Amazing. Take one block of resistance material, set up 2 electrodes equivalent to the air inputs and outputs on the rad, pass current thru it, and the current path is the same as the airflow path behind the rad.
lol
hint: look up 'resistive' and look up 'block.'
another hint: composition of carbon, glue and filler. Getting a clue yet?
No doubt it features in all sorts of places. Hardly very relevant.
thats right! youre getting there.
none whatsoever lol
nope
this is from someone that cant understand how the airflow behind the rad is analogous to the current flow in a resistive block.
even a moment of calculation would show youre about 2 orders of magnitude out.
wrong again
if better means more heat transfer, yes, we agreed that long ago. But why do a bunch of further work that only achieves unnecessary further heat output gains, makes it look ugly, takes time and work... Only a fool would recommend that, surely.
Why would I do that? Why have you now abandoned the previous magnetic analogy? It was garbage, but so is this analogy.
This current analogy differs from the real situation in that an electric current can only flow through the conductors and the atmosphere is an insulator. To make your analogy more relevant, the block, electrodes and battery should be securely fixed to the bottom of a large plastic tank. Now you fill the tank with mercury.
Now have you got it? It short circuits. The current does not flow through the resistance block (heat emitter) because there is another path of little/no resistance.
If you try to pump water, or any fluid, under pressure through a pipe with holes in it, the fluid will flow out of the holes. You are trying to pump a fluid (air) through a channel with no sides on it. Do we need analogies? A large proportion of the air will avoid the heat emitter, which is where you want it to go. There should be highly turbulant flow past the heat emitter to disrupt the boundary layer, if I remember this correctly.
No, we do not want to do that. We want to look up the exact phrase you had used "uniform resistive block". This produces 0 hits.
Looking up "resistive block" produces 170 hits, mostly to do with geology. Looking up "resistive block" AND thermodynamics produces 3 hits, 1 of which concerns seismology and 2 of which are a geeky computer cooling forum.
The phrase "uniform resistive block" is pure bullshit. You have no knowledge of this subject but are using quack technology phrases to try to preserve your 'status'. To preserve your image you are calling those who disagree with you, because they do know something about the subject, fools. You are an offensive, arrogant, ignorant, ill-mannered little man. You are worse than Drivel, at least most people know him to be a bullshit artist.
It does not feature in any thermodynamics texts. It is bullshit.
Because it is not.
Depends how many you had to use. Why would I want to do any calculations when I can see the whole concept suffers from numerous fundamental flaws. I would never take it beyond the proposal, I have better ways of moving heat.
Strange that. The last equipment room I was involved with probably had 15 or 20 such computer fans shifting heat and it was most certainly audible.
Big fundamental problem that would have prevented it working effectively. But since most of the airflow didn't maintain contact with the heat emitter, it was never going to work properly anyway.
Only an ignorant fool would have built such a thing, but you have to call others fools rather than admit the flaws in your methods.
No, the current flows through the resistance block, as stated several times now.
no, the heat emitter is not analogous to the resistance block. The shallow airpath behind the rad is analogous to the resistance block. As stated at various times already.
yup
only if you choose to regard it as a channel with one entry side and 3 exit sides. I dont think modelling it as a channel is too helpful. Certainly hasnt shown you what the airflow would be anyway.
evidently.
if you want maximum heat transfer, sure, but as has been made clear many times already, that isnt a part of the goal here.
So to understand something, you dont want to look at what the words mean! Ok :) Your choice.
it means a block of resistance material. That's electrical resistance. With uniform resistivity. Understand?
ok lol
If I were primarily concerned about preserving social status within this group I'd have stopped replying to you long ago. I guess you didn't figure that out yet.
I'm replying for another reason entirely.
No, I call you a fool because you so clearly are one. It does not enhance my image any, I assure you.
to you, yes
maybe,
not really, not on this one anyway
to you, yes, I just wont simply agree with your statements.
how do you know if I'm little, medium or large? Still making it up as we go eh.
Or male or female?
lol! Lovely, put it on my gravestone.
Its not that you dont understand the subject or almost any of the points made, or even that you cant comprehend repeated individually tailored explanations of it. Your understanding of this thread is so absent you cant even comprehend the intention of the writer.
:) Why dont you ask them. 'Is NT a bullshit artist?'
Did you miss that it was an electronics analogy?
ok :)
:) With due regard old chap, its really quite close. Ohms law doesnt translate accurately to the space behind the rad, but its fairly close. Certaily close enough to give quite a clear picture of whats going on with the airflow.
to understand whats going on maybe?
So, despite the fact that I've done it, and it worked fine, and that I'm not the only one, you, who admittedly has done no calculations, does not understand how to model the airflow path, nor even where the heatflow bottleneck lies, can tell me it wont work. Ok. However, there is a possibility I might not buy it.
heck, why not: go on then, tell us your better way to increase heat output in a room that has a rad too small to deliver enough head under peak requirements. Be sure you list the ways in which its better. Lets say the rad delivers around half the required output.
So you dont know how to make fans nice and quiet, despite your greater understanding of this subject. I see. Did you miss the bit where I explained how that was done?
After this prompt, and with the posts and time at your disposal, can you find it now?
but didnt.
Completely illogical. Even a newcomer to thermodynamics could see where the biggest thermal resistance is, and that upping the airspeed to a handful of times that of natural convection could increase output to double as needed. But not you. Why is that?
Answer the quesion instead of resorting to ad hominem.
In your case. I choose to, I dont have to.
You've yet to point out any. Valid ones that is. Your objections are either reasons why it wont work, which persistently overlook the fact that it worked fine, or ad hominem, which is of no relevance to the question.
From what I can see of this note, you appear to have created a noiseless fan, which is blowing over an an infinite heat capacity source, which is always hot. IME, these three conditions are not feasible. I'd be intrigued to read the detailed analysis of how this miracle is achieved.
OK, I will. I would as any sensible person would do. I would work out the room steady-state heat loss and the size of the radiator(s) required. Then I would install it/them. No fans, no electrical connections and no noise. One has to wonder why you would have built such a thing instead of changing the rad. It's probably because you are incapable of changing a radiator.
I don't think modelling it as a channel is helpful either, which is why I am not modelling it as a channel. It IS a channel with one entry side and 3 exit sides. Try to grasp that concept. This isn't a model, this is reality.
Channel is an unfortunate choice of word, since it would suggest an open horizontal drainage channel & Chezy's equation* to anyone who has studied fluid dynamics. You have never studied fluid mechanics, so it doesn't suggest any such things to you. It is a duct with no sides.
You are fixated on this inappropriate electrical analogy and this is where you keep going so horribly wrong. In an electrical circuit, the current can only flow between the two electrodes. In this situation, the air is flowing from the fan discharge, back to the atmosphere by every route available.
If you could consider your block as a large number of discrete resistors connected across the same PD, then the current in any one resistor will be inversely proportional to the resistance (I = V/R and V is a constant). Something similar happens with your radiator. The airflow will be the maximum at the side bottom of the rad (little hydraulic resistance) and the heat gain will be minimum (little contact with the radiator). The airflow will be the minimum at the top centre (most hydraulic resistance) of the radiator and the temperature will be the maximum (most contact with the radiator). Most of the air will be leaking out the sides of the rad. You've arranged all those stupid little fans; their purpose is to move the air over the heat emitter. Most of the air they move is ineffective, in that it is in brief contact with, and picking up little heat from, the rad. If you'd stuck some sides on the radiator, as I'd suggested, all the air would flow from the bottom to the top and the heat transfer would be maximized.
Perfectly. Exactly like what we have not got here. The resistance is not uniform. The resistance varies according to how far the air travels in the restricted duct/channel. Most of it doesn't travel very far, it leaks out the sides.
It is not close. You only think it is close because you don't understand it. Change your uniform mental block to an array of non-uniform resistors, and it starts to get closer. Low resistance high current at the sides, high resistance low current in the middle.
You explained to me how to make the fans nice and quiet? That must have been the bit where you'd proposed running them at reduced speed. And I'd though that was a joke.
The objection to that lies in the similarity laws*; the flow rate is proportional to the fan speed*. The fan's differential pressure is proportional to the square of the fan speed*. The system differential pressure loss is proportional to the square of the flow rate*. You will excuse me if I don't feel inclined to develop the simultaneous quadratic equations for the system. The system is bollocks.
My responsibility was in cooling the room. The electronic equipment was supplied by others. The electronic cooling fans are often speed controlled by their temperature sensors, but it wasn't my problem. The fans blew heat into the room, the room cooling system removed the heat from the room. The computer fans were noisy. Axial flow fans are noisy, see below.
Quite right, there. I can't think what had caused me to assume that you were a man, Nigel.
The other problem was that you had used axial flow fans. Advantages; cheap and flat Disadvantages; noisy, inefficient. A lot of energy goes into making all that noise. They also generally can't deliver much in the way of a differential pressure. This is why they are used for car radiators, computer cooling and through-wall ventilation of agricultural buildings and why they are little used in building services.
There's a nice graph here, but they call them propeller fans.
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need to look at the pressure developed by axial fans, compared to that developed by centrifugal fans. I had looked up the characteristics of the axial fans on the link supplied by someone previously, but it didn't give a fan curve (P v Q), just gave a flow rate of 27 cfm. This is a wholly pointless value, the flow rate should always be quoted in conjunction with the system resistance for any serious application.
So, if you had imposed any resistance on the pathetic little 3" fans, the flow rate and heat transfer would have dropped off dramatically. That's why convector heaters don't use them. However, there was little resistance because most of the air flows along the path of least resistance, avoids the radiator and avoids picking up any heat.
You'd also configured it to flow upwards. Many fan convectors have a bottom outlet or a low level outlet using the coanda effect * to project warm air into the room before it rises. You are using convection to transfer the heat and the heated air will tend to rise. The tendency is increased by using a top outlet. At best you will get a temperature gradient which is hottest at the ceiling and coldest at floor level. People find this most uncomfortable*. At worst, if you had high ceilings, the heated air would rise straight out of the occupied zone*, so it might be ineffective in Victorian or Edwardian houses. A house just like yours.
I have carried out such mundane remedial works many times. I have never yet cocked up a heat loss calculation (touch wood). My rads are on a secondary MT system with weather compensation*, an indoor reference sensor and optimum start/stop*. This, incidentally, is what you seem to be pontificating about on Periodproperty.com, although you don't seem to know what it's called. The primary CT system supplies the HWS and will serve the ventilation.
There's a whole bunch of objections for you. My objections are not about whether "it worked fine" or whether you just thought it did. You have no understanding of fluids or thermodynamics and it was an ill-informed approach to an problem that could be easily solved by changing the radiator or replacing it with a fan convector. I object to your recommending your daft solutions to others.
Wind your neck in.
This denotes routine thermodynamics/heating expressions which anyone, if they feel inclined, can look up on Google, unlike "uniform resistive block" which is bullshit.
Given a bunch of valid technical reasons why your half-baked convector is Not a Very Good Idea, you clam up.
You've called me every manner of fool, alleged I had no understanding of thermodynamics and been thoroughly offensive. Your only technical input to this thread had been the phrase "uniform resistive block" which is wholly inappropriate.
You have no useful technical knowledge or practical experience in this field, but you are pontificating all over the internet, driven by own inflated opinion of your ability.
Let's do that. Does anyone else think NT is a bullshit merchant? See this.
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must have been really impressed with you.
You don't have any experience of heat recovery at all, do you?
Liar. 'Find messages by this author' shows many of your posts are to uk.comp.homebuilt, one of thoise geeky forums you don't lurk on. 'Uniform resistive block' is a phrase you had completely misunderstood and borrowed from another geeky pc cooling forum. You though you could apply it to your convector, with no understanding of the principles.
Nothing like a few latin words to try to give the impression you know something, eh?
lol, I cant believe youre back for more. How smart.
apologies for having _way_ more important things in life. Your 'valid technical reasons' were no more valid than any other reply of yours. I was tempted to get back to this thread and reply, but whats the point?
no, not every manner, though clearly some
not at all, its obvious you have some, just insufficient. As I've always said.
or wholly misunderstood by you, even after repeated explanation.
wrong again. If that were so, you'd feel no need to keep replying, since my replies would be not worth addressing. Hint: great get-out for sore egos.
yes i post occasionally on uk.comp.homebuilt, but no its not a forum about the geeky cooling stuff you were talking about. Least I've never seen anything like that there afaicr.
no and no.
This is the bit that shows how remarkably dense you are. The predictable flow of electric current in a uniform a resistive block is not a difficult concept at all. It is why the field around a magnet is the shape it is. We can use this approach to model the airflow behind the rad. But no use repeating myself.
sorry for pointing out a fact using very well known words.
This has now gotten past stupid. You really have lost any respect I ever had. You can say whatever you want, I doubt I'll reply - though I dont promise.
Go enjoy your life Aiden. I'm sure there are more constructive things in the world for you. Good luck!
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