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Law Jeng Yih

Ext: 2107

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Multiphase What is multiphase????

A system consists more than one phase such boiling

water: liquid / steam (gas)

Melting ice: solid / liquid

Brewing a cup of coffee: Hot liquid of water and solidground coffee bean

LAW JENG YIH

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Volatility = degree of species tends to transfer

to vapor from liquid or solid

Antoine Equation (most common)

CT

BAP

*

10log

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Example of process:Evaporation, Drying, Humidification (involve transfer of liquid into the gasphase)

Condensation, Dehumidification (involve transfer of the condensablespecies from gas to liquid phase)

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Superheated vapor:

A vapor present in a gas in less than its saturationamount!

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In the definitions to be given, the term refers to any gas-vaporcombination, while

refers to specifically to an air-water system.

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Raoultss Law :

Where :

xA mole fraction in liquid

yA mole fraction in gas

)(*TpxPyp AAAA

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Henrys Law :

Where :xA mole fraction in liquid

yA mole fraction in gas

HA(T) is Henrys Law constant

)(*THxPyp AAAA

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When a liquid is a mixture of severalcomponent:

- when it is heated slowly at const P, thetemp at which the first vapor bubble forms isthe bubble-point temperature at the given P.

- when a gas (vapor) is cooled slowly at const

P, the temp at which the first liq dropletforms is the dew-point temperature at thegiven P.

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Assuming an ideal solution and Raoults lawapplies, the partial pressures of vapor components:

Since we have A, B, present in the system, thesum of partial pressures must be the total pressure(Daltons law)

The bubble-point temperature may be calculatedby trial & error as the Tbp satisfies this eqn.

,...,),(*

BAiTpxp bpiii

...)()(**

bpBBbpAA TpxTpxP

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Again, a gas phase that contains condesablecomponents A, B, C, at fix P. At Tdp it will beequilibrium with the 1st liq that forms. AssumingRaoults law applies, the liq phase mole fraction:

The mole fractions of liq components must sum to1:

The dew-point temperature may be calculated bytrial & error.

,...,,)(

* BAiTp

Pyx

dpi

ii

1...,)()( **

dpB

B

dpA

A

Tp

Py

Tp

Py

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Vapor-liq equilibrium calc for binary (two-component) systems can be simplified usinga Txydiagram at a fix pressure.

Liq phase: T vs xA

Vapor phase: T vs yA

A is usually the more volatile component.

To determine a Tbp for a given liqcomposition, go to the liq curve and read thedesired temperature.

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Move horizontally to the vapor curve todetermine the vapor composition inequilibrium with the liq.

To determine a Tdp for a given vapor mixture,

look at specified mole frac ofA in vaporphase, go to the vapor curve and read thedesired temperature.

Move horizontally to the liq curve todetermine the liq composition in equilibriumwith the vapor.

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If a noncondensable species is present in thegas phase, must use eqn to calc dew point.

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If water and methyl isobutyl ketone (MIBK) aremixed at 25C,

A single phase formed if the mixture contains> 98% water or 97.7% MIBK.

otherwise, it separates into two liq phases: 98% water, 2% MIBK

97.7% MIBK, 2.3% water Termed partially miscible

Termed immiscible if 2% MIBK or 2.3% water isnegligible.

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Water-MIBK-acetone at 25C. Here the solute acetone is completely

miscible with the two solvents H2O and MIBK,although the two solvents are only partially

miscible with each other.

Each apex of the triangle represents a singlecomponent.

Edges represent binary solutions. Exp. edge brepresents solutions of H2O and acetone.

Kmixture of 20.0 wt% MIBK, 65.0% acetone,15.0% water.

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Any mixture whose composition falls inregion A (exp. K), is single-phase liquid.

Region Brepresents a two-phase regionwhich will split up into two layers in

equilibrium with each other.

The lines within region Bis known as a tieline.

Such lines, connect the compositions of twophases in equilibrium with each other.

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Exp. overall composition at M(55.0 wt%water, 15% acetone, 30.0% MIBK) results themixture separates into two phases:

L(85 wt% water, 12% acetone, 3% MIBK)

N(4 wt% water, 20% acetone, 76% MIBK)

When a mixture does not fall on a tie line,interpolation between the lines is necessary

to determine composition of each phase.

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THANK YOU