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Post by satamax on Jul 20, 2015 3:47:53 GMT -8
Fucking bang on! Do you view any similarities to the ram horns?  This one is making it to the library in a sec! |
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Post by peterberg on Jul 20, 2015 6:04:50 GMT -8
But i think the back of the port has to be flat on 3 or 5 cm each side. To actualy start the swirls by means of friction, since on the two flat sides, it's a complete stall of the gases. What's happening in there exactly is friction against the sides of the port, according to Larry Winiarski who, by the way, graduated on pulse jet technology. The flames are bending in there around the sharp corner of the leading edge, slowing down velocity at the sides caused by friction against the boundary layer while in the middle the speed is still very high. At the very end of the port there are other sharp corners and lots of space, so the stream left and right is slowed down while in the middle it speds on. That is the very moment the vortexes are formed. Perhaps you are pointing to the same thing, are you? By rounding the corners of the leading edges, the stagnant layers left and right are getting smaller, effctively making a better shape aerodynamically speaking. The good people at Dragon Heaters did exactly that some years ago and the thing smoked like mad. This might be caused by the fact that the vortexes weren't forming. Of course, at the time I didn't get it. In short, when you are doing away with the sharp corners of the port you probably need to make the port narrower in order to keep the friction high enough. We know for some years now that the vortexes can't be formed without an adequate chimney draw. Edit: In the first couple of seconds of that last video the ram's horns are taking shape. With a wall in front of the venturi and an exhaust opening at the top you're looking at what makes the batch box tick. Knowing how to make it is nice, understanding how it works is much better.  |
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Post by josephcrawley on Jul 20, 2015 6:58:57 GMT -8
Max thanks for the response. Since I enjoy my tea in the morning I can't imagine doind anything that would slow the speed of boiling water like putting a brick between the fire and the cooktop. I appreciate burn efficiency but I balance it against cooking efficiency. So you think the air slots should be on the top corner of the secondary intake away from the fire? I'm really looking for something that works well but doesn't have to be near perfect.
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Post by peterberg on Jul 20, 2015 7:25:01 GMT -8
So you think the air slots should be on the top corner of the secondary intake away from the fire? Yes, that's right. That's the spot where the pressure is lowest. |
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Post by satamax on Jul 20, 2015 11:03:39 GMT -8
But i think the back of the port has to be flat on 3 or 5 cm each side. To actualy start the swirls by means of friction, since on the two flat sides, it's a complete stall of the gases. What's happening in there exactly is friction against the sides of the port, according to Larry Winiarski who, by the way, graduated on pulse jet technology. The flames are bending in there around the sharp corner of the leading edge, slowing down velocity at the sides caused by friction against the boundary layer while in the middle the speed is still very high. At the very end of the port there are other sharp corners and lots of space, so the stream left and right is slowed down while in the middle it speds on. That is the very moment the vortexes are formed. Perhaps you are pointing to the same thing, are you? By rounding the corners of the leading edges, the stagnant layers left and right are getting smaller, effctively making a better shape aerodynamically speaking. The good people at Dragon Heaters did exactly that some years ago and the thing smoked like mad. This might be caused by the fact that the vortexes weren't forming. Of course, at the time I didn't get it. In short, when you are doing away with the sharp corners of the port you probably need to make the port narrower in order to keep the friction high enough. We know for some years now that the vortexes can't be formed without an adequate chimney draw. Edit: In the first couple of seconds of that last video the ram's horns are taking shape. With a wall in front of the venturi and an exhaust opening at the top you're looking at what makes the batch box tick. Knowing how to make it is nice, understanding how it works is much better. Peter, ok, in that video, i think i can see, where the leading edge of the orifice (not a venturi yet!) is pushing the flow away from the orifice's walls. So that might be necessary to create the vortexes. I was pointing at what is happening at the trailing edge of the orifice plate, i've known that since i was a kid. But never paid real attention to what was happening on the leading edge. The sharp bend created by the front of the orifice plate pushes the fluid perpendicular to the flow, that's why there's the two airfoil type shapes starting at the leading edge of the port. So may be a venturi, or even airfoil leading edge is no good. Well, back to cooking rockets. Have you tried big diameter, short heat risers? I'm under the impression that it could be done. up to three or four times the system CSA might be possible. What we're doing is a flame confinement chamber. Where we try to get the flame to be as hot as possible, with enough time and turbulence to mix and burn all the volatiles. The three T's. Remember when i arived here, comming from experiments with cyclone dust exctractors. I said i thought a cyclone cone, with tangential intake could make a good heat riser. You said there would be too much drag. And what about a cone wit a radial intake, like a normal batch heat riser with a port? This could be a way to reduce the height of the heat riser, and still retain it's top velocity. Well, plenty of food for thoughts! I wonder what Cindy and Sandy used as a heat riser? Round or else? Joseph, i think if your flame was insulated, that would just move the hot spot to a point further from the port, that's all. |
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Post by peterberg on Jul 20, 2015 11:44:46 GMT -8
Never tried a big diameter, short heat riser. But this could be done I suppose. In the usual system size heat risers the hottest spot is shifting up when the burn is at its peak and comes down again when the burn is working to its end. When the riser is too short that point could leave the riser which could explain why this configuration experienced overfuelling. Might be that with a wider riser the hot spot is not shifting up that much so a shorter riser could be used. Very interesting!
A riser built as a cone, narrowest part down, would very interesting too. Need to invertigate those possibilities some time. During coming winter I need to reserve some time to build small-scale batch boxes.
Sandy and Cindy used a round cast riser by the way. Nothing unusual with that. They used a computer model to optimize the shape of the combustion chamber, geared to greater velocity. In theory, this velocity could result in better mixing but it didn't.
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Post by satamax on Jul 20, 2015 12:19:40 GMT -8
Well, the cone, i saw it the other way around. Which could also act as a fine ash separator |
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Post by josephcrawley on Aug 1, 2015 15:24:42 GMT -8
www.flickr.com/gp/45224908@N03/k3u1D5Here are the latest changes I've made. The firebox floor os now a grate with primary air entering through the ash pan door. The center of the grate is box tubing which the secondary air passes through. It burns better but isn't smoke free. I think a lpt of my problems are due to poor draft since the stove is outdoors. The stack is about 16 feet.tall but the draft is very poor. I may enclose the stove with temporary cardboard walls just to see if that affects the draft.
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Post by josephcrawley on Aug 5, 2015 16:15:53 GMT -8
I made cardboard "walls" on three side of the stove and the difference in draw was significant. It gave me hope for the stove. Does anyone think I would better with long slot running the length of the secondary air intake instead of the perpendicular slots I now have. Thanks
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Post by Daryl on Aug 6, 2015 5:33:28 GMT -8
I haven't been online much but I wish you the best of luck Josephcrawley !
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Post by alanloy on Aug 16, 2015 14:38:04 GMT -8
I have noticed that most cookstoves have the oven in the traditional below bench height position. This causes issues of fitting in combustion chambers etc. because heat rises.
Why not reconfigure the stove so that the oven is above bench height (as seen in wall ovens). This would allow a flow of heat horizontally from the cook top to the oven (or visa versa) and then out the flue. More space for the combustion process as well.
This might look strange to some (particularly in the middle of a room) but against a wall it should look acceptable.
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Post by satamax on Aug 16, 2015 21:37:33 GMT -8
I have noticed that most cookstoves have the oven in the traditional below bench height position. This causes issues of fitting in combustion chambers etc. because heat rises. Why not reconfigure the stove so that the oven is above bench height (as seen in wall ovens). This would allow a flow of heat horizontally from the cook top to the oven (or visa versa) and then out the flue. More space for the combustion process as well. This might look strange to some (particularly in the middle of a room) but against a wall it should look acceptable. It's been done if i remember well. I will be heading that way. A brick oven, wide enough to accomodate the heat riser and the grids side by side. |
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Post by esbjornaneer on Jan 15, 2016 6:26:49 GMT -8
I made cardboard "walls" on three side of the stove and the difference in draw was significant. It gave me hope for the stove. Does anyone think I would better with long slot running the length of the secondary air intake instead of the perpendicular slots I now have. Thanks How did you get on? Is the build completed? I am contemplating an outdoor range/cook stove with oven for the hot time of year and wouls love to hear what worked and what you would do differently if you were going again. All the best, Esbjorn |
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Post by josephcrawley on Jan 15, 2016 11:11:16 GMT -8
donkey32.proboards.com/thread/1820/masonry-cookstoveThis is what I ended up doing. It works ok the oven eventually gets to a baking temp. The firebox is slow to start. If I had to do it again I would have used IFB to line the firebox instead of hard brick. Also I would have made a clay/perlite mix to coat the inside of the brick around the stove to retain heat. Joseph
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