Browsing by Author "Richard R. Johnson, Committee Chair"

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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.
Field Study and Modeling of an Unglazed Transpired Solar Collector System
(2004-07-08) Maurer, Christine Carol; Richard R. Johnson, Committee Chair; Nancy Ma, Committee Member; James Leach, Committee Member
An unglazed transpired solar collector (UTC) consists of a perforated metal cladding mounted on the south side of a structure. Outdoor air is drawn through the collector for low temperature heating including preheating ventilation air, preheating combustion air, and crop drying. While UTC systems are more commonly used in the Northeast U.S. and Canada, they have not been installed as much in the southeast because of the short heating season. The NC Solar Center installed a data acquisition system to monitor the performance of a UTC system at a manufacturing facility in North Carolina. The main objectives of this project were to evaluate the performance of the components of the system and determine the energy collected and potential monetary savings from the system. The case study was used to understand the principles behind operation of these collectors and compare the monitoring results to previous models of collector performance. A simulation of a UTC system was built in TRNSYS and used to look at the potential for transpired collectors in warmer climates than where UTCs are typically installed. A heat transfer analysis was done to look at the possibility of the collector causing additional heat gain to the building in the summer. The results show that it is possible that the collector causes unwanted heat gain in the summer. Additional investigation could be done to characterize the flow conditions in bypass mode and validate theory with experimental data. Despite the short heating season, some industrial or commercial buildings could still benefit from the technology. The success of the technology depends on site characteristics and building conditions; therefore, transpired collector systems must be considered on a case by case basis. Even if the system works well, space heating is only a minor portion of the energy used in industrial facilities in North Carolina.
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.