Methods for Thermal Measurement

Why and when do we need to measure heat transfer? 

Increasingly important in any technology that requires energetic mechanisms to perform work, the field of thermal transfer is expanding to include more methods of measurement, more inquiry into thermal management, and more understanding of the interaction of electrons and phonons.  The semi-conductor industry is highly dependent on the mitigation of heat produced in excess by the activity of computing circuitry, but it is certainly not the only industry that has keen interest in the development of management techniques.  Runaway heat is the primary cause of sudden Lithium-ion battery failure, and any reductive material technology produces excess heat as well.  All of these require careful management of thermal energy, and that management begins with accurate measurement.

What factors affect the measurement accuracy?

• Base temperature: A net thermal transfer measurement that has a baseline of <100 K will have a different effect on the sample than a measurement with the same net thermal transfer from a baseline of >300 K, for example.
• Method: Using the infrared spectrum to measure the energy will yield different results than a method that measures through the sample.
• Interactions: Electron conductance can cause scattering effects on phonons in the sample, which must be factored into the calculations.
• Physical Connections: Since the sample is a physical material, it must intersect with the measurement apparatus or the energizing factor, either through physical contact or across some distance through radiance.

How does electron transfer compare to phonon transfer?

Electrons and phonons can be compared in much the same way that flowing water represents electron current and ocean waves represent phonon transport.  For electrons, there is a mass transfer when electrons flow.  For phonons, the energy is expressed as lattice vibrations which do not transfer mass.  However, it is important to note that there are significant interactions between the two very different energies.  Electron flow can cause much interference, or scattering, with the base material through which the electrons flow.   This in turn stimulates phonon activity, especially scattering.  Effective thermal transport benefits from non-scattered phonons.

What are some of the common measurement techniques?

• Steady State Analysis: Using two metal plates, the sample is mounted between and one plate is heated to a known temperature while the second plate is measured for steady state change.
• Transient Plane Source: A sensor is placed on or focused on the sample while heat is pulsed into it.  This is a very common technique.
• Infrared Thermography: While heat is introduced into the sample, an infrared sensor maps the diffusion of heat through the sample.
• Thermogravimetric Analysis: This technique measures the mass of the sample over either time or temperature change and is useful to determine the thermal stability of the sample, or its decomposition thresholds.
• TEPT: This technique is a highly accurate method of measuring the thermal diffusivity in small to very small samples.  Transient Electro-Phonon Thermal equipment has been brought to market under patents owned by ACS Material.  A small, simple to use device contains the physical and logical components necessary to accomplish many tests per hour, which makes the development of new materials much more efficient.

Questions about thermal measurements or any other material characterization?

Call the experts at ACS Material to discuss nanomaterials or to characterize most of the many specifications inherent in the tiny domain.