[Stoves] Side holes in TLUD reactor (was Re: Bangladesh TLUD

[Kirk H.]

Paul and All,

I have done some experiments with holes in the side of the reactor wall.  Some variables I tested were hole location, hole size, combinations of locations and sizes, and holes above and below the fuel level (though others are more knowledgeable about holes within the fuel stack).  Some results below:

Holes within the fuel level burns the char and gives turn-down to about ½  power (about 3/4 power without the holes).

Above the fuel level helps stabilize the flame and gives turn-down to about ½ power, and does not burn the char.

Just below the secondary air entrance helps stabilize the flame and gives turn-down to about 1/3 power.  I locate them low enough to be well within the full density, undiluted, still hot gas, and high enough to be close to the secondary flame and keep it ignited.  For my stove this is ¾ inch (1.5 cm.). 

Just below the secondary air entrance combined with any holes below helps stabilize the flame and gives turn-down to about ½ power.  The lower holes seem to have dominance.

For holes just below the secondary air entrance a diameter of about ¼ inch (5 to 7 mm) gives a good size pilot flame.  This size let enough air in to keep a good flame, but not enough air to dilute and cool the gas.

My rule of thumb is one hole for each inch (2.5 cm) of the diameter of the chamber at the secondary air entrance.  These placed evenly around the chamber.

If two holes are placed one above the other and relatively close together, the bottom one uses all the gas, and the top one holds no flame.

The limitation of the pilot flame technique for turn-down (1/3 power) is that the lift of the rising gasses at low power are not enough to hold up the cooler air, and the air starts falling into the reactor chamber, extinguishing the flame.  I put a plate with slits in it (I call it a canopy) over the chamber to concentrate the force of the rising gas.  The plate also holds up most of the air.  I found that the edges of this plate must be below the pilot holes to get the full turn-down to about ¼ power.  Holes below the plate reduces turn-down to ½ power.  Both the pilot flames and the plate help to stabilize the flame.

Hope this helps,

Kirk H.

Sent from Mail for Windows 10

From: Paul Anderson
Sent: Saturday, December 9, 2017 7:12 AM
To: Crispin Pemberton-Pigott; Discussion of biomass cooking stoves
Cc: Julien Winter; Mahbubul Islam - Bangladesh with Julien W; Jorund Buen - Norway - Prime stoves; Kirk Harris
Subject: [Stoves] Side holes in TLUD reactor (was Re: Bangladesh TLUD

Crispin,

Subject line changed because this topic merit further, on goind discussion (and is about holes, not about Bangladesh).

Your comments below are totally correct and raise important questions.   I focus here on the second one, about the side holes.

You point out the multitude of side holes in the Prime stoves (designed by Prof. Nurhuda and sold by Prime, led by Jorund Buen).   And that the Vest has three.  Paal Wendelbo's Peko Pe has several.  Anderson's Champion TLUD (and derivatives in Uganda by Awamu) has none.  Paul Wever's large tall TLUDs (Chip Energy, Stove-pipe stoves) have a few.   And Kirk Harris also deals with the "pilot light" topic to sustain the flame.   And we can add more to this list, even to note those that do not have any side holes. 

My few trials years ago with some holes was inconclusive, but I now think to seriosly consider them again.   

Many, 9, 3, zero is certainly a wide range.   

So, let's try to collectively become better informed about this.   So far, the "theory" (shown to work) is that a small entry of secondary air just above the slowly decending level of the top of the charcoal inside a TLUD stove, produces as small flame (usually light blue because ti is burning CO and maybe H.)

Okay, how many holes?  positions?   diameters?    And what factors (including diameter and height of the fuel chamber, fuel, ND vs FA) are to be considered.

In the end, the practical, funcitonal results are what matter.   So experiments are important to do and to be reported.

Comments, please.   [This topic could be an example of why and how the Stoves Listserv is really valuable.]

Paul   



Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com
On 12/9/2017 7:47 AM, Crispin Pemberton-Pigott wrote:
Dear Paul and Julien
 
I am responding to Paul’s comments on Julien’s earlier message.
 
On Dec 7, 2017, at 6:51 AM, Paul Anderson <psanders at ilstu.edu> wrote:
 
> 1.  The thermal mass is estracting heat, meaning cooler gases inside the chamber, with risk of insufficient temperature for ignition at the top, especially when nearing the end of pyrolysis.
 
Before anyone worries about heat going into the stove body, please perform the trivial calculation about how much heat we are talking about. Just because heat goes into a stove body does not mean a) it is significant, b) that it happens at a time that affects performance of the cooking experience, c) that it is not returned later in the session (which is cooking behaviour-dependent.) Yes, there is heat invested in the stove and usually it is a loss, but the other features of the stove may not only recover that heat through other energy paths, it may make the stove far more accessible by being cheap and easy to make from local materials.

2.  The concrete (or ceramic) inner cylinder does not have any of the side holes (24 in the metal version).  Such holes allow for some "pilot light" effect after the char level is below a hole.    
 
Dr Nurhuda’s very successful TLUD stove had such pilots sprinkled around the fuel chamber. The Vesto uses three holes only, and the purpose is to maintain pilot lights to ensure the flame never goes out. They are placed in a way that guarantees a small portion of char is burned and there is never a need to relight because of a gust of wind.
Regards
Crispin
 


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