Constrained model predictive control of proton exchange membrane fuel cell

A constrained model predictive control (MPC) is designed to regulate the air flow rate of proton exchange membrane fuel cell (PEMFC). Oxygen excess ratio, compressor flow rate and supply manifold pressure are constrained to avoid oxygen starvation, surge and choke phenomena. This is achieved by manipulating compressor voltage and stack current. The choice of the manipulated input to satisfy a constraint is investigated. Surge and choke avoidance is successful, when compressor voltage is manipulated. When stack current is utilized to satisfy surge and choke constraints, a large unrealistic current is needed. Oxygen starvation is successfully avoided utilizing stack current, while compressor voltage manipulation fails to prevent oxygen starvation. Thus, a current governor is implemented to handle oxygen starvation, while the compressor voltage is constrained to avoid surge and choke. Quadratic programming optimization, Laguerre and exponential weight function are employed to reduce the computational burden of the controller. The simulation results prove that the proposed controller managed to satisfy all constraints without any conflict.     

Observation of non-chemical equilibrium effect on Ar-CO2-H2 thermal plasma model by changing pressure

The authors developed a two-dimensional one-temperature chemical non-equilibrium (1T-NCE) model of Ar-CO₂-H₂ inductively coupled thermal plasmas (ICTP) to investigate the effect of pressure variation. The basic concept of one-temperature model is the assumption and treatment of the same energy conservation equation for electrons and heavy particles. The energy conservation equations consider reaction heat effects and energy transfer among the species produced as well as enthalpy flow resulting from diffusion. Assuming twenty two (22) different particles in this model and by solving mass conservation equations for each particle, considering diffusion, convection and net production terms resulting from hundred and ninety eight (198) chemical reactions, chemical non-equilibrium effects were taken into account. Transport and thermodynamic properties of Ar-CO₂-H₂ thermal plasmas were self-consistently calculated using the first-order approximation of the Chapman-Enskog method. Finally results obtained at atmospheric pressure (760 Torr) and at reduced pressure (500, 300 Torr) were compared with results from one-temperature chemical equilibrium (1T-CE) model. And of course, this comparison supported discussion of chemical non-equilibrium effects in the inductively coupled thermal plasmas (ICTP).     

Impact of salts on polyacrylamide hydrolysis and gelation: New insights

Polyacrylamide (PAM) and its derivatives are the most commonly used polymers in the preparation of polymeric gels for water control in petroleum reservoirs. This study involved the use of polyethylenimine (PEI) as a crosslinker for PAM. In this study, we investigated PAM alkaline hydrolysis at high temperatures. The effects of salts [sodium chloride (NaCl) and ammonium chloride (NH₄Cl)] on the degree of hydrolysis (DH) of PAM were investigated. These salts were used as retarders to elongate the gelation time of the PAM/PEI system. The data obtained from ¹³C‐NMR was used to understand the retardation mechanisms by salts. We found that NH₄Cl accelerated the extent of hydrolysis more in comparison with NaCl. Moreover, the apparent viscosity of the hydrolyzed samples was measured. PAM hydrolysis in the presence of NH₄Cl resulted in a lower solution viscosity than that in the presence of NaCl. Therefore, NH₄Cl was more effective in shielding negative charges on the carboxylate groups of the partially hydrolyzed polyacrylamide (PHPA) chain. NaCl and NH₄Cl were compatible with the PHPA/PEI system, but sodium carbonate showed a white precipitate. In addition, high‐temperature/high‐pressure elastic modulus data were reported for the first time for this system. Differential scanning calorimetry was coupled with rheology to explain the PAM/PEI crosslinking in the presence of salts. Models were developed to assess the impact of the salts on the PAM DH and the induction period before gelation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41185.     

Energy and exergy analyses of thin layer drying of mulberry in a forced solar dryer

This paper is concerned with the energy and exergy analyses of the thin layer drying process of mulberry via forced solar dryer. Using the first law of thermodynamics, energy analysis was carried out to estimate the ratios of energy utilization and the amounts of energy gain from the solar air collector. However, exergy analysis was accomplished to determine exergy losses during the drying process by applying the second law of thermodynamics. The drying experiments were conducted at different five drying mass flow rate varied between 0.014 kg/s and 0.036 kg/s. The effects of inlet air velocity and drying time on both energy and exergy were studied. The main values of energy utilization ratio were found to be as 55.2%, 32.19%, 29.2%, 21.5% and 20.5% for the five different drying mass flow rate ranged between 0.014 kg/s and 0.036 kg/s. The main values of exergy loss were found to be as 10.82 W, 6.41 W, 4.92 W, 4.06 W and 2.65 W with the drying mass flow rate varied between 0.014 kg/s and 0.036 kg/s. It was concluded that both energy utilization ratio and exergy loss decreased with increasing drying mass flow rate while the exergetic efficiency increased.     

Indium oxysulfide nanosheet photocatalyst for the hexavalent chromium detoxification and hydrogen evolution reaction

Indium oxysulfide nanosheet (In₂(O,S)₃ NS) had been successfully synthesized by a solution-based process at 90 °C. To further study some properties of photocatalyst, the 90 °C-prepared In₂(O,S)₃ NS was annealed at 350, 400, and 450 °C in air for 2 h. It was found that the nanosheet structure at 90 °C changed to nanoparticle at higher temperature. All the as-prepared and annealed photocatalysts were carefully characterized and examined toward photocatalytic hexavalent chromium (Cr(VI)) reduction. Among the photocatalysts, 90 °C-prepared In₂(O,S)₃ NS exhibited the greatest photocatalytic reduction of Cr(VI) without using any hole scavenger reagent under 150 W visible light illumination. After the Ag deposition on In₂(O,S)₃ NS, the photocatalyst could produce nearly 400 μmol/g hydrogen gas in ethanol solution under 150 W Xe-lamp irradiation for 5 h. The great performance of 90 °C-prepared In₂(O,S)₃ NS was due to the high surface area of nanosheet morphology and the formation of solid solution which significantly increased the visible light absorbance. The photocatalytic activities and their mechanisms of 90 °C-prepared In₂(O,S)₃ NS were evaluated and elaborated in this work.     

Recent Advances in Reactions of Alkylbenzenes Over Novel Zeolites: The Effects of Zeolite Structure and Morphology

Alkylbenzenes form an important segment of petrochemical industry for the manufacture of widely used commodities and specialty products. Since the last review on this topic (8), numerous new zeolite-based catalysts have been synthesized, characterized and evaluated in various transformations of aromatic hydrocarbons. This comprehensive review covers major reactions of mono-, di-, and tri-alkylbenzenes such as disproportionation, alkylation, transalkylation, isomerization, etc., over different zeolite-based acid catalysts. During the last decade, significant progress was made in the synthesis and structure determination of novel zeolites, mesoporous single crystals, hierarchic zeolites and two-dimensional zeolites. These developments have enhanced the understanding of the role of zeolites (effects of structural type, morphology, acid sites, accessibility of acid sites, shape selectivity factors) in transformations of aromatics. In this review, the emphasis is on the influence of the type of acid sites, zeolite topology, and reaction conditions on the activity, selectivity and pathways of these reactions. Thermodynamics and reaction kinetics of transformations of aromatic hydrocarbons are also discussed. This article covers mostly literature published during the period of 2002–2013.     

FVM based numerical study on the effect of solder bump arrangement on capillary driven flip chip underfill process

In this paper, the finite volume method (FVM) based numerical simulation is used for the flow visualization of capillary driven underfill process for different solder bump arrangements of flip chip packages is presented. Three different 3D flip chip package models are developed and simulated using computational fluid dynamic (CFD) code, FLUENT 6.3. Capillary action and cross viscosity model are taken into account in the simulation. One-line dispensing method is applied in the analysis and the volume of fluid (VOF) technique is used to track the flow front. The effect of solder balls arrangement on flow behavior and filling time is studied and the solder balls arrangement is found to affect the flow behavior and filling time. The flow patterns of simulation are observed for three flip chip packages and compared. The ability of the proposed model and FLUENT in handling flip chip underfill problems is proved to be excellent.     

Economic evaluation of floating gardening as a means of adapting to climate change in Bangladesh

This paper offers an economic evaluation of the floating garden as a means of adapting to climate change in Bangladesh. The study showed that the monthly income of some farmers using such gardens increased from US$12.02 to US$48.08. These folk farmers lacked alternative work especially during the monsoon period. The floating garden uses available natural resources, adjusts to wet conditions and helps the flood-prone people to earn a living, and can be an adaptive response to frequent disaster events in Bangladesh.     

Bacterial quality of raw milk investigated by Escherichia coli and isolates analysis for specific virulence-gene markers

The bacterial quality and safety of raw milk sources in Taif region (Western Saudi Arabia) were analyzed for the natural contamination of fecal coliform and Escherichia coli by standard most probable number method. The E. coli isolates were identified to species identity using API 20E and screened for markers of STEC (Stx1, Stx2), ETEC (ST, LT), (EaeA) and ExPEC (CNF1, CNF2, SfaS, PapA, CdtB, IutA, FyuA, TraT) using PCR assays. Thirty-three E. coli strains were recovered from raw milk sample sources, which were contaminated by fecal coliform. None of the investigated isolates reacted positively with the PapA, SfaS and CdtB, ST and LT-specific primers. Markers of STEC and EPEC were each detected in three strains. NTEC was detected in four strains. The most frequent virulence markers were TraT (17 strains), IutA (11 strains) and FyuA (8 strains). Results suggested a possibility of potential public health threat of E. coli originating from raw milk sources.