Articulo Nro 1 Fenomenos

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.

__________________________________________________________________________________________

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


2/4




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


3/4




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.


4/4




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.

Documents

Articulo Nro 1 Fenomenos