Heat Transfer Coefficient of Steel Balls

Discussion in 'Homework Help' started by microelectronix, Apr 20, 2009.

  1. microelectronix

    Thread Starter Member

    Jan 21, 2008
    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.
  2. Darren Holdstock

    Active Member

    Feb 10, 2009
    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.