Flame development characteristics inside a reverse-flow model combustor from early stages of combustion to steady operation

Characteristics of flame development inside a small-scale power generator model combustor featuring a reverse-flow configuration and the influence of such configuration on these characteristics from early stages of combustion to the steady operation of the combustor are investigated experimentally. Simultaneous and high-speed OH* chemiluminescence and pressure measurements are utilized. Two sets of experiments are performed. In the first set, relatively lean premixed methane/air flames with a fuel-air equivalence ratio of 0.7 have been investigated. For these, four experiments pertaining to air flow rates of 100 and 160 standard liters per minute along with two igniter rod positions are performed. For the second set of experiments, the igniter position was fixed, and two fuel-air equivalence ratios of 0.9 and 1 along with two air flow rates of 120 and 130 standard liters per minute are tested. The results pertaining to the first set of experiments suggest that, prior to the appearance of steady thermoacoustic oscillations, three phases, namely, ignition, stabilization, and transition may exist. During the ignition phase, the normalized flame edge velocity can achieve relatively large maximum values owing to the reverse-flow configuration compared to that for closed chambers. The ignition phase is followed by the stabilization phase during which the flame is formed on the flame-holder. During the transition phase, the flame chemiluminescence features one long-period sinusoidal oscillation. Despite significant influence of the reverse-flow configuration on flame dynamics during the ignition and stabilization phases, the spectral characteristics of pressure and flame chemiluminescence oscillations are similar to those of unconfined flames. The results pertaining to the relatively rich flames suggest, depending on the phase of the flame development, the reverse-flow combustor can serve as either a closed or an open system. It was shown that, during the ignition and stabilization phases, the thermoacoustic fluctuations are dominated by small frequencies associated with the structural and acoustic modes. However, during the steady operation, the intrinsic thermoacoustic modes also become apparent and contribute to the thermoacoustic oscillations. The results of this study have implications for improving the ignition quality and mitigating the thermoacoustic oscillations in reverse-flow combustors used for small-scale power generation purposes.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat

Numerical Investigation of the Strain Stiffening Behavior of Mesenchymal Stem Cells on Elastic Substrates

In order to accurately predict the cellular response, it is necessary, along with other factors, to consider the effect of the cell spreading on the substrate. Also, the core tensions, due to the cell spreading, play a crucial role in the fate of a stem cell. Therefore, the exact prediction of these tensions is of particular importance. The effect of the strain stiffening of a mesenchymal cell, in a two-dimensional model, was investigated numerically using finite element method, by exerting a time function displacement, to the cytoplasm boundary. Utilizing Schwartz-Christoffel transformation, a model for cell-spreading was proposed that can be used to achieve accurate cellular responses. Three different models are considered. In the first model, the cell is treated as a non-alive material. That is, the mechanical properties remain constant on the substrate. Two other models, the linear and exponential strain-stiffening, are active models. By comparing the results of these models with the experimental results, it was found that the assumption that the cell is inactive departs the response from the exact amount. Therefore, considering the cell’s living nature, in both linear and exponential models, leads to more similarity of the results, both the tension value and the slope of the variations, with the experimental observations. Furthermore, by increasing the amount of the cell spreading, the difference in the amount of the nucleus stress in active models with the inactive model increases, so that the predicted tension by the linear model reaches 2.3 times that predicted by the non-alive model

A group multicriteria decision making with ANOVA to select optimum parameters of drilling flax fibre composites: A case study

Composite parts are often drilled during assembly. However, it has been well established that drilling process can damage long-fibre composites, and the ideal process parameters need to be investigated based on each given material system, yet under different conflicting design criteria. Here, a multi-criteria decision making (MCDM) approach along with the analysis of variance is aimed to find the best-compromised solution for drilling parameters of a flax fibre composite plate; namely to minimize the top and bottom surface delamination factors while simultaneously maximizing the residual tensile strength of the drilled laminate. Different criteria importance weights along with different MCDM techniques have been modeled to capture different practical design scenarios. Overall, the majority of employed methods suggested a higher spindle speed, a lower feed rate, and a step drill bit geometry. Among the design factors, the feed rate by far played a statistically significant role (>95% confidence level) in controlling the damage outcome and is deemed of prime design concern. It is also shown that the inclusion of subjective weights by experts is a key in such design problems to avoid statistical overinterpretation