Shigemori Ohtani

Solid particle velocity in vertical gaseous suspension flows

Abstract An optical method. which is based on cross-correlating the signals of two photo-sensors. is applied to measure the average velocity of solid particles transported vertically by a turbulent air stream. Particle velocities measured by the method showed two interesting features; the relative velocity was smaller than the terminal velocity of a single particle at lower air velocities but greater at higher velocities. and for smaller sizes of particles it tended to depend on the solid concentration as well. An empirical correlation was presented for the average particles velocity and tested with literature data. The average drag coefficients. which were evaluated indirectly from the measured relative velocities and the pressure drop due to solids alone. exhibited significant increase compared with the standard ones.

ON THE DRYING MECHANISM OF SHRINKAGE MATERIALS

ABSTRACT Effects of moisture content on Liquid transport properties (Permeability and suction pressure) and mechanical properties (Youngs modulus, yield stress and tensile strength) of drying shrinkage materials (Kibnshi, IIaido and mixed clay) were measured and a strong dependence was found. When glass beads are added to the Kibushi, permeability increase and Youngs modulus and yield stress decrease in spite of the same suction pressure and tensile strength. Changes in local moisture content and stress during drying was calculated by using finite-element method, taking into account the stress gradient in addition to the pressure gradient due to osmotic suction.

Simultaneous estimation of thermophysical properties by periodic hot-wire heating method

Abstract A new unsteady heat flux method is proposed to measure thermal conductivity and diffusivity simultaneously, the principle based on an analytical solution for an infinite hollow cylindrical system with a periodic heat source in the center. Thermal conductivity and diffusivity are determined from the amplitude and phase lag of the temperature response within the cylinder. The method also makes it easy to measure the temperature dependency of thermal properties during a continous heating process. The measurement errors caused by the finite specimen size and the displacement of the thermocouple location are estimated numerically to confirm the accuracy of the measurement method. Effective thermal conductivity and diffusivity for the packed beds of aluminum oxide particles and potassium perchlorate particles are measured. The thermophysical properties measured by this method agree well with those measured by conventional methods such as the hot-wire, periodic heating, and continuous heating methods.

Effect of swirling flow on unburned ratio and nitrogen oxide concentration in a spray combustion system

Abstract The effect of swirling flow on the unburned ratio and NO concentration in exhausted gas was studied for slurry [coal-water mixture (CWM)] spray combustion with variations of swirl numbers. A numerical analysis for CWM combustion was performed for axisymmetric flow in a cylindrical geometry. First, to check the performance of three previous k - ϵ turbulence models modified with swirling flow, velocity components of isothermal swirling jets were measured by laser-Doppler anemometry (LDA) and compared with predicted results. The two modified models gave more reliable results than the conventional one. Next, as the swirl number could not be estimated by the angular momentum derived from the vane angle of the circular swirler, the reduction rate of the tangential momentum flux through the tube of the circular swirler was measured and calculated. Both measured and predicted results showed that when the swirl number S ′ given by the vane angle was 2.0, the effective swirl number S eff decreased by about 60% to S ′. To take the results mentioned above into consideration, effects of swirl number on both the exhausted NO concentration and unburned ratio were investigated. The predicted unburned ratio showed good agreement with the experimental results. Both experimental and calculated results showed that the optimum operating conditions controlling the exhausted NO concentration and unburned ratio in this spray combustion system were obtained when the swirl number S eff was about 0.5.

Numerical analysis of turbulent flow in a duct introducing two-stage combustion air.

二段燃焼用空気の導入による炉内流動の変化を測定するために, 内径0.5m×全長2.0mのアクリル製ダクトを用いて, 二段燃焼用空気 (80Nm3/hr) をx/D=0.8の地点にダクトの全周から接線方向に導入した.このときの軸方向および接線方向平均速度をx/D=0.5, 1.5の二点においてレーザー・ドップラー・流速計により測定した.またk-e二方程式モデルに二段燃焼用空気導入モデルを組み込み円筒軸対称座標系でダクト内流動を数値解析し, 測定結果と比較・検討した.その結果, 解析値はダクト内流動を良好に表現し, 二段燃焼用空気導入モデルは適切であることが示された.さらに, 円筒軸対称座標系での解析の妥当性を検討するため, 上記と同一の導入位置, 空気量で実炉と同様に1本の導入管から二段燃焼用空気を導入し, 測定結果を解析結果と比較した.その結果, 流れは軸対称ではなく, 三次元解析が必要であるとの結論を得た.

Gasification and liquefaction for covering meterial of electric cord.

The covering material of an electric cord was pyrolyzed in an atmosphere of nitrogen. The solidified tar yield was got up to 63wt% and the others were produced as gases at the pyrolysis completion under the heating condition of 1°C/min.The partially combustion method and the high pressure pyrolysis method were conducted to reduce the solidified tar yield. The principal components of hydrocarbons, in the partially combustion were C1, C2 and C4. The hydrocarbons above C5 were not detected. The tar was reduced with increases of oxygen concentration and final temperature, while CO and CO2 in-crease with oxygen concentration. On the other hand, the solidified tar in the high pressure pyrolysis method was not producted on the range above 5kg/cm2, and the liquefied oil was done at 75wt% of yield.

Development of a cascade heat pipe.

熱ダイオード特性を持つカスケード型のヒートパイプを試作し, その伝熱特性について実験的に検討した。その結果熱ダイオード効率は0.85以上のものが得られた.また, この試作したヒートパイプの中間部はある温度を境として蒸発部にも凝縮部ともなり得ることが明らかとなった。さらにこの熱入出力反転温度は簡単な式で表現できることが示された.

A New Measurement Method of Liquid Transport Properties

Liquid transport properties, such as suction pressure, permeability and apparent moisture diffusivity, were measured for wide range of degree of liquid saturation within wet material to be dried. Wet sample was pressurized-by N2 gas and drained water through membrane filter was measured continuously by a micro processor system. Suction pressure was determined from the equilibrium data. Permeability and difusivity were estimated from the transient change of the drained water volume, by using a linearized transport equation in each small increment of pressure.

Heat Transfer by Natural Convection under the Frosting Condition in an Enclosed Cavity

密閉系 (底面加熱, 片側壁冷却, 他側壁および天井壁断熱の場合) における空気の自然対流熱伝達に関して結霜過程にある場合について実験を行ない, 系内の温度分布, 熱伝達係数などを求めた. 物質移動の影響をみるため, 熱移動のみがおぎている場合についても温度分布, 熱伝達係数などを求めた。この結果, 結霜をともなう場合のNusselt数は熱移動の入かおきている場合のそれにくらべ, 2～3倍程度大きい値を示した。さらに熱移動のみがおきている場合について, 基礎方程式を数値計算により解き, 温度分布, Nusselt数などを求め, 実験結果と比較した結果よい一致をみた。