It is necessary to establish carbon recycling technology toward the realization of carbon neutrality. In our laboratory, we have focused on the decomposition and reduction ability of atmospheric pressure plasma and have been developing plasma devices for CO₂ decomposition and reduction. Results so far has reported particles containing carbon are deposited on the electrode surface inside the reactor after treating CO₂ with atmospheric pressure plasma. The purpose of this journal is to investigate the generation behavior of plasma jets and to analyze the generated carbon-containing particles by CO₂ and CO plasma jets. A metal plate was irradiated with this CO₂ and CO plasma jet, and the surface of the metal plate was observed and analyzed by SEM-EDX. As a result, trace amounts of carbon-containing particles have been confirmed on the surface of the metal plate. In other words, we have succeeded in producing carbon-containing particles outside of the reactor.

Volatile organic compounds (VOCs) emitted from painting and printing industries are the cause of photochemical smog and suspended particulate matter (SPM) such as PM2.5, and treatment technologies for VOCs as air pollutants have been studied. Nonthermal plasma treatment is one of such methods. In this study, a wet-type catalysis plasma reactor packed with α-alumina and using a water film is proposed to increase the treatment efficiency of VOCs and suppress the generation of byproducts. The decomposition of toluene, a typical VOC, was performed at a gas flow rate of 10 L/min and a water film flow rate of 100 mL/min, and the average toluene decomposition efficiency was 74%. As for byproducts, the use of the water film resulted in no organic byproducts and NOx emissions in the wet process compared to the dry process, and the concentrations of CO₂, CO, and O₃ emissions were also reduced.

In recent years, reduction of CO₂ emissions, a greenhouse gas, is required to mitigate climate change caused by global warming, and CCUS has been attracting attention as a method to achieve this goal. In our laboratory, we are developing a device to decompose and reduce CO₂ separated by CCUS to carbon by atmospheric pressure plasma. In this study, we investigated the effects of reactor geometry and electrode length on CO₂ decomposition and reduction to develop a plasma reactor optimized for CO₂ decomposition, and measured changes in CO₂ decomposition rates in two types of plasma reactors (stand type and cylindrical type) with electrode lengths from 25 to 150 mm. decomposition rate in the range of 25-150 mm electrode length using two types of plasma reactors (stand type and cylindrical type).

Ammonia is attracting attention as a hydrogen carrier that can efficiently transport and store hydrogen to realize a low-carbon society. However, the system exhaust gas contains leakage ammonia in the order of ppm, which must be treated before being released into the atmosphere. In this study, we attempted to adsorb and decompose leakage ammonia using a plasma reactor with a zeolite-filled reaction field. Under the experimental conditions, the characteristics of ammonia decomposition and hydrogen production were investigated when low-concentration ammonia gas (diluted with nitrogen gas) was discharged for decomposition. The ammonia decomposition rate of 91.8% was confirmed for a simulated exhaust gas (NH₃ conc. = 5090 ppm) at a gas feed rate of 2.0 L/min and an applied voltage of 19 kV. The ammonia decomposition rate increased with an increase in the applied voltage and residence time, but it was also confirmed that some ammonia regeneration reactions were occurring.

It has been reported that CO₂ accounts for approximately 76% of the greenhouse gases responsible for climate change. To reduce CO₂ emissions, the development of CCU technology has been actively pursued. We have developed a new method of CO₂ decomposition by vacuum ultraviolet ray (VUV). An excimer lamp capable of emitting a single wavelength of VUV is installed in a VUV photoreactor, and a unique chemical reaction occurs when the VUV is irradiated onto the target gas. In this report, the CO₂ decomposition characteristics of VUV irradiation were investigated for the CO₂/N₂ system; a maximum CO₂ decomposition rate of 3.33 % was obtained in the CO₂/N₂ system using VUV at 172 nm, with an inlet CO₂ concentration of 100 % and a gas residence time of 1020 seconds. The CO₂ decomposition rate increased with increasing residence time and initial CO₂ conc., indicating that the CO₂ decomposition behavior changed depending on the VUV wavelength. The maximum CO₂ decomposition rate by VUV at 146 nm was 3.23%.

Measures to prevent the spread of COVID-19 are critical across the globe. Although a tour bus can carry many people at once, the small closed space is crowded with many people for long periods. Therefore, there is an increased risk of infection on tour buses. The air outlet of an air conditioner is designed to prioritize heating and cooling over ventilation. The aim of this study was to improve the ventilation performance of tour buses. To this end, a large-scale ventilation simulation was carried out using a supercomputer. The results are as follows: (1) when the overall ventilation air flow rate was fixed, it was necessary to intensively install new outlets in the upper rear part of the tour bus for rapid ventilation and (2) the ventilation efficiency was higher when a small number of high-output outlets were installed in the stead of a large number of low-output outlets. The reason for more effective ventilation was to create a large airflow in the tour bus. We proposed the design of a highly efficient ventilation system in a current bus space and elucidated the appropriate layout of ventilation outlets and the optimal protocol for opening windows.

Nuclear power plants are equipped with several facilities to prevent radioactive materials from leaking into the surrounding environment in the event of a severe accident such as a loss of total power supply (station blackout, SBO). One of them is venting to prevent the Primary Containment Vessel (PCV) from being damaged due to pressure increase inside the PCV. In the venting operation, hydrogen and water vapor (vent gas) inside the PCV are released outside the PCV to reduce the pressure inside the PCV and maintain the integrity of the PCV. The filtered containment venting system (FCVS) removes radioactive materials from the vent gas before releasing them to the environment during the venting process. On the other hand, in actually, when the filtered containment venting system is used, the flow rate of the vent gas varies with time after the start of venting because the vent gas is discharged into the environment from PCV. In addition, the removal efficiency of radioactive materials by the filtered containment venting system is greatly affected by the flow pattern of the venturi scrubber nozzle. However, previous studies have not clarified the change in flow pattern due to the change in vent gas flow rate. In this study, the vent gas flow rate into the venturi scrubber nozzle was varied, and the flow pattern inside and outside the nozzle was clarified.

Robot systems capable of experiencing remote environments are urgently required for future lack of manpower and aging society. In this study, development of the tele-existence robot arm in which human beings can experience not only the haptic environment but also the thermal environment was targeted. In this report, the temperature transmission system was developed and the trial operation was conducted. In the test, a remote temperature measurement finger-tip-like unit touching a moderately(50degC)-heated metal block transmitted a PWM signal of a temperature variation to a on-site wearable unit. Reproduction of the remote temperature sensing data was achieved by controlled heating based on the transmitted information in the wearable unit. In this paper the reproducibility was indicated by the result of temperature variation of the temperature measurement unit of on-site finger probe in the wearable unit.

Research on the stable operation of regional microgrids in order to expand the spread of renewable energy toward carbon neutrality in 2050 and to provide a stable supply of electricity in the event of a disaster. In this research, the main power source will be photovoltaic power generation that can be used anywhere, and we will consider equalizing the amount of power generation by distribute power to demand arrea. In addition, by using the EV battery as a storage battery, it is possible to reduce the cost associated with installing the storage battery. This study assumes Morimachi, Hokkaido. Calculate the error in the amount of solar radiation in Morimachi and the surrounding area, based on that, the capacity of the power plant will be distributed . Calculate the power plant capacity and the number of solar module by calculating so that the power demand in the assumed area matches the annual expected power generation amount. After that, the surplus power generation amount for one hour is calculated using 22 May, Annual average, which is the maximum amount of solar radiation, and the storage battery capacity per vehicle is determined. Finally, the number of years of profit recovery compared to the purchase of electricity is 10.639 years. When the recovery period is calculated with the power demand as a variable, it is possible to realize up to about 300 GWh when the investment standard is 20 years.

The research aim of this study is to put forward insights on integrating decentralized renewable energy systems and mobility solutions targeted for the rural parts of the country. Several assessment methods are employed here, including Technological Readiness Assessment (TRA), Life Cycle Assessment (LCA), and visualization tools such as QGIS to understand better how these micro-developments can be done. Furthermore, we developed a solution showing that non-utility scale renewable systems can support electrification needs in rural areas of the country - decentralized and micro-scale hydropower and PV, small scale wind power. As for mobility, rural transport demands can be met while maintaining eco-friendliness with ULVs in place of motorcycles and reduce the overall gasoline consumption. The proposal further suggests integrating non-utility scale generation infrastructure with ULVs to provide a decentralized ecosystem for rural areas.

In order to achieve carbon neutrality by 2050, the introduction of renewable energy sources for the supply of electricity and heat will be necessary. Therefore, this study examines the supply of energy to Hakodate City from a 722 MW rated offshore wind turbine planned off the coast of Hiyama in southern Hokkaido. In the proposed system, the output power is transmitted to Hakodate City via a transmission line. The transmitted power is divided at a substation in the city into (i) power to be supplied to the demand side using transmission lines and (ii) power to produce water electrolysis hydrogen and convert it into MCH. The MCH produced is supplied to fuel cells installed in the city by pipeline via dehydrogenation equipment to supply hydrogen gas to the fuel cells to generate electricity. The heat generated during power generation is stored, and the heat is sent to nearby dwellings and facilities, where it is converted into heating and hot water for use. Considering the efficiency of each device, all output was converted to MCH and supplied, resulting in 18.3% of the annual electricity demand and 9.66% of the annual heat demand. However, when comparing the annual output of wind turbines with the annual energy demand, the output is more. Currently, the optimal values for separating power for water electrolysis and power for transmission are being studied and a more advanced analysis flow is being prepared, including storage of MCH.

Ammonia and hydrogen are attracting attention toward carbon neutrality in 2050. When these ammonia supplychains are introduced, the use of renewable energy is expected to expand. However, it takes a lot of cost and time to develop a power grid to expand renewable energy, so we will consider the case of using the existing Natural gas pipeline for energy transportation. For the ammonia supply-chain using the existing pipeline, the economic efficiency will be evaluated using the method of discounted cash flow, and the environmental performance will be evaluated from the amount of air pollutant reduction in the replaced coal-fired power generation. From the results described above, we will investigate the possibility of introducing ammonia supply-chain derived from renewable energy using the existing Natural gas pipeline. In this research, we examine Sapporo, Japan. Water electrolysis will be performed using the power of offshore wind power generated in Ishikari Bay, and the obtained hydrogen will generate ammonia, which will be transported by the existing Natural gas pipeline. The following three cases will be analyzed. When transport with ammonia, case of compressed hydrogen, and case of reinforced transmission lines. The energy and exergy flow of these cases will be clarified to obtain the total energy and exergy efficiency of the system. Use the method of discounted cash flow to analyze the payback period years from energy efficiency.

Cooling demand has been increasing globally, which has caused an increase in electricity demand. There is a large amount of unused heat, such as waste and solar heat, which can supply cooling heat with smaller electricity consumption by using heat-driven refrigeration systems. We have investigated an ejector refrigeration cycle as one of the heat-driven refrigeration systems that can be driven by a lower-temperature heat source than absorption or adsorption refrigeration systems. Testing the performance of the ejector refrigeration cycle using R1224yd(Z) as a working fluid has already been reported as the COP, refrigeration capacity to the electric power consumption of feed pump, reached over 40. The COP is not a convenient index for evaluating the system because we can not know the distance from the theoretical efficiency, and it is not convenient for comparison with other energy-conversion systems. The theoretical efficiency is presented as unity of the exergy efficiency for any energy-conversion system. The exergy efficiency of our ejector refrigeration cycle testing device reaches 0.33, which is greater than that of PV solar panels, similar to that of air conditioning systems, but smaller than that of a power plant.

Currently, the delivery industry faces various challenges, including a shortage and aging of delivery personnel, deterioration of the working environment, and increased demand for home delivery． Furthermore, COVID-19 has necessitated a shift to contactless and non-face-to-face logistics． A home delivery service using multi-benefit mobility is an effective solution to these issues． Multi-benefit mobility can be used for garbage collection, human transportation, home delivery, and other purposes by using a standard chassis and changing the unit part to suit the intended use． In this study, we developed an automatic delivery robot for home delivery service and planned to improve it to a multi-benefit mobility system． In addition, the technology required to realize a delivery service using an automatic delivery robot that can run on public roads for social implementation in the M area was summarized.

To improve the low-temperature waste heat recovery and its utilization, we proceeded with the development of a low-temperature-driven absorption chiller adopting a double-lift absorption cooling cycle. In the previous reports, we developed a proof-of-concept prototype, and it delivered chilled water at approximately 7 °C when driven by a 60 °C heat source hot water inlet and 30 °C cooling water. We confirmed the reliability of this result from the heat balance of the experimental data, according to the AHRI standard. Cooling capacity in the above conditions was 7.1 kW, which was approx. 1.0 kW smaller than expected. We found approximately 1.31 kW of internal heat loss across the separating plate between the low-temperature evaporator and the low-temperature absorber. The capacity degradation was explained by this internal heat loss clearly. This report examined this cycle’s cooling water temperature characteristics as the next step. We computed the behavior of the prototype when the cooling water varied from 24 °C to 36 °C using a cycle simulator. These results were validated by comparing the calculated results with the experimental data of the prototype. The simulation result agreed with the experiment by ± 5% for the cooling capacity and ±0.01 for the COP. Finally, we predicted the performance of this cycle without the internal heat loss. As a result, we found that cooling capacity increased by 7.9%, and COP improved from 0.32 to 0.36 in approximately 9 °C chilled water output conditions in the case that prevents the internal heat loss.

To date, although performance evaluation of air conditioner considering both of room and air conditioner has been done to realize high efficiency operation in the actual environment, control system of air conditioning has not been considered sufficiently. Therefore, in this study, we simplify the control system of air conditioning and reveal the room temperature change and the other responses against step input of preset temperature to know the effect of air conditioning system on the room temperature control. Also, we considered the effect of trying to keep air and objects in the room at the same temperature as the room characteristic and expressed it by heat transfer coefficient. As a result, it was revealed that it can take time for the room temperature to reach preset temperature and the overshoot can become bigger when heat transfer coefficient is changed even in the simple room. The results show that the control performance of air-conditioning system can be inefficient when the room characteristics is changed.

In order to provide a comfort thermal environment to each occupant whose clothing and thermal sensitivity are different, it is necessary to make a proper temperature gradient in a room. In this study, an inverse method using source-receptor (SR) relationship was used to estimate optimal inlet temperature of each air conditioner to make temperature field close to objective field. To validate the method, the method was applied on an existing class room. The SR relationship was calculated by CFD simulation, and the optimal inlet temperature to approximate temperature field to objective field was estimated by using SR relationship. Though the method worked well, the improvement was small in the numerical experiment, because of spatially weak relationship between the inlet temperature and indoor temperature field.

For the practical application of the low Global Warming Potential (GWP) refrigerant, which has been actively studied recently, it is necessary to determine the optimal amount of charge required for the system and evaluate the performance in the design stage of the HVAC system. However, it is reported that the low GWP refrigerant has the characteristics of zeotropic refrigerant and has different characteristics from the existing refrigerants. Among the various characteristics of refrigerants, the void fraction is one of the essential characteristics concerning the amount of charge of the refrigerant. Therefore, to predict accurately the charge amount of the low-GWP refrigerants including zeotropic refrigerants in the system, it would be required to examine whether the existing void fraction correlation equations can be applied to lowGWP refrigerants. In this study, the void fraction was measured for R454C, which is a low-GWP refrigerant, and among the conventional correlation, the Smith, Chisholm and Steiner correlation were found to predict the void fraction of R454C within acceptable error limits, in that order.

In order to distribute dilute gas into a room with the proper concentration, the gas generator must be controlled appropriately. We determined the optimal source position and generation rate by inverse analysis. The optimization was performed using the SR (Source-Receptor) method, which assumes the linear relationship between the source intensity and the concentration and inversely estimates the source conditions to achieve the objective concentration at target points. In this study, indoor concentration in a classroom was numerically controlled with CFD calculations. The SR method could estimate the optimal location and generation rate of gas generators to approach objective concentration distribution. Optimal source conditions for the class room with a steady flow field was successfully determined. Compared to CFD-only calculations, the SR method significantly reduced the computational cost.

Ice slurry is attracting attention to solve the problems of uneven cooling and difficulty in mass transportation of crushed ice. When the ice slurry is transported through the pipe, there is a concern that the ice may adhere to the pipe, causing blockage. The results of previous studies revealed that surfactants suppressed adhesion, so surfactants were used to suppress adhesion. In addition, catechin is added to the ice slurry to provide a sterilizing effect from the viewpoint of the transportation of fresh foods. In this study, catechin and surfactant are mixed in pure water to measure ice adhesion force and adsorption. The measurements also reveal the ice adhesion force at each concentration.

The expansion of renewable energy power generation is urgently needed to realize a decarbonized society. However, the high cost of butteries used to adjust electricity fluctuations is hindering the expansion of renewable energy power generation. In this study, we aim to develop a new energy storage method for storing excess electricity by using the unique state change of CO₂ hydrate. CO₂ hydrate is produced at about 0℃ under high pressure of several MPa, and can be dissociated at about room temperature. In the proposed system, the cold and warm heat required for the cooling and heating of CO₂ hydrate is obtained from renewable energy. CO₂ hydrate absorbs CO₂ during its formation and releases high-pressure CO₂ hydrate dissociation. Therefore, the pressure in the reaction vessel becomes high after CO₂ hydrate dissociation. In this study, an expander is driven by the high-pressure dissociation gas of CO₂ hydrate and a generator connected to the expander is operated. The amount of electricity generated in this process will be investigated and compared with the amount of electricity generated when the reaction vessel is filled CO₂. The amount of electricity generated was greater when CO₂ hydrate dissociated gas was used to generate electricity than when the reaction vessel was filled only with CO₂.

In recent years, solid-liquid two-phase mixtures called ice slurry, which consist of water and fine ice particles, have attracted attention in food management. One method of producing ice slurry is the supercooling method, in which the liquid is cooled to a supercooled state and then the supercooling is dissipated. However, the supercooled state is unstable. Therefore, active control of the undercooled state is necessary. In their study, the authors investigated the active control of supercooling by the adsorption of surfactant molecules to the interface by adding a nonionic surfactant to pure water. The results revealed that supercooling can be actively controlled by the concentration of nonionic surfactant. In this study, we measured the average supercooling degree of amphoteric surfactant mixtures at pH3 using SUS304 vessels for each concentration change below and above the critical micelle concentration (C.M.C.) to clarify the relationship between pH and the average supercooling degree of the amphoteric surfactant mixtures.