Effect of Leg Geometries, Configurations, and Dimensions on Thermo-mechanical and Power-generation Performance of Thermoelectric Devices

Environmental challenges, such as global warming, growing demand on energy, and diminishing oil sources have accelerated research on alternative energy conversion methods. Thermoelectric power generation is a promising method to convert wasted heat energy into useful electrical energy form. A temperature gradient imposed on a thermoelectric device produces a Seebeck potential. However, this temperature gradient causes thermal stresses due to differential thermal expansions and mismatching of the bonded components of the device. Thermal stresses are critical for thermoelectric devices since they can generate failures, including dislocations, cracks, fatigue fractures, and even breakdown of the entire device. Decreases in power-generation performance and operation lifetime are major consequences of these failures. In order to minimize thermal stresses in the legs without affecting power-generation capabilities, this study concentrates on structural solutions. Thermoelectric devices with non-segmented and segmented legs were modeled. Specifically, the possible effect of various leg geometries, configurations, and dimensions were evaluated using finite-element and statistical methods. Significant changes in the magnitudes and distributions of thermal stresses occurred. Specifically, the maximum equivalent stresses in the rectangular-prism and cylindrical legs were 49.9 MPa and 43.3 MPa, respectively for the temperature gradient of 100ºC. By using cylindrical legs with modified dimensions, decreases in the maximum stresses in legs reached 21.2% without affecting power-generation performance. Moreover, the effect of leg dimensions and coaxial-leg configurations on power generation was significant; in contrast, various leg geometries and rotated-leg configurations had very limited affect. In particular, it was possible to increase power output from 20 mW to 65 mW by simply modifying leg widths and heights within the defined range. It should be noted, however, this modification also increased stress levels. It is concluded that leg geometries, configurations, and dimensions can be redesigned for improved durability and overall performance of thermoelectric devices

A push-pull transducer for ocean wave energy harvesting

Ocean wave energy is one of the primary energy sources, which is available during day and night, in various weather conditions. It was previously proven that energy harvesting from ocean waves could be used to generate electric power to supply sensors or small electronic devices located in buoys. Using a combination of various energy harvesters would enable more remote and unmanned future offshore sensor applications that can facilitate more effective monitoring and control. In this study, we successfully demonstrated a simple, low-cost and environmentally friendly energy harvester which can be optimally used as an Ocean Wave Energy Harvester (OWEH). Please click Additional Files below to see the full abstract

Proceedings of the ASME 2010 Conference on Smart Materials, Adaptive Structures, and Intelligent Systems SMASIS2010 SMASIS2010-3688 DRAFT FEASIBILITY OF USING PIEZOELECTRIC PROBES TO MEASURE VISCOSITY IN NEWTONIAN FLUIDS

ABSTRACT Viscosity plays an important role in modeling fluid flow in different systems. In Newtonian fluids, viscosity is a constant, measureable property. Currently, viscosity is measured using viscometers that use an array of different techniques depending on the application. In this study, pre-stressed lead zirconate titanate (PZT) composites were used as probes to monitor changes in viscosity. The probes are used as an actuator-sensor pair: a voltage of 1V rms will be applied to one probe, the actuator; the second probe, the sensor, receives a vibration wave and turns it into an output voltage. Measurements of gain and phase at different input signal frequencies are analyzed. The fluid-medium where the probes are tested consists of different glycerin-deionized water solutions. Results indicate that the frequency of peak phase shift can be correlated to fluid viscosity. This correlation is exponential with viscosity, with an R 2 of 0.99. Results included viscosity values in the range of 0.8cP to 612cP. Possible applications for this type of sensor are numerous, and are both non-time-dependent (simple viscosity measurements of fluids), and time-dependent

Non-Destructive Evaluation Device for Monitoring Fluid Viscosity

There is an increasing need for non-destructive, low-cost devices for real-time fluid viscosity monitoring. Therefore, in this study, a method based on structural health monitoring is adapted for monitoring fluid properties. A device is built such that an inexpensive and disposable viscosity probe be possible. The design incorporates a sensor/actuator pair using a piezoelectric material layered with copper/brass and capable of monitoring viscosity changes in low volume liquids (e.g., vacutainer vial). Experiments performed with the new device show a definite pattern of wave propagation in viscous solutions. A numerical model is built to investigate the wave propagation in the fluid. For experimental measurements, the sensor part of the device detects the generated pressure wave in fluid (e.g., air, water, glycerin) by the actuator part. The phase shift between the actuator and the sensor signals is then recorded and plotted for different concentrations of glycerin and water at room temperature. The results of this study show a direct correlation between the phase shift and varying viscosity in the ultrasonic frequency range from 6 to 9 MHz. The numerical simulation, performed utilizing acoustic modal and harmonic response analysis, results also demonstrate the same trend as the experimental results: a phase shift increases with the viscosity of the fluid