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7/29/2019 Articulo Nro 1 Fenomenos
1/4
UNIV ERSIDAD DE A NT IOQUIA
F A C UL T Y O F E NGINEE R ING
DEPART MENT OF CHEMICA L ENGINEERING
Phenomenon of mass transfer by concentration gradient
C.G. Julin Andrs, R.H. Carlos Fernando, S.Caterine
Chemical Engineering student. Faculty of Engineering, Universidad de Antioquia. Medellin, Colombia.
__________________________________________________________________________________________
ABSTRACT
This assignment is done with the intention to observe a real process, which shows the behavior of an egg with a
semipermeable membrane in low and high saline concentrated solutions. This process can be explained by Ficks
law, which states that diffusion occurs when a concentration gradient takes place. Where the water from the body
less concentrated of solute moves to the concentrated solution in order to reach an equilibrium and how this
concentration gradient affects the rate of mass transfer.
KEYWORDS: Molecular flux, concentration gradient, Diffusion.
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INTRODUCTION
Diffusion is the movement, under the influence of a
physical stimulus of an individual component through
a mixing. The most common cause of diffusion is a
concentration gradient of the component that it
spreads. A concentration gradient tends to move the
component in a direction such that equalize the
concentrations and cancel the gradient.
When the gradient is maintained by the continuous
supply of components low and high concentration,
the flow of the component diffuses that it is constant.
This movement is exploited in mass transfer
operations.
The mass and heat transfer mechanisms, depend on
the dynamic system in which it occurs. The mass
can be transferred by molecular motion in steady
fluids, aided by the dynamic characteristic of flow,
the forced movement of large groups of molecules.
The molecular diffusion is the transference of one or
more components through other caused by a
concentration difference or of chemical potential
when put in contact two immiscible phases, which it
is stagnant or in laminar regime.
The velocity which one component is transferred in a
mixture will depends to presence concentration
gradient in a point and in a given direction. their
movement is described by the molecular flux, which
7/29/2019 Articulo Nro 1 Fenomenos
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UNIV ERSIDAD DE A NT IOQUIA
F A C UL T Y O F E NGINEE R ING
DEPART MENT OF CHEMICA L ENGINEERING
is related to the diffusivity using first Fick`s law for
isobaric and isothermal systems.
Fick`s law is a law in the form of quantitative
differential equation that describes several cases of
diffusion of matter in a medium in which initially there
is no chemical equilibrium .
HYPHOTESIS
According to Fick's law in situations where there are
gradients of concentration of a substance, It
produces a stream of particles that tends to
homogenize the dissolution and standardize the
concentration, In the case there are differences in
concentration the mass transfer will take place from
the regions with the greatest concentration toward
regions of lower concentration.
It is expected that the egg that is located in the
solution of higher concentration have a weight lose
more significant due to a greater mass transfer.
PROCEDURE AND MATERIALS
The materials used for the realization of the mount
were:
Acetic acid
Two eggs
Two Beakers
Chloride of sodiumWater
The preparation of the experiment of diffusion by
difference of concentration was carried out in the
first place, the disintegration or exposure of the
semipermeable membrane of the egg. This left the
egg with acetic acid for 3 days, in which reacts the
calcium carbonate with the acetic acid producing
sodium acetate and exposing the membrane
permeable, Then prepare two solutions of sodium
chloride and water, one of them to high
concentration and the other to low concentration of
sodium chloride, both solutions to the same pressure
and temperature conditions, we then measure the
weight of the two eggs , after heavy introduces an
egg in each of the solutions, and weigh the eggs
each 15 minutes , to identify loss or gain of mass ,
due to the diffusion .
MATHEMATICAL MODEL
Equation of the first law of Fick for the diffusion In
the form one-dimensional
Where
= Represents the flux density of matter in
molecular mass.
= Is the proportionality factor called diffusion.
A more general equation for the mass transport in
the vector form is
For the specie A
For the specie B
Where
7/29/2019 Articulo Nro 1 Fenomenos
3/4
UNIV ERSIDAD DE A NT IOQUIA
F A C UL T Y O F E NGINEE R ING
DEPART MENT OF CHEMICA L ENGINEERING
In this way, there is only one diffusivity for the
couple A-B which in general is a function of
pressure, temperature and concentration .
EXPERIMENTALS RESULTS AND ANALYSIS
Table 1 .Experimental data
Solution of NaCl more H2O
(High Concentration)
Weight (Grams) Time (Minutes)
94 0
82 15
72 30
63 45
59 60
Fig 1.Solution with High concentration of sodium
chloride
Table 2 .Experimental data
Solution of NaCl more H2O
(Low Concentration)
Weight (Grams) Time (Minutes)
102 0
100 15
99 30
97 45
97 60
Fig 2. Solution with low concentration of sodium
chloride.
Graphic 1. Mass transfer with respect to Time.
7/29/2019 Articulo Nro 1 Fenomenos
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UNIV ERSIDAD DE A NT IOQUIA
F A C UL T Y O F E NGINEE R ING
DEPART MENT OF CHEMICA L ENGINEERING
Fig 3. Samples subjected to a concentration gradient
of high and low sodium chloride respectively.
It is noted that after 60 minutes, is achieved a
greater transfer of mass, represented a decrease in
weight (water), in the egg that was in the solution to
higher concentration.
CONCLUSIONS
Was concludes that in the diffusivity
phenomena, the gradient concentration
plays a very important role , so that the
higher gradient of concentration increase
the mobility in the particles and this is
reflected is faster diffusion .
We can conclude that the speed of mass
transfer decreases with time, due to the fact
that each time is less the concentration
gradient.
When 2 solutions with different
concentrations are put in contact through a
semipermeable membrane (in this case the
interior and exterior of the egg through the
membrane that we still have) there is a
phenomenon of mass transportation since
the dissolution less concentrated to the
more concentrated.
The diffusion tends to return the system to
its equilibrium state of constant
concentration. Through the act of Fick
observed that the diffusive fluxes that
crosses an area is directly proportional to
the concentration gradient.
The study of the mass transfer is important
in the majority of the chemical processes
that require the initial purification of raw
materials and the separation of products and
by-products, as well as to determine the
costs, the analysis and design of certain
industrial equipment for the processes of
separation.
When looking at the behavior of the
semipermeable membrane compared to the
different concentrations, it becomes clear
that in the same interval of time, the mass
transfer occurs at a higher speed to a higher
concentration gradient.
REFERENCES
http://es.wikipedia.org/wiki/%C3%93smos
is
Byrd, R. (2006). Transport phenomena
(Vol. 2 ed). Mexico: Limusa Wiley.
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