Which of the following substances has the lowest thermal conductivity? a) air b) cast iron c) aluminum d) iron

The lowest thermal conductivity (substances with low thermal conductivity are heat insulators, λ <0.25 W / (m * K)) will be possessed by the substance with the lowest thermal conductivity coefficient, since the thermal conductivity is set by the Fourier law:

q = -λ * grad (T), where λ is the constant coefficient of thermal conductivity, T is the temperature.

a) air: λ = 0.022 W / (m * K).

b) cast iron: λ = 62.8 W / (m * K).

c) aluminum: λ = 202 … 236 W / (m * K).

d) iron: λ = 92 W / (m * K).

Answer: a) Air has the lowest thermal conductivity.