Food Techno Engineering Ltd. sells an impingement freezer using CO2 refrigerant for frozen foods. Although we aim to enhance the refrigeration efficiency of the freezer, the behavior of the jet flow from the nozzle is hardly understood. Therefore, we analyzed the flow in the nozzle by the simulation. The model was composed of the plenum chamber and several nozzles. As a result, there was little vertical flow in the vicinity of a plenum room, and the jet flow in the vicinity of a plenum room swung periodically. Therefore, we tried to generate the vertical flow near the plenum room by installing a distributor to the nozzle inlet in the plenum room. Consequently, the fluctuation of the jet flow was eliminated, and the jet flow was able to be uniformed at the flow velocity of 20m/s.

Wettability gradient surface is attracted attention from the applications such as microfluidic devices and biochemical testing. However, the substrate is limited to the non-flexible materials such as silicon substrate because the applicability of fabrication processes. In the present study, we fabricated the wrinkled structure on the flexible polymer substrate through the deposition of thin metal film and the release of stretching after deposition, and the gradient structure was fabricated using mask. In addition, the droplet behavior on the gradient wrinkled structure was observed through droplet deposition experiment and found that the droplet deposited on the wrinkled part was moved directed to the wrinkleless part.

Thermoelectric power generation attracts attention due to the possible application in power sources of IoT devices. The voltage fluctuation of thermoelectric power generation due to the fluctuation of temperature difference causes instability and decreased reliability of the devices. In this study, we propose thermoelectric module with voltage limiter function using a metal-insulator phase transition material. Vanadium dioxide VO₂ is one of metal-insulator phase transition materials, and its Seebeck coefficient is high in the low-temperature insulator phase and low in the metal phase. The output voltage of the thermoelectric module using VO₂ is expected to be constant regardless of temperature fluctuation in the temperature range where insulator and metal phases coexist in the material, i.e., it has voltage limiter function. This paper describes a study of the feasibility of this concept by thermoelectric property measurement and output power measurement.

This study aims to develop a novel water-cooled device that increases heat transfer performance while inhibiting the increase of pumping power for next-generation electronic equipment. Our previous reports have reported that the combination of the pulsating flow, which is the unsteady flow that the supply flow rate is periodically changed likes a blood in the body of human beings, and the rib has higher cooling efficiency. In this study, a relationship between heat transfer performance of pulsating flow and a rib pitch was evaluated to verify an optimal rib clearance for improving heat transfer by pulsating flow through 3D-CFD analysis. It is found that the level of the heat transfer enhancement was dependent on the rib clearances.

In this study, the unsteady behavior that occurred in subcooled boiling in high-speed flow was investigated and considered the effects of superheat and flow velocity on the unsteady behavior. When the heating rate was large, the nucleate boiling changed to a vapor mass in the low speed flow of U_∞ = 1 m/s, whereas unsteady behavior covering in the heating surface was observed at U_∞ = 2.7 m/s. In this case, a phenomenon was observed in which the vapor phase disappeared against the flow. The unsteady behavior tends to slow down the increase in heat flux, suggesting that this phenomenon affected the heat transfer characteristics.

This study describes P-Q curves of the 40mm scale small axial flow fan mounted in high-density packaging electronic equipment. An accurate prediction of supply flow rate by fans strongly affects the reliability of the cooling design. However, in high-density packaging electronic equipment, the fan performance is affected by the mounting components around the fans, and the accurate prediction of the supply flow rate becomes difficult. In this paper, by a CFD analysis, visualization around the fan was conducted while changing the opening position of the obstruction in front of the fan. Through the analysis, it was found that the different opening position causes different tendency of decrease in P-Q curves.

A hole transport layer is one of the main components of a solar cell. It is inserted between the electrode and the storage layer to enable selective charge extraction and to suppress charge recombination at the interface. Nickel oxide is expected to be an inorganic hole transport material with good performance because it has good chemical stability and behaves as a p-type semiconductor in non-stoichiometric compositions. In this study, nickel(II) oxide thin films with non-stoichiometric composition were prepared by controlling the oxygen partial pressure during film deposition using reactive magnetron sputtering, and their properties as hole transport layers were investigated.

Saturated pool boiling heat transfer experiment was performed for the water-base alumina nanofluid of 0.5g/L particle concentration. The thickness and surface roughness of the nanoparticle layer formed on the heat transfer surface were measured. The pool boiling heat transfer coefficient was enhanced slightly in comparison with that in pure water. Then, pool boiling heat transfer experiment was performed using pure water and the nanoparticle-layer deposited heat transfer surface. The heat transfer coefficient was deteriorated in this case, indicating that the nanoparticle layer formed on the heat transfer surface during nucleate boiling in nanofluid acts as a thermal insulation material. The heat transfer enhancement measured in the nanofluid pool boiling in this work can hence be attributed to the nanoparticles dispersed in liquid.

The HCCI engine, which is expected to be the combustion method for next-generation automobile engines, has a problem that strong pressure oscillation is generated under high load condition. From previous studies, this pressure oscillation was greatly reduced by a small amount of air injection before compression. It was considered that this was because the spatial distribution of ignition delay was formed in the combustion chamber cylinder after compression due to the difference in the specific heat ratio of air and fuel premixture. In this study, we investigated the effect of the injection pressure and the injection duration on pressure oscillation intensity under higher load conditions where the equivalence ratio is close to unity.

Various studies have been conducted on ethanol steam reforming, but all of them are based on chemical studies of catalyst and theoretical simulation under ideal condition with a compact-size reactor. So, in order to establish the design criteria of a home-use-size reactor, the authors have studied characteristics of ethanol steam reforming using Cu/ZnO/Al₂O₃ catalyst for a reactor with an inner diameter of 23.5 mm, as well as Shinoki et al. (2011). In the present study, the authors examine the combination of different kinds of catalysts such as Ru/Al₂O₃ catalyst in addition to Cu/ZnO/Al₂O₃ catalyst, and experimentally investigate the influence and the controllability of vaporizer composing the steam reactor, comparing the chemical equilibrium theory. As a result, we confirmed that the temperature fluctuation inside the reactor can be reduced by 40 % in terms of the temperature control of vaporizer. Moreover, obtained concentrations by the present experiment are different from those by Shinoki et al. (2011), with higher efficiency. This suggests the possibility of hybrid steam reforming control and high performance from a chemical equilibrium point of view.

The intermediate wetting state at nano/microstructured surfaces can be described using the partial wetting model between the Wenzel and the Cassie-Baxter models. However, the effective wetting area at solid-liquid interface in the intermediate wetting state is still open for question. In this study, micro-patterned Si surfaces were fabricated by deep reactive-ion etching and its effective wetting area was estimated by the electrochemical impedance measurements. The experimental effective wetting areas were compared with the theoretical predictions and the effect of microstructure size on the wetting state was investigated.

Carbon fiber is almost impossible to be burned out by even high temperature burnt gas because of extremely high melting point of carbon fiber and a low oxygen concentration in burnt gases. In previous studies, self-sustained combustion of carbon fiber in oxygen has been reported. In order to obtain information of the self-sustaining mechanism of the combustion, in this paper, a convenient optical technique to acquire the 2D distribution of high surface temperature of glowing solid material was conducted. In this technique, magnified thermographic view of the high temperature specimen was provided by comparison between RGB brightness information of conventional photograph of the visible light emission of the surface and previously-calculated values from Planck's law and the spectral sensitivity of the camera system.

In this study, we visualized the generation and growth of voids which is induced by the electromigration in 10μm width Al line type interconnections. The temperature distribution near the voids was also measured using two-dimensional thermoreflectance imaging method when current is applied. The growth and recovery (filling) of the voids were observed and the relationship between the void growth and the temperature distribution was evaluated. We found that the temperature increases in the area where group of voids appears and large temperature gradient is formed around the voids, by which the growth of the voids was accelerated.

Non-scanning 3D-CT(Computer Tomography) technique using a multi-directional quantitative schlieren system with flash light sources has been proposed to obtain instantaneous 3D density distributions of flames, supersonic jets and etc. This "Schlieren 3D-CT" is based on (i) simultaneous acquisition of flash-light schlieren images taken from numerous directions, and (ii) 3D-CT reconstruction of the images by an appropriate CT algorithm. In this paper, accuracy of this technique is evaluated and verified by checking with a standard refractive index distribution of a helium jet. Next, the verified 3D distribution of refractive index of premixed flames are successfully converted to appropriate temperature distribution.

PHP is a heat transport device that has a structure in which one flow path is arranged in a bellows shape between the heating part and the cooling part. PHP performs bidirectional heat transport by continuous pulsating vibration of evaporation and condensation, and high thermal conductivity and heat transport efficiency can be expected. However, there is a problem that pulsating vibration and heat transport in the flow path are not stable. The purpose of the research is to promote pulsating vibration and improve the amount of heat transport. Therefore, in this experiment, water and SRW solution are used as the working fluid, and the maximum heat transport amount by the evaporation area and condensed area is reported.

Polymer electrolyte fuel cell (PEFC) are expected to be a next-generation high-efficiency energy conversion device, but the catalyst layer structure and formation process have not yet been sufficiently clarified. To investigate the Nafion film (Ionomer) formation process, an apparatus for Surface Plasmon Resonance imaging (SPR) was developed. Using the apparatus, we succeeded in observing drying process of a water droplet with an incident angle of 43.6°, where the observed images correspond to the SPR curves calculated using reported optical constants. Further, we presented that the appropriate angle of incidence for observing the Nafion film formation process is 71.5°.

When a voltage is applied to a semiconductor light emitting device such as an LED, a thermodynamically non-equilibrium state is generated, resulting in light emission that differs from the blackbody radiation of Planck's law. We have added a Distributed Bragg Reflector (DBR) to the conventional Thermophotonic (TPX) power generation system in order to achieve more efficient energy transport. In this study, we show that the radiation of TPX power generation is enhanced by the DBR by comparing an emitter with a combination of LED and DBR and an emitter with a single layer of LED.

In recent years, a semiconductor device with high power density such as SiC (silicon carbide) is expected to be applied to next-generation automotive inverters. A novel cooling technique is strongly needed to protect devices with high heat flux. We already confirmed that applying the pulsating flow could enhance heat transfer around a cylindrical obstruction while decreasing the time-averaged supply flow rate. In this report, the cooling technology of heating elements with high heat flux was explored using heat transfer by pulsating flow and boiling. The heat transfer was found to remove vapor bubbles around the heating element by pressure fluctuation of pulsating flow.

This paper reports experimentally observed characteristics of smoldering and flaming spread along a cellulosic combustible solid. A thin cylindrical sample was burned in a forced oxidizer flow, and quasi-steady, downward opposed-flow spread was observed. The oxidizer velocity and the oxygen concentration were varied, and the spread velocity and the surface temperature were measured. The results indicated that the maximum surface temperature was a key quantity that controls the combustion mode, i.e., smoldering or flaming.

In recent years, high efficiency heat transport devices are much in demand, because of higher performance of electronic devices. In this study, we tried to develop a new heat transport device. As a new heat transport device, we created a mechanism that a soft matter slides in the pipe. It is expected that the sliding movement makes a temperature boundary layer thinner and it possible to transport more heat than the dream pipe. The experimental results showed that heat was transported more efficiently when it was not filled with water than when not filled with water and when increasing motor speed in filled water.

PHP is a heat transfer device that has a simple structure and in which one flow path is arranged in a meandering tube between the evaporation part and the condensation part. It has the high heat transfer performance by latent and sensible heat. And also, this device is able to be miniaturization due to a simple structure. However, the design guidelines and inside phenomenon of PHP has not realized. In this research, the experiment was done about changing temperature conditions of condensation parts and input power. The purpose is to suggest the ideal heat transfer performance by evaluating heat transfer performance of PHP.

In low-grade thermal energy conversion system, plate heat exchangers that are compact and high-performance are used as evaporators and condensers for applying small available heat source temperature difference. In particular, the understanding of two-phase flow pattern with evaporation in the narrow channel of plate heat exchangers will contribute to the improvement of performance. In this research, the transparent resin made plates are used to visualize and observe the two-phase flow on the herringbone plates in evaporators. In the experiment, the flow patterns of three chevron angle plates are compared with image processing manipulated by the original Python and OpenCV codes. As the results, this process clarified the void fraction variations in the flow, and the flow patterns were estimated by the void fractions in the low void fraction range.

The purpose of this study is to demonstrate the feasibility of hydrogen combustion with water spray using two-fluid nozzle. In the nozzle, water is atomized by the fuel, hydrogen. Therefore, the fuel and water are dispersed from the nozzle simultaneously. As a result, water is sprayed in hydrogen diffusion flame and evaporated. In addition, hydrogen is diluted by its vapor and thus, the reduction of NOx emission is expected due to temperature fall and slow combustion. This paper reports the demonstration of stoichiometry hydrogen combustion of 6.0kW heat release rate with water evaporation using two-fluid nozzle.

In this study, we have investigated a water jet self-standing firefighting hose that can provide a solid water stream easily and safely from on the ground to fires occurring at a second or third floor in houses and buildings. The flexible vinyl hose at whose end a L-shaped nozzle is attached obtains a force coming from a water flow through the bent part of the nozzle. The force makes the hose bow-shaped, and it stands steadily by itself. As a result, the nozzle exit rises up and the water jet is delivered from higher location to the burning area. In this experiment, the rise-up characteristics of the self-standing water jet hose was examined by varying the hose length, the nozzle length and the mass of the nozzle. The data was organized with two different types of non-dimensional parameters.

To measure concentration fluctuation accurately by a fast-response flame ionization detector (FFID), the frequency response function should be known, and measured signals need to be compensated appropriately. In the present study, we numerically analyzed the convection and diffusion equations of concentration developing in a laminar pipe flow. Then, we have obtained the response functions of the cross-sectional mean concentration at several downstream locations by varying the frequency of concentration fluctuation at the inlet of the pipe. It is found that the theoretical and numerical results are in good agreement. Based on the response function obtained, we may compensate the attenuated concentration signals rationally.

This paper focuses on the flickering characteristics of jet diffusion flames. Jet diffusion flames are known to flicker because of buoyancy effects. On the other hand, the turbulent-flame regime exists at high Reynolds numbers. Both the buoyancy and the turbulent effects may coexist depending the flow condition (i.e., the burner diameter and the fuel flow velocity). In this study, experiments were conducted with varied burner diameters and the fuel flow velocities to study such effects. The transient motions of flame tips were monitored and the governing oscillation mode was identified. The influences of dimensionless parameters, the Reynolds and the Froude numbers, are discussed herein.

From the viewpoint of the adsorption of nonionic surfactant molecule to the interface, the active control of the supercooling degree was examined. And, it was clarified that the supercooling degree could be actively controlled by the change of the surfactant concentration. In this paper, in order to improve the controllability of the degree of supercooling, amphoteric surfactants were mixed with pure water fixed at pH 8 (amphoteric surfactant molecules are anionic), and the degree of supercooling was measured at various concentrations under voltage application. The characteristics of the degree of supercooling in the case of amphoteric surfactants were clarified by comparing the results of applied and non-applied voltages.

Lithium-air battery attracts great attention because of its high energy density. However, due to the low solubility and diffusivity of oxygen in the electrolyte, oxygen transport to the reaction site of the positive electrode is limited. In this study, discharge experiments using glassy carbon were conducted to investigate the positive electrode structure effective for improving oxygen transport. The results showed that a smaller contact angle between the carbon and the electrolyte can improve the positive electrode performance. By optimizing the electrode structure and the electrolyte wettability, it is expected that oxygen transport (performance of the positive electrode) will be improved.

In conventional studies, the ice adhesion force to a cooling metal surface was often measured in a macro-scale. However, the measured ice adhesion force to a metal surfaces in a macro-scale is an apparent value including a force to break the ice due to its metal surface’s unevenness, and it is not possible to measure the accurate ice adhesion force. Therefore, one of the authors developed the method to measure the accurate adhesion force in a nano-scale using Scanning Probe Microscope (SPM). In this study, the adhesion forces of ice made with the addition of cationic surfactant on a voltage-applied aluminum plate was measured while changing the applied voltage, and the effect of the applied voltage and the surfactant on the ice adhesion force was clarified.

In the vulcanization process to give elasticity to rubber products, the heating method is important to give optimal characteristics. In this process, steam and nitrogen gas are supplied to a sealed vessel whose inner wall is rubber, and the wall heat transfer is considered to be a complex phenomenon due to condensation and convection. Understanding and predicting such phenomena contributes to the optimization of heating methods. In this study, experiments were conducted using a simulated stainless-steel vessel for various inlet direction to measure wall heat transfer during steam and nitrogen gas supply to understand the phenomena.

Solid oxide fuel cells (SOFCs) are known for their fuel flexibility and high energy conversion efficiency. Hydrogen is one of the ideal fuels for SOFC; however, a SOFC system fueled with pure hydrogen or ammonia always underperforms in comparison to those fueled with hydrocarbon fuels. This paper deals with thermodynamic analyses of novel dead-end anode (DEA) SOFC systems. Particularly, the impact of fuel types on the system’s efficiency is systematically studied with hydrogen, ammonia, methanol, ethanol, dimethyl ether (DME) and natural gas. The comparison shows that the energy and exergy efficiencies of dead end anode SOFC fed with ammonia can be close to that of natural gas.

We evaluated the surface charge properties of a 3nm monolayer molybdenum disulfide (MoS₂) nanopore, exposed to a potassium chloride (KCl) aqueous solution, by measuring the ionic current as an external electric potential bias was applied across it. It was indicated that the ionic current was governed by the surface conductance at low concentrations as the electric double layer was thicker than/comparable to the pore radius. As a result, the ionic current was largely independent of the salt concentration when it was lower than 0.05 M (where the Debye length was close to 1.5 nm) consistent with the electric double layer theory. Furthermore, by considering a site-bonding model we estimated the equilibrium constant (pK=6) and number density ( =1/nm²) of surface functional groups on MoS2 in aqueous solutions. The acquired information can be useful for plenty of nanopore applications.

In This paper, the heat transfer characteristics were evaluated using a microchannel heat exchanger that is actually in use. The microchannel heat exchanger consists of aluminum fins combined with flat perforated tubes with multiple channels made of aluminum. Although the specific heat transfer area of this heat exchanger is larger than that of the conventional type, the multiple flow paths may cause maldistribution and flow oscillation. Experimental results clearly expressed the decay of the heat transfer performance by nonuniformity of heat flux.

Near-limit characteristics of flame spread are of importance from the fire-safety point of view. This paper presents results of opposed-flow flame-spread experiments in a narrow channel. With an increase in the opposed-flow velocity, the spread velocity first increases and then slightly decreases. Flame spread was not possible when the opposed-flow velocity was less than the lower limit or greater than the upper limit. A steady, 1-D heat equation was derived, and the values of its heat-release and heat-loss terms were inversely determined from experimentally measured temperature distributions. The ratio of the total heat release rate to the value of complete combustion was then calculated. It was found that the ratio generally increases with an increase in the opposed-flow velocity. The ratio had a non-zero value, around 20%, even at the lower limit.

Numerical simulation has been performed to study the dynamics of the capillary flow in open rectangular channels. The results are compared with the existing experimental data and the analytical solutions in terms of the liquid-gas interface shape, the cross-sectional velocity distributions and the mobility parameter. From the comparison, it is suggested that the agreement between the experimental and analytical results for the mobility parameter reported in the literature is just a coincidence and that further investigation of the flow near the contact-line is necessary to accurately predict the mobility parameter.

Numerical simulations were conducted by using OpenFOAM to investigate the flow and heat transfer characteristics around a heating cylinder with rotational vibration. In a previous study, it was reported that the drag force of a rotating oscillating cylinder was lower than that of a stationary cylinder. Therefore, it is expected that the application of rotational vibration to a heated circular tube can expand the dissimilarity between momentum and heat transport and lead to higher efficiency of heat exchangers. In this study, numerical simulations were conducted to clarify the effects of Reynolds number Re, rotational speed ratio V_r, and forced Strouhal number S_f on flow resistance and heat transfer characteristics.