FLOW REGIME DRIVEN THERMAL ENHANCEMENT IN INTERNALLY-GROOVED TUBES

Internally-grooved refrigeration tubes maximize tube-side evaporative heat transfer rates and have been identified as a most promising technology for integration into compact cold plates. Unfortunately, the absence of phenomenological insights and physical models hinders the extrapolation of grooved-tube performance to new applications. The success of regime-based heat transfer correlations for smooth tubes has motivated the current effort to explore the relationship between flow regimes and enhanced heat transfer in internally-grooved tubes. In this thesis, a detailed analysis of smooth and internally-grooved tube data reveals that performance improvement in internally-grooved tubes at low-to-intermediate mass flux is a result of early flow regime transition. Based on this analysis, a new flow regime map and corresponding heat transfer coefficient correlation, which account for the increased wetted angle, turbulence, and Gregorig effects unique to internally-grooved tubes, were developed. A two-phase test facility was designed and fabricated to validate the newly-developed flow regime map and regime-based heat transfer coefficient correlation. As part of this setup, a non-intrusive optical technique was developed to study the dynamic nature of two-phase flows. It was found that different flow regimes result in unique temporally varying film thickness profiles. Using these profiles, quantitative flow regime identification measures were developed, including the ability to explain and quantify the more subtle transitions that exist between dominant flow regimes. Flow regime data, based on the newly-developed method, and heat transfer coefficient data, using infrared thermography, were collected for two-phase HFE-7100 flow in horizontal 2.62mm - 8.84mm diameter smooth and internally-grooved tubes with mass fluxes from 25-300 kg/m²s, heat fluxes from 4-56 kW/m², and vapor qualities approaching 1. In total, over 6500 combined data points for the adiabatic and diabatic smooth and internally-grooved tubes were acquired. Based on results from the experiments and a reinterpretation of data from independent researchers, it was established that heat transfer enhancement in internally-grooved tubes at low-to-intermediate mass flux is primarily due to early flow regime transition to Annular flow. The regime-based heat transfer coefficient outperformed empirical correlations from the literature, with mean and absolute deviations of 4.0% and 32% for the full range of data collected.

“In The Good Old Days of Long Ago": Echoes of Vaudeville and Minstrelsy in the Music of Uncle Dave Macon

Uncle Dave Macon provided an essential link between nineteenth-century, urban popular stage music (especially the minstrel show and vaudeville) and commercialized country music of the 1920s. He preserved through his recordings a large body of songs and banjo techniques that had their origins in urban-based, nineteenth-century vaudeville and minstrelsy. Like the minstrel and vaudeville performers of the nineteenth century, Macon told jokes and stories, employed attention-grabbing stage gimmicks, marketed himself with boastful or outrageous slogans, and dressed with individual flair. At the same time, Macon incorporated many features from the rural-based folk music of Middle Tennessee. Overall, Macon’s repertoire, musical style, and stage persona (which included elements of the rube, country gentleman, and old man) demonstrated his deep absorption, and subsequent reinterpretation, of nineteenth-century musical traditions. Macon’s career offers a case study in how nineteenth-century performance styles, repertoire, and stage practices became a part of country music in the 1920s. As an artist steeped in two separate, but overlapping, types of nineteenth-century music—stage and folk—Macon was well-positioned to influence the development of the new commercial genre. He brought together several strains of nineteenth-century music to form a modern, twentieth-century musical product ideally suited to the new mass media of records, radio, and film. By tracing Macon’s career and studying his music, we can observe how the cross-currents of rural and popular entertainment during the nineteenth and early twentieth centuries interacted to form the commercial genre we now know as country music.