In a ball bearing production facility, steel balls (k=50 W/m.K, c=0.460 kJ/kg.K, ρ=7865 kg/m3) that are each of 13,99 mm in diameter are annealed by first heating them to 870 oC and then slowly cooling in air to 125 oC. If the cooling air stream temperature is 60 oC, and it has a convective heat transfer coefficient of 35 W/m2.K), determine the time [s] required for the cooling.

In a ball bearing production facility, steel balls (k=50 W/m.K, c=0.460 kJ/kg.K, ρ=7865 kg/m3) that are each of 13,99 mm in diameter are annealed by first heating them to 870 oC and then slowly cooling in air to 125 oC. If the cooling air stream temperature is 60 oC, and it has a convective heat transfer coefficient of 35 W/m2.K), determine the time [s] required for the cooling.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.36P

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1.60 Two electric resistance heaters with a 20 cm length and a 2 cm diameter are inserted into a well-insulated 40-L tank of water that is initially at 300 K. If each heater dissipates 500 W, what is the time required for bringing the water temperature in the tank to 340 K? State your assumption for your analysis.
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Plasma spraying is a process used to coat the surface of a material with a protective layer to prevent material degradation. In a plasma spray process, the protective coating in powder form is injected into a plasma jet. The powder is then heated until the droplets coalesce and are propelled over the surface of the material. Once deposited on the surface of the material, the molten droplets solidify and form a protective coating layer. Consider a plasma spray process using alumina (k = 30 W/m K, ρ = 3970 kg/m³ and cp = 800 J/kg K) powder that is injected into a plasma jet at T∞ = 15,000 ° C and h = 10,000 W/m²·K. Alumina powder is made up of spherically shaped particles with a mean diameter of 60 μm and a melting point of 2300 °C. Determine the amount of time it would take for the particles, with an initial temperature of 20 °C, to reach their melting point from the time they are injected into the plasma jet. Note: Give the solution from fundamental concepts of how the heat flow…
Plasma spraying is a process used to coat the surface of a material with a protective layer to prevent material degradation. In a plasma spray process, the protective coating in powder form is injected into a plasma jet. The powder is then heated until the droplets coalesce and are propelled over the surface of the material. Once deposited on the surface of the material, the molten droplets solidify and form a protective coating layer. Consider a plasma spray process using alumina (k = 30 W/m K, ρ = 3970 kg/m³ and cp = 800 J/kg K) powder that is injected into a plasma jet at T∞ = 15,000 ° C and h = 10,000 W/m²·K. Alumina powder is made up of spherical-shaped particles with a mean diameter of 60 μm and a melting point of 2300 °C.Solving, the amount of time it would take for the particles, with an initial temperature of 20 °C, to reach their melting point from the time they are injected into the plasma jet is 5,25x10 -4 s. Explain how the heat flow behaves in the system, using the…