Solar Drier Prototype

Fraser and I have just completed our Vesta powered food drier Mark I. In the past two weeks we have built an additional Vesta and we have done a considerable amount of tinsmithing, the results of which can be seen here:

The whole contraption pivots around the central post of the Vesta, which is more or less of the same design as the previous model. The drier sits atop a chassis which is joined to the central post by a hinged boom made of heavy angle iron. The two bicycle wheels are angled such that their axles point directly at the post.

Those bicycle wheels. At first we looked in the hardware stores for new wheels, but all the hard rubber wheels of the diameter that we wanted were built for huge loads and were more expensive than need be. Fraser quite rightly said that we could find a child's bike for cheap and have a smoother ride. I added 'small child's bike' to the list of things to keep my eyes open for as we ran our various errands.

Soon thereafter we came across a second hand store, the likes of which you'll see every few blocks in most lower income residential neighbourhoods here in Puerto Penasco. On the sidewalk (or what may pass for a sidewalk) in front of someone's house, there are racks of clothing, toys, kitchenware, exercise machines and a wide variety of bits and bobs. It's essentially a permanent garage sale. Neighbours get rid of their unwanted stuff conveniently and she who sells stuff waits for another neighbour to need the object in question.

In the slew of stuff for sale I spied a bike of the size we were looking for. In the right condition too. Not too old, but old enough to be cheap. We pull up, get out and I ask the woman how much for the bike.
"Oh, no, I couldn't sell it, it belongs to my son." she says.
Toying with the idea that this could be a gringo upsell tactic I reply "Really? That's a shame we've been looking all over for one that size... it's just right."
She considers. "Well, let's ask him. MANUEL!!" she calls out to the house. A little boy comes cruising out of the courtyard on a bigger, nicer bike with the chain rusted and hanging loose. "Want to sell your little bike?"
"No!" he shouts, dismounts his bigger bike, runs to the smaller one and zooms off. His mother and I look at eachother and smile. "How does 100 pesos sound?" An eyebrow raises. Too high. "About right" she replies.

Manuel comes zooming back and his mother tells him this bike is too small for him anyway and that with the money he can fix the chain on his big bike. "And have enough left over for candy" I chip in.
"500 pesos!" he exclaims, his eyes big, licking his lips. We laugh. His mom tells me to hand him the money (100 pesos!) and he immediately runs off to show his friends. Later that day I did this to his bike:

I'm working on a more thorough montage for the construction of this latest Vesta as well as some of the construction of the drier.

Over the course of this latest building phase we've vacillated between thinking of ourselves as very clever and utter fools. We're quite happy with the result so far but there is still doubt as to whether or not it will work as it did when grandad built it in his head. I'm of the opinion that it won't, and will need forced air to work properly. Grandad is coming around to this perspective in his way.

http://solardevicesforthirdworld.webs.com/

It has been cloudy for the past few days and so we've been working on a back up plan. Our idea of using steel screen as a heat exchanger at the focal point took Fraser's fancy and he thought that the same principle could be applied to the more conventional solar drier which looks something like this ----------------->

So we've built a test collector roughly the same shape as the glass portion of the collector to the right, only 1 foot deep with 14 layers of steel screen to absorb the sunlight.
While I am sure that it will perform better than a flat black sheet metal collector, I think that it is overkill. The central idea being porosity means more surface area which means more contact with air which means more effective transfer of heat. No doubt it will work better, but expense and difficulty of construction have drained my enthusiasm. Nevertheless, out curiosity is piqued and we will construct two other collectors of the same size: one of the flat black sheet metal and another, somewhere on the spectrum between sheet metal and screen.

I think that, while interesting, the experiments will come to nothing much of value because in my experience and research I've found that passive drying does not provide the level of control, heat or airflow that a more 'active' drier does and so cannot produce the same quality of product. We shall see.