Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

Abstract

A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k ¼ (e 2 /D) 1/2 . To generalize this approach, sensitivity analysis is conducted for materials having a range of thermal conductivities. Application to nuclear fuel is consider by performing experimental validation using two materials (CaF 2 and SiO 2 ) having thermal properties representative of fresh and high burnup nuclear fuel.

Investigation of thermal transport in composites and ion beam irradiated materials for nuclear energy applications

“…Those include spot size of both beams, thickness of the metallic transducer layer, and thermal interface resistance between transducer and material. 31,36 Most of the results presented in the following sections were acquired using a spatial scan TR presented below. We also provide one example where TDTR and FDTR are used.…”

“…30 Frequency domain TR (FDTR) uses continuous wave lasers and examines the phase lag between excitation pulse and temperature as a function of a modulation frequency. 31,32 In this work, we primarily use a variation of TR that relies on spatially resolved measurement where the temperature profile around the excitation spot is measured. [33][34][35] Our choice of this approach stems from its attractiveness for use in hot cell applications, where the exact knowledge of some of the experimental parameters is not required.…”

Parametric study of the frequency-domain thermoreflectance technique

“…In neutron irradiated fuel, from the center to the exterior, to fuel rim, the microstructure may change drastically over a few millimeters. 13 For ion-irradiated samples, a multi-layered structure may also be present due the possibility of a coating layer, damaged layer, ion implantation layer, and the original material. 20 When measuring such samples, a multi-layered model may be used, which necessitates the derivation of an n-layered thermal model.…”

“…Photothermal techniques include photothermal displacement, 7 photothermal beam deflection (or "mirage"), 8 photothermal radiometry (PTR), 9 and photothermal reflectance (or thermoreflectance). [10][11][12][13] Thermoreflectance techniques may be distinguished as one of the two measurement types: time-domain and frequencydomain measurements. In the frequency-domain thermoreflectance technique, a layered sample (an n-layer model is presented but the results are later presented for a single layer on a substrate) is heated by the absorption of a modulated (sinusoidal) heat source supplied by a pump laser.…”

“…Thus, this approach is preferred by many. 10,11,13,[15][16][17] However, the 1D model does not consider heat flow parallel to the layers; therefore, the range of applicability of the 1D model requires a)…”