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1、Everyfreesurfaceemitsenergyintheformofelectromagneticwaves;theamountofenergyisafunctionofthesurfacetemperature.Thisemittedenergyisknownasradiantthermalenergy.Thenatureofthisradiantenergyisnotcompletelyunderstood,butlawshavebeenformulatedthatdescribeitsbehavior.Itisrec
2、ognizedthat,aswithotherformsofradiantenergy,radiantheatenergyistransmittedintheformofelectromagneticwaves.Thecompleteformulationofthelawsgoverningradiantheatenergymustconsiderthatthisenergyisquantized,thatis,theenergyistransferredinquanta.Incontrastwithothermodesofhea
3、ttransfer,nomediumisrequiredtotransmitradiantenergy.Infactsomegases,forinstance,carbondioxideandwatervapor,absorbsomeoftheradiantenergypassingthroughthem.每一个自由表面都会以电磁波的形式发射能量，能量的量是表面温度的函数。这种发射的能量被称为辐射热能。这种辐射能的性质是不完全理解的，但已经制定了法律，描述其行为。这是公认的，与其他形式的辐射能，辐射热能以电磁波形式传播。控制辐射能
4、的法律的制定必须考虑到这种能量是量子化的，即，能量转移量子。与其他模式相比，传热，无需介质传输辐射能。事实上，例如，二氧化碳和水蒸气，吸收一些辐射能通过它们。Forafixedsetofconditions,anyfreesurfaceemitsradiantenergyofvaryingwavelengths.Thefrequencyofvibration(v)ofradiantwavesisdependentsolelyonthesourceofradiationandisindependentofthemediumthrou
5、ghwhichtheypass.Thevelocityofradiantwavesisafunctionsolelyofthemediumthroughwhichtheypass.Thus,thewavelengthisafunctionofboththesourceandthemedium.对于一个固定的条件，任何自由表面发射的辐射能的不同波长。辐射波的振动频率是完全依赖于辐射源，是独立的介质，通过它们传递。辐射波的速度是一个函数的介质，通过它们传递。因此，波长是源和介质的函数。Allfreesurfacesreceiverad
6、iantenergyfromallothersurfacesthattheycan“see,”thatis,surfacesindirectlineofsight.Mostproblemsinradiantdealwiththenetradiantenergyexchangedbetweenagivensurfaceandthosethatsurroundit.Incommonparlance,theterm”heatexchangedbyradiation”isused.Itmustbeemphasized,however,th
7、atradiationisnotheat.Heatisconductedtoasurface.Byvirtueofthetemperatureofasurface,electromagneticwavestransmitenergyfromthesurface.Whenthesestrikeanothersurface,partoftheenergywillbeabsorbed,tendingtoincreasethetemperatureofthesurfacestruckbythem,andpartwillbereflecte
8、d.Whentheobjectistransparent,orpartiallyso,toradiantwaves,someofalloftheradiantenergyreceivedbythesurfacewillpassintotheobje
