Mechanical Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2795
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Item Clinorotation time-lapse microscopy for live-cell assays in simulated microgravity(2013) Yew, Alvin G.; Hsieh, Adam; Atencia, Javier; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To address the health risks associated with long-term manned space exploration, we require an understanding of the cellular processes that drive physiological alterations. Since experiments in spaceflight are expensive, clinorotation is commonly used to simulate the effects of microgravity in ground experiments. However, conventional clinostats prohibit live-cell imaging needed to characterize the time-evolution of cell behavior and they also have limited control of chemical microenvironments in cell cultures. In this dissertation, I present my work in developing Clinorotation Time-lapse Microscopy (CTM), a microscope stage-amenable, lab-on-chip technique that can accommodate a wide range of simulated microgravity investigations. I demonstrate CTM with stem cells and show significant, time-dependent alterations to morphology. Additionally, I derive momentum and mass transport equations for microcavities that can be incorporated into various lab-on-chip designs. Altogether, this work represents a significant step forward in space biology research.Item EFFECTS OF PREHEATED COMBUSTION AIR ON LAMINAR COFLOW DIFFUSION FLAMES UNDER NORMAL AND MICROGRAVITY CONDITIONS(2005-08-30) Ghaderi Yeganeh, Mohammad; Gupta, Ashwani K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Global energy consumption has been increasing around the world, owing to the rapid growth of industrialization and improvements in the standard of living. As a result, more carbon dioxide and nitrogen oxide are being released into the environment. Therefore, techniques for achieving combustion at reduced carbon dioxide and nitric oxide emission levels have drawn increased attention. Combustion with a highly preheated air and low-oxygen concentration has been shown to provide significant energy savings, reduce pollution and equipment size, and uniform thermal characteristics within the combustion chamber. However, the fundamental understanding of this technique is limited. The motivation of the present study is to identify the effects of preheated combustion air on laminar coflow diffusion flames. Combustion characteristics of laminar coflow diffusion flames are evaluated for the effects of preheated combustion air temperature under normal and low-gravity conditions. Experimental measurements are conducted using direct flame photography, particle image velocimetry (PIV) and optical emission spectroscopy diagnostics. Laminar coflow diffusion flames are examined under four experimental conditions: normal-temperature/normal-gravity (case I), preheated-temperature/normal gravity (case II), normal-temperature/low-gravity (case III), and preheated-temperature/low-gravity (case IV). Comparisons between these four cases yield significant insights. In our studies, increasing the combustion air temperature by 400 K (from 300 K to 700 K), causes a 37.1% reduction in the flame length and about a 25% increase in peak flame temperature. The results also show that a 400 K increase in the preheated air temperature increases CH concentration of the flame by about 83.3% (CH is a marker for the rate of chemical reaction), and also increases the C2 concentration by about 60% (C2 is a marker for the soot precursor). It can therefore be concluded that preheating the combustion air increases the energy release intensity, flame temperature, C2 concentration, and, presumably, NOx production. Our work is the first to consider preheated temperature/low-gravity combustion. The results of our experiments reveal new insights. Where as increasing the temperature of the combustion air reduces the laminar flame width under normal-gravity, we find that, in a low-gravity environment, increasing the combustion air temperature causes a significant increase in the flame width.