Advanced Mass Transfer

Induced draught cooling tower?

An induced draught cooling tower uses a fan on the top of tower to pull air through

Water is sprayed from at top, trickeltes down increasing surface area

Air enters from bottom, moves upward by counter-current flow and evaportaes part of the water, then cooling the rest.

Calculations involving Induced draught cooling tower

(check sheet)

Advantages of Induced drught cooling tower

• efficient airflow control

• better temperature control

• reduced risk of recirculation

Operating line equation for air water cooling tower

-Hot water is cooled by air through evaporative cooling

-air gains mositure and enthalpy as it flows counter current to water

energy lost by water = energy gained by gas

(look at formula on sheet)

Operating line equation for air water cooling tower

Filteration Methods

-Vaccum (rotary vaccum filter)

-Pressure

-Centrifugal

Filteration Methods

Vacuum filters are applicable when the filter cake should be freely accessible. This can facilitate automatic cake handling. (vacuum filters cannot handle hot liquids • The pressure difference across vacuum filters is very limited, and the residual moisture of the filter cake is higher than with pressure filters

• Pressure filters are preferred when the product must be kept in a closed system for safety reasons, or if the residual moisture content is important. The handling of the filter cake is obviously more difficult in a pressure filter.

• Centrifugal filters: require more technical equipment, but produces yield solids with lower residual moisture

Rotary vaccum filter

• a continous filter where a rotating drum is partially submerged in slurry

• Vaccum draws liquid through a filter cloth, forming a cake, which is then wasshed and dried before discharge.

Rotary vaccum filter - Advantages and Disadvantages

Advantages:

• continous operation

• lower labour cost requirements

• more consistent output

Disadvantages

• higher capital costs

• less flexible for changing conditions

• more maintance due to moving parts

Centrifugal pressure

-pressure developed in a fluid due to rotional motion, acting outward from axis.

(revise equation on sheet)

Crystals

• most highly organised type of non-living matter that is formed by arranging its consitiuent particles (atoms, molecules and ions) in an ordelry 3D array called particles

(momorise crystal structures)

Derive equation to express filteration time at constant pressure

check sheet

Pshychometric ratio

refines ratio of sisible heat transfer to latent heat transfer per unit temperature difference.

Assumptions

• steady state operation

• no heat transfer to surroundings

• mD,Ain = mD,Aout

• negligable kinteic and potential energy

• perfect contact between water droplets and air

• Isothermal operation

derive an expression for population density of crystals produced in an MGMPR crytalisers based on inital population density.

check sheet

What percent of nuclei removed after growing 50 um

Volumetric flowrate that increases 95% of nuclei

Adiabatic Saturation temperature

Adiabatic packed bed humidifier