Request for solar still
We are currently running a training, undertaking last minute preparations for a WASH Cluster training course for WASH in emergencies for field workers working in the emergency in Somalia. We are trying to make the course very practical and would like to include a solar still in the practicals but despite trying we haven’t been able to find on the web any dimensions of a still. Would there be any chance that someone could assist us (quickly – i.e. by Monday) to let us know the dimensions of a unit. In particular we are looking for the following dimensions: a) Optimal water depth within the unit b) Optimal distance between bottom of the unit and the sloping glass roof c) Optimal width of glass
My experience is limited - one coral atoll in the Indian ocean but here are a few thoughts. My guess is that much will depend on: • the salinity of the water • the latitude • what is available locally. My memory is that you do not want the water to become too saline otherwise the water does not evaporate so easily, but on the other hand too much water being added cools everything down - I suspect that there is a lot of discussion somewhere between batch and continuous processes....
As a starting point I would tilt the glass to the same as the latitude so that the midday sun went straight through - but increase this if the water drops did not run down to the pane. Optimal distance - instinct would be to keep this small consistent with being able to drain the water off the glass
Width of glass? Not sure if this is thickness or panel size - my guess would be to use the largest and thickest available easily - largest to be efficient, thickest to have some chance that accidents did not happen (i.e. window rather than picture glass) http://www.epsea.org/stills.html gives some pictures at least to scale off.
Why not tell your training course participants that they could buy ready made "WaterCone" solar stills off-the-shelf? see http://www.watercone.com/product.html I haven't used one myself yet, but they look lightweight, portable, and ideal for use in emergencies if you have a large number of batteries to be topped up with distilled water. Drinking distilled water, as you know, is not the best option as it is lacking essential minerals found in surface or groundwater, and can have an adverse effect on the body (something to do with osmosis).
VITA have plans on the internet for building a simple solar still, see http://www.cd3wd.com/cd3wd_40/VITA/SOLRSTL2/EN/SOLRSTL2.HTM Bilal A. Akash, Mousa S. Mohsen and Waleed Nayfeh Renewable Energy Research Centre, Department of Mechanical and Industrial Engineering, Applied Science University, Amman 11931, Jordan This paper presents experimental results obtained using the basin type solar still. The experiments were conducted in Jordan using a solar still with various cover tilt angles of 15, 25, 35, 45 and 55°.
An optimum tilt angle for water production was found to be 35° during the month of May. Salt was added to study the effect of the salinity of water on solar distillation. Distilled water production decreased with salinity. The effect of water depth was also studied. The results show that water production decreased in a somewhat linear relationship with increasing water depth in the still. Maybe you could try getting hold of a copy of that article? See also the Journal Desalination ISSN 0011-9164 1993, vol. 94, no1, pp. 55-68 (11 ref.) "Optimum conditions for a solar still and its use for a greenhouse using the nutrient film technique"
At the following website is a design for a DIY solar still about 1m by 1m in size http://www3.telus.net/farallon/#The_first_model
About 2 or 3 feet in diameter is adequate for a small quantity of water for batteries for a solar power system or for a single family if they really have no other, better, source of water (see for example http://www.scribd.com/doc/2956738/solar-still it's not a reader-friendly site though!)
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