The wonderful physics of heat exchangers

    Quote from ele

    FALSE !

    you can easily find commercial HVAC system of 1MW power:

    http://www.emersonclimate.com/…or_systems_up_to_1MW.aspx


    As usual Jed you pretend to be expert of everything but you are not even able to make an internet search.


    As usual Ele you are missing the point.


    The link describes a heat pump with 1MW cooling at 150kW power in. You will note that for Rossi's heat exchanger any power used, unless very small, is quite impossible due to the fact that the FPL power figures and the ecat power in figures match.


    Hence Rossi's heat exchanger is just not possible.

    Quote from THHuxleynew

    The word Conductibita does not translate to English, although Termica is Italian for Thermal, and itseems likely that Conductibita ismeant to mean Conductivity. This title does not exist on the web.

    What you are not able to translate Conducibilità Termica ? Is simply "Thermal conductivity"


    and again Voilà a nice table in Italian searched as Conducibilità Termica http://fisicatecnica.altervista.org/tabelle/tab_conduc.htm

    ans of course in english:


    https://www.nde-ed.org/Educati…l/ThermalConductivity.htm


    THH, as for children : Shame on you ! you are not able to use google translator and google !

    I've just realised.


    Ele - read what I said? The reference was Conductibita which is not a word. However, as you would note if you had read my post, I reckoned Wong meant Conductibilita. He must have written down what Rossi gave him wrong.


    The mystery though is why did Rossi give this site as a reference when it does not have the relevant coefficient? Note that neither your table nor the referenced OPPO site has the relevant isothermal rod to forced air figure.

    Quote from THHuxleynew

    The link describes a heat pump with 1MW cooling at 150kW power in. You will note that for Rossi's heat exchanger any power used, unless very small, is quite impossible due to the fact that the FPL power figures and the ecat power in figures match.


    Hence Rossi's heat exchanger is just not possible.

    THH if I produce 1MW of heat + 20kW what I have to dissipate is just 1.02MW . Just that ! 1MW cooling wil do.


    My searches were very quick and demonstrate that you are just building a "Card castle" without any ground.

    As usual the thesis here "IH had not sufficient experts, we are much better of anybody".

    But if that was so evident why you have not gone to court to testify ?

    Probably, you are the first that knows that what you are saying is false and you would not able to repeat it under oath !

    Quote from JedRothwell

    300 people generate ~30 kW of heat.

    Yes internally and you of course ignore heat coming from ambient (external sun light on the building, weather conditions ecc...) that can rise that figure. Sun delivers approximately 1kW of heat per square meter of surface so 1MW on 100 square meters = 10763.9 square foot that is approximately the area for a 600 seats theater.

    Quote from JedRothwell

    You are missing the point. I am talking about the HVAC systems, not the people. The HVAC cannot cope with much more than 30 kW. They are not designed for higher power levels. 100 or 200 kW would completely overwhelm them.


    A person dancing (to techno or similar) produces 300W heat.


    200 gurning ravers can produce around 60kW in a 12x12m area, and that's just a small club... Imagine a 2000 capacity venue... The HVAC works fine.... It has to.

    And come to think of it... It seems Rossi can't use the internet either... Why weld hundreds of metres of pipe together when he could have got an off-the-shelf solution from Bowman???


    Answer: Because buying from Bowman would have left a paper trail, which would have necessitated faking the documents when Rossi realised post-fact that he needed a heat exchanger. Far too risky when a simple phonecall to Bowman would have exposed him.



    (Based on steel price and site-welding costs, I reckon a Bowman heat exchanger would have probably worked out much, much cheaper)

    Quote from Zeus46

    200 gurning ravers can produce around 60kW in a 12x12m area, and that's just a small club... Imagine a 2000 capacity venue... The HVAC works fine.... It has to.

    Again you are missing the point. Sigh. The point is that an ordinary office building does not have extra HVAC capacity. It can remove ~60 kW of heat, like a movie theater. It cannot remove 100 or 200 kW. With that much heat it will be unbearably hot.


    Yes, you can always build a facility with more heat removal capacity. But Rossi's office building was nothing special, and no one builds an ordinary office or warehouse with the capacity to accomodate 2,000 people exercising at high rates. That would be a waste of money.

    Right, I see now. I think the point we are trying to arrive at is...


    Quote from JedRothwell

    Are you saying this is approximately how much heat can be dissipated with an normal building, with conventional HVAC? I think it is less than this. Two real-world examples:


    The average U.S. movie theater capacity is 200 to 300 people....


    THH's rather wide estimate of <200-500kW is theoretically how much heat can leave an poorly insulated industrial unit (the size of Doral) through the walls, floor, windows and roof. I basically agree with this, based on my own estimates of the U-values of the structure.


    Yes, maybe the Doral HVAC was limited to 30kW or so, but that's almost insignificant given the amount of heat that can dissipate through the structure, assuming a large temperature rise inside. I don't think THH considered the HVAC, based on what he wrote, and neither did I... (Possibly because we aren't used to such systems in similar situations the UK, as most of the time the weather is temperate enough not to need it).


    You say a packed movie theatre would get hot inside, we say Doral should have been hot inside. Seems fair enough?

    And - to answer Ele's missing the point entirely posts:


    • Were Rossi really needing to dispose of 500kW or so of energy an HVAC would do that just fine. But, with typical heat pump efficiency of 6 or so he could never have used it, or the FPL data would show this.
    • His proposed design could sort-of have worked, but again with an efficiency such that he could never have used it without FPL power input much larger than was.
    • In any case all the circumstantial evidence points to this theoretical heat exchanger never existing
    Quote from ele

    Is just one of the many sites and references. Conductivity is a property of materials and has nothing to do with forced air.


    Regarding forced air the term Heat Tranfer is used:

    https://www.google.nl/search?r…ivity+of+materials+forced


    Ele - you are taking a while to catch up with this. You are quite correct that Rossi/Wong got that reference wrong. You are quite correct (assuming you have worked this out) that the 200W/m^2K is an oft-quoted coefficient for forced air heat transfer over isothermal rods - at least on the internet. No respectable reference will give a one-size-fits-all figure since it depends on both air velocity (obviously) and rod diameter (less obviously, but look at the equations).


    Do you agree, or not, with my spreadsheet analysis. I've given refs for most of the equations I think?

    Quote from THHuxleynew

    PS - what I'd like is for the ECW guys (and specifically E48) to read the above and answer. E48's answer to the conversation about erroneous HTC is that it would be Ok if the wind velocity was high enough, which could be got from a design with baffles. That is sort of true - though Wong left out any mention of baffles there is no requirement on him to do that. But the power argument knocks this on the head.


    I'll try to attract some attention for your calculations on ECW.


    In the meantime I'm working through your spreadsheet. I don't understand the mass velocity, G. Dimensionally, it seems to have units of a mass flux [Kg/m^2*s] rather than a mass velocity. And can you explain how this comes into the formula for deltaP and the rationale for that?

    Quote from Zeus46

    You say a packed movie theatre would get hot inside, we say Doral should have been hot inside. Seems fair enough?

    First, it was not hot inside.


    Second, with 100 to 200 kW it would not have been merely "hot" -- it would have been intolerably hot, so that no one could stay inside for long. It wasn't, as I said.

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