Determine the instantaneous rate of heat transfer from a 15c

Determine the instantaneous rate of heat transfer from a 1.5-cm-diameter ball bearing with a surface temperature of 150°C submerged in an oil bath at 75°C if the surface convective heat transfer coefficient is 850 W/m² °C. (Ans.: 45 W)

Solution

h= 850 W/m2 °C

r = 0.75 x 10^(-2) m

T₀ = 150 °C T_inf = 75 °C

So, instantaneous rate of heat transfer = h x A x (T_{0 -} T_inf)

= 850 x 4 x 3.14 x(0.75 x 10^(-2))^2 x (1560-75) = 45.0622 W