Speakers

More Accurate Analytical Solution for the Modified Transient Plain Source Method

Abstract:

The Modified Transient Plain Source (MTPS) method is a popular one for thermal effusivity and even for other thermal properties tests. The theory used currently for the method assumes that heat capacity of the heater and thermal contact resistances on its surfaces are negligibly small. Obviously, this assumption causes some unknown errors – especially at the early moments of time. To minimize the errors caused by using this imperfect theory the manufacturers of the MTPS devices must run multiple calibrations using several reference materials of known thermal effusivity. Theoretically this kind of method could work as an absolute one with no calibrations at all if a more accurate theory was used – e.g. the Guarded Hot Plate method uses only the measured electric power per square area of the heater, plates’ temperature difference and the sample’s thickness to calculate the absolute value of thermal conductivity. I.e. using accurate theory of the MTPS method we could get absolute values of thermal effusivity.

Now a new, significantly more accurate, analytical solution for the MTPS method is obtained where effects of the heater’s either heat capacity or thermal contact resistance are properly accounted. The heater’s temperatures calculated using the new formulas were numerically compared to its temperatures calculated using the old working formula and were verified using the Finite Differences Method calculations. These new, relatively simple formulas are used to analyze the effect of the heater’s heat capacity or the thermal contact resistance on the various materials tests’ results, what practically was never done before. The heater’s areal heat capacity is calculated using its thickness and volumetric specific heat, or it possibly can be measured directly using its temperature rise rate at the very first moment of time. Thermal contact resistance on the heater’s surfaces is estimated as thickness of the Kapton film divided by the Kapton’s thermal conductivity. These values, as well as the substrate’s thermal effusivity, are used in the new formulas to improve significantly the accuracy and convenience of the MTPS method.

Thermal conductivity measurements of thermal energy storage materials

Abstract:

Thermal Energy Storage (TES) is an important technology for energy conservation and utilizing fluctuating renewable energy sources and waste heat. Heat transport in TES applications is extremely important as it influences the thermal performance in charging and discharging of the heat storage system.

This work focuses on the use of already available and standardized measurement devices like Laser Flash (LFA), Heat Flow Meter (HFM) and Transient Hot Bridge (THB) to determine the thermal conductivity of phase change (PCM) and thermochemical materials (TCM). Thermal diffusivity a(T) measurements of an organic PCM based on the LFA method indicated a good reproducibility for the solid phase but challenges due to liquid capillary ascension and low viscosity in the liquid phase of the sample. In contrast, thermal conductivity experiments via the THB method have shown their assets in the liquid phase but on the other hand unsatisfactory results in the solid phase due to varying contact conditions between foil sensor and sample. A numerical investigation of a LFA liquid sample holder system filled with pure water has shown the transient and spatial temperature field distribution inside the sample holder system and the influence on the measured half time depending on the detector focus.

Furthermore, measurement protocols to analyze the effective thermal diffusivity aeff (T) and effective thermal conductivity λeff(T) of powdery TCM candidates were developed. The results represent the strong dependency on the actual bulk density of the measured sample. Finally, a detailed investigation on of packed beds consisting of a Yttria-stabilized zirconia powder with different particle diameters based on the LFA, THB and HFM method were performed and compared. The LFA results indicate a significant relation between the aeff (T) and the used gas conditions. Under ambient conditions, the HFM and THB method indicate comparable λeff (T) data while LFA showed significant higher values. Considerations about a non-uniform distribution of the powder inside the LFA sample holder system led to the assumption, that the evaluated bulk densities are not correct and also plane-parallelism is not given, which is a requirement for accurate LFA measurements.

Method for determination of thermal conductivity of open and closed cell materials at cryogenic temperatures

Abstract:

Measurement of the thermal conductivity of open and closed cell materials in a non-vacuum environment at cryogenic temperatures requires the application of a suitable cryogen. In the temperature range below the boiling point of liquid nitrogen, usage of the noble gas helium having the lowest boiling point among all elements, represents a challenge. Because helium has a small molar mass of approximately 4 g/mol in comparison to approximately 28 g/mol for nitrogen gas, gaseous helium effuses almost 3 times faster through microscopic pores according to Graham’s law. Furthermore, gaseous helium has a significantly higher thermal conductivity at atmospheric pressure than nitrogen by an average factor of 7. This appears to result in a higher apparent thermal conductivity of the open and closed cell material.

The ASTM Standard Test Method for steady-state heat flux measurements and thermal transmission properties by means of the guarded-hot-plate apparatus was used to measure the thermal conductivity of thermally insulating cellular glass at cryogenic temperatures. Measurements were performed in helium as well as nitrogen atmospheres in the upper temperature range allowing an offset value, caused by the increased heat flow through helium, to be determined. The offset value was used to correct the thermal conductivity values obtained at lower temperatures in helium atmosphere.

Dr. Lucas Lindsay received a BS degree in physics from the College of Charleston in 2004. He did his PhD work on theoretical thermal transport in carbon nanostructures at Boston College and received his PhD in 2010. Following this he taught physics for two years at Christopher Newport University, then spent three years as a National Research Council Postdoctoral Fellow at the U.S. Naval Research Laboratory in Washington, D.C. He has been a research scientist in the Materials Science and Technology Division at Oak Ridge National Laboratory since 2014. He received the Department of Energy Early Career Award in 2019. His general research area is the theoretical description of vibrational and transport properties of condensed matter.

He will present Unveiling the Theory of Thermal Conductivity: Insights into Phonons and Heat Transfer Mechanisms.

Study of heat conduction in human skin irradiated with a dedicated laser for heating gold nanoparticles for cancer photothermoablation

Abstract:

The primary purpose of this study is to evaluate the process of heat conduction in skin subjected to photothermoablation in a customized chamber measured with a thermal imaging camera. Investigation of the effect of gold nanoparticles on the skin surface and their laser irradiation on the conditions of heat flow into the skin will be preliminarily determined by determining temperature-time curves. Both an experimental rig and Computational Fluid Dynamics (CFD) numerical calculations are used to verify the results. CFD uses mass, momentum and energy balances; however, in the present issue, the determination of the temperature field in the solid remains crucial in the first estimation of the results.

Tissue samples (medical waste after procedures) after gold application are transferred to the laser laboratory for irradiation with an electromagnetic energy source of about 1 W. During the study, spherical gold nanoparticles will be used, which, using different laser wavelengths – from visible light to short-wave infrared region (SWIR), will serve as a source for converting electromagnetic energy into heat.

Analyses of heat transfer over time are conducted using thermal imaging cameras with recording of the temperature change on the heated surface. Selected results of the measurement campaign will also be analysed using CFD-type tools to indicate the possibility of determining the depth and size of the heated area. The experimental and numerical results will be confronted with the literature on an ongoing basis. The present research results will be used in the future to determine the power, wavelength, heating time in terms of optimizing the process of photothermoablation of tumors.

Theoretical investigations of the photothermal effect and energy conversion for metallic nanostructures deposited on insulated materials

Abstract:

Photothermal effect in metallic nanostructures has been extensively studied for a dozen years due their high biocompatibility and the effective energy conversion rate. Moreover, the immediate temperature increase, which occurs as a result of the illumination, could be applied in the biophysical systems where germs or tumors are to be completely inactivated or overheated. However, there is a low number lack of theoretical methods that could predict the temperature increase and the energy conversion rate, and yet assist in water purification station or clinical trials. This work aims to compare experiments with three different theoretical models, which have been developed and adjusted by authors.

The first theory includes the Rayleigh-Drude approximation within size and shape effects described by optical cross-sections, whereas the second model assumes the efficiency of the energy conversion measured by a laser-power meter. On the other hand, the third approach considers the combined analytical solutions for unsteady heat transfer and the nanofluidic equations determining the effective thermal diffusivity. All models are tested and examined using the platforms where cetyltrimethylammonium bromide (CTAB)-stabilized gold nanorods have been uniformly deposited on a thin 0.4-inch round sheet made of optical borosilicate glass. The platforms are subsequently subjected to 0.5-W visible- and infrared-range laser illumination. The obtained results indicate that the maximum temperature from experiments reaches 𝑇𝑚𝑎𝑥=121.0C o (249.8F o) in approximately ten seconds and remains constant for the rest of the illumination time. As long as each model provides a satisfactory trend over time, the first and the second theories exhibit the best agreement with experimental values (𝑇1=118.9C o (246.0F o) and 𝑇2=120.1C o (248.2F o)), and outperform the third model as respectively overestimated at the 25% level.

Thermophysical properties of fluids – care, collecting, and connecting

Abstract:

Fluids in modern technology are being taxed to perform in applications with delicate balances of viscosity, stability, heat transfer, and system protection. Based on the “three-C’s” of care, collecting, & connecting, this talk will explore the arena of understanding lubricant, non-aqueous fluids, combining thermal, rheological and thermophysical analysis techniques. The fluids discussed in this talk encompass a wide range of applications, including coolants, heat transfer agents, and various petroleum-based packages. Working with fluids that naturally exhibit a relatively narrow range of stability and thermophysical properties requires care. Which techniques should be used? What are the characteristics and limitations of each fluid? Such a narrow range of values requires a large volume of samples for a deeper understanding, therefore collecting this extensive data requires efficiency and a high level of checks and balances. How do we know we have the right answer? How much variation do we really see? “Connecting” is how we use this knowledge to enable communications with customers and project leaders. What matters most? What alterations can be made? Educating them of the holistic view and the possibilities drives future successes.

Material Relocation Test Study of Pellet to Cladding Interaction in Fast Reactor Design

Abstract:

During Pellet to Cladding Interaction phenomenon, the confirmed material relocation due to thermal melting and thermal diffusion is studied based on ASTM E793, ASTM E2585 and ASTM E1461. These kinetic parameters of the PCI can be established into the fuel center-line melting criterion for assuring that the axial or radial relocation of molten fuel would not be allowed to contact with the cladding in Fast Reactor design.