NCES Presentation on Solar Collectors

7/24/2019 NCES Presentation on Solar Collectors

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SOLAR ENERGY COLLECTORSSOLAR ENERGY COLLECTORS

Non Conventional EnergyNon Conventional Energy

SourcesSources

References : G.D RAIReferences : G.D RAI


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SOAR COEC!ORS:

Collector is a device which absorbs the incoming solarradiation, converts it into heat, and transfers this

heat toa uid (usually air, water, or oil) owing through thecollector.


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COLLECTORS

Collecting FluidsMounting

Flat (or)

Nonconcentric AdjustableStationary Liquid as (or) Air

Concentric

(or)

Focussing


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Flat-plate collectors, developed byHottel and hillier in the !"#$s,

are the most common type ofsolar collector which are widelyused for domestic household hot-water heating , air heating

%emperature can be upto "$$

&n the 'on-concentrating type, thecollector area is the same as theabsorber area.

"lat or Non concentric ty#e collector


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Flat (or)

Non

concentric

Fluid Ty!e Air Ty!e

"$ID !%&E : 'eat !ransfer (e)iu( is *ater or any ot+er li,ui)

AIR !%&E : 'eat !ransfer (e)iu( is air or gas.


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A ty#ical )iagra(s of""lat #late solar

t+er(al collectors#


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Co(#onents of "lat #late collectorCo(#onents of "lat #late collector

LAZIN

ABSORBER

HEADERS

INSULATION

CONTAINER

-- !+ese can asor ot+ )irect an) )i/use)

ea( ra)iations


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GA0ING:GA0ING:

o 1a)e of one or (ore covers of trans#arent (aterial like glass or #lastic..

o It is use) to re)uce convective an) ra)iative +eat losses fro( t+e asorer.

o It is o#a,ue to t+e infrare) ra)iations.

A2SOR2ER :A2SOR2ER :

o It is usually (a)e of co##er or steel (etal.

o !+e surface is covere) *it+ a t+in coating of #ri(er an) t+en 3at lack #aint of +ig+asor#tance +uge

#aint (ay increase t+e resistance to +eat tranfer

o Coating is a##lie) on t+e surface to (a4i(i5e t+e asor#tance of solar energy an)(ini(i5es t+e

ra)iation e(itte) y #late.

!$2ES OR 'EADERS :!$2ES OR 'EADERS :

o A tue t+at is attac+e) to asorer or so(eti(es it is a #art of asorer #late.

o If t+e *orking 3ui) is air 6 t+e 3o* #assage s+oul) e elo* t+e asorer #late to(ini(i5e +eat losses.


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Insulation:Insulation:

!+ese are so(e (aterials suc+ as 7erglass an) t+ey are #lace) at t+e ackan) si)es of

t+e collector to re)uce +eat losses. eg. *ool6 7er etc...

Container :Container :

8+ic+ encloses t+e ot+er co(#onents toget+er an) #rotects fro( t+e *eat+er.


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"lat #late collectors"lat #late collectors


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"lat #late collector "lui) !y#e"lat #late collector "lui) !y#e


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Cross sectional arrange(ents t+roug+Cross sectional arrange(ents t+roug+

t+e collector #latest+e collector #lates!ue in stri# ty#e!ue in stri# ty#e

GlazingRiser

Absorbing plate

Insulation

A

BBGlazing

Riser

Absorbing plate

Insulation


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CGlazing

Riser

Absorbing plate

Insulation

DD

Glazing

Riser

Absorbing plate

Insulation

!ues ra5e) to!ues ra5e) toasorerasorer

Cross sectional arrange(entsCross sectional arrange(ents

t+roug+ t+e collector #latest+roug+ t+e collector #lates


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8orking &rinci#le

unlight passes through theglaing and stri*es the

absorber plate, which heatsup, and solar energy isconverted into heat energy.%his the heat is transferred to

the uid passing through pipesattached to the absorber plateby means of convective heattransfer.


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Gla5ing )esign

Due to t*o glass s+eets are use) losses )ue to air convection arefurt+er re)uce) 6 t+is is (ainly use) an) i(#ortant in *in)y areas.

Ra)iation losses in infrare) s#ectru( are re)uce) to 9; fro(ciency)ecreases.

!+e air s#ace et*een t+e cover an) t+e asorer #revents +eatloss y convection

'o*ever if one *atc+es t+e electro(agnetic s#ectru(


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As cover is made of glass

It allows the solar radiations of wavelength < 2m

and is opa!ue for wavelength " 2m

$t is seen %ro& electro&agnetic s!ectru& t'at in%rared

radiations 'aing aelengt' * 2m

As a result infrared are opa!ue and does not pass

#oo heat is trapped inside the space between the cover and

absorber plate similar to green house effect and $eeps it hot%

&owever some of heat occurs due to conduction ' convection ' and

radiation thereb( effecting the overall efficienc(overall efficienc(%


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)his can be met b( following steps *++

It can be reduced b( using ,water white glass, with low iron content

Reflection which is order of -./ can be met b( gentll( itching the

glass surface h(dro flouric acid%

Gla5ing )esign consi)erationsGla5ing )esign consi)erations


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Asorer )esignAsorer )esign

Coating done on the absorber surface is called ,selective coatings ,

,Blac$ chrome, is e0tensivel( used coating which is of 2m

thic$ness

'eat trans#ort syte('eat trans#ort syte(

&eat generated in the absorber is continuosl( ta$en b( the flow of

medium through tubes%


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111


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Non !orus absorberNon !orus absorber * Air flows above and beneath the absorber%

+orus Absorber+orus Absorber * Air flows through the absorber%

Air ,eaters

Non !orus

Absorber+orus

Absorber


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Non &orus Air +eaterNon &orus Air +eater


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Air !y#e "lat #late collectorsAir !y#e "lat #late collectors

$se) co((only for s#ace +eating an)

agricultural +eating a##lications.

+ %ypicalFlat plate collectorolar air heater


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Collectors *it+ #orus asorersCollectors *it+ #orus asorers


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Design of Air #late collectorDesign of Air #late collector

&eavil( insulated material li$e mineral wool is coated beneath the

surface of absorber

)he most favourable orientation of the panel is facing due south with

an inclination of -.o

latitude with the horizontal%

Air as medium of heat transfer eliminates the corrossion and

freezing problems which are more when water is used%

Air is passed through the baffles arranged in zig zag pattern

between the absorber and insulation where fins provides the morecontact area thereb( more amount of heat to transfer%


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A##licationsA##lications

"lat &late"lat &late

collectorscollectors

Air collectorsAir collectors

&eating Buildings

Dr(ing Agricultural roducts

&eating Green houses%

&eat source for heat engines%

Both Beam and Diffuse radiations

orientation need not be towards sun

little maintaince

simplier than concentric plate t(pe

A)vantagesA)vantages


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!+er(al Analysis of "lat &late Collectors!+er(al Analysis of "lat &late Collectors


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!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors If I is the intensit( of solar radiation' in 34m 2' incident on the aperture plane of the

solar collector having a collector surface area of A' in m2

)hen the amount of solar radiation received b( the collector is *

&owever' as it is shown 5igure 2' a part of this radiation is reflected bac$ to the s$('&owever' as it is shown 5igure 2' a part of this radiation is reflected bac$ to the s$('

another component is absorbed b( the glazing and the rest is transmitted through theanother component is absorbed b( the glazing and the rest is transmitted through theglazing and reaches the absorber plate as short wave radiation%glazing and reaches the absorber plate as short wave radiation%

)herefore the conversion factor indicates the percentage of the solar ra(s penetrating)herefore the conversion factor indicates the percentage of the solar ra(s penetrating

the transparent cover of the collector 6transmission7 and the percentage beingthe transparent cover of the collector 6transmission7 and the percentage being

absorbed%absorbed%

Basicall(' it is the product of the rate of transmission of the cover and the absorptionBasicall(' it is the product of the rate of transmission of the cover and the absorptionrate of the absorber and is given b(rate of the absorber and is given b(


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!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors As the collector absorbs heat its temperature is getting higher than that ofthe surrounding and heat is lost to the atmosphere b( convection and

radiation%

)he rate of heat loss 68o7 depends on the collector overall heat loss

coefficient 69:7 and the collector temperature%


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9nder stead( state conditions

)he rate of useful energ( e0tracted b( the collector 68u7' e0pressed as

!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors

It is also $nown that the rate of e0traction of heat from the collector ma( be

measured b( means of the amount of heat carried awa( in the fluid passed

through it' that is*


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It is convenient to define a !uantit( that relates the actual useful energ(

gain of a collector to the useful gain if the whole collector surface were at

the fluid inlet temperature% )his !uantit( is $nown as ;the collector heat

removal factor 65R7 and is e0pressed as*

!+er(al Analysis of "lat &late!+er(al Analysis of "lat &lateCollectorsCollectors


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Concentric ty#e collector :Concentric ty#e collector :


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si(#le concentric collectorsi(#le concentric collector


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\

Ty!es o% concentric collectorsTy!es o% concentric collectors

a7 5lat plate collector with ad=ustable mirrors

b7 Compounded parabolic collector

c7 C(lindrical parabolic collector

d7 >irror strip reflector 6or7 >oving reflector with fi0ed concentrator

e7 5resnel lens collector

f7 arabolic trough collector


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Beam radiation is reflected from the

number of individual mirrors called

heliostatsto the central receiver at the top%

9pto 2???9pto 2?????CC

Cylin)ricalCylin)rical#araolic#araolictroug+troug+collectorcollector


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"resnel ens Collector"resnel ens Collector

&t is at on one side and has ne

longitudinal grooves on the

other

%he angles of these grooves are

such that the radiation is

brought to the focus

ens are made of plastic sheets.

sed upto /$$$C


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&araolic troug+ collector&araolic troug+ collector

solar radiation coming in a

particular direction is collected

and is collected on the focus of

the parabola


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!+er(al Analysis of concentrate collectors!+er(al Analysis of concentrate collectors

$n)er t+e stea)y state con)itions *e +ave :$n)er t+e stea)y state con)itions *e +ave :

@!uation is written assuming that the contribution of diffuse beam

radiations are negligible


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And 8-the overall loss coefficient can be given as *


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CONC$SION

:ong lasting

Cheaper than other water heating s(stems%

&owever'the( re!uires large areas

Also solar energ( is free

If we do not include the initial cost for installation and the maintenance%

5inall( besides these we should remember b( using solar energ( we canprotect nature


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!+e En)!+e En)

NCES Presentation on Solar Collectors

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