A fuel cell can be best defined as an electrochemical converter of fuel and oxidant of chemical energy to electrical energy. The important components of micro fuel cells are the electrodes and catalysts because the kinetics and rates of the electrochemical reactions depend on their materials. All fuel cells consist of two electrodes: the anode, where fuel oxidation takes place, and the cathode, which is used to reduce the oxidants. The present review article highlights the use of a range of electrodes made up of different materials, a variety of catalysts that have been used in previous studies, and their fabrication materials and approaches. In this article, electrodes and catalysts are classified into two types based on the design approach applied to produce the micro fuel cell: micro fuel cell design and conventional assembly design. Most previous studies on fuel cells have demonstrated that the construction and position of the electrodes play crucial roles in improving the performance of micro fuel cells.

Power consumption reduction investigations attracted the attention of enormous numbers of researchers in the past few decades due to its high academic and economic impacts. The pumping power losses during the transportation of crude oils are considered as one of the main power consuming applications due to the turbulent mode of transportation. Investigating the possible solutions for this problem is expensive and time consuming due to the large apparatuses needed to simulate the flow in real pipelines. Rotating disk apparatus (RDA) is an instrument mainly comprising a rotating disk and an electrical motor to rotate the disk, which was implemented as an efficient and economical path to simulate what can be done in pipelines through generating a controlled degree of turbulence. This technique was also used in many other scientific applications due to its dynamic mode of operation. For example, a rotating disk electrode was used in electrodeposition processes and to characterize deposition film thickness and uniformity. The rotating disk reactor was employed to investigate the reaction rate between fluids and solid surfaces. The present work evaluates the RDA from different prospective and applications in order to introduce it as an efficient research tools for future dynamic investigations.

Pipelines and tubes play important roles in transporting economic liquids, such as water, petroleum derivatives, and crude oil. However, turbulence reduces the initial flow rate at which liquids are pumped, thereby making liquid transportation through pipelines inefficient. This study focuses on enhancing the drag reduction (DR) phenomenon within a rotating disk apparatus (RDA) using polymer-surfactant additives. The complex mixture of polyisobutylene (PIB) and sodium dioctyl sulfosuccinate (SDS) was used. These materials were tested individually and as a complex mixture in RDA at various concentrations and rotational speeds (rpm). The morphology of this complex was investigated using transmission electronic microscopy (TEM). The reduction of the degradation level caused by the continuous circulation of surfactant additives in RDA could improve the long-term DR level. Experimental result shows that the maximum %DR of the complex mixture was 21.455% at 3000 rpm, while the PIB and SDS were 19.197% and 8.03%, respectively. Therefore, the complex mixture had better performance than these substances alone and were highly dependent on the alkyl chain of the surfactant.

No abstract

No abstract

Rotating disks are applied in many industrial heat and mass transfer systems because of their high mixing performance. The presence of non-Newtonian viscous liquids in these systems limits the mixing performance, thereby affecting the required heat and mass transfer. In this study, passive, active, and interactive drag-reduction techniques are proposed to enhance the mixing and drag-reduction performance of rotating disks and are experimentally tested. An SV-grooved surface (triangular shaped) is engraved on a disk attached to a rotating disk apparatus to test the liquid resistance based on torque readings and the velocity profile using a miniature laser Doppler velocimeter (Mini-LDV, MicroPro). The polymer polyisobutylene and the surfactant sodium lauryl ether sulfate are chosen as the passive-active integrated drag-reduction components in an experiment using different additive concentrations and polymer-surfactant complexes in the same tests. The experimental results show that the selected passive design of the riblets can enhance flow by 8% and that this percentage increases when polymeric additives and polymer-surfactant complexes are introduced. The velocity profile results show that high-velocity zones are created above the rotating surface and that these zones contribute significantly to enhancing the mixing intensity in the dragreduction system.

The drag reduction characteristics in a rotating disk apparatus were investigated by using structured disks with different riblet types and dimensions. Two disk types were fabricated with right angle triangular (RAT) grooves and space v-shape (SV) grooves, with six dimensions for each type. A highaccuracy rotating disk apparatus was fabricated and then used to investigate the turbulent drag reduction characterization of the disk in diesel fuel. In this work, the effects of several parameters are investigated; riblet types, riblet dimensions, and rotational disk speed (rpm) on the drag reduction performance. It was found that the surface structure of the disk reduced the drag, this was clearly seen from the comparison of torque values of smooth and structured disks. Drag reduction for structured disks was higher than that for smooth disks, and SV-grooves showed better drag reduction performance than RAT-grooves. In addition, it was observed that the drag reduction performance increased with decreasing groove height for both groove types. The maximum drag reduction achieved in this study was 37.368% for SV-groove at 1000 rpm, compared with30% for RAT-groove, at the same rotational speed.

No abstract