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Follow on Google News |  A Significant Breakthrough In Viscosity Measurement Of Non-Newtonian FluidsA&D Company, Limited has recently advanced their own technology for their tuning fork vibro viscometer by adding the capability of quickly changing the shear rate and expanding its scope of applications, now including rheology testing.
The tuning fork vibro method, which A&D commercialized about 20 years ago, has since helped thousands of researchers who had once struggled to obtain consistent results in measurements of low viscosities. With conventional viscometers, it was difficult to perform stable, precise measurement when the sample viscosity fell to 100 mPa.s or lower. Yet the tuning fork vibro viscometer, whose sensitivity was heightened through sharp resonance phenomena, could even detect viscosities below the level of water (as low as 0.3 mPa.s) – with unparalleled speed, ease and precision. Tuning fork vibro method To briefly explain the mechanism of the tuning fork vibro method, two thin sensor plates in a tuning fork arrangement are vibrated with electromagnetic force at their natural (resonant) frequency of 30 Hz within the sample fluid. Viscosity is then calculated based on the proportional relationship between the viscous resistance of the sample fluid and the amount of electric current required to drive and maintain the sensor plates at a constant vibration amplitude. Today, this method is recognized as a Japanese industrial standard for viscosity measurement of liquids (JIS Z8803). The tuning fork vibro viscometer is also accredited as a standard device for the Japan Calibration Service System (JCSS) along with capillary and rotational viscometers. Limitation and renovation While the tuning fork vibro viscometer provided a number of hitherto-unachievable advantages and greatly broadened the range of possible research applications, it had its limitations. Notably, since the sensor plates always vibrated at the same frequency with the same amplitude, the user was unable to manipulate the shear rate these sensors produced. It was therefore not possible to evaluate the behaviors of non-Newtonian fluids such as paints and creams in response to varying shear rates. To overcome this weakness, A&D developed a tuning fork vibro viscometer whose sensor plate amplitude is made variable to eight levels (between 0.07 and 1.2mm peak-to-peak) With this new capability, the tuning fork vibro method is now a great alternative for viscosity measurement of non-Newtonian fluids, providing various unique benefits. Here are some examples: Distinctive strengths Easy setup and very quick measurement Compared with conventional methods, it takes much less time for the user to set the sample fluid, start measurement, and obtain the viscosity value (the RV-10000 requires only 20 seconds to stabilize). Moreover, since the sensor plates have a very small thermal capacity, they cause minimal temperature change to the sample fluid upon immersion, realizing fast and stable viscosity measurement. It is also very easy to clean the sensor after measurement – all that needs to be done is wipe off the sample residue with alcohol. Simultaneous measurements of temperature and viscosity A temperature sensor (0 to 160°C range) is located between the two viscosity sensor plates, enabling accurate measurement of viscosity’s dependence on temperature. Further, by using the accessory water jacket with a commercially- Wide dynamic range of measurement The RV-10000 has a viscosity detection system that singly measures from very low to high viscosity in quick succession (max. 0.3 to 25,000 mPa.s), which makes the instrument highly versatile and able to cover measurement of various types of fluids by itself. It also allows continuous measurements of viscosity variation over time and/or temperature changes at differing shear rates. Unrivalled sensitivity and precision The high sensitivity of the RV-10000 even allows such uses as finding the cloud point of surfactants and controlling the drinking sensation of beverages. In addition, the RV-10000 achieves repeatability as high as 1% of the measured value (by standard deviation) for the entire measurement range, providing the user with consistent results and allowing reliable comparison of those results. Little interference to the sample fluid The low-frequency, low-amplitude vibration causes only minute displacement in the sample fluid and hence keeps changes to its temperature and physical structure to a minimum. This enables highly stable measurements of viscosity variations over a long period of time. It also enables the measurement of fluids such as foams (e.g. whipped cream) without breaking their tiny air bubbles or dispersion systems (e.g. colloids) while they are settling (dispersion can alternatively be maintained using a microstirrer) Measurements of fluids in motion The two sensor plates vibrate in opposite directions, meaning that even if the sample fluid is flowing or being stirred during measurements, the errors of each sensor plate are cancelled out by those of the other. It is therefore possible, for example, to measure the viscosity of a flowing fluid in a production line and maintain data compatibility between the laboratory and the field. Easy calibration by the user Both one-point and two point calibrations are possible using either viscosity standard liquids or fluids of known viscosities. With the RV-10000, there is no need to spend time and money having the instrument calibrated by an outside specialist. For a viscosity range around 1 mPa.s, a highly useful, “simplified calibration function” is available. The user only has to prepare purified water and perform a simple one-key operation, and the RV-10000 will automatically calibrate itself using stored information on the viscosity of purified water at each temperature. Windows Communication Tools Software “WinCT-Viscosity” Finally, the RV-10000 comes with the dedicated software WinCT-Viscosity. It includes the graphing program RsVisco, which receives the viscosity and temperature data from the RV-10000 and creates a graph on a PC in real time. Such a graph visualizes viscosity that varies with time and/or temperature at different shear rates, and thereby makes it easy to monitor the cure processes of polymers, adhesive or proteins, measure viscosity variations of lubricants or engine oils due to temperature changes, etc. Additional details, technical reports and application examples can be found on the A&D website at http://www.aandd.jp/ End
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