3- Stainless steel ball bearings have a diameter of 1.2 cm are to be quenched in water. The balls leave the oven at a uniform temperature of 900°C and are exposed to air at 30°C for a while before they are dropped into the water. If the temperature of the balls is not to fall below 850°C prior to quenching and the heat transfer coefficient in the air is 125 W/m? °C, determine how long they can stand in the air before being dropped into the water.

3- Stainless steel ball bearings have a diameter of 1.2 cm are to be quenched in water. The balls leave the oven at a uniform temperature of 900°C and are exposed to air at 30°C for a while before they are dropped into the water. If the temperature of the balls is not to fall below 850°C prior to quenching and the heat transfer coefficient in the air is 125 W/m? °C, determine how long they can stand in the air before being dropped into the water.

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Concept explainers

Conduction and Convection

When energy travels from one object to another it is said to have undergone heat transfer. Heat transfer is nothing but the transfer of thermal energy or internal energy from one thing to another, like e.g., when a vessel with water, kept on top of a burner, heats up because of the flame underneath it.

Question

3- Stainless steel ball bearings have a diameter of 1.2 cm are to be quenched in water. The
balls leave the oven at a uniform temperature of 900°C and are exposed to air at 30°C for
a while before they are dropped into the water. If the temperature of the balls is not to fall
below 850°C prior to quenching and the heat transfer coefficient in the air is 125 W/m² -
°C, determine how long they can stand in the air before being dropped into the water.
Given:
Stainless steel [ k= 15.1 W/m.°C, p= 8085 kg/m3, and Cp= 0.480 kJ/kg.°C. and a=3.95 × 106
m³/s]

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