Instruments falling ball

Another method to determine viscosity uses the falling-ball viscometer. Determine viscosity by noting the time it takes for a ball to fall through the distance between two marks on a tube filled with the unknown liquid (the tube is generally in a constant-temperature bath). Use balls of different weights to measure a wide range of viscosities. Calculate the viscosity by using manufacturer-supplied constants for the ball used. These instruments can be quite precise for Newtonian liquids, that is, liquids that do not have viscosities that vary with flow (more correctly, shear) rate. 

Texture analyzers are also used to assess deformability of a fluid, using penetration force vs. depth profiles, etc. These instruments in addition to Brookfield and Haake viscometers are common QC metrics. Other methods include viscosity flow cups and bubble or falling ball viscometers, and several relevant standard test methods include ASTM D1200, DIN/ISO 2431, ASTM D5125, BS3900 Part A6, ASTM D1545, and ASTM D1725. 

In this instrument a liquid is caused to rotate in an outer cylinder, and it causes a torque to be applied to the torsion wire attached to the inner cylinder. The. viscosity is calculated from the torque, the apparatus being calibrated. Another device for measuring viscosity is the falling-ball viscometer (Figure 11.16e). The viscosity is calculated from the time reciuired for the ball to fall from one position to another. 

There are generally two approaches to the measurement of viscosity namely, controlled stress and controlled strain. In controlled stress, a known stress is applied to the fluid and the resultant shear rate is measured. Conversely, in controlled strain a known strain, or more accurately rate of strain (shear rate) is applied and the stress is measured. A falling ball viscometer is a controlled stress viscometer in which the applied stress comes from the size of the ball and gravity whereas the Brookfield viscometer is an example of a controlled strain instrument where the rate of strain is related to the rotational speed applied. 

The unsuitable nature of many commercial instruments which are in common use clearly illustrates the confusion prevalent in the field of viscometric measurements. Many instruments measure some combination of properties which depend only partly on the fluid consistency since the flow is not laminar. In others the shear rates are indeterminate and the data cannot be interpreted completely. Examples of such units include rotational viscometers with inserted baffles, as in the modified Stormer instruments in which the fluid flows through an orifice, as in the Saybolt or Engler viscometers instruments in which a ball, disk, or cylinder falls through the fluid, as in the Gardiner mobilometer. Recently even the use of a vibrating reed has been claimed to be useful for measurement of non-Newtonian viscosities (M14, W10), although theoretical studies (R6, W10) show that true physical properties are obviously not obtainable in these instruments for such fluids. These various instru-... 

The falling sphere instrument is representative of this class of viscometer and is employed with higher viscosity liquids. A stainless steel ball is allowed to sink through a column of the liquid under test, and the time taken to fall from one designated level to another at its terminal falling velocity is recorded. In order that the terminal... 

A pendulum may be used (Charpy, Izod, tensile impact) to determine the work of fracture (Brown, 1999). Instrumented devices provided with piezoelectric transducers are also available load-time or load-displacement curves can be recorded (Merle et al., 1985), giving as much information as static tests. Servohydraulic or pneumatic setups and falling weight devices are also used. The drop ball test from the US Food and Drug Administration, is especially useful for optical lenses (acrylate networks). 

Many impact tests measure the energy required to break a standard sample under certain specified conditions. The most widely used tests are the lzod test (pendulum-type instrument with notched sample, which is struck on the free end), the Charpy test (pendulum-type instrument with sample supported at the two ends and struck in the middle), the falling-weight test (standard ball dropped from known height), and the high-speed stress-strain test. 

To make a viscosity determination the instrument is rotated about 180 so that the ball falls to the top of the instrument. The instrument is then rotated rapidly back against the stop. When the metal ball reaches the bottom of the tube it makes electrical contact with... 

Answer In the event of a serious power. Instrumental, or operator failure, the safety system must act rapidly to shut down the reactor. Examples are the free-falling vertical rods, the 3-X balls, and the hydraulic accumulators. Another exaople Is that failure of a vacinim tube In a Beckman will cause that Beckman to give a trip signal. 

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