During arc welding of aluminum, molten metal droplets are ejected. some of these droplets are hot enough to ignite and form sparks. most droplets are ejected at lower temperatures and simply cool down. a molten droplet has a diameter of 0.5 mm and is initially at ti=1600 °k with a velocity of 1 m/s. assuming a combined radiation-convection heat transfer coefficient of 20 w/m2 . °k, estimate the rate of cooling (dt/dt) for the droplet in air at t=20 °c. use the following properties for liquid aluminum at 1600 °k: density= 2100 kg/m3, c=1100 j/kg. °k., k=200 w/m. °k.