Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 82 views

    Department of Chemical Engineering: (An Autonomous Institution Affiliated To JNTUK, AP)

    Uploaded by

    sagar
    This document is a lecture outline from GMR Institute of Technology on the topic of relative and percentage saturation or dew point. It begins by defining saturation and partial saturation when a gas is in contact with a liquid. It explains that relative saturation is the ratio of the vapor's partial pressure to its vapor pressure if saturated, while percentage saturation is the ratio of actual vapor moles to moles at saturation. For water vapor, relative saturation is called relative humidity and percentage saturation is percentage humidity. The document provides equations to convert between relative saturation and percentage saturation. It concludes by defining dew point as the temperature at which a gas reaches 100% relative humidity and any further cooling will cause condensation.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Department of Chemical Engineering: (An Autonomous Institution Affiliated To JNTUK, AP)

    Uploaded by

    sagar
    82 views6 pages
    This document is a lecture outline from GMR Institute of Technology on the topic of relative and percentage saturation or dew point. It begins by defining saturation and partial saturation when a gas is in contact with a liquid. It explains that relative saturation is the ratio of the vapor's partial pressure to its vapor pressure if saturated, while percentage saturation is the ratio of actual vapor moles to moles at saturation. For water vapor, relative saturation is called relative humidity and percentage saturation is percentage humidity. The document provides equations to convert between relative saturation and percentage saturation. It concludes by defining dew point as the temperature at which a gas reaches 100% relative humidity and any further cooling will cause condensation.

    Original Title

    Notes-10.pdf

    Copyright

    © © All Rights Reserved

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    This document is a lecture outline from GMR Institute of Technology on the topic of relative and percentage saturation or dew point. It begins by defining saturation and partial saturation when a gas is in contact with a liquid. It explains that relative saturation is the ratio of the vapor's partial pressure to its vapor pressure if saturated, while percentage saturation is the ratio of actual vapor moles to moles at saturation. For water vapor, relative saturation is called relative humidity and percentage saturation is percentage humidity. The document provides equations to convert between relative saturation and percentage saturation. It concludes by defining dew point as the temperature at which a gas reaches 100% relative humidity and any further cooling will cause condensation.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    82 views6 pages

    Department of Chemical Engineering: (An Autonomous Institution Affiliated To JNTUK, AP)

    Uploaded by

    sagar
    This document is a lecture outline from GMR Institute of Technology on the topic of relative and percentage saturation or dew point. It begins by defining saturation and partial saturation when a gas is in contact with a liquid. It explains that relative saturation is the ratio of the vapor's partial pressure to its vapor pressure if saturated, while percentage saturation is the ratio of actual vapor moles to moles at saturation. For water vapor, relative saturation is called relative humidity and percentage saturation is percentage humidity. The document provides equations to convert between relative saturation and percentage saturation. It concludes by defining dew point as the temperature at which a gas reaches 100% relative humidity and any further cooling will cause condensation.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    You are on page 1of 6

    GMR Institute of Technology

    Rajam, Andhra Pradesh


    (An Autonomous Institution Affiliated to JNTUK, AP)

    Department of Chemical Engineering


    rd
    Class 3 Sem. - B. Tech. (Chemical Engineering)
    Course Chemical Process Calculations Course Code CHEM-2403
    Prepared by Mr. P. Satya Sagar, Sr. Assistant Professor
    Lecture Topic Relative and percentage saturation or dew point
    Course Outcome CCHEM203.2 Program Outcome PO1,PO13
    Duration 50 min Lecture 10 of 45 Unit I
    REMEMBER UNDERSTAND APPLY ANALYSE EVALUATE CREATE
    Learning Level
    (Tick whichever is applicable)

    1. Objectives
    Understand the basic concepts of Relative and percentage saturation or dew point
    2. Topic Learning Outcomes: After the completion of the class the students will able to:
    a. Calculate Relative saturation and percentage saturation or dew point
    b. Rephrase the definitions of Relative saturation, Percentage saturation and Dew point
    3. Teaching Methodology
    a. Chalk & Talk/Presentation mode
    4. Applications
    Drying, condensation, distillation, air conditioning, air separation, humidification and
    dehumidification
    5. Evocation

    Form No. AC 04. 00.2016 GMRIT, Rajam, Andhra Pradesh 1


    6. Discussion

    Humidity and Saturation: When a gas or a gaseous mixture remains in contact with a liquid
    surface, it will acquire vapor from the liquid until the partial pressure of the vapor in the gas
    mixture equals the vapor pressure of the liquid at its existing temperature. When the vapor
    concentration reaches this equilibrium value the gas is said to be satureated with the vapor. It is
    not possible for the gas to contain a greater stable concentration of vapor. The vapor content of a
    saturated gas is determined entirely by the vapor pressure of the liquid and may be predicted
    directly from vapor pressure data. Thus for ideal gases
    pv
    Vv = V ----- (1)
    P
    When Vv = pure component volume of vapor
    pv = partial pressure of vapor = vapor pressure of liquid at existing temperature.
    V = total volume
    P = total pressure
    From equation 1 the percentage composition by volume of a vapor saturated gas may be
    calculated. When the ideal gas law is applicable, the composition by volume of a vapor saturated
    gas is independent of the nature of the gas but is dependent on the nature and temperatures of the
    liquid and on the total pressure. The composition by weight varies with the nature of both the
    gas and the liquid, the temperature and the total pressure.
    Partial Saturation: If a gas contains a vapor in such proportion that its partial pressure is less
    than the vapor pressure of the liquid at the existing temperature, the mixture is but partially
    saturated.
    The relative saturation of such a mixture may be defined as the percentage ratio of
    the partial pressure of the vapor to the vapor pressure of the liquid at the existing temperature.
    The relative saturation is therefore a function of both the composition of the mixture and its
    temperature as well as of the nature of the vapor.
    From its definition it follows that the relative saturation also represents the following ratios:
    (a)The ratio of the percentage of vapor by volume to the percentage by volume that would be
    present were the gas saturated at the existing temperature and total pressure.
    (b)The ratio of the weight of vapor per unit volume of mixture to the weight per unit volume

    Form No. AC 04. 00.2016 GMRIT, Rajam, Andhra Pradesh 2


    present at saturation at the existing temperature and total pressure.
    Another useful means for expressing the degree of saturation of a vapor-bearing gas
    may be termed the percentage saturation. The percentage saturation is defined as the
    percentage ratio of the existing moles of vapor per mole of vapor-free gas to the moles of vapor
    that would be present per mole of vapor-free gas if the mixture were saturated at the existing
    temperature and pressure. The percentage saturation also represents the ratio of the existing
    weight of vapor per unit weight of vapor-free gas to the weight of vapor that would exist per unit
    weight of vapor-free gas if the mixture were saturated at the existing temperature and pressure.
    Care must be exercised that the relative saturation and the percentage saturation are not
    confused. They approach equality when the vapor concentrations approach zero but are different
    at all other conditions. The quantitative relationship between the two terms is readily derived
    from their definition. Thus,
    pv
    Relative saturation in % = (100) = yr
    ps

    Where pv = partial pressure of vapor


    ps = vapor pressure of pure liquid
    nv
    % saturation = (100) = ys
    ns

    Where nv = moles of vapor per mole of vapor free gas actually present
    ns = moles of vapor per mole of vapor free gas at saturation
    From Daltons law

    nv pv ns ps
    = and =
    1 p pv 1 p ps

    nv p p ps
    or = v
    ns ps p pv

    p ps
    Hence yp= yr
    p pv

    Where p = total pressure.


    It can be observed that the saturated vapor pressure Ps is always greater than partial pressure of

    Form No. AC 04. 00.2016 GMRIT, Rajam, Andhra Pradesh 3


    the vapor Pv, hence the percentage saturation is always less than the relative saturation.
    Humidity: Most commonly occurring case of water vapor in gases of all kinds, special
    attention has been given and a special terminology has been developed. The humidity H of the
    gas is generally defined as the weight of water per unit weight of moisture free gas. This is also
    known as absolute humidity. The molal humidity Hm is the number of moles of water per mole
    of moisture free gas. When the vapor under consideration is water, the percentage saturation is
    termed the percentage humidity. The relative saturation becomes the relative humidity.
    Considerable confusion exists in the literature in the use of these terms, and care must always be
    exercised to avoid misuse
    Dewpoint
    If the air is gradually cooled while maintaining the moisture content constant, the relative
    humidity will rise until it reaches 100%. This temperature, at which the moisture content in the
    air will saturate the air, is called the dew point . If the air is cooled further, some of the moisture
    will condense.

    Form No. AC 04. 00.2016 GMRIT, Rajam, Andhra Pradesh 4


    7. Mind Map:

    8. Readings:
    1. Hougen, Olaf A., and Kenneth M. Watson. "Chemical Process Principles-Part 1: Material
    and Energy Blances." (1948)
    2. Himmelblau, David Mautner, and James B. Riggs. Basic principles and calculations in
    chemical engineering. FT Press, 2012
    3. Bhatt, B. I., and S. M. Vora. Stoichiometry:(si units). Tata McGraw-Hill Pub. Co., 1996
    4. http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html

    9. Questions:
    Remember:
    1. Dene saturation, partial saturation, relative saturation and percentage saturation.
    Apply:
    1. The partial pressure of ethyl acetate in a hydrogen-ethyl acetate mixture at 400C and 1 atm
    total pressure is 75 mm Hg. Calculate
    i. The humidity of the mixture.
    ii. The percentage humidity.

    Form No. AC 04. 00.2016 GMRIT, Rajam, Andhra Pradesh 5


    iii. The relative humidity.
    10. Key Words:
    Dew point,
    Humidity,
    Molar humidity,
    Daltons law,
    relative saturation
    percentage saturation

    Form No. AC 04. 00.2016 GMRIT, Rajam, Andhra Pradesh 6

    You might also like