In summary, the range of k is limited by the range of available thicknesses of the material samples as well as the specified range of R for the tester. WinTIM Software includes the "k-Test Wizard" that helps with the selection of material thickness selections for optimum accuracy of thermal conductivity measurement.

Question: How can I measure the thermal conductivity of very thin grease samples?
Answer: The method recommended by ASTM D5470 for measuring thermal conductivity of the material while excluding the effects of surface contact resistance is to test a range of material thicknesses, plot the R*A (Y-axis) versus sample thickness (X-axis), and determine the best fit straight line for this data. The measured value of thermal conductivity, k, is the reciprocal of the slope of this line; the combined contact resistance (RA) for the upper and lower test surfaces will be the Y-intercept. A minimum of 3 different sample thicknesses is recommended with as large a span of thickness as is practical. Generally stacked materials cannot be used to achieve this variety of sample thickness since each additional layer in the stack adds additional contact resistance which will become included with the measurement of k resulting a poor accuracy result. The figure contained in Contract Material Test Services illustrates the recommended technique.

Question: Can I use a chiller that I already in my lab?
Answer: The chiller requirements are a) +/-0.1°C temperature stability with a range of set points from 10°C to 35°C, b) heat load capacity at least of 500 watts, and c) flow rate of 6 lpm (1.5 gpm) @ 280 kPa (40 psi). If plans for testing over a range of sample temperatures is intended, serial/USB chiller control (versus manual control) will simplify the overall progress of the test operation. Manual chiller control can be an acceptable alternative although the operator will be prompted for a chiller set point change once or twice per test. For testing phase change materials (PCMs), serial chiller control is required.

Question: What pressure should I use for testing my material sample?
Answer: The answer to this question depends the type of material to be tested. Generally, higher contact pressures yield lower surface contact resistances. In the latest version of ASTM D5470, there are 3 categories of materials:

Type I: Liquid materials that exhibit unlimited deformation when a stress is applied. These include greases, pastes, and phase change materials. These materials exhibit no evidence of elastic behavior or the tendency to return to initial shape after deflection stresses are removed. [Materials of this type are tested at specified thickness without regard to the pressure applied. Here the sample thickness is fixed either by using the TIM Tester in the Specified Thickness Mode or by using various type of spacers or shims to regulate the thickness of the sample. Surface contact resistance for Type I materials are close to zero.]

Type II: Elastic solids where stresses of deformation are ultimately balanced by internal material stresses thus limiting further deformation. Examples include gels, soft and hard rubbers. These materials exhibit linear elastic properties with significant compression deflection relative to material thickness. [Materials of this type can be tested on the TIM Tester in either Controlled Pressure or Controlled Thickness modes depending on the elasticity of the material. Generally, Controlled Pressure is the method of choice although some types soft material exhibit progressively decreasing surface contact resistance and/or thickness over a long period of time. This makes repeatable test results difficult to achieve in a short period of time since the test result depends on the duration of pressure application. For these types of materials, Controlled Thickness Mode testing should be performed. ASTM D5470 recommends the use of 5% deflection from the uncompressed starting thickness.]

Type III: Inelastic solids which exhibit negligible deflection; examples include ceramics, metals, and some types of plastics. Although these materials are elastic in nature, deflection is insignificant relative to the material thickness.
[Materials of this type require accurate sample preparation to ensure that the hot and cold test surfaces are flat to within 0.5 microns (0.00002") and parallel to within 5 microns (0.0002") which will minimize the surface contact resistance. In addition, the test surfaces are treated with oil or light thermal grease to exclude air from the contact surfaces and further reduce the contact resistance. Controlled Pressure Mode is used with a minimum of contact pressure of 2000 kPa (300 psi).]

Question: Can the TIM Tester 1300 test phase change materials (PCM's)?
Answer: WinTIM version 1.2 offers the capabilities to test PCMs at pre-test temperatures of up to 80°C. In addition, a serial controlled chiller is required for PCM testing.

Question: What is the range of sample area-sizes that can be tested?
Answer: Samples should always be provided in 3.3 cm (1.3") diameter size for the best accuracy. Samples cannot be larger than this optimal although samples between 2.5 cm and 3.3 cm can be tested with some loss of accuracy. A sample die-cutter is provided with the TIM Tester 1300 to for cutting 3.3 cm samples in type II materials.