×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

quick question regarding addition of a steel plate

quick question regarding addition of a steel plate

quick question regarding addition of a steel plate

(OP)
Hello

I have an aluminium light fitting (see attachment) which has 3 LED's inside.  The temperature of the LED's is around 95 degrees under normal operating conditions.   When we added in a mild steel plate 0.90mm thick, we expected the temperature of the LED's to rise, but it didn't, the temperature actually reduced!  

As the thermal conductivity of steel is less than aluminium, the steel plate should surely act as a thermal barrier, and the temperature should rise. But this is not the case, can anyone provide a short explanation.

It's actually a good thing that the temperature doesn't rise, as the lower the temp of the LED, the longer it lasts. I just don't understand why it went down!  

RE: quick question regarding addition of a steel plate

WHERE DID YOU ADD THE STEEL PLATE?

And why is it surprising?  Is the thermal conductivity of the steel worse than that of air?  Did the overall surface area decrease?

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: quick question regarding addition of a steel plate

(OP)
Hi IRStuff, thanks for your help,

The alu body is made from an alu plate 6mm thick, that is connected to the alu finned section, the steel plate was added in between them.

As I understand it, the less heatsinking, the higher the temperature of the LED.  But although the K of steel is higher than air, it is less than alu. Even though the surface area is slightly increased, by the steel plate 0.9mm thick, I thought that as there are two additional thermal boundaries, and a material of lower K than alu added to the body, then the temperature of the LED would have increased?

Or am I just not understanding heat transfer basics!!

  

RE: quick question regarding addition of a steel plate

Note that you already had one interface, so you only added one additional interface, in addition to the bulk thermal resistance.

What was the change in temperature?

IF you added thermal resistance, then yes, you'd expect a temperature rise.  However, if the plate is only .9 mm, that's equivalent to about 3.6 mm of Al, which should not be that drastic an increase, in of itself.  

Moreover, it's possible, not knowing the full details of the structure, that the steel is actually improving the transmission of heat from the body to the fins, through a better thermal contact, and/or better heat spreading.  

My impression from the drawing is that the body is essentially hollow and the heat is being transmitted to the fins along the rim of the body.  If so, then the heat has to work its way back to the center of the heat sink before it can move up to the top.  The steel would then reduce the thermal resistance to the center of the heat sink.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: quick question regarding addition of a steel plate

In effect you have slightly increased the surface area exposed to the ambient temprature.

RE: quick question regarding addition of a steel plate

Instead of steel, use a thin phenolic plate if you want to increase the LED temp.  

RE: quick question regarding addition of a steel plate

(OP)
Thank you both very much, you've been great help!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources