Fuel size effect on pinewood combustion in a packed bed

In this paper, particle size effect on pinewood combustion in a stationary packed bed was investigated. Mass loss rate, temperature profile at different bed locations and gas compositions in the out-of-bed flue gases were measured at a fixed primary air flow rate. Pinewood cubes was fired with size ranging from 5 to 35 mm. A unique numerical model applicable to thermally thick particles was proposed and relevant equations were solved to simulate the non-homogeneous characteristics of the burning process. It is found that at the operating conditions of the current study, smaller particles are quicker to ignite than larger particles and have distinctive combustion stages; burning rate is also higher with smaller fuel size; and smaller fuels have a thinner reaction zone and result in both higher CO and CH₄ concentrations in the out-of-bed flue gases; on the other hand, larger particles produced a higher flame temperature and result in higher H₂ concentration in the flue gases. Larger particles also cause the combustion process becoming more transient where the burning rate varies for most part of the combustion process.     

Polarisation characteristics of fused-fibre coupler as quarter-wave device in 1.55?m-wavelength region

Polarisation characteristics of the fused-taper-twisted single-mode-fibre coupler as a quarter-wave device are reported for the first time. In the case that circular polarisation is launched into the input port of the fused-fibre coupler, linear polarisation was observed at two output ports of the coupler, and an extinction ratio of about 30dB was obtained.     

Research activities on next-generation mobile communications and services in Korea

In this article we present a perspective on next-generation mobile communications and services. As a preliminary research work on next-generation mobile communications, we exploit what next-generation mobile services will be (S. Ryu et al., May 2003). We define next-generation mobile services as a hierarchy of services consisting of three different service levels: the service areas, the service functionalities, and the service technologies. We derive these service levels by means of scenario-based analysis. Next we propose conceptual reference network architecture, focusing on the realization of the service technologies. We divide the network into four different parts: a user equipments and access part, a network service provisioning layer part, a network control layer part, and non-mobile network operator service pan, according to characteristics of information and service flows within a network. In this reference network architecture, service elements such as servers, processors, and gateways are placed in each network part to support the derived next-generation mobile services. Finally, we give a brief introduction of research and development activities for next-generation mobile communication systems and services in Korea.     

Hydrogen production in fluidized bed by chemical-looping cycle

To investigate the feasibility of a chemical-looping hydrogen generation system, we investigated the reduction and water splitting reaction characteristics for three mediators and two reducing gas in a bubbling fluidized bed reactor (0.02 m I.D.). For three oxygen carrier particles (NiO/bentonite, Fe₂O₃/bentonite, (NiO:Fe₂O₃)/bentonite), hydrogen was used as a reduction gas and water was used as an oxidation gas. For (NiO: Fe₂O₃)/bentonite particle, carbon monoxide, which is the main component in the syngas from coal or heavy residue, was used as a reducing gas to check reactivity for the carbon containing fuels and carbon deposition characteristics. Based on the reactivity tests, (NiO: Fe₂O₃)/bentonite particle was selected as the best mediator for the chemical-looping hydrogen generation system to achieve stable continuous operation. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

β-tricalcium phosphate nanoparticles adhered carbon nanofibrous membrane for human osteoblasts cell culture

β-tricalcium phosphate nanoparticles adhered carbon nanofibrous (β-TCP@CNFs) membranes were prepared by electrospinning and sintering a mixed solution of triethylphosphate, calcium nitrate tetrahydrate, and PAN. Crystalline structure and morphology of β-TCP@CNFs were characterized by XRD, SEM, and TEM observations. The diameter of the β-TCP nanoparticles was in the range of 30-60 nm, they were well distributed on the surface of CNFs. Human osteoblasts cells were actively proliferated on the β-TCP@CNFs membrane due to the far extended adhesion area and biocompatibility.     

Novel concepts for reliability technology

We begin by examining the diverse connotations of the term quality. The desirable shape traced by the failure rate of the entire life of a good product, which might be called a hockey-stick line rather than a bathtub curve, is introduced. From the hockey-stick line and the definition of reliability, we extract two measurements. The terms r-reliability (failure rate) and durability (product life) are then explained. The conceptual analysis of failure mechanics explains that reliability technology pertains to the design area.The desirable shape of the failure-rate curve of electronic items, the hockey-stick line, clarifies that mean time to failure (MTTF) as the inverse of failure rate can be regarded as nominal life. We then discuss the BX life which is different from the MTTF, and reliability relationships between components and the set product. We recommend reshaped definitions of r-reliability and durability.We clarify the procedure to improve reliability and to identify the failure mode in order to find for right solutions and recommend a generalized life-stress failure model.     

Design analysis of a solid nitrogen cooled “permanent” high-temperature superconducting magnet system

Potential performance advantages of a solid nitrogen cooled “permanent” high-temperature superconducting (SN2/HTS) magnet system over a liquid helium cooled low-temperature superconducting (LHe/LTS) system are explored. The SN2/HTS system design includes a second solid heat capacitor that cools a radiation shield. Recooling of the heat capacitors is performed with a demountable cryocooler. The SN2/HTS system offers both enhanced stability and improved portability over a LHe/LTS system.Design codes are constructed to compare the SN2/HTS system design with a LHe/LTS design for a general permanent superconducting magnet system employing a room temperature bore. The codes predict the system volume and mass that should be expected for a given set of design requirements, i.e. field strength and bore size, and a given set of conductor properties. The results indicate that present HTS conductor critical current and index are not yet sufficient for producing SN2/HTS systems of a size that is comparable with that expected for a LHe/LTS system; however, the conductor properties of Bi2223/Ag have been consistently improving, and new HTS conductors are expected to be developed in the near future. The codes are used to determine the minimum Bi2223/Ag conductor performance required for a SN2/HTS system to be competitive with a LHe/LTS system.