Methods of measurements

1. The objects of rheological studies

2. Classification of methods of measurement of rheological characteristics

The objects of rheological research in food industry covers a wide range of aggregate States of materials, ranging from solids to low-viscosity liquids. This, as well as the diversity of rheological research requires exceptional diversity of devices, such as the operating principle and design features.

Methods of physical-chemical mechanics are increasingly used in various fields of food production. Determination of structural-mechanical properties (SMS) food masses connected with the necessity of constant technological monitoring of production. Significant deviations SMS from the accepted norms can affect not only the decline in the quality of finished products, but also on the performance of equipment under the separate technological processes. Therefore, the main task of rheology is the definition of properties variation occurring under the influence of certain factors.

Measurement methods SMS are very numerous, because on the one hand, a huge variety of real fluids and disperse systems, and on the other hand, a wide range of practical conditions of their flow.

By mean of the measured value rheological methods are divided into four groups (table 2.1). This classification is to a certain extent conditional, because some devices allow you to vary the two values at constant third.

The first two methods are most widely spread, especially in viscosimetry. The first method is the method of constant shear rate is usually implemented through the application of Electromechanical or hydraulic drive. The strength of the resistance of a medium is measured by the various dynamometers.

The second method - the method of constant load or structurally much easier, as the speed of movement or rotation measuring body easily measured with an ordinary stopwatch or write on the ribbon diagram.

Table 2.1. Classification of methods of measurement of rheological characteristics

The third method of measuring the constant force of loading due to the constant weight of the mobile device. Time of measurement typically remain 180 to 300 C) and is taken slightly longer than the period of relaxation. On instruments of the measure the depth of the material indenter special form at a decreasing rate, which in the limit reaches zero.

The fourth method allows square diagram obtained in the coordinates of «force - displacement», to determine the strain energy and the ordinate the chart shows the effort. In addition, in the devices of this group energy can be calculated based on the power if the device is equipped with a recording or showing the wattmeter or counter.

Classification STAMP of Volarovich rheological research methods and instruments can be divided into integrated, enabling to determine the net effect of current, and on the differential, allowing direct observation of the deformation of time at each point of a disperse system it.

Differential methods allow to watch the changing field of stresses and strains in time when investigating complex cases flow of structured systems. This observation can be done visually, as well as using fluoroscopy, microcinema etc. Differential methods provide only a qualitative description of the investigated phenomenon. For example, in the study of flow of a viscoplastic material in the gap between the two cylinders BTW, Volarovich with the staff before the test inflicted on the surface of the material aluminium powder. Under deformation (when rotating inner cylinder) on the surface of the material clearly delineated two zones: zone of plastic flow; b) the elastic state (figure 2.1).

Integral methods allow to watch the cumulative effect of the flow. Depending on the conditions of the study using model analysis of each individual case determine the number of independent mechanical properties of the studied systems necessary for the solution of the task. The most sophisticated the methods capillary and rotational viscosity, the introduction of a cone, longitudinal displacement of the plate, and ball viscometer.

List of literature

1. Machikhin Waerloga food products : a manual / Y.A Machikhin, J.K. Berman ; Yu. A. Machikhin, Yu. K. Berman. - M : MGUPP. - 1999, P.1. - 250 C. Instances: total:10 - XP1(1), B2(2), A1(7)

2. Slash EAST of Engineering rheology biotechnology environments : a manual for students of higher educational institutions on "Technology of raw materials and products of animal origin / C. D. Slash, Ya. I. Vinogradov, A. D. Malyshev. - SPb. : Giord, 2005. - 648 S. : Il. Instances: total:10 - items(1), HR(1), B2(1), C(1), A1(2), A4(4)

Lecture 11.

Date: 2015-12-24; view: 885