Showing papers by "Yutaka Asako published in 2006"

Heat Transfer Characteristics of Gaseous Flows in Micro-Channel with Negative Heat Flux

Abstract: Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with constant heat flux for which the value is negative for no-slip flow. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian method. The computations are performed for channels with constant heat flux ranging from −104 to −102 W/m2. The channel height ranges from 10 to 100 μ m and the aspect ratio of the channel height and length is 200. The stagnation pressure is chosen such that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure is fixed at the atmosphere. The wall and bulk temperatures in micro-channels with negative heat flux are compared with those of positive heat flux cases obtained in our previous work and also those of the incompressible flow in a conventional sized channel. In the case of fast flow, temperatures normalized by heat flux have different trends whether heat flux value is positive or negative. A correla...

Scale Effect on the Gaseous Flow Around a Micro-Scaled Gas Turbine Blade

Abstract: Two-dimensional compressible momentum and energy equations are solved on gaseous flows around a micro-scaled gas turbine blade (GE-E3) for which the axial chord length ranges from 86.1 μ m to 86.1 mm to obtain the scale effect. The numerical methodology is based on Arbitrary-Lagrangian-Eulerian (ALE) method. The flow is assumed to be “no heat conduction” flow. The computations were performed for gaseous flow around a single blade with periodical conditions imposed along the boundaries in the pitch directions. The study is focused on the effect of the scale of the turbine blade on the performance. The predicted pressure distribution on both the pressure and suction sides of the conventional sized blade and both the inlet and outlet Mach numbers were compared with available experimental data to verify the code, and the scale effect was discussed.

Heat Transfer Characteristics of Gaseous Flows in Micro-Channels With Constant Wall Temperature: Cooled From Walls

Abstract: Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with CWT (constant wall temperature) whose temperature is lower than the inlet temperature. The combined effect of viscous dissipation and compressibility is also investigated. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The stagnation temperature is fixed at 300K and the computations were done for the wall temperature of 250K, 280K, and 290K. The bulk temperature based on the static temperature and the total temperature are compared with those of the heated case and also compared with those of the incompressible flow in a conventional sized channel. The identical heat transfer coefficients are obtained for both heated and cooled cases of the incompressible flow. However, in the case of the gaseous flow in micro-channels, different heat transfer coefficients are obtained for each heated and cooled case. A correlation for the prediction of the heat transfer rate of the gaseous flow in the micro-channel is proposed.Copyright © 2006 by ASME

Performance of Gaseous Parallel-Flow Micro Heat Exchangers

Abstract: Heat exchangers performance of two-stream parallel-flow gas-gas type micro-heat exchangers is investigated numerically. The flow passages of the micro-heat exchangers are parallel-plate channels with heights in the range of 10 to 100 μm and selected lengths of 12.7 and 25.4 mm. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian method. The computations were performed to find the effects of capacity ratio, channel height and length on the heat exchange characteristics of micro heat exchangers. The results are presented in form of temperature contours, bulk temperatures, total temperatures and heat flux variation along the channel. Also, the correlation between the effectiveness and Ntu is discussed.Copyright © 2006 by ASME

Heat Protection Characteristics of Fire Protection Materials of High Water Content Using Sodium Silicate

Abstract: 耐火庫用耐火材の遮熱性能を向上させるために,耐 火材の熱拡散率を低くする試みがなされている。熱拡 散率は熱伝導率を熱容量で除したものなので,それを 低くするためには,熱伝導率を下げるか熱容量を大き くすれば良い。熱伝導率を下げるにはパーライトや気 泡を混合する方法がある。耐火材中の水分はその蒸発 潜熱が見かけ上熱容量を大きくする働きをするので, 熱容量を大きくする方法の一つとして高含水化が試み られている。最近,金らは潮解性をもつ塩化カルシウ ム水溶液を吸水性樹脂に吸水させたゲル1)をパーライ トモルタルに分散混合させた高含水耐火材2)(以下 「ゲル混合耐火材」と呼ぶ)を提案した。この耐火材 は含水率が周囲の温度と湿度により変化するが,経年 減少しない特徴を持ち,含水率が高く,遮熱性能は従 来のそれよりも著しく向上した。しかし,塩化カルシ ウムによる耐火庫鋼板の腐食が解決すべき課題として 残された。そこで,本研究では塩化カルシウムと同様 に潮解性を持つが,腐食性のないケイ酸ナトリウムを 保水材に用いることを提案し,その含水率,蒸発潜熱, 熱伝導率等の基礎熱物性および遮熱性能を報告するも のである。