Talk:Stack effect

SI equation was wrong

The constant of 0.342 was incorrect. I changed it to 0.0342 for pressures in kPa which I subsequently changed to 34.21 for pressures in Pa. The P was defined incorrectly as total pressure. I changed the definition to ΔP being the available pressure drop. I also added a caution that the equations only applied to buildings and they do not apply to combustion chimneys.

It very depressing to find mistakes like this in article. I can only assume that someone found the equation in the USA customary units and then made an order-of-magnitude error in converting to SI units by misplacing the decimal point. Such errors would not happen if people learned to always make a sanity check calculation before publishing an equation.- mbeychok 07:10, 12 April 2006 (UTC)

• It IS very depressing to find grammatical errors like this in AN article. Such errors would not happen if people learned to always proofread before publishing a statement. -- P199 12:33, 13 April 2006 (UTC)

Very cute!! But it evades the point that there are all too many mistakes in many of the Wikipedia technical articles. - mbeychok 15:43, 13 April 2006 (UTC)

The split infinitive "to always proofread" has gone unremarked for over a decade. This is very depressing. 115.64.142.162 (talk) 04:20, 8 January 2017 (UTC)

• "That pressure difference ( ΔP ) is the driving force for the stack effect and it can be calculated with the equations presented below" - I did not find that equation in the presented sources. — Preceding unsigned comment added by 176.101.193.168 (talk) 06:48, 13 November 2020 (UTC)

Reverted the move and name change by User:Tmangray

User:Tmangray moved and changed the name of this article to "Chimney effect" simply because he unilaterally decided that it was a more common name than "Stack effect". I disagree with his change and with his having done so without any prior notice or discussion here on this Talk page. The most common usage by far in thousands of industrial plants and power plants worldwide is "Stack effect" as well as in the engineering/technical literature.

There is an existing article called "Chimney" in Wikipedia which has a section, Chimney#Chimney_draught_or_draft, devoted to the subject of stack effect or chimney effect. Any non-technical reader would probably go there first and would find that section. They don't need this article as well.

This article was intended for a more technical readership that encompasses industrial people (engineers, plant operators, plant managers) as well as science and engineering students,

I don't mean to be disrespectful or snide, but I don't think that User:Tmangray should appoint himself to unilaterally be the arbiter of what term is more common. Using the advanced search function in Google, the phrase "stack effect" got 71,000 hits and the phrase "chimney stack" got 49,400 hits. I have reverted the move and name change back to what it was before User:Tmangray changed it. - mbeychok 21:36, 18 July 2006 (UTC)

Just a postscript thought for User:Tmangray to consider: why not redirect Chimney effect to Chimney? Would that serve your purposes? - mbeychok 21:43, 18 July 2006 (UTC)

• I started this article (while Mbeychok greatly expanded it) and my intent was to explain the technical/physical aspects of the stack effect - this is the proper term because (as is explained in the article) the effect is not just limited to chimneys. Therefore I completely agree with User:Mbeychok on all his points and this article should remain "Stack Effect". -- P199 17:25, 19 July 2006 (UTC)

Nonsense qualification

The article currently says: "The equation applies only to buildings where air is both inside and outside the buildings." Does that really need to be said? How many buildings are there that do not have air both inside and outside? The few I can think of are vehicles like submarines and spacecraft, or structures like storage tanks, none of which are buildings as such. 129.97.79.144 19:10, 30 April 2007 (UTC)

Actually, it might be worth stating. An example of a "building" where this isn't the case is on board a ship. The boiler would be below the water line, requiring air to flow down prior to flowing up. Another example: shipboard fires. If there is a fire that is in a vertical compartment (ie, ladderwell) where the top is at teh waterline, the air would flow down, then back up, possibly effecting the dynamics. I'm not enough of an expert in either to quantify the effects. —Preceding unsigned comment added by 66.75.134.107 (talk) 16:00, 20 June 2009 (UTC)

Link missing

Ref 3 link is dead

Regards, Tom 211.147.76.161 (talk) 07:38, 23 February 2009 (UTC)
:₳New link is
http://www.wbdg.org/resources/naturalventilation.php Kennethjyoung (talk) 00:20, 4 July 2009 (UTC)

Reference cited doesn't provide equation used in article

That pressure difference ( ΔP ) is the driving force for the stack effect and it can be calculated with the equations presented below.^[1][2]

The equation used in the article doesn't match the citation reference equation. Kennethjyoung (talk) 00:28, 4 July 2009 (UTC)

Hi. I'm reading the same article and checking the citation reference, and in both references, there's no trace of the mentioned equation, as Kennethjyoung mentioned 11 years ago. PabloKWiki (talk) 14:22, 31 March 2020 (UTC) Found a bibliographic reference with the mentioned equation. Will edit the referencies and keep the old and non correspondent references in external links (as they are very useful presetnations) PabloKWiki (talk) 22:43, 31 March 2020 (UTC)

Removed External Link

The external link directed me to a page that was essentially a purchase page for a related book. Very little useful information about the Stack Effect on the page itself. Removed the link. —Preceding unsigned comment added by 76.19.93.26 (talk) 14:42, 5 March 2010 (UTC)

But if the book's content is highly relevant, the link is appropriate; relevance of the web page about it is not the appropriate metric. (I haven't looked at the edit, link or book in question yet, but rationale given suggests the removal was inappropriate.)--Elvey^(t•c) 21:22, 14 June 2016 (UTC)

missing explanation, where the constant C stems from

there should be a remark, how C was derived, which assumptions it is based on to make this number traceable. —Preceding unsigned comment added by 194.88.178.76 (talk) 08:57, 10 November 2009 (UTC)

The C seems to be, at least partially, a unit conversion factor. It is also simplifying away a lot of the physics details, hiding other factors like the densities of air and the flue gases. This article is missing a lot of the physics discussion one would expect in an article about fluid mechanics. A more thorough exploration of the topic is given here, on The Engineeering Toolbox. Unfortunately they don't appear to cite sources either. It's been mentioned already that our article here cites a source that doesn't even contain this equation. Saprophage (talk) 18:16, 10 January 2016 (UTC)

It looks like the basis of the equation is that delta_P (the pressure head that is created by the stack effect) is assumed to be equal to delta_rho * g * delta_h, where rho is the density, g is gravity and h is the height (so in this equation, a = delta_h). Using the ideal gas law, the density is rho = P/(R * T), where R is the universal gas constant. So delta_rho = P/R *(1/T_1 - 1/T_2). So C is simply g/R. In S.I. units, that would be 9.81m/s^2 / 287 J/kg K, which is equal to 0.342 K/m.

Dubious

Surely C is not the same in U.S. customary units as in SI units!?!--Elvey^(t•c) 19:45, 14 June 2016 (UTC)

C is unitless in this equation, so it's the same value regardless of what units you are using. This equation in particular seems to work for any units, so do we really need the SI/american distinction? Jeff B. (talk) 22:12, 30 May 2018 (UTC)

Huh? Basic physics errors?

Am I missing something or is something very wrong? We speak of hot air sucking smoke up a chimney/hot air up a stack, but physically, that's inaccurate. It's the pressure of the atmosphere pushing down that causes the less dense hot air to be pushed up the chimney/stack. So the image and caption (replicated at right:

The stack effect in chimneys: the gauges represent absolute air pressure and the airflow is indicated with light grey arrows. The gauge dials move clockwise with increasing pressure.

) is all wrong, no!? Air density is low in/near the bottom of the chimney, but the air pressure isn't. Right? According to the source, http://www.ides-edu.eu/wp-content/uploads/2013/04/Ventilation_lecture-2_PH-Alleen-lezen.pdf, (page 9, slide 2) indoor and outdoor air at the same altitude is not at the same pressure but I'm pretty damn sure the source is inaccurate. Anyone have a more authoritative source handy to confirm I'm right? --Elvey^(t•c) 21:22, 14 June 2016 (UTC)

By the way, if it were accurate, the inflatable chimney idea would face a likely insurmountable challenge: if there were relatively low air pressure, as depicted, in/near the bottom of the chimney, it would tend to cause it to collapse/be crushed by the outside air pressure. --Elvey^(t•c) 21:22, 14 June 2016 (UTC)

The picture is misleading at the very least. The pressure difference due to body forces is several orders of magnitude bigger than the pressure difference between the bottom of the chimney and the bottom ambient air. The only pressure difference there is due to the inlet losses. I just did a model for a 10m tall 0.4m dia chimney with a heat load driving a 0.2m/s average velocity. The pressure difference between the inside and outside of the bottom of the chimney was 2 Pa, and the pressure difference from top to bottom was 117 Pa. Jeff B. (talk) 22:12, 30 May 2018 (UTC)

The picture is fully correct, I do not understand why it is misleading (picture seems older than comments above thus not modified since?). First sentence of first comment (Elvey) is correct but after that, it reads strange to me. -> Because the air density is lower in the building or chimney then it results that the air pressure (made by the weight of air volume above it, weight = density*volume) at the bottom of the building is lower than outside (less weight along the height of the building). For the inflatable chimney, I don't see the problem, being inflatable or not as nothing to do with this, except if you don't inflate it then maybe it is not a useful case to discuss.

For the order of magnitude question (JeffryBeckman), doesn't the picture shows indeed a bigger pressure difference between top vs down than outside vs inside? I am sorry but it seems you misunderstand the real drive of this effect: the flow is not moving up like a cold flow being heated along a hot wall is. The flow is created because the inside air is hot: it creates a pressure difference at the bottom (2Pa apparently in your case) and this pressure difference makes an air flow to the bottom of the chimney. The existing air in the chimney is pushed out as new air goes in. The difference in absolute pressure at different altitudes is not the concern here, it is the local pressure gradient (anywhere) that enables the air to flow. The height of the chimney, together with the temperature difference drive the pressure difference at the bottom but only with the power of 0.5 while the absolute pressure changes with the power of 1 with the height, thus the order of magnitude is completely understandable. And thus you other sentence is also wrong (The only pressure difference there is due to the inlet losses.) It is the oppposite, the orifice pressure loss is equal (due) to the pressure difference. Flow is the consequence of the pressure difference not the other way around. Kevin (talk) 16:56, 4 October 2019 (UTC+2)

The pressure difference between inside and outside depends on the aperture. We most naturally imagine a chimney as being completely open at the top, with a relatively small aperture at the bottom. In that case, the pressure at the top will be approximately equal to ambient pressure, and the pressure inside will be lower at the bottom because the weight of air is less in the chimney. But we could have a tube that's open at the bottom and has a small aperture at the top, and air would still flow. There would still be a substantial pressure difference across the small aperture, and negligible difference at the open end. Note that we're pretty much assuming that (other than in the aperture itself) the flow rates are low, so that hydrostatic equilibrium is a good approximation to the actual distribution of pressures. --Dan Wylie-Sears 2 (talk) 02:19, 1 November 2019 (UTC)

Grenfell Tower fire

@CplDHicks2: Is it now certain that 71 people died? The last thing I heard was that 71 was the best guess, some of the bodies were burnt to ash and there were a number of suspected extra residents and visitors. Regards, Martin of Sheffield (talk) 18:49, 10 December 2017 (UTC)

The Met Police declared the final death toll in November. CplDHicks2 (talk) 18:59, 10 December 2017 (UTC)

Thanks for that, I'd missed the revising down last month, I thought they were still considering 100+. I won't say good, but at least it's slightly less bad news. Martin of Sheffield (talk) 21:40, 10 December 2017 (UTC)

Sad story all around, unfortunately. Fair question on your part though, I should have added a reference to a source in the first place. Cheers. CplDHicks2 (talk) 03:57, 11 December 2017 (UTC)

"Stack effect" or "the stack effect"?

I notice that currently the first sentence begins, "Stack effect or chimney effect is the movement of air into and out of buildings...", with no beginning "the". But most of the article text refers to "the stack effect". So I added "the" to the beginning of the first sentence. This edit was undone by User:P199, with the explanation that "the" is unnecessary.

Compare articles such as Photoelectric effect, Doppler effect, Certainty effect, Halo effect, Dunning–Kruger effect, Bystander effect, and Hall effect, which all begin with "The ___ effect". That's the typical way that such an effect is referred to, and the article text demonstrates this.

On the other hand, Ground effect (aerodynamics) does not have a beginning "the", but that's because ground effect isn't typically called "the ground effect"—it's just called "ground effect", as demonstrated by the article text.

I don't know the typical usage in this case. If it's typically called just "stack effect", then it seems to me that the article text needs to be cleaned up to remove extraneous uses of "the" in the phrase "the stack effect". On the other hand, if it is typically called "the stack effect", then I think the first sentence should have "the" too. —Bkell (talk) 14:12, 23 June 2022 (UTC)

The provided examples of comparative articles above are all wrong - they don't need "the", like this article, because it is an uncountable or mass noun. It is explained well at English articles: "the definite article is not used with generic nouns (plural or uncountable): cars have accelerators, happiness is contagious, referring to cars in general and happiness in general (compare the happiness I felt yesterday, specifying particular happiness)." Regards, -- P 1 9 9  ✉ 14:29, 23 June 2022 (UTC)

I don't think that sentence is applicable here. "Stack effect" is certainly not plural, and the usage throughout the article text ("the stack effect") suggests it is not uncountable. —Bkell (talk) 14:37, 23 June 2022 (UTC)

I wouldn't rely on its usage throughout the article as a reliable guide to grammar. Anyway, I have made my point, and I find debates about inconsequential word use (note: no "the") so tiresome. I no longer care either way. -- P 1 9 9  ✉ 14:50, 23 June 2022 (UTC)

OK, then I will reinsert "the", to be consistent with the rest of the article text and similar articles. If you can demonstrate with reliable sources that it is an exception like "ground effect"—that it is commonly called just "stack effect", rather than "the stack effect"—I will be happy to take "the" out again. —Bkell (talk) 14:55, 23 June 2022 (UTC)