chemia - Studia

ANDRA TĂMAŞ, MARTIN VINCZE
From the analysis of rheological equations can be observed the
non-Newtonian behavior with yield point τ
0
, similar to the yield-pseudoplastic
fluids, with flow exponent n < 1. Also, for the samples with τ ≠ 0
0 , it is observed
that the temperature increasing leads to the increase of the shear stress
values, with preservation of non-Newtonian behavior.
A particular situation presents PA 2.5-8 sample to t= 39.5°C, to which
is noticed the shape curve change with the shear rate increasing. For the
−1
presumptive inflection point corresponding to γ& = 215.7 s and τ =19.5 Pa the
apparent viscosity is obtained η = τ & γ = 0. 09Pa
⋅ s and, taking into account
a
the geometrical dimensions of S/S 1 system, the calculated Ta
Re
value is
0.75 (laminar domain being for Ta
Re
≤ 60 ) [3].
In Figures 2 and 3 is shown the τ = f (γ&
) dependence for PC 1 and
PC 5 solutions at different temperature values, and in Table 5 are the obtained
rheological equations.
1% B + 99% sol.1
25
20
Shear stress, Pa
15
10
5
0
0 100 200 300 400 500 600 700 800
Shear rate, s -1
t=25C t=32C t=39.5C
Figure 2. Dependence τ = f (γ&
) for sample PC 1
5% B + 95% sol.1
80
70
60
Shear stress, Pa
50
40
30
20
10
0
0 100 200 300 400 500
Shear rate, s -1
t=25C t=32C t=39.5C
Figure 3. Dependence τ = (γ ) for sample PC 5
f
&
250