Jessica Townsend

A benchmark study on the thermal conductivity of nanofluids

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Nanofluid Properties and Their Effects on Convective Heat Transfer in an Electronics Cooling Application

In the search for new, more effective coolant fluids, nanoparticle suspensions have shown promise due to their enhanced thermal conductivity. However, there is a concomitant increase in the viscosity, requiring an increase in pumping power to achieve the same flow rate. Studies of flow cooling in simple geometries indicate that there is a benefit to using nanofluids, but it is difficult to justify extending these results to the far more complicated geometries. Moreover, with the variability of property measurements found in literature, it is possible to show conflicting results from the same set of flow-cooling data. In this work we present a self-contained study of the properties and effectiveness of an alumina in water nanofluid. Flow-cooling is studied in an off-the-shelf fluid cooling package for electronics to examine the effects of the particulates in a practical scenario. We measure the thermal conductivity and viscosity of the same suspensions to assure consistent interpretation of our results. We find that, while there is no anomalous enhancement of the thermal properties or transport, there is a benefit to using a low volume fraction alumina nanoparticle suspension over using the base fluid alone. In fact, there is an optimal volume fraction (1%) for this nanofluid and electronics cooling system combination that maximizes the heat dissipated. However, we find that this benefit decreases as the volume fraction, and hence the viscosity, increases. Understanding where the trade-off between viscosity increase and thermal conductivity increase occurs is critical to designing an electronics cooling system using a nanofluid as a coolant.

The creation and inauguration of engineering leadership: UTEP and Olin College innovation project

The Franklin W. Olin College of Engineering (Olin College) and The University of Texas at El Paso (UTEP) are partnering in a project to create a new engineering program that educates career-ready engineering innovators while simultaneously increasing recruitment and retention among historically underrepresented students. Through the Olin-UTEP Partnership for Change: Adoption and Adaptation of Innovative Practices for 21st Century Engineering project, supported by the Department of Education and the Argosy Foundation, UTEP is pioneering a novel undergraduate engineering leadership program (E-Lead), focused on innovation, collaboration, communication, and human-centered engineering embedded in rigorous technical education. The program is being modeled on the curriculum and pedagogy of Olin College, a private, highly selective engineering college respected and nationally recognized for its premier innovative engineering education. The adaptation to UTEP is of national interest, since UTEP is a public, urban institution with a 21st-century demographic [1] and successful transformation of Olin approaches to UTEP can demonstrate scalable impact broadly pertinent to many other commuter campuses and public institutions. By conveying these approaches to UTEP, a minority institution serving a largely Hispanic population in the region of Texas with the lowest median income [2], we aim to demonstrably adapt and scale successful innovation-supportive pedagogies to meet important national needs for a diverse and empowered 21st century engineering sciences workforce.

Model collaboration for advancing student-centered engineering education

The University of Texas at El Paso (UTEP) and the Franklin W. Olin College of Engineering (Olin) are establishing a student-centered hands-on interactive approach to engineering education (similar to Olins) at UTEP, where it will reside in UTEPs innovative B.S. in Leadership Engineering (LE) program. The goal of the proposed collaboration is to catalyze UTEPs educational innovation through a cross-campus collaboration between the two institutions by incorporating the Olin educational process, both design and features, into the first offerings of the Bachelor of Science in Leadership Engineering (BSLE) program. Specifically, the collaboration includes faculty exchanges between the two institutions; a series of retreats for planning and assessment; curriculum development; and student recruitment practices. The 21st century workplace demands a new engineer - one who effectively contributes to solving problems using innovation, creativity, and strategic foresight. Graduates of the Olin-UTEP developed Bachelor of Science in Leadership Engineering (LE) program will possess these attributes through the programs rigorous yet flexible major in engineering, and in-depth study of leadership and its effect upon technology and society. In this panel we will share the context for our innovative approach, key features of the partnership to date, and acclaim the value of inter-institutional sharing.

Cooling Performance Limits of a Turbine Blade With Potassium Evaporative Cooling

A new method of turbine blade cooling, the Return Flow Cascade, has been developed in which vaporization of a liquid metal such as potassium is used to maintain the blade surface at a nearly uniform temperature. Turbine blades cooled using this technology have lower blade temperature levels compared to that available with conventional air cooling, potentially resulting in higher firing temperatures or a choice of a wider range of materials for the hot gas path. The detailed operation of the Return Flow Cascade is described including fluid mechanics and heat transfer phenomena that occur at high heat flux and radial acceleration levels characteristic of modem gas turbine engines. The performance limits of the Return Flow Cascade are identified by the development of a theoretical model that estimates the performance of the system for a range of operating conditions found in the experimental test rig and in an actual gas turbine engine. These limits include vapor choking in the internal blade passages, pool boiling limits in the blade, and surface tension restriction of liquid flow. Cascade initiation limits predicted by the internal vapor choking model are in good agreement with experimental results from testing performed at the Massachusetts Institute of Technology.Copyright

Work in progress — Impact of early design instruction on capstone experiences

In the Olin College curriculum, students have significant, early, and continuous exposure to user-oriented design principles. As a result, our students have a very user-centered approach to problem solving that has affected our yearlong, industry-sponsored capstone in several ways. We have reflected on five years of capstone engagements in order to learn how our program has changed because of the design emphasis in our curriculum. The significance of our work is to inform the many departments that are already undertaking design-centric curriculum reform on how they may modify their capstone experiences to best take advantage of new student understanding, and what to expect when using design principles to engage industry problems.