DE3237130A1 - Bellows- and -capillary viscometer - Google Patents

Abstract

In commercial falling-sphere or capillary viscometers, the spheres have to be raised again, for example by tipping the apparatus or the measuring substance has to be sucked up in the capillary viscometer in order to repeat the measurement, it being necessary for a phase boundary (usually a liqid/gas boundary) to be present. Automatic operation and replacement of the substance within the measurement series (for instance to observe viscosity changes in a production plant) are not possible or are only possible with considerable effort. In the apparatus claimed, a thin-walled bellows is electromagnetically compressed and old substance is expelled. "Fresh substance" is then drawn in from the outside via a capillary during the free expansion of the bellows. Regardless of pressure and temperature, the bellows position determines the pressure difference across the capillary and the bellows movement determines the flow velocity. The viscosity is given by the signals obtained from a distance transducer. The small space requirement makes possible automatic measurements in high-pressure plants and flowing media, and also parallel operation of a plurality of measuring inserts.

Description

Bellows capillary viscometer

The invention relates to a method and a device because of their simple structure, their easy controllability and their low volume requirements Among other things for measurements in closed systems, in high and maximum pressure Ap repairs and can be used in flowing media.

Problem: To measure the viscosity of liquids there there are different viscometer designs, which are generally classified into groups a) Falling ball or falling body viscometer b) Capillary viscometer c) Rotation viscometer and d) vibration viscometers can be subdivided.

The various measuring methods can be briefly characterized as follows With the falling ball viscometers, a ball (Pallkorper) runs in one against the Horizontal inclined calibrated tube coming down, and used as a measure of viscosity the time it takes the ball to travel a distance between two Measurement marks required.

In the case of a capillary viscometer, the is in a U-shape in one leg Capillary inserted, and it is in the same or in the other leg, the keg substance sucked up or pushed up. Under the pressure of the supernatant column of liquid the measured substance is pressed through the capillary. As a measure of the viscosity is the time it takes for a given volume of substance to pass through the capillary needed.

A rotary viscometer consists of two coaxial cylinders, one of which rotates with a fixed number of revolutions. On the second cylinder Then, depending on the viscosity of the substance to be measured, a torque acts that is measured will.

In the case of a Schtingllns viscometer, the periodically moved Measuring body according to the viscosity of the medium to be given a damping of the Exercise exercised. The attenuation is measured.

The types (a) and (b) used - i.e. eye drop and capillary viscometers - require the ball to be returned to the upper one in order to repeat the measurement Starting position (at a) or the renewed generation of the driving pressure difference sucking up or pushing up the substance in one leg of the viscometer.

Type (c) - the rotary viscometer is free of these conditions, however, this type of device is due to its relatively large cross-section - especially in the Compared to that of a capillary viscometer - for the precise measurement of small Vis Kosan not suitable. The main field of application of the Fotaticns viscometer is therefore in the determination of the flow behavior depending on the shear gradient, i.e. in the detection of deviations from Newtonian behavior. With types (a) and (b) Newtonian behavior is assumed.

With device type (d) - vibration viscometer - there is no stationary one Flow of the liquid. It also loads inertial forces into the measurement a. Furthermore, the boundary conditions are difficult to grasp, so this type so far has not found much application.

Particular difficulties arise with all types of viscometers, when measurements at high pressures, measurements in flowing media or continuous, fully automatic Measurements and registration of the results are required.

For this and other applications the task arises, a device to develop, e.g. for installation in systems or in high and ultra-high pressure equipment including the control of the viscometer only requires a small amount of space in which the yessubstance as possible without great precautions, i.e.

can be exchanged almost during operation the has a good reproducibility of the measurements with a simple structure, and its Results can easily be registered and evaluated.

The principle of the bellows capillary iscometer.

A characteristic feature of the claimed bellows capillary viscometer is that the pressure differential required to create a viscous flow no longer due to the difference in height of the substance to be measured in cor.munizieriden tubes but is generated by compressing a bellows.

This has the following advantages: 1) The compression of the bellows is - in contrast to sucking up the substance to be measured in the simplest way by actuation a small built-in electric lifting magnet, 2) the driving force The force does not depend - as is the case with conventional capillary viscometers - at a fixed height difference dr columns of liquid depend on the density of the substance to be measured, which changes with the pressure and the temperature changes. It is only determined by the spring constant of the bellows, which is almost independent of pressure and temperature.

3) The interface that is present in conventional capillary viscometers Measuring liquid / air, the measurements at high pressures because of the solubility of the gas would be severely fouled in the liquid is omitted.

A second characteristic feature of the bellows eapillar viscometer claimed consists in the fact that the passage of the meniscus through two marks is no longer optical for the time determination is observed but the movement of the bellows base the flow of the liquid through a capillary electrically via an inductive one Displacement transducer is displayed.

This has the following advantages: 1) When installing the measuring insert only electrical feed-throughs are not used in systems or high-pressure equipment but windows and optical equipment needed.

2) The use of the inductive displacement transducer enables monitoring of the entire measuring process. The time for running through can be about two "sarks" a certain way .

distance can be measured and recorded in the usual way.

3) In the case of uncomfortably long measuring times, you can "park" without making any changes at the measuring insert and thus freely measurable without assembly and thus the to measuring time can be adapted to the respective temperature and pressure conditions.

This is of particular advantage because, for example, when measuring viscosity on oils the measuring times with the print (with fixed marks) by 7 powers of ten and can change more.

A third characteristic feature of our viscometer lies in that the force required to generate the pressure difference, which is of the Lifting electromagnets have to be applied by transmitting pressure via a piston with a suitable cross-section the lifting force of the electromagnet ar. can be fitted.

The lifting magnet does not act directly on the bottom of the bellows, which is to be pressed or stretched together, rather is in the head flange of the Bellows a calibrated tube is used in which a piston guided by a magnet runs.

This is particularly important when the device is designed as a high pressure viscometer useful, since for technical reasons the diameter of high pressure equipment are very limited (e.g. 20 mm) and now through the piston transmission the generation a certain pressure difference at the bellows required force under the corresponding Yerlangerung the piston path can be reduced.

The details are given using the exemplary embodiment of an ultrahigh-pressure viscometer explained below.

The dimensioning of a high pressure viscometer as an example The mode of operation and the dimensions can be seen from Fig.1.

When the reversing solenoid A is switched on, clutch B , which allows small lateral shifts, and the pierced piston rod C the piston D with the inserted capillary E in the calibrated tube F downwards emotional.

Since, due to the current level of the current, there is little substance over the Capillary E and the piston rod C provided with longitudinal and transverse bores H flows outside, an overpressure builds up in the bellows B compared to the outside space. The bellows G is stretched as a result.

After piston D has reached the lower end position, the same applies the pressure difference is slowly reduced again by removing food from the interior of the bellows flows into the outer space L via the capillary.

The bellows accordingly slowly pulls itself onto the original one Length together, the movement of the bottom of the bellows through the inductive Displacement transducer 1 is displayed on a measuring bridge outside the system.

The time course of the bellows expansion is through given, whereby the initial elongation is taken into account by the dead weight mg. C is the spring constant of the bellows.

The following then applies to the viscosity where r is the radius of the capillary, L is the length of the capillary, A is the effective cross section of the bellows and t is the time.

Two adjustable marks on the zero instrument are used to measure the time the measuring bridge an electronic clock on or. canceled and thus the runtime between two selectable waypoints s1 and s2 measured and printed out.

However, other forms of registration can also be used, depending on the application use the bellows movement.

E.g. by interrupting a beam of light between two Optical fibers in the passage of an ark, as shown in Fig.1a. In another embodiment, the movement of the bellows base is achieved by immersion of a core between the plates of a capacitor via the change in capacitance registered as shown in hub.1 b.

To repeat the measuring process, the reversing magnet is turned in the opposite direction Direction operated i.e. the piston D with the capillary E is pulled upwards. After reaching the upper end position of the piston, substance flows off kiss Outside L into the bellows G, and it can be measured in an analogous manner as with the "downward gear". The measurement can therefore take place in both directions of movement.

The spiral spring K is used to set the zero position, and can also used to exert an additional force to that of the bellows.

All parts are mounted in a jacket tube M, with which at the same time the Keß insert on the closure of a high pressure autoclave for, for example, 10 kbar can be attached. This means that it is easy to assemble, even when in use guaranteed in high pressure autoclaves. Blank page

Claims (5)

Claims. Method and device for measuring the viscosity of liquids characterized in that the pressure difference required to generate a viscous flow is created by tensioning a thin-walled bellows. 2. Method and device for measuring liquid-riding viscosities characterized in that the comiression or dilation of the bellows is direct or effected with an inserted cylinder with piston by an electromagnet will. 3. Method and device for measuring liquid viscosities characterized in that the elongation (elongation) of the bellows for measuring the Pressure difference on the capillary is used. 4. Method and device for viscosity measurement, characterized in that that the movement of the bellows a) with an inductive displacement transducer, or b) through the interruption of a light beam or c) by the change in capacitance of a Capacitor added when passing through a handlebar fastened at the bottom of the Ealges and is used to measure the flow time of the substance through the capillary. 5. The method and apparatus according to claim 1 to 4, characterized in that the signals triggered by the baig movement are also used for Continuous measurements, switching the electromagnet, printing out the measuring time and to automatically reset the electronic watch between two measurements.