The ignitability of the R290/air mixture by arc discharge at the gap of the electric contacts was experimentally examined. A series of ignition tests were conducted by opening and closing a pair of electric contacts, and the voltage between the anode and cathode, and the current through the circuit were measured. The varieties of electric load, power consumption of the circuit, and composition of the R290/air mixture were varied under the experimental conditions. The ignition frequency showed an upward convex curve against the equivalence ratio, and it was taken maximum value near ϕ = 1.3 (approximately 5 vol% of C₃H₈). It was easier to ignite when the electrical contacts were opened than when they were closed. It was also observed that ignition occurred more easily with increased power consumption. The minimum energy generated at the gap of the electric contact in the case of ignition (E_{arc_m} ) was much larger than the minimum ignition energy (E_min). This was because the contribution rate of energy available for ignition was much smaller than in the case of capacitive spark ignition. The net energy contributing to ignition (E_cont) is less than 6% of the E_{arc_m} at most because go or no-go of ignition can be distinguished well by comparing and Econt(=0.006E_{arc_m}). This almost coincides with the data reported in the literature.

In order to improve the boiling cooling heat transfer, the effect of a porous coating layer with a large porosity on the natural convection boiling heat transfer was investigated using a frost layer formed and grown on the surface of an oxygen-free copper sphere with diameter d=25mm as a coating layer under natural convection. First, the thickness of the frost layer formed and grown on the spherical surface, the amount of frost deposition, and the heat transfer characteristics during frost deposition were clarified, and the physical properties of the frost layer, such as apparent density and apparent thermal conductivity, were investigated. Next, the thickness of the frost layer was varied from 0.29 mm to 0.95 mm, and it was shown that the enhancement of heat transfer can be achieved in the whole boiling range by covering the frost layer. As a result, the effectiveness of the method of accelerated boiling cooling using the frost layer coating layer as a high heat flux and high heat transfer coefficient cooling technology was clarified.

A novel frosting model based on Burton–Cabrera–Frank theory is developed. The proposed model contains correction factors for the amount of desublimation (βinn and βsf) and a parameter related to effective diffusivity in frost (F). βinn should be set to approximately 10^-3 because of the impact of released latent heat and vapor consumption due to desublimation at nearby interfaces, and the growing ability of ice crystals depending on their crystallographic orientation. In addition, F should be set to approximately 5 to account for the effect of complex transportation of water vapor in frost. Without considering this effect, the frost becomes dense only near the surface. The density distribution becomes inconsistent with experimental findings. This compromises calculation accuracy. Moreover, calculations are performed to validate our model under the following frosting conditions: 243.15 K ≤ Tp ≤ 263.15 K and 8 g/m³ ≤ ρv ≤ 16 g/m³, where Tp is the cold plate temperature, and ρv is the absolute humidity. The results show that the present model can predict the frost mass and average frost thickness with a maximum error of less than 15% at 600 s under a wide range of conditions.

Frost formation in cryogenic heat exchangers causes problems in utilizing the cold energy of cryogenic fuels. Frosting on the cryogenic surface is accompanied by mist formation, and the frosting mechanisms have not been fully elucidated due to the complexity of the phenomena. In this study, we investigated frost formation on a flat plate under forced convection. We observed mist layer with a laser sheet light source and frost crystals using a macro lens camera. In addition, frost mass, frost shape, and mist layer height were quantitatively measured. The mist was observed at cooling surface temperatures below 75°C. It was quantitatively revealed that the lower the cooling surface temperature, the longer the mist generation time, and the greater the effect on mass and frost shape. It was found that frost formation begins with mist deposition when the mist forms, but eventually, the frosting mechanism transits to desublimation due to the increase in the surface temperature with frost growth.

All three themes of food technology development in the roadmap of refrigeration and air conditioning technology 2050, issued by the Japan Society of Refrigerating and Air Conditioning Engineers in 2020, are closely related to the cold chain. This paper reviews research trends in the food cold chain since 2000 and discusses future prospects of the themes of food technology development in the roadmap of refrigeration and air conditioning technology. A total of 197 papers included “food” and “cold chain” in the main text and “cold chain” in the title among all research and review papers since 2010 in all academic journals included in ScienceDirect, and two-third of the papers (130 papers) were published within recent five years. Among three themes of food technology development in the roadmap of refrigeration and air conditioning technology 2050, establishing a quality evaluation model for comprehensively assessing a set of freezing, thawing, and eating was considered to be the most challenging issue due to the lack of directly helpful papers for attaining the goal within the range of previous studies reviewed by this paper.

It is considered that the supercharging effect occurs at the second cylinder of the two-stage compressor as well as in the single stage compressor. However, the conditions for causing supercharging effect are not clear, nor is the characteristic of intermediate pressure variation itself. Therefore, in this study, a one-dimensional simulation model for the two-stage compressor was developed. Numerical simulations regarding the rotational phase difference between two cylinders and the resonance of the standing wave in the connection pipe were conducted. Simulation results showed that the average suction pressure changes periodically with respect to the phase difference due to the supercharging effect. And if the standing wave in the connection pipe is in resonance, the supercharging effect will be enhanced. However, even if the standing wave is in resonance, the supercharging effect will not occur unless the phase difference is not appropriate.

A carbon-neutral society is working towards the realization. One of the energy-saving solution is an energy management system. This paper proposes utilizing solar power through energy-saving and energy management by connecting air conditioning and water heating systems to direct current (DC) and constructs a system which includes solar panels and batteries. We constructed an experimental bench system, confirmed its fundamental performances, and demonstrated the potential for improving the coefficient of performance (COP) through the control of DC voltage. Furthermore, simulations conducted throughout one year, we confirmed a 40% reduction of system losses by connecting DC and verified the effective utilization of generated power by operating the heat pump water heater at the daytime.

In this study, a heat conversion system that supplied heat at temperature between 150 ^oC and 200 ^oC was proposed. By combining a CPC-type solar collector, which is suitable for collecting heat up to approximately 150 ^oC, and an adsorption heat pump with heat transformer cycle, this system can output heat at a higher temperature than the collected heat. In addition, using weather data for one month each in winter and summer, a theoretical prediction of hourly heat output was performed. The superiority of this system was recognized in the case of heat supply in a high temperature range where the amount of heat supplied by the collector alone was small or zero. Calculations showed that this system was suitable for heat supply at temperatures from 160 ^oC in winter and 180 ^oC in summer up to 210 ^oC each. Furthermore, when the output temperature was fixed, the optimum temperature rise range of the adsorption heat transformer cycle, which showed the maximum value of the heat output, could be predicted. Finally, it was found that the heat collected at 150 ^oC could be heated to 275^oC in winter and 225^oC in summer.

This study experimentally investigated the wetting transition behavior of deposited fakir droplets and in-situ condensed droplets on different microstructured surfaces. Diamond-like carbon was introduced as the substrate for superhydrophobic surfaces (SHS) to enhance the durability of the microstructure and ensure the repeatability of the experiment data. An important outcome of this study is demonstrating a slippery superhydrophobic surface with a low depinning force that suppresses the transition from the Cassie–Baxter state to the Wenzel state for microdroplets less than 0.37 mm in diameter. By selecting an appropriate pillar pitch and employing tapered micropillars with small pillar widths, the solid-liquid contact at the three-phase contact line was reduced, and low depinning forces were obtained. In the case of in-situ condensed droplets, the interface of the SHS was modified by introducing multiscale roughness via the coating of nanoparticles on the micropillars; and by enclosing the micropillars with walls. The new interface could also effectively suppress the wetting transition of condensed droplets (for drop diameter > 900 μm) during their growth via merging with neighboring droplets. The SHS with the modified interface is expected to show better performance for dropwise condensation and anti-icing.