A metal ball of diameter 60 mm is initially at 220°C. The

A metal ball of diameter 60 mm is initially at 220°C. The ball is suddenly cooled by an air jet of 20°C. The heat transfer coefficient is 200 W/m²K. The specific heat, thermal conductivity and density of the metal ball are 400 J/kgK, 400 W/mK and 9000 kg/m³, respectively. The ball temperature (in °C) after 90 seconds will be approximately

C_P = 400 J /kg-K
K = 400 W/mK
ρ = 9000 kg/m³
Time (τ) = 90 sec

	hA			τ
	ρVC_P

	T_i - T_∞	= e
	T - T_∞

Put	A	=	3	= 100
	v		R

	hA		τ =		200 ×	3	×	1	×	1		× 90 = 0.5
	ρVC_P					0.03		9000		400

	220 - 20	= e^0.5
	T - 20

By solving, we get T = 141.3°C