# Question Cold air chamber is proposed for quenching steel ball bearings of diameter, D = 0.1 m and initial temperature T = 400°C. Air in the chamber is maintained at -15°C by a refrigeration system, and the steel balls pass through the chamber on a conveyor belt. Optimum bearing production requires that 70% of the initial thermal energy content of the ball above -15°C be removed. Radiation effects may be neglected, and the convection heat transfer coefficient within the chamber is 100 W/m².K. Estimate the residence time of the balls within the chamber, and recommend a drive velocity of the conveyor. The following properties may be used for the steel: k = 73 W/m.K, a = 2 x 10-5 m²/s, and cp = 450 J/kg.K. Ball bearing Cooling chamber 50 m

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Transcribed Image Text: Cold air chamber is proposed for quenching steel ball bearings of diameter, D = 0.1 m and initial temperature T = 400°C. Air in the chamber is maintained at -15°C by a refrigeration system, and the steel balls pass through the chamber on a conveyor belt. Optimum bearing production requires that 70% of the initial thermal energy content of the ball above -15°C be removed. Radiation effects may be neglected, and the convection heat transfer coefficient within the chamber is 100 W/m².K. Estimate the residence time of the balls within the chamber, and recommend a drive velocity of the conveyor. The following properties may be used for the steel: k = 73 W/m.K, a = 2 x 10-5 m²/s, and cp = 450 J/kg.K. Ball bearing Cooling chamber 50 m
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Transcribed Image Text: Cold air chamber is proposed for quenching steel ball bearings of diameter, D = 0.1 m and initial temperature T = 400°C. Air in the chamber is maintained at -15°C by a refrigeration system, and the steel balls pass through the chamber on a conveyor belt. Optimum bearing production requires that 70% of the initial thermal energy content of the ball above -15°C be removed. Radiation effects may be neglected, and the convection heat transfer coefficient within the chamber is 100 W/m².K. Estimate the residence time of the balls within the chamber, and recommend a drive velocity of the conveyor. The following properties may be used for the steel: k = 73 W/m.K, a = 2 x 10-5 m²/s, and cp = 450 J/kg.K. Ball bearing Cooling chamber 50 m