In the automotive industry, aluminum foil corrugated tubes for automotive heat insulation can be used as copper tubes for protection purposes in shifter cables, speed indicator cables, hydraulic systems, power cables, and liquefied petroleum gas systems. So, what are the factors that affect the performance of automotive heat insulation tubes? We have sorted out this issue and identified several important reasons, summarized as follows.
1. Temperature has a direct impact on the thermal conductivity of various insulation materials. As the temperature increases, the thermal conductivity of the material rises. This is because when the temperature rises, the thermal motion of the solid molecules in the material intensifies, and the thermal conduction of air in the pores of the material and the radiation between the pore walls also increase. However, this effect is not significant within the temperature range of 0-50℃. Only for materials at high temperatures or negative temperatures, the impact of temperature needs to be considered.
2. At room temperature, the thermal conductivity of loose granular materials decreases as the particle size decreases. When the particle size is large, the size of the gaps between particles increases, and the thermal conductivity of the air trapped within these gaps inevitably increases. Furthermore, the smaller the particle size, the less its thermal conductivity is affected by temperature changes.
3. In thermal insulation materials, most of the heat is conducted through the gas in the pores. Therefore, the thermal conductivity of thermal insulation materials is largely determined by the type of filling gas. In cryogenic engineering, if helium or hydrogen is used as a filling gas, it can be approximated as a first-order approximation that the thermal conductivity of the thermal insulation material is comparable to that of these gases, as both helium and hydrogen have relatively high thermal conductivities.
