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    Contoh Soal

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    anjar
    Using Bell's method, the shell-side heat transfer coefficient and pressure drop were calculated for a heat exchanger to sub-cool methanol from 95°C to 40°C using brackish water as the coolant. The shell-side heat transfer coefficient was determined to be 1246 W/m2°C. The total clean pressure drop across the shell side was calculated to be 8.05 kPa and the fouled pressure drop was estimated to be 11.3 kPa.

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    Contoh Soal

    Uploaded by

    anjar
    117 views7 pages
    Using Bell's method, the shell-side heat transfer coefficient and pressure drop were calculated for a heat exchanger to sub-cool methanol from 95°C to 40°C using brackish water as the coolant. The shell-side heat transfer coefficient was determined to be 1246 W/m2°C. The total clean pressure drop across the shell side was calculated to be 8.05 kPa and the fouled pressure drop was estimated to be 11.3 kPa.

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    CONTOH SOAL

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    Using Bell's method, the shell-side heat transfer coefficient and pressure drop were calculated for a heat exchanger to sub-cool methanol from 95°C to 40°C using brackish water as the coolant. The shell-side heat transfer coefficient was determined to be 1246 W/m2°C. The total clean pressure drop across the shell side was calculated to be 8.05 kPa and the fouled pressure drop was estimated to be 11.3 kPa.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    117 views7 pages

    Contoh Soal

    Uploaded by

    anjar
    Using Bell's method, the shell-side heat transfer coefficient and pressure drop were calculated for a heat exchanger to sub-cool methanol from 95°C to 40°C using brackish water as the coolant. The shell-side heat transfer coefficient was determined to be 1246 W/m2°C. The total clean pressure drop across the shell side was calculated to be 8.05 kPa and the fouled pressure drop was estimated to be 11.3 kPa.

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    CONTOH SOAL

    Using Bells method, calculate the shell-side heat transfer coefficient and pressure drop for the
    exchanger design to sub-cool condensate from a methanol condenser from 950C to 400C. Flow-rate of
    methanol 100,000 kg/h. brackish water will be used as the coolant, with a temperature rise from 250 to
    400C. Because coolant is corrosive, so assign to tube side.

    Heat capacity methanol = 2.84 kJ/kg0C


    Heat load = (100,000/3600)[2.84(95-40)] = 4340 kW
    Heat capacity water = 4.2 kJ/kg 0C
    Cooling water flow = 4340/4.2(40-25) = 68.9 kg/s
    Tlm = 31 0C

    Summary of tube design


    Number of tubes = 918
    Shell i.d. = 894 mm
    Bundle diameter = 826 mm
    Tube o.d = 20 mm
    pitch 1.25 = 25 mm
    Tube length = 4830 mm
    Baffle pitch = 356 mm
    Solution

    Heat-transfer coefficient
    Ideal bank coefficient, hoc
    25 20
    As 894 356 10 6 0.062m 2
    25
    100,000 1
    Gs 448kg / s m 2
    3600 0.062
    Gs d o 448 20 10 3
    Re 26,353
    0.34 10 3
    From Fig. Heat transfer factor for cross-flow tube banks, jh = 5.3 x 10-5
    Neglect viscosity correction factor (/w).
    0.19 3
    hoc 2272W / m 2 0C
    1

    3
    5.3 10 26,353 5.1 3

    20 10
    Tube row correction factor, Fn
    Tube vertical pitch pt = 0.87 x 25 = 21.8 mm
    Baffle cut height Hc = 0.25 x 894 = 224 mm
    Height between baffle tips = 894 2 x 224 = 446 mm
    446
    N cv 20
    21.8
    From Fig. Tube row correction factor, Fn = 1.03
    Window correction factor, Fw

    224 mm
    190 mm

    446 mm

    826
    Hb 894(0.5 0.25) 190mm
    2
    190
    " Bundle cut " 0.23(23 per cent )
    826
    From Fig. Baffle geometrical factors at cut of 0.23
    Ra = 0.18
    Tube in one window area, Nw = 918 x 0.18 = 165
    Tube in cross-flow area, Nc = 918 2 x 165 = 588
    2 165
    Rw 0.36
    918

    From Fig. Window correction factor, Fw = 1.02


    Bypass correction, Fb
    Ab (894 826)356 10 6 0.024m 2
    0.024
    Ab / As 0.39
    0.062
    Fb exp[ 1.35 0.39] 0.59
    Very low, sealing strips needed; try one strip for each five vertical rows.
    Ns/Ncv = 1/5
    Fb = exp[-1.35 x 0.39(1-(2/5)1/3] = 0.87
    Leakage correction, FL
    Using clearances as specified in the Standards,
    Tube-to-baffle 1/32 in = 0.8 mm
    Baffle-to-shell 3/16 in = 4.8 mm
    0.8
    Atb 20 (918 165) 18.9 103 mm2 0.019m 2
    2
    From Fig. baffle geometrical factors, 25 per cent cut (0.25), b = 2.1 rads
    4.8
    Asb 894(2 2.1) 8.98 103 mm2 0.009m 2
    2
    AL (0.019 0.009) 0.028m 2
    0.028
    AL / As 0.45
    0.062
    From Fig. Coefficient for FL, heat transferL = 0.3
    FL = 1 0.3[(0.019 + 2 x 0.009)/0.028] = 0.60
    Shell-side coefficient

    hs 2272 1.03 1.02 0.87 0.60 1246 W/m 2 0 C


    Appreciably lower than that predicted by Kerns method (compare this value with the previous example)

    Pressure drop
    Cross-flow zone
    From fig. friction factor for cross-flow tube banks at Re = 26,353 dor 1.25 pitch, jf = 5.6x10-2
    Gs 448
    us 0.60 m/s
    750

    Neglecting viscosity term (/w).


    2 750 0.6 2
    Pi 8 5.6 10 20 1209.6 N / m 2
    2
    ( 4.0)
    F 'b exp[ 4.0 0.39(1 (2 / 5)1/ 3 )] 0.66

    From Fig. Coefficient for FL, pressure drop L = 0.52


    FL = 1 0.52[(0.019 + 2 x 0.009)/0.028] = 0.31
    Pc = 1209.6 x 0.66 x 0.31 = 248 N/m2
    Window zone
    From Fig. baffle geometrical factors, for baffle cut 25 per cent (0.25), Ra = 0.19

    Aw 894 2 0.19 165 20 2 67.4 103 mm2
    4 4
    100,000 1 1
    uw 0.55m / s
    3600 750 0.067
    u s u wu s 0.57m / s
    190
    N wv 8
    21.8
    750 0.57 2
    Pw 0.31(2 0.6 8) 257 N / m 2
    2
    End zone
    Pe 1209.6[(8 20) / 20]0.66 1118 N / m 2
    Total pressure drop
    4830
    Number of baffles N b 1 12
    356
    Ps 2 1118 248(12 1) 12 257 8048 N / m 2 8.05kPa(1.2 psi )

    This is for the exchanger in the clean condition. Using the factors given in Table Ratio of Fouled to Clean
    Pressure Drop to estimate the pressure drop in the fouled condition.
    Ps 1.4 8.05 11.3kPa

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