The resulting film has a thickness determined by the viscosity and the surface tension of the coating liquid, as well as the pulling velocity. We measured the thickness of films resulting from dip coating in different velocities and for different viscosities, in the range of
10–250 μm
.
How is liquid film thickness calculated?
t = m/Ad
, where m is the mass, A the area and d the density of the film material as Dmitry Zaitsev suggests. Be careful, this formula is not accurate as d changes.
What is the significance of film thickness in mass transfer?
depth of penetration of solute
in liquid element3. the thickness of stagnant film that offers the same resistance to mass transfer as is actualy being offered under given hydrodynamic conditions.
What is the assumption of the film theory?
In this section, the theoretical models to quantitatively describe the mass transfer across such an interface will be presented. This theory is well known as film model. The key assumption is
that the whole resistance to the diffusional mass transfer is entirely residing in the fluids themselves.
Who developed the film theory in mass transfer?
Developed by
Lewis-Whitman
(1924). Assuming that • There are two stagnant layers of film at the interface. The mass transfer across the films is by molecular diffusion. The bulks of gas and liquid are homogeneous with respect to solute.
What instrument measures thickness?
A vernier caliper
is a high-precision measurement tool that can be used in multiple types of measurements. It can measure thickness, diameter and even inside diameter for pipes.
How is film thickness measured?
The thickness of a single-layer film can be measured easily using
a spectrophotometer
. Note, however, that this is possible only for film thickness in a range of approximately 0.3 to 60 μm, and that the refractive index of the film material is required for measurement.
How do you calculate thickness?
We obtain the thickness of the solid
by dividing its volume by its length and its width
; that is, we divide 24 cm
3
by 4 cm and 3 cm. In this example, the thickness of the solid is 2 cm.
How do you find the thickness of a cylinder?
- Solution:
- Total surface area of hollow cylinder = 4620 sq.cm.
- Height (h) = 7cm.
- Let the inner radius of the hollow cylinder is ‘r’ cm and outer radius is ‘R’ cm ‘ then.
- Thickness of the cylinder = (R – r)cm.
- Area of base ring = 115 sq.cm.
- Total surface area of hollow cylinder = 4620 sq.cm.
How does ellipsometry work?
Ellipsometry
measures a change in polarization as light reflects or transmits from a material structure
. The polarization change is represented as an amplitude ratio, Ψ, and the phase difference, Δ. The measured response depends on optical properties and thickness of individual materials.
What is the two-film theory?
The standard two-film theory (STFT) is
a diffusion-based mechanism that can be used to describe gas mass transfer across liquid film
. Fundamental assumptions of the STFT impose serious limitations on its ability to predict mass transfer coefficients.
What are the assumptions followed in two-film theory?
Assumptions of two-film theory: Steady-state: concentrations at any position in the tower do not change with time.
Interface between the gas phase and the liquid phase is a sharp boundary
.
What are the theories of mass transfer?
- 2.1. Two-film theory. …
- 2.2. Penetration theory. …
- 2.3. Surface renewal theory.
What is convective mass transfer?
Convective mass transfer is
the movement of material by the action of a fluid
. … Mass transfer – such as drying, evaporation or dissolution. Heat transfer – heat and mass transfer processes are analogous, and a mass transfer model may be more convenient to use.
How does viscosity affect mass transfer?
High solvent viscosity can leads
to slow diffusion of gas
through the gas- liquid interface (indirect effect) and modify the local hydrodynamics by generating a more stabilized liquid film on the packing surface (direct effect). As a result, mass transfer between phases can be significantly reduced.
What is y * in mass transfer?
yA* is
the concentration (mole fraction) in vapor phase that is in equilibrium with xAL
. Driving force for mass transfer: ( yAG – yA* ) in the gas phase (as indicated by line PC) and ( xA* – xAL ) in the liquid phase (line PD). See the Figure below. NOTE : for most situations the asterisk ‘*’ is not shown.
