## Time and cfm for cooling aluminum rods

## Time and cfm for cooling aluminum rods

(OP)

Good afternoon;

Could someone assist me in verifying my calculation? Or point me in the right direction to a reasonable estimation?

I am attempting to work out a decent mathematical model for cooling round solid rods on a cooling bed. The material needs cooled from a high of 700*F to 150*F with a max summer temp of ~90*F.

Cooling bed 150' x 40'

Aluminum rods in 3,5,8"

Up to 120' length

Delta T 450*F

I have a possible solution available currently.

#1 up to 6 individual fans at 34K cfm 1.75"wg spaced every 20' blowing perpendicular to the rod as a fin.

I performed a mass comparison:

Mass of 20' section in size of 3,5,8"; times specific heat divided by ration of temps.

Mass of fan times specific heat.

I divided the total heat required by the fan total cooling capacity which gave me:

2" 3 min.

5" 16 min.

8" 41 min.

I can't use water per customer requirements. The cooling bed is the most open location which supports our plans. I wish to follow KISS which leads us to forced air cooling.

Thanks

Rich

Could someone assist me in verifying my calculation? Or point me in the right direction to a reasonable estimation?

I am attempting to work out a decent mathematical model for cooling round solid rods on a cooling bed. The material needs cooled from a high of 700*F to 150*F with a max summer temp of ~90*F.

Cooling bed 150' x 40'

Aluminum rods in 3,5,8"

Up to 120' length

Delta T 450*F

I have a possible solution available currently.

#1 up to 6 individual fans at 34K cfm 1.75"wg spaced every 20' blowing perpendicular to the rod as a fin.

I performed a mass comparison:

Mass of 20' section in size of 3,5,8"; times specific heat divided by ration of temps.

Mass of fan times specific heat.

I divided the total heat required by the fan total cooling capacity which gave me:

2" 3 min.

5" 16 min.

8" 41 min.

I can't use water per customer requirements. The cooling bed is the most open location which supports our plans. I wish to follow KISS which leads us to forced air cooling.

Thanks

Rich

## RE: Time and cfm for cooling aluminum rods

Because you have not considered connective heart transfer coefficient aluminum to air.

## RE: Time and cfm for cooling aluminum rods

https://www.engineersedge.com/heat_transfer/convec...

Thanks

## RE: Time and cfm for cooling aluminum rods

You do not yet.

It will likely not be constantly.

## RE: Time and cfm for cooling aluminum rods

TTFN (ta ta for now)

I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

## RE: Time and cfm for cooling aluminum rods

Could I model a 20' section as representative of the length with 1 fan at the center line?

Then the Hc could be averaged from center of the fan to the end?

Thanks for the replies.

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

If I have a known fan doing 34K cfm

Use CFM* delta t *1.08 = btu/hr

The aluminum is a set variable.

mass * specific heat * delta T = btu

I understand the temp of the surface will be cooling than the temp of the center.

I am using Bohn and Keith Heat and mass transfer. The example I found uses biot and fourier numbers for graphing.

Thanks

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

Are they uniformly hot (as if coming out of a furnace,) then cooling off in mid-air (whether forced or natural convection)?

Or are they connected at one end to a hot mass, then the heat energy flows down the rods through the open air flowing past the three groups of rods?

No fins on the horizontal solid rods, right?

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

## RE: Time and cfm for cooling aluminum rods

Bset regards, Morten

## RE: Time and cfm for cooling aluminum rods

Not a thermal engineer of any kind, just curious. Wouldn't the forced convection heat transfer mode dominate? Then following on from the convective heat transfer wouldn't conductive heat transfer be the next most significant? Or am I misunderstanding what a cooling bed is? (I'm picturing a group of rods sat on a metal tray of some sort). Wouldn't radiative heat transfer be the least significant mode at these temperatures? And wouldn't the magnitude of the convective heat transfer render the other modes insignificant?

I just have this vague recollection from university that the magnitude of heat transfer via forced convection is something like 10

^{6}times the magnitude of heat transfer via conduction, which is again something like 10^{4}times the magnitude of the radiative heat transfer (in most everyday engineering situations).Thanks,

GSTP

Graduate Mechanical Design Engineer

UK

## RE: Time and cfm for cooling aluminum rods

TTFN (ta ta for now)

I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm