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A method to intensify the mixing process of scalar components within shear-thinning fluids was proposed. A conical Taylor–Couette flow enabled fluid elements to circulate in the entire fluid column owing to the global circulation flow (i.e., meridional flow) for keeping good local mixing within Taylor cells. The global convection and mixing characteristics were numerically investigated. The meridional flow was found to be enhanced with increasing shear-thinning. In addition, ......

The objective of this study is to estimate the drying characteristics of a relatively large material immersed in a fluidized bed under reduced pressure by measuring the constant drying rate. The constant drying-rate period in a fluidized bed under reduced pressure is difficult to measure because it is extremely short. To maintain the constant drying-rate period, distilled water is directly supplied to the drying material. Through our experiment, the heat transfer coefficient of the material surface was also determined. The results were compared with data on hot air drying. The constant drying rate is higher for fluidized bed drying than for hot air drying. It suggests that the heat transfer coefficient on the surface of the drying material is much larger for fluidized bed drying than for hot air drying. For fluidized bed drying, the effect of pressure in the drying chamber on the heat transfer coefficient is slight at the same normalized mass velocity of dry air (G/Gmf). The temperature difference...

In this study, a Taylor-Couette flow reactor (TCFR) was applied to starch hydrolysis accompanied with an intricate viscosity change during reaction for the purpose of process intensification. In industries, several reactors are used in starch hydrolysis, namely gelatinization, liquefaction, and saccharification. It was possible to conduct a continuous starch hydrolysis with one TCFR. In addition, a sufficient reducing sugar yield was obtained in the Taylor vortex flow regime. However, the yield decreased at a higher effective Reynolds number (Reeff) due to axial dispersion through a bypass flow generated by the wavy motion of Taylor cells. In order to immobilize Taylor vortex flow at this condition, a ribbed inner cylinder was employed which suppressed axial dispersion at the higher Reeff. As a result, a higher reducing sugar yield was successfully obtained than that by using a standard cylinder, demonstrating that the optimization of TCFR geometry has the potential for process intensification.

A high-temperature wide-range humidity sensor has been developed using wetted material temperature measurement. A porous ceramic is used as a sensing element; it has a small tube for supplying water to maintain a wetted surface. However, the water supplied to the elements can affect the surface temperature. In this study, we experimentally investigate the accuracy of the developed sensor and its contributing factors-convective heat transfer, evaporation, radiant heat, and the water supplied to the wetted material-under the conditions of a gas flow temperature of 200 °C, gas flow velocity of 3 or 5 m/s, flow rate of supplied water of 0.01-0.05 g/s, and steam mole fraction of 0.03-1.00. Further, we calculate the heat flux and the surface temperature using a one-dimensional heat transfer model to clarify the effects of the each of the abovementioned factors. Consequently, we conclude that the supplied water strongly affects the accuracy of the developed sensor. We also improve the measurement error of the steam mole fraction from 0.07 to 0.03 by the controlling the flow rate of the supplied water.

The effects of dry-bulb and wet-bulb temperatures on the dryingtime of a wet spherical porous material in humid hot air and superheated steam were investigated. A wet spherical brick was used as the sample porous material. The experimental results revealed that the normalized drying characteristics curves in the falling drying rate period obtained under different experimental conditions were all in good agreement. In addition, the time required to reduce the moisture content below the critical moisture content was almost the same under all wet-bulb conditions at the same constant drying rate, regardless of steam condensation.

Amaranth seeds can be popped under suitable heating conditions. On the basis of experimental results obtained in our laboratory, we have developed a prototype of a continuous processing system for commercial application. In addition, the effects of gas temperature, flow rate, and feed speed on the popping quality of seeds, such as their volume expansion ratio and yield, were examined. The experimental results showed that the undersized yield ratio increased with the flow speed, whereas it decreased with an increase in the gas temperature. In addition, to achieve a high expansion ratio and maximum output, the feed speed was increased with the gas temperature. Furthermore, measuring the differential pressure in the test section of the experimental apparatus enabled the estimation of the quantity of seeds therein during the popping experiment.

For fluidized bed drying under a reduced pressure, the effect of the humidity of the drying gas on the drying characteristics of porous materials immersed in the bed was examined experimentally and theoretically. The temperature at the sample center increased with the humidity at relatively high pressures in the drying chamber (101.3 and 50 kPa), and the degree of the increment in the temperature with the humidity increased with the chamber pressure. The effect of the humidity on the temperature at the sample center and the drying time was insignificant at a relatively low chamber pressure (20 kPa).

非親水性多孔平板の減率乾燥期間に，蒸発面後退で現れる乾き圏内の水蒸気移動を，水蒸気–空気2成分系の非等全圧一方拡散式に基づいて理論的に考察した．考察は，熱風乾燥，空気漏れを考慮した過熱水蒸気乾燥と真空乾燥を想定した条件について行った．その結果，微分形式でのみ知られていた厳密式を近似積分して非等全圧一方拡散近似式を得ることに成功した．この式およびKnudsen流れを考慮した等全圧一方拡散式，水蒸気流れ式，考慮しない両式の計五つの近似式を，厳密式による結果と比較検討し，乾燥速度と内部全圧上昇に対して近似式の適用範囲を考察した．非等全圧一方拡散近似式は厳密式と広範囲において良く一致した．全圧上昇の小さいミクロンサイズ以上の細孔内では等全圧一方拡散式が，高温熱風乾燥，過熱水蒸気乾燥，真空乾燥で細孔内が水蒸気のみで満たされると近似できる場合は水蒸気流れ式が有効だった．全圧上昇が無視できないサブミクロンサイズ以下の細孔で共存空気の存在も無視できない場合は非等全圧一方拡散式のみが有効だった.

乾燥過程における材料温度変化を用いて乾燥速度を簡便に測定する方法を提案し，非親水性多孔平板であるガラス微粒子層の対流乾燥，伝導併用対流乾燥，および高分子溶液膜であるPVA水溶液膜の対流乾燥実験結果に対してこの方法を適用することでその実用性を検討した．その結果，水分蒸発を伴わない乾き材料昇温期間や材料温度変化がきわめて小さな微量水分蒸発期間を除いてこの方法の有効性が示唆された．この方法は質量変化法の適用が難しい高速熱風下で乾燥所要時間の著しく短い塗膜などの乾燥速度の測定に応用できると期待される.

Dependency of absorbed power by microwave on the local moisture content in a glass particle layer was measured with a new method; that is, heating the wet layer. The heating experiment was performed using a laboratory-scale combined convective and microwave heater/dryer that was manufactured by modifying a domestic microwave oven at 2.45 GHz. The measured result was strongly dependent on the local moisture content and showed a maximum and a minimum within the measured range of the moisture content. This dependency can be explained by the assumption that moisture in the wet layer behaves as a mass of the free water. The combined drying rate of the wet layer measured with the heater/dryer was simulated with both the power dependency and the experimental convective-only drying rate. Power dependency on temperature is as important as the moisture content in the simulation. Simulated results agree very well with experimental ones.

For clarification of the mechanism of heat and mass transfer in the early stages of superheated steam drying which accompanies condensation and evaporation, we had done both the experiments and the simple calculation for a semiinfinite heat transfer model. And we found the existence of "reverse point" at which neither condensation nor evaporation occurs in the early stage of superheated steam drying. In this report, in order to investigate the physical reason of the reverse point and its change according to the shapes of heat transfer model, similar analytical and experimental methods were applied for both a spherical and a large slab heat transfer models. As a result, restoration time changes in the range of 3.2∼10times the reverse time with changes of scale, heat transfer rate and initial temperature of the heat transfer models.

To clarify the mechanism of heat and mass transfer in the early stages of superheated steam drying which accompanies condensation and evaporation, an experiment in which a water surface was used as the dried material was conducted under atmospheric pressure. Temperature profiles in both the gas phase and the liquid phase near the water surface and the liquid level were measured precisely. From the results, heat transfer rates at the water surface and the amount of steam condensed into water were determined; in addition, the relationship between these two was investigated both experimentally and theoretically. Furthermore, a characteristic curve of drying accompanying condensation and evaporation in the early stages of superheated steam drying was derived semiempirically. In this drying characteristic curve, there is a point at which neither condensation nor evaporation occurs. This is defined as the “reverse point.” Introduction of this reverse point and the time ratio for condensation and evaporation during the early stages of superheated steam drying are clarified. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 352–366, 1999

A numerical study on a combined radiation and forced convection heat transfer of superheated steam, which is a radiation participating real gas, in thermally developing laminar flow through a parallel-plate channel has been conducted to investigate characteristics of superheated steam drying. The integrodifferential energy equation was solved using an implicit finite-difference technique with a marching solution procedure and an exponential wide-band model for the treatment of the radiative transfer part. Comparison of results with and without gas radiation in various conditions shows that fluid radiation decreases the temperature of the main stream, but increases the total heat flux at a heat transfer surface. Furthermore, the results show that the fluid radiation decreases the inversion point temperature approximately to 150 to 240 °C with the increase of optical thickness. This numerical result agrees in an order of magnitude with the previous experimental studies, but is about 100 K lower than that of former theoretical predictions without considering fluid radiation. © 2000 Scripta Technica, Heat Trans Asian Res, 29(5): 385–399, 2000

Surface tension induced (Marangoni-Benard) convection occurs at a surface of lithium bromide (LiBr) aqueous solution with addition of a small amount of surfactant was observed in order to investigate a mechanism of absorption enhancement by surfactant. Real time type laser holographic interferometry was used to visualize the transient phenomena occurred at/beneath the LiBr aqueous solution's surface in the very beginning(0-20msec) of steam absorption under vacuum condition(0.7kPa). Experiments were performed varying the initial surfactant concentration from 0 to 200ppm and the liquid layer thickness of 3-5mm. Pentagonal or hexagonal cell's patterns were observed at the surface clearly. And those cells evolved from small to large size instantly. Thereafter large scale chaotic eddies were induced at the surface.

A theoretical and experimental study is conducted to investigate the detached volume from a pendant drop on the surface of a sphere. Observation of drop detachment by high-speed video camera reveals that the movement of the upper part of the neck of the drop is quite slow compared to that of the detaching lower part. The surface profile of the upper part was calculated approximately as a static problem using the axisymmetric Laplace equation. Using the drop profile, the system energy, including the work done by the solid–liquid wetting behavior, was calculated. Based on the condition of minimum energy, the volume of the detached part V was calculated. The volume V increases with the sphere diameter and approaches the value for the pendant drop attached to a plate. In addition, V is strongly dependent on the wettability between the sphere and the liquid and decreases with the receding contact angle. The detached volume of the water drop was measured for spheres of porous brick of various diameters. The experimental and theoretical results were found to be in good agreement. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/htj.20305

乾燥途中の含水多孔平板を乾燥表面に近い乾き圏と内部の湿り圏に分割し，各圏のマイクロ乾燥と誘電高周波乾燥における発熱率を推定するモデル「精密法」を提案した．さらに，提案したモデルを簡略化して「一様材料近似法」と「一様電界強度近似法」を提案し，これらの方法と精密法の結果を，モデル計算を通して比較検討した．その結果，湿り圏での含水率が小さければ，両圏の各発熱率の推定には一様電界強度近似法のみが利用でき，両圏の合計発熱率の推定には両近似法が利用できた．一方，湿り圏での含水率が大きくなれば，両圏の各発熱率および合計発熱率の推定に一様電界強度近似法は利用できなくなったが，両圏の合計発熱率の推定には一様材料近似法が利用できる場合もあった．