24. (a) A large rotomoulded polyethylene tank is 4 m wide, 3 m high and 2 m deep. If it is manufactured in a sheet metal

[answerhappygod]

24 A A Large Rotomoulded Polyethylene Tank Is 4 M Wide 3 M High And 2 M Deep If It Is Manufactured In A Sheet Metal 1 (51.53 KiB) Viewed 27 times

24. (a) A large rotomoulded polyethylene tank is 4 m wide, 3 m high and 2 m deep. If it is manufactured in a sheet metal mould of the same dimensions, what mass of polyethylene powder is required to ensure that the product has a wall thickness of 8 mm. The density of polyethylene is 970 kg/m [4 marks] (b) If the rotationally moulded polyethylene product in (a) has a final wall thickness of 8 mm, estimate the time taken for the inner free surface of the moulding to cool from 180°C to 75°C when the temperature in the cooler is 12°C. The thermal diffusivity of the polyethylene is 1.1x10-7 m/s. [8 marks] (C) If it was possible to reduce the temperature of the cooler to 6°C, by how much would this reduce the part cooling time? [5 marks) (d) If the product is removed from the mould at 75ºC and the centreline temperature of the plastic may be taken as the average of the skin temperatures, calculate how long it will take the centreline temperature to cool to 25°C if the product is subjected to fan blown air at a temperature of 15°C? The heat transfer coefficient for fan blown air is 79 W/(m2K) and the thermal conductivity of the plastic is 0.33 W/mK. The data in Figs 04.1 and 24.2 may be used. [8 marks) Q4(a) 403.5 kg, (b) 4.66 min, (C) -0.15 min, (d) 6.06 min