Conventional fossil-based energy sources have numerous environmental demerits; sustainable and renewable sources are attracting the undivided attention of researchers owing to their valuable physical and chemical features. Several industrial-scale technologies are employing hydrogen as a green energy source as the most preferential source. Not only is hydrogen a potent energy carrier but also it is not detrimental to the environment. Among many other hydrogen production processes, steam reforming of methanol (SRM) is deemed a practical method due to its low energy consumption. Cu, Ni, noble metals, etc., are the salient catalysts in SRM. Many researchers have conducted thorough studies incorporating improvement of the catalysts’ activity, mechanism predictions, and the impacts of operational parameters and reformers. This review concentrates on the SRM catalysts, supports, promoters, and the effect of the operational parameters on the process efficiency and H₂ production yield. In this regard, the methanol conversion, H₂ and CO selectivity, and operating parameters are notably contingent on the surface characterization and chemistry of the catalysts. Herein, Cu-, Ni-, and noble metal-based catalysts on various metal oxide supports, such as Al₂O₃ and ZnO, are assessed meticulously in the SRM process from the standpoint of mechanism and catalyst characterization. Most of the peer-reviewed studies had encountered agglomeration, metal particle sintering at high temperatures, coke formation, and deactivation of catalysts as the prevalent barriers. Hence, the novel methods of conquering the above-mentioned obstacles are evaluated in this review. Employment of diverse synthetic methods, bimetallic catalysts, distinct catalyst promoters, and unconventional supports, such as metal–organic frameworks, carbon nanotubes, and zeolites, are the salient routes to overcome the metal dispersion and thermal stability issues. In addition, the influence of operational parameters (temperature of the process, steam/carbon ratio, and feed flow rate) has been weighed painstakingly, along with introducing the research gap and future perspectives in the territory of SRM catalysts.

Fuel cells today have a variety of applications, such as fueling vehicles, which lead to a reduction in conventional fuel consumption and environmental pollution. On the other hand, in the present era, unmanned aerial vehicle (UAV) is known as one of the most important unmanned systems for delivering postal packages, environmental monitoring, disaster relief, and military target. However, the performance of fuel cells is affected by their operating pressure and temperature. In addition, due to some political and technical considerations, the performance of these systems (especially UAV based on fuel cells) is very rare in the literature. The present work provides a conceptual design of UAV propulsion system based on a fuel cell system and a battery. The performance of two different fuel cells, namely the alkaline fuel cell (AFC) and proton exchange membrane fuel cell (PEMFC), is examined separately and compared. Mission and constraint analyses of the system, as well as weight distribution of UAV, are provided. Furthermore, the performance of the UAV propulsion system in different flight modes and the performance of fuel cells under atmospheric conditions are discussed. It should be noted that reference UAV data are used for input parameters. It was found that the total power required by the UAV to carry out the mission is equal to 1253.7 W, which the share of takeoff, climb, cruise, and maximum speed flight modes were 321.3, 608.5, 118.3, and 205.6 W, respectively. Furthermore, the UAV under study, in this paper, has flight endurance of about 7.4 hours. Also, the required area of the PEMFC and AFC to supply the UAV power under the study conditions is about 0.03 and 0.6 m², respectively. Finally, it observed that with increasing altitude (in the absence of a heating system) the performance of both fuel cells is greatly reduced.

The current study investigates the two-phase turbulentnanofluid flow insidein a heat exchanger tube equipped with a novel type of conical turbulators having two parallel rows of holes, for first time.The range of Reynolds number was between 4000and20000 under turbulent flow regime and uniform wall temperature condition.Water is considered as the base fluid and TiO2 nanoparticles with volume fractions of0–2.5% are added as the second phase to the base fluid.The effect of number of the conical insert turbulators, number of the holes and volume fraction of the nanoparticles on flow field,average Nusselt number,friction factor and performance evaluation criterion(PEC) have been numerically investigated.The results show that the proposed turbulators create vortices and recirculating currents that have significant effect on heat transfer.As number ofthe turbulators increases,Nusselt number increases obviously.However,the presence of holes also reduces the friction factor andpressure drop that is related to lower resistance in the flow path.In general,the use of perforated conical turbulators improves PEC by creating controlled turbulent flows.Onthe otherhand,the useof added nanoparticles also enhances heat transfer.The presented turbulators increase PEC up to43% compared to the smooth tube,if the parameters are determined properly.The maximum PEC of1.43 is obtained at M=8,N=4 and Re=4100,which shows good performance compared to othertypes of turbulators.