Faktor faktor yang mempengaruhi laju konveksi kalor

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Faktor-faktor yang mempengaruhi laju konveksi kalor : Luas permukaan benda (A), semakin luas permukaan benda yang bersentuhan dengan fluida, semakin cepat kalor dipindahkan. Perbedaan suhu (∆T), semakin besar beda suhu benda dengan permukaan fluida, semakin cepat kalor dipindahkan Koefisien konveksi (h), bergantung pada bentuk, kedudukan permukaan dan diperoleh dengan percobaan. Misal h tubuh manusia adalah 7,1 Js -1 m -2 K -1
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Laju Konveksi Laju Konveksi T A h t Q t Q = laju konveksi (J/s) h = koefisien konveksi (W/m 2 K) A = luas permukaan benda yang bersentuhan Δ T = perbedaan suhu antara benda dan fluida(K) dengan fluida(m 2 )
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C. RADIASI (PANCARAN) adalah perpindahan kalor tanpa melalui zat perantara. (pancaran energi dari permukaan sebuah benda dalam bentuk gelombang elektromagnetik) Misal, panas matahari sampai ke bumi melalui ruang hampa udara. Catatan : 1. Permukaan hitam sempurna sebagai pemancar dan penyerap kalor yang baik (e=1) 2. Pemukaan putih mengkilap sebagai pemancar dan penyerap kalor radiasi yang buruk (0<e<1). Pemanfaatan radiasi : efek rumah kaca, panel surya.
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Perpindahan kalor tanpa zat perantara Perpindahan kalor tanpa zat perantara R R A A D D I I A A S S I I T A A = luas permukaan (m 2 ) T = suhu mutlak permukaan (K)
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Faktor-faktor yang mempengaruhi laju kalor radiasi : (dinyatakan dalam hukum Stefan-Boltzman) “Energi yang dipancarkan oleh suatu permukaan hitam dalam bentuk radiasi kalor tiap satuan waktu (Q/t) sebanding dengan luas permukaan (A) dan sebanding dengan pangkat empat suhu mutlak permukaan (T 4 )”
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Laju Radiasi Laju Radiasi 4 AT e t Q t Q = laju radiasi(J/s) e = emisivitas (0 < e < 1) σ = Tetapan Stefan-Boltzman T = suhu mutlak(K) = 5,67 x 10 -8 Wm -2 K -4
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Permukaan hitam dan kusam merupakan penyerap dan pemancar radiasi yang baik Permukaan putih dan mengkilap merupakan Penyerap dan pemancar radiasi yang buruk Termoskop adalah alat yang digunakan untuk mengetahui adanya pemancaran kalor
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