Measurements of thermal conductivity anisotropy in polymer materials

A thermal conductivity probe has been developed based on a modified hot wire approach. Three types of measurement techniques using this apparatus have also been developed. All techniques are nondestructive, have flexible sample sizes and have test times under 5 minutes. The instrument is fully automated with gathering and manipulation of data by the acquisition software. The techniques have been used on a variety of solid samples from insulations to glasses to oriented polymers.; The first test is used to find the parameter (krhocp) of a material, where k = thermal conductivity, rho = density and cp = heat capacity. The test is complete in 30 seconds with high repeatability of +/-2%. Such information is useful for characterizing materials and is used with information from the next two tests to yield thermal conductivity and the anisotropy ratio of thermal conductivity.; The second test results in a value of thermal diffusivity, alpha = k/rhocp. This information when combined with test 1 results in the determination of thermal conductivity, k. This test is the longest, taking up to five minutes to complete depending on the sample. This test is also only an order of magnitude estimation. Examples of uses of the values of diffusivity and thermal conductivity are in calculating heating and cooling times for a material as well as its insulating properties.; The third test is used on oriented samples such as wood or machined polymers. The development of this test was the major goal of the PhD research. In this test the anisotropy function ka/kt is measured where the relation is the ratio of the thermal conductivity in the axial direction to that of the transverse direction. This parameter has been related to the degree of orientation and therefore to the strength of the sample. This method of indirectly measuring strength could facilitate the study of property development and material optimization.; The third test is an example of a test specific to the production and study of oriented polymers. This probe and its three measurement techniques could be customized to fit the needs of other industries.