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Heat transfer due to conduction
- to slow down the heat transfer rate from the feed side to the permeate side, a thicker membrane should be used

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- scaling will occur due to salt water over time
- heating of the cold permeate: when temp at the permeate increases, the driving force is affected -> Δpi will be smaller, hence lower flux is obtained. This is known as temperature polarisation

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Ensures separation of liquid particles

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from the formula,
a change in partial pressure of the component can be caused by a change in mole fraction ( removal or addition of gas ) and a change in total pressure

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Desalination in countries with geothermal energy

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Desalination in countries with geothermal energy

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Desalination in high solar radiation countiries

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Desalination in high solar radiation countiries

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To separate liquid water from water vapour

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To separate liquid water from water vapour

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This is to allow water vapour to condense on a cooler surface in order to recover the desalinated water

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Uses pumping systems to create pressure for osmosis to occur through membranes

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Uses heat to separate vapor from liquid water which is then put through a membrane to separate the aqueous solution

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Flux force relationship
vapor flux = membrane based parameter * pressure difference between warm feed and cold permeate

- the higher the difference in pressure between the feed and permeate sides -> the greater the flux rate will be

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Avoid constriction of pores from which block vapors from permeating

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The membrane in the distillation process acts as a vapour gap that allows vapour to pass through.

Hydrophobic and porous membrane

hydrophobic membrane will not let water pass through as if it does the air gap will become flooded with water affecting the pathway of the vapour.

porous membrane - will ensure vapour to pass through the membrane to the cooler side.

How is selectivity achieved ?
The volatility of the vapour, the vapour with a higher volatility will be able to pass through the membrane first hence by collecting the more volatile vapour first then collecting what comes next selectivity can be achieved.  ( volatility calculated with vapour pressure, Antoine equation, higher vapour pressure more Volatile)

In some cases only one parameter will be passing through such as salt water, where salt will not be able to evaporate into vapour but water will hence only water vapour will be passing through.

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Higher temperature, higher average energy of particles --> more particles have sufficient energy to escape from the surface of liquid --> increases saturated vapor pressure

Higher temperature = higher vapor pressure

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Water vapour: Liquid

Vapour pressure increases exponentially when temperature increases

Vapour pressure difference --> driving force
Vapour molecules will transport through the pores of the membrane from the high vapour pressure side to the low vapour pressure side

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partial pressure of gas is pressure exerted by each type of gas in a gas mixture.
The formula can be expressed in components of partial pressure or the moles of the component.
Pi = Xi * P  ---------- 1
Xi = Pi/P = ni/n      -------- 2

Where:

xi = mole fraction of any individual gas component in a gas mixture

pi = partial pressure of any individual gas component in a gas mixture

ni = moles of any individual gas component in a gas mixture

n = total moles of the gas mixture

p = total pressure of the gas mixture

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- A separation process where a micro-porous hydrophobic membrane separates two aqueous solutions at different temp