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    Process Heat Transfer, Elsevier (2007) - 220

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    Hammad zia 32

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    Process Heat Transfer, Elsevier (2007) - 220

    Uploaded by

    Hammad zia 32
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    Process Heat Transfer, Elsevier (2007)-220

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    Process Heat Transfer, Elsevier (2007) - 220

    Uploaded by

    Hammad zia 32

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    © All Rights Reserved
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    of 1

    D E S I G N OF S H E L L - A N D - T U B E HEAT E X C H A N G E R S 5/213

    JH -- 0.5(1 + B / d s ) (0.08Re 06821 + 0.7 Re 01772)

    = 0.5(1 + 0.3)[0.08(33,057) 6821 -t- 0.7(33,057) 01772]


    JH - - 6 5 . 7 7
    ho --JH (k/De) Prl/3 (#/#w) 0"14

    = 65.77 (0.08/0.1058) (11.31)1/3 (1.0)


    ho - 112 B t u / h 9ft 2 .o F

    d) Calculate fin efficiency.


    T h e fin efficiency is calculated f r o m E q u a t i o n s (2.27) and (5.12) with k - 64 B t u / h . ft 2. ~ for
    Admiralty brass. Fin d i m e n s i o n s are obtained from Table B.4.
    r - fin t h i c k n e s s - 0.011 in. - 0.0009167 ft
    /'1 -- root tube radius - 0.625/2 - 0.3125 in.

    r2 - rl + fin h e i g h t - 0.3125 + 0.05 - 0.3625 in.


    r2c - r2 + T/2 - 0.3625 + 0.011/2 - 0.3680 in.
    d / - (r2c - r~)[1 + 0.35 In (r2c/r~)] - (0.3680 - 0.3125)[1 + 0.35 In (0.3680/0.3125)]
    7J - 0.058676 in. - 0.0048897 ft
    m - ( 2 h / k r ) ~ - (2 x 112/64 x 0.0009167) o.5 - 61.7903 ft -1
    m ~ - 61.7903 x 0.0048897 - 0.302136

    tanh (0.302136)
    =0.971
    rlf - 0.302136

    T h e w e i g h t e d efficiency of the finned s u r f a c e is given by E q u a t i o n (2.31). T h e fin and p r i m e


    s u r f a c e a r e a s p e r inch of t u b e l e n g t h are first calculated to d e t e r m i n e the area ratios:

    Afin s -2Nf:r(r2c - r21) - 19 x 27r[ (0.3680) 2 - (0.3125)21 - 4.5087 in 2.

    A p r i m e - 27rrl ( L - Nfr) - 27r x 0 . 3 1 2 5 ( 1 . 0 - 19 x 0.011) - 1.5531 in 2.


    A~ns/ATot- 4.5087/(4.5087 + 1.5531) - 0.744
    A1Jrime / A Tot - 1 - 0.744 - 0.256

    qw - (Aprime/ATot) + qf (A~ns/ATot) - 0.256 + 0.971 x 0.744


    r/w - 0 . 9 7 8

    (m) Calculate wall t e m p e r a t u r e s .


    T h e wall t e m p e r a t u r e s u s e d to obtain viscosity c o r r e c t i o n factors are given by E q u a t i o n s (4.38)
    and (4.39). F r o m Table B.4, t h e ratio of e x t e r n a l to internal t u b e s u r f a c e a r e a iS A T o t / A i - 3.91.
    Hence,

    m
    hitav e nu hol]w (ATot/Ai) Tav e
    h i nu hoqw(ATot/Ai)

    1253 x 102.5 + 112 x 0.978 x 3.91 x 195


    1253 + 112 • 0.978 • 3.91

    T p - 126~

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