Heat transfer at box

[engmechs]

Hi all,

I am a new comer, and I have a question, regarding an heat transfer application to a steel box unit. The box is mounted at wall ceiling corner, it has a heat generation source inside the box. The est. power source pumped into the box is about 10 to 15 W. Aim is to minimze temp. increase within the box as much as possible.

My initial plan is to mount a heat conduit from heat source to connect to a heat sink for convection. What do you think? Make sense?

Thanks in advance.

Mechengs

 

[ko99]

Yes, that's typically the best way to handle it. A few suggestions:

1. The heat sink fins should be exposed to the external air.
2. Fins are best oriented vertically with space above and below for air entry and exit.
3. Leave sufficient spacing between the fins to encourage natural convection: air gap of ~0.20" is a good start.
4. You'll get better performance if you can connect your 'conduit' directly to the heat sink (not the steel).
5. Size the conduit to handle the power (estimate with dT = L/KA)
6. Pay attention to the thermal interfaces.
7. You didn't describe the heat source, but it's important to connect the conduit directly to it, or calculate the additional dT if you can't.

These are general suggestions. 10-15W is not a lot and the heat transfer path can probably handle some imperfections and still perform satisfactorily.




ko (

http://www.ecooling.biz)

 

[engmechs]

Thanks ko99 for your comments!

What happen if the power input is doubled? What sort of limitations will this design encounter?

 

[ko99]

If the power is doubled, the temperature rise is doubled.

I can't tell you the limitations since I don't know the details but if your situation is typical, the sink-to-air will be the limitation. By this I mean you may have the design freedom to size the conduit sufficiently and minimize interface losses, but you may not be able to make the heat sink large enough. If you hit this point, forced convection (a fan) is the most common solution, but certainly not the only one.

ko (

http://www.ecooling.biz)

 

[engmechs]

Putting a fan in the unit, what about the airflow volume to pass the heat sink? Since the design is for ceiling corner mount, the heat sink is primarily located at the back. Enough airflow is another factor. ie. Air inlet & air outlet area to keep continuous air movement. Is that right?

 

[ko99]

Not sure I understand your question.

Yes, you want free air movement thru the fins. For example the fins should not extend right up to the ceiling or there's no exit path.

Putting a fan inside a sealed box is not going to help much. The fan should blow on the sink fins. If natural convection isn't enough and you can't put a fan outside the sealed enclosure, you'll need another solution.

Of course, if you can add vents to the box, then you don't need the conduit to an external sink: just put the sink directly on the heat source and add an internal fan if necessary.

ko (

http://www.ecooling.biz)

 

[engmechs]

Thanks for your comments again. I have a clearer idea on this issue. Really appreciate it.

May I ask another question: What happen if I want to make the box a properly sealed type design to make it water resistant, at the same time, still want to use the heat sink idea. My concerns would be the cable connections & the fan itself would be the weakest spots in the idea. Wouldn't it? I found some type of water resistant fan, but I have no experience in it. Can you shine some lights on it?