[OT] - Process Cooling Methods

Before I jump into my question, here is some background.

We have a production line where we make hot metal parts that need to cool before dumping them into a bin. Our old technology to do this is a conveyor through an air tunnel where we blow fresh air across the parts. "Normally" this method works OK but on occasion our finished parts go out of spec. This is commonly seen as a relatively small problem and almost nobody is paying it much attention. However, we are about to build another line and I am questioning the wisdom of installing the same technology. Clearly "fresh" air swings wildly in both temperature and humidity from day-to-day, season-to-season and, consequently, we can't help but see a variation in the effectiveness of heat removal.

My question is this: short of putting in a huge air conditioning system to process the air before it is used in the cooling conveyor, does anyone know of other effective ways to reduce the variability caused by using fresh air?

Thanks in advance.

Steve

How about changing the speed of the cooling conveyor, based on outside air temperature ?

Or changing the speed of the air in the tunnel ?

I'm in the process of trying to solve the same problem at the exit of a paint system in our plant. The solution I'm trying to get installed is a high-velocity air blow off system at the exit of our cooling tunnel. The equipment is made by a company called Air Force One (www.af1.com). It uses a blower to force ambient air at high velocity across the parts as they move down the conveyor. I've used this equipment in the past as a means for drying parts after a wash station and it was extremely effective at that. Since I have not been successful yet at getting the equipment approved in our plant, I can't vouch for its effectiveness for this application, but the company claims to have been able to cool hot, heavy parts to within 25 deg F of ambient in one pass. If your parts are heavy enough to withstand the near hurricane conditions the system creates, or are secured enough on the conveyor, this might work for you as well.

theDave2 said:

How about changing the speed of the cooling conveyor, based on outside air temperature ?

Or changing the speed of the air in the tunnel ?

Click to expand...

I have already designed in control-ability to both of these by way of VFDs on all AC motors. Furthermore 60Hz corresponds to the nominal speed we think we need for each motor.

cbuysse said:

..If your parts are heavy enough to withstand the near hurricane conditions the system creates, or are secured enough on the conveyor, this might work for you as well.

Click to expand...

Unfortunately there is a cooling rate I also have to try to work around (I should have mentioned this in my initial write-up..sorry). This means that I can't just overpower it and get the parts too cool, too fast.

Steve

A possible solution
setup a radiator (car or truck type) filled with water
duct your air through it
The temperature should remain fairly constant

What is the temperature range there - centigrade please - It's too long ago since I remember Farenheight

Is it possible that your conveyor belt may be 'heating up' as your process is running - you may need to force cool the actual belt before it sees the next part.

iant - I like it. I don't know if anybody else here will, but that's at least the kind of thinking I am looking for.

The temperature range is ~870C (1600F) at the beginning of the conveyor and then discharge at something less than 590C (~1100F), so, as you suggest, the conveyor is definitely heating up as we run. And, no, we are not attempting to cool it in any way - yet.

Steve

I don't know the volume, but if you are just using ambient air now, how much more control do you want?

If you have a cooling tower somewhere with excess capacity, I'd run that supply through a standard industrial air/water heat exchanger in the ducts. There are many made for this purpose. There can be a problem if the external air temperature is too cold though, then the coils will freeze unless you keep the water flowing.

Thanks rdrast, that is probably what I will propose. We have a number of cooling towers - most are pretty loaded already, but we'll see - so coming up with a heat exchanger system should be do-able.

As for cold weather, this should be a known issue. As I mentioned, we already have cooling towers so we should not introduce any new problems there. Furthermore, having air that is too hot and too humid air (I believe) will be my big problem. We already have motorized louvers in the design that will let us draw air from either inside the plant or from outside. Hopefully this will allow us to compensate for cold weather. If it doesn't, we can pipe the heat exchanger to utilize warm water in winter.

Steve

Steve,
I only mentioned the cold, as we have similar systems here, which use outside air from ducts through the wall, and even with precautions manage to freeze at least one of the heat exchangers each winter.

For the humidity, most of the industrial heat exchanger coils have a drip pan at the bottom of the enclosure, and we just pump the condensate into a convenient drain with little self-contained sump pumps.

For our 'cold' supplies, we do run the heat exchanger source through a set of two way valves, and do an auto switchover from the chill water to the heated water when the outside ambient drops below 40F. After that, we use control valves to control the flow through the exchanger, maintaining a minimum flow when on hot water.

So you have a Delta T of 300 deg.C over the length of your chain mesh conveyor - Are you blowing air from multiple sources ?
Can or do you blow air through the conveyor at the same time?
I believe a closed loop water type heat exchanger system with several output duct sections would be your best option.
Evap. type systems are too humid ans A/C systems are too expensive to run.

Seems to me that using a water/air exchanger will increase the humidity levels in your cooling air stream. That is not a desired outcome in your situation (as you have stated).

Conceptual thought ...
We use vortex air conditioners that use compressed air to cool control cabinets.
Could you use that technology to lower the ambient temperature of your cooling air stream? This would not introduce humidity into the air stream.

Like I said, just a thought.

I said Closed Loop - like a car or truck radiator system.
No contact with the water at all.
Force air through the radiator fins (Heat Exchanger)

A slight missunderstanding

Like Oakley I was about to suggest vortex coolers as I'm a big fan of them. We use them for cooling control cabinets too, especially ATEX enclosures. It's amazing how much cooling that you can get from such a small device

Steve has said he needs a more controlled cooling process in post #4

I guess knowing the size of the system might be helpful here, too. We have two conveyors, each with its own tunnel and each will be using two (2) 10,000 cfm fans, one supply and one exhaust, to create our air flow. That makes a total of four (4) fans.

Steve