Droplet evaporation on heated hydrophobic and superhydrophobic surfaces

The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (similar to 160 degrees) and demonstrate low roll-off angle (similar to 1 degrees), while the hydrophobic substrate supports corresponding values of 120 degrees and similar to 10 degrees. The substrates are heated to different constant temperatures in the range of 40-60 degrees C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact angle, contact radius, and volume evolution over time, are experimentally tracked. The droplets are observed to evaporate primarily in a constant-contact-angle mode where the contact line slides along the surface. The measurements are compared with predictions from a model based on diffusion of vapor into the ambient that assumes isothermal conditions. This vapor-diffusion-only model captures the qualitative evaporation characteristics on both test substrates, but reasonable quantitative agreement is achieved only for the hydrophobic surface. The superhydrophobic surface demonstrates significant deviation between the measured evaporation rate and that obtained using the vapor-diffusion-only model, with the difference being amplified as the substrate temperature is increased. A simple model considering thermal diffusion through the droplet is used to highlight the important role of evaporative cooling at the droplet interface in determining the droplet evaporation characteristics on superhydrophobic surfaces

Simultaneous measurement of temperature and strain in electronic packages using multi-frame super-resolution infrared thermography and digital image correlation

For microelectronic components and systems, reliability under thermomechanical stress is of critical importance. Experimental characterization of hotspots and temperature gradients, which can lead to deformation in the component, relies on accurate mapping of the surface temperature. One method of non-invasively acquiring this data is through infrared (IR) thermography. However, IR thermography is often limited by the typically low resolution of such cameras. Additionally, the unique surface finish preparations required to infer physical deformation using digital image correlation (DIC) generally interferes with the ability to measure the temperature with IR thermography, which prefers a uniform high emissivity. This work introduces a one-shot technique for the simultaneous measurement of surface temperature and deformation using multiframe super-resolution-enhanced IR imaging combined with digital image correlation (DIC) analysis. Multiframe super-resolution processing uses several sub-pixel shifted images, interpolating the image set to extract additional information and create a single higher-resolution image. Measurement of physical deformation is incorporated using a test sample with a black background and low-emissivity speckle features, heated in a manner that induces a non-uniform temperature field and stretched to induce physical deformation. Through processing and filtering, data from the black surface regions used for surface temperature mapping are separated from the speckle features used to track deformation with DIC. This method allows DIC to be performed on the IR images, yielding a deformation field consistent with the applied tensioning. While both the low- and super-resolution data sets can be successfully processed with DIC, super-resolution helps reduce noise in the extracted deformation fields. As for temperature measurement, using super-resolution is shown to allow for better removal of the speckle features and reduce noise, as quantified by a lower mean deviation from the spatial moving average

University of the Future Colombia-Purdue Workshop Report

The University of the Future Workshop, a joint Colombia-Purdue event, was held at Purdue University in West Lafayette, Indiana, October 28-29, 2014. Participants included rectors and board members from six top universities in Colombia, along with executive directors of NGOs, government representatives from the U.S. and Colombia, and Purdue faculty and administrators. The workshop was focused on a dialog among participants on key programs and focuses that will allow universities to be responsive to the 21st century needs of the Americas. This report is a summary of the workshop and is based on the contributions of all the participants. Key themes such as transformative education, collaborative networks of excellence for research education and innovation, and innovation ecosystems are summarized. Recommendations to accelerate transformation of the universities are presented, including the development of networks of excellence in key focus areas

Informe sobre el Taller Universidad del Futuro Colombia-Purdue

El Taller Universidad del Futuro, un evento conjunto de Colombia y Purdue, se llevó a cabo en la Universidad de Purdue en West Lafayette, Indiana, el 28 y 29 de octubre de 2014. Entre sus participantes hubo rectores y consejeros de seis importantes universidades de Colombia, junto con directores ejecutivos de ONG, funcionarios públicos de Estados Unidos y Colombia, y profesores y administradores de Purdue. El taller se centró en el diálogo entre los participantes sobre los programas y áreas de investigación clave que permitirán que las universidades den respuesta a las necesidades del siglo XXI en toda América. Este informe es un resumen del taller y se basa en las contribuciones de todos los participantes. Se sintetizan temas clave como la educación transformadora, las redes de excelencia para la educación y la innovación en colaboración, y los ecosistemas de innovación. Se presentan, además, recomendaciones para acelerar la transformación de las universidades, por ejemplo, el desarrollo de redes de excelencia en áreas clave

IMECE2005-79555 FLOW BOILING IN A MICROCHANNEL HEAT SINK

ABSTRACT Flow boiling heat transfer in a microchannel heat sink is experimentally investigated. The microchannels considered are 275 µm wide and 636 µm deep, and the experiments are conducted at inlet water temperatures in the range of 66 to 95°C and mass fluxes of 341 to 936 kg/m 2 s. Convective boiling heat transfer coefficients are measured and compared to predictions from correlations proposed for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in the microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new heat transfer model is developed to correlate the data in the saturated boiling regime. Good agreement with the experimental measurements indicates that this correlation is suitable for use in the design of twophase microchannel heat sinks

A Concept Paper on Networks of Excellence for Research and Education

Research and education ecosystems, foundational components of knowledge-based economies, are relatively underdeveloped in Latin America. The entire ecosystem of a research university — including resources, corporate partnerships, and research — must capitalize on a symbiosis between the research, education and commercialization missions. A university cannot transform unilaterally nor can universities sustain the required transformation without government and industry participation. Initiatives to accelerate the development of research university ecosystems are critical for the realization of knowledge-based economies and resilient civil societies. To accelerate the development of research and education ecosystems across the Americas, the authors propose to establish “Networks of Excellence” in key focus areas. Each Network of Excellence will be multi-institutional, multi-sector (university, corporate, government, NGO) and multi-national. These multi-faceted networks will allow participants to define and share programs, policies, and content, significantly leverage the resources provided for related programs, and identify opportunities to leapfrog existing programs. Proposed themes for networks include regional grand challenges and cross-cutting capabilities

A Comprehensive Model of a Miniature-Scale Linear Compressor for Electronics Cooling

A comprehensive model of a miniature-scale linear compressor for electronics cooling is presented. Linear compressors are appealing for refrigeration applications in electronics cooling. A small number of moving components translates to less theoretical frictional losses and the possibility that this technology could scale to smaller physical sizes better than conventional compressors. The model developed here incorporates all of the major components of the linear compressor including dynamics associated with the piston motion. The results of the compressor model were validated using experimental data from a prototype linear compressor. The prototype compressor has an overall displacement of approximately 3cm3 ,an average stroke of 0.6 cm. The prototype compressor was custom built for this work andutilizes custom parts with the exception of the mechanical springs and the linear motor. The model results showed good agreement when validated against the experimental results. The piston stroke is predicted within 1.3% MAE. The volumetric and overall isentropic effciencies are predicted within 24% and 31%, MAE respectively