著者

金子 暁子 野村 康通 高木 周 松本 洋一郎 阿部 豊

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.78, no.786, pp.207-217, 2012 (Released:2012-02-25)

参考文献数

14

被引用文献数

8 19

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Microbubble has distinguished characteristics of large surface area to unit volume and small buoyancy. Recently microbubble generators with low energy and high performance are required to wide applications. In the present study, we propose one new effective technique to generate tiny bubbles with less than 200μm diameter utilizing a venturi tube under high void fraction condition. The objective of the present study is to elucidate the mechanism of bubble breakup phenomena in the venturi tube and to clarify the effects of parameters which are necessary to realize an optimum system experimentally. Under low velocity condition, bubbles which were observed with a high speed camera parted gradually in a wide region. On the contrary under high velocity condition, bubbles expanded after passing through the throat and shrank rapidly. Since the speed of sound in gas-liquid system is extremely lower than that of single-phase flow, the bubble breakup phenomenon in the venturi tube is explained as the supersonic flow in a Laval nozzle. With rapid pressure recovery in diverging area, expanding bubbles collapse violently. The tiny bubbles are generated due to the surface instability of shrinking bubbles.

著者

村瀬 英一 森上 修 橋本 英樹 松崎 伊生

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.805, pp.1839-1847, 2013 (Released:2013-09-25)

参考文献数

9

被引用文献数

1

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Spark ignition of premixed gases was experimentally studied. Minimum ignition energy and initial burning velocity, which is a burning velocity at an initial stage of flame propagation, were measured and their dependences on equivalence ratio were discussed. Minimum ignition energy takes a minimum value when equivalence ratio is around 0.9 for methane/air mixtures, and around 1.5 for n-butane/air mixtures, which corresponds with the study of Lewis and von Elbe. A shadowgraph technique was used to observe the growth of the flame kernels. A burning velocity was measured from the images of the flame kernel, and initial burning velocity was defined as a burning velocity at the moment when the equivalent radius of the flame kernel is approximately 3.0mm. Initial burning velocity takes a maximum value when equivalence ratio is around 0.9 for methane/air mixtures, and around 1.5 for n-butane/air mixtures, while laminar burning velocity of well-grown flame takes a maximum value when equivalence ratio is around 1.1 for both mixtures as known well. This is caused by the curvature of flame surface at the initial stage. It is suggested that the equivalence-ratio dependence of minimum ignition energy is derived from that of initial burning velocity.

著者

佐藤 航

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.801, pp.1027-1037, 2013 (Released:2013-05-25)

参考文献数

18

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I describe our study on a cooling device that is based on the electrocaloric effect (ECE). The ECE causes increases and decreases in the temperature of a dielectric material by changing the electric field. I used a multi layer ceramic capacitor (MLC) to demonstrate the temperature change based on the ECE. The temperature change of commercial MLCs can be controlled by applying a voltage to them and the maximum change is 0.55 K when using 300 V. However, these changes occurred sequentially by applying and removing the voltage. Therefore, it was difficult to apply this phenomenon to a cooling device. I used a heat pipe that had an anisotropic heat conduction feature in this study to separate the heating and cooling. I developed a cooling device consisting of MLCs and a heat pipe containing acetone as the working fluid. The MLCs were set in the bottom of the heat pipe as the cold side and the other side of the heat pipe was attached to a heat sink as the hot side. Only the heat of the ECE in this device was transferred to the heat sink. The temperature of the cold side decreased by applying and removing the voltage periodically. This device demonstrated that the temperature of an MLC dropped 0.49 K when using 300 V at 0.10 Hz frequency.

著者

野原 正寛 金子 雄大 萩原 俊輔 永田 晴紀

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.77, no.777, pp.1249-1258, 2011 (Released:2011-05-25)

参考文献数

6

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The authors have been developing Cascaded Multistage Impinging-jet (CAMUI) type hybrid rockets. A CAMUI type hybrid rocket uses a fuel grain consisting of several cylindrical fuel blocks with two ports. To minimize both of c* loss due to O/F shifting and residual fuel weight after burning, an appropriate design of initial fuel grain shape is necessary. However, obtaining an optimum design of initial grain shape is not easy because there are many design variables influencing one another. To solve this problem, the authors employed Genetic Algorithm (GA) combined with a numerical model forecasting performance history of a CAMUI type motor. GA can acquire an approximate optimum solution for problems with a vast search space in practical time. The numerical model gives c* loss and residual fuel weight to evaluate the degree of performance of each initial fuel grain shape. A fuel grain design proposed by this method showed residual fuel weight as small as 6.36% of the initial weight and c* loss less than 1%.

著者

山本 昌平 坂口 大作 植木 弘信 石田 正弘

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.799, pp.380-389, 2013 (Released:2013-03-25)

参考文献数

16

被引用文献数

5

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In order to realize a premixed compression ignition (PCI) engine by utilizing bio-alcohol, combustion characteristics of bio-alcohol blended with gas oil were compared between ethanol and n-butanol in a diesel engine. The effects of the ethanol blend ratio and the butanol blend ratio on ignition delay, premixed combustion, diffusion combustion, fuel consumption and exhaust emissions such as smoke density, nitrogen oxide (NOx) and so on were investigated experimentally. It is found that ethanol almost burns out together with low evaporation temperature composition of gas oil in the premixed combustion period and the heat release in the diffusion combustion is based on mainly high evaporation temperature composition of gas oil, then, soot is formed in the diffusion combustion of gas oil. On the other hand, a part of butanol burns in the diffusion combustion, and the combustion of butanol in the diffusion stage is not the cause of soot formation. Butanol is more useful in diesel engine compared with ethanol because butanol can be blended with gas oil without surface-active agent, and fuel consumption and smoke are almost equal in both blend fuels if the alcohol blend ratio is the same.

著者

佐藤 範和 竹内 伸太郎 梶島 岳夫 稲垣 昌英 堀之内 成明

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.803, pp.1219-1231, 2013 (Released:2013-07-25)

参考文献数

13

被引用文献数

1 1

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A new discretization scheme of a Cartesian grid method for flow with heat transfer is proposed. The energy transport equation is discretized directly even in the boundary cells involving either the Dirichlet (isothermal) or the Neumann (iso-heat-flux/adiabatic) boundary conditions in order to ensure the energy conservation in those cells. The basic idea of this discretization is the same as the discretization scheme which is previously proposed by the present authors for boundary forcing in incompressible flow simulations. Moreover, the temperature gradients in both the normal and tangential directions at boundaries are required in the present method for representing the Neumann boundary condition on the Cartesian grids which do not necessarily coincide with the body geometries. The tangential components of the temperature gradients at boundaries are calculated by the extrapolations from the surrounding temperature field. Accuracy evaluations are conducted in a convective heat transfer problem in a flow between concentric cylindrical walls under the several different types of thermal boundary conditions applied at the inner and outer walls. It is confirmed that the present method significantly improves the accuracy orders for the temperature as well as the error magnitudes under both types of thermal boundary conditions. In particular, because the temperature gradients are correctly considered at the boundary cells where the Neumann boundary conditions are enforced, the same level of accuracy order is also maintained even in cases of non-uniformly distributed temperature at those boundaries.

著者

杉井 泰介 石井 英二

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.77, no.781, pp.1779-1790, 2011 (Released:2011-09-25)

参考文献数

23

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We present a simulation of meso-scale fluid in a grooved channel conducted using the many-body dissipative particle dynamics (MDPD) method. The simulation system consists of a straight channel with a rectangular groove and a liquid that fills the channel. In the simulation, an instantaneous liquid interface was defined and the time-series variation of the angle between the channel wall and the interface was investigated. The calculated angle was found to satisfy the Gibbs' inequality condition when the interface passes the corner of the groove. We also investigated the behavior in which the liquid filled the groove by varying the contact angle between the liquid and the channel wall. The results show that the feasibility of filling the groove, which depends on the contact angles between the liquid and the grooved/non-grooved channel wall, qualitatively agrees with the geometrical analysis. We also showed that a smaller contact angle between the liquid and the grooved channel wall and a larger contact angle between the liquid and the non-grooved channel wall causes the liquid to fill the groove.

著者

甲村 圭司 中村 佳朗

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.804, pp.1489-1499, 2013 (Released:2013-08-25)

参考文献数

10

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Aerodynamic noise with discrete frequencies is generated in an unexpected way from a slit between a flat plate, which is placed in parallel to the main flow, and a wedge that is placed normal to the flow. To study this phenomenon, we examined the discrete frequency noise generated by a subsonic air jet flow from a slit. It was found that the slit height and the plate length have considerable effects on the noise generation. In addition, the discrete frequency noise was generated only when the values of these parameters are within a limited range. Furthermore, it was found that the noise frequency is proportional to the jet velocity and is inversely proportional to the plate length. Finally, it was made clear from the present study that the interaction of the vortex, which is generated from the shear layer due to a wedge, with the wake of a flat plate is a major cause for the discrete noise due to a slit.

著者

鈴木 貴之 加藤 千幸

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.808, pp.2743-2758, 2013 (Released:2013-12-25)

参考文献数

15

被引用文献数

1 2

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Over the past two decades, many types of homogeneous models have been proposed for the numerical simulation of cavitating flows. Homogeneous models represent cavitation by the media whose density continuously varies from the value corresponding to liquid to that to gas. Recent studies have, however, revealed that the present homogenous models are unable to predict the breakdown characteristics of cavitating hydrofoils. The objective of this study is to clarify causes of such inability of homogeneous models to predict breakdown characteristics of cavitating hydrofoil accurately. Theoretical analysis shows that the present cavitation models inevitably cause kinetic energy loss through expansion and contraction of the media. To illustrate this fact, we computed cavitating flows in a venturi and around a hydrofoil (NACA0015) with a homogeneous model and investigated the computed flow field in detail. It is shown that the expansion and contraction of the media based on the homogeneous model do in fact cause kinetic energy loss and as a result, a region of low velocity appears downstream of the cavity. This results in a decrease of lift force in a partial cavitation condition, which is not observed in the corresponding measurements.

著者

岩岸 知崇 中村 尚彦 本村 真治 中川 幸二

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.77, no.779, pp.1445-1456, 2011 (Released:2011-07-25)

参考文献数

7

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A flapping water turbine is a kind of power generating machine which extracts mechanical energy from flowing water by swing of blade motion. In this study, we carried out numerical simulation of blade motion and experiment on river. In the simulation, we made numerical integration of momentum equation about roll angle and compared the result with experiment in water channel. The disagreement in roll angle between the simulation and the result of experiment were discussed by using analytical model and basic data of blade fluid dynamic characteristics. The result of river experiment showed that flapping water turbine can extract energy from stream with rippling surface and turbulence.