"Cooling by Evaporation in a Porous Pot" by Marzan Rahman

Reading through an undergraduate research project conducted by Marzan Rahman,(a student of Dr Nadeem Malik at Queen Mary University London) entitled Cooling by evaporation in a porous pot

Here are a few points which I found interesting about this project

· Mentions evaporation is a special case of vapourisation where which only occurs at the surface of the liquid;

o However the reference given for this is a wiki page – is there any proper reference for this?

· Uses wet cloth as lid for Desert Fridge;

o HT through the upper surface (including the exposed sand) is not acconted for in the 1D model of the DF we are developing - is negligible or must we consider this later?

· Assumes the purpose of the sand layer is for insulation.

o If this is the case since we have heat transfer processes occurring in both direction (we want to draw heat out as well), so is insulation a good thing?

· Assumes it is necessary to add cold water

o Why? I guess it would help as a buffer as the water would draw heat as it increases in temperature, but would the lower temperature reduce the rate of vapourisation thus reducing the performance as well?

· Claims convection draws heat through the porous layers

o Wouldn’t the mass flow rate of water b through the porous layers be far too small for there to be any significant convection as opposed to simple conduction?

· States: “evaporated water molecule diffuse through the porous clay pot wall in inside the inner pot… the concentration of water is greater than the air molecules present inside the inner pot. So the evaporated water molecule diffuses inside the inner pot and drive away the hot air molecule.

o Not sure I understand this idea. Is it suggested that water evaporated from the outside surface somehow diffuses though to the inner chamber? Would it not all evaporate directly into the surrounding air?

o In any case how would this process” drive away the hot air molecule”?

....... to be continued...