I want the smallest possible radiator. Are there any almost silent fan assisted designs available?

[meow2222]

I know what Im talking about.

NT

[Aidan]

It won't.

You could get the fan and heater matrix from a car. The heater matrix is copper pipes expanded into ali fins. The fins are so closely packed on some that, at first glance, they look like a block of grooved aluminium. At a flying guess, I'd think you'd get 1 kW from a heater battery 200mm square, depending on the fin density, but much smaller than a rad, with or without fans.

Centrifugal fans. The options are axial flow (Vent-Axias), centrifugal or mixed flow. The impellers in fan convectors are centrifugal but are forward curved. Real, efficient, commercial fans have backward curved blades (or is that the other way round?), but look very different to the injection moulded forward curved jobs. Try Ziehl if you want to make something fancy with speed controls. Quality, but much =A3s.

Rads are frequently run off variable temperature systems, modulating boilers or weather compensated. Convectors should be run from a constant temperature system; it will still put out some heat but a variable temperature system would play havoc with any accurate control systems.

[Aidan]

Once upon a time, there was an article in a car magazine about a car being developed by some racing car constructors. They had had the bright idea of dispensing with the conventional radiator (similar to a heater battery). They were making the car with a double-skinned body; by circulating the coolant through the space, they would cool the car (similar to a CH radiator) and get rid of the drag caused by all those finny things.

A certain fluids lecturer spotted this. Dr. M (for it was he) wrote to the editor saying that, whilst this was a splended idea, he calculated the car would need a surface area similar to that of a bus (double decker) to dissipate the heat. The letter was printed. The racing car constructors replied. They said their idea would work, that these academics should stick to their labs and leave the construction of racing cars to those who knew the business, ie.., them. The letter was printed.

Come the great unveiling and the car was rolled out to much press interest. It sped off around the circuit. Then it stopped in a cloud of steam. It was wheeled back into the workshop for minor adjustments to resolve this teething problem. It hasn't been seen since.

[Anna Kettle]

[Matt]

So it was really fast then?

:-)

[Peter]

Thanks Aidan, That's good advice for my looming project.

[Aidan]

Good for sprints :-))

[look]

I agree, with forced convection the rate of cooling is faster than with natural convection (for the same temperature difference) So as long as you increase the flowrate thro' rad you will get more heat output. The heat output to size ratio can be optimised by design as in car rads or fan convectors, just as the design of a normal convector rad attempts to maximse the heat output by natural convection in a design acceptable for domestic use.

Robert royall at which net

[Set Square]

Does it have to be?

[Aidan]

Do you not think that the rate of heat transfer from the fluid to the inside surface of the radiator might be dependent on & limited by the surface area?

[Pete C]

Some fans with LEDs could look nice, more k3wl than arty maybe...

Anyway, the OP should have better luck looking for a cross flow fan (AKA tangential fan):

..etc

One of the coolermaster ones with a car heater matrix would form a nice 'mini Myson'.

I'd try a row of 80mm PC case fans first, they are pretty quiet on 5v and 3-7v 2A wall wart could run a whole load of them. eBuyer have a pretty good range.

cheers, Pete.

[meow2222]

And?

If you think that supports your case...

Its not worth getting into, you dont understand basic thermodynamics.

NT

[meow2222]

To some people, anything is art! The idea is to put the fans out of sight at the bottom behind the rad. They need to be run on reduced voltage to keep them quiet. Unfanned airlfow is so slow that even modest air movement can triple output.

NT

[Aidan]

And it is an anecdote which was used to illustrate that CH radiators that work by natural convection & radiation are not the same as radiators that are designed to use forced convection to dissipate heat. Horses for courses.

What case? I have no case. If you feel an urge to stick fans on CH radiators, go right ahead. Personally, I wouldn't bother. There are better ways of making fan convectors. What any fool can do for a quid.......

Ooooh, Hissssssy, Hissy!

Strangely, the one book that was on my desk when I read that comment was 'Applied Thermodynamics for Engineering Technologists' by Eastop & McConkey. It is, in fact, my second copy which I bought from E-Bay, the first was bought in 1976 and disintegrated from excessive use a couple of years ago. Nor was it out for use in this discussion; my son's Tech homework was about the R101 & I had refreshed my acquaintance with the perfect gas laws in order to work out the lift of the R100, from the figures for the weight & volume given in Nevil Shute's autobiography 'Slide Rule'.

If I gave a crap, I might have taken umbrage there.

[Calvin]

I don't think that's right. The fin design on all radiators I've seen is pretty basic - no more than a thin sheet of steel made into a wavy shape and spot welded to the panel. The transfer of heat from the panel to the fins is limited by the design and I think that you'd find that with a powerful fan you could get the fin temperature down quite low but the panel temperature would remain high simply because of the poor thermal transfer characteristic. Next time your heating is on try feeling the temperature on the panel, on the fins near the panel and on the end of the fins furthest from the panel. I've often toyed with the idea of boosting certain rads in this way and I suspect it would work to some degree if I could be bothered.

Wet fan heaters such as Mysons plinth heaters use a longitudinal fan and one of the features of all such fans is that over time they "sag". Once that happens they become unbalanced and start to get noisy. I know, I've got one :-( For that reason I wouldn't bother with a longitudinal fan below a panel radiator. If I was playing with such a design I'd go for small electronics fans running very slowly.

[look]

I would agree that there are many factors which affect the total heat output and without detailed modelling or actual measurements determining exactly how much each factor affects the output is difficult. However I have noticed that in myson fan convectors and skirting board convectors the fins are attached to a simple pipe, whose internal surface area is much smaller than that of a normal rad. Therefore I would assume that transfer of heat from the water to the rad is not normally a problem.

My advise would be to attach a few computer fans to a double convector rad, let the rad get to a stable temperature - measure the inlet to outlet temp diff , switch fans on and see if the temp diff increases significantly.

Robert royall at which net

[Aidan]

What's stopping you? Let us know how it turns out.

[Aidan]

There is one corrugated fin, spot welded on at about 15mm intervals. Let us say there's two fins per inch.

On proper heater batteries, the copper pipes are passed through ali or copper sheet fins which have holes punched in them. 12 or 18 fins per inch is not unusual. The pipes are hydraulically expanded to ensure a wide contact area between the pipe and the fin metal.

Now, why do you think they'd do all that? Do you think it might be possible that the amount of heat transferred is somehow related to the surface area of the heated metal?

Granny. Eggs. Suck

[meow2222]

no, just getting real.

sounds like you ought to know better then

NT

[The Natural Philosopher]

Yes. fan blown 'wet' heaters. Mine have 'smiths' on them About 1.5KW output. About 500mm square, fit in 4" depth.