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    Che421 HW NO.1

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    Mohamed Elbehlil
    This document contains two problems related to diffusion through stagnant air films. Problem 1 involves calculating the daily loss of benzene evaporating from a circular tank through a 5mm thick air film. Problem 2 involves calculating the molar flux and evaporation time of a 1mm deep pool of water evaporating through a 5mm air film. Both problems involve diffusion, vapor pressures, and other relevant chemical engineering concepts.

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    Che421 HW NO.1

    Uploaded by

    Mohamed Elbehlil
    54 views1 page
    This document contains two problems related to diffusion through stagnant air films. Problem 1 involves calculating the daily loss of benzene evaporating from a circular tank through a 5mm thick air film. Problem 2 involves calculating the molar flux and evaporation time of a 1mm deep pool of water evaporating through a 5mm air film. Both problems involve diffusion, vapor pressures, and other relevant chemical engineering concepts.

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    HOMEWORK ASSIGNMENT ON DIFFUSION MASS TRANSFER

    Original Title

    Che421 HW NO.1

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    This document contains two problems related to diffusion through stagnant air films. Problem 1 involves calculating the daily loss of benzene evaporating from a circular tank through a 5mm thick air film. Problem 2 involves calculating the molar flux and evaporation time of a 1mm deep pool of water evaporating through a 5mm air film. Both problems involve diffusion, vapor pressures, and other relevant chemical engineering concepts.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    54 views1 page

    Che421 HW NO.1

    Uploaded by

    Mohamed Elbehlil
    This document contains two problems related to diffusion through stagnant air films. Problem 1 involves calculating the daily loss of benzene evaporating from a circular tank through a 5mm thick air film. Problem 2 involves calculating the molar flux and evaporation time of a 1mm deep pool of water evaporating through a 5mm air film. Both problems involve diffusion, vapor pressures, and other relevant chemical engineering concepts.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    of 1

    Faculty of Engineering

    Chemical Engineering Department


    Mass Transfer Che421 Spring 2013
    Assignment (1)

    Problem 1: Diffusion through a stagnant air film

    A circular tank 6 m in diameter contains benzene at 22oC, which is exposed the


    atmosphere for 6 hours per working day in such manner that the liquid is covered
    with a stagnant air film estimated to be 5 mm thick. The concentration of benzene
    beyond the stagnant air film is negligible. The vapour pressure of benzene at 22 oC
    is 100 mm Hg. if a litter of benzene costs 2.500 $/L , Estimate the daily loss due
    to evaporation of benzene. The specific gravity and diffusivity of benzene at
    storage conditions are 0.88 and 0.299x2.581x10-5 m2/s, respectively. Molecular
    weight of benzene is 78 kg/kmol. Universal gas constant is 8.314 kJ/kmol.K. The
    atmospheric pressure may be taken as 1.013 bar. (1 bar = 100 kN/m 2 = 750 mm
    Hg),

    Problem 2 : Diffusion through a stagnant air film

    A pool of water 1 mm in depth lies on a horizontal surface in contact with dry air
    at 20oC and 1 atm. Evaporation takes place and can be treated as molecular
    diffusion through a 5 mm thick film of moist air immediately above the water
    surface. Above this gas film, water vapor is assumed to be perfectly mixed with
    the surrounding (with the zero partial pressure). Assuming that evaporation does
    not affect the temperature of water, calculate (i) the molar flux of water vapor
    from the surface, and (ii) the time taken for complete evaporation of the liquid.
    Diffusivity of water in air can be taken as 2.6x10-5 m2/s, saturated vapor pressure
    of water at 20oC as 2340 N/m2 and gas constant as 8314 J/kmol.K.

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