Stacked Plate Radiators 1

[TChronos]

In the 1960's, several auto companies experimented with stacked plate radiators. Here are a couple of pics and a write up:

http://xked.com/gallery/zoom/?id=4943

http://www.dewitts.com/images/product_940.jpg

http://www.dewitts.com/pages/dewitts.asp

This style of heat exchanger is still used for oil coolers, but you no longer see radiators made this way.

The advantages seem pretty obvious to me: greater tube/fin contact, simple construction, high strength, light weight, and less flow restriction. The only downside I see is that they are harder to repair, since the tanks and tubes are integral. The obvious question is, why are they no longer used?

 

[daubery]

Hi TChronos,

You have a very interesting question there. Those are really great links.

I wonder if these radiators were just either too costly to produce, or perhaps had very high production problems due to their complexity?

I note that some new charge-air-cooler designs have recently emerged with a similar design.

I would too love to know the answer to your question.

Regards,

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )

 

[TChronos]

They were cheap to produce. The problem has to lie with maintainability.

 

[shabba]

I am far from an expert as you guys probably are, especially Des, but correct me if I am wrong in thinking that, a series of tubes has more surface area than a 'plate'? Furthermore, isn't it an advantage of modern style tube-type (for want of a better expression) rads that the tubes han be staggered? for increased turbulence?

It is a very interesting point though. In fact, all the air-oil HE's I've seen have been 'plate' types, I wonder if the increased contiguous cross-section aids higher viscosity fluids? Have engine coolants become less viscose?

 

[TChronos]

I think the flat plate allows more contact between tube and fin, which greatly adds to cooling. Fin design can always be manipulated for more airside turbulence. Plate-style oil coolers often incorporate "turbulators" into the fluid side: these are corrugated internal structures which promote turbulence.

Another advantage is that the flat plate design allows additional heat transfer via the tanks.

I think there's a lot of virtue to the design, still wondering why it was abandoned.

 

[daubery]

Hi 'shabba',

In practice, the flat-tube / plate-type of tube actually produces a radiator with superior 'Heat-Transfer per Unit Volume' - power density...

A lot has to do with the multi-louver fin design for flat tubes / stacked plates, being far more efficient than that found with round tubes in 'flat-fin' radiators.

Stacked flat plates are fantastic from a modular point of view - to get more surface area, just add more plates...

I will do some more investigating & come back to this thread when I have a more clear understanding of why these designs were discontinued...

Regards,

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )

 

[finman]

I think the reasoning behind the Stacked plate method being sidetracked is the cost of tooling and the amount of waste material generated by the pressing of the elements.
Fin and tube method of assembly generates very little scrap material and is far more flexible to radiator size change.

On the manufacturing side it's easier to braze a fin and tube unit with a continuous "Nocolock" brazing plant, (it's difficult to get the flux around all of the joints in a stacked plate unit!). I think most of the stacked plate manufacturers used to use Salt bath brazing which is currently falling in favour possibly due to environmental pressures.

If we are talking just Water radiator here then repairwise I do not see any specific advantage in either method

 

[daubery]

Good comments 'finman'... I would agree with you on the waste material generated from pressing the plates...

Another thought, what material gauges were used for these plates - and their associated fins?

My reasoning here is that with the constant economic pressure on material down-gauging & cost-cutting, in addition to weight-saving - perhaps the current brazed Nocolok flat-tube/corrugated multi-fin designs may be superior... in terms of cost & mass...

Regards,

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )

 

[finman]

Des, I think you need to take on the full picture not just the material content. On the units I've experience of, the Nocolock Radiators win, Cheaper to make, less waste and with clever design of the secondary surface better performance.

I've disected a couple of Stacked type oil coolers, the plates were 0.5mm thick with 0.30mm thick fins, old technology!

We built a number of different configurations of Nocolock brazed units utilising both the standard type of seam welded tube (0.3mm wall) and Extruded tubes (1.0mm wall) with optional inserts in both. Fins were around 0.127mm. We covered Water radiators, Charge Air Coolers and Oil coolers from 150 x 80 x 32mm upto 1400 x 800 x 150mm all on one line using the same build fixtures and material stock.

 

[TChronos]

A few more questions:

1) I don't see why a stacked plate design would necessarily mean a thicker fin: what precludes use of a .127mm fin?

2) A stacked plate line would be able to produce cores of any height, but would be limited to the widths of the available stampings. Wouldn't a standard set of widths provide adequate flexibility? I think that a dozen stampings of various lengths would cover the most common automotive applications. Alternatively, a bar and plate style (ie a plate core, with separate header tanks) would allow any width to be made with a single extrusion, rather than a pressing. Bar and plate would also minimize waste.

3) DeWitt claims to manufacture using controlled atmosphere brazing...doesn't that eliminate the environmentally unfriendly salt bath?

4)Doesn't the plate style have better power density?

I'm going to have access to a vintage stacked plate radiator shortly, I'll post dimensions.

 

[daubery]

A thought... What about continuous feeds of top & bottom 'tube shells' (chevron pattern)... tube-chevron-profiler stops momentarily to provide clean ends... We now have a nice thin/narrow plate-type tube... Feed in fin... move fin/tube matrix... repeat process...

Result, thin materials, strong core matrix.

Tube ends can be 'wrapped over' before headers are applied...

Another option is a continuous top/bottom tube shell machine, with partial edge brazing (or full edge brazing - tricky, but possible) - you now have a formed tube... clean up tune ends for entry into header... Backfill tube-header joint with special slurry prior to entry into furnace...

Fin thickness can now be reduced to around 0.80 mm allowing for more refined louvers... & much improved heat-transfer & 'power density'... you may just be shocked as to HOW much...

Some ideas for further thought... (I have had design concepts for "core matrix 'sheet'" ie. standardised core-matrix, cropped to size... for a long time...). Now, this is a project I would LOVE to be involved in...

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )

 

[finman]

Hey don't get carried away, I didn't say that stacked plate materials needed to be thicker! it's just the ones I've measured are thicker.

I don't think that many OEM's would go for the 12 basic sizes units though, every enquiry that I've be connected with gives a "space envelope" and a performance requirement, this is want drives the size flexibility issue, every user wants something different.

I did an exercise on rationalising a range of radiators for one model of one make of car, the OEM catalogue listed 52 different units! not all of them were different core lengths I grant you but this gives some idea of the scale of the issue.

I must admit I've never heard of DeWitts! but are they in the league of Delphi, Valeo, Behr etc etc.

I guess you sum up your points of view when you are examining "Vintage" radiators!!!!!!! (tongue in cheek, sorry mate)

 

[TChronos]

DeWitts is a tiny manufacturer, their one and only product, as far as I know, is a repro of the stacked plate radiators used in 60's Corvettes.

My project is similar, reproducing a stacked core radiator used in a vintage car. The cost of tooling for the plates is prohibitive for the size of the market. I'm hunting for potential applications for the same stamping, to help offset the set up cost. That's why I'm interested in understanding the strengths and weaknesses of the design.

 

[daubery]

Hi 'finman & TChronos',

With my idea I was refering to using 'extremely thin gauge strip' as the basic construction material... to give a very lightweight end product... can even be manufactured in Nocolok or CuproBraze technology... obviously geared to high-volume production, though... :-(

Actually, it is amazing what you can do with strip - multiport tubes etc...

Regards,

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )

 

[finman]

TChronos I mistook your intensions, It may prove to be a good construction for Class 8 truck Charge Air, I know may application share the same basic block size, also the static hydraulic cooler market maybe a potential target.

 

[homevictory]

Gentlemen:

Please see the following link:

http://www.longmfg.com/web/longwebf...cc05256c650003652a/$FILE/LNG013_Cat_Final.pdf

My point is it is still in use.

Tony Liang

 

[finman]

I don't think that any of the contributors to this thread dispute the fact that stacked plate units are still in use.

The application is usually for oil cooling and sold in modular sizes as an "off the shelf" product.

The thread is to discuss it's use in high volume water radiator applications and why it fell out of favour (see the first message).

 

[DrCool]

All of you have very interesting and informative comments. My 2cents coming from the Aviation and Marine industry (not automotive) has a diferent perspective.
We seldom manufactured radiators but employed vacuum brazing to make mostly oil coolers for General Aviation aircraft.
Nokolok is for high volume and as I understand requires licencing for the use of this process, we could never compete with Long and Modine because of this. Controlled Atmosphere or "CAB" is also high volume and expensive to implement and maintain, thats why you probably don't see too many small outfits offering CAB.
Vacuum brazing is a little tricky but has virtually replaced the old "Salt Vats" although George industries in Elmira, NY still maintains this process as it still has it's place for certain items. Vacuum furnaces are cheap and can be fired up and run with small batches of cores if necessary, The design of heat exchangers has also evolved from the use of theses furnaces as well. A lighter cross section and thinner tube sheets all combine for a more efficient cooler and the aluminum industry has answered the demand for brazable cladding and special alloys designed specifically for this purpose...but where are the stacked plate units they are now the design of choice for corrosive environments, especially the marine industry. Hope this reply was informative!

Bill Kay
Sandusky OH

 

[finman]

Hi DrCool.
I must admit to being Pro CAB as that is my experience, we successfully managed to produce low volumes in batches with our furnace line.
I'm not so sure that the Vacuum - Cab comparisons hold up to well as I believe that component fit up has to be far closer with Vacuum than with CAB, this add to the manufactured costs.
We were taken over by a far larger company that used Vacuum brazing with a first time pass rate of 15-20%, we utilised CAB on a far tighter budget and were achieving 85-90% first time passes (this was within 6 months of getting our furnace line running and improvements were in place to get to the magic 95-97%).
In the UK there are quite a few smaller companys utilising home brewed CAB lines, take a look at Pace Products' web site.
All of my manufacturing experience is with Air Blast units (radiators) although I'm confident that I could braze a stacked plate unit if the need arose.
I'm interested to hear more on using Aluminium Stacked plate units in corrosive atmospheres, do you use a special coating to protect the aluminium?

 

[TChronos]

"they are now the design of choice for corrosive environments, especially the marine industry. "

Dr Cool: Are they being used as oil coolers? Or for glycol coolants? Can you point me to some examples?