Conference Agenda

The evolution of air conditioning systems, alongside new refrigerants, highlights the importance of studying compres- sor lubricants. Employing nanolubricants in heating, ventilation, and air conditioning (HVAC) systems will result in improvement in heat transfer, reduction in energy consumption, and overall system performance enhancement, thereby advancing efficiency in HVAC systems operations. In this work, we integrated short single-walled carbon nanotubes (Short-SWCNTs), short multi-walled carbon nanotubes (Short-MWCNTs) as well as graphene into POE32 oil to enhance the overall thermophysical and tribological properties of the mixture for compressors applications. Stability characteristics such as dispersion stability and sedimentation behavior were assessed using the two-step method to ensure the uniform dispersion of nanoparticles within the oil and enhance the homogeneity of nanolubricant. In this study, the investigated nanoparticles were analyzed at various volume fractions (0.01, 0.025, 0.05, and 0.1 vol.%) to identify the concentration for optimal stability performance. The experimental results showed that the samples have long term stability with short-MWCNT having the highest stability. In summary, this study is pivotal for optimizing nanofluid stability in energy-efficient air conditioning compressors.

Heat pumps have recently become popular as a means of heating in cold regions thanks to the reduction of CO2 emissions and reinforcement of energy security they provide. POE is a type of refrigeration oil that lubricates the compressor in heat pumps. R32 is currently utilized as a refrigerant for room air conditioners, and R454B may also be popularized in the future.

When refrigerant is discharged from the compressor, a small amount of oil is also discharged and circulates through the system. Assuming operation in cold regions, the evaporator and the suction line to the compressor, both of which are located outdoors, are exposed to extremely low temperatures, which increases their risk of oil retention due to the high viscosity of the refrigerant-oil mixture. Oil retention in the components can lead to two serious problems. The first one is compressor failure: if a sufficient amount of oil in the system does not return to the compressor, there will be a shortage of oil in the compressor, leading to poor lubrication. The second one is a decrease in efficiency: retention of oil causes a pressure drop of the refrigerant in the evaporator and the suction line to the compressor, leading to a decrease in COP.

To solve these problems, we developed a refrigeration oil that exhibits excellent low-temperature fluidity as a refrigerant-oil mixture by modifying the solubility of R32 and R454B in oil. In this study, we report the method and various characteristics.

POE refrigeration lubricants are synthesized by different polyols and fatty acids, these various combinations can create different lubricant properties to meet requirements from different refrigeration systems. As global phase down schedule of HFCs, refrigeration lubricant makers focus on modifying structures of incumbent lubricants to apply for alternative refrigerant, such as expanding miscibility range in R32, or reducing viscosity-dilution in R1234ze. However, the modifications usually focus on the miscibility, solubility and working viscosity, there are no many attentions on the other properties, such as refrigerant absorption, desorption, heat transfer, and foaming. Our goal in this paper is to check the effect on foaming property from related structure modification.

Foaming is important phenomenon in refrigeration system, it affects not only oil return, but lead to start-up problem. To detailed describing foaming phenomenon, two stages of bubble life must be taken into consideration: bubble generation stage and bubble stable/collapse stage. After investigating a lot of parameters, such as refrigerant solubility in lubricant, surface tension, vapor pressure, viscosity, density, and temperature, we find each parameter can play a different role on bubble generation and collapse stage. We try to give a preliminary look on how lubricant chemical structure effect on these parameters, and further checking foaming phenomenon of refrigerant-lubricant mixture through conducting experiments.

In this study, fully branched and fully linear POE with ISO32 and ISO55 were chosen to mix with traditional HFCs, and alternative low GWP refrigerants by different ratios, and conducted foaming tests under different pressure. We also discuss viscosity effect by comparing different viscosity grades range from ISO32 to ISO170. This investigation will provide a better understanding of foaming mechanism, and the direction to well-design lubricants to overcome foaming issue in refrigeration system.

Global warming, driven by the increase in greenhouse gases, presents significant challenges to our environment and society. Refrigeration systems, extensively used across various fields, impact these challenges through both direct emissions from refrigerant leakage and indirect emissions due to energy consumption. Recently, in response to the growing demand for low GWP refrigerants to mitigate global warming, a variety of such refrigerants are being considered depending on the specific needs of different regions and applications. The mixture properties of refrigerants with refrigeration lubricants significantly differ based on their structure, leading to continuous improvements in refrigeration lubricants alongside the evolution of refrigerants. Therefore, designing refrigeration lubricants suitable for each refrigerant is important　for the development of efficient refrigeration equipment. In this presentation, we report on the properties and performance of refrigeration lubricants under the atmospheres of next-generation low GWP refrigerants.

Refrigerant dissolution into refrigeration oil considerably decreases the viscosity of refrigeration oil. The dissolution of refrigerant into the oil in a compression chamber during a compression process is generally neglected because it is thought that the compression process is instantaneous and the refrigerant cannot be dissolved into the oil film in such a short time. However, if the oil film is very thin, the dissolution of refrigerant may decrease the oil viscosity. In this study, the dissolution of refrigerant into thin oil film was examined by designing a test device that uses an optical-fiber probe (OFP) method to evaluate the transient change in refrigerant concentration in oil during the compression process. The OFP can detect changes in a returned light intensity by refractive index change due to refrigerant dissolved in the oil film. Since more light is reflected from the interface of the oil film as the oil film thickness decreases, which causes the intensity of the returned light to increase, a mirror is installed above the OFP to eliminate the reflected light from the interface. As a result, the returned light intensity from the OFP is not affected by the oil film thickness, even in conditions where the film is very thin. The dissolution process of the refrigerant into the oil film was successfully detected in the oil film, whose thickness ranged from 0.23 to 0.51 mm. In this thickness range, the refrigerant dissolution during the compression process can be ignored because the dissolution time is much longer than the compression time. Furthermore, the dissolution of R32 into the oil film was found to be faster than that of R410A. Based on the estimation of the refrigerant dissolution into the thin oil film by a one-dimensional diffusion model, it is suggested that the refrigerant dissolution during the compression process affects the oil viscosity when the oil film thickness is less than approximately 0.01 mm.