How it Works - Biolite

So to answer the question of how it works, I'm posting this diagram I pulled from Biolite's web site.  Essentially it generates electricity using a thermoelectric generator (TEG).    TEG convert heat energy into electrical energy.  TEGs are made from thermoelectric modules which are solid-state integrated circuits that employ three established thermoelectric effects known as the Peltier, Seebeck and Thomson effects. It is the Seebeck effect that is responsible for electrical power generation. Their construction consists of pairs of p-type and n-type semiconductor materials forming a thermocouple. These thermocouples are then connected electrically forming an array of multiple thermocouples (thermopile). They are then sandwiched between two thin ceramic wafers.

Thermoelectric generators have been in use for many years by NASA to power spacecraft and the oil and gas industry to power remote monitoring stations around the globe.

So for you engineers (By Jeffrey Snyder);

A thermoelectric produces electrical power from heat flow across a temperature gradient.    As the heat flows from hot to cold, free charge carriers (electrons or holes) in the material are also driven to the cold end.  The resulting voltage (V) is proportional  to the temperature difference (∆T) via the Seebeck coefficient,  α, (V =  α∆T).

A thermoelectric generator converts heat (Q) into electrical power (P) with efficiency η.  

 P = ηQ  (1)

The amount of heat,  Q, that can be directed though the thermoelectric materials frequently depends on the size of the heat exchangers used to harvest the heat on the hot side and reject it on the cold side. As the heat exchangers are typically much larger than the thermoelectric generators themselves, when size is a constraint (or high P/V is desired) the design for maximum power P = ηQ Small Thermoelectric Generators may take precedence over maximum efficiency. In this case the temperature difference (and therefore thermoelectric efficiency as described below) may be only half that between the heat source and sink.   The efficiency of a thermoelectric converter depends heavily on the temperature difference  ∆T =  Th –  Tc across the device. This is because the thermoelectric generator, like all heat engines, cannot have an efficiency greater than that of a Carnot cycle (∆T/Th). The efficiency of a thermoelectric generator is typically defined as

(2)

Where the first term is the Carnot efficiency and ZT is the figure of merit for the device. While the calculation of a thermoelectric generator. Many thermoelectric couples (top) of n-type and p-type thermoelectric semiconductors are connected electrically in series and thermally in parallel to make a thermoelectric generator. The flow of heat drives the free electrons (e-) and holes (h+) producing electrical power from heat.

While the calculation of η thermoelectric generator efficiency can be complex, use of the average

material figure of merit, zT, can provide an approximation for ZT.

(3)

Here, Seebeck coefficient (α), electrical resistivity (ρ), and thermal conductivity (κ) are temperature (T) dependent materials properties.    Recently, the field of thermoelectric materials is rapidly growing with the

discovery of complex, high-efficiency materials. A diverse array of new approaches, from complexity within

the unit cell to nanostructured bulk, nanowire and thin film materials, have all lead to high efficiency materials.

Biolite Camp Stove

So my Biolite camp stove arrived yesterday.   After some experimentation I can say that bark definitely not a good idea unless you like smoke.   Pinecones are a close second on the list of what not to use.   Twigs, branches, kindling worked the best.   Fire took about 30 seconds to get going before I could start cooking.   I boiled a pot of water in about 3 minutes.   So next, tried scrambled eggs.    Easy to use, just turned down the fan to low - nice even heat.

Biolite Stove

So I found this camp stove from Biolite in a recent Popular Science magazine.   I tracked down the web site and investigated for my self.     The stove weighs in at just over 2lbs.   Not bad for backpacking.   My Whisperlite and white gas easily hit that mark when full.   The nice thing about this is that it fully nests and is roughly the size of a water bottle when nested.    It burns only wood - they claim it can boil water in 5 minutes.   And it is capable of charging at 2W your electronic devices.   All for $129.00.    It is so new, however, that orders are being filled on a first come first serve basis.

  

Here is a little video demonstrating how it works from the company.

The following video is one from a customer that posted this on youtube.    This one shows how to assemble and start it.

Patrol Box - Chapter 4

The sides, back, and top have been had the tongue & grooves cut into them and now for the initial dry fit before final glue up.   Once the glue has set.  The boxes are workable in 2 hours, but I generally wait 24 hours before doing anything substantial.

Here are a couple of the assembled boxes waiting for final sanding and finishing before the lids and shelving are installed.
 

Patrol Box - Chapter 3

The drawings don't account for the thickness of the surfaced wood as I didn't know how much material I'd have to remove before I drew up the design or how structurally stable the material would be in setting the depth of my joints.   Depending on the piece I was cutting, I made them a little longer to account for this difference between the original drawing and the finished cedar boards.  

Adrian cutting the tongue and grooves on the router table for each piece.

As can be seen from the photograph, the boards still retain quite a bit of the character the weathering left behind.   These surface cracks do not run through the wood nor will they cause any structural concerns for the finished project.

This photograph shows one of the assembled sides.   Gorilla glue was used instead of traditional wood glue primarily because this box will be used outside.   Gorilla glue is a water activated polyvinyl acetate that once cures, cannot be solubilized by water.  The patrol box is a great application for this glue.

Patrol Box - Chapter 2

The first step was collecting old cedar fencing from a local fencing company.   The weathering of the fencing results in about 20% loss of wood.    The first step is to remove the sections of the fencing that are clearly splitting or have been nailed.   This is to prevent damage to the planner blades.

This is a photograph of what the fencing looked like before processing.   My son, working on his carpentry merit badge, helped cull the fence boards, remove the nails, and plane and grade each piece of wood.

The boards required four passes, two on each side, through the planner.   Each pass removed about 1/64" of material.   The surfaced boards were then edge ripped on the table saw to square them up before the project of building the boxes could begin.   In all, we processed 400 fence boards and created five bags of cedar shavings that we used in our garden.

The finished boards above staged for the next part of the project - cutting the pieces for the boxes.

Patrol Box - Chapter 1

The troop has a large equipment box that has had a tendency to become more chaotic after each camp out.   It is equipped with everything a troop needs on a camp out and then some.    The real problem is having several patrols each needing the same equipment.  Hence the start of the patrol box project.     I researched many different designs on the internet and felt that before choosing one I should list out criteria a good box would have.

1. Needs to be small and light enough for two young scouts to handle = meaning it needs to be about 75% of the size of the troop box.
2. Organizable - equipment must be easy to find and easy to maintain in the box.
3. Durable - the patrol box must be able to survive repeated use by scouts (although not as a chair).
4. Storable - it has to fit into the limited storage space the troop maintains.
5. Functional - the box needs to be more than just a container.

Using these criteria I drew up the following design for a patrol box.