Certain liquids essential to the' operation of equipment. for example mercury, are poisonous orcan give off poisonous vapours. Wear appropriate protective clothing when handling such'substances. Clean up any spillage immediately and ventilate areas'thoroughly using extraction
- equiIJ.lTlent ]3e'!yare of slippery floors.'-' '-"~,-- ---.-.
(b) Do not allow food to be brought into or conswned in the laboratory. Never use chemicalbeakers as drinkingvessels.
(c) Where poisonous vapours are involved, smoking must be forbidden. Notices should bedisplayed to enforce this.
(d) Poisons and very toxic materials must be kept in a locked cupboard or store and checkedregularly. Use of such substances should be supervised.
(e) When diluting concentrated acids and alkalis, the acid or alkali should be added slowly towater while stining. The reverse should never be attempted. .
. 9. Avoiding Cuts and Burns - ...
(a) Take care when handling sharp edged components. Do not exert undue force on glass orfragile items.
(b) Hot surfaces cannotin most cases be totally shielded and can produce severebums even whennot 'visibly' hot Use common sense and think which parts of the equipmentare likely to behot
10. Eye Protection
(a) Goggles must be worn whenever there is risk to the eyes. Risk may arise from powders, liqpid
splashes, vapours oil splinters. Beware of debris from fast moving air streams. Alkalinesolutions are particularly dangerous to the eyes.
(b) Never look directly at a strong source of light sucl,1as a laser or Xenon arc lamp. Ensure thatequipment using such a source is positioned so that passers-by cannot accidentally view thesource or reflected ray.
(c) Facilities for eye irrigation should a1\yays be available. ,
11. Ear Protection
(a) Ear protectors must be'worn when operating noisy equipment
-,-
5 "
12. Clothing
(a) Suitable clothing should be worn in the laboratory. Loose gannents can cause serious injuryif caught in rotating machinery. Ties, rings on fingers, etc., should be removed in thesesituations.
(b) Additional protective clothing should be available for all members of staff and students asappropriate.
13. Guards and Safe!! Devices
n~ (aL9uards and safetydevic:::sare installedonequipmentto protecttheoperator.Theequipmentmust not be operated with such devices removed. --- -- - - - ----------
(b) Safety valves, cut-outs or other safety devices will have been set to protect the equipment.Interference with these devices may create a potential hazard.
(c) It is not possible to guard the,operator against all contingencies. Use common sense at alltimes when in the laboratory.
(d) Before starting a rotating machine, make sure staff are aware how to stop it in an emergency.
(e) Ensure that speed control devices are ~ways set at ,zerobefore starting equipment.
14. First Aid
(a) If an accident does occur in the laboratory it is essential that first aid equipment is availableand that the supervisor knows how to use it.
(b) A notice giving details of a proficient fmt-aider should be prominently displayed.
(c) A 'short list' of the antidotes for the chemicals used in a particular laboratory should tX;prominently displayed.
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InENTIFICATION DIAGFlAM
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Light Source
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THERMAL RADIATION UNIT FIG.2.
8
H960 THERMAL RADIAnON UNIT
INTRODUCTION
Thermal radiation 18 a mode of heat transfer which differs significantly from the pther two modes,namely conduction and convection. The fact that radiant energy transfer occurs across a vacuum isoften'disturbing to students unless the theory relating to properties of electromagneticwaves has beenpresented. .
The engineer is not directly concerned with the mechanism by which heat transfer occurs, but a soundknowledge of the properties and laws relating to the topic is required
The Hilton Radiation Unit consists of a pair of electrically heated radiant heat and light sources,logeilier~with"a'Comprehengivevrange~ohargets"and~measuring1instrumentation,-7- ~U~" - ~.""
, ,. .
The unit has been desiined to demonstrate the Cundamentallawsrelating to radiation. By perfo'mung -, -
a series of simple experiments the student may verify the relevant equations and appreciate the ..behaviour of radiation. '
" ,
RECEIPT OF EQUIPMENTr'l( -.,.
Sales in the United Kingdom -The apparatus should be carefully unpacked and the components checked against the Packing List.
--- AnY'omissions or breakages should be notified to P.A. Hilton Limited within three days of receipt
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Sales Overseas .
The apparatus should be carefully unpacked and the components checked against the Packing List.
Ani omissions or breakages should be notified immediately to the Insurance Agent stated on theInsurance Certificate if the goods were!nsured by P.A. Hilton Ltd. '
Your own insurers should be notified immediately if insurance was arranged by yourselves.
/
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-" 9 ..
DESCRIPTION (Refer to Fig.2, Page 7)"
The unit consists of a horizontal .bench mounted track (1) fitted with a heat-radiation source at one endand a light source at the other. Between the two sources may be placed either a heat radiation detector
(13) or a light meter (16). In addition, a number of accessories can be fitted for e~peririlental purposes.These include metal plates with thermocouples attached, (5,6), two vertically orientated metal plates (14)to fonnah' aperture, and a number -of acrylic filters, (10,11,12), The ra~tion detectoJS and theaccessories are all clamped to stands (7,8,9,15) which enable them to be positioned at different distancesfrom the appropriate source. Distances are measured with a reversible scale (17) mounted on the frontof the track.
Electrical power for the two. radiation sources is supplied from an.instrument console (3) and iscontrolled by a solid-state regulator. A step down ~sformer (2) provides a low voltage supply for theheat source. TemperatUresof the two metal-plates used in~conjunction with the heat radiation sourceare displaye(rbff'h..atgitaI~re:ad-()ui;'either"reading7beingselecte4by a change over switch..,Output from~~~__~.the heat radiation detector is amplified and displayedon a second digital read.out The light meter isself-contained.
INSTALLATION REQUIREMENTS
The equipment should be installed on a firm, level work surface ~ indicated below:
~ --~ --,-- --~.-
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FIG. 3.
The location should be remote from heaters or other sources of radiation and should preferably be adarkened room for light experiments. If a darkened room is not available, the apparatus should belocated 'in subdued lighting away from direct sunlight. /
A single phase electrical supply is reqUired.
No other services are necessary.
,
10
COMMISSIONING
The unit should be assembled as shown in Figs. 4 to 13, Pages 12 to 21.
. 220/240V Units .
A Residual Current Circuit Breaker is provided to be wall mounted near'to 'where the unit will belocated. Connect the 3m length of cable provided to a suitable fixed power supply via a fused isolatingoutlet for SA which complies with the local electrical installation regulations.
Brown cableBlue cableGreenlY ellow'cable
LIVE or LINENEU1RAL
EARTH OI"ground
Connect the Live and Neutral of the other end of this cable to ttie top tefminalsof the RCCK The;:~-
earth wire is connected to the separate terminal strip (see Diagram RCCB 107 at the re& of the manual)..
The power cable will be found emerging from the rear of the unit. This is connected to the lowertenninals of the RCCB and the earth terminal strip.
."" ..,'>:.--", .' ,
llO/120V Units:",> " '
A suitably rated transformer is supplied with the unit and allows input voltages of between 110 'i1nd'130Volts (in S volt steps) to be connected.
The unit and RCCB are connected in the same manner as described for 220V units above. However; ,-the 3m cable is connected to the output of the transfonner and not directly to the supply. :"
Before connecting the supply cable to the transfonner, the local mean voltage should be measured. ,
When this has been detennined, the Live input of the supplyshould be connected to the terminal havingthe nearest voltage label. The Neutral of the supply is connected to the OVterminal and the Earth orGround of the supply is connected to the terminal labelled 'E' or -::- (see diagram TRANl00 at the
rear of the manual).
The supply cable, cable gland and switched and fused outlet should be suitable for supplying lOA andbe to a standard corresponding to the local regulations.
The transformer should be placed in a protected position, but where air can circulate freely.
The RCCB is operated by use of the ON/OFF lever.,
In the event of an earth leakage occurring, the RCCB will switch off, isolating the supply from the
RCCB onwar~. However, this will only operate successfully if the unit is connected to a good earth.
Should the RCCB. trip, the mains supply to the unit should be disconnected and the cause of the fault
determined. The, RCCj3 can then be reset to the "ON" po,sition and the unit operated,
Every thr~e months the RCCB should be checked by a competent person:- To do this, switch on bothat the mains and the unit. Push the "TEST" button on the RCCB and ensure that the unit is isolated.
If the power remains on, the RCCB is faulty and will need to be replaced by a qualified electrician.
Having connected the apparatus to the electrical supply, correct operation should be checked as follows:
Turn the power control on the console fully anti-clockwise (minimum).
Connect the"light source supply cable to the power output socket ('C') on the instrument console.
~,'., <."
11
Set the ON/OFF switch on the console to the ON position and check the meters are illuminated.
Observe that the illumination of the light source increases as the power control on the console is turnedclockwise.
Check the lightrneter ~nds to the change in illumination of the light source.
Turn the power controLfully anti-clockwise and set the console ON/OFF switch to the OFF position.
Disconnect the light source supply cable from the power output socket ('C') on the console.
Connect.the heater supply transformer cable to the power output socket ('C') on the console. Ensurethat the heateris connectedto the socketon the side of the transformer. .
,~--- - -
Connect the radiometer cable to the socket ('D') beneath the radi()me;~do~t-on the console -'--- -"- --
Connect the leads from two metal plates to the sockets ('A') and ('B') beneath the thermometer readouton the console.
Set the ON/OFF switch on the console to the ON position and check the meters are illuminated.
Set the thermocouple selector switch to position 'A' then 'B' and check the thermometer indicates thetemperature of the metal plates in both positions. (Temperature of the plates should be approximatelyequal to the ambient air temperatureprior to heating.) .
.J'"
R"eir1()v~"the plastic protective cover from the front of the radiometer if fitted and check the meter on. the console indicates zero. A reading other than zero will be obtained if the walls of the room are at
.-- ." a different temperature to the air.
Turn the power control on the console clockwise and check the front surface of the hearer increases intemperature.
Note: When initially using the heater operate the power control at reduced settings and allow thetemperature to increase slowly. This will avoid excessive smell from the element and black frontsurface finish.' .
As,.the smface temperature of the heat source increases observe increases in the readouts of temperatureand radiation. .
Turn the power control on the console fully anti-clockwise and set the ON/OFF switclyto the OFF
.'. - posi~~n.
, . '.,., Commissioning is now complete.
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12
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InstrurentConsoleFig -13
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'-Heater SupplyTransfouner
THERMAL RADIATION UNIT FIG. 4.
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Heated Plate(Radiation Source)
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Connect to Socket enHeater Supply- Transfomer
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HEAT RADIATION-SOURCE FIG.5.
15-;,
JIll'~
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t Variable Apert~e(Gap)...
--- ------
Insulation Tcwards--Detector
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.. Silvered surface- I~ -,. Towards Heat Source ~,
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':7:Stand..,; .
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"DCDTIIRI=" PI ATE ON STANlL FIG. 7. .
17
Detector 'l'c:1NardsLight Source
~~ NJ Batteriesrequired tocperate thisunit
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Rotary Scale
Travel Clarrp
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LIGHT METER ON DETECTOR STANO. FIG.9.
18
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Filter Plates
@ .Filter PlateStand
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FILTER PLATES ON STANO.
Store Filter Plateswith care to avoiddamage
--- . -- -~ -------
Do N:Jr ~sitionclose to Heat Source
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19
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Connect to Soc~et C
on Instrurrent Console
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Diffuser
(Light Source)
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(J)()»rm
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. . "" c:Note. A: distance from face of A :;: 3Heat Source and Light Source, to
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the 50mm.measurement on the ::rScale as indicated. . Scale ....
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I Scale :
b11""" 0800 .00 '00 "O ~OO ..,., 100 400D oc:==r- -r '-""""'I""".""T_~-~':'~'-T ""L. .~' ..' .'.J'" 'fTT'Tlo . 0. r
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Mains Input Lead
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Bra,.m
Li ve (Hot)~......, Blue
Neutral ~~~~~")~'~4
, Green~ellCMJ;:arth ~,'~~
Fuse Rating - 5 Arrps
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Connect Mains Leadto rear of Console
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, Inst.rurentConsole '
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AP~r Control
~: Selector Switch, A or B
N....
On/OffSwitch
"
32
4. EMISSIVITY n
ExperimentTo demonstrate how the emissivity of radiating surfaces in proximity to each other will affect the surfacetemperatures and the heat emitted.
Equipment Set. Up
Temperaturereading T
Radiometer
reading R\
HeatMetal
plates
Set scale to O'ie. normal to track
'-~"----.,I II L
"- -..". ,-_.J
The pair of metal plates should be sequentially combinedfor the tests (A, B, C, D and E as iliown in this
diagram, using the black and polished plates provided.Care should be taken to connect each plate thermocouplelead to the corresponding socket on the instrumentconsole.
~ A B
.. 0 1+0I
c
2
0 E
1+1 0.12 2
Summary of Theory
The object of Experiment 3 was to detemrine' the emissivity of different surfaces by measurement of theintensity of radiation emitted by the surface at a panicular temperature. This experiment demonstrates the
practical aspects C?femissivity by comparing the temperatures of surfaces receiving aDdemitting rad?tion.
Initial Values of Variables to be Used
Distance from radiometer to heat source (X) =11Ormn(1 plate)=l30rmn (2 plates)
Distance from heat source to nearest metal plate <y) =5Omm
Note: The second metal plate is fixed 2Omm from the flI'Stby the position of the slots in the stand.,
Readln2s to be taken
Record the temperature of each metal plate (I) and the radiometer readings (R) for combinations A. B, C,D and E of the black and polished metal plates. f:or ease of comparison of results it is suggested that thepower control on the instrument console is set to maximum for each combination.
Anow sufficient time to achieve thermal equilibrium in each test before noting the various readings.
.,
33
Results
- -
Students should compare the results obtained from each test and explain the differences in terms of theemissivity combinations used.
TYPICAL RESULTS
Experiment 3 detennined approximate values for the emissivity of metal plates having different surfacefinishes;
The above results show the effect of emissivity when different plates are combined/
- . In each configurationthe temperatureand radiometerreadings are consistentwith the theory of emissivity. whereby a polished surface (having a low value of emissiVity) does not receive or emit much radiation
compared with a black surface which does.
.
Temperature Plate TemperatUre Plate Radiometer Plate Combination
TEST.- . 1 2 Reading (R)
°C °C Wm-z
A ---- Blackonly
B --- Polished only
C Black to Polished
D Black to Black
E ---- - - - ---- Polished to Black- -
Temperature Plate TemperatUre Plate Radiometer Plate Combination'.. 1 2 Reading (R)TEST-
.°C °C Wm-z
A 197 ----- 451 Blackonly
B 114 --- 33 Polishedonly
C 207 44 8 Black o Polished'.
D 197 70 69 Black to Black
:E 112 35 14 Polished to Black
34
5. KIRCHOFF'SLAW
Experiment .
To determine the validity of IGrchoff's Law which states that the emissivity of a grey surface is equalto its absorptivityof radiationreceived from another surfacewhen in a condition of thermalequilibrium.
EQuipment Set-Up
Heat Set scale to 0°ie. normal to trackRadiometer
reading (R) r-""I \I II 11 1
. '.
. .. - -.
'ON' switch
lsetect thermocouple with switch
Place the radiometer on a bench away from the heat source. Set the power to the heat source tomaximum and allow the temperature of the metal plate to stabilise.
Summary or TheorvFor a grey body having area AI' temperature TI'emissivity GI and absorptivity <XIsmrounded by ablaCk enclosure of area Al at the same temperatureTI' then for thermal equilibrium the grey body mustabsorb as much radiation as it emits.
Le. <X~ (j TI' At =Et (j TI4 Al from which <X= E
Initial Valuesor Variablesto be UsedDistance from radiometer stand to heat source (X) = llOmmDistance from black metal plate to heat sowce (Y) = 50mm
Readings to be takenEnsure that the equipment has fully stabilised, i.e. temperatureof metal plate is steady and radiometerreading is zero when pointed at the walls of the room. ..
Briefly return the radiometer to its stand and record the reading of plate temperature and radiometer.
Remove the radiometer from its stand, discoQIlect the connecting cable and place the radiometer in acold location for several minutes, e.g. refrigerator.
Quickly return the radiometer to the equipment and record the radiometer readings for the metal plateand walls of the room.
35
Remove the radiometer again and place it in a warm location for several minutes (e.g.' drying cabinet.DO NOT EXCEED 70°C). -
Note: Whep the radiometer is returned to the equipment from the cold or warm location it willgradrially~tum to roomtemperatUrecausingreadingsto drift . ,
This experiment is only a demonstration and accurate, steady readings are not required.
Results
Temperature of metal plate:
When the walls of the room and the radiometer are at the same temperature the reading on theradiometer is zero, showing that no radiation is received by the radiometer.
However, when the radiometer is colder than the walls, the reading increases and when the radiometeris warmer than the walls, the reading is negative (radiation emitted by the radiometer). Similarly, thereading from the radiometer increases and decreases. when sensing the hot. metal plate.
The only conclusion from these findings is that the reading on the radiometer is the nett value, I.e.radiation is emitted by the radiometer, the walls of the room and the hot metal plate, and the readingis the difference between the radiation received and emitted by/fr()mthe radiometer.
Having established that all bodies continuously emit and receive radiation it is a logical step to qualifyKirchhoffs uw. -
Iia body was capable of emitting more radiation than it received or vice-versa, it would never stabiliseat the temperature of its slllTOundings.
For stabilisation to occur, the radiation emitted by the body must match the radiation received by thebody when its temperature matches the surroundings. This is Kirchhoffs Law. /
TYPICAL RESULTS
Temperature of metal plate: 197°C
The above results confinn the statements on Page 35, namely tha! the reading from the radiometerdepends on the temperature of the radiometer relative to the object being measured and all bodies musttherefore emit and receive radiation.
. RADIOMETER READINGS \'IV m-ZJx.. ==. ,.. ;- -'. -
CONDITION OF RADIOMETER METAL PLATE WALLS OF ROOM
RADIOMETER AT ROOM TEMPERATURE
COLD RADIOMETER
HOT RADIOMETER '
RADIOMETERREADINGS\'IVm-%)
CONDmON OF,RADIOMETER METAL I>LATI;. WALLS OF ROOM
RADIOMETER AT ROOM TEMPERATURE 447 0
COLD RADIOMETER 460 35
HOT RADIOMETER 423 -12
36"
~
6. AREAFACTORS
~erbneDt "
To demonstrate that the exchange of radiant energy fromone surface to another is dependentupon theirinterconnecting geometry, Le. a function of the amount that each surface can 'see' of the other.
EQuipment Set. UpA~erture plate
~~--.u
Select thermocouple 1with switch
When using the.. aperture plate make sure theinsulation faces the radiometer" and the silveredsurfacefacesthe heatsource. " Variable
The power control on the instrument console shouldbe set to maximum for this experiment.
Summary of TheoryThe heat transfer rate from one radiating black surface to another is dependent on the amount that eachsurface can 'see' of the other surface. In order to solve radiant heat transfer problems an area factorF is introduced where F is defined by the fraction of energy emitted per unit time by one surface thatis intercepted by the other surface.
Thus the time rate of radiant heat transfer (Q1~ between two black surfaces of area A1 and A,. at
temperatures T1 and T1 respectively, is given by: /
Q11 =AIFll (J (T14 -T1~)
Area factors are found by analysis,numericalapproximation and analogy, and results forcommon configurations have been publishedin graphical form..
rDitial Values of Variables to be UsedDistance from radiometer to heat source
Distance from aperture plate to heat source(X) =300mm(Y)=2OOmm
",.-op
37
Note: The black plate should be placed in the stand' and moved close to the heat source, i.e.approximately 5Omm.
Readings to be TakenOnce the temperatureof the black plate (T) has reached a steady value,record the radiometer readings(R) for a range of apertures from 6Ommdown to zero in steps of 5mm. 'Care should be taken whensetting the apertures to ensure that the plates are equally disposed either side of the track centre-line.Ensure the plates are both vertical and securely clamped before taking ~ radiometer reading.
ResuJts:
"~"i~BlaCk'pliUe~tlm'peratille (T)':::~~o~'~~~~~o,c'~'m..._.
..
,,' .-
A plot of radiometer reading versus aperturewill result in a curye similar' to.that shoWn:Students should aCcount for the result interms. of- the- area factor between the black
plate ~d the radiometer.
Radiometer
,Readirlg
(R)
ApertureCfnm)
TYPICAL RESULTS
Black plate temperature (T) = 245°C /
The resulting graph is shown on Page 38.
..
Apenuremm 60. 55 ,50 45 AO 3$ 30 25 20 15 10 5 0
Radiometer.
Reading (R)
-Aperture mm 60 55 50 45 40 35 30 25 20 15 10 5 0.Radiometer 228 228 210 171 114 68 8
Reading (R)..
38
--~~ --u-AREA FACTORS
..'
'e:t
'"<:
:;;
~ 100a:~
~"e0:;;
0a:
"
300
200
0 10 20 30
"'~r1ur. (mm) "
'0
,
50 / 60
,- -- -,
II
II
I ! 1.---
I I 1,- /" V
I I I I ./V
I I I VI I I I
- '/ I I I/'
I I I I I I V II I I I i 1/ V II I I I / V1 I II I II I/V IVi I I
r" I I
."
39
7. INVERSESQUARELAW FOR UGHT
Experiment -To show that the illuminance of a surface is inversely proportional to the square of the distance of thesurface from the ligbt source~
EQuipment Set-Up
-.--------- ~ --- --
~._----
Set scale to o'
(E) il. norm
\~ to track
Light light-. meter - -- c - source--
Detectorface
x
Set powercontrol to
maximum r-lI I
I I---!
Reading X
It is necessary to set up the equipment in a darkened room in order to eliminate the influence of --ambient light -conditions.
-"
Summary of TheoryThe luminous flux CPrfrom a point lightsource is considered to spatially radiate andproduce an illwninance"E. on a spherical-surface at radius r from the light .somce.Since the surface area of the sphere is givenby 4m2, the illuminance is inverselyproportional to the square of the distance of,the surface from the light source.
/
Initial Values of Variablesto be Used
.Distance from light source (X) = lOOmm to ligh~ meter
Reacfinl!Sto be Taken
Reco~ the light meter readings (E) and the distance from the light source (X) for a number of positionsof the light meter along the horizontal tIacL '
; 40
Results
X (mm) IE (lux) B~
~eter Reading
100
~ :12.~ I
~~
--- -- -. -.' --- -. .-- - ~---- --- -- - - .---- - ---.
log 10 e
IIIIIIII ,L___-
Slope of line:::: - 2
log 10 X
A log-log plot of light meter reading against distance will result in a straight line having a negative slope of
approximately -2 verifying the inverse square relati~nship between distance and illuminance.
TYPICAL RESULTS
See graph. Page 41.
,
Distance X (mm) 100 200 250 300 350 400
Light eter Reading E (lux) 420 110 70 45 30 20
LoglO X 2.000 2.301 2.398 2.477 2.544 2.602
LoglO E 2.623 2.041 1.845 1.653 1.477 1.361
41
. INVERSE SQUARE LAW FOR LIGHT
2.0 2.1 2.2 2.) 2.' 2.5 2.5
I~,.X
...,
....
Slope '" 1.55 - 2.2 '" -0.652.5 - 2.2 0.3Slope.= ~
/
..- .:..'
..
.
..... ,.i'--..
2.5 ........
'""""""
...............
"""""
..........- _. .- . "'"
0/1
--- .H
I-I .
t".....................
r--....2.0 """""
...........
0' ...............'"
I
;..........IT!
.......
I --- - -- -- -- -- -- _: K I---- --- "
1.5c
............0.. -
I
................
. - -
. '.."'
c ,.-
42
8. LAMBERT'SCOSINELAW
ExnerimentTo showthat the energyradiatedin,any direction.atan arlglewith a surfaceis equalto the normalradiationmultipliedby thecosineof the anglebetweenthedirection.of radiationandthenonna!to thesurface.
EQuioment Set-Up
Lightmeter(E)
Lightsource
The light source shoUld berotated. to each desired anglerelative to the track andclamped in position beforetaking measurements.
Track
JSet powercontrol. to
r-,I II I
I :';.:01
Readin~-:7 .J
Angle scale
It~is n~ssar:y to set up theequipJDent in a darkened roomin order to eliminate theinfluence of ambient lightconditions. .
Summary of TheoryLambert's Law of diffuse radiation states that: IcjI= IN Cos cjI
where: IN=intensity of radiation in normal directionIcjI= intensity of radiation in a direction at angle cjIto the normal.
/
Initial Valuesof Variables to be UsedDistance from light source to light meter (X) = lOOmm
Readinl!S to be TakenRecord the light meter readings at 100 intervals for each angle of the light source relative to the trackbetween the limits of :1:900either side of the track centre line.
43
Results
--------
lightmeter
reading(lux)
When a curve of light meter reading isplotted against the angular.positionof thelight source. a typical cosine profile willresult. Students should account for anydifference between a superimposedtheoretical curve and the experimentallyobservedresults.
Anale (!tI°)
90 60 30 0 30 60 90
TYPICAL RESULTS
IcjI=IN Cos cjIIN=425 lux :. Theoretical values can be calculated for 14>as follows:
.,J.
Angle above track 0 10 20 30 40 50 60 70 80 90centre-line- (4)°)
LiBh MeterReading (lux)
Angle below track 0 10 20 30 40 50 60 70 80 90centre-lliie (4)°)
Light Meter I IReading (lux) I I
.
Angle above track 0 10 20 30 40 50 60 70 80 90centre-lliie (4)°)
Light Meter 425 420 415 390 360 300 225 40 60 0Reading (lux)
, ...
'Angle below track 0 10 20 30 40 50 60 70 80 90centre-lliie (cjl°) /
Light Meter 425 420 410 390 360 300 220 150 60 0Reading (lux)
Angle cjl° 0 10 20 30 40 50 60 . 70 80 90
Cos 4> 1.0 0.98 0.94 0.87 0.77 0.64 0.50 0.34 0.17 0
INTheoretical 425 429 399 368 326 273 213 145 74 0-
-; 200:>
coc:
~ 150..a:....;;
:t 100:Eco::;
".--*44
The resulting graphs (actual readings and theoretical values) are plotted below:
LAMBERTS COSINE LAW
~oo
350
300
250
50
00 ~ ~ ro ro ~ w ~ ~ ro 0 ro ~ ~ ~ ~ ~ ro ~ ~
Angle I ~ )
/
:.-"1 r--.V ......, I I I I
/ X Exp.riIMntai
I \..
I I .I I<:) T tTti<d
I I \ .. - -
j \rl \
I / \ I/
\ I I
/ \ I
1/ .- -I
/ - ,\ I I I I
,- I -S I I I
II I
.'.. I I I I I I
/ ! \ I/
'.
.".~ .:<:
4S '-
9. LAMBERT'SLAW OF ABSORPTION
ExperimentTo showthat light passing throughnon-opaquematteris reducedin intensityin proportionto thethicknessand absorptivityof the m~.
Equipment Set-Up Filter.
plates to track
,~,-,--,--~-- ',, ,-,--
Detectorface,, -.- --
Set power
control to"--1I II I1---
Lightmeter
(E)maximum
FILTER SEQUENCE FORVARIABLE ABSORPTIVITYDEMONSTRATION
FILTER SEQUENCE FORVARIABLE THICKNESSTEST
/
It is necessary to set up the equipment in a darkened room in order to ellininate the influence ofambient light conditions.
Summary or Theorv
~ ~ 0: [J ~ ; I :Q~
'1x.r
Absorptivity of materi~1 (0:)
Lightsource
I IIlluminance (E)
0 [g" 0 : [Q, I '-i P.
0 : -: : 0 "l'
I :f£i .. i.0 -;:= 0 ,,: -. , .\--1 .
0 :. 1::lQ 0 «Q, I ,
46
The luminous intensity (I) after having penettated the material to a distance (X) is given by: I =Iv e-x.
where: oc= absorptivity of the materialX =thickness of materialIv =original luminous intensityI =luminous intensity after traverse.
Initial Values of Variables to be Used
Distance from light source to filter plateDistance from light source to light meter
X) =lOOmm(Y) =200mm
~~Readlngs to be TakenRecord the light meter readmgsT1!Sfwith~n(J{"llters~inposition and then with each of the filters of increasingoptical density in succession. Repeat this procedure, but using instead increasing thicknesses of filters havingthe same optical density, i.e. the medium density material.
."-'
Results
(a) Variable Optical Density Demonstration...
..f .-.
(b) Variable Filter Thickness Test
.,
The results of the variable optical density test will clearly indicate that luminous intensity is reduced as theabsorptivity of the filter material increases. It is suggested that students evaluate the various absorptivitiesusing the equation given, although these values cannot be verified.
However, the results of the variable meer thickness test will deinonstrate that luminous intensity is reducedin proportion to the thickness of filter material. It is suggested that students evaluate the absorptivity fromeach measurement and verify that this is constant for the filter material.
/
,
FILTER TYPE No FIlter Pale Medium Dark.-..
Light Meter Reading (lux)
FILTER THICKNESS (mm) 0 3 6 9
.Light Meter Reading (lux)
47::.
TYPICAL RESULTS
(a) Variabie Optical Density Demonstration
-.-;rI = I"e
-1n(!II) wh8re:c = 3 xlO-3m... ... =:c
' -_H' '",,"", ", .c~ ~ '-~-.. ~' n~- -.~--
From the above readings:
c<: (pale) . = 14.8
c<: (M~um) = 175.1
c<: (Dark) =814.1
i.e. as the absorptivity of the filter material increases (filter becomes darker) the luminous intensity afterthe filter is reduced. . -,'
(b) Variable Filter Thickness Test
. ,
-oo;rI = I"e
-In(II!) where:c =-:. ... = :c. '.,
/
i.e. the absorptivity of the filter material is constant, the luminous intensity after the filter falling withincreasing thickness of filter. ' .
FILTER TYPE No Filter Pale Medium Dark
Light Meter Reading (lux) 11.5 110 68 10
FIL1ER THICKNESS (mm) 0 3 6 9
Light Meter Reading (lux) 115 68 40 22
,. For: -.: x= 3mm c<:(Medium) = 175.1
. x=6mm c<:(Medium) = 176.0
x = 9mm ex (Medium) = 183.8
'ii.:;..."
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2 LOCATE SUITABLE POSITIONFOR RCCBNEAR TO EOUIPMENT
3 REMOVECOVERFROMENCLOSURE
4 POSITONMOUNTINGBASE. HARK OFF DRILL THROUGH2 HOLES
5 FIX BASE AT LOCATIONUSINGSUITABLE SCREWS.6 CLIP RCCBTO BASE
, . .7 RE~OVE LENGTH OF OUTER Sf:!EATH ON BOTH EOUIPMENTCABLE AND LOOSE CABLE6 CONNECTLIVE AND NEUTRAL CABLt::STO RCCBTERMINALS
9 CONNECTEARTH CABLES TO EARTH TERMINAL ON"BASE
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TITLE: RCCB INSTALLATlm,1 Oale: 22.2.90 DRG. No.
TO BE USE ONUNIT Scale. - RCCB107SERIALNo.--"=- I ~ - - - OI~LY no/rig.- -~--_u
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Dimensions:mm by:
@CJLlml!s untess"olherwlse slaled; Fracl/ons . 1/64' ProJection:
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TITLE, TRANSFORMER COtMEdTIONS 110/120V UNITS Da'e: 19,10.89~ITI.: Scola.
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