1. The final treatment of a novel polymer material requires holding the material

above a temperature of 100°C for 5 minutes. This is achieved by suspending

the polymer rod in a moving airstream that has a free air temperature of

150°C. The rod is held vertically, with the air stream moving horizontally.

The air velocity is 10m/s. The polymer rod has a diameter of 5cm and a length

of 2m. Physical properties are shown in the table below.

Material

Air

Air

Value

1.16 kg/m³

1006 J/kgK

11.0 W/mK

Property

Density

Specific heat capacity

Polymer

Thermal conductivity

Polymer Specific heat capacity

1200 J/kgK

Polymer Density

1500 kg/m³

a) Sketch a suitable arrangement including a heating element.

[3 marks]

b) Using a value of the heat transfer coefficient of 80 W/m°K, and taking care

to justify the approach you adopt, calculate the total time required to heat-

treat the sample.

[6 marks]

c) Further study of the novel polymer suggests that the polymer should

remain below a temperature of 135°C to minimise reduction in the

structural strength of the polymer. Demonstrate whether this criterion is

met or not.

[6 marks]

d) One of the engineering team working with you on this project proposes a

reduction in the heated free air temperature to 110°C to save energy.

Assess this proposal in terms of:

i. The total cycle time for treatment of one rod

ii.

The relative energy cost when compared to the original condition of

using heated air at 150°C.

Note that the air is heated from an ambient temperature of 20°C and

assume all properties of the gas (except the free air temperature) remain

constant.

Consequently, provide an informed response to the engineer's suggestion.