Direct Measurement Of Thermal Conductivity Research Articles

Direct measurement of CVD diamond film thermal conductivity by using photoacoustics

Photoacoustics (PA) is a type of photothermal effect and differs from the other one, known as the “mirage” effect, by the generation of thermal deflection waves as acoustic waves in a gas adjacent to the sample due to the modulated light absorption. We analyzed the feasibility of using PA for direct measurement of thermal conductivity of diamond films. The method was tested on two types of diamond polycrystalline films grown by chemical vapor deposition in plasma of direct current and microwave discharges. The thermal conductivity properties of the diamond films obtained are discussed by taking into account the Raman, photoluminescent, cathodoluminescent and other properties of these materials. The thermal conductivity values are shown to depend on polycrystalline diamond film structural characteristics that are defined by the conditions of the deposition.

Thermal conductivity reduction in GaAs-AlAs distributed Bragg reflectors

Self-heating of vertical-cavity laser diodes is strongly affected by the thermal conductivity of the distributed Bragg reflectors (DBRs). Binary GaAs-AlAs DBRs are expected to be good heat conductors, but investigations of GaAs-AlAs superlattices indicate strong interface scattering of phonons. For the first time, we present direct thermal conductivity measurements of separated GaAs-AlAs DBRs with a quarter-wave layer thickness of more than 100 nm (tuned to 1.55-μm wavelength). Using an ac calorimetric method and finite element analysis, we measure about 50% thermal conductivity reduction compared to the average bulk value. GaAs-AlAs DBR's for shorter wavelengths are expected to show an even lower thermal conductivity.

Thermal Diffusivity/Conductivity of Alumina—Silicon Carbide Composites

Thermal diffusivity and conductivity values for several Al2O3‐SiC whisker composites were determined. The thermal diffusivity values spanned the range from 373 to 1473 K, and thermal conductivity data wre obtained between 305 and 365 K. The thermal diffusivity decreased with increasing temperature and increased with SiC‐whisker content. An estimate of the thermal conductivity of the whiskers was obtained from the direct thermal conductivity measurements, but attempts to derive whisker conductivity values from the thermal diffusivity data were not successful because the laser flash method lacks the required accuracy and precision. Specimens were subjected to two different thermal quench experiments to investigate the effect of thermal history on diffusivity. In the most severe case, multiple 1073‐ to 373‐K quenches, radial cracks were observed in the test specimens; however, there was no change in diffusivity. The lack of sensitivity to thermal cycling appears to be related to the sample size.

Evaluation of local tissue blood flow by continuous direct measurement of thermal conductivity.

ArticleEvaluation of local tissue blood flow by continuous direct measurement of thermal conductivity.L Levy, H Graichen, J A Stolwijk, and M CalabresiL Levy, H Graichen, J A Stolwijk, and M CalabresiPublished Online:01 May 1967https://doi.org/10.1152/jappl.1967.22.5.1026MoreSectionsPDF (766 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByNoninvasive, in vivo determination of uterine fibroid thermal conductivity in MRI-guided high intensity focused ultrasound therapy27 August 2014 | Journal of Magnetic Resonance Imaging, Vol. 41, No. 6Flow Measurement13 April 2011Changes in skin thermal clearance during anaesthesiaAnaesthesia, Vol. 41, No. 4Skin blood flow changes in anaesthetized humans: comparison between skin thermal clearance and finger pulse amplitude measurementEuropean Journal of Applied Physiology and Occupational Physiology, Vol. 54, No. 6Combined Intracranial Pressure and Multilevel Continuous Local Cerebral Blood Flow Monitoring: Local Perfusion FluctuationsProposed methods for the measurement of regional renal blood flow using heat transfer analysisAnnals of Biomedical Engineering, Vol. 13, No. 3-4Cortical blood flow: thermal diffusion vs isotope clearance.Stroke, Vol. 12, No. 4The effect of alpha-adrenergic innervation on caudate blood flowAnnals of Neurology, Vol. 7, No. 2NONINVASIVE MEASUREMENT OF NET OXYGEN TRANSPORT: A FEASIBILITY STUDYCerebral blood flow regulation. II. Vasodilator mechanisms.Stroke, Vol. 8, No. 2Cerebral blood flow regulation: vascular resistance adjustments in the circle of Willis.Stroke, Vol. 7, No. 2 More from this issue > Volume 22Issue 5May 1967Pages 1026-9 https://doi.org/10.1152/jappl.1967.22.5.1026PubMed6025742History Published online 1 May 1967 Published in print 1 May 1967 Metrics