Wire torque

The apparatus is shown in Fig. 4.1. The body of the extraction vessel is made from Pyrex. Separation is effected by absorption of a batch containing both phases into a porous 2 cm diameter nickel-chrome alloy disc (A), the upper surface of which is domed. The disc is mounted on the end of a stainless-steel shaft (B) turned by a geared high-torque electric motor. The disc-shaft-motor assembly can he transported along its axis of rotation to any of three stations. The assembly is shown at its bottom station, with the porous disc within the inner vessel (C), around which is a collar (D) forming the first annular pocket (E). The collar itself forms the inner wall of the second annular pocket (F), the outer wall of which extends upwards to support a Perspex Hd (G) on which the rotor (H) is situated. The inner vessel and both annular pockets are fitted with drain valves. A stiff piece of platinum wire is passed through the Hd into the glassware as far as the level of the first annular pocket. 

On the other hand, to generate a torque T in a wire, the axial load at the center of the spring should be... 

Fig. F.7. Stiffness of a helical spring, (a) A fictitious position with a zero pitch, (b) When the pitch h of a spring increases, the twisting angle of the wire increases. The torque also increases. Using the formula for torsion, the stiffness of a helical spring is obtained.

Few details of the apparatus are given in ISO 4663, it is simply stated that means shall be provided to measure frequency to 1% ( 5% in a transition region), amplitude to 1% and, for method C, the supplied energy to 2%. It is suggested that a moment of inertia of about 0.03 gm is suitable for the inertia member which may be a disc or rod. For methods B and C the torsion wire should be of such dimensions that its restoring torque is not more than 25% of the total restoring torque due to the test piece and suspension. BS 903 (equivalent to method B of ISO 4663) suggests that moments of inertia between 50 and 500 g cm are suitable and states that the tensile strain on the test piece should be between 0 and 5%. The British... 

The wire comes to rest at an angle 6 when the magnetic torque and elastic torque balance (see Fig. 13b). 

If, instead of a straight wire segment, a current-carrying loop is placed in the magnetic field, a torque (turning force) is exerted on the loop. The torque, t, is given by ... 

A pressurized direct-drive concentric cylinder viscometer system (Figure 3-21) was used to obtain shear rate versus shear stress data on a tomato puree at several fixed temperatures between 76 and 120°C (Figure 3-22), and temperature versus apparent viscosity data at several shear rates on a 4% waxy rice (WR) starch dispersion during gelatinization over the temperature range 30 to 110°C (Figure 3-23) (Rao et al., 1998). The drive motor, torque unit, and concentric cylinder unit and temperature control vessel of a Haake RV2 viscometer system (Haake Inc.) were placed in a chamber (PRC) that could be pressurized to 0.2 MPa (two atmospheres). The temperature control vessel was insulated to minimize heat loss. A eopper-constantan (36 gage wires) thermocouple plaeed in the well of the inner eoneentric eylinder measured the temperature of the test sample. 

In a plate-plate geometry, the top of the sample is attached to a rigid frame of moment of inertia I, which in turn is supported by a thin wire. A torque M = Mq Qxp(imt) is applied to the rigid frame. Determine the relaxation moduli of the sample. 

Note that the expression for G is similar to that of Eq. (P7.2.4) if the torque of the wire is negligible in comparison with that of the sample and the torque is nil. 

Dense-phase flow properties can be predicted by measuring the viscosity and deaeration rate of a fluidized bed in a laboratory test (117). This method appears to be especially useful for evaluating the flow characteristics in standpipes. The viscosity is measured by means of a Brookfield viscometer, which consists of a cylindrical wire-screen spindle rotated about its axis by an electric motor through a torsion spring. The torque required to rotate the spindle is measured by displacement of the... 

Parts of these problems are circumvented by using the classical knife-edge surface viscometer developed by Brown et al, 1958 ) and variations of it as the double knife-edge surface viscometer and the blunt knife-edge viscometer. For each of these it is crucial that the knife just touches the monolayer, but does not break it. Therefore the knife-edge has to be non-wetting. However, placing the knife precisely in the surface remains a cumbersome manipulation. Theoretical expressions for the torque upon the torsion wire have been derived for the various types. 

The vision of braking and steering by wire will demand new, extremely reliable sensors. Even in early implementations of steer-by-wire systems, in which manual control can override any system failure, more than one sensor is normally used for the sake of redundancy. Many of the sensor principles required are already established in the market, including steering-angle sensors (e.g., for vehicle dynamics control) and pedal-position sensors. Mechanical action or feedback control, however, will drive the emergence of torque and force sensors. 

FIGURE 10.33 Principles of interfacial rheological measurements, (a) In shear. A thin disc (D) is at an O-W interface and is made to rotate (or oscillate) the torque on the disc can be measured, e.g., via a torsion wire (T). (b) In expansion/compression. Barriers (B) at an O-W interface are moved, thereby increasing or decreasing the interfacial area between them the interfacial tension is measured by means of a Wilhelmy plate (P). Both kinds of measurement can also be made at A-W and A-O surfaces. 

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. 

In such a device a motor-driven cylindrical cup is rotated at a constant speed. The fluid being tested is in the thin, annular region between the cup and the bob. The shear stress generated by the fluid on the wall of the bob tends to turn the bob, but this turning motion is resisted tiy the torsion wire which supports the bob. The bob takes up a position wherejthe torque exerted by the torsion wire is equal and opposite to the torque supplied by the fluid shear on its surface from its position, as indicated by a pointer and scale and the calibration of the torsion wire, one can readily compute the shear stress at the wall. 

Stirrer speed - the minimum speed used is usually that which keeps the wire clean and does not allow a fibre mat to form. Higher speeds can be used when endeavouring to match the retention achieved on a particular paper machine (on the original Britt Jars stirrer torque can also be varied). 

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