Pure methanol at 20^0C is contained between two parallel plates separated by a g

Question

Pure methanol at 20^0C is contained between two parallel plates separated by a gap of 0.1cm. Give a value and units (use SI units) for the shear stress required to maintain the upper plate moving at a constant velocity of 20 cm/sec.b) Give a value and units for the shear rate.c) If the system is cooled to 10*C, do you expect the required shear stress to increase, decrease or remain the same? Why? In the above problem, suppose you do an experiment where you measure the shear stress needed to maintain the plate at 20 cm/sec at 20#C, then you cool the system to 10#C and make the measurement again. You discover that the required shear stress did not change the way you expected it to. List at least five possible reasons for the discrepancy.

Explanation / Answer

The units for shear stess is force per unit area or can be represented as F/ L2

In SI units it is N/m2

Now, in the given problem Force F = ma = 1 * 20 /100 = 0.2 N/m2

And the shear rate is 20 cm/sec *0.1 cm = 2cm2/sec

The shear stress will increase by decreasing its temperature to 10 C as the properties of the fluid like viscosity changes at 10 C when compared to 20 C.

That is the value of viscosity increases, thus the value of shear stress increases

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.