Prince Charming
True or False?
Negative rate of diffusion means transfer from low to high concentration
FALSE. Diffusing in the opposite direction NOT diffusing opposing concentration
Differentiate Flooding and Channeling
Flooding - condition where the liquid cannot flow down and being blown out with the gas (concerned with column height)
Channeling - tendency of liquid to select preferred paths for its flow down the packing
True or False
I can have a psychrometric chart with varying pressures
FALSE.
You can have psychrometric chart each at different pressures but not one for varying pressures.
True or False.
The constant rate period is mostly dependent on the free moisture.
FALSE. Free moisture is comprised of bounded and unbounded moisture. Since bounded mositure are found deep into a solid, it is relatively harder to release the water to air, meaning a slower / non-constant period.
Differentiate Adsorption and Absorption
Adsorption - surface
Absorption - surface and inner, affected by porosity
Jₐₓ (kgmol/m2-s) is the more generalize term for mass transfer and Nₐ (kgmol/s) is specified for a specific area of transfer.
Why is it not ideal to operate at a minimum liquid flow rate?
Too many stages, larger column
Why do we observe fog, mist etc. when dry and wet bulb temperature are equal?
Since they are equal, water vapor starts to form liquid water. However due to equal temperature, these liquid form does not immediately "pour" rather be stable in the air.
Why does drying have an initial dip as the operation starts?
A warming-up period is necessary to start the mass transfer to proceed
Why is a high solubility of a carrier solvent not preferred for adsorption?
It will be carried mostly by the solvent and less or no mass transfer occur in the solid.
It is the ratio of fluid boundary layer to mass transfer boundary layer thickness
Schmidt (u/DAB*rho) - fluid / mass transfer boundary
Sherwood (k*L/D) - convective / diffusive
Lewis (a/DAB) - thermal / mass diffusivity
Prandtl - (u/a*rho or u*Cp/k) - momentum to thermal diffusivity
Why is there a lower pressure drop in packed columns than plate columns?
Packed columns have movable or flowing packings unlike in trays where they are connected or welded into the column
What is a psychrometric ratio?
A dimensionaless ratio of convective heat transfer to the product of convective mass transfer coefficient and humid heat (h/kC)
It relates the difference between the absolute and saturation humidity to the difference between dry bulb and adiabatic saturation temperature.
True or False.
Drying kinetics of a material is dependent on particle size
TRUE. Particle size correlates to the surface area or drying surface. It is correlated in terms of porosity.
Why are isotherms used when correlating data?
Isotherms are correlations used to fit data into a single line for better usage in adsorption applications. It is noted however that these isotherms are not fixed to specific mixtures but are rough estimates to correlate data.
How is diffusivity (DAB) affected by the decrease in diameter across the column
Diffusivity is NOT affected by diameter, only by temperature, pressure, and nature of components.
Explain why gas absorption has an operating line above equilibrium line and vice verse for desorption
Gas absorption = gas to liquid
From the bottom, gas transfers to equilibrium (down) decreasing concentration
Desorption
From bottom, gas transfers to equilibrium (up) increasing concentration
How does liquid/gas ratio affect the cooling tower design?
It determines the amount of gas and liquid travelling into the column which corresponds to temperature, saturation; affecting the design.
Explain how does (a) crystallization and (b) shrinkage occur in drying
(a) Crystallization due to loss of water turning soluble components into crystals (not solution form)
(b) Shrinkage of porous substances occur when drying occurs rapidly where the material wasn't abke to withstand large and continuous mass transfer
True or False.
In a binary mixture of less soluble and inert stream, a surface can utilize chemisorption and physisorption if the surface is only used for chemisorption purposes
FALSE. Since it is a binary mixture, the soluble component will be adsorbed by the surface. Highlighting selectivity and purpose of the chemisorption process, only chemisorption will apply.
The initial and final general equation for diffusion plus convection for flux is sent to your viber. Explain to me how is it correlated to diffusion and convection (how each term represents them) and how do they relate to a speed of an observer hacve to move for (a) stationary component and (b) net mass flux equal to zero.
First term = diffusion or Jaz
Second term = convection or as a whole
a) Stationary
for one to be stationary, calculate using unicomponent diffusion where Na = ca*va to get velocity.
b) Net mass flux = Na = ca*va = Jaz + c*vm
for it to have a net mass flux = 0, then the observer must move the total net mass flux then calculate va
Differentiate NTU and HTU
Number of transfer unit is a measure of difficulty of separation
Height of transfer unit is a measure of separation effectiveness for a packing
NTU = how many times for equilibrium conditions
HTU = how long to reach equilibrium conditions
Why can't a range in a cooling tower reach the approach?
Why is co-current drying used for heat sensitive materials?
It prevents overheating by placing the hottest gas in contact with the wettest material.
Explain why hysterisis occurs.
Hysterisis occurs when there is a lag to return to its original state. In terms of adsorption, as the pressure decreases, not all of the particles dettach at a rate similar to their attach rate. This may be due to IMF (van der wals) forces between particles and not just the surface of the adsorbing material