Week 3 - Thermo-physical Questions

Question 1

List the thermo-physical properties of building materials that influence dynamic conduction characteristics and give the corresponding thermo-physical unit.

Answer 1

1. conductivity (W/m.K);
2. density (kg/m3); and
3. specific heat capacity (J/kg.K).

Question 2

On what parameters do the thermo-physical properties depend?

Answer 2

1. temperature;
2. moisture content; and
3. internal structure (degree of homogeneity and anisotropy).

Question 3

Identify two building materials that have time-dependent thermo-physical properties. Indicate the properties that are not constant and identify the independent parameter on which the change depends

Answer 3

1. external bricks - conductivity depends on moisture content; and
2. phase change materials - conductivity and specific heat capacity depend on temperature.

Question 4

Consider two materials, A and B, described by the following thermal properties. Which material transmits a heat flux fluctuation the fastest and why? Which material absorbs a surface heat flux less readily and why?

Diffusivity (m2/s) Effusivity (J/m2.C1/2)
A 1.3 x 10e-7 1.5 x 10e3
B 0.5 x 10e-4 6.5

Answer 4

1. B because the thermal diffusivity is highest.

2. B because the thermal effusivity is lowest.