Recently, hydrogen is paid the most attention all over the world, because the CO₂ emission can be reduced by an increase of its usage. In our previous study, hydrogen has been added in the premixed methane-air flame. The OH chemiluminescence intensity and the burning velocity were experimentally obtained, using a Bunsen burner. For further study, we investigated OH concentration by using the OH-PLIF technique. Especially, the OH fluorescence intensity was measured by keeping the burning velocity constant. The premixed gas velocity of CH₄-H₂-air mixture was 1.3 m/s. For comparison, OH chemiluminescence intensity was measured. Results showed that even when the hydrogen ratio in the total fuel of methane and hydrogen was changed, the OH fluorescence intensity was almost constant. On the other hand, OH chemiluminescence intensity decreased monotonically. Conclusively, different from the OH chemiluminescence intensity, the OH fluorescence intensity can be a good marker to evaluate the burning velocity in the combustion of mixed fuel of hydrogen and methane.

In this study, we experimentally investigated soot and NOx in a diffusion flame on a coaxial burner. By applying a dielectric-barrier-discharge (DBD) plasma, we tried to reduce these emissions. When the DBD plasma was exposed to the air flow, the height of the luminous flame slightly decreased. By considering the fact that the flame height without the DBD plasma is proportional to the fuel flow rate, the DBD plasma surely affects the soot concentration of the luminous flame. Based on the LII image, the soot region identified by the LII signal corresponds to the luminous flame zone. This soot distribution is similar even when the DBD plasma is activated, but the soot concentration of the luminous flame zone is reduced. As the air flow rate increases, the reduction of the integrated LII signal by the DBD plasma is smaller. This could be because the plasma is only active at the exit of the air flow, and the effect of the plasma is relatively weaker when the air flow rate increases. As for NOx emission, it is confirmed that the EINOx without plasma increases by increasing the air flow rate, showing that the thermal NOx could increase. Overall, when the plasma is activated, the EINOx always increases at any air flow rate. That is, the simultaneous reduction of soot and NOx cannot be achieved.

The mixing process is used not only to homogenize the materials, but also to bring out better functionality by mixing different materials. In the mixing process, temperature control during mixing is important to prevent thermal deterioration of the material and control chemical reactions. In this study, a 3D model was used to numerically simulate the flow field around a single rotating rotor in a partially filled chamber to investigate the thermal flow characteristics of a highly viscous fluid. The liquids examined contained glycerin, a Newtonian fluid, and carboxymethyl cellulose (CMC) aqueous solution, a non-Newtonian fluid. A three-wing rotor was chosen as the mixing rotor and the shear heating of viscous fluid was modeled by heating the tip of the rotor wing with a heater. Obtained simulation results of the temperature distribution around the rotor was agreed well with the independently performed experimental results. Evaluation of thermal flow properties was performed using history particles. Also, in order to analyze the temperature field, the flow rate through the rotor tip was used to classify the effect on the flow field. As a result, it was found that there was a correlation between the shear-thinning property and the temperature non-uniformity, and the flow rate ratio between the passing flow rate and the circulating flow rate due to the shear-thinning property of the fluid affected the thermal diffusion of the high temperature part.

Two-dimensional axisymmetric numerical simulations were performed for a Bunsen flame to investigate the OH concentration and heat release rate of methane-hydrogen premixed flames. The OH production rate of the premixed flame increases as the hydrogen ratio in the fuel increases. Resultantly, the OH concentration in the premixed flame increases with the larger heat release rate, but the OH concentration in the diffusion flame remains almost unchanged. The higher the total equivalence ratio, the greater the change in OH concentration and the heat release rate. This could be due to the fact that most of the hydrogen in the fuel reacts in the premixed flame. Independent of the total equivalence ratio, the relationship between the maximum OH concentration in the premixed flame and the OH fluorescence intensity measured by the PLIF technique shows some similarity in both methane and methane-hydrogen flames. Since the same linearity between the maximum value of the heat release rate and the burning velocity is observed, it is derived that the heat release rate in the premixed flame can be estimated by the burning velocity.

The multiple-ion-probe method detects flames using a plurality of ion probes installed on the wall of a combustion chamber and by reconstructing the dynamic behavior of the flame front along the wall. Although this method is effective only close to the wall, it can indirectly aid in visualizing flame propagation behavior. Because this method has an extremely high time resolution, it can accurately measure high-speed phenomena such as knocking in a spark-ignition engine. This study aims to establish a method to automatically determine the characteristics of combustion for each mixture using the acquired data from a multiple-ion-probe measurement system; various propagating flames in combustible mixtures with different compositions were used. The combustible mixture was composed of methane or LPG as the fuel and argon or nitrogen as the diluent. A stoichiometric mixture of fuel and oxygen was diluted by changing the diluent ratio to prepare fourteen types of mixtures for investigation. From the obtained individual experimental data, twelve types of scalar features were extracted and compared with the experimental data. We compared the scalar features extracted from the output data of the multiple-ion probe with the different combustion modes obtained in the series of experiments; we found that a few of the features strongly responded to specific propagation states. Thus, we confirmed that by using the features, it is possible to determine the characteristics of the propagation states; such characteristics are difficult to determine merely from the flame surface shape reconstructed from the multiple-ion-probe data.

In 2021, more than 40 countries have agreed with "de-coal" statement at the COP26. The torrefied solid biofuels have come to attract attention as promising alternative fuels to coal in coal-fired power plants and industrial boilers. However, the energy property such as higher heating value (HHV) and energy yield of torrefied biomass, which is one of the most important fuel properties, has been evaluated by means of experiments for various biomass species so far. That is, the torrefaction conditions to produce torrefied solid biofuel with predetermined HHV have been provided only empirically. In this study, a generalized HHV estimation method applicable to any torrefied woody biomass is investigated based on pyrolysis kinetics of primary constituent polymers of woody biomass, cellulose, lignin and xylan. Analyses of pyrolysis kinetics of constituent polymers are conducted by assuming that the process in non-isothermal pyrolysis experiments is modeled as the single reaction. The HHVs of torrefied constituent polymers are obtained by isothermal torrefaction experiments, and the experimental correlations of HHV of torrefied constituent polymers are proposed as a function of solid mass yield. For a given woody biomass whose mass fractions of three constituent polymers are known, HHV of torrefied woody biomass produced with any torrefaction condition can be estimated by applying pyrolysis kinetic models and experimental correlations of HHV for three constituent polymers to the torrefaction process of woody biomass. From the comparison between estimated HHV of torrefied woody biomass and experimental data, it is concluded that the generalized HHV estimation method can be useful for evaluating HHV of torrefied woody biomass with about 10% accuracy, although the HHV is somewhat underestimated.

Heat transfer enhancement is essential in low Reynolds number flow because recent small heat exchangers require narrow flow passages. In the present study, we conducted direct numerical simulations of the channel flow to investigate the turbulence sustaining effect by feedback blowing and suction from the wall. The initial flow field corresponded to the fully developed turbulent channel flow, and the Reynolds number suddenly decreased at the beginning of the simulation. The results indicated that there are two approaches for the turbulence maintenance. If the amplitude of the blowing and suction is high, then the sensor detects the blowing and suction from the wall, and the velocity fluctuation corresponds to self-maintenance. Then, we obtained large heat transfer. However, the gain was small. If the amplitude is moderate, then the blowing from the wall to the low-speed streaky structures pushes up, and the suction attracts the high-speed streak toward the wall. The effect to increase the Reynolds shear stress and heat transfer results in the promotion of the turbulence and heat transfer with high gain.

An experiment study was conducted on the operational characteristics of the JEST-type loop thermosyphon when an initial liquid level of a working fluid was lowered. This thermosyphon was invented in 2012 by one of the authors with a jet explosion stream technology (JEST) for cooling high-heat-generation and high-heat-flux CPUs. The present experiment aims at lowering the height of the thermosyphon for rack-level thermal management in a datacenter. Hydrofluoroether (HFE)-7000 was used as the working fluid. In experiment, an evaporator section of the thermosyphon was heated with a heating block while a condenser section was water-cooled using a thermostatic bath. Temporal changes in temperatures of the thermosyphon were obtained with thermocouples. Moreover, the circulation flow rate of the working fluid in the thermosyphon was obtained with a simple measurement method. The initial liquid level of the working fluid was changed as 166, 268, 368 mm while the height of the thermosyphon was 1200 mm. Experimental results are shown regarding the effect of the initial liquid level on the circulation flow rates of the vapor and liquid phases of the working fluid as well as the heat transfer coefficient at the evaporator section. An additional experiment was also conducted when the height of the thermosyphon was lowered from 1200 mm to 480 mm. It was confirmed that the thermal performance of the thermosyphon decreased when the initial liquid level was lowered; however, the thermal performance was recovered by lowering the height of the thermosyphon. Therefore, the JEST-type loop thermosyphon can be applied to the rack-level thermal management in a datacenter.

This study has investigated experimentally the effects of hydrogen addition and turbulence on the ignition and the flame-kernel development characteristics in isotropic and homogeneous turbulence for propane mixtures. In this study, the lean- and rich-fueled hydrogen added propane mixtures with different equivalence ratios (φ=0.5~1.4) and hydrogen additional rates (δ_H=0.0~1.0) are prepared, while maintaining the laminar burning velocity (S_L0=25 or 15 cm/s). First, in order to investigate the ignition and flame-kernel development in quiescence, the minimum ignition energy Ei_min and the relationship between the flame radius and the burning velocity of meso-scale laminar flames in the range of flame radii r_f approximately from 1 to 5 mm are examined quantitatively by using sequential schlieren photography in a constant volume vessel. Then, the experiments in isotropic and homogeneous turbulence are carried out for two turbulence level with the turbulence intensity u’ being approximately 0.35 and 1.76 m/s. Ei_min for each mixture is also defined experimentally at each u’. It is found that the effects of hydrogen addition and turbulence on the ignition and the burning velocity of meso-scale flame characteristics are much different between the lean and the rich hydrogen added propane mixtures. It also becomes clear that there is a good relationship between Ei_min characteristics in turbulence and Lewis number or the Markstein number. Additionally, the transition region of the minimum ignition energy could be summarized regardless of φ, δ_H and u’/S_L0 by using the proposed turbulent Karlovitz number based on the burning velocity of the meso-scale flame in quiescence.

Combustion measurements using laser diagnostics are vital for experimentally revealing both qualitative and quantitative flame characteristics. This paper focuses on the application of the quantitative OH laser-induced fluorescence (OH-LIF) method for high-pressure and high-temperature flames. Under high-pressure conditions, the intense OH chemiluminescence drastically decreases the signal to noise ratio (S/N). However, OH(2,0) band excitation is an alternative method to the typical OH(0,0) or OH(1,0) band excitation LIF under high-pressures. OH(2,0) band LIF sufficiently maintains the S/N under high-pressure because the OH fluorescence can be detected away from the peak OH chemiluminescence wavelength. In addition, the bi-directional LIF method is known as a quantitative OH concentration measurement that can ignore the quenching factor. Therefore, this study proposed a quantitative OH concentration measurement by combining the OH(2,0) band LIF and bidirectional LIF methods for high-pressure and high-temperature flames. First, an H₂/air premixed flame created by a McKenna burner under atmospheric pressure was used to validate the quantitative OH(2,0) band bidirectional LIF method. Furthermore, a CH₄/O₂/N₂ oxygen-enriched premixed flame created by a multi-hole calibration burner was used to verify the method under high-pressure (~0.5 MPa) and high temperature (~2900 K) conditions. A comparison of the experimental and numerical results revealed that the calculated OH concentrations were within the experimental uncertainty for the McKenna burner configuration. The experimental OH concentration results under high-pressure conditions deviated approximately 10%–20%, but they were also in good correlation with the calculation. In addition, the qualitative correlations with equivalence ratio and pressure variation were also acceptable. Although further consideration of the method is desirable for high-pressure turbulent flames, the results in this study showed that the OH(2,0) band bi-directional LIF method is feasible for measuring OH concentration in high-pressure and high-temperature flames.

Electromagnetic induction controlled automated steel teeming (EICAST) is a ladle-sand-free technology applied to the steel teeming process for clean steel practice. The temperature of the induction coil in the EICAST system greatly influence its service life. In this paper, a numerical model was developed to predict the temperature evolution of the induction coil without or with a nano thermal insulation felt (WDS) during the whole thermal cycle of ladle. Industrial experiment was conducted for the model validation. The results indicate that WDS reduces the coil temperature at the ladle baking and secondary refining stages, however it causes a rapid jump in the coil temperature from 309°C to 707°C during the induction heating process. Because the coil temperature is high enough compared to its ambient temperature after the induction heating stage, the temperature of the induction coil using WDS heat insulation material drops to 461°C constantly at the steel teeming stage. The measured temperatures of the nozzle brick and coil in the industrial experiment correspond well with the calculated ones by numerical simulation. The developed model could be used to predict the coil temperature evolution and improve coil cooling strategy at each stage of the whole thermal cycle process of ladle for the industrial application.

In this study, we have investigated turbulent premixed flames affected by local stretch in a swirl flow, measured by the simultaneous OH-PLIF/SPIV system. Evaluating the transient of burning velocity and stretch rate, the flow and the flame dynamics in a cyclone-jet combustor were discussed. The flame front was determined by the OH fluorescence signal. Results show that the axial mean velocity becomes the maximum around the center axis, whereas the axial or the radial rms velocity takes the maximum at the position far from the center axis. These could be caused by the velocity fluctuation due to the flame and flow interactions. According to the local burning velocity and the stretch rate, the estimated Markstein number (Ma) roughly matches the value of the laminar flame. With an increase of the swirl number (S_w), the rms velocity is enlarged. Interestingly, the probability of higher burning velocity increases at larger S_w. At the same time, the flame extinction occurs more frequently. Thus, it is derived that the swirl flow has a positive effect to increase the local burning velocity, but it simultaneously has a negative effect which causes the local flame extinction.

In this study, effect of the ambient relative humidity on the vapor concentration of ethanol-water mixture droplet on PTFE substrate was observed. Ethanol-water mixtures were prepared at 100 vol% (pure ethanol), 75 vol%, 50 vol%, 25 vol%, and 0 vol% (Pure water) by ethanol volume fraction. Relative humidity inside the test chamber was controlled at 33%RH, 52%RH, and 75%RH using saturated salt solution technique. Vapor concentration field was acquired by both applying Abel inverse transform to the Schlieren image and simulating with OpenFOAM source code. Pure ethanol had smaller value of mole fraction at the center than ethanol water mixture which was similar to the refractive index field. Two peaks of the mole fraction value were observed at the side of droplet in the case of pure ethanol from the concentration field, which was due to the presence of the droplet that blocked the downward movement of the ethanol vapor which was heavier than air and forced it to horizontally move to the edge of the droplet. On the other hand, one peak at the middle was found in the case of ethanol-water mixtures. Comparison of the concentration field between experimental result and simulation showed consistency in pure ethanol case and deviation became larger as ethanol portion decreased. Results of pure water and low ethanol concentration case (25 vol%) were obtained from simulation alone due to the limitation of Z-type Schlieren.

More and more attention has been paid to ejector refrigeration system using low grade thermal for cooling. Ejector is the most important part of this system, and its operating condition and structure are the two important parameters affecting system performance, especially the NXP value of ejector is a hot research topic at present. The optimal NXP was found by many experimental or numerical studies, but the theory about how to design an optimum nozzle position was rare. In order to verify whether the NXP value calculated with the free beam theory is suitable for the ejector designed by thermodynamic method, an ejector and a steam ejector refrigeration facility were designed for experimental investigation with a thermodynamic model using real fluid properties. The experimental values were compared with the theoretical design values and the optimum nozzle exit position was studied in experiment, and then the effect of operating condition on system critical performance were researched with optimum NXP. The results indicate that the system acquired a COP of 0.17 at T_g=70℃, T_e=15℃and T_c=28℃, the experimental value of ejector entrainment ratio matched satisfactorily with theoretical value well, and so did the critical back pressure. The system COP and cooling effect under designed NXP value were superior to those with ±10mm change.