Heat extraction characteristics by coaxial heat exchanger

This study was performed to investigate the heat extraction characteristics from shallow geothermal resources using a coaxial heat exchanger. First, a computer simulation program for a coaxial heat exchanger was checked and verified by laboratory experiments. After inspecting the effectiveness of the computer program described herein, a numerical simulation for a real scale model was conducted under the condition that the heat transfer mechanism in the stratum was heat conduction. Unsteady heat extraction characteristics are presented herein, and the effects of the tube material, inner diameter, and circular modes on the heat extraction rate are discussed. From the computer results it was found that the heat extraction performance using a coaxial heat exchanger greatly depended on the factors mentioned above in the range of the parameters covered in this study. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 496–513, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20083     

Sintering Kinetics at Isothermal Shrinkage: Effect of Specific Surface Area on the Initial Sintering Stage of Fine Zirconia Powder

The isothermal shrinkage behaviors of fine zirconia powders (containing 2.8–2.9 mol% Y₂O₃) with specific surface areas of about 6 and 16 m²/g were investigated to clarify the effect of specific surface area on the initial sintering stage. The shrinkage of powder compact was measured under constant temperatures in the range of 1000°–1100°C. The increase in specific surface area enhanced the densification rate with increasing temperature. The values of activation energy ( Q ) and frequency-factor term (β₀) of diffusion at initial sintering were estimated by applying the sintering-rate equation to the isothermal shrinkage data. The Q of diffusion changes little but the β₀ increases with the increase in specific surface area. It is therefore concluded that the increase in the specific surface area of fine zirconia powder enhances the shrinkage rate because of an increase in the β₀ at the initial stage of sintering.     

Demonstrative drop tests of transport and storage full-scale canisters with high corrosion-resistant material

The concrete modular dry storage technologies are becoming widely used, aiming at better economic performances. With longer perspective, there are still key issues related to safety standards in operation and maintenance during storage and unloading/loading for transportation, long-term integrity of the storage components. On the other hands, due to the lack of the experimental studies related to tipping-over or drop event scenarios, it is very important to evaluate the characteristics of the behavior of the components, such as the multi-purpose canister (MPC) subjected to impact loads. Therefore, we executed the demonstration drop test program using double-lid welded MPCs, with the aim of obtaining basic data for regulating safety. This paper introduces the summary of our drop test program.     

Effect of Contact Stiffness on Creep-Groan Occurrence on a Simple Caliper-Slider Experimental Model

In this paper, a fundamental mechanism for creep-groan generation is investigated by adopting a simple yet effective caliper-slider experimental model. Contact condition, which is a function of three parameters, namely normal force, contact roughness, and material combination, is connected with the creep-groan phenomenon in terms of contact stiffness. Creep-groan generation is determined by analyzing the frequency characteristic of the generated vibration acceleration when the sliding commences due to a simultaneous application and release of force in the tangential and normal directions, respectively. As per the obtained results, creep-groan occurrence or absence in the employed experimental model may be classified into three regions based upon the value of the contact stiffness, i.e., occurrence, non-occurrence, and mixed regions. The results also indicate that creep-groan occurrence in this caliper-slider experimental model can be avoided by controlling the value of contact stiffness in an effective manner.