Precise process temperature control of 0.001℃ under noise-temperature change of 0.1℃ is required in semiconductor manufacturing process. We studied control methods to minimize temperature change at an object position in a 2 dimensional vertical plate with a varying noise-heat-generation, natural convection cooling, and a control-heater. We numerically calculated 2 dimensional unsteady thermal conduction in the plate with feedback control, feed-forward control, and model predictive control of the control-heater. The temperature change at the object position can be decreased 1/80 times smaller than that without control-heat-generation by the feedback control with two monitoring temperatures. The temperature change at the object position can be decreased 1/1000 times (0.002℃) by the model predictive control of 5s interval with step response pattern and two monitoring temperatures. We found that the accuracy of the predictive model is very important for precise temperature control. Experiment was performed for the model predictive control with network model pattern, and the experimental result agreed with the calculation result.

View full abstract

Capillary pressure versus saturation curve is important for the estimation of drainage property of porous media such as gas diffusion layers (GDLs) of polymer electrolyte fuel cells. The Leverett function is proposed for correlating dimensionless capillary pressure with saturation in the soil science field. In this paper we use the lattice Boltzmann method for the calculation of capillary pressure in GDL and investigate the applicability of the Leverett function in GDL. It is found that the standard Leverett function is not applied to estimate the capillary pressure versus saturation curve, particularly when the wettability and the viscosity are changed.

View full abstract

Experimental studies using 2t/d and 200t/d coal gasifier were carried out to investigate the inception criteria for entrainment of molten slag droplet in an entrained flow coal gasifier. It was clarified that average gas dynamic pressure P_d and liquid film Reynolds number Re_f influenced strongly the phenomenon of entrainment of molten slag. The formula of the critical gas dynamic pressure P_<dc> and the critical Weber number We_c=1.73, which could be applied to the large-scale gasifier, were obtained as inception criteria for the phenomenon. It was clearly shown that the flow pattern in the large-scale gasifier could be different from the smaller gasifier by means of numerical simulation analysis and that the critical velocity U_<gc> decreases relatively along with the scaling-up of the gasifier.

View full abstract

Under the consideration of global warming, improvement of vehicle's fuel economy is a major challenge. Reduction of aerodynamic drag is an important item in vehicle engineering. However, as vehicle is also strongly oriented to design, aerodynamic drag must be reduced maintaining flexibility of design. In order to do so, it is necessary to clarify the characteristic flow structure around vehicle that increases aerodynamic drag. This means it is essential to optimize the flow field while allowing design flexibility. This study used a sedan type vehicle which allows design flexibility in an attempt to clarify the flow structure around vehicle that increases aerodynamic drag. As an initial report, this study reveals the flow structure above trunk deck by investigating wakes behind vehicles with different aerodynamic drag. As a result, it was clarified that trailing vortices behind vehicle enhance to increase aerodynamic drag of vehicle, as front pillar vortices enhance above trunk deck.

View full abstract

A theoretical and experimental consideration is conducted to investigate the bubble separation from an air injected into a liquid turbulent boundary layer. There exist three patterns of bubble separation dependent on the jet velocity, i.e., (a) single bubble, (b) ccalescent bubble, and (c) continuous jet. First, the critical jet velocity from (a) to (b) is theoretically estimated from the condition that the jet from the nozzle overtakes the rear end of the separated bubble which shrinks due to the action of surface tension. The calculated results roughly reproduce the experimental results observed by the high-speed video camera. The process of bubble separation from the continuous jet (c) can be classified into two patterns, i.e., (i) the bubble separates from the swell at the front end of jet, (ii) the jet breaks due to the instability on the liquid-gas interface. The separated bubble diameter of pattern (i) is theoretically determined by considering the force balance at the front end of jet between surface tension, drag from the frees stream and virtual mass force. Also the bubble diameter of pattern (ii) is calculated from the most unstable wavelength of Rayleigh instability. Both theoretical results agree well with those obtained experimentally.

View full abstract

There are a few studies on the drag-reducing effect of nonionic surfactant solutions which are nontoxic and biodegradable, while a lot of investigations for cationic surfactant solution have been performed so far. First, the drag-reducing effects of nonionic surfactant solutions such as oleyldimethylamineoxide (ODMAO) and alkyl polyglycoside (APG) were investigated by measuring the pressure drop in the pipe flow. Second, we investigated the drag-reducing effect of a nonionic surfactant on the turbulent boundary layer using a two-component laser-Doppler velocimetry (LDV) and particle image velocimetry (PIV) systems. At the temperature of nonionic surfactant solutions T=25℃, the maximum drag reduction ratios for ODMAO 500ppm and APG 6000ppm were about 50% and 15%, respectively, in the boundary layer flow, although the drag reduction ratio for both surfactant solution was larger than 60% in pipe flow. Turbulence statistics and structures for ODMAO 500ppm showed the behavior of typical dragreducing flow such as suppression of turbulence and modification of near-wall vortices, while velocity fields for APG 6000ppm were similar to those of water.

View full abstract

The present paper describes the mechanical losses of a swing-piston type rotary compressor, which has a groove on the outside surface of its piston and a vane engaging with the groove at the tip, compered with a rolling-piston type rotary compressor. Theoretical analysis showed an improvement in mechanical efficiency, attributable to reduction of mechanical loss from the reduced sliding velocity at the vane tip. Experimental results showed that the swing-piston type rotary compressor demonstrated higher mechanical, indicated, volumetric, and compressor efficiency than the rolling piston type one. Due to the increased sliding surface area and the reduced sliding velocity between the vane tip and the piston of the swing piston type, efficiency was improved and reliability may be improved.

View full abstract

Numerical calculation was done to estimate the flow rate in filtration of internal filtration enhanced dialyzer, in which the measurement of filtration rate is difficult. Using a finite volume method incorporated the variations in hollow fiber density with vessel taper, the effect of vessel taper was estimated. Permeability was used instead of the filtration coefficient, which depends on fluid viscosity, to determine the filtration quantity in internal filtration and to consider the change in blood viscosity with filtration. As the result of the present calculations, the filtration flow rate based on the filtration coefficient is found to be 10% lager than the one with the permeability measured by blood experiment.

View full abstract

Numerical simulations of 2-dimensional (2D) unsteady cavitating flows were carried out. Various conditions of the number of blades, incidence angles and cavitation numbers were considered. When the incidence angle increased or the cavitation number decreased, the steady balanced cavitation transited to unsteady and non-uniform patterns. Typical patterns reported in the previous studies for 3- and 4-blades were successfully reproduced. In this study, cascades of the larger numbers of blades were dealt with to consider the generality of unsteadiness by reducing the influence of periodicity. The cavitation is basically triggered in the backward next section. However, the period of time for growing causes complexity in the discrimination of propagation. In most cases of rotating partial cavitation, except for 4-blades, the cavity develops in the second passage of backward direction after the decay of largest cavity. In case of many blades, multiple cavities rotate simultaneously and the particular patterns observed in cascades of small even numbers of blades attenuate.

View full abstract

Single-blade centrifugal pump is used as a sewage pump widely. However, single-blade centrifugal pump impeller is acted on a big radial thrust during the pump operation because the impeller is an asymmetry geometrically. Therefore when the reliability of the pump is secured, it is necessary to grasp a radial thrust quantitatively and elucidate the behavior and outbreak mechanism. This study investigated the radial thrust acting on single-blade centrifugal impeller by an experiment and CFD analysis. As a result, the behavior of the radial thrust with the flow rate change was clarified. Furthemore, the radial thrust was divided to an unsteady component, a momentum component and a pressure component by applying unsteady conservation of momentum to this impeller. The grand total of these components accorded with the radial thrust that calculated by direct CFD analysis well. And the behavior of each divided component was shown. In addition, the effect of those components that gave to the radial thrust was clarified.

View full abstract

A blower driven by the thermal edge flow was shown to promote the freeze-drying processes. First, the pressure rise due to the thermal edge flow was confirmed by using an accumulation unit and the pressure rise of 5Pa was obtained. Next, the effect of the blower for sublimation from frozen material was confirmed by using frozen sponges containing some amount of water. The necessary time for drying by using the blower was roughly half of that without the blower, and the efficiency of the sublimation was shown to depend on the combination of the effects of the blower and the surrounding vacuum pressure.

View full abstract

The film boiling heat transfer around a vertical silver cylinder with a convex hemispherical bottom was investigated experimentally for quiescent water at atmospheric pressure. The experiments have been carried out by a quenching method. The diameter and length of test cylinder are 32mm and 48mm, respectively. The test cylinder was heated to about 600℃ in an electric furnace and then cooled in saturated or subcooled water with the immersion depth of about 100mm. The degree of liquid subcooling was varied from 0K to 30K. The analytical solutions for saturated and subcooled boiling are obtained by applying the two-phase boundary layer theory for the vapor film with the smooth interface. The experimental data can be correlated within ±15% by the present prediction method. Also, the lower limit of film boiling was examined in terms of wall heat flux and degree of superheating.

View full abstract

Highly subcooled boiling at high heat flux results in emission of microbubbles from boiling bubbles. This paper proposes a new MEMS heat transfer surface to generate single boiling bubbles in ideal situations and to observe the bubble growth and fission. The surface has seven thermocouples for temperature measurement and nickel electrodes for hydrogen generation, and back-side thin film heaters for transient heating. In a stagnant water pool, the heater makes superheated liquid layer and a hydrogen bubble triggers growth of a boiling bubble. Thermocouple signals reveal evaporation of liquid layer, dryout, and rewetting. Dependence of bubbling feature on heat flux and heating time during highly subcooled boiling is summarized as a bubbling pattern map. Under the conditions of high heat flux, and long heating time, growing bubbles largely deform and generate tiny bubbles from their top part.

View full abstract

A pressure-dependent transition (5kPa-100kPa) of carbon nanotube (CNT) morphology in plasma enhanced chemical vapor deposition (PECVD) is presented. High-purity, vertically-aligned single-walled CNTs (SWCNTs) were synthesized only when PECVD was used at atmospheric pressure, while multi-walled CNTs were preferentially synthesized when the total pressure was lower than 20kPa. In the reduced pressure range, nanostructured catalysts were easily coagulated at the initial stage of CNT nucleation even if an excess supply of reactive species and high-energy ion bombardment were absent. If catalyst coagulation was avoided at the moment of CNT uncleation, SWCNTs were grown in the root growth regime even at 5kPa; however, the top CNT layer was contaminated by amorphous carbon, produced as a result of excess supply of reactive species.

View full abstract

A high emphasis is placed on disposal of exhaust gas from diesel engines, because of an increasing concern about pollution of the atmosphere. Honeycomb supported catalytic agents is commonly used for NO oxidation into NO_2, which is adopted to develop continuously DPF system. However, the measurement of NO and NO_2 concentrations in the honeycomb is very difficult, because it is assembled with a lot of millimeter-sized channels. So, it is necessary to investigate and understand the phenomenon in the honeycomb by the numerical simulation. We have carried out the numerical study on NO oxidation by platinum catalyst in a channel using detailed elementary reaction kinetics for exhaust gas and platinum catalytic surface. Then, the details of NO oxidation on Pt surface in a channel, including species mass fraction in the gas, coverage on catalytic surface and reaction rate of the elementary reaction, are obtained. Especially, the effects of the supported amount of catalyst, the composition and the temperature of inflowing exhaust gas on No oxidation have been examined, and the catalytic reaction mechanism has become clear.

View full abstract

In this study, we focused on the fiber yielding system from fused coal ash to expand the ash utilization as building materials because slag inhibits the elution of toxic heavy metals, such as Hg, Pb, and As, to undetectable levels. In particular, fiber materials from coal ash slag are expected to be utilized as thermal insulator and acoustic materials. We designed a coal ash fusing furnace which is suitable for fiber manufacturing and recovery processes. To manufacture safe and homogeneous fibrous materials, slag viscosity had to be stabilized as approximately 1Pa・s at the slag-tapping hole of the furnace. But the slag temperature at 1Pa・s was too high to measure. We estimated the temperature at 1Pa・s using Riboud's and Urbain's expression. To control the slag viscosity and temperature, CaCO_3 addition to coal ash was effective. When the basicity (CaO/SiO_2 (wt%/wt%)) of the coal ash sample was 0.98, the fused slag temperature at 1Pa・s was estimated as 1563℃. Then, we verified that to yield 1Pa・s fusing slag from 120kg/h coal ash, the necessary fuel quantity of the coal ash fusing furnace was 40kg/h coal and 4m^3N/h LPG.

View full abstract

Effect of the preferential diffusion between oxygen and fuel molecules is observed as the cellular flame in laminar premixed flames. When the diffusion coefficient of the deficient species is larger, the deficient species diffuses preferentially to the reaction zone to cause the local stratification of the mixture ratio along the flame. Therefore, the cellular flame is established. If the preferential diffusion should occur in propane-air turbulent premixed flames, the wrinkle scale of rich flames would be smaller than that of lean flames, consequently, the turbulent burning velocity and/or the heat release rate of the former would be larger than those of the latter. Based on these considerations, traces of the preferential diffusion are sought from experimental results of propane-air turbulent premixed flames. Comparing the radius of curvature of the flamelet of rich and lean propane-air flames with the same laminar burning velocity, the radius of curvature of the flamelet of the former are smaller than those of the latter. The gas expansion ratio across the flamelet of the former is larger than that in the latter. The magnitudes of the flamelet velocity vector of the former are larger than the latter.

View full abstract

In order to use palm kernel oil as a diesel fuel, the combustion characteristics and exhaust emissions of palm kernel oil methyl ester (PkME) are investigated using a direct injection diesel engine, and are compared with palm oil methyl ester, coconut oil methyl ester (CME) and JIS No. 2 gas oil. The thermal efficiency of PkME is almost the same as those of the other test fuels. The exhaust emissions of PkME are almost the same as those of CME, and lower than those of the gas oil. It is concluded that PkME is a good alternative diesel fuel. Also, to reduce the pour point of PkME, -5℃, palm kernel oil ethyl ester (PkEE) and butyl ester (PkBE) are made by using ethanol and 1-butanol, respectively. The pour points of PkEE (-7.5℃) and PkBE (-10℃) are lower than that of PkME. PkEE and PkBE also are tested using the diesel engine. PkEE and PkBE have almost the same thermal efficiency and exhaust emissions compared with PkME although they have slightly higher HC and CO emissions. It is concluded that PkBE is an alternative diesel fuel with low pour point.

View full abstract

In order to understand the effects of unsaturated fatty acid compositions on biodiesel combustion, the combustion characteristics and exhaust emissions of high oleic safflower oil methyl ester (SFME_<HO>), high linoleic safflower oil methyl ester (SFME_<HL>) and linseed oil methyl ester (LME) are investigated using a direct injection diesel engine, and are compared with JIS no. 2 gas oil. As a result, the all ester test fuels have same thermal efficiency compared with the gas oil. Also, the all ester test fuels have higher NO_x emission and lower smoke emission at high load condition compared with the gas oil. From the experimental results of test ester fuels, it is concluded that with higher amounts of more unsaturated fatty acid methyl ester, biodiesel has lower kinematic viscosity and lower oxidation stability, and has longer ignition delay at all load conditions, higher HC and CO emissions at low load condition and higher NO_x emission at high load condition.

View full abstract

In order to reduce the emissions of a dual fuel diesel engine fuelling biodiesel as an ignition fuel, the combustion characteristics and exhaust emissions of the dual fuel with coconut oil methyl ester and CNG (C_<CNG>) are investigated by comparing to the dual fuels with rapeseed oil methyl ester/CNG (R_<CNG>) and JIS no. 2 gas oil/CNG (G_<CNG>). The results show that the operable condition of C_<CNG> is almost the same as that of R_<CNG> and G_<CNG>. The dual fuel diesel engine with C_<CNG> can be operated when the equivalence ratio of the intake premixed CNG is about 0.1 to 0.49. The thermal efficiency of C_<CNG> is almost the same as that of R_<CNG> and G_<CNG>. C_<CNG> has lower smoke emissions compared with R_<CNG>. It is concluded that coconut oil biodiesel can be used as an ignition fuel on dual fuel diesel engines.

View full abstract

This study discusses exhaust gas emissions and engine performance in premixed diesel combustion with a sufficient premixing period where low temperature oxidation is inhibited with methanol. Diesel fuel was directly injected at around 40℃A BTDC and methanol was introduced with intake port injection. While the inhibitor effect of methanol on low temperature oxidation retards the heat release and suppresses the rapid combustion, the inhibitor effect decreased when reducing uniformity of the premixed diesel fuel. As a result, the ignition timing can be retarded more with earlier injection timings and smaller quantities of diesel fuel. The operating range is limited by both misfiring and knocking, and an optimum quantity of methanol can prevent knocking while excessive methanol results in misfiring. When the injection timing of diesel fuel was set at 40℃A BTDC, without EGR and methanol, the operating range is limited below 0.25MPa BMEP due to knocking, but a combination of methanol port injection and EGR can achieve 0.55MPa BMEP. While ordinary diesel combustion maintaining low NO_x with EGR cannot prevent smoke emissions when BMEP exceeds 0.4MPa, the combination of methanol and EGR can establish ultra low NO_x and smokeless operation with high thermal efficiency even at 0.5MPa BMEP. The THC and CO increased with methanol introduction, but CO could be efficiently removed with an oxidation catalyst. The THC is also reduced with the oxidation catalyst, but remains at around 800ppm.

View full abstract

The particle densities and Blaines of fly ashes generated in a pulverized coal combustion test facility and pulverized coal-fired power stations are compared. Particle densities of fly ashes from the test facility and the power stations show similar tendency with particle size of fly ash. Blaines of fly ash from the test facility and the power stations can be specified in the same manner. Blaines of fly ashes decrease with decrease in particle size, and increase with decrease in circularity of particle for all fly ashes from the test facility and the power stations. These results show that the properties of fly ash from the test facility can be reflected to those of the power stations.

View full abstract