Spatial Measurements of Thermal Properties
Over the life of nuclear fuel, inhomogeneous structures develop, negatively impacting thermal properties. New fuels are under development, but to model performance and determine safe operational conditions a more accurate knowledge of how the properties change is needed. Measurement systems capable of small–scale, pointwise thermal property measurements and low cost are necessary to measure these properties and integrate into hot cells where electronics are likely to fail during fuel investigation. This project develops a cheaper, smaller, and easily replaceable Fluorescent Scanning Thermal Microscope (FSTM) using the blue laser and focusing circuitry from an Xbox HD-DVD player. The FSTM also incorporates novel fluorescent thermometry methods to determine thermal diffusivity. The FSTM requires minimal sample preparation, does not require access to both sides of the sample, and components can be easily swapped out if damaged, as is common in irradiated hot cells. Using the optical head from the Xbox for sensing temperature changes, an infrared laser diode provides periodic heating to the sample, and the blue laser induces fluorescence in Rhodamine B deposited on the sample’s surface. Thermal properties are fit to modulated temperature models from the literature based on the phase delay response at different modulated heating frequencies.
Thermophysical Properties of Molten Salt
Based on the recent push by the Department of Energy to develop Molten Salt Reactor (MSR) technologies, there has been a need to accurately measure the heat transfer characteristics of salt, especially irradiated salts. Four critical thermophysical properties are of interest, namely density, specific heat capacity, thermal diffusivity, and thermal conductivity. Literature values of density and specific heat capacity for pure fluoride salts or chloride salts are relatively robust, but inclusion of impurities and their effect on properties is not well documented. For thermal conductivity and thermal diffusivity, the state of knowledge in the literature is significantly worse, largely because of the difficulty in measuring these properties at high temperatures in an electrically conducting, corrosive liquid. The TEMP lab at BYU is pursuing the development of two types of thermal conductivity sensors (a needle probe and a transient hot wire probe) that would be able to measure the properties of salts. These probes operate using electrical heating and monitor changes in temperature to determine the heat transfer into the surrounding salt. Because of the large variation in literature values of the salts, this multi-sensor approach is needed to reduce the uncertainty on the measured values.
Microfluidic Temperature Control
The short-term goal of this project is to develop temperature sensing technology to control and measure spatial temperature with ±0.1°C accuracy. This is made possible by 3D printing of sensors, heaters, and coolers in a microfluidic chip, which also allows this technology to be cheap and accessible for many applications. Our long-term goal is to apply these technologies beyond the DNA analysis focus of this proposal to additional biothermal process research to diagnose and treat disease. The innovative new technologies are: μm-sized 3D printing, unique quantum dot shape-based fluorescence thermometry temperature sensors, machine learning-based analysis, tightly coupled modeling & prototyping, and customizable heater geometries.
Friction Stir Welding (FSW)
The research objective of this proposal is to directly quantify heat transfer in real-time during friction stir welding (FSW). To accomplish this, a new approach to measure the thermal contact resistances (Rth) and heat transfer coefficients (h) at all interfaces within the weld assembly (Figure 1a) is proposed. Estimates of h in the literature vary by 2-3 orders of magnitude (Figure 1b), rendering model predictions of friction stir welding inaccurate. The current approach of adjusting both heat transfer coefficients and friction coefficients to match experimental data is inadequate to achieve truly predictive models. To address the current deficiency in measuring heat transfer in FSW and the associated weakness in modeling predictions, we propose to test the hypothesis that thermal wave techniques will enable accurate measurement of heat transfer coefficients (h), especially those between the rapidly rotating tool and the workpiece. This will lead to more useful modeling of welding temperatures, torques, loads, and material flow in FSW. Better model predictions will promote more rapid development and deployment of frictions stir technologies in a variety of industries where Edisonian trial and error in welding development are still common practice.
Figure 2. a) Complex interactions between parameters during FSW shown in gray lines , with black lines showing how tool rotation rate affects weld temperature in current models. Operators are able to control process inputs , which give rise to process effects such as heat generation or shear stresses , which generate stress and temperature distributions based on system properties , giving rise to the final weld microstructure and properties . The red dotted line represents how the heat transfer parameters thermal contact resistance ) and heat transfer coefficients () are critical for determining welding temperatures, but current models can only guess these values. b) Key parameters during friction stir welding (FSW) responsible for heat generation and weld characteristics. Images adapted from , .