# Answer to Question #241215 in Mechanical Engineering for shaym

Question #241215

A spherical ball of diameter 20 mm is initially maintained at a uniform temperature of 400 °C. It is first subjected to heat (h = 10 * W/(m ^ 2 - K)) treatment first by passing ambient air at 20 °C until the temperature at its center line is lowered down to 335 °C. The spherical ball is next dipped in a liquid pool at 20 °C with a very high heat transfer coefficient (h = 6000 * W/(m ^ 2 - K)) due to boiling until the center of the sphere cools down to 50 °C. What is the overall time required to complete this heat treatment plus quenching process.

Assume the following material properties: rho = 3000 kg / (m ^ 3) , C =

1000 J kg-K' rho = 3000 kg / (m ^ 3) , a = 6.66 x 10-6 m² / sec

1
2021-09-24T02:12:50-0400

D=20mm,r=10mm=0.01m

h1=10W/m2K

T1=335°C

h2=6000W/m2K

T2=50°C

C=1000J/kgK

=6.66*10-6m2/s

t1=187.6s

t2=3.91s

Overall time,t=t1+t2

=(187.6+3.91)s

=191.51s

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