# Heat Transfer Coefficient of Steel Balls

#### microelectronix

Joined Jan 21, 2008
20
Hello all,

I have a homework problem due tomorrow and I just can't figure it out. Its asking to find the heat transfer coefficient of a steel ball (W//m^2-C) with this given info:

density=8085 kg/m^3
k=15.1 W/m-C (thermal conductivity)
C=0.480 kJ/kg-C (specific heat)
alpha=3.91E-6 m^2/s (???)

Initial Temperature: 900C
Final Temperature: 600C
Air Temperature: 30C
Ball Diameter: 1.2cm

I've been going over the chapters on transient heat analysis but I don't really know where to start, given all the formulas that involve h involve other variables (such as rate of heat transfer) that I don't have. I was also thinking that finding the thermal resistance would help, since its the inverse of that.

#### Darren Holdstock

Joined Feb 10, 2009
262
I think this is a surface-area-to-volume-ratio question. Find the surface area and mass (which is proportional to volume) of your sphere, refer back to your course notes, and treat it like any other solid object.

Spheres have the lowest SA:Vol ratio of any solid, which is why they're such popular shapes with cactuses.