This paper is devoted to an investigation on the methane sensing properties of graphene (G), decorated with silver nanoparticles (AgNPs), under ambient conditions. To do so, we first present an effective modification in the standard manner of decorating graphene by AgNPs. From structural analysis of the product (AgNPs/G), it is concluded that graphene is indeed decorated by AgNPs of a mean size 29.3 nm, free of aggregation, with a uniform distribution. The so-produced material is then used, as a resistivity-based sensor, to examine its response to the presence of methane gas. Our measurements are performed at relatively low temperatures, for various silver-to-graphene mass ratios (SGMRs) and methane concentrations. To account for the effects of humidity, we have made the measurements, at room temperature, for different levels of humidity. Our results demonstrate that an increase in the SGMR enhances the response of AgNPs/G to methane with an optimum value of SGMR ≅ 12%. It is also illustrated that for methane concentrations less than 2000 ppm, the maximal response increases linearly and rapidly, even at room temperature. Moreover, we demonstrate that AgNPs/G is of low limit of detection, highly stable, selective, reversible, repeatable, and sensor-to-sensor reproducible, for methane sensing. The results thus promise a low-cost and simple-to-fabricate methane sensing device.

No abstract

Piano key weir is a new type of spillways designed to improve the discharge capacity of dams. Generally, increasing the upstream hydraulic load in piano key weirs results in reduced discharge capacity of the weir. Accordingly, the present study investigated the effects of triangular notch on the discharge coefficient of piano key weirs. The 3D flow field over the piano key weirs was simulated in FLOW-3D software in order to study the flow hydraulics and compare the discharge rates, and the effect of each model on the flow field over the weirs and discharge coefficient was investigated. The results suggested that data of the numerical model were appropriately consistent with that of the laboratory model. According to the results, the discharge coefficient of the triangular piano key weirs was 25% higher than that of the rectangular piano key weirs. It was also observed that changing the notch shape of the piano key weir increased the discharge coefficient of the piano key weir by 36% and 13% for the heights of 5 cm of 7.5 cm, respectively.