Absorption and Adsorption

Question 1

What is absorption

Answer 1

The process in which a fluid is dissolved by a liquid or a solid (absorbent)

Question 2

What is adsorption

Answer 2

The process in which atoms/molecules (it could be gas, liquid or dissolved solid) adhere to a surface of the adsorbent

Question 3

Describe each process

Answer 3

Absorption - involves the entire volume of the absorbing substance

Adsorption - surface-based process where a film of adsorbate is created on the surface

Question 4

What are 2 common working pairs for absorption

Answer 4

water/lithium bromide

ammonia/water

Question 5

What are 3 common working pairs for adsorption

Answer 5

zeolite/water
silica gel/water
activated carbon/ammonia

Question 6

What do liquid absorption machines offer

Answer 6

Higher COPs

Question 7

Issues with liquid absorption machines

Answer 7

crystilisation of the sorbent, corrosion, efficiency losses from circulation pumps

Question 8

solid adsorption machines - what’s good?

Answer 8

lower thermodynamic efficiency but can be driven by lower temperatures (waste heat for example)
not affected by motion

Question 9

isometric

Answer 9

same number of atoms

Question 10

Describe stage 1 of the adsorption cycle

Answer 10

Adsorbent is heated pressure rises from evap to cond pressure

Question 11

Describe stage 2 of the adsorption cycle

Answer 11

adsorbent continues to heat, refrigerant condenses in vessel 2

Question 12

Describe stage 3 of the adsorption cycle

Answer 12

Adsorbent cooled, pressure decreases from cond to evap pressure

Question 13

Describe stage 4 of the adsorption cycle

Answer 13

Adsorbent continues to be cooled and starts adsorbing the refrigerant whilst it evaporates in the evaporator

Question 14

What is the adsorption cooling energy equation

Answer 14

(xconc - xdilute) x ( hg evaporation - hf condensing)

aka
xconc - xdilute) x ( bottom left when its a gas - top right when its a liquid