Understanding of the Mechanism for Laser Ablation-Assisted Patterning of Graphene/ITO Double Layers: Role of Effective Thermal Energy Transfer

Demand for the fabrication of high-performance, transparent electronic devices with improved electronic and mechanical properties is significantly increasing for various applications. In this context, it is essential to develop highly transparent and conductive electrodes for the realization of such devices. To this end, in this work, a chemical vapor deposition (CVD)-grown graphene was transferred to both glass and polyethylene terephthalate (PET) substrates that had been pre-coated with an indium tin oxide (ITO) layer and then subsequently patterned by using a laser-ablation method for a low-cost, simple, and high-throughput process. A comparison of the results of the laser ablation of such a graphene/ITO double layer with those of the ITO single-layered films reveals that a larger amount of effective thermal energy of the laser used is transferred in the lateral direction along the graphene upper layer in the graphene/ITO double-layered structure, attributable to the high thermal conductivity of graphene. The transferred thermal energy is expected to melt and evaporate the lower ITO layer at a relatively lower threshold energy of laser ablation. The transient analysis of the temperature profiles indicates that the graphene layers can act as both an effective thermal diffuser and converter for the planar heat transfer. Raman spectroscopy was used to investigate the graphite peak on the ITO layer where the graphene upper layer was selectively removed because of the incomplete heating and removal process for the ITO layer by the laterally transferred effective thermal energy of the laser beam. Our approach could have broad implications for designing highly transparent and conductive electrodes as well as a new way of nanoscale patterning for other optoelectronic-device applications using laser-ablation methods.

Thermal Diffusion Performance of a Diffuser by various Guide Vanes configurations

The use of vane-less diffuser with large diffusion angle has shown a setback in the diffusion process of high temperature working fluids. The hot gas flow was characterized as a jet-like flow. This paper presents problem, encountered practically, using a vane-less diffuser with large diffusion angle and how the problem is solved by CFD simulation. The investigated thermal diffuser has a length of 0.3 m, an inlet to outlet crosssectional area ratio of 1:25 and diffusion angle of 115.44o. To resolve the jet-like flow problem and poor distribution of the flow temperature at the diffuser outlet, the study suggested the use of guide-vanes into the diffuser. The study employed CFD simulation by ANSYS-FLUENT software to analyze the flow and thermal process in the diffuser. Three different shapes of guide vanes; block-shaped, oval-shaped and airfoil-shaped were considered in this study and at different vanes diffusion angles, as well as vane-less case, which was adopted as the bench mark case. The simulation results of the velocity, temperature and pressure at the diffuser outlet were compared for all cases. It was found that the guide vanes with symmetrical airfoil profile provided the best performance with most uniform distribution at the outlet of the diffuser. Also, the airfoil-shaped guide vanes resulted in lower pressure losses compared to the block-shaped and oval-shaped guide vanes. According to the analysis results, the diffuser was redesigned to improve the diffusion and temperature distribution across the diffuser outlet.

Hydrogen Production by a Steam Reforming Reactor for Heavy Hydrocarbons

The authors develop a small and simple steam-reforming reactor in a home-use size for n-dodecane as a heavy-hydrocarbons fuel. Under the thermal condition controlled by electric heaters and a gas burner with a thermal diffuser, the authors measure the inside-temperature profile and the hydrogen-molecule ratio (concentration) RH2, together with the molecule ratios RCH4, RCO and RCO2 of other main gas components such as CH4, CO and CO2, respectively. Besides, the authors conduct numerical simulations based on a thermal-equilibrium theory, in addition to experiments. As a result, the authors successfully achieve suitable inside-temperature profiles. And, the effects of the liquid-hourly-space velocity LHSV upon RH2, RCH4, RCO and RCO2 are shown, experimentally. For LHSV ≤ 1, the experimental results agree well with the thermal equilibrium theory. This is in consistent with high conversion ratio XC12H26 ≳ 80%. Furthermore, the authors reveal the effects of the temperature T inside the reactor upon the molecule ratios, comparing with the thermal-equilibrium theory.

Shape Sensitivity Formulation for Axisymmetric Thermal Conducting Solids

A direct differentiation method is presented for the shape design sensitivity analysis of axisymmetric thermal conducting solids. Based purely on the standard boundary integral equation (BIE) formulation, a new BIE is derived using the material derivative concept. Design derivatives in terms of shape change are directly calculated by solving the derived BIE. The present direct method has a computational advantage over the adjoint variable method, in the sense that it avoids the problem of solving for the adjoint system with the singular boundary condition. Numerical accuracy of the method is studied through three examples. The sensitivities by the present method are compared with analytic sensitivities for two problems of a hollow cylinder and a hollow sphere, and are then compared with those by finite differences for a thermal diffuser problem. As a practical application to numerical optimization, an optimal shape of the thermal diffuser to minimize the weight under a prescribed constraint is found by use of an optimization routine.

Aircraft Fuel Pumps: Where We’re at (A Review of Some Problems and Their Current Solutions)

European-designed tank-mounted boost pumps, the thermal diffuser, engine driven backing pumps and gear pumps have all changed, and improved, over the last few years. This paper outlines the reasons for the changes, the problems they are designed to overcome, and the efficacy of the solutions offered.