What is the correction of the thermal conductivity coefficient of polyurethane foam?

When using polyurethane rigid foam as an insulation material, it is essential to understand the thermal conductivity λ of polyurethane foam. It is well-known that the thermal conductivity coefficient λ of PU foam is related to the foam's density and usage temperature. Factors like construction method and formula composition also affect the foam's λ value. However, these influencing factors can be addressed by measuring the actual λ value.

Typically, λ values are measured at room temperature, but actual usage temperatures can vary significantly, depending on the working conditions. Therefore, it is necessary to understand the relationship between temperature conditions and λ to derive the correction formula for λ based on temperature (T).

Figure 11-1 shows the relationship between the λ value of polyurethane rigid foam and temperature (T).

From Figure 11-1, it can be seen that within a certain temperature range, λ and T have a linear relationship. According to this, the relationship between λ and T can be expressed as:

λ = λ₀ + 0.00012△T (11-37)

Where:

λ is the thermal conductivity under usage conditions.

λ₀ is the thermal conductivity measured at 20°C.

△T is the difference between the usage temperature and room temperature.

Example:
For a PU foam insulation project, the thermal conductivity λ₀ provided by the manufacturer is 0.0232 W/(m·K). Now, if the foam is used in insulation at 60°C and 0°C, what would the λ value be in these conditions?

λ₆n = [23.2 + 0.12 × (60-20) × 10⁻³ = 0.028 W/(m·K)]
λ₀ = 0.0232 + 0.00012 × (0-20) = 0.0208 W/(m·K)

These values closely match the measured results. The relationship between λ value and foam density is shown in Figure 11-2.