[Stoves] Skirt design questions

[Christa Roth]

Dear Dean, I don't think anybody questions the usefulness of skirts. The real question is how to make them practical for real users in real households out there who have dozens of different shapes and sizes of cooking pots, buckets and frying pans with and without handles and who want to use them all on ONE stove, because they have only space and resources to afford just that ONE stove. So if that one improved stove is not as convenient as the three stones they are using, they will keep on using the three stones because they can use them conveniently with any size and shape of pot....
The challenge is to get from theory to practice without compromising too much on the efficiency. In other words: how wrong can you afford to have the gap and still get enough improvement on the heat transfer efficiency to justify the investment into a skirt at all....
Let's discuss this further in Bangalore

Christa Roth
Technical Advisor Malawi - Tanzania - Zambia
Programme for Biomass Energy Conservation in Southern Africa

in Zambia: 
c/o GTZ office, Private Bag RW37x, Plot No. 6469 Kariba Road, Kalundu, Lusaka
Tel +260 1 2919 -18 / 19 / 20, Fax +260 1 291 946
 
in Malawi:
c/o Info Centre for Food&Fuel Security Promotion Mulanje 
P.O. Box 438, Mulanje, Malawi, Phone +265-1-466 279, Fax -466 435

Mobile Phones (only available when I am in the respective country):
Zambia +260 97 207 870, Malawi +265 8 860 936, Tanzania +255 787 20 10 15
  ----- Original Message ----- 
  From: Dean Still 
  To: 'Discussion of biomass cooking stoves' 
  Sent: Thursday, February 22, 2007 6:14 PM
  Subject: Re: [Stoves] Skirt design questions


  Dear All,

  Skirts might be very helpful because by getting the gap right between the
  skirt and the pot three good things could happen, I think:

  Increased velocity (better heat transfer to pot)
  Control over excess air entering the combustion chamber (Higher Delta T plus
  fewer emissions?)
  Increased surface area of pot exposed to flue gases

  Getting increased velocity by decreasing constant cross sectional area,
  higher temperatures due to less excess air entering the fire, improving the
  heat exchanger (the pot), by using one short cylinder of sheet metal
  definitely is interesting! We are trying .75 constant cross sectional area
  now for the gap size. Then rate of burn goes down (less air) but time to
  boil, fuel use, and emissions are decreased by about a third compared to the
  same stove without a skirt.

  Best,

  Dean