Numerical analysis of pulsating heat pipe based on separated flow model

The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper, a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency of oscillation. Also the average temperature of vapor plugs decreased.     

Aerodynamic noise generation in centrifugal turbomachinery

The objective of this research was to identify which aspects of the fluid dynamics are associated with noise generation in centrifugal turbomachinery. Research emphasis was placed on the generation of noise at frequencies other than the blade passage tones. In order to avoid noise generated by the interaction of the discharged flow and stationary objects outside of the impeller, experiments are performed on a centrifugal impeller without diffuser and casing. With this discharge configuration, the radiated noise spectra are shown to be dominated by harmonically related broad humps at low frequency. These were proven to be generated by the interaction of a coherent unsteady flow structure rotating around the impeller discharge and the trailing edges of the impeller blades.     

The property of hydrogen separation from CO2 mixture using Pd-based membranes for carbon capture and storage (CCS)

This study investigates the module configuration for upscaling CO₂ capture capacity to a bench-scale in hydrogen selective Pd-based composite membranes. In order to confirm effective upscaling, four plate-type membranes of two inch diameter were stacked in a newly designed plate-and-frame type module, reaching a total membrane surface area of 6.64 × 10⁻³ m² (66.4 cm²). A pure gas test carried out using H₂ and He confirmed that there were no effects of module configuration in gas permeation behavior, indicating that the upscale of the separation capacity by numbering-up of membranes using our module design was successful. The CO₂ enrichment test was conducted using a 40%CO₂ + 60%H₂ mixture (i.e. a similar composition for the coal gasifier after both the shift reaction and H₂O removal), under high feed pressure and flow rate, i.e. 600–2100 kPa and 0.48–0.72 N m³ h⁻¹. The mixture gas test confirmed that the bench-scale membrane module could enrich 40% of the CO₂ at a feed flow rate of 0.48 N m³ h⁻¹ up to 93% with a hydrogen recovery ratio of >90% at 673 K and a total feed pressure of 2100 kPa, i.e. ∼4 times CO₂ enrichment capacity of one membrane.     

Novel micro-channel methane reformer assisted combustion reaction for hydrogen production

A metal catalyst-containing, 80 ml, micro-channel reactor (MCR) with a section dedicated to combustion reaction was investigated for the potential application of on-board methane steam reforming (MSR) to hydrogen production. The metal catalyst was introduced into the MCR as a shape of a thin plate that was diffusion-bonded with the other micro-channel plates. The combustion reaction was performed on the other side of the MCR for direct provision of the necessary heat for the endothermic MSR and for miniaturizing the system volume. In the MCR, both the methane conversion and the hydrogen production rate are extremely high compared with those of the equilibrium under atmospheric pressure. The required heat of reaction is successfully provided by the combustion of either hydrogen or the methane mixture on the other side of the MCR without the need for any heating cartridges. This novel micro-channel reformer is suitable for application as a compact fuel processor due to its production of hydrogen-rich syn-gas, small volume, simple catalyst loading and use of an active and easily stackable catalyst.     

Si-modified Pt/CeO2 catalyst for a single-stage water-gas shift reaction

Si-modified Pt/CeO₂ catalysts were prepared for a water-gas shift (WGS) reaction and the effects of this silica addition on the textural and structural characteristics, reducibility and WGS reaction performance of Pt/CeO₂ were investigated. The surface areas of the prepared catalysts increased and both interplanar spacing and average crystalline size of ceria gradually decreased with Si content, resulting in less crystalline and smaller particles. Si addition up to 20 wt. % facilitated the bulk reduction of ceria by inducing significant hydrogen consumption. The oxygen defects in the support, associated with lower valence state cerium, increased with the Si addition. These modifications offer a promising potential to increase the density of hydroxyl groups on the surface of the ceria and consequently increase the concentration of surface intermediate species. The addition of Si to ceria improved the catalytic performance for the WGS reaction, in spite of its irreducible nature. Pt catalysts supported on Si-modified ceria, with a Si content of 5-10 wt.%, exhibited a 2.5-fold increase in reaction rate and turnover frequency (TOF) compared to that of Pt/CeO₂.     

Hydrogen-storage properties of gravity cast and melt spun Mg–Ni–Nb2O5 alloys

95%(gravity cast Mg–23.5Ni)–-5%Nb₂O₅ alloy was prepared by horizontal ball milling in n-hexane of gravity cast Mg–23.5wt%Ni with Spex milled Nb₂O₅. Melt spun Mg–23.5wt%Ni after heat treatment at 523 K for 1 h was also ground by planetary ball milling with finer Nb₂O₅ prepared by milling with NaCl. The activated 90%(melt spun Mg–23.5Ni)–10%Nb₂O₅ alloy shows higher hydriding and dehydriding rates than the activated 95%(gravity cast Mg–23.5Ni)–5%Nb₂O₅ alloy, thanks to the homogeneous distribution of fine Mg₂Ni phase in melt spun Mg–23.5Ni and the finer Nb₂O₅ addition to melt spun Mg–23.5Ni, which leads to the effective diminution of the Mg particle size. The activated 90%(ms Mg–23.5Ni)–10%Nb₂O₅ alloy absorbs 4.70 wt%H at 573 K under 12 bar H₂ for 10 min, and desorbs 4.75 wt%H at 573 K under 1.0 bar H₂ for 25 min.     

Flow analysis of engine cooling system for a passenger vehicle

A numerical simulation is carried out to analyze the flow field of cooling air through the radiator and engine compartment. In order to consider the strong effect of the suction-type flow by the cooling fan at engine idling condition, a potential flow analysis is attempted by the assumption of a line sink located at the position of the cooling fan. The governing equations for steady two-dimensional, incompressible, turbulent flow are solved with the two-equationk-ε model for turbulence. The velocity profiles in the underhood engine compartment and around the front-end of a real vehicle are measured to compare with the numerical results. The agreement between the numerical and experimental results is fairly good. It is concluded that a two-dimensional computation is a fast and efficient tool for predicting the effect of front-end design on the cooling air flow through the radiator.     

Miniaturized inertia Generators as power supplies for small-caliber fuzes

This paper describes miniaturized inertia generators for converting mechanical energy into electrical energy for military applications, especially as power supplies for electrical fuzes. In order to minimize the volume of the generators, our design adopted a ring-shaped magnet enclosing a coil assembly. The inertia generators are intended not to ignite an electrical detonator but to charge a capacitor that drives the electric circuit of fuze. A mechanical safety system, a shear plate, is used as a release mechanism for the inertia generators to prevent them from operating accidentally. We designed the inertia generators by using the simulation results of an electromagnetic analysis tool. In an experimental study, we performed safety tests on the shear plate and firing tests of the fabricated inertia generators. The present inertia generators show that a voltage of 14.2 V was charged on a capacitor of 30 /spl mu/F within the charging time of 0.68 ms and the critical acceleration for safety was 5000 G, verifying that the inertia generators can be used as power supplies for small-caliber electrical fuzes.     

Development of a hydrogen purifier with Pd-based composite membrane

A hydrogen purifier equipped with Pd-Cu-Ni/PNS membranes has been developed to purify low-grade hydrogen and supply it to processes requiring high-purity hydrogen. The purifier does not include any purge system to flush out hydrogen from the membrane module to prevent membrane embrittlement because there is no α-β phase transition below the critical point of the Pd-H system, making the purifier simple. The hydrogen purifier was tested with three different grades of hydrogen, 90, 99 and 99.9%, to determine the effects of the grade of feed hydrogen on the hydrogen permeation behavior. A lower grade required a lower recovery ratio of the purifier to obtain a given relative hydrogen permeation flux. It was confirmed that the purifier can provide high-purity hydrogen to a gas chromatograph (GC) for carrier and make-up gases. A 75-day durability test provided evidence that the hydrogen purifier could be useful for extended periods as needed for commercial processes.     

Pd effect on reliability of Ag bonding wires in microelectronic devices in high-humidity environments

We investigated the effect of Pd concentration in Pd-doped Ag wires on the humidity reliability and interfacial corrosion characteristics between Ag wire and Al metallization. Additionally, we confirmed no corrosion problem between Ag wire and noble metal (Pd, Au) metallization, even after a pressure cooker test (PCT). The chemical composition of the tested Ag wires was pure Ag, Ag-1wt% Pd and Ag-3wt% Pd. These wires were bonded to Al and noble metal (Au, Pd) metallization using a thermo-sonic bonder. The interfaces were characterized by focused ion beam (FIB), high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The interface corrosion of Pd doped Ag wires was significantly reduced as the Pd concentration in the Ag wires increased. Furthermore, the Ag wires on the noble metal (Au, Pd) metallization exhibited stable reliability during the PCT.