BioMEMS 2

(a) Calculate the Reynolds number, N_R, for glycerin at 25^oC with the diameter of the pipe is 150 mm, moving with the velocity at 3.8 m/s, and the density, ρ, is 1258 kg/m³ and the dynamic viscosity, η, is 0.96 kg/ms.

What is the behavior of Re (NR) of a fluid flow below a threshold value?

Which of these statements are true?

• An interface is a smooth surface separating two materials.

• The balance of relative forces at an interface leads to surface tension

• The interfaces are ideally smooth and the molecules from these materials show good separation at the interface.

• In reality, the interfaces are not smooth, molecules from these materials mingle at an interface.

Which of this tells us about the Van der Waals forces?

• It arises from electrostatic interaction of ions or of ionic groups.

• It is an electrostatic attraction between polar groups of the molecule.

• The attraction and repulsion forces which arises between atoms and molecules.

• The forces resulted from covalent bonding in molecules.

E is usually presents the:

• The total surface area of an interface.

• Total energy stored in the interface.

• Effective surface area of a molecule

• The characteristic dimension of a molecule.

What is the unit for surface tension?

What are the effects can contribute to capillary action?

• Minimization of surface energy.

• Pressure difference due to curvature of interface.

• Specific force of the movement of liquid through thin tubes.

• Maximization of surface energy.

If the liquid is water, solids with a contact angle more than 90^o are:

Which of these describe capillary rise?

• It is a balance of surface energy and gravitational potential energy.

• Best describe by Jurin's Law.

• For a contact angle less than 90^o, the liquid will rise in the tube.

• For a contact angle less than 90^o, the liquid will fall in the tube

The maximum height of a liquid in a capillary tube is inversely proportional to the tube's diameter. (True or False?)