Effects of amplitude modulation on perception of wind turbine noise

Wind turbine noise is considered to be easily detectable and highly annoying at relatively lower sound levels than other noise sources. Many previous studies attributed this characteristic to amplitude modulation. However, it is unclear whether amplitude modulation is the main cause of these properties of wind turbine noise. Therefore, the aim of the current study is to identify the relationship between amplitude modulation and these two properties of wind turbine noise. For this investigation, two experiments were conducted. In the first experiment, 12 participants determined the detection thresholds of six target sounds in the presence of background noise. In the second experiment, 12 participants matched the loudness of modified sounds without amplitude modulation to that of target sounds with amplitude modulation. The results showed that the detection threshold was lowered as the modulation depth increased; additionally, sounds with amplitude modulation had higher subjective loudness than those without amplitude modulation.     

Study of hydrogen production in light assisted microbial electrolysis cell operated with dye sensitized solar cell

Hydrogen production with light as an additional energy source in a microbial electrolysis cell (MEC) is described. A ruthenium-dye (N719) sensitized solar cell with an open circuit potential (V_oc) of 602 mV was connected to the MEC. Hydrogen production was carried out by irradiating the DSSC connected across the MEC with a light intensity of 40 mW/cm² and also with natural sunlight. The DSSC was stable during various batch experiments. The acetate conversion efficiency and the coulombic efficiency based on the average of first two batches were 30.5 ± 2.5% and 40 ± 2% respectively. The cathodic recovery efficiency ranged from 72% to 86% during repeated batch experiments with an average of 78 ± 2.5%.     

Effect of hydrodymamic force and prolonged oxygen exposure on the performance of anodic biofilm in microbial electrolysis cells

In this work, the significance of Reynolds number (N_Re) in evaluating the performance of hydrogen production in MECs was demonstrated. Experiments performed with the same anode under the same operating conditions (applied potential, pH, stirring speed and substrate concentration) showed different performances when operated with different stirrers. An average increase of 30% in hydrogen production was obtained by increasing the diameter of the stirring bar from 1.2 cm to 2.8 cm. This increased the N_Re from ≈900 to ≈4900. The anodic bacteria communities on MEC's anodes were also shown to be unaffected when exposed to oxygen for a prolonged period of time outside the reactor by storing them in buffer solution. This however was not enough to get rid of methanogenic bacteria which were still active on the electrodes after exposing them to oxygen in the air for 24 h and in buffer solution for 5 days.     

Effect of multi-bend geometry on deflagration to detonation transition of a hydrocarbon-air mixture in tubes

We present a numerical investigation of gaseous deflagration-to-detonation transition (DDT) triggered by a shock in a multi-bend geometry. The ethylene-air mixture filled rigid tube with obstacles is considered for understanding the effects of complex confinement and initial flame size on DDT. Our calculations show generation of hot spots by flame and strong shock interactions, and flame propagation is either restrained or accelerated due to the wall obstacles of both straight and bent tubes. The effect of initial flame size on DDT in complex confinement geometry is analyzed as well as the hot spot formation on promoting shock–flame interaction, leading to a full detonation.     

Effect of variation of hydrophobicity of anode diffusion media along the through-plane direction in direct methanol fuel cells

Reducing methanol crossover from the anode to cathode in direct methanol fuel cells (DMFCs) is critical for attaining high cell performance and fuel utilization, particularly when highly concentrated methanol fuel is fed into DMFCs. In this study, we present a novel design of anode diffusion media (DM) wherein spatial variation of hydrophobicity along the through-plane direction is realized by special polytetrafluoroethylene (PTFE) coating procedure. According to the capillary transport theory for porous media, the anode DM design can significantly affect both methanol and water transport processes in DMFCs. To examine its influence, three different membrane-electrode assemblies are fabricated and tested for various methanol feed concentrations. Polarization curves show that cell performance at high methanol feed concentration conditions is greatly improved with the anode DM design with increasing hydrophobicity toward the anode catalyst layer. In addition, we investigate the influence of the wettability of the anode microporous layer (MPL) on cell performance and show that for DMFC operation at high methanol feed concentration, the hydrophilic anode MPL fabricated with an ionomer binder is more beneficial than conventional hydrophobic MPLs fabricated with PTFE. This paper highlights that controlling wetting characteristics of the anode DM and MPL is of paramount importance for mitigating methanol crossover in DMFCs.     

Numerical modeling and simulations of active direct methanol fuel cell (DMFC) systems under various ambient temperatures and operating conditions

Direct methanol fuel cells (DMFCs) are potential candidates for portable backup power generation and auxiliary power units owing to their advantageous features, such as ease of fuel storage and delivery. Optimizing each component of a DMFC system is critical to improving the overall system performance and power density. This paper presents an active DMFC system model, in which a one-dimensional DMFC stack model is combined with major system components, including fuel and water tanks, liquid–gas separator, heat exchangers, pumps, and blowers. The model is implemented using a commercial flow-sheet simulator, ASPEN-HYSYS, and then applied to an active DMFC system to analyze the effects of the DMFC operating parameters and heat management. Special emphasis is placed on establishing active control strategies for the DMFC stack temperature, methanol crossover rate, and water recovery by optimizing the system components and operating conditions. Overall, this study helps identify innovative active DMFC system designs and configurations.     

A planar catalytic combustion sensor using nano-crystalline F-doped SnO2 as a supporting material for hydrogen detection

A planar catlytic combustion gas sensor based on Pd/Pt catalyst supported on F-doped SnO₂ nano-crystalline materials has been designed and fabricated for hydrogen detection. The sensor consists of platinum heaters on an alumina plate coated with a catalytic layer and compensating layer. This sensor exhibited better performance than that of the sensors employing sensing material of Pd/Pt catalyst on γ-Al₂O₃ and of Pd/Pt catalyst on nano-crystalline SnO₂. The detection limit of the sensor at 370 °C is in the concentration range of 0.5–5% (v/v), with an excellent linearity of signal voltage to the hydrogen gas concentration.