In this study, attempts have been made to utilize ammonia in the industrial heating field, in which highly preheated air around 1000°C is used under high temperature atmosphere inside the furnace 1200°C. The high temperature inlet air and atmosphere are realized in the bench-scale furnace. Ammonia and methane in the fraction of 30%-NH₃ and 70%-CH₄ based on lower heating value, corresponding volumetric fraction of 55%-NH₃ and 45%-CH₄ is used as fuel under the fixed thermal input of 40-kW. On the furnace, the nozzle burner is installed in which fuel nozzles are installed inner side of the annular air nozzle, and furthermore, injection nozzles called “F2 nozzle” are installed on the top side of the furnace to inject NH₃ separately from the air. To stabilize the combustion field, CH₄ is injected from the burner for all cases. Results of exhaust gas measurements show that over 1000ppm of NO_x is emitted for NH₃ burner injection, however, in the case F2#1-NH₃ injection from x = 0.3-m where x is the distance from the burner, NO_x is drastically decreased to 464ppm even with high temperature inlet air and atmosphere. NO_x concentration is further decreased by increasing the distance of the F2-NH₃ nozzle from the air, then, NO_x is reduced to 160ppm for F2#6-NH₃ injection which is located at 3.3-m from the burner air. Furthermore, unburned NH₃ and N₂O are not detected for all cases of examined. As a result of species measurement inside the furnace for F2#6 NH₃ injection case, it is found that the O₂ concentration is significantly low at the upstream of NH₃ injection position, thus, injecting NH₃ into the low O₂ concentration region is considered to be effective to reduce NO_x even for NH₃ combustion with high temperature inlet air and atmosphere.

The formation process of an initial flame kernel in laser ignition was analytically examined for understanding its experimentally-observed hugeness. First, we evaluated the thermodynamic state of the laser-heated plasma by examining the laser-absorption waves in the detonation mode and in the radiation mode, taking account of lateral energy loss. Second, we evaluated the mechanical energy loss during the plasma expansion to the initial pressure. In addition, we evaluated the thermodynamic state of the plasma after its expansion to the initial pressure. In this evaluation, we calculated not only the isentropic-expansion process but also the effects of thermal diffusion from the hot plasma to the ambient gas in an approximate manner. During the course of this study, we developed some empirical formulas for the properties of air plasma to examine analytically the formation process of an initial flame kernel in laser ignition. It has been found that the laser-absorption wave must be in the detonation mode for typical laser-ignition conditions, and that the hugeness of the initial flame kernel is ascribed not only to the hydrodynamic expansion of the high-pressure laser-heated plasma but also to the thermal diffusion from the high-temperature plasma to the ambient gas. Finally, we derived the scaling laws for the size, internal energy, and temperature of the initial flame kernel with respect to the incident energy flux and absorbed energy of the igniting laser.

This study investigates the combustion and emission characteristics of water-in-diesel emulsified fuels, focusing on varying water content and droplet sizes. Emulsified fuels were prepared with water contents ranging from 2 to 24 vol% and droplet diameters of <3 μm, 26.5 μm, and 39.8 μm, produced using both strong stirring and membrane emulsification methods. These fuels were tested in a single cylinder, air-cooled direct injection diesel engine at a constant speed of 2300 rpm. The results showed that increasing water content generally decreased engine output power due to reduced diesel fraction and latent heat effects. However, thermal efficiency improved up to 14 vol% for small droplets and 20 vol% for larger droplets, driven by an extended ignition delay and higher peak heat release during premixed combustion. Beyond these water content thresholds, thermal efficiency declined due to increased ratio of phase-specific combustion durations after and before CA50 i.e., burn ratio, leading to energy losses from prolonged diffusion-controlled combustion. Emission measurements indicated that higher water content reduced NOx and soot emissions but increased CO levels. This study concludes that emulsified fuels with larger water droplets and 20 vol% water content offer the best balance between thermal efficiency and emission reduction.

In this study, we investigate membrane distillation (MD), which is a promising desalination technology. Conventional evaporation methods require seawater to be heated to its boiling point, and reverse osmosis (RO) methods require the liquid to be pressurized to a high pressure. MD is a technology that enables freshwater production without imposing high temperature and pressure conditions. This technology uses the phase transition of water in seawater to separate the generated water vapour from seawater using separation membranes with nanoscale pores. The driving force of the water vapour is the difference in water vapour pressure before and after passing through the separation membranes, which depends on the temperatures near both ends of the separation membrane surfaces. We analysed heat and mass transport by using a thermal network method assuming a 1D steady state. The network models were applied to a direct contact membrane distillation (DCMD) and a permeate gap membrane distillation (PGMD) and compared with experimental values for distillation simply using pure water. The results show that, for the temperatures, the experimental and calculated values agreed about the membrane surface temperatures within approximately 7.5 % to 15 % of the temperature difference between the hot water and cooling water temperatures, and for the permeate fluxes, the experimental and calculated values were consistent within 25 % of the calculated values.

This study investigated a premixed propane-air flame in a partially tapered swirl burner. Experimentally, we found that a flame resembling a morning glory flower formed at an equivalence ratio near the lean flammability limit. A numerical simulation of the flame with detailed chemistry revealed that the upstream flame tip existing at the central axis in the recirculation zone was significantly weakened, whereas the curved flame convex downstream was significantly strengthened. In addition, high peaks of temperature, heat release rate (HRR), and concentrations of OH, O, and H radicals were formed immediately behind the latter curved flame, which enabled the flame to exist stably under conditions very close to the lean flammability limit. Subsequently, to identify the influence of the Lewis number on the flame shape, adiabatic methane-air swirling flames were simulated with the Lewis numbers manipulated between 0.90 and 1.20. The results show that an increase in the Lewis number from unity changes the flame shape from a circular paraboloid to one somewhat similar to a morning-glory flower, whereas a decrease in the Lewis number from unity changes the flame shape from a circular paraboloid to one somewhat similar to a comet. This result suggests that the large difference in flame shapes among hydrogen-air, methane-air, and propane-air under very lean conditions is due to the difference in their Lewis numbers.

In recent years, industrial boilers that generate power from biomass have drawn a lot of attention. Nevertheless, a sizable portion of thermal energy is frequently lost to the environment as flue gas throughout the process. Stirling engine: a very efficient external combustion engine and little emissions as compared to other available engines, would be a good solution to overcome this issue as it can be used with any type of heat source. When the Stirling engine is connected to a heat source with a lower temperature, it exhibits a significant reduction in performance. Consequently, in this study a computational fluid dynamic (CFD) simulation model of Stirling engine was introduced in order to evaluate the possibility of recovering low temperature waste heat from biomass combustion. It has been shown to be effective in delivering useful, comprehensive information for further improvement of the engine. Then further parametric analysis will be investigated to enhance the engine’s performance. The investigation involving waste heat from wood pellets, coconut husk and bagasse as heat source then demonstrates the engine’s ability to recover and utilize heat as low as 70°C and generate power output ranging from 30 to 40 W and thermal efficiency of around 14%. Parametric analysis using different regenerator porosities, engine speeds and working fluid gases were also carried out to determine the optimal Stirling engine’s performance. The results demonstrate optimum performance at 0.85-0.9 of porosity and engine speed of 700 rpm and above. Overall, the results showed promising outcomes of Stirling engine to recover low temperature heat from biomass.

With the increasingly stringent emission requirements for shipping, methanol is a promising alternative fuel. The effects of mixing ratio and ambient temperature on the spray and ignition characteristics of high proportion methanol / Polyoxymethylene dimethyl ethers (PODE) blended fuel were studied on the visual constant volume combustion bomb experimental platform. The maximum mixing ratio of methanol was 70 %. The spray penetration, spray cone angle and spray area of the blended fuel increase with the increase of methanol ratio. During the development of the blended, the spray penetration first increases and then decreases, and finally tend to be stable. The time for the spray penetration to reach its peak is negatively correlated with the ambient temperature. As the methanol blending ratio increases, the flame spontaneous luminescence intensity and flame area decrease, and the ignition delay period prolongs. The increase of ambient temperature can improve the combustion performance of the blended fuel, but the effect of the mixing ratio on the fuel ignition gradually weakens with the increase of ambient temperature. It is of great significance to study the spray and ignition characteristics of high proportion methanol / PODE blended fuel for the application of high proportion methanol fuel in marine diesel engines.

The rapid progression of industrialization and the integration of artificial intelligence in recent years emphasizes the critical need for efficient thermal cooling solutions. Despite significant strides in technology, existing liquid cooling methods, notably boiling heat transfer and spray cooling, encounter substantial obstacles attributable to the well-documented Leidenfrost effect. Upon contact with a highly heated surface, a liquid generates a vapor layer that acts as an insulator, elevating the liquid above the surface and severely impeding heat transfer efficiency. While notable advancements have been achieved in mitigating the Leidenfrost effect, a comprehensive understanding of the underlying mechanisms remains limited. Furthermore, challenges persist in sustaining high-temperature environments across diverse structures, materials, and technologies, impeding progress in this domain. This review aims to provide a thorough account of fundamental tactics for suppressing the Leidenfrost phenomenon on high-temperature substrates. It will underscore distinctive attributes and challenges while exploring avenues for the development of efficient and sustainable thermal management solutions.

Pulsating heat pipes (PHPs) are valuable for compact cooling applications. This study introduces a novel heat pipe design: a flat-plate heat pipe with a closed meandering channel and sintered metal porous sidewalls (porous HP). The effects of initial liquid volume fraction and inclination angle on heat transfer characteristics and flow behavior were examined and compared with those of a conventional PHP. The porous HP contains a rectangular meandering channel, 1.0 mm wide and 0.8 mm deep, with 20 turns. Its sintered metal porous structure, made from fine copper powder, has a tree-like morphology and 0.65 porosity. FC-72 served as the working fluid. At an inclination angle of 0°, boiling did not occur; however, thermal resistance was lower with liquid filling than without, indicating heat transfer through evaporation and capillary-driven recirculation. In the bottom-heated condition with an inclination angle greater than 0°, boiling and self-excited oscillations emerged despite the side walls being composed of porous material, significantly reducing thermal resistance. The lowest thermal resistance was recorded at a liquid fraction of 0.7 and an inclination angle of 90°. Flow oscillations in the meandering channel and liquid wetting within the porous medium enhanced heat transfer. The porous HP achieved a lower minimum thermal resistance and higher maximum effective thermal conductivity than conventional PHP.

Flames propagate in mixture flows with inhomogeneous concentration distributions in practical combustors, such as gasoline direct-injection engines and gas turbine engines. Clarifying the effect of fuel-type differences on the response characteristics of a flame propagating through a nonuniform concentration field will help develop such combustors. This study experimentally investigates the response characteristics (flame position x_f, velocity gradient g, CH radical emission intensity CH, and burning velocity Su) of lean methane–air and propane–air wall-stagnation-flow premixed flames to sinusoidal oscillations in the equivalence ratio φ at oscillation frequencies f of 5–50 Hz. Through experiments, MATLAB analysis, particle image velocimetry, and high-speed photography, we find the following: As f increases, the responses of x_f, g (flame stretch rate), CH, and Su to the fluctuating φ at the burner outlet are delayed, especially in the case of the dynamic propane flame, which has a small fuel diffusion coefficient. Regardless of fuel type, the frequency characteristics of Su are similar to those of g, and as f increases, the minimum CH of the dynamic flame becomes lower than that of the steady flame and has a local minimum value. However, because of the Lewis number effect, the maximum CH of the dynamic methane flame (CH_d,_max) exceeds that of the steady flame (CH_s,_max) and assumes a maximum value with an increase in f. For the dynamic propane flame, even as f increases, CH_d,_max does not exceed CH_s,_max and monotonically decreases. Finally, due to preferential diffusion, the combustion intensity of the dynamic methane flame becomes stronger than that of the dynamic propane flame when the nondimensional frequency (2πf/g) exceeds approximately unity.

In this study, the pyrolysis kinetics and mechanism of rice straw were investigated using thermogravimetric analysis (TGA) and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). The activation energy and thermodynamic parameters including the pre-exponential factor, Gibbs free energy, enthalpy, and entropy were calculated by the Kissinger-Akahira-Sunose (KAS) and Friedman (FR) methods. The Criado method was further used to determine the kinetic model of rice straw during the pyrolysis process. The Py-GC/MS results showed that the main components in the rice straw pyrolysis products were carbon dioxide, carbonyl compounds, phenolic compounds, aliphatic compounds, aromatic hydrocarbons, and heterocyclic compounds. The mean values of E_a obtained by the KAS and FR methods were 181.6 and 182.1 kJ/mol, respectively. When α was less than 0.45, the three-dimensional diffusion (D3) model fit well with the thermal degradation of rice straw, while for α>0.45, it transformed into a random nucleation (F3) model. The value of enthalpy change indicated that the formation of the activated complex required an additional 5 kJ/mol of energy; beyond the activation energy, the mean value of entropy during the thermal degradation process was about 10.53 J·mol⁻¹·K⁻¹, indicating that the system was more closely balanced with thermodynamics and that the thermal degradation process was relatively easy to carry out. Therefore, the findings of this study highlight the favorable conditions for the energy utilization of rice straw biomass.

Passive production of synthesis gas from liquid methanol was investigated using a combined packed bed reactor. Small porous particles were packed into the lower part of a reactor tube to draw liquid due to capillary action, while large porous particles were packed into the upper part to reduce the flow resistance of the reacting gas. When the packed tube was heated from the side surface, a liquid region, two-phase region, and dry region were formed along the tube axis. Upward liquid-vapor flow was induced by enhancement of the capillary pressure due to evaporation. The mass flow rate in the steady state increased in proportion to the heating rate and was as much 2.3 times the vapor production rate that corresponded to the heating rate of the two-phase region. Such a large flow rate was presumed to be due to the heat conducted from the dry region to the two-phase region as the result of a large temperature gradient produced in the dry region. The process in the packed tube was analyzed using a one-dimensional model based on the mass, force, and energy balances for each phase, where the heat conduction in the axial direction was accounted for. The calculated temperature profile and the methanol conversion agreed with those measured experimentally. A significant portion of the heat supplied to the drying region was distributed to produce vapor, the ratio of which was dependent on the magnitude of the conduction factor, ΣA_ik_i. The effects of the axial heat flow on the mass flow rate (vapor production rate), methanol conversion and the gas production rate are discussed.

The smoldering spread and extinction behavior are significantly impacted by both wind velocity and angle. However, this combined effect has not been extensively quantified. This study investigates the influence of the wind angle, ranging from θ₀ = 0° (concurrent smoldering spread) to θ₀ = 180° (opposed smoldering spread), which is defined as the angle between the directions of the forced airflow and the reaction propagation, on blow-off limit and smoldering spread rate of 2.5 mm incense sticks using a rotating apparatus. The experimental results indicate an increase in smoldering rates and blow-off wind velocity as θ₀ decreases. The maximum average smoldering rate is about 2.5 cm/min at θ₀ = 0°, while it is less than 1 cm/min at θ₀ = 180°. The blow-off wind velocity is 15 m/s at θ₀ = 0° and 5 m/s at θ₀ = 180°. The blow-off limit was discussed based on Damköhler number (Da). A simplified heat transfer analysis, coupled with computational fluid dynamics simulation, was used to calculate the smoldering rate. The simple model captures the experimental trend of the increasing smoldering rate at low wind velocity. A higher smoldering temperature results in a higher smoldering rate. Additionally, the higher smoldering rate observed at θ₀ = 0° was reproduced, emphasizing the significant role of heat transfer. To maintain a steady smoldering rate, all the heat produced by the reactions must be removed, which occurs most efficiently at θ₀ = 0°, leading to the highest smoldering rate.

A deep convolutional neural network model (DCNN) is developed to quantify the tortuosity factor of porous electrodes of solid oxide fuel cells (SOFCs). The DCNN model is first trained using synthetic three-dimensional (3D) structure datasets generated by either a generative adversarial network (GAN) or a simple sphere-packing algorithm. Validation of the trained DCNN model is performed by applying it to the analysis of real Ni-YSZ anode structure datasets obtained by focused ion beam scanning electron microscopy (FIB-SEM). Sufficient estimation accuracy is achieved when the DCNN model is trained using the structures generated by the GAN, with the coefficient of determination of 0.9586, 0.9839, and 0.8674 for the Ni, YSZ, and pore phases, respectively. To further improve the model accuracy, the data adjustment is applied to the training datasets to equalize the frequency distribution of the tortuosity factors. As a result, the estimation accuracy is notably improved for all phases, particularly the pore phase achieving the coefficient of determination of 0.9230. In addition, since the DCNN model is designed to analyze 3D structures with arbitrary sizes in each dimension by adopting the global average pooling layer, its estimation accuracy for analyzing structures with different volumes is investigated. The results demonstrate that the developed DCNN model has sufficient estimation accuracy even for larger structures than those used in the training. The constructed DCNN model represents a significant step towards surrogate modeling for structure quantification of energy materials.

In this study, the impact of surface radiation on the natural convection inside a differentially heated cubic cavity was experimentally evaluated. The thermal boundary layer near the vertical isothermal walls was visualized for cases with two emissivity of 0.1 and 0.94 on the top and bottom walls, using a phase-shifting Mach–Zehnder interferometer. The temperature around the vertical isothermal walls was determined through imaging process. Three-dimensional numerical simulation was also performed using OpenFOAM 2.3.1. The temperature distributions obtained from experiments and numerical simulations were compared. Experimental results indicated that the fluid around the top and bottom walls is cooled and heated, respectively, with high emissivity (ε = 0.94), which was also confirmed by the numerical simulations. This result was explained by the difference in the radiative heat flux on these walls, which originated from the radiation absorption at the wall surfaces. This effect of emissivity affects the development of natural convection along the isothermal vertical walls. Particularly around the upstream region of natural convection, where the thermal boundary layer was relatively thin, the thermal boundary layer thickness is thicker with high emissivity than for those with low emissivity. On the other hand, around the downstream region, this thickness is thinner with high emissivity. These results can contribute to the development of boundary layer control techniques with surface radiation.

This study visualizes the time-variation of the generation, growth, and pattern of voids induced by the electromigration in Al micro-line type interconnections. The two-dimensional temperature distribution near the voids was measured simultaneously using thermoreflectance imaging (TRI) technique. The effects of temperature distribution caused by Joule heating and heat conduction on the void spatial and temporal characteristics are discussed. Measurements were conducted with the base temperature of the line set to room temperature and high temperature conditions. The measurement results and discussion give new insights into the understanding of the thermal characteristics of the voids and heat transfer properties of interconnections, contributing to the advancement of application design and reliability physics. The thermoreflectance coefficients for Au, Si and Al materials were calibrated, and the temperature of the Au line subjected to Joule heating was measured and compared with numerical computation to validate the present measurement method. The pattern of the void generation at the cathode side of the Al line differed between the room- and high-base-temperature cases. The time-variation of the void area followed the power law, and generated three different slopes over time in the room-base-temperature case. The local temperature and its gradient significantly affected the void growth. Furthermore, the void growth rate and the line temperature near the voids followed an exponential relation in the void growth period. It was also found that the temperature gradient of the line can reduce the size reduction of voids after they were generated. These results highlight that the temperature plays an important role in local void growth characteristics in multiple ways.

In the serious accident at Fukushima Daiichi Nuclear Power Station, the presence of steam together with flammable organic compounds affected the hydrogen explosion. To investigate the effects of addition of inert gas, i.e. steam or nitrogen, on the explosion characteristics, we conducted the experiments of spherically expanding hydrogen-methane-air premixed flames in closed combustion vessels. Two types of vessels were used, and expanding flames were caught by Schlieren method. The flame propagation velocity depending on the flame radius was obtained by analyzing Schlieren images. When the flame radius was sufficiently small, smooth surface was found. The addition of inert gas to hydrogen-methane-air premixtures caused the decrease of propagation velocity of unstretched flame. When the flame radius was large, on the other hand, cellular surface generated by intrinsic instability was found. In this range, the flame acceleration was confirmed, which was induced by the evolution of cellular surface. We obtained the parameters of flame acceleration model and predicted the flame propagation velocity depending on the flame radius. The increment coefficient normalized by the propagation velocity of unstretched flame became larger at low equivalence ratios, which was due to stronger diffusive-thermal instability. Under the same equivalence ratio, the inert gas addition caused the increase of normalized increment coefficient. This denoted that the inert gas addition promoted the instability of premixed flames, which was due to the reduction of the effective Lewis number. The maximum pressure in a combustion vessel became lower in the case of inert gas addition. Moreover, the maximum pressure of experiments was lower than that of calculations under the adiabatic conditions, because of heat loss during premixed combustion. The obtained results were valuable knowledge to elucidate the hydrogen explosion at Fukushima Daiichi Nuclear Power Station.