Language：English   Publishing type：Research paper (scientific journal)   Publisher：Taylor and Francis Ltd.  

We performed a direct numerical simulation (DNS) of the turbulent natural convection between two parallel plates at a Rayleigh number of Ra = 8.0 × 106, focusing on the turbulent natural convection affected by radiation in an optically thick fluid (τ ≥ 10). When the effects of the radiation were considered, the flow structure and temperature distribution in the channel changed as the optical thickness of the fluid increased. The effects of the radiation on the turbulent natural convection were clearly explained by the turbulence statistics from the DNS results.

DOI： 10.1080/10407782.2017.1412713

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

This paper describes a volumetric solar receiver that is vertically integrated with beam-down optics for condensed light irradiation. The heat-transfer performance of a silicon carbide honeycomb receiver was investigated using a 30-kWth solar simulator and numerical simulation. The experiments achieved an air temperature of 840 K at the receiver outlet by varying the operational parameters. Numerical simulations were performed for a vertical honeycomb block with beam-down irradiation and a horizontal honeycomb block with tower-type irradiation to elucidate the effects of buoyancy. Three blocks with different sizes were simulated for a variety of operational parameters. When the block was oriented vertically, the flow and temperature fields remained nearly symmetric in and near the receiver. In contrast, when it was oriented horizontally, the flow and temperature became asymmetric, with the hot spot moving toward the receiver's side wall and the stream in the receiver being reversed. The vertical orientation's robustness to buoyancy effects prevented any reduction in the receiver efficiency or outlet temperature and suppressed the thermal leakage.

DOI： 10.1016/j.energy.2017.11.147

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this study, a numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model to study the particle-fluid flow of the fluidized bed reactor for solar beam-down concentrating system. The contact forces between the particles have been calculated by the spring-dashpot model, based on the soft-sphere method. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. To investigate the influence of fluid flow rate and particle size on the flow pattern of the reactor, simulations have been performed for various conditions. The results indicate that the large size particles induce three-dimensional effects as they are accumulated at the central axis region. The average bed height of the left tower increased by 23.4% when increasing the flow rate about 70%. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.powtec.2017.06.060

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The flow and heat transfer in a curved channel were numerically analyzed for their spatial advancement under the influence of streamline curvature. The simulation was made for the curved channel of the radius ratio 0.92. The curved channel was provided with the fully developed velocity and thermal profile in a straight channel at the mean velocity Reynolds numbers up to 20,400. The number of grid points was more than 3.00 x 10(8) for the case of the highest Reynolds number. The local Nusselt number indicated that the heat transfer was enhanced on the outer wall of the curved channel and such enhancement was notable over the downstream area of phi >= 80 degrees. This heat transfer enhancement came from the large-scale organized vortex which intensified the lateral convection of the secondary stream and caused high values of the turbulent heat flux. The pre-multiplied spectrum was used to analyze the spatial advancement of the large-scale organized vortex. The spectrum indicated that the large-scale vortex was produced from the initial disturbance in the straight channel and the vortex grew and expanded to nearly the channel full width. It was shown that the advancement of the vortex was almost independent from the Reynolds numbers. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2017.01.012

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

This paper presents a numerical analysis of unconstrained melting of high temperature(>1000K) phase change material (PCM) inside a cylindrical container. Sodium chloride and Silicon carbide have been used as phase change material and shell of the capsule respectively. The control volume discretization approach has been used to solve the conservation equations of mass, momentum and energy. The enthalpy-porosity method has been used to track the solidliquid interface of the PCM during melting process. Transient numerical simulations have been performed in order to study the influence of radius of the capsule and the Stefan number on the heat transfer rate. The simulation results show that the counter-clockwise Buoyancy driven convection over the top part of the solid PCM enhances the melting rate quite faster than the bottom part.

DOI： 10.1063/1.4984427

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

A window-type, solar fluidized bed receiver with quartz sand particles was tested by a 100-kWth novel beam-down solar concentrating system at Miyazaki, Japan. A compound parabolic concentrator (CPC) was placed above the quartz window of the receiver to increase the concentration of the solar fluxes from the beam-down solar concentrating system. The solar tests were performed in the middle of December, 2015. The central bed temperature of the receiver was reached around 960-1100 degrees C. It was found that only 20 Ndm(3)/min of air flow rate was enough to create the uniform fluidization of the particles at the given temperature range. It was predicted that if the central bed temperature could have been higher than 1100 degrees C if solar receiver test had conducted in other seasons than winter. The next solar campaign of the receiver test will be carried out in October, 2016.

DOI： 10.1063/1.4984469

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME  

Direct numerical simulation was performed for the heat transfer of airflow in the entrance region of a channel with repeated rib protrusions. The rib-pitch to rib-height ratio (Pi/H) was increased from 2.0 to 16.0 by four steps. The rib-height ratio (H/d) was maintained constant at 0.20. The distribution of heat transfer coefficient numerically simulated agreed with the experiment by Kattchee and Mackewicz (1963, "Effects of Boundary Layer Turbulence Promoters on the Local Film Coefficients of ML-1 Fuel Elements," Nucl. Sci. Eng., 16, pp. 31-38). The enhancement parameter was used to evaluate the heat transfer performance by a ribbed channel. This parameter was defined as the ratio of the mean Nusselt number for the ribbed channel against the smooth channel consuming the same pumping power. The simulation result revealed that the enhancement parameter was maximized for Pi/H = 2 to 4 over the upstream ribs (x/delta < 2) and was remained high for Pi/H = 4, 8, and 16 over the downstream ribs (x/delta > 4). Therefore, the optimal rib pitch was smaller for the upstream ribs, and increased to the developed region. The mechanisms underlying this trend were discussed through observation of the streamlines, mean temperature, turbulence statistics, and instantaneous structures. The turbulence was increased over the ribbed wall for the cases of medium to wide rib pitch (Pi/H = 4, 8, and 16), whereas the turbulence increase appeared only over the upstream ribs (x/delta < 2) for the cases of narrow rib pitch (Pi/H = 2). The excellent performance of the wider rib pitch (Pi/H = 4, 8, and 16) at the downstream ribs (x/delta > 2) was resulted from the turbulence increase activating the turbulent heat transport. Whereas, the superiority by the narrower rib pitch (Pi/H = 2, 4) comes from the turbulence activation, and the renewed thin boundary layer which continues due to the densely allocated ribs.

DOI： 10.1115/1.4034052

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

This paper proposes the improvement of microfluidic mixture using the unsteady electroosmotic vortices induced by a staggered array of electrodes. The unsteady electroosmotic forces near two walls, having opposite directions near two walls, were shown to drive organized vortices to contribute for the enhanced mixing. Examination was given to the flow field involving unsteady vortices and their role for the particle mixing. Numerical simulation was made to evaluate the particle mixing process and to reveal how the particle mixing occurred under influence of disturbance by unsteady vortices. The Reynolds number was set to 0.005 and 1.0 changing the oscillation frequency and the electric field intensity. Efficiency of particle mixing was evaluated by the variance intensity of particle number fraction. The agreement between the simulation for the steady electroosmotic flow and the existing paper, and the grid convergence vindicated the simulation code presently used. The numerical results for unsteady electroosmotic flow demonstrated that the particle mixing was controlled by the oscillation frequency and the balanced time scales of the flow perturbation and convection was essential to the particle mixing. The particle flow was displayed to discuss the phenomenology related to the particle mixing. This revealed that the intermingling of particles within main and secondary vortices crucial for the mixing process whereas the outside streams exerted by the vortices were not effective on it. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cej.2015.12.013

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This paper describes the thermal collector type loop thermosiphon for low-temperature waste heat recovery. Water is used as the working fluid for heat transport at temperatures 100 degrees C and higher. The loop thermosiphon comprises of a thermal receiver, a condenser, and riser and downcomer tubes. The thermal receiver is made of a cupper plate brazed by meandering heat transfer tube. This receiver collects the thermal radiation from the electric heater at the heat transfer area of 1000 cm(2) (40 cm x 25 cm), and transports the heat by vaporization of water to the condenser having heat transfer area of 62 cm(2). In the no inclination mode, the thermosiphon is upright so that the thermal receiver and the condenser are placed vertically. In this mode, the effective thermal conductivity exceeds 60 kW/(m K) when the thermal receiver temperature was higher than 125 degrees C for the water filling ratio alpha = 30-70%. Although the effective thermal conductivity is deteriorated for the higher filling ratio alpha = 80% and 90%, the effects from the filling ratio are tiny for alpha = 30-70%. The experimental tests were also made for the negatively inclined mode where the inlet and exit ports of the receiver were directed downward and for the positively inclined modes where they were directed upward. The tests revealed that the negative inclination almost halted the heat transport. However, the tests also indicated that the positive inclination showed the performance comparable to the no inclination mode for the cases up to the inclination angle 90 degrees. (C) 2015 Elsevier Ltd. All sights reserved.

DOI： 10.1016/j.applthermaleng.2015.09.004

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

A novel concept of particles fluidized bed receiver/reactor with a beam-down solar concentrating optics was performed using a 30-kW(th) window type receiver by a big sun-simulator. A fluidized bed of quartz sand particles was created by passing air from the bottom distributor of the receiver, and about 30 kW(th) of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directly irradiated on the top of the fluidized bed in the receiver through a quartz window. The particle bed temperature at the center position of the fluidized bed went up to a temperature range from 1050 to 1200 degrees C by the visible light irradiation with the average heat flux of about 950 kW/m(2), depending on the air flow rate. The output air temperature from the receiver reached 1000 - 1060 degrees C.

DOI： 10.1063/1.4949206

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Mechanisms for dissimilarities between momentum and heat transport in a disturbed turbulent channel flow of air were studied through direct numerical simulations. A square rib protrusion with an aspect ratio of up to 64 was used to minimize constraints that the side boundary imposed on the wake and the related heat transfer. Channel walls were heated to maintain isothermal conditions. The frictional Reynolds number was set to either 150 or 300. The maximum number of grid points was 96,993,280. A grid convergence test showed that numerical results were independent of grid resolution. The mean pressure obtained from numerical simulation agreed with existing experimental data. Heat transfer characteristics were evaluated using the spatial mean Nusselt number over the ribbed wall and over rib surfaces. This Nusselt number was compared with that for a smooth channel at the same pumping power; the comparison showed that heat transfer increased by as much as 10%. This increase was caused by the simultaneous increase in heat transfer and reduction in skin friction behind the rib over a wall length of 30 times the rib height. Thus, the dissimilarity between local heat and momentum transport involved improving bulk heat transfer and reducing losses to skin friction. Mechanisms leading to the transport dissimilarity were studied via instantaneous structures, turbulence statistics, and spectral analyses. The results suggest that spanwise vortices shed from the rib contributed to the transport dissimilarity. Spanwise vortices entrained fresh fluid into the near-wall region, increasing heat transfer and reducing skin friction simultaneously. This behavior is consistent with reports in the literature obtained by visualization (Yao et al.) and by RANS simulation (Inaoka et al.). The novelty in the present study was that turbulent spanwise vortices and related thermal fields could be reproduced without using a turbulence model. This approach enabled us to know structures of the vortices and the flow three-dimensionality. (C) 2015 Published by Elsevier Ltd.

DOI： 10.1016/j.ijheatmasstransfer.2015.02.018

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME  

We tested a thermosyphon loop with water as the working fluid using heating rates between 100W and 400W. Four kinds of core blocks were installed in the evaporator and tested: a hollow block, and blocks with narrow holes: Phi 2.2 mm x 90; Phi 2.5mm x 55; and Phi 4.0 mm x 30. The temperature distribution indicated stable flow circulation inside the thermosyphon at low volume ratios but was unstable when the volume ratio was increased higher than 30%. The characteristics of the flow pattern are summarized as a flow map showing the heating rate versus the volume ratio. The recovered heat and the thermal resistance of the thermosyphon loop were clearly improved by using the core blocks with narrow holes instead of hollow blocks for the treated volume ratios from 20% to 80%. The thermal resistance increased when the volume ratio reached high values, suggesting that the effects from the abnormality of the flow circulation affected thermal resistance. The velocity of the gas stream in the thermosyphon was estimated by assuming an isothermal state, and it is diagrammed showing the heating rate at different temperatures. The current experiment of the thermosyphon loop is plotted in this diagram, which indicates the need for a wide margin due to the limitations of the sonic velocity and the pressure head at the full height of the heat pipe.

DOI： 10.1115/1.4027417

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME  

A direct numerical simulation is made for the incompressible turbulent flow in the 180 deg curved channel with a long straight portion connected to its exit port. An examination is made for how the organized coherent vortex grows and decays in the curved channel: the radius ratio of 0.92, the aspect ratio of 7.2, and the succeeding straight section length of 75 times the channel half width. The 1552 x 91 x 128 (-18,427,136) grids are allocated to the computational domain. The frictional-velocity-based Reynolds number is kept at 150 to resolve the long domain including curved and straight regions. In contrast to that the coherent vortex grows along the concave wall, the vortex remains strong in the convex-wall side after the curvature accompanying a tail of the small-scale turbulence near the convex wall. The dissimilarity between the onset and disappearing of the coherent vortex essentially comes from the mean pressure gradient, which aids or averts the near-wall fluid oppositely between the curvature inlet and the exit. The mean flow is decelerated near the inlet of the convex wall to destabilize the flow and to trigger the onset of the coherent vortex. Contrary, the mean flow is accelerated near the exit of the convex wall to weaken the coherent vortex, and is decelerated near the exit of the concave wall to enhance the turbulence. Therefore, the turbulence enhancement and attenuation occurs oppositely between the inlet and exit of the curvature, and the coherent vortex draws a wake in the convex-side rather than the concave-side where it starts.

DOI： 10.1115/1.4024591

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

The near-wall turbulent heat transport of the three orthogonal directions was directly solved for the Prandtl numbers ranging from 0.025 to 5.0 to validate the algebraic models of the turbulent heat flux. Two kinds of thermal situations were considered in the low Reynolds number turbulent flow: (a) the case with a uniform heat flux in the spanwise direction (UHF) and (b) the case with the mean spanwise temperature gradient (STG). Among the turbulent heat flux models tested, the model of Rogers preferably predicted over the treated range of the Prandtl numbers, but it failed to reproduce the low Prandtl number effects very accurately. This paper revealed that the coefficient of the Rotta model can be modified to include the low Prandtl number effects by means of the correlation between the exact coefficient suggested by DNS and the Prandtl number. [DOI: 10.1115/1.4005077]

DOI： 10.1115/1.4005077

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The purpose of this study is to clarify the radiation effects on mixed turbulent convection in a horizontal channel. The present study provides turbulence statistics using direct numerical simulation (DNS) in an optically thin medium. When the radiation effect is considered, the flow structure and the temperature distribution in the channel change with an increase in the optical thickness of the fluid. The radiation effect changes the distributions of the temperature fluctuation intensity and the turbulent heat flux. These radiation effects on mixed convection can be clearly explained by the turbulence statistics obtained from the DNS results. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2012.01.006

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

A newly developed electric furnace was used to pyrolyze benzene, methane, or acetylene diluted by a nonreactive gas, and the carbon aggregates were separated from the hydrogen-rich gases. The temperature was changed up to 2200K for various levels of initial concentration of hydrocarbon and residence time, and how the experimental parameters affected the mean diameter of carbon aggregates was examined. The temperature increase in experiments led to reduction of the mean diameter of the carbon aggregates, whereas increase in the initial concentration of hydrocarbon or the residence time resulted in slightly lifting it. The mean diameter removed of temperature effects correlated well with the initial carbon atom mol concentration of hydrocarbon, N-C, and this parameter was used to develop the experimental equations. This article presents three kinds of experimental equations, and the prediction accuracy was confirmed to be improved when accounting for increasing the experimental parameters.

DOI： 10.1080/00102202.2012.691582

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Heat transfer and fluid flow in a single-rib mounting channel were investigated by directly solving Navier-Stokes and energy equations. The flow and thermal fields were considered to be fully developed at the inlet of the channel, and the simulation was made for spatial advancement of turbulent heat transfer. The Reynolds number based on the friction velocity at the inlet and the channel half width was 150. The Prandtl number was 0.71. The budgets for turbulent heat fluxes and temperature variance at various sections were presented and were investigated, which would be useful for testing and developing turbulence models. Near a circular vortex in front of the rib, pressure diffusion terms made an important contribution. Remarkable production terms were generated near a reattachment point. Production and dissipation terms were not dominant in front of and above the rib, and a time scale ratio exceeded 2.0 in the region.

DOI： 10.1299/jtst.7.120

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Fuji Technology Press  

Turbine engines have been used as high reliable, safe engines in airline transportation. Safety is the most important factor in the social use of aerial robots. We started research on Aerial Cargo Robots (ACR) in 2004. The first flight of an ACR prototype was successfully achieved on November 22, 2005. The ACR prototype consists of a flexible airfoil, twin micro-turbo-jet engines and a gravity center control unit. The ACR meets the following requirements for safety: touchable, i.e., without propellers or rotors
a low sink rate the same as a parachute, i.e., below 1.0 m/sec
a low stall speed, i.e., less than 30 km/h
and a redundancy arrangement control system. The most important safety specification is the use of a silent turbojet engine for the ACR thruster. This paper reports the results of turbojet engine development for aerial robots.

DOI： 10.20965/jrm.2012.p1040

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Direct numerical simulation was performed for the spatially advancing turbulent flow in a two-dimensional curved channel. The fully developed turbulence was introduced into the curved channel through a straight part, and observation was made for how the near-wall turbulence advanced along curved walls. The frictional Reynolds number, Re(tau 0), was fixed at 150, whereas the radius ratio of the curved channel, alpha, was changed at three steps; 0.8, 0.92, and 0.975. Five computational tests were performed, which include simulations with changing the spanwise length of the channel or the grid arrangement. The maximum number of grid points was 43,610,112 (=936 x 91 x 512) used in the case of alpha = 0.92. Numerical results for the curved flow were nearly free from the grid arrangement or the spanwise length of the channel, and changes of the mean velocity qualitatively agreed with the experiment by Kobayashi [Trans. Jpn. Soc. Mech. Eng., Ser. B 57, 4064 (1991)], which both supported credibility of the simulation. The spanwise pre-multiplied power spectrum and the spanwise two-point correlation captured the peaks corresponding to the micro-scale structures near the straight wall, which continuously grew along the concave wall and advanced to exhibit the wave length of organized flows. Therefore, the micro-scale structures such as quasi-stream vortices and the ejection near the outer wall of the straight channel were suggested to trigger the onset of initial seeds of the organized structure, which grew into the large scale vortices expanding almost over the channel width.(C) 2011 American Institute of Physics. [doi: 10.1063/1.3584126]

DOI： 10.1063/1.3584126

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

Direct numerical simulation was performed for the spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel equating the radius ratio to 0.92 or 0.8. The frictional Reynolds number was fixed at 150, whereas the Prandtl number was set at 0.71. According to the numerical result, the remarkable enhancement of heat transfer occurred on the outer wall, suggesting the organized vortex activated the heat transfer. The budgets of Reynolds stresses clarified that the onset and growth of the organized flow was assisted by the direct energy transfer from the mean flow.

DOI： 10.1080/10407782.2011.588562

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Thermal radiation in a turbulent natural convection plays an important role in a wide area of engineering and nature. The purposes of this study are to investigate the effects of turbulent fluctuation on radiative heat transfer, and to evaluate radiative heat transfer models applied to turbulent natural convection. The present radiative heat transfer analysis of a turbulent natural convection using direct numerical simulation (DNS) provides a useful fundamental data for the complete coupling simulation in the future.

DOI： 10.1299/jtst.6.449

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

DOI： 10.1007/978-94-007-2482-2_49

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

The purpose of this paper is to consider a possibility of the independent column approximation for solving the radiative heat fluxes in a 3D turbulent channel flow. This simulation method is the simplest extension of the plane-parallel radiative heat transfer. The test case of the temperature profile was obtained from the direct numerical simulation. We demonstrate the comparison between the 3D radiative transfer simulation and the independent column approximation with an inhomogeneous temperature field and optical properties. The above mentioned results show the trivial discrepancies between the 3D simulation and the independent column approximation. The required processing time for the independent column approximation is much faster than the 3D radiative transfer simulation due to the simple algorithm. Although the independent column simulation is restricted to simple configurations such as channel flow in this paper, wide application areas are expected due to the computational efficiency.

DOI： 10.1115/1.4000240

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

The purpose of this study is to develop the radiation element method by ray emission method (REM2) code appropriate for coupling with the bioheat transfer equation, and to clarify the photothermal effect of various parameters inside biological tissues. First, the REM2, which involves the air-tissue interface effect, is validated with the existing literature. In order to clarify the effects of optical and thermophysical properties of biological tissues, a one-dimensional tissue model of CW light transport and bioheat transfer is employed. The present study provides nondimensional results, which are obtained by varying refractive index, extinction coefficient, scattering albedo, blood perfusion parameter, and conduction-radiation parameter, show valuable guidance for understanding the coupled light and bioheat transport in tissues.

DOI： 10.1080/10407782.2010.516698

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Heat transfer and fluid flow in a single-rib mounting channel were investigated by directly solving Navier-Stokes and energy equations. Flow and thermal fields were considered to be fully developed at the inlet of the channel, and the simulation was made for spatial advancement of turbulent heat transfer. Keeping the frictional Reynolds number, Re-tau 0, at 150, the rib height ratio was changed in four steps from H/delta = 0.05 to H/delta = 0.4. Computational results were confirmed to be nearly independent of grid meshes. In addition, numerical accuracy was confirmed through close agreement between computed mean pressure and the experiment by Yao et al. (1995). The numerical results revealed that the highest value of the mean Nusslet number was as large as 1.3 times the smooth surface consuming the same pumping power, and the local enhancement of heat transfer was correlated with the turbulence increase near the rib front and the reattachment point. According to the Reynolds stress budgets for H/delta = 0.2, there were mechanisms to induce powerful fluctuations: (1) Streamwise fluctuation was increased through production by flow deceleration in the upstream of the rib; (2) Redistribution to wall-normal and spanwise fluctuations was fortified by the fluid splattering to the rib front. Therefore, excellent performance of heat transfer was concluded to occur due to flow structures, which induce the strong disturbance near the rib front triggering smooth transition of the separated shear layer.

DOI： 10.1299/jtst.5.135

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The objective of this study is to develop a new simulator for laser therapy. In order to minimize undesired effects on the laser therapy, it is important to precisely predict for heat and photon transport inside a biological tissue. In the present study, the photon transport is solved with the Radiation Element Method by Ray Emission Model (REM2), and then coupled with bioheat transfer equation. The dimensionless results become valuable guidance for developing a laser therapy system.

DOI： 10.1299/jtst.4.314

Web of Science

researchmap

Language：English   Publisher：The Japan Society of Mechanical Engineers  

An air-cooling system of a small capacity of several kilo-watts using only water refrigerant as a non-CFCs (Chlorofluorocarbon) technology is examined. The experimental device consists of two stages. The first stage is composed of a vacuum pump and a vacuum chamber of about 60 L in volume. The second stage has two heat exchangers (the exchanger located outside the vacuum chamber is a dummy cooling load) and a water circulating pump. An air-conditioner indoor unit or a heater is used as a dummy cooling load. The temperature and humidity characteristics are measured at each place. Consequently, the ability to cool the room air is ensured by an air-cooling system using only water refrigerant. A new vacuum pump, that can exhaust a large amount of water vapor, is developed and its properties are measured. It seems that the engine-based vacuum pump performance is sufficient to drive the air cooling system with water refrigerant.

DOI： 10.1299/jee.3.135

CiNii Article

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00312923684?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Baking processes are widely acknowledged as being crucial steps in Photomask manufacture, and in particular, the Post-Exposure Bake (PEB) is regarded as the most critical. For 45nm-node Photomasks, and subsequent technology generations, the performance requirements for baking systems significantly exceed those of currently-available equipment. In comparison with Silicon Wafers, Photomask substrates, (typically 6inch square quartz), exhibit markedly different thermal properties. These differences conspire to make Photomask precision baking far more difficult than is the case for wafers.
Multi-zone heating systems have been developed, and in principle offer a practical tuning method allowing better surface temperature uniformity of Photomasks during critical bake steps to be achieved. The best of these systems compensate, to some extent, for multiple causes of temperature non-uniformity within the baking system. Generally however, the root causes of temperature non-uniformity in the baking process have not all been identified, still less eliminated, and thus there remains a limit to the degree of control of Photomask surface temperature which can be achieved.
In this study, we devised a "Thermal model" of the Photomask baking process. This model has enabled us to identify root causes of non-uniformity of Photomask surface temperatures, as well as providing a quantitative way of assessing how Photomask baking systems may be improved. We present simulation results from the model, as well as actual test data measured by sensor array plate.

DOI： 10.1117/12.685497

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Coherent structures of temperature fields in the near-wall turbulence (y(+) < 60) were educed by a conditional sampling technique from the DNS data. Treated situation is the fully developed turbulent channel flow for two kinds of temperature fields: (a) the uniform heat Aux assigned on two walls of the channel (UHF) and (b) the constant spanwise mean temperature gradient imposed on the flow over the whole channel width (STG). Following conclusions are obtained. (1) Flow and temperature fields around the quasi-streamwise vortex are roughly uniform in the streamwise direction. (2) Temperature distribution in/around the vortex for UHF and that for STG are similar in shape with azimuthal phase difference of about 90<degrees>. (3) Mechanisms for destruction of turbulent heat flux are similar between UHF case and STG case. (C) 2001 Elsevier Science Inc. All rights reserved.

DOI： 10.1016/S0142-727X(01)00082-0

Web of Science

CiNii Article

researchmap

DOI： 10.1016/S0017-9310(99)00141-6

CiNii Article

researchmap

researchmap

DOI： 10.1016/S0017-9310(98)00072-6

CiNii Article

researchmap

researchmap

DOI： 10.2115/fiber.55.3_143

CiNii Article

researchmap

DOI： 10.1299/kikaib.65.2077

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A three dimensional steady numerical analysis has been made for both of staggered array and in-lined array of two-row plate-finned tubes heat exchanger unit located in a uniform flow. The structures of the flow and thermal fields have been examined for conduction-convection conjugate heat transfer problem of the studied fin-and-tube model. The results of the numerical analysis revealed some important effects of geometric parameters on heat transfer from the fin-and-tube surface for each array of two-row tubes. The effects of fin thickness, fin pitch, fin length, tube pitch and Reynolds number on heat exchange rate, Nusselt number, heat transfer rate, and pressure coefficient were examined parametrically. Though space mean Nusselt number and heat transfer rate have no big difference between the two array cases, slightly better heat transfer performance is attained in the staggered array case as Reynolds number or fin pitch is increased. On the contrary, pressure loss obtained in the staggered array case is larger than that obtained in the in-lined array case.

DOI： 10.1299/kikaib.65.2077

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5761

DOI： 10.1299/kikaib.64.1809

CiNii Article

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A three dimensional steady numerical analysis has been made for a one unit of single row plate-finned tube heat exchanger located in a uniform flow. The structures of the flow and thermal fields have been examined for conduction-convection conjugate heat transfer problem of the studied fin-and-tube model. The results of the numerical analysis revealed some important effects of geometric parameters on heat transfer from the fin-and-tube surface. The effects of fin thickness, fin pitch, fin length, tube pitch and Reynolds number on Nusselt number, heat transfer rate, fin efficiency and pressure coefficient were examined parametrically. Upstream half of the fin surface yielded a much higher heat transfer coefficient than the downstream half of the fin surface. Especially, the values of fin local heat transfer coefficient is nearly zero in the near region of the tube. As Reynolds number increases, the fin efficiency and the pressure coefficient decrease.

DOI： 10.1299/kikaib.64.534

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5754

DOI： 10.1299/kikaib.64.2971

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Following the previous works by Maekawa et al. (1991) and Kawada et al. (1991), some turbulence statistics including the triple velocity-temperature correlations were measured in a turbulent boundary layer with a constant temperature for a spanwise direction. Examination was given to the turbulent heat flux budget and also to the reliability of some existing turbulence models. It was revealed that there are remarkable discrepancy between the predicted triple velocity-temperature correlations by the gradient-type model (Launder (1978)) and the experimental result. However, the examination for the turbulent heat flux budget clarified that the budget lies in near local equilibrium except for the near-wall region. Thus, the reliability of the pressure-temperature gradient correlation model is found to be rather important for the prediction of the spanwise turbulent heat flux. The prediction performance of the pressure-temperature gradient correlation model was investigated using two kinds of the models (Launder (1975)), Maekawa et al. (1979). It was found that predicted values by these models show good agreement with the experimental result.

DOI： 10.1299/kikaib.64.2971

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5758

Three-dimensional numerical simulations were carried out for mixed convective flows over a backward-facing step in a rectangular duct. Reynolds number, expansion ratio and aspect ratio were kept constant at Re=125, ER=2 and AR=16, respectively. Heat flux at the wall downstream of the step was kept uniform, while other walls were kept at adiabatic condition. Effect of the inclination angles, ft, ft, was the main objective in this study. It was found that when θ1 was varied, the effect of buoyancy became prominent at θ1 = 0°, 180°, while the effect was relatively small for the two horizontal cases(θ1 = 90°, 270°). However, there was still small difference between θ1 = 90° and 270° in the region immediately after the step where the flow was relatively slow. When ft was varied, flow and thermal fields could no longer be considered as two dimensional, except when θ1=-90°, 90°. The maximum Nusselt Number, which appears symmetrically near the side walls in pure forced convection cases, was obtained at only one location close to the lower side wall.

DOI： 10.1299/kikaib.64.1809

Scopus

researchmap

DOI： 10.1299/kikaib.64.3801

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper analytically treats of the heat-flow through the periodically varying thermal-resistance thin layer lain between conductors or the heat-flow between two periodically contacting conductors. During one cycle of the period, p, thermal-conductance of the thin layer temporally changes in a stepwise profile, and takes two different values, R_c and R_d over the time spans, φp and (1-φ) p, respectively. Analytical solution for the effective thermal-conductance, R_e, of the thin layer was algebraically approximated using R_c, R_d, φ and the harmonic mean, R_<ab>, of the characteristic thermal-conductances of the two conductors. Algebraical approximation was also made for the maximum temperature amplitude, Δθ^*_<max>, arising at the joint ends of conductors. This approximation suggests the following features of Δθ^*_<max>, Δθ^*_<max> takes the maximum value, (Δθ^*_<max>)_<max>, at specified value of φ, φ_<max>, φ_<max> depends only single parameter R_c/R_d, and becomes large with increase of this parameter. On the other hand, (Δθ^*_<max>)_<max> depends not only R_c/R_d but also R_d.

DOI： 10.1299/kikaib.64.3801

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5759

DOI： 10.1299/kikaib.64.534

researchmap

DOI： 10.1299/kikaib.64.856

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Direct numerical simulation was performed for a turbulent channel flow where the time mean temperature has a spanwise gradient. As the first step of succesive investigations, turbulence statistics related to the spanwise heat transfer were examined. A computational code based on the finite difference scheme was developed for this purpose. The calculated statistics on the flow field were found to be in good agreement with the result of the existing direct numerical simulation by Kasagi et al. (1992). The eddy diffusivity ratio, ε_<nz>/ε_m and the Reynolds normal stress ratio, <ω^2>^^^-/<υ^2>^^^- show rapid increase toward the wall, as pointed out by Maekawa et al. (1991). However, the rapidincrease region of the ε_<nz>/ε_m was nearer to the wall than the Maekwa's result and found to roughly agree with that of the <ω^2>^^^-/<υ^2>^^^-. This result implies that, in the near-wall region, the spanwise turbulent heat flux per its production rate shows rough agreement with the wall-normal turbulent heat flux per its production rate. In addition, two point correlation coefficient, Q_<wθ> also agrees with Q_<vθ> in the range of y^+<75. In these points, the heat transfer in the present case has some analogy with that in the heated-wall case. Moreover, the budget of the spanwise turbulent heat flux was examined. It was found that the budget shows near local equilibrium except for the near-wall region.

DOI： 10.1299/kikaib.64.856

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5755

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Two-and three-dimensional numerical simulations have been performed for mixed convective upward flows over a backward-facing step in a duct. The Reynolds number, expansion ratio and aspect ratio (in 3D sim.) were kept constant at Re=125,ER=2 and AR=16,respectively. The heat flux at the wall downstream of the step was uniform, while the straight wall, the step and the side walls (in 3D sim.) were assumed to be adiabatic. The effect of the buoyancy level, Ri^*, was the major interest in this study. It was found that the reattachment point and the peak Nusselt number point moved upstream as Ri^* was increased, while the secondary recirculation region, which developed at the corner of the step, became larger. It was also found that there existed a secondary flow in a cross section immediately downstream of the step. Flow directed toward the center of the duct becomes more intensive as Ri^* increases, which possibly results in an increase in the level of three-dimensionality of the flow and thermal fields.

DOI： 10.1299/kikaib.63.2817

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5752

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Two dimensional calculation was performed for combined convection heat transfer in a channel with two ribs attached to one wall, following the previous study on forced convection case without buoyancy. The flow is heated from the surfaces of both ribs and the present study dealt with the two cases of buoyancy-assisting flow and buoyancy-opposing flow. The effect of Reynolds number, Re_L, and modified Richardson number, Ri^*, was examined keeping space between ribs, σ, and blockage ratio, τ, constant (σ=3.0,τ=0.5). Increasing the magnitude of buoyancy, unsteady flows predicted by the present calculation are stabilized in both of two cases. Serious deterioration of Nusselt number on the 2nd rib suddenly occurrs in a certain range of Ri^* due to the flow stabilization. This is because flow unsteadiness plays an important roll for heat transfer enhancement as was described in the previous study. However, in buoyancy-assisting flow, similar deterioration of Nusselt number also appears on the 2nd rib even if flow remains steady. This is caused by the disappearance of strong rotating flow which exists in the cavity between the both ribs and keeps fluid in the cavity cooler.

DOI： 10.1299/kikaib.63.3362

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5753

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Two dimensional calculation was performed for combined convection heat transfer in a channel with two ribs attached to one wall, following the previous study on forced convection case without buoyancy. The flow is heated from the surfaces of both ribs and the present study dealt with the two cases of buoyancy-assisting flow and buoyancy-opposing flow. The effect of Reynolds number, Re_L, and modified Richardson number, Ri^*, was examined keeping space between ribs, σ, and blockage ratio, τ, constant (σ=3.0,τ=0.5). Increasing the magnitude of buoyancy, unsteady flows predicted by the present calculation are stabilized in both of two cases. Serious deterioration of Nusselt number on the 2nd rib suddenly occurrs in a certain range of Ri^* due to the flow stabilization. This is because flow unsteadiness plays an important roll for heat transfer enhancement as was described in the previous study. However, in buoyancy-assisting flow, similar deterioration of Nusselt number also appears on the 2nd rib even if flow remains steady. This is caused by the disappearance of strong rotating flow which exists in the cavity between the both ribs and keeps fluid in the cavity cooler.

DOI： 10.1299/kikaib.63.3362

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5753

DOI： 10.1299/kikaib.63.2817

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Linear stability analysis was performed for channel flow with two ribs attached to one wall. Effects of perturbations with an infinitely small amplitude on a fundamental steady flow in the channel were numerically investigated. The fundamental flow corresponds to one of the steady solutions of the Navier-Stokes equations. Time-asymptotic solutions of the perturbation equations reach the least stable mode of the channel flow. Growth or decay of the perturbations was supposed to occur everywhere in the flow with a constant amplification factor, since the logarithmic value of the maximum transverse perturbation velocity of the least stable mode changed linearly with time at all monitoring locations in the channel. In addition, a direct numerical calculation was performed using the two-dimensional Navier-Stokes equations to investigate the characteristics of nonlinear stability, the results of which showed a similar growth pattern to those derived from the perturbation equations. The flow instability with an increase of the Reynolds number was found to depend on the value of the source functioning term of the perturbation vorticity equation derived from the perturbation equations.

DOI： 10.1299/kikaib.62.2782

CiNii Article

researchmap

DOI： 10.1299/kikaib.62.3675

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Three-dimensional numerical computation was performed for the developing region of flow and thermal fields in finned channels. The channel studied here has a heated region of finite length to which plate fin arrays are attached in order to improve its heat transfer performance. The performance was evaluated using Nu_L^^*, an apparent Nusselt number corresponding to the heat transfer rate per unit heated area. The effect of fin height, fin pitch, fin length and Reynolds number on Nusselt number was examined parametrically. As the fin height increases with the fin pitch kept constant, Nu_L^^* increases monotonically. The maximum value of Nu_L^^* was obtained when the top of the fin reached the top wall of the channel. When the fin pitch was changed with the fin height kept constant, the numerical results demonstrated two tendencies. In the case with clearance between the fin top and the wall, there existed the optimal fin pitch leading to maximum Nu_L^^*. In the case without clearance, Nu_L^^* increases with decrease of fin pitch. The optimal fin pitch gradually decreased with decrease of fin length and/or with increase of Reynolds number. The ratio of the j-factor to the f-factor was also obtained to evaluate the performance of the fins.

DOI： 10.1299/kikaib.62.3675

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5751

DOI： 10.1299/kikaib.62.1937

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Heating a cylinder should affect the flow pattern around it and the heat transfer from its surface. Numerical computation of the flow and related heat transfer has been carried out for a circular cylinder mounted in a channel flow for a free-forced combined convection regime. In the case that buoyancy assists the flow, the results showed that the transition from unsteady flow to steady flow occurred under different conditions depending on the Ri number, Re number and blockage ratio. With a constant Re number, the critical Ri number at which the transition occurs decreases with increasing blockage ratio, and with a constant Ri number, the transition Re number increases with the blockage ratio. In the case of negative buoyancy, on the other hand, the increase of the Ri number facilitates the growth of the length scale of the Karman vortices. The buoyancy effect on flow instability is less conspicuous compared with that in the above two cases in the case of horizontal flow, but local heat transfer characteristics are still changed by the buoyancy effects.

DOI： 10.1299/kikaib.62.1937

CiNii Article

CiNii Books

researchmap

Other Link： http://hdl.handle.net/10191/5748

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Linear stability analysis was performed for channel flow with two ribs attached to one wall. Effects of perturbations with an infinitely small amplitude on a fundamental steady flow in the channel were numerically investigated. The fundamental flow corresponds to one of the steady solutions of the Navier-Stokes equations. Time-asymptotic solutions of the perturbation equations reach the least stable mode of the channel flow. Growth or decay of the perturbations was supposed to occur everywhere in the flow with a constant amplification factor, since the logarithmic value of the maximum transverse perturbation velocity of the least stable mode changed linearly with time at all monitoring locations in the channel. In addition, a direct numerical calculation was performed using the two-dimensional Navier-Stokes equations to investigate the characteristics of nonlinear stability, the results of which showed a similar growth pattern to those derived from the perturbation equations. The flow instability with an increase of the Reynolds number was found to depend on the value of the source functioning term of the perturbation vorticity equation derived from the perturbation equations.

DOI： 10.1299/kikaib.62.2782

CiNii Article

researchmap

researchmap

Applicant：国立大学法人 新潟大学

Application no：特願2013-556494  Date applied：2013.1

Patent/Registration no：特許第5986589号  Date issued：2016.8

J-GLOBAL

researchmap

Applicant：国立大学法人 新潟大学, 株式会社新潟ティーエルオー

Application no：特願2004-297999  Date applied：2004.10

Announcement no：特開2006-110416  Date announced：2006.4

J-GLOBAL

researchmap

Applicant：株式会社新潟ティーエルオー

Application no：特願2004-008556  Date applied：2004.1

Announcement no：特開2005-201546  Date announced：2005.7

J-GLOBAL

researchmap

Applicant：株式会社北村製作所

Application no：特願2002-330841  Date applied：2002.11

Announcement no：特開2004-163033  Date announced：2004.6

J-GLOBAL

researchmap