The Figure 1 is a multilayer pipe known as the PEX-AI-PEX pipe, whereby: A: PEX layers,
B: Adhesive layers, C: Intermediate aluminium layer. Compared to other plastic pipes, the
multilayer pipes with the intermediate aluminium layer have the advantages including the
enhancement in internal pressure resistance, ductility, tightness to oxygen diffusion,
dimensional stability due to its lower expansion coefficient, and longer life. However, little is
known on its ability to conduct heat. Each of the layer has its respective thermal conductivity:
$k_A = 0.41 W/m.K$, $k_B = 0.363W/m.K$, and $k_C = 247W/m.K$. During a flow of water at an average
temperature of 60°C, the outer surface of the external wall temperature of the pipe measured at
35°C.
A
BCB
A
Figure 1
a) Calculate the heat loss through 2 m length of pipe walls if the internal PEX has the
diameter of 25 mm, internal and external adhesive have the thicknesses of 2 mm,
intermediate aluminum is 3.5 mm thick and both internal and external PEX are 5 mm
thick.
[15 Marks]
[CO1, PO1, C4]
b) The designers are unhappy with the heat loss. Hence, they propose to reduce the
thickness of intermediate aluminum by 50%. Can the heat loss be reduced? Explain
your answer.
[10 Marks]
[CO1, PO1, C4]
