Testing.2 – Thermal Conductivity Testing of Varying Density Polyurethane Boards

Aug 7, 2015 | Blog, Testing |

Thermal conductivity, thermal diffusivity and volumetric heat capacity were measured for a series of polyurethane boards of varying density. The Hot Disk transient plane source (TPS) method was used to measure the thermophysical properties of the polyurethane boards. The Hot Disk TPS method can measure thermal conductivity, thermal diffusivity and volumetric heat capacity of solids, liquids, pastes and powders. Thermal conductivities from 0.001 W/m•K up to 1800 W/m•K can be determined using this method. 

Eight polyurethane boards of different density were investigated using the standard TPS module. Two samples of the same board were acquired and used as obtained. The board densities ranged from 198 kg/m3 to 1633 kg/m3. The physical dimensions of each board were taken using digital calipers, and the mass of each board was also measured. Using this data, the density of each individual board was calculated, and then average density was calculated for each set of boards. See Figure 1 for the polyurethane board samples. 

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Figure 1. Pairs of polyurethane boards that were analyzed using the Hot Disk TPS technique.

The TPS standard (bulk) module was used to perform the measurements. Experimental setup involves placing a Hot Disk sensor between two pieces of the same material and applying a light pressure to help ensure good contact between the sensor and sample pieces. Five measurements were made for each pair of polyurethane boards and the average was taken. All experiments were performed at room temperature (24 °C). 

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Figure 2. Experimental setup for measurements.

 

  Table 1. Experimental thermal and physical properties of analyzed polyurethane boards. 

Sample Number  Thermal Conductivity (W/mK)  Thermal Diffusivity (mm2/s)  Volumetric Heat Capacity (MJ/m3K)  Density (kg/m3
0.8654  0.4271  2.026  1633 
0.2685  0.1700  1.580  1261 
0.1710  0.1645  1.039  843 
0.1510  0.1710  0.8831  736 
0.1276  0.1566  0.8143  654 
0.1184  0.1630  0.7265  587 
0.06653  0.1856  0.3592  291 
0.05525  0.2187  0.2538  198 

The experimental results show that thermal conductivity and heat capacity increase with density, while thermal diffusivity does not have a defined trend with respect to density. As a material becomes more dense, it contains less air pockets, which inhibit heat transfer due to their low thermal conductivity. Thus a material that is more dense will have a higher thermal conductivity; this trend can be seen from the results.   

Thermal diffusivity is proportional to thermal conductivity, density and specific heat capacity and thus small changes in each of these properties can result in a significant change in the thermal diffusivity. There is quite a large difference in thermal conductivity values and densities over the series of polyurethane boards and these large differences could account for thermal diffusivity not showing a trend.