Ethylene glycol flows at 0.01 kg/s through a 3-mm diameter, thin-walled tube. The tube is coiled and submerged in well-stirred water bath ma

Question

Ethylene glycol flows at 0.01 kg/s through a 3-mm diameter, thin-walled tube. The tube is coiled and submerged in well-stirred water bath maintained at 25°C. If the fluid enters the tube at 85°C, what heat rate and tube length are required for the fluid to leave at 35°C?

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Nguyệt Ánh 6 months 2021-07-11T14:48:19+00:00 1 Answers 93 views 0

Answers ( )

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    2021-07-11T14:50:02+00:00

    Answer:

    heat rate= 1281W

    length = 15.8m

    Explanation:

    we have this data to answer this question with

    Tmi = 85 degrees

    Tmo = 35 degrees

    Ts = 25 dgrees

    flow rate = 25 degrees

    using engine oil property from table a-5

    Tm = Tmo – TMi/2 = 333k

    u =0.522×10⁻²

    k = 0.26

    pr = 51.3

    cp = 2562 J/kg.k

    mcp(Tmo-Tmi) =

    0.01 x 2562(35-85)

    = 1281 W

    we find the change in Tim

    = [(35-25)-(85-25)]/ln[(35-25)/(85-25)]

    = -50/ln0.167

    = -50/-1.78976

    = 27.9°c

    we finf the required reynold number

    4×0.01/πx0.003×0.522×10⁻²

    = 0.04/0.00004921

    = 812.8

    = 813

    we find approximate correlation

    NuD = hd/k

    NuD = 3.66

    3.66 = 0.003D/0.26

    cross multiply

    0.003D = 3.66×0.26

    D = 3.66×0.26/0.003

    = 317.2

    As = 1281/317×27.9

    = 0.145

    As = πDL

    L = As/πD

    = 0.145/π0.003

    = 0.145/0.009429

    L = 15.378

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