• Aerodynamic heating of the student rocket project-5 sounding rocket

      Mudunuri, Venkata; Goering, Douglas; Das, Debendra K.; Hawkins, Joseph (2005-05)
      This thesis deals with the calculation of the flow properties and heat transfer around the rocket nose cone for Student Rocket Project-5 (SRP-5). Governing differential equations are presented for this purpose, giving the fundamental relations between the skin temperature and flight history. The determination of all the required parameters in the equations is discussed, and the Runge-Kutta numerical method of integration is used to obtain the solution. A model to implement the above equations to predict skin temperature for the given trajectory was built in SIMULINK®. Individual sub-systems of the SIMULINK® model are used to calculate local tree-stream values, Reynolds number, heat absorption capacity and skin friction coefficient. The SIMULINK® model was used to predict the variation of the skin temperature for the SRP-5 flight trajectory. The simulation results also show comparisons of the different subsystem outputs with data provided by the contractor for the NASA Sounding Rocket Contract (NSROC).
    • Analysis and control of time-periodic systems with time delay via chebyshev polynomials

      Ma, Haitao (2003-08)
      A technique for studying the transient response and the stability properties of dynamic systems modeled by delay-differential equations (DDEs) with time-periodic parameters is presented in this thesis. The approach is based on an orthogonal polynomial expansion (shifted Chebyshev approximation). In each time interval with length equal to the delay period, the dynamic system can be reduced to a set of linear difference equations for the Chebyshev expansion coefficients of the state vector in the previous and current intervals. In this way, the transient response of the dynamic system can be directly obtained and the stability properties are found to be determined by a linear map which is the "infinite-dimensional Floquet transition matrix". The technique is then used to study the stability of an elastic system subjected to periodically-varying retarded follower forces, solve a finite horizon optimal control problem via quadratic cost function, and design a delayed feedback controller by using both numerical and symbolic approaches to control the chaotic behavior of a nonlinear delay differential equation.
    • Analysis of a generic flip chip under shock and vibration

      Kasturi, Uday Bhaskar; Chen, Cheng-fu; Butcher, Eric; Lin, Chuen-Sen (2004-12)
      A flip chip package, underfilled or non-underfilled, was analyzed under mechanical shock and/or vibration at the device and board levels, respectively. For the tests at the device level, the maximum stress developed at the corner-most solder joint. The horizontal drop orientation, with the chip facing up, produced the worst scenario for solder joint lifetime prediction. The underfilled package is better than non-underfilled under the excitation of mechanical shock and vibration. Parametric studies of the underfill material strength suggested that the higher the elastic modulus, the better it carried the mechanical shock. However, practically the upper bound of the elastic modulus is limited to avoid die cracking due to thermal mismatch of material expansion. The combined loading of thermal residual stress and mechanical shock was also conducted to study their influence on the solder lifetime prediction. It was found that the thermal pre-stressed condition plays a key role for the von Mises stress excursion, but has almost no influence on the shock-induced normal stress. The phenomenon appears similarly in the board level testing, but with worse reliability in solders due to the higher stresses induced.
    • Analysis of an oscillating plate coupled with fluid

      Nash, Michael J.; Peng, Jifeng; Sheng, Gang; Lin, Chuen-Sen (2013-12)
      The mechanical vibration of an oscillating cantilever plate is studied to determine the interaction of a plate coupled with air and with water. Experimental data was collected and analyzed using multiple methods including Fast Fourier Transform, wavelet analysis, and the Hilbert-Huang Transform (HHT) to characterize the behavior of the plate. The HHT is able to process nonlinear and nonstationary signals and provides more meaningful information compared to the traditionally used Fourier transform for similar applications. The HHT was found to be appropriate and more descriptive for the analysis of coupled fluid-structure systems. Digital Particle Image Velocimetry (DPIV) was also used to analyze the circulation and energy transferred to the fluid.
    • Analysis of ground source heat pumps in sub-Arctic conditions

      Bishop, Stephen; Peterson, Rorik; Daanen, Ronald; Shur, Yuri (2014-05)
      The Purpose of this project is to investigate the factors involved in the application of a ground source heat pump in subarctic conditions. This project originated with the construction of a ground source heat pump (GSHP) built at Cold Climate Housing Research Center's (CCHRC) Research Testing Facility. The GSHP built by CCHRC is an experiment to test the viability of a GSHP with different surface coverings. Specifically, this project will focus on different soil and atmospheric properties to gauge their effect on a GSHP in sub-arctic conditions. The project is primarily broken into 3 main sections which test in simulation: the effects of soil and atmospheric properties on heat flow into soil, the effects of these properties on a hypothetical GSHP and applying this to a simulation of CCHRC's GSHP. Additionally, some mitigation efforts were attem pted in simulation to improve the viability of the GSHP built by CCHRC.
    • Analytical and numerical studies on macro and micro scale heat sinks for electronics applications

      Kulkarni, Devdatta P. (2003-08)
      From the practice in computer industry the standard approach for electronics cooling is fan-cooled heat sinks. We developed thermal models for forced convection heat sinks. An Intel Pentium ill chip has been adopted as a preliminary design case to develop necessary equations. We found the heat dissipated from the aluminum heat sink, based upon different modes of airflow over the fins. We also considered radiation heat transfer. We performed transient heat transfer analysis to determine the time to attain the steady state temperature for the whole system for macro and micro scale also. Next, we refined our one-dimensional analytical convection analysis using the numerical analysis. This was done using the computational fluid dynamics code Fluent to obtain accurate velocity fields over the fins. Using these improved velocities, convective heat transfer coefficients were computed. Next, we have miniaturized the processor chip size to the micrometer scale and have designed a heat sink based upon the models we have developed. Calculations of mean free path and Knudsen number shows the continuum theory for air still holds for our designed micro-channels. Equations for natural convection heat sinks are also explored as a part of this study. In the microscale study, we did forced and natural convection analysis.
    • Axisymmetric numerical heat transfer analysis of natural gas hydrates reservoir

      Subbaihaannadurai, Vijayagandeeban; Das, Debendra K.; Patil, Shirish L.; Goering, Douglas J. (2004-12)
      Gas hydrates are crystalline substances, occurring in nature under high pressure and low temperature. Numerical studies were conducted on dissociation of gas hydrate to recover natural gas. The model is a cylindrical geometry with a wellbore at the center through which hot water is injected. Through this thermal stimulation technique frozen hydrate reservoir is melted and natural gas is released. The computational fluid dynamics software FLUENT was adopted to generate the model. The initial model was solely comprised of a hydrate layer. This model was refined by adding the overburden and the underburden to the hydrate and exploring the thermal regime of the entire composite medium. Unsteady state results showing the dissociation front propagation with respect to time were calculated. In the first part, the hydrate medium is dissociated by the conduction phenomenon only. In the second part, due to the porous nature of the hydrate medium, both conduction and convection phenomena are considered. This thesis presents the following results obtained from simulations using Fluent. They are: temperature rise within the reservoir with time, temperature profiles in the radial direction, and steady and transient state solutions of the dissociation of gas hydrate with the liquid fraction in the reservoir. Comparison of our results with a finite difference model and a finite element model is also included. Volumes of gas released with respect to time and thermal efficiency ratios are also determined.
    • Building a toolset for fuel cell turbine hybrid modeling

      Burbank, Winston S. (2006-12)
      Fuel cell/gas turbine hybrids show promise of high efficiency power generation, with electrical efficiencies of 70% or better shown by modeling, although these efficiency levels have not yet been demonstrated in hardware. Modeling of such systems is important to optimize and control these complex systems. This work describes a modeling tool developed to examine steady-state operation of different hybrid configurations. This model focuses on the area of compressor-turbine modeling, which is a key component of properly controlling fuel cell/gas turbine hybrids. Through side-by-side comparisons, this model has been tested and verified by Dr. Wolf of Brayton Energy [1]. This modeling tool will be used in further work to evaluate various configurations of turbines and fuel cells in hybrid configurations, focusing on both the performance and cost of such systems.
    • Buoyancy Effects On Building Pressurization In Extreme Cold Climates

      Bargar, Harold Edward; Das, Debendra K.; Goering, Douglas J.; Johnson, Ronald A.; Lin, Chuen-Sen; Quang, Pham X. (2003)
      This research investigates building pressurization due to buoyancy effect. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) presents an idealized equation to calculate the buoyancy effect. This dissertation compares differential pressure measurements from an actual building exposed to extremely cold temperatures to this idealized model. It also presents new statistical models based on the collected data. These new models should provide engineers with improved tools to properly account for building pressurization for designs in extreme cold climates. Building pressurization, the differential pressure between the interior of a building and its exterior surroundings, is an important design consideration. Pressurization is the driving force in building infiltration/exfiltration. It also affects air flow within building zones. Improper calculation of pressurization can result in under-sizing the building's heating and cooling systems, improper operation of air distribution systems, improper operation of elevators, and freezing and failure of water distribution and circulation systems. Building pressurization is affected by: wind (speed and direction), exterior-to-interior temperature difference, and mechanical equipment operation. In extreme cold climates, the predominant effect is air buoyancy due to temperature differences across the building envelope. The larger the temperature difference, the larger the buoyancy effect. In extreme cold climates, the largest temperature differences often occur at times when wind speed is negligible. This dissertation also demonstrates the use of existing data sources such as building automation systems to collect data for basic research. Modern systems automation provides a tremendous amount of data that, in the past, had to be collected through separate instrumentation and data acquisition systems. Taking advantage of existing automation systems can provide the required data at greatly reduced costs when compared to previous industry practices. The statistical analysis approach taken in this research expands the tools for engineering design. Actual interactions of real world variables are analyzed and used to produce prediction models. These techniques allow the model to incorporate relationships which may not be fully understood at the underlying principle level but are evidenced in the data collected from actual installations.* *This dissertation includes a CD that is compound (contains both a paper copy and CD as part of the dissertation). The CD requires the following applications: Internet Browser; Adobe Acrobat; Microsoft Office; Image Viewer.
    • A case/control analysis and comparison of indoor air quality in Alaskan homes

      Dinakaran, Satish; Johnson, Ron; Naidu, Sathy; Lin, Chuen-Sen; Seifert, Rich (2005-08)
      Indoor Air Quality (IAQ) parameters such as CO, CO₂, relative humidity, temperature, radon, particulate matter, formaldehyde, benzene, toluene, hexane, Total Volatile Organic Compounds (TVOC) and microbial matter were monitored before and after remediation in 36 low-income homes in Alaska (Hooper Bay and Fairbanks). The objective was to see if there was any improvement in IAQ with remediation. Hooper Bay homes had significantly higher levels of CO₂ and relative humidity compared to Fairbanks homes both before and after remediation. There was a general reduction in CO₂ with remediation, although it was not statistically significant. When IAQ in two moderate-income homes in Fairbanks was compared with that in the remediated low-income homes, it was observed that indoor CO₂ levels were affected by ventilation rates and per capita floor area. A single zone model to predict concentration of indoor pollutants was constructed, using steady state and transient mass conservation, to predict, metabolically produced CO₂, and particulate matter when no indoor sources were present. The cost of energy to reduce indoor CO₂ levels in one of the homes by increasing ventilation by either using an exhaust-only system or a Heat Recovery Ventilator (HRV) is discussed.
    • Cofiring coal and biomass at Aurora Power Plant in Fairbanks, Alaska

      Wright, Zackery; Huang, Daisy; Nicholls, David; Peterson, Rorik; Schnabel, William (2016-05)
      Biomass energy has been a topic of great interest over the previous few years in Alaska; especially when various fuel sources were priced at a record high. Interior Alaska has the potential to utilize woody biomass to offset the use of coal in many of its power generating facilities. In this study, woody biomass in the form of clean aspen (Populus tremuloides) chips was cofired with Usibelli coal at the Aurora Power Plant facility in downtown Fairbanks, Alaska. Biomass was successfully cofired at low average rates of 2.4% and 4.81% of total energy value. Combustion gasses were analyzed using measuring probes in the exhaust stack. The 2.4% biomass test saw, on average, an increase in CO and CO₂ by 95ppm and 2%, respectively. A decrease in NOx of 1ppm was observed. During the 4.81% biomass test, CO increased by 83ppm, NOx decreased by 18ppm, and CO decreased by 1%. Opacity increased by 0.1% during the 2.4% biomass test and 0.17% during the 4.81% biomass test. The challenges facing a small scale facility in Interior Alaska are also presented. The testing exemplified that the use of biomass in stoker/grate boilers in Alaska is technically feasible with relative ease. No technical barriers to cofiring at low levels on an on-going basis were found at the Aurora Power Plant and this conclusion would likely hold true at similar facilities in interior Alaska.
    • Comparison of resistance-based strain gauges and fiber bragg gratings in the presence of electromagnetic interference emitted from an electric motor

      Keller, Douglas Jr.; Peterson, Rorik; Fochesatto, Javier; Chen, Cheng-fu (2018-12)
      This thesis reports a performance analysis of resistance based strain gauges and fiber optic fiber Bragg gratings in an environment contaminated by high levels of electromagnetic interference. The obtained results are directly applicable to the development of aerospace vehicles propelled by electrical motors. An area of importance in this relatively new technology is characterizing the mechanical loadings coming off a propulsion device in a stationary setup. This characterization is usually accomplished through the utilization of load cells. The majority of the load cells used in such an application are based on measurements acquired through resistance strain gauges. However, electric motors are known to radiate electromagnetic interference (EMI), which in the case of brushless DC motors is pulsing, alternating, square waves. This EMI severely degrades the signal produced by the resistance strain gauge. This degradation is due to the gauge's metallic construction, acting as an antenna for the EMI. To evaluate the performance of alternative strain measuring methods, a load cell implementing both the resistance strain gauge and fiber Bragg grating sensor, the latter of which is immune to EMI, was designed as a test article. The load cell was calibrated and demonstrated a thrust load sensitivity of 1.93 ±0.04 lbf through the strain gauge system and 0.56 ±0.56 lbf through the fiber Bragg grating system. The device was subjected to both mechanical loading and EMI to quantify the effect of the EMI on the resistance strain gauge. Testing of the device included operating a brushless DC motor, with a coupled flywheel, attached to the load cell at a range of angular velocities from 500 to 2400 RPM. During laboratory testing the resistance strain gauge signal exhibited an important amount of signal spikes and electrical noise, introduced by the EMI contamination; the fiber Bragg grating did not. The spikes increased linearly with the speed of the motor. The electrical noise required bandpass filtering to extract the mechanical signal, which was obtained without noise in the fiber Bragg grating signal. The resistance strain gauge signal, at a maximum, had a signal to noise ratio of 0.0443; the fiber Bragg grating signal, at a minimum, had a signal to noise ratio of 2.0114. These results demonstrated the fiber Bragg grating is more applicable in an EMI contaminated environment.
    • Corrosion behavior and residual stress of microarc oxidation coated AZ31 magnesium alloy for biomedical applications

      Gu, Yanhong; Bandopadhyay, Sukumar; Severin, Kenneth P.; Chen, Cheng-fu; Kim, Sunwoo (2012-08)
      Mg alloys are potentially new biomaterials for bone repair or replacement. Appropriate coating is, however, needed to make the Mg alloy more resistant to corrosion. In this research, protective microarc oxidation (MAO) coatings were produced on AZ31 Mg alloys in sodium phosphate electrolyte. The coatings were produced under varying pulse frequency, applied voltage, oxidation time and electrolyte concentrations. This research analyzed the effects of the above four MAO process control parameters on the residual stresses and the corrosion behavior. Optimization of the MAO control parameters would allow production of AZ31 Mg alloy with high corrosion resistance. It is well accepted that residual stress and corrosion behavior are two significant factors in the development of AZ31 Mg alloys. The residual stresses in the MAO coatings were evaluated by the X-ray diffraction (XRD)-sin²ψ method. A predictive model of the residual stresses is proposed and a principal components analysis (PCA) was conducted to determine the contribution of the MAO control parameter on the residual stresses. Long-term corrosion behavior of MAO-coated Mg alloys was evaluated by the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The porosity of the samples after various immersion durations was evaluated by the potentiodynamic polarization method. The pre- and post- corrosion microstructures and the phase composition of MAO-coated samples were studied. Post-corrosion phase identification showed that hydroxyapatite (HA) was formed on the surface of the samples. The ratio of Ca/P in HA was determined by the X-Ray Fluorescence (XRF) technique. The degradation of the MAO-coated AZ31 alloys is reduced due to the MAO coating and the formation of a corrosion product layer. A predictive model of the corrosion current density is proposed and a PCA was conducted to determine the contributions of the individual MAO control parameter on the corrosion rate. The corrosion process and mechanism of MAO-coated AZ31 alloys in SBF were modeled based on the electrochemical corrosion results and the pre- and post-corrosion surface analysis. It is believed that under optimized control parameters, the MAO-coated AZ31 Mg alloy is superior implant material for biomedical applications.
    • Corrosion behavior of microarc oxidation and polycaprolactone coatings applied to AZ31 magnesium alloy evaluated in simulated body fluid and balanced salt solution

      Wilke, Benjamin M.; Zhang, Lei; Peterson, Rorik; Zhang, Junqing; Chen, Cheng-fu (2015-08)
      Recent research in orthopedic implant materials has focused on the use of magnesium alloys as a base material due to its mechanical properties similar to that of human bone. Rapid corrosion of magnesium materials in aqueous environments poses a significant hurdle to their application as a biomedical implant. A variety of coatings have been shown to improve the corrosion resistance of magnesium based materials in simulated body fluid environments including microarc oxidation and polymer coatings. However, formulation and corrosion rates vary significantly between solution types. Furthermore, in vivo results have shown that many common in vitro solutions over estimate corrosion rates. In addition to variations between solutions needing to be resolved, there has been little work performed to characterize large sample corrosion under stress. This is an essential step in evaluating concept performance at a macro scale, for application as a human implant. The experiments performed and presented in this thesis primarily involve the comparison of conventional simulated body fluid (c-SBF) and Earle's balanced salt solution (EBSS). Samples evaluated in these environments are microarc oxidation (MAO) coated AZ31 magnesium alloy and polycaprolactone dip-coated AZ31. MAO coated samples were created for a range of process settings to observe the effect of processing on corrosion performance. A dependence of MAO coating thickness on process voltage was found which augmented the initial corrosion resistance values observed via electrochemical testing. Both MAO and PCL coatings were found to improve the corrosion resistance of the samples as compared to uncoated AZ31. It was found that all variations (MAO, PCL, and uncoated) showed a reduced corrosion rate in EBSS as compared to c-SBF. This corrosion reduction was apparent through potentiodynamic scanning, electrochemical impedance spectroscopy, and visual inspection. Preliminary mechanical corrosion results, in the form of constant extension testing, showed no dependence of corrosion on stress level. Future work may be aimed towards expanding modes of mechanical testing and further refining simulated body fluids to fit with in vivo test results.
    • Corrosion behavior of titanium dioxide (TiO₂)-coated Al alloy in saline environment

      Rabbey, Md Fazlay; Zhang, Lei; Zhang, Junqing; Huang, Daisy; Peterson, Rorik (2018-08)
      Al alloys have been used in many applications, however, they are susceptible to corrosion when exposed in saline environment. In this work, TiO₂ nanoellipsoids with aspect ratios (AR) of 1, 2, 4 and 6 were synthesized, TiO₂ coatings of AR 1, AR2, AR4, and AR6 were fabricated on AA2024-T3 Al alloy substrate, and their corrosion behaviors in the saline environment were investigated by analyzing the scanning electron microscope (SEM) imaging, potentiodynamic polarization scans and electrochemical impedance spectroscopy. TiO₂-coated Al samples showed better corrosion performance compared to the bare Al sample. Among the coated samples, TiO₂ AR6 coated samples showed lower corrosion rate compared to other samples. Although TiO₂ nanoellipsoids coatings show good corrosion resistance, it is noted that TiO₂ coatings are porous, which allows the penetration of corrosive media through the pores to reach the surface of the substrate. A polystyrene (PS)-TiO₂ AR6 nanocomposite coating was fabricated, where the pores of the coatings were sealed by polystyrene, which is expected to further improve the corrosion resistance of TiO₂ coatings.
    • Dynamics simulation of human box delivering task

      Owens, Paul Davis; Xiang, Yujiang; Peterson, Rorik; Chen, Cheng-fu (2018-05)
      The dynamic optimization of a box delivery motion is a complex task. The key component is to achieve an optimized motion associated with the box weight, delivering speed, and location. This thesis addresses one solution for determining the optimal delivery of a box. The delivering task is divided into five subtasks: lifting, transition step, carrying, transition step, and unloading. Each task is simulated independently with appropriate boundary conditions so that they can be stitched together to render a complete delivering task. Each task is formulated as an optimization problem. The design variables are joint angle profiles. For lifting and carrying task, the objective function is the dynamic effort. The unloading task is a byproduct of the lifting task, but done in reverse, starting with holding the box and ending with it at its final position. In contrast, for transition task, the objective function is the combination of dynamic effort and joint discomfort. The various joint parameters are analyzed consisting of joint torque, joint angles, and ground reactive forces. A viable optimization motion is generated from the simulation results. It is also empirically validated. This research holds significance for professions containing heavy box lifting and delivering tasks and would like to reduce the chance of injury.
    • Effects of electromigration on the reliability of radio frequency microelectro mechanical switches

      Karri, Naveen Kishore (2004-12)
      Radio Frequency (RF) Micro-Electro-Mechanical System (MEMS) switches have many advantages over semiconductor switches. Despite these advantages they are not implemented in reliability demanding space, defense and commercial applications because of reliability concerns. Although some failure modes have been identified so far, other failure modes are still under research. Electromigration, a well-known failure mechanism in interconnects, was recently recognized as a possible cause of failure in micro-switches. However, there have been no instances of electromigration studies in the literature. This thesis presents a preliminary study on the electromigration failure and its impact on the lifetime of MEMS switches. A simulation program that emulates the electromigration process was developed. Parametric studies were performed to study the impact of impact certain parameters on electromigration process. The combined effects of Joule heating and electromigration were analyzed. Unlike passivated interconnects, the micro-switch is cantilevered and suspended in an inert medium without encapsulation. The electromigration lifetime estimation program developed in this thesis is applicable to all such free structures. Joule heating has been demonstrated to be a key factor in the electromigration failure of micro-switches. Results showed that the electromigration process is very slow at the beginning. After a certain time, the resistance is found to increase exponentially, increasing the temperature of the strip drastically toward failure. The same trend is also observed in a gold micro-switch, but with much slower rate of electromigration degradation, indicating a longer lifetime.
    • Electric thermal storage in isolated wind diesel power systems: use of distributed secondary loads for frequency regulation

      Janssen, Nicholas T.; Wies, Richard W.; Peterson, Rorik A.; Mueller-Stoffels, Marc; Xiang, Yujiang (2017-08)
      Isolated coastal utilities in Arctic villages commonly use a mix of diesel and wind power to provide electrical service to their consumers. It is common for such communities to experience periods of high wind generation for which no immediate demand exists and either waste, curtail, or poorly utilize the surplus. The objective of the present work is to explore (through mathematical and numerical modelling) the technical feasibility of and optimization strategies for distributing this excess wind energy as domestic space heat for use as a cleaner, more economical alternative to fossil fuels. Autonomously controlled Electric Thermal Storage (ETS) devices are considered as a solution to decouple the supply of excess wind power with domestic heat demand without the need for communication infrastructure or a second distribution circuit. First, using numerical heat transfer analysis, it is shown that the performance of an ETS heater core can be generalized and expressed in terms of its physical properties and simple geometric dimensions in such a way as to inform system sizing and economic performance studies for prospective applications. Furthermore, a collection of autonomous ETS units is shown (using a full-scale lab-validated mathematical model) to possess the ability to assume the role of partial and/or sole frequency regulator on a hybrid wind-diesel system. Several design changes are proposed, which render the commercially-available units more amenable to frequency regulation. Ultimately, ETS is shown to be a promising alternative means of utilizing excess renewable energy for domestic space heat while providing additional stability to the electrical grid.
    • Evaluation and parametric modeling of 50 kW organic rankine cycle for waste heat recovery from rural Alaska diesel generator power plants

      Avadhanula, Vamshi Krishna; Lin, Chuen-Sen; Das, Debendra K.; Bargar, Harold E.; Kim, Sunwoo (2015-08)
      In rural Alaska, there are about 180 villages that run independent electrical power systems using diesel generator sets. A diesel engine generator loses fuel energy in the form of waste heat through the charge air cooler (after cooler), the jacket water cooler, friction, and exhaust. Diesel engine jacket water and exhaust account for about 20% and 30% of the total fuel energy, respectively. In previous studies it has been demonstrated that about 80% of the heat present in jacket water and 50% of the heat from exhaust gases can be recovered for useful purposes such as heating, power generation, refrigeration, and desalination. In this study, the diesel engine waste heat application selected was power generation using an organic Rankine cycle (ORC) heat engine. The basic principle of an ORC system is similar to that of the traditional steam Rankine cycle; the only difference is the working fluid. The working fluids generally used in an ORC are refrigerants, such as R11, R113, R123, R134a, R245fa, and HFE-7000. The working fluid in the ORC system under study is R245fa. A typical ORC consists of a pump, preheater, evaporator, expansion machine (expander), and condenser. The working fluid is pressurized through the pump and supplied to the preheater and evaporator, where it is heated by the heat source. The working fluid exits the evaporator as vapor or liquid/vapor. It expands in the expander, generating power. The low-pressure working fluid exiting the expansion machine is liquefied in the condenser by a cooling source, returned to the pump, and the cycle repeats. At the University of Alaska Fairbanks (UAF) power plant, a lab experimental setup was designed: a hot water loop (heat source) and cold water loop (heat sink) for testing the 50 kW ORC power unit. Different diesel engine waste heat recovery conditions were simulated to study the unit's reliability and performance. After lab testing, the ORC system was installed permanently on a 2 MW Caterpillar diesel engine for jacket water heat recovery in Tok, Alaska, and tested further. These two tests provide for the goals of the present dissertation which are: (i) testing of a 50 kW ORC system for different heat source and heat sink supply conditions, (ii) develop guidelines on applying the present 50 kW ORC system for individual rural Alaska diesel gen-sets, (iii) develop empirical models for the screw expander, (iv) develop heat transfer correlations for single-phase and two-phase evaporation, and two-phase condensation for refrigerant R245fa in the preheater, evaporator and condenser, respectively, and (v) parametric modeling and validation of the present ORC system using the empirical correlations developed for a screw expander and R245fa in heat exchangers to predict the performance of the ORC system for individual diesel generator sets. The lab experimental data were used to plot performance maps for the power unit. These maps were plotted with respect to hot water supply temperature for different ORC parameters, such as heat input to power unit in evaporator and preheater, heat rejection by power unit in condenser, operating power output, payback period, and emissions. An example of how performance maps can be used is included in this dissertation. As detailed in this dissertation, the resulting lab experimental data were used to develop guidelines for independent diesel power plant personnel installing this ORC power unit. The factors influencing selection of a waste heat recovery application (heating or power) are also discussed. A procedure to find a match between the ORC system and any rural diesel generator set is presented. Based on annual electrical load information published in Power Cost Equalization data for individual villages, a list of villages where this ORC system could potentially be beneficial is included. During lab work at the UAF power plant, experimental data were also collected on the refrigerant side (R245fa) of the ORC system. Inlet and outlet pressures and temperatures of each component (evaporator, pump, and expander) of the ORC were measured. Two empirical models to predict screw expander power output were developed. The first model was based on polytropic work output, and the second was based on isentropic work output. Both models predicted screw expander power output within ±10% error limits. Experimental data pertaining to the preheater, evaporator, and condenser were used to develop R245fa heat transfer correlations for single-phase and two-phase evaporation and two-phase condensation in respective heat exchangers. For this study the preheater, evaporator, and condenser were brazed plate heat exchangers (BPHEs). For single-phase heat transfer in the preheater, a Dittus-Boelter type of correlation was developed for R245fa and hot water. For R245fa evaporation in the evaporator, two heat transfer correlations were proposed based on two-phase equation formats given in the literature. For condensation of R245fa in the condenser, one heat transfer correlation was proposed based on a format given in the literature. All the proposed heat transfer correlations were observed to have good agreement with experimental data. Finally, an ORC parametric model for predicting power unit performance (such as power output, heat input, and heat rejection) was developed using the screw expander model and proposed heat transfer correlations for R245fa in heat exchangers. The inputs for the parametric model are heating fluid supply conditions (flow rate and temperature) and cooling fluid supply conditions, generally the only information available in rural Alaska power plant locations. The developed ORC parametric model was validated using both lab experimental data and field installation data. Validation has shown that the ORC computation model is acceptable for predicting ORC performance for different individual diesel gen-sets.
    • Exhaust thimble for arctic environments

      Evans, Mark P.; Peterson, Rorik; Kim, Sun woo; Lin, Chuen-Sen (2016-05)