Browsing by Subject "Thermal model"
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Item Control-oriented modeling of dynamic thermal behavior and two‒phase fluid flow in porous media for PEM fuel cells(2013-12) Hadisujoto, Budi Sutanto; Moon, T. J. (Tess J.); Chen, Dongmei, Ph. D.The driving force behind research in alternative clean and renewable energy has been the desire to reduce emissions and dependence on fossil fuels. In the United States, ground vehicles account for 30% of total carbon emission, and significantly contribute to other harmful emissions. This issue causes environmental concerns and threat to human health. On the other hand, the demand on fossil fuel grows with the increasing energy consumption worldwide. Particularly in the United States of America, transportation absorbs 75% of this energy source. There is an urgent need to reduce the transportation dependence on fossil fuel for the purpose of national security. Polymer electrolyte membrane (PEM) fuel cells are strong potential candidates to replace the traditional combustion engines. Even though research effort has transferred the fuel cell technology into real‒world vehicle applications, there are still several challenges hindering the fuel cell technology commercialization, such as hydrogen supply infrastructure, cost of the fuel cell vehicles, on‒board hydrogen storage, public acceptance, and more importantly the performance, durability, and reliability of the PEM fuel cell vehicles themselves. One of the key factors that affect the fuel cell performance and life is the run‒time thermal and water management. The temperature directly affects the humidification of the fuel cell stack and plays a critical role in avoiding liquid water flooding as well as membrane dehydration which affect the performance and long term reliability. There are many models exists in the literature. However, there are still lacks of control‒oriented modeling techniques that describe the coupled heat and mass transfer dynamics, and experimental validation is rarely performed for these models. In order to establish an in‒depth understanding and enable control design to achieve optimal performance in real‒time, this research has explored modeling techniques to describe the coupled heat and mass transfer dynamics inside a PEM fuel cell. This dissertation is to report our findings on modeling the temperature dynamics of the gas and liquid flow in the porous media for the purpose of control development. The developed thermal model captures the temperature dynamics without using much computation power commonly found in CFD models. The model results agree very well with the experimental validation of a 1.5 kW fuel cell stack after calibrations. Relative gain array (RGA) was performed to investigate the coupling between inputs and outputs and to explore the possibility of using a single‒input single‒output (SISO) control scheme for this multi‒input multi‒output (MIMO) system. The RGA analyses showed that SISO control design would be effective for controlling the fuel cell stack alone. Adding auxiliary components to the fuel cell stack, such as compressor to supply the pressurized air, requires a MIMO control framework. The developed model of describing water transport in porous media improves the modeling accuracy by adding catalyst layers and utilizing an empirically derived capillary pressure model. Comparing with other control‒oriented models in the literature, the developed model improves accuracy and provides more insights of the liquid water transport during transient response.Item Estimation of temperature-dependent parameters using an integrated thermal and hydraulics simulator for drilling applications(2018-12-07) Fallah, AmirHossein; Chen, Dongmei, Ph. D.; Oort, Eric vanToday, wells are being drilled under complex conditions with complex well geometries, under High-Pressure High-Temperature (HPHT) conditions, with risk of riser gas unloading in deepwater operations, while using Managed Pressure Drilling (MPD) techniques, etc., resulting in a clear need for comprehensive multi-phase hydraulics software to simulate these conditions. To address this need, a thermal model is developed and added to a previously developed multi-phase software package. The de-coupled thermal model is able to estimate the temperature in the drillstring and the annulus fluids, as well as the formation temperature adjacent to the well, using an advanced explicit finite volume approach integrated with a semi-implicit scheme used in the hydraulics model. The model solves the energy equation for the wellbore fluids, assuming that the gas and liquid phases are at the same temperature. Comprehensive thermal resistance networks are used to calculate the heat transfer between the annulus and drillstring fluids, the annulus fluid and the formation, and in the formation. For better accuracy, axial heat conduction in the drilling fluid and heat generation at the bit are accounted for. Results of the model are compared against the well-known Hasan and Kabir model and commercial software, showing a very good match for both steady-state and transient cases. To show the importance of accurate temperature estimations, offshore and onshore kick scenarios are simulated for different drilling fluids and kick control methods. Using a comprehensive heat transfer model, a user-friendly Graphical User Interface (GUI) and advanced numerical schemes makes this model a robust tool for estimation of the drilling fluid and the formation during complex well control applications. The developed model is able to estimate crucial parameters during complex conditions, such as the pressure and temperature profiles, increased pit gain and outflow during kicks, gas solubility and unloading at low pressures, and even temperature-dependent formation strength. The addition of the energy equation comes without loss of previous modeling capabilities of the hydraulics simulator, such as accounting for area discontinuity in the well and drillstring, non-Newtonian fluid rheology, MPD techniques, and arbitrary 3-D well trajectoriesItem Radiant and thermal energy transport in planktonic and benthic algae systems for sustainable biofuel production(2011-05) Murphy, Thomas Eugene; Berberoglu, Halil; Howell, John R.Biofuel production from microalgal biomass offers a clean and sustainable liquid fuel alternative to fossil fuels. In addition, algae cultivation is advantageous over traditional biofuel feedstocks as (i) it does not compete with food production, (ii) it potentially has a much greater areal productivity, (iii) it does not require arable land, and (iv) it can use marginal sources of water not suitable for irrigation or drinking. However, current algae cultivation technologies suffer from (i) low solar energy conversion effiencies, (ii) large thermal fluctuations which negatively affect the productivity, and (iii) large evaporative losses which make the process highly water intensive. This thesis reports a numerical study that address these key issues of planktonic as well as benthic algal photobioreactor technologies. First, radiant energy transfer in planktonic algal photobioreactors containing cells with different levels of pigmentation was studied. Chlamydomonas reinhardtii and its truncated chlorophyll antenna transformant tla1 were used as model organisms. Based on these simulations guidelines are derived for scaling the size and microorganism concentration of photobioreactors cultivating cells with different levels of pigmentation to achieve maximum photosynthetic productivity. To achieve this, the local irradiance obtained from the solution of the radiative transport equation (RTE) was coupled with the specific photosynthetic rates of the microorganisms to predict both the local and total photosynthetic rates in a photobioreactor. For irradiances less than 50 W/m2, the use of genetically modified strains with reduced pigmentation was shown to have negligible effect on increasing photobioreactor productivity. However, at irradiances up to 1000 W/m2, improvements of up to 30% were possible with cells having 63% less pigment concentration. It was determined that the ability of tla1 to transmit light deeper into the photobioreactor was the primary mechanism by which a photobioreactor using the modified strain can achieve greater productivity. Furthermore, it was determined photobioreactors using each strain have dead zones in which the local photosynthetic rate is negligible due to nearly complete light attenuation. These dead zones occur at local optical thicknesses greater than 169 and 275 in photobioreactors using the wild strain and the genetically modified strain, respectively. In addition, a thermal model of an algae biofilm photobioreactor was developed to assess the thermal fluctuations and evaporative loss rate of these novel photobioreactors under varying outdoor conditions. The model took into account air temperature, irradiance, relative humidity, and wind speed as inputs and computed the temperature and evaporative loss rate as a function of time and location in the photobioreactor. The model was run for a week-long period in each season using weather data from Memphis, TN. The range of the daily algae temperature variation was observed to be 13.2C, 12.4C, 12.8C, and 9.4C in the spring, summer, winter, and fall, respectively. Furthermore, without active cooling, the characteristic evaporative water loss from the system is approximately 6.3 L/m2-day, 7.0 L/m2-day, 4.9 L/m2-day, and 1.5 L/m2-day in the spring, summer, fall, and winter, respectively.