QUIZ Steady Heat Conduction

Hendi Saryanto, ST, M. Eng

SISTEM RADIALSOAL:

1. Uap air suhu 320oC mengalir di dalam sebuah pipa stainless steel (k= 15 W/m.oC) yang mempunyai diameter dalam dan luar 5 cm dan 5,5 cm. Pipa dibalut dengan insulasi glass wool (k= 0,038 W/m.oC) setebal 3 cm. Terjadi kehilangan kalor ke sekelililing yang suhunya 5oC secara konveksi alami dan radiasi. Koeffisien perpindahan kalor gabungan konveksi alami dan radiasi adalah 15 W/m2.oC. Asumsikan koeffisien perpindahan kalor permukaan dalam pipa 80 W/m2.oC. Tentukan laju kehilangan kalor dari uap persatuan panjang pipa , penurunan suhu pada dinding pipa dan penurunan suhu pada lapisan insulasi.

2. Sebuah kawat listrik berdiameter 2 mm dan panjang 10 m dibalut erat dengan isolator plastik ( k= 0,15W/m.oC ) setebal 1 mm. Pada kawat mengalir arus sebesar 10 A dengan tegangan 8 V. Jika suhu udara sekitar kawat 30oC dan koefisien perpindahan kalor permukaan kawat ke udara, h= 24 W/m2.oC, tentukanlah suhu permukaan kawat dalam keadaan stedi. Jika tebal isolator plastik digandakan apakah suhu permukaan kawat tersebut menurun atau meningkat ?JAWABAN

1. Perhatikan gambar berikut ini :

Diketahui :Tateam= 320 oC

kss= 15 W/m.oC

rss,in= 0.025 m

rss,out= 0.0275 m

kinsl,GW= 0.038 W/m.oC

T

= 5 oC

h

= 15 W/m2.oC

hi= 80 W/m2.oC

rout= 0.0575 mPenyelesaian :a. Laju kehilangan kalor Q dari uap per satuan panjang pipa :

Ket :R1 = Tahanan thermal konveksi dalam pipa

R2 = R3 = Tahanan thermal konduksi

R4 = Tahanan thermal konveksi lingkungan

Maka :

Jadi :

b. Penurunan suhu pada diniding pipa :

c. Penurunan suhu pada lapisan insulation :

2. Diketahui :

dkawat tembaga= 2 mm = 2 x 10-3 mm (rkawat tembaga =1 x 10-3 mm)Panjang= 10 m

Linsulation= 1 mm = 1 x 10-3 mmI

= 10 A

V

= 8 volt

Tair

= 30oC

h

= 24 W/m2.oCk

= 0.15 W/m.oCPenyelesaian :

Suhu permukaan kawat dalam keadaan stedy :

Jika tebal isolator plastik digandakan (2mm) apakah suhu permukaan kawat akan meningkat atau menurunkah ? Jawabannya M E N I N G K A TPenyelesaian :

Suhu permukaan kawat dalam keadaan stedy :

Pipa SS

Insulasi

Glass wool

320oC

T=5oC

Q

rss,in

3 cm

rss,out

steam

Tss, kulit dalam

Tss, kulit luar

Tglass wool,kulit luar

EMBED Equation.3

Tglass wool,kulit dalam

R1

R4

R3

R2

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r2=1mm

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r1=1mm

q

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1mm

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R2

R1

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r2=2mm

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r1=1mm

q

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1mm

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R2

R1

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