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Typus
KomplettPlagiat
Bearbeiter
Hindemith
Gesichtet
Yes.png
Untersuchte Arbeit:
Seite: 72, Zeilen: 1 ff. (entire page)
Quelle: Russo 2008
Seite(n): 1, 2, 9, Zeilen: 1: 18 ff.; 2: 1 ff.; 9: 1 ff.
The viscometer is called "suspended level" because the liquid initially drawn into the small upper bulb is not connected to the reservoir as it flows down the capillary during measurement. The capillary is suspended above the reservoir. In conjunction with the pressure-equalization tube, this ensures that the only pressure difference between the top of the bulb and the bottom of the capillary is that due to the hydrostatic pressure i.e., the weight of the liquid. Other designs, e.g., the Cannon-Fenske viscometer, do not provide for this, and will give erroneous results in an intrinsic viscosity determination. Such viscometers are useful in other experiments--e.g., checking the stability of some polymer solution, where one is only interested in measuring a change in the flow time.

Basic Relations for Capillary Viscometry

Here is presented the basic relation of capillary viscometry, which is known as Poiseulle's law [250].

Mrs 072a diss.png

Where:

· Q is the volumetric flow rate through the capillary in cm3/s;

· P is the pressure head forcing the liquid through the capillary (usually, just the hydrostatic pressure of the liquid itself);

· R is the radius of the capillary;

· l is the length of the capillary; and,

· η is the viscosity

The bulb volume in the Ubellohde viscometer is fixed. Thus, the flow rate, Q, is just inversely proportional to the time between marks. Since P is usually the hydrostatic pressure, which is proportional to the density of the fluid, we have:

η ∝ tρ

This simple relationship is the "ideal gas law" of capillary [sic]


[250] S.F. Sun, Physical chemistry of macromolecules: basic principles and issues, 2nd edition - Hoboken, NJ : Wiley, 2004

The viscometer is called "suspended level" because the liquid initially drawn into the small upper bulb is not connected to the reservoir as it flows down the capillary during measurement. The capillary is suspended above the reservoir. In conjunction with the pressure-equalization tube, this ensures that the only pressure difference between the top of the bulb and the bottom of the capillary is that due to the hydrostatic pressure--i.e., the weight of the liquid. Other designs, e.g., the Cannon-Fenske viscometer, do not provide for this, and will give erroneous results in an intrinsic viscosity determination. Such

[page 2]

viscometers are useful in other experiments--e.g., checking the stability of some polymer solution, where one is only interested in measuring a change in the flow time.

[page 9]

Appendix 1. Basic Relations for Capillary Viscometry

Here is presented the basic relation of capillary viscometry, which is known as Poiseulle's law. [...]

Mrs 072a source.png

where:

• Q is the volumetric flow rate through the capillary in cm3/s;

• P is the pressure head forcing the liquid through the capillary (usually, just the hydrostatic pressure of the liquid itself);

• R is the radius of the capillary;

• l is the length of the capillary; and,

• η is the viscosity

[...]

The bulb volume in the Ubellohde viscometer is fixed. Thus, the flow rate, Q, is just inversely proportional to the time between marks. Since P is usually the hydrostatic pressure, which is proportional to the density of the fluid, we have:

η ∝ tρ

This simple relationship is the "ideal gas law" of capillary viscosity (i.e., you should remember it!).

Anmerkungen

The source is not given.

The reference [250] does contain Poiseulle's law, but not the text parallels.

Sichter
(Hindemith) Singulus

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