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Thread: water level related to steam and stabilityarch

  1. #1
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    water level related to steam and stabilityarch

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi All
    when doing research for adjusting the water level in the boiler I found this site:
    http://coffeetime.wikidot.com/boiler-fill-level-and-shot-temperature
    Previously Id been told that lower water levels meant less flushing and cooler shots- not the case:
    Low water=higher shot temps (but poorer steaming)
    High Water levels = lower shot temps, but better steaming (unless its far too high)

    but theres also the issue of: This efficiency of steam to transfer heat is why shot stability is improved with lower water levels. Many years ago I read about some manufacturers passing the HX only through steam in an attempt to improve shot stability and also make the HX more efficient for shot after shot.

    Makes for interesting thoughts as to what Chris is doing with his pimping the Giotto mods?
    Brett

  2. #2
    Super Moderator Javaphile's Avatar
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    Re: water level related to steam and stabilityarch

    Ill maybe buy it for the brewing temp bit but not for the steaming.

    Steaming has nothing to do with whether water or steam transfers heat to the HX better. Your frothing steam comes from a tap directly into the top end of the boiler, not from the HX. Steaming power has nothing to do with the HX. Discounting the recovery speed of the boiler steaming ability is determined solely by the temp/pressure and the amount of steam available.

    Assuming that the temp/pressure in the boiler is the same in both situations you will have better steaming with low water as there is more steam in the boiler.


    Java "Isnt Science fun!?" phile

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    Re: water level related to steam and stabilityarch

    Mmmmm interesting...

    Well re brew temperature Ive read an article claiming the reverse is true...

    Both the steam and the water are at the same temperature in the boiler (around 120C)....

    Water transfers heat more readily than steam.... if you want a quick test place your hand under the steam wand when flat out..... and it doesnt even feel hot - but if you are stupid enough place your hand under the boiling water outlet and it will be just a tad hotter!!! (Dont sue me for the damage to your hand by the way!!!)
    Id advise substituting a thermometer for this little experiment ::)
    Mal.


    The article (on "tuning" HX machines) stated if you increase the water level so that more of the HX is in water it will transfer more heat at a fixed flow rate - greater brew temp..... lower the water level.... more of the HX in steam with its poor thermal transfer rate.... lower brew temp as less heat flows into the water at that same flow rate.

    But if left idle for a while..... it will make no difference as 120C is 120C .... whether it is from water or steam!

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    Re: water level related to steam and stabilityarch

    Quote Originally Posted by Javaphile link=1184127347/0#1 date=1184132006
    Ill maybe buy it for the brewing temp bit but not for the steaming.

    Steaming has nothing to do with whether water or steam transfers heat to the HX better. Your frothing steam comes from a tap directly into the top end of the boiler, not from the HX. Steaming power has nothing to do with the HX. Discounting the recovery speed of the boiler steaming ability is determined solely by the temp/pressure and the amount of steam available.

    Assuming that the temp/pressure in the boiler is the same in both situations you will have better steaming with low water as there is more steam in the boiler.


    Java "Isnt Science fun!?" phile
    Interesting isnt it?
    I raised the water level by a fraction in the Boema and suddenly the steam was full of water. Phil must have had the water level at that critical level.
    For me the steam wasnt the critical part but the hx flush bit- I was interested in why the Boema needs almost zero flush to be at temp whereas the Bez needs a lot- ok there are design differences between hxs but I was wondering if the fact that the Bos level is high and the Bezs is quite low was a factor.
    Brett

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    Re: water level related to steam and stabilityarch

    Quote Originally Posted by telemaster link=1184127347/0#3 date=1184133640

    For me the steam wasnt the critical part but the hx flush bit- I was interested in why the Boema needs almost zero flush to be at temp whereas the Bez needs a lot- ok there are design differences between hxs but I was wondering if the fact that the Bos level is high and the Bezs is quite low was a factor.
    Brett
    Brett,

    I personally think it is more about design of the HX system and boiler pressure (temperature) than the actual water level - whichever view of its affect you believe.

    Some HX machines - like the La Cimbali - have what looks like a small boiler in the main boiler, others have only a tube running through the boiler so some can supply a lot of superheated water whilst other supply only a bit after idle.

    Also how hot is the group at rest.... some maintain brew temp so it doesnt steal much heat from the boiling water coming out..... others are at a lower temp - and therefore heating them up cools the water.....

    To me its all about the design- if the designer was after fast recovery..... if left idle it probably needs a longer cooling flush (real high volume machines).... others probably are designed for greater "long term stability" and yet others are a compromise..... some have hot water circulation in the group assembly, others dont.... some have a tightly coupled group/boiler design (basically bolted together) and others have the group somewhat thermally isolated etc.... etc....

    Basically I believe you learn to use what works for your machine - and go with that!

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    Re: water level related to steam and stabilityarch

    Hi JavaB
    I totally agree- work with what youve got.
    Brett

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    Re: water level related to steam and stabilityarch


    I agree with JavaB... The design has more to say about how a machine operates than most of these parameters.

    One of the critical factors that rarely gets mentioned is the injector design. Im still dabbling with these issues, but a HX machine relies on mixing to achieve a constant temp. That means the injector design is a major factor. For example, you may be able to shorten the injector and run the boiler at a higher temp and so on... Im still thinking about this, but it seems close to the way they actually work. I know the latest incarnation of the Bezzeras have changed their injectors to achieve virtually flush free performance. A small flush is always warranted just to set up the system.

    Cheers,

    Mark.

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    Re: water level related to steam and stabilityarch

    I would agree that design is the major factor, but understanding the greater heating ability of steam relative to water has made it easier to tweak boiler level and to predict what small changes will do.
    Brett

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    Re: water level related to steam and stabilityarch

    I think there are some flaws in the article. Going back to my old chemistry classes..... Water is a much better conductor of heat than gas. And steam is the gaseous state of water.

    JavaB is right about the steam not feeling hot -- when I carelessly drain the wand before frothing, I do it into a small espresso glass. Steam splashes back up onto my fingers but it is very tolerable.

    FOR ME, WHO DOES NOT DO IT ON PURPOSE -- SO DONT FLAY YOUR SKIN BY EXPERIMENTING!!

    By contrast, touch the metal steam wand, and the conduction of heat will be instantly noticeable as a nasty burn. And I keep fingers well clear of the water wand and shower screens.

    Aso the author says that sweat is a better coolant than being drenched in water. Huh? Cooling happens when the more excited molecules of liquid -- the "hotter" ones --- fly off a surface, leaving the "cooler" ones behind.

    Evaporated molecules tend to congregate and saturate the space above the surface theyve left. Then, no more can leave the surface to cool it.

    If they can be persuaded to move on--by a breeze --- more hotties can take their place and cool the surface/skin.

    And that, boys and girls, is the end of tonights science lesson.

    Good night,

    --Robusto

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    Re: water level related to steam and stabilityarch

    OK.... gone back to physics first principles to get the answer!!

    I kilogram of water at 120C has a specific heat of 4.18 Kjoules where 1 KG of steam at 120C only has a specific heat of 2.02 Kjoules (so it only contains half the heat.... per degree drop in temperature for a given weight).

    But....

    I cubic meter of water at 120C contains a bit over a 980 Kg of water .... or 980 X 4.18 Kjoules of energy per degree drop...... whereas 1 cubic meter of steam at 120C only weighs 0.59 Kg..... so it will only transfer 0.59 X 2.02 Kjoules of energy for the same 1 degree drop of a 1 cubic meter volume....

    So steam has FAR less energy per unit volume than water.... and will therefore transfer far less heat to the HX than water will....

    Bottom line - if you want a lower brew temp - lower your water level!!

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    Re: water level related to steam and stabilityarch

    Ok guys- it was an interesting read I guess and passed the time!
    So were back to Bezzera = lots of flush and very quick recovery because of design, Boema = less flush slower recovery because of design (and smaller boiler re the recovery).
    Genuine thanks for the science lessons- I must admit his reasoning was a surprise,
    Brett

    ps, Robusto, that bit about hotties on the skin?

  12. #12
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    Re: water level related to steam and stabilityarch

    Very convincing set of numbers, JavaB. I think some people think of steam as a powerful force because it used to power locomotives. Of course, it wasnt the calorific value of the substance which pushed pistons, but its pressure.

    Telemaster, the temperature of water molecules is never even. There are minute differentials. Some will always be in a more excited or hotter state than others. They are the ones which will evaporate from the liquid state first.

    -Robusto

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    Re: water level related to steam and stabilityarch

    Quote Originally Posted by robusto link=1184127347/0#11 date=1184196143
    Very convincing set of numbers, JavaB. *I think some people think of steam as a powerful force because it used to power locomotives. Of course, it wasnt the calorific value of the substance which pushed pistons, but its pressure.

    Telemaster, the temperature of water molecules is never even. *There are minute differentials. Some will always be in a more excited or hotter state than others. They are the ones which will evaporate from the liquid state first.

    -Robusto
    Sorry, I was looking for a double entendre
    brett



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