INFLUENCE OF TRIBO–ELECTRICITY ON THE PROCESS OF CONVECTION DRYING.

Dr. Ph. of Technical Sciences, Professor, Nikolay S. Nikolaev.

Dr. Ph. of Technical Sciences, Academic IAR, Michail Ya. Burlev.

Tribo–electricity is phenomenon of electrical charges due friction particles each other two materials. Acquisition their electrical charges are equal to the absolute value and opposite in sign.

This phenomenon occurs during the process of convection drying of skim milk. This significantly may reduce the effectiveness of the equipment due to adhesion particle product in the drying plant walls. For developing of the measures to eliminate this negative process is necessary to investigate the mechanism of its occurrence.

Known some a number of methods and devices for measuring electric charge as the mass, so and individual particles. [1, 2, 3] The most common is a method of measuring of the potential with using of the cylinder of Faraday (English physicist 1791 – 1867). This method was used in our experiments.

The essence of this method is to charge potential of the specified capacity (C) and then measuring the potential of its. The cylinder of Faraday consists from of receiver particles (metal capacity) in the shielding earthed casing.

Receiver particles are isolated from earthed casing through dielectric material with a large resistance, for example: – fluorine plastic. It is necessary to increase the time of the dissipation of electric charges from the measuring contour. In addition, the receiver particles (metal capacity) connects screened conductor with recording devices, for example – electrostatic voltmeter and electric capacitance meter (electrometer).

For the measuring tribo – electricity of the electrical charges particles a bio – object was developed experimental installation, which presented in Figure 1

In process the convective drying occurs the emergence of the electric charge due friction particles of dry skim milk each other. Or with a surface of a different material, for example – air channels and drying plant walls.

Electric charges particles were determined on the inclined surface made of metal and dielectrics (polyethylene, nylon). Identify potential particles of dry skim milk conducted at temperature T = 18° С and relative air humidity 75 – 80%

Specific electric charge of particles (Coulomb/kg), was determined according to the formula:

CU

q sp = --------

m

С – capacitance measurement circuit, (Farad);

U – voltage, Volt;

m – the mass of particles of dry skim milk, kg.

Found with increasing length of the traversed path, as shown in Figure 2 of particles of dry skim milk greatly increased contact specific area of particles with the surface of the metal inclined surface.

This contributed to the ascending values of specific electrical charges. All the particles of dry skim milk are gaining positive polarity charges because the free electrons are generated easily passed metal the inclined surface – conductor.

Tribo – electricity effect is the result of an exchange between the contacting surfaces of particles and, according to some authors [4, 5, 6], is associated with the formation of a common contact of electric double layer that serves as the direct source of static charges.

Energy state surfaces before its contact is characterized by a certain equilibrium condition.

qx10⁸ Coulomb/kg.

6
5		The inclined surface L = 0 – 100 mm – metal L = 100 – 300 mm – fluorine plastic
4			U = 0 Volt
3			U = 100 Volt
2			U = 150 Volt
1

0 100 200 Lx10^-3 m.

Fig. 2.

Tribo – charge particles of dry skim milk depending on the length of the path.

On contact surfaces of energy state is being violated, because them in contact consists of a surface with different level of surface energy [7].

Newly formed electric double layer, equal to more than one micrometric, is characterized by new energy state.

When you break a contact on each particle are uncompensated electric charges of opposite sign, the value of which is determined by the kinetics of processes taking place in the formation and rupture of electric double layer in place of contact of particles.

Kinetics for each individual case reports of electric charges depends on a number of factors associated with electrical – physical characteristic of the contacting of phases and the specific conditions under which the process of tribo – electrization [8, 9].

When replacing the metal inclined surface on the dielectric (polyethylene and nylon) in tribo – electrization were accumulated charges of opposite polarity, both the metal inclined surface and the particles of dry skim milk.

This increased the difference of the potential between the surface of the metal inclined surface and particles, which gravitation to metal inclined surface.

Study on the tribo – electricity of particles of dry skimmed milk necessary for understanding and managing the phenomena occurring during the course of production processes of drying of various materials, including dried skimmed milk.

When spraying condensed skim milk in a spray dryer, with the subsequent subsidence of dry powder on the wall of the drying plant, the transportation of powder in the air canal, etc., is an undesirable build-up of static charges that ground circuit drying plant or take other protection methods. This should be taken into account when designing the drying plants in order to reduce the negative effects of ignition of dry skim milk in the drying process [10].

LITERATURE:

1. Andrianov E.I Methods for determination of structurally – mechanical properties of powder materials. – Chemistry, 1982. – P. 121 – 152.

2. Barfut J., Taylor J. Polar dielectrics and applications. – M. 1981 – 230 p.

3. Revnivtsev V.I. Physical bases of electrical separation. M. 1983. – 270 p.

4. Ilyukhin V.V., Burlev M. Zhukavets E.V. Drying milk using electric fields. «Dairy industry ". M. 2011. No. 8. – 12 p.

5. Krapivin S.A. Plasma – chemical manufacturing processes. – L. 1981. – 245 p.

6. Lipatov N.N. "Design principles of composition and improvement of technology of meat and dairy products. Abstract dissertation. – M., 1988. – 56 p.

7. Urakaev F. H. Theoretical estimation of pulse pressure and temperature on contact rubbing particles into dispersal units. – Favorites of the Academy of Sciences. 1978 – No. 7 – 1. Series of chemical sciences, ISS. 3 – p. 5 – 10.

8. Duchin S.S., Deraygin B.V. Electrophoresis. – M.: Science, 1976. – 327 p.

9. Kondakov V. N., Korobov, M.M., Gritsuk N.G., Dotsenko, N.M. Pneumatic and hydraulic transport in the food industry. – M., 1973. – 184 p.

10. Verhey J.G.P., Lammers W.L. The Netherland of Milk Dairy Technology, 1973, v. 27, No. 2, p. 79 – 84.

Annotation

This article examines the phenomenon of electric charges while rubbing each other particles (tribo – electricity) when the flow of convection drying of skim milk. Shows the experimental installation to study this phenomenon. The results of tribo – charging particles of dry skim milk depending from the length of the path. Felt the need to study this phenomenon to develop ways to eliminate its negative impact on the process of convection drying.

Autors:

MOSCOW STATE UNIVERSITY of Food Industry, RUSSIA, Moscow.

Talalichin str. 33.

1. Dr. Ph. of Technical Sciences, Professor, Nikolay S. Nikolaev.

2. Dr. Ph. of Technical Sciences, Academic IAR, Michail Ya. Burlev.

Address: 119049 RUSSIA, Moscow, Zhitnaya str. 10 – 121.

+7 499 238 77 85 tel.

+7 495 953 64 47 fax.

e-mail: burlevm@yandex.ru