RESPONSI

MATA KULIAH: DASAR KETEKNIKAN PENGOLAHAN

Gedung Pascasarjana THP, 16-17 JUNI 2014

Fluid flow

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Fluid flow

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Fluid flow

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Fluid flow

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Item Pipa lurus Fitting Contraction Enlargment

f Laminar/ Turbulen(pipa halus/kasar) - - -

EF - - Kf(V1)2/α [1-(A1/A2)2](V1)2/α

ΔP 2f(v2)Lρ/D 2f(v2)L’ρ/D EF x ρ EF x ρ

L’/D lihat Tabel 6.3

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Contoh soal

Sebuah sample diuji menggunakan viskometer rotasional. Pada skala pembacaan penuh, percobaan tersebut menghasilkan konstanta pegas = 6374 dyne-cm. Tentukan parameter reologinya jika OD = 2 cm, ID= 1.5 cm, serta L= 6cm. Hasil percobaan menunjukkan hasil sbb :

N (RPM) Torsi (skala penuh)

2 18

4 30

10 58

20 100

Solution

Contoh soal

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Hitung tekanan yang harus diberikan pompa untuk mengalirkan 400 L/menit

fluida yang mempunyai densitas 1.052 g/cm3 dan viskositas 100 cP. Fluida

tersebut mengalir melalui sanitary pipe (1.50-in nominal) dengan panjang 60

m. Pipa lurus dan mempunyai ketinggian yng sama, dan bagian pengeluaran

terbuka (tekanan atmosfir). Diketahui bahwa sanitary pipe yang digunakan

merupakan pipa kasar terbuat dari commercial steel.

Solution:

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det

m01.0

det 60

1menit

1000L

1m

menit

L 600 =Q

33

xx

333

36

3 m

kg1520

10

kg

m

cm10

cm

g 1.52=

gxx

sPa.1.0m.s

kg1.0

cm.s

g1poise 1cP 100=

det/052.10(0.0356/2)

1

det01.0

area

Q=

22

3

mm

xm

Diameter (1.50 in nominal, sanitary pipe)< : D = 1.402 in = 0.0356 m

L = 60

8

061.5439

1.0

0356.0052.101520

Re

xx

D

Pa

xxxx

D

LfP

4762372

0356.0

152060)052.10(0092.02

)(2

2

2

(turbulen) f melihat diagram Moody, ɛ = 0.046 mm = 0.000046

ɛ/D = 0.000046/0.0356 = 0.001292 ≈ 0.001

f = 0.0092

Solution:

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Sebuah fluida dengan 1.05 g/cm3 dan viskositas 200 cP

dialirkan melalui sanitary pipe (3-in nominal) sepanjang 20

m yang disambung dengan sanitary pipe (2-in nominal)

sepanjang 20 m dan memiliki bagian exhaust pipa yang

terbuka. Pada pipa yang lebih besar dipasang 90° elbow

std. Berpakah power (dalam KW) yang harus dihasilkan

pompa agar memenuhi laju alir fluida sebesar 12 L/detik?

Contoh soal

Solution

Heat Transfer

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Konduksi

q = hA (Tw – Tf)

Konveksi

q = T1 – T2

x/kA

melalui Dinding datar

q = (T1 – T2) (r2 – r1)/(kAlm) = (T1 – T2) R Alm = A2 – A1

ln(A2/A1) R=ln(r2/r1)/(2kL)

Konduksi Melalui Silinder

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Kombinasi

q = U A Toverall, U = 1/ (1/hi +kA/xA+ 1/ho)

melalui Dinding datar

Heat Transfer

Silinder

q = T1-T4

1/hiAi + (ro-ri)/kAAAlm + 1/hoAo

q = UiAi(T1-T4) = UoAo(T1-T4)

Ui = 1 1/hi +(ro-ri)Ai/kAAAlm+ Ai/Aoho

Uo = 1 Ao/Aihi +(ro-ri)Ao/kAAAlm+ 1/ho

Contoh soal

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1. What is the rate of saturated steam(kg/h) with 120.8 kPa pressure is required to heat 100 kg/h of juice from 58C to 95C? Assume that the heat capacity of the juice is 4 kJ/kgC.

solution:

Q = m.Cp.ΔT = m. ΔH use steam table

Q = 100 kg/h x 4 kJ/kgC x (95-58)C = 14800 kJ/h

ΔH = 2683.8 – 440.15 = 2243.65 kJ/kg

m = Q/ΔH = 6.596 kg/h

Latihan soal

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a. For quick preparation of a cup of hot chocolate in a cafeteria, cocoa powder and sugar are added in a cup of water and the solution is heated by direct steam injection. If the initial temperature of all the ingredients is 15 C, the final temperature is 95C, the mass of the solution is 150 g initially, and the heat capacity of the solution is 3.8 kJ/kg C, calculate how much saturated steam at 110 C will be used. State your assumptions.

Contoh soal

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Contoh: 2. Hitung penyerapan panas (secara konduksi) per m2 luas permukaan dari es balok dengan ketebalan 15 cm, dengan suhu di dalam 270 K dan suhu luar 273 K. Konduktivitas panas es 2.25 W/m.K Penyelesaian: Q/A = k.ΔT/ Δx = 2.25 (273-270)/0.15 = 45 W/m2

Contoh soal

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Contoh: 3. Hitung panas yang diserap secara konveksi per m2 luas permukaan dari es balok dengan ketebalan 15 cm yang diletakkan pada bak penyimpanan (bagian ujung-unjung dan bawah terisolasi) dan bagian atas terkena udara. Suhu di dalam es 270 K dan suhu luar es 273 K. Konduktivitas panas es 2.25 W/m.K, koefisien transfer panas udara(h),6 W/m2.K asumsikan suhu udara 298 K. Penyelesaian:

(Q/A)2 =h(Tudara – Tes)=6 (298-273) = 150 W/m2

Contoh soal

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Contoh: 4. Hitung panas total yang diserap per m2 luas permukaan dari es balok dengan ketebalan 15 cm yang diletakkan pada bak penyimpanan (bagian ujung-unjung dan bawah terisolasi) dan bagian atas terkena udara. Suhu di dalam es 270 K dan suhu luar es 273 K. Konduktivitas panas es 2.25 W/m.K, koefisien transfer panas udara(h),6 W/m2.K asumsikan suhu udara 298 K. Penyelesaian: (Q/A)1 = U Toverall

= (1/6+2.25/0.15)x (298-270) = 424.67 W/m2

Contoh soal

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5. A stainless steel pipe (k= 17 W/mC) is being used to convey heated oil. The inside surface temperature is 130C. The pipe is 2 cm thick with an inside diameter of 8 cm. The pipe is insulated with 0.04 m thick insulation (k= 0.035 W/mC). The outer insulation temperature is 25C. Calculate the temperature of interface between steel and isulation. Assume steady-state conditions.

Pipa silinder seri

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6. Find the heat transfer per unit area through the composite wall. Assume one-dimensional heat flow.

Given:

kA = 150 W/mC

kB = 30 W/mC

kC = 50 W/mC

kD = 70 W/mC

AB = AD

T = 370C

C A

D

B q AA = AC = 0.1 m2

T = 66C

2.5 cm

7.5 cm

5.0 cm

plate seri, peralel

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b. A certain material has a thickness of 30 cm and a thermal conductivity of 0.04 W/mC. At a particular instant in time the temperature distribution with x, the distance from the left face, is T = 150x2 - 30x, where x is in meters. Calculate the heat flow rates at x = 0 and x = 30 cm. Is the solid heating up or cooling down?

c. A certain material 2.5 cm thick, with a cross-sectional area of 0.1 m2, has one side maintained at 35C and the other at 95C. The temperature at the center plane of the material is 62C, and the heat flow through the material is 1 kW. Obtain an expression for the thermal conductivity of the material as a function of temperature.

Latihan soal

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d. One side of a copper block 5 cm thick is maintained at 260C. The other side is covered with a layer of fiber glass 2.5 cm thick. The outside of the fiber glass is maintained at 38C, and the total heat flow through the copper-fiber-glass combination is 44 kW. What is the area of the slab?

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