College of Engineering

Theses and dissertations submitted to the College of Engineering

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Pb-Ca-Sn alloys are one of the primary materials for the positive grids of automotive batteries. Various studies have been done to improve the mechanical and electrochemical properties of such alloys. Despite these developments, corrosion of the positive grids remains to be one of the main causes of battery failure. The study aims to determine the corrosion behavior of different parts of an as-cast Pb-Ca-Sn alloy used in service to provide insights on improving grid design and casting conditions.

The XRF results showed that the elemental composition of each grid location was comparable with each other averaging 97.85 wt% Pb, and 1.4 wt% Sn. The Ca content was determined at 0.07 wt% through ICP-OES. The microstructures of each grid location are characterized by Pb-rich α phase with eutectic mixtures on the intercellular boundaries. Differences in grain size and cellular size exist between the grid locations. Location A has higher grain and cellular sizes than locations B and C.

Electrochemical techniques such as Electrochemical Impedance Spectroscopy (EIS), Liner Sweep Voltammetry (LSV), and Cyclic Polarization (CP) were applied on different grid locations at varying sulfuric acid (H2SO4) concentrations and temperatures. A three-electrode set-up was used with the Pb-Ca-Sn alloys as the working electrode, a platinum sheet as the counter electrode, and a mercury/mercurous sulfate reference electrode (Hg/H2SO4) in saturated potassium sulfate (2M K2SO4) solution.

An electrical circuit model representing the electrochemical system consisting of electrolyte layer, electrical double layer, porous PbSO4 layer, and metal surface was fitted on the Nyquist plots to determine the charge transfer (R_CT ) and polarization resistance (R_P). Results showed that R_CT decreased with the increase in temperature indicating a decrease in corrosion resistance. The R_P was affected by the change H¬2SO4 concentration and temperature. The R_P increase with acid concentration at elevated temperature seemed to relate with the formation of a thicker corrosion layer indicating faster corrosion rates.

On the other hand, LSV results showed that the corrosion potential (E_corr) shifted towards the negative potential as the acid concentration increased. The LSV results also validated the results derived from EIS that at elevated temperature, the (R_P) increased with the acid concentration. The corrosion rates derived from Tafel plots vary from 0.34 to 1.48 mm/year at 28℃, and from 0.21 to 2.73 mm/year at 40℃.

The difference between the repassivation potential (E_P) and breakdown potential E_b derived from CP results indicated that the different grid locations had a small tendency for pitting. Photomicrographs showed the presence of such pits.

And in general, differences in the corrosion behavior of the three grid locations exist based on the results of R_CT derived from EIS, and R_P derived from LSV.

Development of inexpensive materials for hydrogen production from water and sunlight is one promising route researchers are eyeing on for years. Molybdenum disulfide (MoS2) containing metallic phase (1T) has been one of the good candidates comparable with platinum as hydrogen evolution promoter. The motivation of this study was on giving emphasis on the formation of morphological face contact that enhances charge transfer. 2D MoS2 nanosheets containing 1T and 2H phases (inhomogeneous) and 2D Cadmium sulfide (CdS) sheets/flakes were successfully synthesized using hydrothermal and solvothermal reactions, respectively, and their composites were prepared using physical method (i.e. grinding). These materials were characterized using XRD patterns, XRF semi-quantitative analysis, FTIR spectroscopy, UV-Vis diffuse reflectance spectroscopy, and FE-SEM imaging. The estimated direct band gap of pristine CdS, which was 2.32 eV, was unaffected in the presence of MoS2 indicating the successful adsorption of MoS2 on CdS. CdS alone had a hydrogen production rate of 6.5 μmol/gcath. An apparent synergistic effect of the two materials was observed with a hydrogen production rate of 1036.1 µmol/gcath for the 15wt% MoS2/CdS composite equivalent to 159-fold enhancement of photocatalytic activity. This composite retained ~80% of its photocatalytic activity after 10 hours of use. This work presented an idea on the significance of face contact (2D-2D) between inhomogeneous MoS2 and CdS which can be used for future applications in photocatalysis. This study also provided an applicability of the material if used in the Philippine setting by using the average annual temperature of the country as operating temperature for the reaction.

The extensive use of antibiotics for therapeutic and prophylactic utilization in livestock production has increased the possibility of antibiotic pollution of our environment. Antibiotic pollution poses a range of risks to human health, economic productivity, ecosystem services and long term sustainability of agricultural activity. Composting is an accepted recycling and reuse technique for manure, turning the waste into a valuable resource. However, the efficiency in removing pollutants of emerging concern such as antibiotic needs improvement. In the study, microorganisms were isolated from vermicompost and evaluated as inoculant in composting chicken manure spike with antibiotics. Aspergillus niger and Aspergillus flavus were isolated from vermicompost and evaluated as to antibiotic resistance and potential for mass production as inoculant. Results showed that the fungal species showed increased growth in the presence of various concentration of antibiotics and had luxuriant growth in various substrate tested. Inoculant induced composting registered 83-93% removal of tylosin and 50-65% removal for oxytetracycline. The inoculant were among the primary fungal species observed during the time of significant antibiotic removal. Biodegradation was the primary removal pathway for tylosin, and enzymes associated with the inoculant may also have contributed to tylosin removal through oxidation. Temperature was the main factor affecting the removal of oxytetracycline. Thermophilic temperature was not observed during the study thus resulting in low oxytetracycline removal efficiency. A. flavus and A. Niger together with other fungal species observed (Lichthemia romosa, Trichosporon asahii and Cladosporium oxysporum) may contribute to improving the removal efficiency of antibiotics during inoculant induced composting of chicken manure.

Water, an essential resource for all life on earth, is the prime mover and is essentially an integral part of every development. Water resources planning and development covers protection, storage, and water distribution. Therefore, events that alter and suppress water supply are of great concern to the water resource system and should be addressed overtime. Natural disasters like earthquakes and volcanic eruptions, though indirectly concerned on climatological variables of the water cycle, may pose an integral damage in the water resource system. Notwithstanding the destruction caused by a volcanic eruption in particular, the deposition of volcanic materials on the river systems and watersheds becomes indispensable and is a great challenge to the water resources engineers.

The devastating eruption of Mt. Pinatubo in 1991 that impacts the country’s society, natural resources, and the global environment continued after more than two decades burying the two irrigation systems of Tarlac province, the Tarlac River Irrigation System (TARRIS) and the San Miguel-O’Donnell River Irrigation System (SMORIS). The head water basin of the O’Donnell River was not spared from such disaster, depositing voluminous lahar in the channel bed of the major stream. The low impounding reservoir of the Armenia Dam located at the outlet of the O’Donnell River basin serving for irrigation and flood mitigation purposes becomes totally buried in lahar.

In parallel with the national thrust on resiliency, the National Irrigation Administration aimed to continue and improve irrigation services amidst the destruction. The developments on the appurtenant structures of the dam were aimed at improving the serviced area for irrigation despite the loss of the impounding reservoir. One of the NIA’s rehabilitation project on SMORIS is the construction of an infiltration gallery to collect water on the buried small impounding reservoir through horizontal perforated pipes leading to a collecting gallery passing the dam intake.

Infiltration galleries have a wide variety of applications in water resources management such as recharging confined and unconfined aquifers, a water-diversion option for surface water, a water treatment option for improving the potability of water, reduction of generated surface runoff and flooding. Studies on the analysis of the infiltration gallery for its effectiveness on these specified applications were based on field investigations using test pits. This study, therefore, focuses on developing a procedure for analyzing the infiltration gallery using groundwater flow (GWF) model in consideration to the draining surface water using flow duration curves (FDC).

The major objective of this study is to determine the reliability of available water that can be extracted through a horizontal infiltration gallery at the Armenia Dam along O’Donnell River. The reliability analysis is based on dependable flow analysis (i.e., flow duration curves) of surface water inflows to the infiltration gallery and subsequently the extracted water. Essentially, this study is to make analytical and numerical GWF model of the system under the present conditions of the riverbed and the horizontal infiltration gallery. This research will prove the following hypotheses: - The reliability of infiltration galleries for water supply can be effectively analyzed through ground water flow models using flow duration curves of the draining surface water ; - The estimated flux at the horizontal infiltration gallery using analytical and numerical modeling does not vary significantly.

The FDC has gained acceptance and credibility by researchers and hydrologists in various water resources problems and applications. This paper provided a different perspective in constructing the FDC for ungauged and partially gauged basins as employed in most of the referenced studies using techniques of synthesizing FDC and regionalizing it for small and large catchments. In this study, the historical streamflow data required to construct the FDC was derived through rainfall-runoff modelling in HEC-HMS using 39 years of rainfall data. The GIS data and ArcMap software geoprocessing provided greater accuracy in the loss and transform parameter input of the model which was calibrated using partial streamflow data that is within the rainfall record. The calibrated model was then used to simulate the 39 years of streamflow describing the full range of runoff response characteristics at the basin outlet.

The continuous simulated streamflow used in FDC offers a better diagnostic tool for assessing the flow on the infiltration gallery. The flow at 60%, 80% and 90% exceedance probability were used in defining the boundary conditions of the GWF model to analyze the flow conditions at the horizontal infiltration gallery. The analytical solution is a two dimensional steady-state flux distribution at the horizontal perforated pipes using Fourier integral as presented by Liongson, 2007. The numerical analysis for the head and flux distribution is a finite difference method as implemented in MODFLOW 6.0 of the USGS. The graphical user interface of MODFLOW, Model Muse, was used in discretization and flow simulation within the infiltration gallery. The validity of the results was verified from the comparative analysis of the analytical and numerical solutions.

The rainfall-runoff model calibration indicates a good fit of the observed and simulated flow data with an index quantified by PWRMSE of 57.49. The model overestimates the observed flow by only 0.06% and underestimates the observed peak flow by 23.3%. This indicates that, relative to the magnitude of flow, the model is unbiased at 0.91% and the random errors in the prediction are small as quantified by the RMSE standard deviation of 0.3. Results revealed that O’Donnell River is capable of sustaining a flow of approximately 6.7 m3/sec seventy percent (60%) of the time, 3.2 m3/sec eighty percent (80%) of the time and 2.1 m3/sec ninety percent (90%) of the time.

Carbon nanotubes (CNTs) are one of the most promising discoveries in modern science. Since its discovery in 1991, CNTs have captured a great deal of attention worldwide because of their exceptional mechanical, electrical and thermal properties. CNTs have emerged as a potentially effective reinforcing material in improving mechanical and thermal capabilities of phase change materials (PCMs). Capric acid as PCMs draws much interest to scientists because of its heat storage capacity, accessibility, cost-effectiveness, and low reactivity. However, their properties remain to be below average if no enhancing elements are added. In this study, the mechanical and thermal properties were examined with varying parameters such as packing density, CNT type, and length-over-diameter (L/D) ratio. By virtue of molecular dynamics simulation, a dense amorphous cell was created using the Forcite module of BIOVIA Material Studio software and simulations were performed. The CA packing density increases both its mechanical properties and thermal conductivity while CNT type did not reveal any effect on them. Whereas the mechanical properties (except elastic modulus) and thermal conductivity increase with L/D ratio. The amorphous cells were subjected to different temperature and pressure using the dynamics task of Forcite and results showed that temperature had no influence on thermal conductivity when the PCM is in a solid state, and had a decreasing trend in a liquid state. No trend was found with the effect of pressure. The latent heat of fusion of the PCM was found to be 333.65 kJ/mol, a ten-fold increase of that of pure CA.