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Question -

A ‘thermacole’ icebox is a cheap and efficient method for storing small quantities of cooked food in summer in particular. A cubical icebox of side 30 cm has a thickness of 5.0 cm. If 4.0 kg of ice is put in the box, estimate the amount of ice remaining after 6 h. The outside temperature is 45°C, and coefficient of thermal conductivity of thermacole is 0.01 Js-1 m-1 °C-1 [Heat of fusion of water = 335 x 103 J kg-1 ].



Answer -

Each side of the cubical box (having 6 faces) is 30 cm = 0.30 m.Therefore, the total surface area’ of the icebox exposed to outside air is A =6 x (0.30 m)2 = 0.54 m2. The thickness of the iceboxis d = 5.0 cm = 0.05 m, time of exposure t = 6h = 6 x 3600 s and temperaturedifference T1 – T2 = 45°C – 0°C = 45°C.
.•. Total heat entering the icebox in 6 h is given by

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