Heat Transfer by Radiation PDF

7 fofdj.k }kjk Å"ek lapj.k HEAT TRANSFER BY RADIATION * General– Å’eh; fofdj.k 3cm>  >7800 Å okys fo|qr pqEcdh; rjax gSaA bl fof/k ls lapj.k ds fy;s ek/;e vuko”;d gSA fuokZr esa budk osx C gksrk gSA ;g Å’ek lapj.k dh lokZf/...

7 fofdj.k }kjk Å"ek lapj.k HEAT TRANSFER BY RADIATION * General– Å’eh; fofdj.k 3cm>  >7800 Å okys fo|qr pqEcdh; rjax gSaA bl fof/k ls lapj.k ds fy;s ek/;e vuko”;d gSA fuokZr esa budk osx C gksrk gSA ;g Å’ek lapj.k dh lokZf/kd rst fof/k gSA buds vf/kdka”k xq.k çdk”k ln`”; gksrs gSaA * Å’eh; fofdj.k dh rhozrk I “çfr bZdkbZ {ks=Qy gksdj yEcor~ fn”kk esa cgus okyh Å’eh; ÅtkZ dh nj gSA” ;g ,d lfn”k jkf”k  cal   k.cal   joule watt  gS, ftldh bdkbZ   or  2  or  2  2  rFkk foeh; lw= [ MT–3 ] gSA  cm  sec  m s   m s m  2  ( cgs) ( mks ) ( SI ) I IR * n”kkZ ldrs gSa fd, 1mks = 0.1cgs = 4200 SI rhozrk * A {ks=Qy gksdj t le; esa yEcor~ fn”kk esa xqtjus okyh dqy Å’eh; ÅtkZ dk eku gS, Q = (IAt) cal etc. rFkk “kfä, (Q/t) = P = (IA) cal/sec etc. 1.fdlh lrg dh çd`fr (Nature of a surface)– nf”kZr fp= ij ÅtkZ laj{k.k ls (IR + IA + IT) = I IA bldk vFkZ gS fd r a t1 ftles, IT r = ( I R / I) = ijkorZu xq.kkad (reflection coefficient) ;k ijkorZu {kerk (reflecting power) gSA a = ( I A / I) = vo”kks’k.k xq.kkad (absorption coefficient) ;k vo”kks’k.k {kerk (absorpting power) gSA t = ( I T / I) = lapj.k xq.kkad (transmission coefficient) ;k lapj.k {kerk gSA * i`Fkdr%, çR;sd bdkbZ ghu, foekghu rFkk 1 ls de gSaA * rhu lEHkkoukvksa esa ls lokZf/kd egRoiw.kZ r 0, t 0 gSA vr% a 1. bldk vFkZ ;g gS fd ;g lHkh  (light + heat + vU;) dk iw.kZ vo”kks’kh gSA izd`fr esa ,slk dksbZ ugha gSA ds”k 95%. dkty 97% rFkk platinum black 98% (loZJs’B) vo”kks’kh gSA * pwf¡ d çdk”k vFkok Å’ek dk dksbZ ijkorZu ;k lapj.k ugha gksrk, vr% ;g dkyh çrhr gksrh gSA blfy;s bls iw.kZ d`f’.kdk (perfect black body, PBB) Hkh dgrs gSA * mPp rki, ij PBB  (s) çnku djrh gS vr% bls iw.kZ mRlthZ vFkok iw.kZ fofdjd Hkh dgrs gSaA * bldk mRltZu o.kZØe lnSo gh lrr~ (continous) gksrk gSA 2. mRltZu {kerk (emissive power/total radiancy) : “bdkbZ {ks=Qy ls bdkbZ le; esa mRlftZr gksus okyh fofdj.k ÅtkZ dh ek=kA” bdkbZ rFkk foek,a I tSlh gh gSaA d`’.k fi.M ds fy;s E rFkk vU; oLrq ds fy;s e }kjk nf”kZr ;g jkf”k, rkiØe ds lkFk rsth ls c