radiation
DESCRIPTION
RadiationTRANSCRIPT
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Radiation
Black Body and Gray Body
Derryl, gilang, Juriwon, Mei
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Outline
• Definisi• Emisivitas + Soal• Black Body +Soal• Grey Body +Soal• Faktor Pengaruh + Soal
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Definisi Radiasi
? A
B
T1
T2
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Q = ε σ A T4
dimana:Q = panas (Btu atau Watt)ε = emisivitasσ = ketetapan bolzman (5,67 x 10-8 W/m2.K4 atau 0,1714 x 10-8 Btu/hr.ft2.R4)A = Luas permukaan teradiasi (m2)T = suhu (K)
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Sifat-sifat benda yang menerima energi radiasi:
ρ = faktor refleksi (refleksivitas)
α = faktor absorpsi (absorpsivitas)
τ = faktor transmisi (transmisivitas)
ρ + α + τ = 1
Kebanyakan benda padat tidak meneruskan
radiasi thermal τ = 0, sehingga ρ+α = 1
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Emisivitas = daya pancar• Perbandingan antara energi yang dapat dipancarkan oleh benda itu
pada suhu T dibandingkan dengan energi yang dipancarkan oleh benda hitam pada suhu yang sama
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BLACK BODY• Benda yang sifatnya dapat menyerap energi yang dating
seluruhnya (100%) disebut benda hitam (blackbody)
• α= 1; ρ= 0
• Emisi benda hitam, ε= 1 → ε = α = 1
• Q = σ A T4
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Contoh Soal
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Grey BodyBenda yang dapat memantulkan energi yang datang 100%
disebut benda putih sempurna (absolutely white)
ρ= 1 ; α= 0
Emisi benda putih, ε= 0 → ε = α = 0
Benda yang diantara black body dan white body disebut
benda abu-abu (grey body) 0 < ε < 1
Q = ε σ A T4
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Contoh Soal• Dua buah benda seperti pada gambar, terjadi perpindahan panas
secara radiasi, berapa besar laju pancaran dan laju perpindahan panas yang diserap?
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Faktor Pengaruh Radiasi
- Bentuk- Jarak- Bidang
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Soal
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Terima kasih