Ice slurry is a mixture of micro ice particles and water or an aqueous solution, and is expected to be used in various fields such as food cooling and pipe cleaning. However, the agglomeration force of ice particles poses a problem of blockage in pipes. The agglomeration force between ice particles has not been quantitatively evaluated, and its existence is only known empirically. Therefore, the purpose of this study was to quantitatively evaluate the agglomeration force acting on ice particles. The agglomeration force was calculated from the maximum weight that could be held by a simple loading experiment on an ice slurry without flow. In this study, ice slurries were generated using sodium chloride and ethanol as solutes. The agglomeration force of ice particles was found to increase with an increase in the IPF and a decrease in the solute concentration. For the same molar mass, there was little difference depending on the solute.

Nowadays, hydrofluorocarbons used as refrigerants in air conditioning systems are being reevaluated worldwide due to their substantial environmental impact and high global warming potential. This has driven the advancement of next-generation refrigerants HFO1123 considered as a component candidate for next-generation refrigerant mixture due to its zero-ozone depletion potential and low global warming potential (GWP). However, no experimental data regarding its thermal conductivity are available in the open literature. This study investigates the thermal conductivity of HFO1123 in both the liquid and vapor phases. The accuracy and reliability of the apparatus were validated by measuring the thermal conductivity of R134a. The thermal conductivity of HFO1123 was measured using the transient hot-wire technique, employing a platinum wire with a diameter of 15 µm. Experiments were conducted over a temperature range from 233 K to 313 K and pressures between 0.52 MPa and 4.30 MPa. The estimated combined uncertainty of the thermal conductivity measurements is 1.14% for the liquid phase and 1.62% for the vapor phase. The experimental data of HFO1123 were compared with REFPROP 10.0, a predictive extended corresponding states (ECS) model. Furthermore, the residual entropy scaling (RES) technique-based thermal conductivity model of HFO1123 has been applied using the experimental data.

From the perspective of HFC emission control, the maintenance obligation of commercial air conditioners places a heavy burden on both the air conditioner manager and the service provider. Recently, remote monitoring technology utilizing IoT data has been attracting attention as a solution to this issue. Conventional refrigerant leak detection technologies use AI models based on operating or simulation data, but require large-scale data collection and features redesign when adapting to new models. In this study, we proposed a feature design that can be applied uniformly across different models, enabling rapid adaptation to new models. In addition, we improved the method for configurations with different pipe lengths by adding training data and features. The effectiveness of the proposed method was demonstrated through simulation and validation using actual operational data, which revealed differences in estimation results between normal and insufficient refrigerant conditions.

Freeze-dried foods have the advantage of minimal thermal denaturation, allowing for long-term storage at room temperature. Additionally, they are lightweight and have excellent rehydration properties when hot water is added, which makes them suitable for use in soups, porridge, and space food. The mechanism behind the formation of a high-concentration layer on the surface of the sample during freezing was investigated. Observations of the freezing process revealed that as the sample freezes from the outside, the solution in the center becomes concentrated, and a mushy zone was observed in the center. Observation of shapes of the ice extracted from the sample during freezing showed that the ice in the middle of the sample was indented. Additionally, sugar concentration measurements showed that the sample solution gradually concentrated and reaches the eutectic point. Detailed surface sugar concentration measurements revealed that a high-concentration layer formed within the top 1mm of the sample surface, but no high-concentration layer was formed in the outermost 0.5mm. Based on these experimental results, the mechanism of high-concentration layer formation on the sample surface during freezing was elucidated, and a freezing model was proposed.

To utilize low-temperature waste heat below 200 oC effectively, this study focused on a chemical heat storage system employing magnesium sulfate (MgSO₄) hydrates. To overcome practical challenges such as particle agglomeration and low hydration rate of MgSO4, we conducted a fundamental study on the composites of MgSO4 hydrate with mesoporous materials. We prepared the composites using MgSO4 and mesoporous silicas or mesoporous carbons (MPCs), and evaluated pore structure, hydration rates, and heat storage densities of the composites. The results demonstrated that the hydration reactions of the composites proceeded significantly faster than that of pure MgSO₄. Notably, the MPC/MgSO₄ composite achieved a heat storage density of 1130 kJ/kg (per unit mass) and 807 kJ/L (per unit packed bed volume) within 1800 seconds of hydration.

In the widely researches of carbon capture utilization and storage technology to address climate issues caused by greenhouse gas emissions, improving the purity of captured CO2 is a crucial direction. This study proposes a system design that integrates a trans-critical CO2/ionic liquid(IL) absorption refrigeration system(TsCO2-ARS) with a conventional post-combustion amine-based absorption carbon capture system(ACCS). By introducing the CO2 product from the ACCS into the TsCO2-ARS, the aim is to remove water vapor from the CO2 product while minimizing the additional energy demand imposed on the system by the CO2 purification process by using heat exchangers. Measured operational data from a pilot-scale amine-based ACCS were used for the simulation calculations in this study. For TsCO2-ARS, based on vapor-liquid equilibrium experiment data of CO2/ILs and Peng-Robinson equation of state (PR-EoS), the circulation ratio, the cooling capacity and the coefficient of performance, COP of the TsCO2-ARS under optimal working conditions were calculated. For the ACCS-TsCO2-ARS hybrid system, the total thermal energy consumption and energy change in heat exchangers were calculated and compared. The results of this study provide valuable insights for the design and optimization of the CO2 purification technology.

The mechanism of heat-induced gelation of frozen surimi proteins aligns well with the theoretical framework on protein gelation proposed by J.C. Sheftel et al. in their publication. It is well established that the gelation process of surimi proteins proceeds as follows: (1) When mixed with 2.5–3.0% NaCl at temperatures below 10°C (as in the case of walleye pollock), the thick filaments (myosin polymers) within myofibrils dissociate into myosin monomers. (2) During incubation at low temperatures, the presence of NaCl induces partial unfolding (denaturation) of the proteins, exposing hydrophobic regions of the polypeptide chains. (3) The rate of gelation of these partially unfolded proteins depends on the applied temperature. At lower temperatures (5–30°C for walleye pollock), a set-gel forms gradually via intermolecular hydrophobic interactions.Further heating to higher temperatures (85–90°C) significantly increases the rigidity of the set-gel due to extensive hydrophobic interactions, disulfide (S-S) bond formation, and isopeptide bond formation. Conversely, direct heating at high temperatures induces rapid and extensive protein unfolding, leading to coagulation via irregular interactions.

Effective utilization of unused thermal energy is a critical issue for achieving a low-carbon society, and thermochemical energy storage has been attracting attention as a potential solution. Potassium carbonate, with its favorable safety and system stability, is a promising candidate for low temperature thermochemical energy storage. However, the slow hydration kinetics presents a challenge. This study aims to improve both the hydration kinetics and thermal conductivity by supporting potassium carbonate on expanded graphite. As a result, the thermal conductivity increased by a factor of 1.39 to 1.52, while the dehydration onset temperature decreased by over 7ºC, and the hydration kinetics was also enhanced, maintaining cyclic stability. Furthermore, the addition of 1% lithium chloride, aimed at mitigating the hydrophobic effect of expanded graphite, led to a further improvement in hydration kinetics. The dehydration onset temperature also decreased by approximately 6ºC, demonstrating the potential of this material as an effective thermochemical energy storage material with a low regeneration temperature.

The improvement of refrigerator cycle performance was investigated herein. We suggested the thermal and electric hybrid absorption refrigerator cycle. We selected the refrigerant and absorbent as HFC-134a and 1-Butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [BMIM][Tf2N] (Ionic Liquid), respectively. The coefficient of performance (COP) based on input heat energy for the regeneration absorbent and electric power for the compressor was calculated via a static analysis, based on a state equilibrium to evaluate the effect of a compressor work on COP and regeneration temperature. The results show that the hybrid cycle could generate cold heat below 273.15 K, and driven below the regeneration temperature of 333.15 K using a compressor. The absorption pressure of the working compressor increased as the amount of absorption in ionic liquid and COP_system were high. The COP_system was affected by the regeneration temperature, which controlled the input sensible heat and amount of absorption in ionic liquid. For the heat source at temperatures 333.15–363.15 K, the hybrid cycle is superior to the mechanical cycle in terms of COP_electricity. COP_electricity was affected by the liquid pump efficiency. The COP_electricity of the hybrid cycle was higher than the that of the mechanical type if the liquid pump efficiency is higher than 0.1.

To develop for a simple and portable air cooling system, this study investigated a method that utilizes both the cold heat generated when urea is dissolved in water and the latent heat of evaporation absorbed during the evaporation of water in aqueous solution. In the basic experiments, air was blown into water and aqueous urea solution, and fillings were placed in the vessel to promote gas-liquid contact. As a result, the liquid temperature was effectively cooled. A numerical model based on the heat and mass balances were developed to investigate the air blowing process. The depression of vapor pressure due to the addition of urea was considered in the calculation. The present model reasonably predicted the tendency of the easured liquid temperatures especially for using fillings in the experiment. The cooling system is numerically investigated and showed that the effect of urea concentration on cooling by evaporative latent heat was small under low humidity conditions.

Unlike current performance rating standards, in emulator-type load-based tests the tested unit is operated as it would in an actual building. As the native control of the system is kept active, testing facilities are required to evaluate dynamic response of the tested unit. Therefore, various thermal and transport delays occurring within the testing facility may have a significant impact on the recorded performance, and different features across different laboratories may limit result reproducibility. The emulator-type load-based testing methodology responds to this need, and it has been demonstrated that a certain degree of accuracy can be obtained in interlaboratory tests. However, specific measures to improve the reproducibility of dynamic tests have been an open problem in previous studies. Therefore, a new feed-forward compensation technique based on a linearized model that represents the delay characteristics of the condition generator in following the target temperature and humidity signal from the emulator is developed in this study. With the proposed technique, temperature and humidity in the test room can follow the target signal from the room emulator with maximum delays within 60 seconds under various test conditions, and the deviation of the recorded performance can be kept within 2% across different test equipment.

This study aims to develop a unified and simple method for estimating the energy performance of a wide variety of industrial heat pumps. First, energy performance data on industrial heat pumps available in the Japanese market are collected and analyzed. Then, based on the regression analysis, two types of correlations between Lorenz efficiency, which is the second law efficiency, and logarithmic mean temperature lift are developed. The first type correlation can estimate the average COP (coefficient of performance) of industrial heat pumps with single stage cycles with an accuracy of approximately within ±10%. On the other hand, the second type correlation represents the highest performance of existing technologies including two stage cycles and cascade cycles. Both correlations can be calculated by inputting 6 parameters: heat source medium, heat sink medium, heat source inlet and outlet temperatures, and heat sink inlet and outlet temperatures.

The objective of this study is to clarify the temperature and humidity distribution in the desiccant rotor. Thus we focused on the small sensors for “Internet of Things”. In the previous study, we created a measuring system to install the small sensor unit inside the desiccant rotor, continuous measurement inside the rotating material become possible. First part of this report, we confirm the correcting method for sensor response delay when temperature and humidity input were changed was examined. And so, the results of the test, the response delay showed the same characteristics regardless of the differences in air temperature and humidity. The correction equations for the temperature and humidity were obtained. Second part of this report, adsorption/desorption measuring test to visualize inside the rotors was conducted. Two kinds of desiccant rotors with small sensors were created to compare the performance. The small sensors were buried at several points from surface to another side of rotor. Fig. A-1 shows temperature and humidity distribution in the circumferential direction of desiccant rotor. At a regeneration temperature of 55°C, the dehumidification amount decreases with a peak at a rotation angle of 0.3, while the regeneration amount decreases with a peak at a rotation angle of 0.7. Fig. A-2 shows the variation in dehumidification amount along the rotor thickness direction. The dehumidification amount was calculated by averaging the sensor measurements inside the rotor. For Rotor A, 75% of dehumidification was completed at thickness of 100 mm, whereas Rotor B achieved only 56 % of dehumidification. A few dehumidification was shown between 100 – 200 mm thickness of rotor A. Therefore, reducing the rotor thickness should be considered.

The objective of this report is to clarify the temperature and humidity distribution in the desiccant rotor in the variety of latent heat loads. Thus, we focused on the small sensors for “Internet of Things”. In the previous study, we created a measuring system to install the small sensing and logging unit inside the desiccant rotor, continuous measurement inside the rotating material was achieved. Firstly, we confirm the correcting method for sensor response delay when temperature and humidity input were changed was examined. And so, the basic experiment to confirm the response delay was conducted, the delay showed the same characteristics regardless of the differences in air temperature and humidity. The correction equations for the temperature and humidity were obtained. Secondly, an experiment was conducted to visualize the inside of the rotors. Two kinds of desiccant rotors with small sensors were created to compare the changes in dehumidification. The small sensors were embedded at five points from surface to another side of rotor. Fig. A-1 shows the absolute humidity distribution in the thickness direction of each desiccant rotor. In the case of xOA=14g/kgDA, Rotor A dehumidified by approximately 4 g/kgDA over three quarters of the thickness. However, dehumidification wasn’t occurred in the other one-quarter section. On the other hand, Roter C continued dehumidification throughout the entire thickness direction. Under the condition of xOA=5g/kgDA, Rotor C completed dehumidification within the first one-quarter section of the thickness direction. Fig. A-2 shows the variations of relative humidity and equilibrium adsorption amount in the rotor. From this figure, it can be observed that Rotor A does not perform dehumidification along the thickness direction, with the internal relative humidity decreasing from 23% to 8%. The equilibrium adsorption amount, obtained from the adsorption isotherm within Rotor A, is lower than 16 mg/g. The variation in dehumidification amount along the thickness direction is interpretable in terms of the characteristics of the adsorption isotherm. In the Case of the low latent heat load, Rotor A, which has a higher adsorption capacity, was lower amount of dehumidification than Rotor B. This is attributed to the difference in the slope of the adsorption isotherms in the low humidity range.

A higher concentration of LiBr is effective in achieving an even higher performance in LiBr/water absorption heat pump (AHP), but crystal growth occurs and causes blocking fluid stream once the concentration reaches its saturation point. It was pointed that a fine particle slurry of LiBr crystal is formed under a super saturation condition when zeolite powder is suspended into the solution. Then the slurry possesses a potential to improve remarkably the output of heat. This paper proposes a concept of the self-condensation effect contributing to not only significantly higher temperature generation beyond the equilibrium for working in a heating-up mode of AHP but also enlargement of the heat capacity as a heat storage material. The adiabatic maximum temperature in the absorber was estimated based on thermodynamic equilibrium, energy and mass conservation, and the thermodynamic properties for different crystal concentrations in the slurry and evaporator temperatures assuming the case of a batch process in two columns consisting of absorber and evaporator. The slurry with higher crystal concentration than 0.3 kg-crystal/kg-slurry and 0.1 kg-crystal/kg-slurry has the potential to generate a maximum temperature of more than 150 °C under given evaporator temperature of 60 °C and 80 °C, respectively. In addition, the slurry can generate temperatures up to 80 °C with its heat storage capacity peaks at 1300 kJ/kg-slurry while the homogeneous solution heats up only to a low level of temperature at 65 °C with the heat storage capacity of 900 kJ/kg-solution, assuming that the initial temperatures of the solution and the evaporator are fixed at 25 °C and heat over 40 °C is utilized.

An offset-fin type thermal storage module was designed to increase the rate of water vapor diffusion in the thermal storage layer and to promote heat exchange with the thermal storage material by using calcium chloride as the thermal storage material. This study identified the dominant factors of the performance of the offset-fin module based on the results of 200 cycles of heat-charging and discharging. The performance was simulated using machine learning to accelerate the calculation process. A comparison of the experimental and simulation results by using machine learning clarified that the expansion of the thermal storage material has a significant impact on the performance of the thermal storage module.

Liquid film flow is a promising method for reducing refrigerant charge in heat exchangers compared to flooded-type heat exchangers. To investigate the evaporation heat transfer characteristics of shear-driven liquid film flow, where the liquid film is influenced by interfacial shear stress generated by co-current gas flow, experiments were conducted to observe liquid film behavior and evaluate local heat transfer coefficients. This study focused on the effect of liquid flow rate on the film behavior and heat transfer performance of this shear-driven liquid film flow.

A frost-free heat exchanger using silicone oil is developed in this study. This heat exchanger directly exchanges heat between air and silicone oil. First, an orthogonal flow heat exchanger is constructed, where the flow of air is orthogonal to that of silicone oil. In this heat exchanger, oil is scattered downstream because of air flow. Piano wires are placed in an oil column to prevent oil scattering. Oil flows along the wires, and the oil flow is stabilized successfully. However, air flow causes the oil surface to ripple and the surface of the piano wires to be exposed partially to the air. Ice accumulates at the exposed surface and eventually obstructs the oil outlet. Ice accumulation is reduced slightly by applying a hydrophobic coating to the piano wires. However, the coating does not prevent outlet obstruction. Next, we improve the heat exchanger as the oil flows in the same direction as the air. This improvement allows us to remove the piano wires. The developed heat exchanger can be operated without frost formation for 1 h where, during the operation, the pressure loss of the heat exchanger does not increase.

In the refrigeration and air-conditioning industry, various refrigerants have been proposed and studied to cope with global warming and climate change. In recent years, not only fluorine-containing refrigerants but also hydrocarbon refrigerants such as propane (R 290) have started to be adopted mainly for applications with a small amount of refrigerant charge volume in various countries. Since R 290 has a high combustibility and an excessively high solubility in conventional refrigeration oils such as mineral oil or polyol ester (POE), a refrigeration oil in which a refrigerant is hardly soluble may be adopted in order to improve safeness and performances. In general, a refrigeration oil which is hardly soluble in a refrigerant is considered to be poor in oil return to a compressor. However, in this study, the refrigerant solubility of the refrigeration oil and the influence thereof, particularly the possibility that even a refrigeration oil having low solubility has no problem in oil return, including an HFC/HFO refrigerant, are reported.

The objective of this study is to examine a double effect scheme of adsorption refrigeration cycle experimentally. The cycle consists of high temperature cycle (HTC) and low temperature cycle (LTC) where the adsorption heat of HTC is transferred to LTC for the desorption by circulating fluid. Because LTC works without external heat input, COP can be higher than conventional single stage adsorption cycle. This study experimentally investigated how the double effect scheme worked. Silica-gel and FAM-Z02 were selected as adsorbents for LTC and HTC, respectively. The results with the heat source temperature of 90 ℃ indicated that LTC produced cooling with the adsorption heat of HTC, and HTC also generated cooling with the circulating fluid at approximately 50 ℃. Hence, the double effect scheme has been confirmed to work successfully. This study investigated the effect of adsorbent mass allocation to HTC and LTC on the performance in terms of SCP, where 9 cases were examined. The results also suggested that COP could be approximately twice as high as the conventional single stage adsorption cycle because only HTC consumed external heat.

This study investigated the solid-liquid equilibrium data and performance of a HFO-1123/R744 cascade refrigeration cycle. The experimental liquidus temperature obtained by the cooling curve method agreed with the Schröder-van Laar equation with an activity coefficient of 1. COP and volumetric capacity of a cascade cycle using R32 and HFO-1123/R744 in the primary and secondary cycles were numerically evaluated at operating temperatures of -40 ℃, -50 ℃, and -60 ℃. The pinch temperature in the cascade heat exchanger was set as 3 K. For an operation temperature of -40 ℃, the COP is lower than R23, however, the volumetric capacity exceeds R23 at mole fractions of HFO-1123 below 0.19. For -60 ℃, no composition has both COP and volumetric capacity greater than R23, and a third component must be considered.

The effect of adding sodium caseinate on ice recrystallization in 40 wt% sucrose solution at -10°C was investigated. A minor effect on the ice recrystallization rate constant was observed up to 2 wt% sodium caseinate. However, at higher concentrations, a decrease in the recrystallization rate was noted, indicating a suppressive effect on ice recrystallization. Differential scanning calorimetry revealed a linear decrease in the amount of freezable water with an increase in sodium caseinate concentration. Dielectric relaxation measurements at 25°C indicated an increase in the amount of free water with higher sodium caseinate concentrations, while the relaxation time of the water coupled with solutes tended to increase. It was suggested that the effect of adding sodium caseinate on ice crystal recrystallization was due to the combined result of the reduction in the amount of freezable water, the increase in free water content, and the decrease in water mobility.

This research investigates frost growth characteristics on silver iodide (AgI) and platinum (Pt) stripe patterned surfaces, fabricated using UV-lithography, under desublimation and condensation frosting conditions. Different frost growth behaviors were observed between AgI and Pt patterns, i.e. horizontal frost with dendrite-shaped ice crystals grew on the AgI stripes, and a combined frost growth of dendritic horizontal growth at the stripe edges and random growth at the top were observed for the Pt stripes. This study provides new insights into the influences of ice nucleation agents such as AgI for controlling the frost height and density.

This study verifies the effect of temperature and humidity environment on cell structure of vegetables in long-term storage. The time-course changes in the cell structure, were evaluated after storing the vegetables in the “brine type refrigerator” capable of maintaining low temperature and humid environment or the generic direct expansion type refrigerator for several months. The results showed that the yellowing of the outer leaves on the cabbages stored in the brine type refrigerator were inhibited, and structural collapse of stoma was conspicuous on the yellowing leaves compared with the healthy leaves. On the carrots, cell structure collapse was limited in both xylem and phloem when stored in the brine type refrigerator. From the above results, it was found that the brine refrigerator inhibited the damage in the cell structure and made it possible to store with high freshness compared with the direct expansion type refrigerator.

This article investigates the experimental viscosity data and modeling of two binary refrigerant mixtures, R454B and R454C, recognized as low global warming potential (GWP) alternatives to conventional high-GWP refrigerants. Viscosity was measured for both refrigerants in liquid and vapor phases using a tandem capillary tube method. For R454B, the viscosity measurements spanned temperatures from (233 to 313) K in the liquid phase and (323 to 373) K in the vapor phase, under pressures up to 4.07 MPa. For R454C, measurements were taken from (233 to 343) K in the liquid phase and from (343 to 393) K in the vapor phase, with pressures reaching 4.01 MPa. The research used two sets of experiments focusing on low (233 to 293) K and high (303 to 393) K temperature ranges, adhering to the same measurement principles. The expanded uncertainties for viscosity in liquid and vapor phases were kept below 2.2% and 2.4%, respectively. Furthermore, prediction of viscosity of the two mixtures has been carried out using Extended Corresponding States (ECS) that comes with REFPROP version 10.0. It was observed that for vapor phase viscosity predicted by REFPROP is higher than the experimental value, especially for R454C.

For the purpose of proper refrigerant distribution in heat exchangers for air conditioners,we prototyped a refrigerant distributor with a new structure that distributes gas-liquid separated refrigerant using a slit pipe.Observation of the flow state by the visualization model and evaluation of the variation of the liquid-phase branch ratio as a distribution characteristic revealed the following. The height of the refrigerant liquid level formed in the gas-liquid separation space of the prototype distributor (slit type) decreases with increasing dryness. Comparing the distribution characteristics of the current collision type four-branch distributor and the prototype distributor (slit type), the conditions without inclination and the high flow rate condition (Gr=20 kg/h), the current distributor is superior,but the under inclination conditions and low flow conditions (Gr=10 kg/h), the prototype distributor has an advantage over the conventional four-branch distributor.

The performance of a 2 kW class heat pump cycle was calculated to evaluate COP, volumetric capacity, and irreversible losses for the binary mixture refrigerants containing HFO-1123 with a very low global warming potential, HFO-1123/R32, HFO-1123/R290, and HFO-1123/R152a. In the calculations, the minimum temperature difference at the outlet of the crossflow heat exchanger was fixed at 5 K assuming an air heat source, and the required heat transfer area was varied for comparison. At an HFO-1123 mass fraction of 0.6, HFO-1123/R32 exhibited the highest cooling COP of 6.1, meanwhile HFO-1123/R290 and HFO-1123/R152a exhibited COPs 1.1 and 1.4 lower than that. The large temperature glide increased the irreversible losses in the heat exchangers and significantly influenced the COP. Therefore, calculations were performed using a counter-flow heat exchanger model. The COP of HFO-1123/R290 was increased by 1.2 compared to that of the cross flow heat exchange, which was comparable to that of HFO-1123/R32.

Various physical properties have been vigorously investigated for the urgent need to shift to refrigerants with low global warming potentials. Although the measurement of global warming potential has progressed, a simple prediction method will be useful in considering new candidate substances. Quantum chemical calculations were performed for the conventional refrigerants R23, R32, and the ethylene derivatives R1123, R1132a, R1132(E), and R1132(Z). The radiative efficiencies were 10% to 60% higher than the measured. The atmospheric lifetimes were estimated from a newly developed correlation, confirmed between the energy barrier obtained at M06-2X/aug-cc-pVTZ and the rate constant at 272 K. Although the lifetime of R23 was predicted to be 116 years longer than that of the other derivatives, the other predicted lifetimes were consistent within one year for an atmospheric lifetime of approximately ten years. The calculation was matched within a factor of 0.76 to 1.35, even for a lifetime shorter than 0.1 years. The GWPs calculated above were consistent with the IPCC reported within ±50%. However, the GWP of R1132(E) was 2.24 times higher than the literature value.

In air conditioning systems where the transition to environmentally friendly refrigerants is progressing, the challenge is to use refrigerants with a temperature gradient. Refrigerants with a temperature gradient have different compositions in the liquid and gas phases, so the bias in the gas-liquid distribution at the pipe branch has a significant impact on controllability. In this study, we conducted a gas-liquid two-phase flow analysis using Large eddy simulation (LES) for a shape that branches from a horizontal pipe in the vertical upward direction, and clarified the effect of the length of the outlet pipe on the gas-liquid distribution characteristics. In addition, by expressing the outlet dryness obtained by LES with a one-dimensional model based on the length of the outlet pipe, we developed a simple distribution prediction formula that can be applied to the analysis of the entire air conditioning system.

A study was conducted to quantify the amount of refrigerant dissolved in refrigeration oil for the purpose of estimating the composition change of mixed refrigerants that are non-azeotropic in an air-conditioner. In the case of a binary non-azeotropic mixture of R 1132(E) [trans-1,2-difluoroethylene] and R 1234yf, R 1234yf preferentially dissolves in the refrigeration oil, and the amount of R 1234yf dissolved in the refrigeration oil was estimated as the temperature and pressure increased. It was found that the ratio of R 1132(E) in the mixed refrigerant composition tended to increase relative to the inclusion composition as the temperature decreased and the pressure increased.

Considering the importance of low GWP refrigerant blends and their constituents, this study aimed to clarify the flammability characteristics of CO2/propane (R290) blends at all blend compositions up to non-flammable. First, the flammability limits were evaluated using the evaluation method newly adopted in the High Pressure Gas Safety Act (HPGSA), and the results were compared with the ASHRAE method. The burning velocity was evaluated by microgravity experiments in the immediate vicinity of the non-flammable composition. Furthermore, to contribute to practical safety evaluation, the quenching distance was evaluated near the boundary of the mildly flammable (2L) class with a maximum burning velocity of 10 cms^-1. Second, by formulating these properties as a function of the mass or mole fraction of CO2, it became possible to predict all the flammability characteristics values at all blend compositions up to non-flammable and determine the flammability class according to ISO 817 and HPGSA.

R 1132(E), an HFO refrigerant with extremely low GWP and high efficiency, is known to occur self-decomposition reaction by external energy source. In this study, we evaluated the conditions for occurrence of self-decomposition and the discharge energy in compressor for using of R 1132(E) mixed refrigerants. It was found that self-decomposition was less likely to occur as the R 1132(E) concentration decreased, and refrigerants containing R 1132(E) at < 35mass% was stable for excessive discharge energies. The quantification of the discharge energy showed that the energy in 2.2kW compressor was less than 1J. From these results, the composition ratio of R 1132(E) mixed refrigerants which can be used stably as refrigerant were clarified. .It was clarified that these results indicated clarifying the conditions for stable use of R 1132(E) mixed refrigerant.

Under the worldwide situation of the shift to the next-generation refrigerants with low global warming potential (GWP), there is a demand to evaluate the fundamental thermophysical properties of low-GWP refrigerants, which is essential for their practical application. In this study, we developed a speed of sound measurement apparatus in the liquid phase using a commercially available ultrasonic-pulse sound velocity sensor. The apparatus was calibrated using pure water and R1336mzz(Z) (cis-1,1,1,4,4,4-hexafluoro-2-butene) as the reference standards for speed of sound, and R1234yf (2,3,3,3- tetrafluoropropene) was measured to confirm the soundness of the speed of sound measurement. As a result, it was confirmed that the speed of sound for R1234yf in the liquid phase agreed with the existing values within the claimed uncertainty. The relative standard uncertainty of the speed of sound measurement in the liquid phase was estimated to be 0.084 %. Using the developed liquid -phase speed of sound measurement apparatus, R1336mzz(E) (trans-1,1,1,4,4,4-hexafluoro-2-butene) and R13I1 (trifluoroiodomethane) were measured as the low-GWP refrigerants since their liquid-phase speed of sound have not been reported yet. The speed of sound data for R1336mzz(E) were obtained at 28 points in the temperature range from 283 K to 343 K and pressure range from 1 MPa to 7 MPa, and those for R13I1 were obtained at 28 points in the temperature range from 273 K to 333 K and pressure range from 1 MPa to 7 MPa. The obtained speed of sound data were compared with the calculated values from the existing equations of state for R1336mzz(E) and R13I1, and it was found that the present measurement data for R1336zz(E) and R13I1 were smaller by down to 9 % and 2.4 %, respectively.

In recent years, zeotropic mixed refrigerants have become a strong candidate for next-generation refrigerants due to restrictions on conventional refrigerants to reduce global warming. The refrigeration oil used in the compressor is selected for its compatibility with refrigerants to return to the compressor more easily. However, it is also known that the dissolution of refrigerants into refrigeration oil cause a change in the physical properties of the mixture, which affects the performance of the refrigerant compressor. Therefore, to realize early conversion to next-generation refrigerants, it is necessary to find out how refrigerants dissolve in refrigeration oil to ensure that compressors work well and are reliable. Especially for zeotropic mixed refrigerant, the dissolved composition may differ from the original composition. This study aimed to reveal the dissolution behavior of zeotropic mixed refrigerants into the refrigeration oil. The experiment was set to measure the dissolved composition at saturation condition and compare the dissolved composition at the initial dissolution state and at saturation condition. R454C, a mixture of R32 and R1234yf, was used as the zeotropic mixed refrigerant, and POE oil was used as the refrigeration oil. The measurement results showed that the refrigerant dissolved in the refrigeration oil had almost the same composition as the charged before mixing. However, when the dissolved composition was measured in the pressure range below the dew point at a liquid temperature of 80℃, the amount of R1234yf was approximately 4% higher than that of the charged composition. Furthermore, at a liquid temperature of 80℃, the liquid phase separation with different refrigerant mixture ratios was observed in the solubility range from 67% to 82%.

In this study, we analyzed the impact of feature selection on the predictive performance of common machine learning models for estimating the coecient of performance (COP) of a heat pump system. The dataset consisted of heating operation test data from a heat pump cycle using refrigerant R32. Various feature groups were created from control variables and measurement data, and the relationship between these features and the machine learning models was examined. The results indicated that stepwise linear regression provided the highest predictive accuracy when only control variables were used. While, linear regression and Gaussian process regression provided high accuracy models when measured data were included as features. Moreover, kernel-based machine learning models, such as Gaussian process regression and support vector regression, demonstrated high predictive accuracy even with a limited number of features or when key explanatory variables, such as the COP-defining variable, were excluded. Additionally, the study showed that models with high accuracy could be built using a small number of features, particularly those with a strong correlation to the objective variable.

Polysaccharides are widely used to preserve the texture of frozen desserts like ice cream by inhibiting ice recrystallization. Despite recent significant advances in research, a clear comprehension of the ice recrystallization inhibition mechanism of polysaccharides remains elusive. Some previous studies hypothesized that the ice recrystallization inhibition originates from the interaction between polysaccharides and ice crystal surface and tried to correlate it with the ice crystal shape. In this work, we have developed a novel method for analyzing the shape change of ice crystals during storage by curvature calculation. This method depicts the ice crystal shapes as the distribution of curvatures well expressing the changes of the ice crystal shapes. The newly developed method has been applied to evaluate the shape changes of ice crystals during the storage of sucrose solutions with and without kappa-carrageenan. The changes in curvature distributions revealed that ice crystals were rectangular with flat edges in the pure sucrose solution and were comparatively round in the sucrose/kappa-carrageenan solutions at longer storage time, which was not characterized in the roundness changes, showing the potentiality of using the curvature distribution to evaluate the shape change of ice crystals appropriately during storage.

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.