In the design of heat exchangers, a combination of thermal fluid simulation and various optimization methods has been studied to find a structure that satisfies trade-off performance such as heat transfer coefficient and airflow resistance. However, most of the methods reported before are methods for single-objective optimization, on the other hand, multi-objective optimization methods have problems such as reducing the number of analyzes. In this report, we apply design of experiments and multiple regression analysis to find the possible range of heat transfer coefficient and airflow resistance with fewer analysis times, and devised a method to derive the optimum structure that matches the specifications from that range. Furthermore, the effectiveness of this design method was verified by applying it to the design of a flat tube heat exchanger, and how to improve prediction accuracy was presented.

In the field of evaporators used for refrigeration and air conditioning equipment, it is required to reduce refrigerant charge due to new refrigerant rules. Methods using liquid film flows such as falling film have been getting attention because of the less refrigerant charge than that of fully flooded heat exchangers. One of the promising methods is the shear-driven liquid film flow. This method makes the liquid film thinner by flowing a fast gas stream, resulting in higher heat transfer performance. In our research, we designed an experiment system to observe liquid film behavior and measure the local heat transfer coefficient simultaneously. The effect of heat flux on the liquid film behaviors and the corresponding heat transfer coefficient of the shear driven liquid film flow is experimentally investigated.

This study experimentally investigated the heat transfer and flow characteristics of falling film boiling of R1234ze(E) on a vertical plate to clarify the effects of behaviors of boiling bubble, liquid film breakdown and dry patch on heat transfer and flow characteristics to HFO refrigerants. The liquid film flowed down with waves at the vapor-liquid interface. The generation and collapse of boiling bubbles were observed in the liquid film. As the heat flux increased, while the film Reynolds number decreased, the size of the dry patches increased. However, the dry patches were rewetted by thicker liquid film flowing at higher liquid mass flow rate. The heat transfer coefficients increased with increasing heat flux and refrigerant pressures and drastically decreased owing to the expansion of dry patches. In addition, the wet area fractions and heat transfer coefficients began decreasing at almost the same film Reynolds number.

We propose a method to enhance boiling heat transfer on the inner surface of a pipe by grooving the inner surface and filling the grooves with silicone sealant. Experiments were conducted to measure temperature variation of a pipe cooled with liquid nitrogen and liquid hydrogen. Stainless steel pipes with an outside diameter of 1/2 inch (12.7 mm) and a length of 120 mm were used in the experiments. Experiments were conducted using the pipes having different spacing of the grooves on the inner surface. The effect on the cooling rate and the heat flux calculated from the temperature variation in time were investigated. In the experiments using liquid nitrogen, the modified pipe reduced the cooling time by 1/3.6 due to the suppression of film boiling. By contrast, the cooling time could not be reduced in the experiment using liquid hydrogen. The unique physical properties of hydrogen and its heat transfer characteristics may have affected the results.

The objective of this study was to determine the most efficient method for extracting oil from North Pacific krill (Euphausia pacifica). A rapid, single-step extraction using a mixture of acetone and ethanol was employed, and heat treatment was applied to the krill. Additionally, argon gas (Ar) was used during the extraction process to prevent lipid oxidation. The results demonstrated that heat treatment, both in air and under Ar conditions, resulted in higher lipid yields (2.14% and 2.12%, respectively). The extracted krill oil underwent analysis to determine the content of neutral lipids (NLs), polar lipids (PLs), and free fatty acids (FFAs). The krill oil heated under Ar conditions exhibited the highest NLs content but a lower amount of PLs. However, the FFAs content increased for both heated krill samples. Moreover, all krill oils exhibited high levels of n-3 polyunsaturated fatty acids, particularly elevated PLs content, which included icosapentaenoic acid (IPA) and docosahexaenoic acid (DHA) (18.83 – 26.64 and 26.45 - 33.87 g/100 g of lipid, respectively). These components were present in the extracts, with greater prominence observed for the Ar treatment condition. However, the peroxidation value and presence of thiobarbituric acid reactive substances indicated that heat induced lipid oxidation, thereby reducing the lipid quality. Therefore, heat treatment proved beneficial in enhancing lipid yield, although it also had a negative impact on lipid quality. Conversely, the use of Ar during extraction was found to delay lipid oxidation compared to other extraction methods.

In recent years, while demand for heat energy is high in the industrial field, there is a strong need to improve the efficiency of conversion to heat power and other forms of heat energy for processes with low utilization efficiency and the release of surplus heat such as steam that has value in actual factory and other processes. We have proposed the introduction of heat pump technology as a solution to this need. By efficiently raising the temperature of waste heat to a reusable level and by introducing heat pumps to processes with low utilization efficiency, it is expected that significant energy-saving efficiency can be achieved for the entire process. On the other hand, it is necessary to determine the effect of introducing heat pumps based on the annual operation plan of the process in advance, but it is difficult to analyze this effect experimentally. For this reason, it is effective to establish a method to analyze the effect of introducing heat pumps relatively easily by introducing mathematical analysis. In this study, we report a simulation technology to clarify the installation effect of industrial heat pumps by establishing a versatile analysis logic that can easily analyze the annual installation effect of heat pumps consisting of various refrigerants and cycles.

The emulator-type load-based testing methodology is proposed for evaluating the actual performance of air conditioners. The methodology consists of a software that can arbitrarily simulate the dynamic modulation of the building side load-environment, and a testing facility for the real-time measurement of the system performance based on the air-enthalpy method. This paper investigates repeatability and reproducibility of the results obtained from this testing methodology. Round-robin tests were conducted for the same air conditioner within three different testing facilities. The reproducibility level of the corresponding test results demonstrated a deviation within 5%. On the other hand, it was pointed out that the followability of the temperature of the equipment could have a significant influence on the control response of the air conditioner, and as a result, on the level of reproducibility of the test results.

Different types of refrigerator have various partial load performance in terms of fuel or electricity consumption. It is not clear what operation is effective to reduce input energy when different types of refrigerator are combined because the total performance depends on the characteristics of partial load. The objective of this study is to derive the optimal solutions theoretically under the objective function minimizing input when two types of refrigerator with different partial load performance are involved to provide cooling in single time period. The results indicate the conditions where two types work together or one of them is advantageous. Furthermore, assuming quadratic functions of partial load performance, this study also reveals mathematical expression of the competitiveness in terms of the parameters of the quadratic function. Based on the theoretical solutions, a numerical example is also shown comparing the competitiveness of compression chillers and an absorption chiller.

The powder type activated carbon MSC-30 was adopted to analyze the adsorption characteristics of the working pairs utilizing a low Global Warming Potential(GWP) freon refrigerant in this study. The MSC-30 has a larger specific surface area than silica gel which has been widely used as an adsorbent since it is expected to be able to obtain a larger adsorption amount. The low GWP freon refrigerant R 1233zd (E) was selected as an adsorbent in this study, and it is compared with R 1234yf which is the same GWP refrigerant. It was observed that R 1233zd(E) showed a higher adsorbed quantity and a faster adsorption speed than R 1234yf. The isosteric heat of adsorption was predicted taking into account the volume change in the adsorbed phase, it was observed to be approximately the same for both working pairs. These kinds of fundamental information on adsorption working pairs can be considered useful information to utilize activated carbon for the collection, separation, and regeneration of freon refrigerant.

In this research, we focused on the latent heat emulsion to investigate the creation of phase-change cold storage material that maintains fluidity below 0 ℃. The D-phase emulsification method was used to generate the emulsion. And it was generated by using an aqueous solution of ethylene glycol as a dispersion medium and dodecane as a phase change material. The experimental results showed that a fine emulsion was generated by using polyoxyethylene (20) sorbitan monooleate and sorbitan monooleate as surfactants. The average particle diameter of the sample was approximately 0.24 μm. Additionally, from an evaluation experiment using the sample, it was ascertained that the sample could maintain emulsified state for 90 days and it could remain fluid even when the phase change material in the sample was solidified. Moreover, it was revealed that the sample had approximately 60 mJ/mg enthalpy of fusion from the measurement result of a differential scanning calorimeter.

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.

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.

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 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.

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.

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 E_cont(=0.006E_{arc m}). This almost coincides with the data reported in the literature.

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.

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.

Industrial heat pump is recognized as one of decarbonization technologies in industry by a couple of its high efficiency and electrification with low carbon electricity. For expanding applications of heat pumps into various industrial heating processes, it is necessary to increase the supply temperature of heat pumps. Recently, some new refrigerants have been developed, which allows to expand the options of refrigerants expected to be applied to high temperature heat pumps. The purpose of this study is to illustrate working domain map which can determine the promising refrigerant and the upper limit of heat pumping temperature lift for each supply temperature. With thermodynamic analysis for simple heat pump cycle, refrigerant selection in the wide range of the heat pump supply temperature from 60°C to 200°C is analyzed comprehensively for 17 pure refrigerants currently available on the market. In addition, the effect of an energy efficiency improvement by two-stage cycle with economizer is examined on the refrigerant selection.

Some studies examined that acoustic wave could enhance the adsorption process where the velocity amplitude dominated the enhancement effect. The objective of this study is to investigate the adsorption enhancement effect induced by oscillating flow experimentally. The frequency of the oscillation is as small as 0.05 Hz, which is much lower than the acoustic wave. An oscillating flow with reverse flow was successfully created using 2 blowers. It was observed that almost no enhancement happened when non-dimensional velocity amplitude is about unity while the effect increases as the velocity amplitude becomes large. It was also confirmed that the effect decreases when the air humidity from the downstream side of the adsorbent is low. It suggests that the reverse flow transfers humidity from down stream side. The results indicate that oscillating flow with reverse flow is essential for the enhancement, and it is necessary to supply moist air to the both side of the adsorbent pack to attain the effect.

The red blood cells in the blood can flow inside the capillary blood vessel for the deformation of themselves. In order to add the deformation characteristics to the latent heat capsule, gelatin capsule was used in this study. The purpose of this study has been to investigate the flow drag and heat transfer characteristics of gelatin capsule slurry containing latent heat storage material (= heptadecane) in the straight pipe. When the phase of enclosed heptadecane is different (solid, or liquid), the gelatin capsule diameter is not different, but its softness is different by visual observation. From the flow drag and heat transfer characteristics of gelatin capsule slurry containing heptadecane on the straight pipe test section, the friction factor of this gelatin capsule slurry agrees well with that of the water flow in any capsule concentration. On the other hand, the heat transfer of this gelatin capsule slurry was higher than that of water with increasing capsule concentration. And the heat transfer coefficient containing liquid heptadecane is larger than that containing solid hepatadecane. These are due to that the gelatin capsules breaks a temperature boundary layer near the pipe wall. This tendency was influenced by the deformation of gelatin capsule.

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.

In many positive displacement compressors, it is important to design oil supply structures to seal and lubricate small clearances with oil, but unknowing of the presence of oil film in them hinders their effective design. In this study, a new gas-liquid detection method in a small clearance is being developed, in which the tip of an optical fiber probe is placed in a small cavity formed on the clearance surface. This method thus requires that a fluid entering the clearance also fills the cavity to ensure that the probe contacts the inlet fluid to be detected. Characteristics of filling the cavity without the probe were investigated by experiment and calculation of two-phase flow, which revealed that the cavity is filled with inlet fluid when the Weber number is less than around one. The calculation with the probe also demonstrated phase changes in 10-µm clearance can be detected by this method.

For the gas-liquid two-phase refrigerant flow in the multi-pass channel with a vertical header and horizontal branch tubes that simulates the parallel-flow type heat exchanger used for residential and commercial air conditioners, the influence of evaporation of liquid refrigerant in branch tubes on the gas-liquid distribution characteristics in the channel was experimentally investigated. The test channel had a vertical header with a height of 81.5 mm and 8 horizontal aluminum microchannel branch tubes connected in parallel to the header at a pitch of 10 mm, and all the branch tubes were heated evenly at 20 – 100 W/tube. It was found that the excessive liquid distribution to the lowermost branch tube was suppressed by heating the branch tubes, while the amount of liquid distributed to the upper branch tubes increased. As a result, the uniformity of the liquid distribution was improved by the evaporation of the liquid refrigerant in branch tubes.

Ammonia falling film and pool boiling evaporation experiments were conducted on three horizontally placed types of stainless tubes, namely smooth, low fin and 3D fin and enhancement of heat transfer was examined. For the falling film tests, heat transfer coefficients of the smooth tube decreased with increasing circumferential angle starting from the top of the tube. For finned tubes, however, liquid film was held between the fins, thus causing decrease in heat transfer coefficients. A comparison of average heat transfer coefficients in the low Reynolds number range shows that the smooth tube had the highest heat transfer coefficients followed by 3D and low finned tubes respectively. Heat transfer enhancement by the fins was not observed. In the high Reynolds number range, convection occurred in the liquid film between the fins of the 3D tube but it was not very significant and the heat transfer coefficients are similar to those of the smooth tube. Pool boiling heat transfer coefficients of the smooth tube agree well with Jung et al. correlation while those of the low fin and 3-D fin are 20-30% lower. A comparison of falling film and pool boiling heat transfer coefficients of the three types of test tubes shows that falling film heat transfer is higher than pool boiling.