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This study experimentally and numerically investigated the thermo-fluid dynamics of Taylor–Couette flow with an axial temperature gradient from the chemical engineering perspective. A Taylor–Couette apparatus with a jacket vertically divided into two parts was used in the experiments. Based on the flow visualization and temperature measurement for glycerol aqueous solutions with various concentrations, the flow pattern was classified into six modes: heat convection dominant mode (Case I), heat convection-Taylor vortex flow alternate mode (Case II), Taylor vortex flow dominant mode (Case III), fluctuation maintaining Taylor cell structure mode (Case IV), segregation between Couette flow and Taylor vortex flow mode (Case V) and upward motion mode (Case VI). These flow modes weremapped in terms of the Reynolds and Grashof numbers. Cases II, IV, V and VI are regarded as transition flow patterns between Case I and Case III, depending on the concentration. In addition, numerical simulations showed that in Case II, heat transfer was enhanced when the Taylor–Couette flow was altered by heat convection. Moreover, the average Nusselt number with the alternate flow was higher than that with the stable Taylor vortex flow. Thus, the interaction between heat convection and Taylor–Couette flow is an effective tool to enhance heat transfer. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical transactions paper (Part 2)’.

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, ......

Agitation is often encountered in various processes, such as ice cream manufacture and suspension freeze-concentration of liquid food. This study investigated the effect of agitation speed on the freezing process of an aqueous sucrose solution as a preliminary investigation for the development of processes that include both agitation and freezing. A batch-type freezer with an anchor impeller was used. Frozen samples at a higher agitation speed started to melt at a lower temperature. 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).

The effects of air humidity when drying with superheated steam (SHS) were examined considering displacement by SHS. A wetted raw starch sphere (ball) was used as the model material. It was found that the humidity profile strongly affects the mass change and properties of the products. The material became porous when it was dried with pure SHS from start to finish, which differs both from products dried with high-humidity air alone, and from products dried with air followed by SHS within a few minutes. A prediction method for adiabatic saturation temperature over a wide range of humidity is also proposed.

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.

Amaranth seeds can be popped by evaporation of contained moisture during heating. The relationships among the expansion ratio by popping and the type of heating media, gas temperature, initial moisture content of the seeds and heating time were clarified based on empirical study. And using a simple calculation model, the popping mechanism and effect of initial condensation of superheated steam were investigated. According to the results, the maximum volume of the seeds after popping was 8.7 times greater than that of raw seeds at optimal conditions. Compared with the case of hot air, the expansion ratio by superheated steam was slightly lower.

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.

The effect of the initial moisture content (X(0)) of amaranth seeds on expansion volume after popping was examined in hot air and superheated steam (SHS), using a fluidized bed system (FBS). The moisturized seeds were prepared under various vapor pressures due to various saturated salt solutions. In hot air, the maximum expansion volume was shown by seeds having X(0) of 0.16 at 260 degrees C for 15 sec, reaching 8.7-fold of the pre-popped seeds. Heating by SHS decreased the volume slightly. Thus, popping of amaranth seeds is influenced not only by the moisture content of the seeds, but also by moisture in the heat media.