ENGCB224-20B Assignment 2 PDF

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ENGCB224-20B: Assignment 2 Due: 5pm Friday 31st July 2020

Problem 2.1 A house has a composite wall of wood (exterior) (k = 0.12 W m-1 K-1, 20 mm thick), fibreglass insulation (k = 0.045 W m-1 K-1, 70 mm thick) and plasterboard (interior) (k = 0.25 W m-1 K-1, 10 mm thick). Determine the total heat loss through the wall when the inside temperature is 20 °C, the outside temperature is -10 °C, the inside heat transfer coefficient is 15 W m-2 K-1, and the outside heat transfer coefficient is 65 W m2 -1 K . Also, determine the temperature at the interface between the plasterboard and the insulation, assuming contact resistance is negligible.

Problem 2.2 Steam at 150 °C flows in a stainless steel pipe which has a thermal conductivity of 16 W m-1 K-1 whose inner and outer diameters are 5 and 6 cm respectively. The pipe is covered with 3 cm think insulation having a thermal conductivity of 0.035 W m-1 K-1. The combined convection and radiation heat transfer coefficient at the outside surface of the insulation is 20 W m-2 K-1 and the surroundings are at 10 °C. Assuming that the heat transfer coefficient on the inside surface is sufficiently high that the inside pipe surface is at the steam temperature, calculate the heat loss per unit length of the pipe as well as the temperature drops across the insulation.

Problem 2.3 A spherical tank (inside diameter 950 mm, wall thickness 6 mm) made of cast iron (k = 57 W m-1 K-1) is to be used to store a vapour/liquid mixture at 2 °C while it is waiting to be used in an industrial process. Calculate the percentage reduction in the rate of heat infiltration (compared to the case of no insulation) if the tank is covered in a 35 mm layer of insulation (k = 0.04 W m-1 K-1) assuming the inside and outside heat transfer coefficients are 85 W m-2 K-1 and 25 W m-2 K-1, respectively and that the ambient temperature is 35 °C....