SU894474A1 - Device for determination of newtonian fluid viscosity - Google Patents

Description

(54). METHOD FOR DETERMINING THE VISCOSITY OF NEWTONIAN LIQUID

This invention relates to a technique for continuously measuring the viscosity of Newtonian fluids.

A known method for determining the viscosity of a liquid at a given temperature as sugals of measured values, one of which is proportional to the uncorrected monitored parameter, and the other to the deviation of the temperature of the liquid from the given one. In this case, the proportionality coefficient is adjusted in the latter so that, irrespective of the temperature value, the stability of the specified sum 1 is ensured.

There is also known a method for determining the viscosity of a fluid in a stream by measuring moments when it is formed simultaneously in two rotational viscometers with inversely proportional velocities. The torque values found are used to calculate viscosity 2.

Closest to the proposed method for determining the viscosity of the fluid flow, which consists in passing the fluid at a POST-5-S velocity through a thermally insulated vessel, measuring and sequentially comparing the temperatures of the flow Hii inlet and outlet

vessel. The viscosity of the fluid is judged by the magnitude of the mismatch between the measured temperatures, using the known flow properties and the operating parameters of the vessel 3.

The disadvantage of this method is the dependence of the result of measuring viscosity on the magnitude of measuring the temperature of a liquid as it passes through a measuring vessel, which is especially important for highly viscous polymer melts, in which the viscosity depends very significantly on temperature.

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The purpose of the invention is to improve the accuracy of measuring the viscosity of liquids in a stream, especially highly viscous melts of WWII and polymer solutions.

The goal is achieved by the fact that the measured temperature difference between the flow at the inlet and outlet of the heat-insulated vessel is compared with its specified value, subjected to

Claims (3)

 mechanically deforming the flow of fluid in the vessel, changing the rate of deformation of the fluid when the measured temperature difference deviates from the desired value, maintain a constant specified temperature difference, and measure the strain rate at which the fluid viscosity is judged. The temperature difference between the flow at the inlet and outlet of the thermally insulated LT vessel due to the dissipation of the deformation energy in the fluid flowing through the vessel with the volumetric rate over a period of time (tj-t) in the absence of heat dissipation, finding and comparing the heat balance tj J u) M dt C, 9 (tj-t,) (1) where W, m is the speed and moment of deformation, respectively; p, c is the density and heat capacity of the liquid being measured. Since the moment and speed of deformation in the general case are not time functions, after converting the numerator and reducing the common factor in the right side of equation (1), we get) n (.IS loJ / CpV Expressing the moment M through the components of the well-known formula for viscosity of a Newtonian fluid in a rotary device and K-I and (x: after appropriate substitution in equation (2)) we obtain the equation of the GETs from which it follows that in order to preserve the constant temperature differential as the main thermal condition and in the measuring vessel, the strain rate should be adjusted inversely with the viscosity to a power of 0.5. After replacing the factors in the equation of the equation (4) with one K 4.19-10x / .U, solving this equation for viscosity, we find the CAT ) i.e. at the constant heat flux of the liquid entering the measuring vessel and the temperature gradient measured at the inlet and outlet of the vessel, the viscosity is a function of the only variable, the strain rate. The higher accuracy of measuring the viscosity of a fluid is achieved by eliminating the effect of temperature change on the measurement result. In this case, when the temperature changes constant, the strain rate changes, which, as is known, does not affect the result of measuring the viscosity of a new fluid. laminar flow areas. Example 1. A polyester molten melt is PET (c. 0.488 kcal / kg-deg r, 11.8 g / cm 3), which is a Newtonian liquid with a motor speed of less than 500 with a temperature passed through a vessel with bulk velocity and temperature-controlled 0.02 l / s, in the vessel there is a deforming organ of the stirrer, the rotation frequency of which can be changed from 20 to 80 o.b / min. The previously found value of the constructive constant K ,. included in the formula (5) is equal to 2.75 hu. Gradually increasing the frequency of rotation of the stirrer, the flow temperature at the outlet was adjusted to 286 ° C. The rotational speed of the stirrer is 62 rpm. The melt viscosity calculated by equation (b) for the above conditions is 286 Pa-s, which corresponds to the viscosity of the same melt, found in terms of the characteristic viscosity index of the solution of this polyester in orthochlorophenol, Pr and Mp 2 To control the viscosity of the polyester PET melt, depending on the conditions of its preparation, the melt is passed through a thermostated measuring vessel operating under the same conditions as those indicated in the previous example. The temperature at the outlet of the vessel is set at 284, bs. By gradually increasing the frequency of rotation of the stirrer, the melt temperature at the outlet is increased to a previously set value equal to. The rotational speed of the stirrer is 77 rpm. The viscosity calculated by equation (5) in this case is 186 Pa. S, which corresponds to the viscosity of the same polyester melt, found through the characteristic viscosity index. A scale similarly calibrated to an instrument measuring the frequency of rotation of the mixer, in the full range of possible values of viscosity (for this example being 186–286 Pa-s), allows monitoring the viscosity with a higher accuracy the resulting product. The preferred area of application of the method of measuring viscosity in a stream is Newtonian liquids with a viscosity of 100 Pa-e (1000 P) and more, such as, for example, melts and polymer solutions, latexes; If necessary, the proposed method can be applied to measure the viscosity of liquids of hundreds of poises. In this case, it is necessary to increase the frequency of rotation of the formation of an org-ana or use a special design of it that does not dissolve the high shear rates of the test fluid in the laminar flow region. The use of the proposed method of viscosity measurement, invariant to temperature measurement conditions, provides more accurate and reliable control of the viscosity of the liquid under study, in particular, in systems of automated control of technological processes for the production of synthetic fibers and provides savings in this industry. The invention The method for determining the viscosity of a Newtonian fluid in a stream, consisting in passing a fluid at a constant speed through a thermally insulated vessel, weighing and then comparing the flow temperatures at the inlet and outlet of this vessel, characterized in that in order to improve the measurement accuracy , the measured temperature difference between the flow at the inlet and outlet of the vessel is compared with its predetermined value, the fluid flow in the vessel is subjected to mechanical deformation, the deformation rate of the liquid is changed when the deviation is measured second temperature difference from the set, said temperature difference is maintained constant and measured rate of deformation, which is judged by the viscosity of the fluid. Sources of Figures taken into account during the examination I. USSR Copyright Certificate 285333, cl. G 01 N 11/00, 1969. 2. USSR author's certificate 321721, cl. G. 01 N 11/00, 1970. 3. US patent 3,930,399 cl. G 01 N I / 00, 1978 (prototype).