Browsing by Author "James W. Leach, Committee Member"

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A 100 Motor Study: Investigating pre-EPAct Motors as a Subset of the Industrial Motor Population with Regards to the Economics of Motor Repair and Replace Decisions
(2005-04-05) Kaufman, Nicole Marie; Alexander O. Hobbs, Committee Member; James W. Leach, Committee Member; Richard R. Johnson, Committee Chair
In the absence of hard data, the engineering world tends to be overly conservative in estimating benefits of change. The hypothesis herein discussed is that with hard data, the economics of motor repair/replace decisions could change significantly. If true, this could appreciably boost the efficiency of the industrial motor population by affecting the penetration of high-efficiency motors, such as NEMA Premiums. The energy savings from motor replacement depend on the difference between the efficiency of the new motor and the old motor. There has been a great deal of work investigating new motor efficiency and very little work investigating the actual running efficiency of older motors in the field. Motors that have operated for years experiencing failures and repairs may operate below their original nameplate or assumed efficiency. This study is a preliminary investigation of the efficiency of motors in industrial settings with the purpose of updating currently available motor analysis software tools to reflect more accurately the economic benefits of utilizing high-efficiency industrial induction motors.
Measurement and Critical Investigation of the Actual Annual Daylighting Performance of a Middle School in North Carolina
(2008-08-20) Athalye, Rahul Anand; Herbert M. Eckerlin, Committee Chair; James W. Leach, Committee Member; Stephen D. Terry, Committee Member; Wayne J. Place, Committee Member
This research investigates and documents the performance of the daylighting design at Northern Guilford Middle School over an entire year. Photometric sensors and dataloggers were used to collect illumination data from the school from March 2007 to February 2008. A few experiments were performed as well during this period to determine the effect of certain design elements on the daylighting. The daylighting design uses a unique curved translucent interior light-shelf that is intended to distribute light deep into the classroom. Illumination values at fixed locations within a classroom are presented on a monthly basis as a direct measure of the daylighting performance. The research indicates that this daylighting design is highly dependent on direct beam sunlight falling on the translucent light-shelf with the annual daylighting performance varying depending upon the position of the sun in the sky. The daylighting performance can be identified as being distinctly different for the winter, equinox and summer periods. On an average, the illumination levels in the winter are well above 300 fc, near the equinox at 300 fc while in the summer they fall below the 50 footcandle target required in a school classroom. Tests performed on the three classrooms wings oriented 10° different from each other revealed uneven performance and that the large white reflective roof contributes about 50% to the daylighting in classrooms on the north side of each of the wing hallways. The high light levels during winter months cause problems with projectors and other visual aids that are used more frequently now than before for teaching in schools. Also, like with many side-lit daylighting systems, there is a significant drop in light levels from the front to the back of the classroom. The relatively low position of the interior light-shelf in the south-side classroom introduces discomfort glare during the winter months when direct light falls on the light-shelf. The research emphasizes the changing light levels over the seasons, the high front to back gradient and the inconsistent performance of different wings as the major issues with this daylighting design. Despite some of these issues, this design need not be discarded, especially since it is the most cost effective amongst other daylighting strategies implemented across schools in North Carolina. An accurate physical model would allow real world testing of methods to alleviate some of the problems in this design. Of importance too, is the effect of daylighting on the energy performance of the school, which needs to be investigated as well. Perhaps the most novel component of this design, the curved light-shelf, needs to be worked upon before its performance can be predicted and optimized under various solar conditions.
Novel Simulation of Anaerobic Digestion Using Computational Fluid Dynamics
(2002-11-13) Fleming, Jason Graham; James W. Leach, Committee Member; Jiayang Cheng, Committee Member; Herbert M. Eckerlin, Committee Member; Kevin M. Lyons, Committee Member; Richard R. Johnson, Committee Chair
In an effort to optimize the economy and performance of covered anaerobic reactor systems, a comprehensive dynamic and mechanistic model was created to simulate the constituent processes of full-scale anaerobic digestion. These processes included the following: bulk fluid motion, sedimentation, bubble mixing, bubble entrainment, buoyant mixing, advection, biological reactions, internal heat transfer, and heat exchange with the environment. This model contrasted with conventional models that assumed uniform concentrations and temperature throughout the reacting medium. Novel numerical simulation techniques were developed to simulate the heat and mass transfer resulting from two phase gas-liquid flow and unsteady buoyancy driven flow. The complete model was implemented in a computer code called LagoonSim3D. Three years of performance data from a full-scale covered anaerobic digestion system in central North Carolina were used to quantify unknown parameters as well as validate the LagoonSim3D software. The LagoonSim3D software predicted the temperature of the covered lagoon within 5.7% and the dynamic monthly gas production within 11%. The external convective heat transfer coefficient was found to be a linear function of wind speed. The convective heat transfer coefficient of the gas gap between the cover and the slurry was found to be 10 W/m²K. The average particle settling velocity was found to be 0.02 cm/s. These previously unknown parameters were important for the design of future anaerobic digestion systems. The validated LagoonSim3D model was used to determine the effect of design changes on reactor performance. In part, it was found that the case study system had at least twice the optimal volume, and a nearly optimal depth. It was also found that the performance of the case study system could be improved by cutting the flush water volume in half. It was concluded that the LagoonSim3D software enabled a flexible and general evaluation of covered anaerobic lagoon designs that was not possible with previously available steady state and complete-mix models.