Rotational pendulum

Other techniques that have been introduced recently in association with adsorption manometry include the use of a magnetic suspension balance (Dreisbach et al., 1996) and a rotational pendulum (Keller, 1995). 

In the first case we speak of libration, in the second of rotation. Examples of these are the oscillating pendulum and the rotating pendulum respectively (see below). 

Rotating pendulum SplitMopkinson bar test Ballistic experiments... 

Abstract The physical and experimental technique of gas adsorption measurements by slow oscillations of a rotational pendulum or, hkewise, the relaxational motion of a freely floating rotator are described. Combinations of the pendulum with either gravimetric or volumetric measurements are outhned. These especially are suited to measure the absorption or solubility of gases in non-rigid or swelling sorbent materials like polymers. Pros and cons of these methods are discussed in brief. List of symbols. References. 

MEASUREMENT OF PURE GAS ADSORPTION EQUILIBRIA (N=l) BY SLOW OSCILLATIONS OF A ROTATIONAL PENDULUM... 

Rotational pendulum for measurements of gas adsorption equilibria by observing slow damped oscillations. Height of instrument 1.5 m. More parameters of the instrument are given in Sect. 2.4. 

Figure 5.2. Experimental setup for oscillometric measurements of gas adsorption equilibria using a rotational pendulum [5.1, 5.2].

In this section we present relations between the moment of inertia (J), of the rotational pendulum and measurable parameters of its slow, damped harmonic oscillations, namely the frequency (co) and the logarithmic decrement (A). As the geometry of the pendulum normally is known, from these relations, set up for oscillations in both vacuum and in a sorptive gas atmosphere, the mass of the pendulum and hence the mass of an adsorbed phase included in it can be calculated - at least in principle. 

Scheme of a rotational pendulum of mass (mt) bearing a ring slit with radii (Rj, RJ and height (d) which can be loaded with sorbent material of mass (m ). The torsional wire of length (L,) and diameter (2r, ) has a retarding moment (Do) and internal damping coefficient (Ro). 

The equation of motion of the rotational pendulum loaded with sorbent material (m ) is [5.1,5.2] ... 

After the fading away of initial disturbances the motion of the rotational pendulum in vacuum always can be described by a simple damped harmonic oscillation. Eor initial conditions a(0) = oq, a(0) = 0, we have for the angular amplitude... 

The rotational pendulum depicted in Fig. 5.1 has been used to perform gas adsorption equilibria measurements on a variety of sorbent materials and sorptive gases. Some geometric and physical parameters of the instrument are given in Table 5.1, cp. also Fig. 5.4. 

Table 5.1. Geometrical and physical parameters of the rotational pendulum Figure S. I.

Rotational Pendulum for combined oscillometric-gravimetric sorption measurements of gases in swelling (polymeric) materials. IFT University of Siegen, 1999. 

We also would like to draw reader s attention to the possibility to combine oscillometric, gravimetric, and manometric measurements in a single experiment. The schematic diagram of such an instrument is given in Figure 5.16. It basically consists of a rotational pendulum, a microbalance (two beams as indicated in Fig. 5.16 or single beam as sketched in Fig. 5.15) and a storage vessel for the sorptive gas. This instrument would allow cosorption... 

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