Question

CHAPTER FOUR UNSTEADY STATE CONDUCTION 1. A long 18 cm diameter bar made of hardwood (k = 0.159 W/m·K, a = 1.75 X10^{-7} m^2/s) is exposed to air at 30 °C with a heat transfer coefficient of 8.83 W/m^2·K. If the center temperature of the bar is measured to be 15 °C after a period of 3 hours, determine the initial temperature of the bar. 2. Consider a 7.6 cm by 3 cm diameter cylindrical lamb meat chunk (? = 1030 kg/m^3, Cp = 3.49 kJ/kg·K, k = 0.456 W/m·K, a = 1.3 X10^{-7} m^2/s), fifteen such meat chunks initially at 2 °C are dropped into boiling water at 95 °C with a heat transfer coefficient of 1200 W/m^2·K. Determine a) The amount of heat transfer during the first 8 minutes of cooking, b) the time it takes for the center temperature of the meat chunk to rise to 75 °C. EXTERNAL FORCED CONVECTION

          CHAPTER FOUR
UNSTEADY STATE CONDUCTION
1. A long 18 cm diameter bar made of hardwood (k = 0.159 W/m·K, a = 1.75 X10^{-7} m^2/s) is
exposed to air at 30 °C with a heat transfer coefficient of 8.83 W/m^2·K. If the center
temperature of the bar is measured to be 15 °C after a period of 3 hours, determine the
initial temperature of the bar.
2. Consider a 7.6 cm by 3 cm diameter cylindrical lamb meat chunk (? = 1030 kg/m^3, Cp
= 3.49 kJ/kg·K, k = 0.456 W/m·K, a = 1.3 X10^{-7} m^2/s), fifteen such meat chunks initially
at 2 °C are dropped into boiling water at 95 °C with a heat transfer coefficient of 1200
W/m^2·K. Determine a) The amount of heat transfer during the first 8 minutes of
cooking, b) the time it takes for the center temperature of the meat chunk to rise to 75
°C.
EXTERNAL FORCED CONVECTION

CHAPTER FOUR
UNSTEADY STATE CONDUCTION
1. A long 18 cm diameter bar made of hardwood (k = 0.159 W/m·K, a = 1.75 X10^-7 m^2/s) is
exposed to air at 30 °C with a heat transfer coefficient of 8.83 W/m^2·K. If the center
temperature of the bar is measured to be 15 °C after a period of 3 hours, determine the
initial temperature of the bar.
2. Consider a 7.6 cm by 3 cm diameter cylindrical lamb meat chunk (? = 1030 kg/m^3, Cp
= 3.49 kJ/kg·K, k = 0.456 W/m·K, a = 1.3 X10^-7 m^2/s), fifteen such meat chunks initially
at 2 °C are dropped into boiling water at 95 °C with a heat transfer coefficient of 1200
W/m^2·K. Determine a) The amount of heat transfer during the first 8 minutes of
cooking, b) the time it takes for the center temperature of the meat chunk to rise to 75
°C.
EXTERNAL FORCED CONVECTION

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