Using dampers for correct smoke retention/residence time

GrateEggspectations

Canugghead said:

If I may digress... 0-400 wangs is all the rage in the Traeger world. Set temp to 400, place wings on cold grate and switch on, cook 30 min, flip, another 30 min.  I tried that today, but since my baby Traeger runs hotter than full sized ones, I went 0-380, 30 min, flip, 10 min. It was really good and smokier but not too much compared to usual hot and fast. 

I dunno, may be it worked well because meat was cold and pellet pooper was smokiest at start up.

What is “Traeger”?

dbCooper

Mark_B_Good said:

dbCooper said:

Mark_B_Good said:

A couple of things, and some of these are stated above.
- once the volatiles (VOCs) have burned off ... the smoke is what you actually want to penetrate the meat and add flavor.  It's really only during the initial heat up, just don't put the meat on too early. But once you've heated up and it's stable ... the smoke is what you want.

In terms of dwell time ... you're not really changing much by opening or closing the top vent.  Let me explain.  Air in + combustion gases = air out ... the flow cannot be changed. It is directly linked to your burn temperature ... pretty much, at a given temperature, you will generate a certain vent gas flow. It does not change, unless you change the burn temperature (higher or lower temperature).  The volume of the egg is fixed (the dome volume) ... the time the vent gases spend in the egg is simple math:

time (in seconds) = freeboard volume of egg (cubic ft) / vent gas flow (cubic ft/second) ... if both freeboard volume and vent gas flow are fixed (at a given burn temperature) ... then you can see, irrespective of what you do with the vent opening ... the dwell time is unchanged.  

What happens is the velocity of the gas exiting the vent increases as you close the vent ... flow remains same, but that flow = vent gas velocity x the area of the vent opening ... so as you decrease vent opening, the gas velocity increases to compensate ... so it can release whatever vent gas flow is generated inside.

THIS is what does happen ... there is more recirculation of gases inside the egg, as you close the vent (more of a convection oven ... and the concentration of smoke increases somewhat).  So the smoke actually hits the meat in circular motion many more times before it exits, as you close the top vent.

@Mark_B_Good

This is not accurate.  If true it means air flow is constant regardless of vent opening(s).  How then does the temperature decrease when the vent(s) openings are reduced?

*edit to add - I'd really like to see your data/videos showing the convection patterns inside the Egg, that is something I've always been curious about.

I was trying to keep it simple for everyone to understand.

The reality is ... the pressure in the egg DOES go up marginally due to back pressure from the vent.  This increase in pressure does cause a restriction in flow intake to the vent, and hence less oxygen flow in, so burn rate goes down. This is the reality of your experience, WHEN you close the vent.

BUT - you missed something VERY important in my message ... it's critical (and I did it on purpose to help everyone understand what is going on). I said at "A GIVEN TEMPERATURE"!  To get to the same temperature, whether the vent is open more or less ... you need to be burning coal at the same rate, which means SAME oxygen flow in, and same vent gas flow out!

@Mark_B_Good

I didn't miss "at a given temp", that is gist of why I stated your initial post is not accurate.  You correctly noted Flow = Vent Area x Velocity.  Say my Egg is stabilized at temp X, with bottom vent at Y, and top vent at Z.  I then decide to introduce some vortex smoke action by reducing Z and increasing velocity.  Guaranteed that the "given temp" will now be reduced as any increase in velocity will not win against the reduced vent area.

Maybe you missed stating you run with a blower?  That might make sense of what you are claiming.  My position is from running naturally aspirated.

lousubcap

Kinda like running a NA V-8 ICE.  Not to sidetrack the above...

fishlessman

JohnInCarolina said:

Legume said:

Can you address this the fracture mechanics of the egg now?

You want me to explain why it cracks?  Or you want me to design one that doesn't ?  

JohnInCarolina said:

Legume said:

Can you address this the fracture mechanics of the egg now?

You want me to explain why it cracks?  Or you want me to design one that doesn't ?  

One could use more chunks, add chips or pellets later in the cook, but please tell me the square vent in the bottom of an egg is just wrong😆

Legume

Temp doesn't go down when you close a vent more because of thermal mass, it does drop eventually, irregardless of the wind speed velocity of an unladen swallow.  I didn't mention this earlier on purpose.  Don't ask me what type of swallow, I don't have that much time.

JohnInCarolina

Legume said:

Temp doesn't go down when you close a vent more because of thermal mass, it does drop eventually, irregardless of the wind speed velocity of an unladen swallow.  I didn't mention this earlier on purpose.  Don't ask me what type of swallow, I don't have that much time.

You’ve always struck me as more of a spitter anyway.

Mark_B_Good

dbCooper said:

Mark_B_Good said:

dbCooper said:

Mark_B_Good said:

A couple of things, and some of these are stated above.
- once the volatiles (VOCs) have burned off ... the smoke is what you actually want to penetrate the meat and add flavor.  It's really only during the initial heat up, just don't put the meat on too early. But once you've heated up and it's stable ... the smoke is what you want.

In terms of dwell time ... you're not really changing much by opening or closing the top vent.  Let me explain.  Air in + combustion gases = air out ... the flow cannot be changed. It is directly linked to your burn temperature ... pretty much, at a given temperature, you will generate a certain vent gas flow. It does not change, unless you change the burn temperature (higher or lower temperature).  The volume of the egg is fixed (the dome volume) ... the time the vent gases spend in the egg is simple math:

time (in seconds) = freeboard volume of egg (cubic ft) / vent gas flow (cubic ft/second) ... if both freeboard volume and vent gas flow are fixed (at a given burn temperature) ... then you can see, irrespective of what you do with the vent opening ... the dwell time is unchanged.  

What happens is the velocity of the gas exiting the vent increases as you close the vent ... flow remains same, but that flow = vent gas velocity x the area of the vent opening ... so as you decrease vent opening, the gas velocity increases to compensate ... so it can release whatever vent gas flow is generated inside.

THIS is what does happen ... there is more recirculation of gases inside the egg, as you close the vent (more of a convection oven ... and the concentration of smoke increases somewhat).  So the smoke actually hits the meat in circular motion many more times before it exits, as you close the top vent.

@Mark_B_Good

This is not accurate.  If true it means air flow is constant regardless of vent opening(s).  How then does the temperature decrease when the vent(s) openings are reduced?

*edit to add - I'd really like to see your data/videos showing the convection patterns inside the Egg, that is something I've always been curious about.

I was trying to keep it simple for everyone to understand.

The reality is ... the pressure in the egg DOES go up marginally due to back pressure from the vent.  This increase in pressure does cause a restriction in flow intake to the vent, and hence less oxygen flow in, so burn rate goes down. This is the reality of your experience, WHEN you close the vent.

BUT - you missed something VERY important in my message ... it's critical (and I did it on purpose to help everyone understand what is going on). I said at "A GIVEN TEMPERATURE"!  To get to the same temperature, whether the vent is open more or less ... you need to be burning coal at the same rate, which means SAME oxygen flow in, and same vent gas flow out!

@Mark_B_Good

I didn't miss "at a given temp", that is gist of why I stated your initial post is not accurate.  You correctly noted Flow = Vent Area x Velocity.  Say my Egg is stabilized at temp X, with bottom vent at Y, and top vent at Z.  I then decide to introduce some vortex smoke action by reducing Z and increasing velocity.  Guaranteed that the "given temp" will now be reduced as any increase in velocity will not win against the reduced vent area.

Maybe you missed stating you run with a blower?  That might make sense of what you are claiming.  My position is from running naturally aspirated.

Well, I can close the vent from 100% open to 90% open, and I bet the temperature won't change one bit.  So, it is possible to close the vent without impacting the temperature.

Mark_B_Good

dbCooper said:

Mark_B_Good said:

dbCooper said:

Mark_B_Good said:

A couple of things, and some of these are stated above.
- once the volatiles (VOCs) have burned off ... the smoke is what you actually want to penetrate the meat and add flavor.  It's really only during the initial heat up, just don't put the meat on too early. But once you've heated up and it's stable ... the smoke is what you want.

In terms of dwell time ... you're not really changing much by opening or closing the top vent.  Let me explain.  Air in + combustion gases = air out ... the flow cannot be changed. It is directly linked to your burn temperature ... pretty much, at a given temperature, you will generate a certain vent gas flow. It does not change, unless you change the burn temperature (higher or lower temperature).  The volume of the egg is fixed (the dome volume) ... the time the vent gases spend in the egg is simple math:

time (in seconds) = freeboard volume of egg (cubic ft) / vent gas flow (cubic ft/second) ... if both freeboard volume and vent gas flow are fixed (at a given burn temperature) ... then you can see, irrespective of what you do with the vent opening ... the dwell time is unchanged.  

What happens is the velocity of the gas exiting the vent increases as you close the vent ... flow remains same, but that flow = vent gas velocity x the area of the vent opening ... so as you decrease vent opening, the gas velocity increases to compensate ... so it can release whatever vent gas flow is generated inside.

THIS is what does happen ... there is more recirculation of gases inside the egg, as you close the vent (more of a convection oven ... and the concentration of smoke increases somewhat).  So the smoke actually hits the meat in circular motion many more times before it exits, as you close the top vent.

@Mark_B_Good

This is not accurate.  If true it means air flow is constant regardless of vent opening(s).  How then does the temperature decrease when the vent(s) openings are reduced?

*edit to add - I'd really like to see your data/videos showing the convection patterns inside the Egg, that is something I've always been curious about.

I was trying to keep it simple for everyone to understand.

The reality is ... the pressure in the egg DOES go up marginally due to back pressure from the vent.  This increase in pressure does cause a restriction in flow intake to the vent, and hence less oxygen flow in, so burn rate goes down. This is the reality of your experience, WHEN you close the vent.

BUT - you missed something VERY important in my message ... it's critical (and I did it on purpose to help everyone understand what is going on). I said at "A GIVEN TEMPERATURE"!  To get to the same temperature, whether the vent is open more or less ... you need to be burning coal at the same rate, which means SAME oxygen flow in, and same vent gas flow out!

@Mark_B_Good

I didn't miss "at a given temp", that is gist of why I stated your initial post is not accurate.  You correctly noted Flow = Vent Area x Velocity.  Say my Egg is stabilized at temp X, with bottom vent at Y, and top vent at Z.  I then decide to introduce some vortex smoke action by reducing Z and increasing velocity.  Guaranteed that the "given temp" will now be reduced as any increase in velocity will not win against the reduced vent area.

Maybe you missed stating you run with a blower?  That might make sense of what you are claiming.  My position is from running naturally aspirated.

I don't mean to be pedantic, but if you go back and read your response, it is clear you missed "at a given temp" ...  you stated, in first sentence "This is not accurate" ... but anyhow, it doesn't matter ... it's not a contest.

dbCooper

@Mark_B_Good

Like you, I'm not interested in being confrontational or winning some "contest", it's all about turning out great food.  The OP is new to the blog and possibly new to Egging.  My motivation in posting was to help him by pointing out info that was inaccurate, specifically that reducing the top vent opening will not impact air flow/charcoal burn rate and the stable given temperature.  The 100% to 90% example you provided is a straw man argument, thus irrelevant.

The top vent cap as normally used for a low and slow (minimally open) will impact flow and temps if the opening is changed.  I still use the old style DFMT, adjusting just the petals for fine tuning temps.