Search

Ultra-low temperature chillers have seen increasing demand with the advancement of semiconductor technology. Mixed refrigerant (MR) cascade refrigeration systems (CRSs) are widely utilized for their stability and high cooling performance at low temperatures. Extensive research has been conducted on optimizing MR, which has a significant impact on CRS performance. However, most previous studies have either fixed the system pressure or used the refrigeration effect as the sole performance indicator. This did not account for the potential of achieving higher performance with an optimal MR composition at the same target temperature. In this study, a detailed parametric analysis was performed to investigate how the mass fractions of high-, mid-, and low boiling point refrigerants affect the coefficient of performance (COP) and exergy in ultra-low temperature CRSs without fixing the suction pressure. The analysis revealed that at the point of maximum COP, the refrigeration effect was relatively low, highlighting the limitations of using the refrigeration effect alone as a performance indicator. Additionally, COP was found to inversely correlate with total exergy destruction. As cascade temperature increases, COP tends to decrease, emphasizing the need for appropriate cascade temperature selection for MR CRS performance. This study introduces a novel approach to optimizing MR composition under various operating conditions, contributing to the advancement of ultra-low temperature CRSs. [ABSTRACT FROM AUTHOR]

This study investigates the implementation of a cryogenic chiller utilizing a mixed-refrigerant cascade refrigeration cycle (MRCRC). In this setup, R-404A is employed in the high-temperature circuit (HTC), while a mixture of refrigerants is utilized in the low-temperature circuit (LTC). Unlike a conventional MRCRC that operates without a receiver to maintain the composition ratio, this research explores the impact of receiver installation on system performance. Experiments were conducted with and without a receiver to assess performance improvements and device behavior. With a fixed refrigerant charge of 4 kg, the suction and discharge pressures of the LTC compressor remained low and stable after the receiver's installation. The addition of a receiver significantly reduced the cooling time, with further reductions observed as the refrigerant charge increased. The system achieved evaporative heat capacities of 0.59, 1.76, and 2 kW for refrigerant charges of 4, 7, and 9 kg, respectively. Notably, at the maximum refrigerant charge of 11 kg, the evaporative heat capacity peaked at 3.3 kW. These findings indicate that incorporating a receiver is crucial for enhancing the cooling performance of cryogenic coolers using mixed refrigerants and stabilizing device operation. This contrasts with previous studies that omitted receivers due to concerns over potential alterations in the composition ratio of the mixed refrigerant. [ABSTRACT FROM AUTHOR]

Recent advancements in cryogenic etching, characterized by high aspect ratios and etching rates, address the growing demand for enhanced performance and reduced power consumption in electronics. To precisely maintain the temperature under high loads, the cascade mixed-refrigerant cycle (CMRC) is predominantly used. However, most refrigerants currently used in semiconductor cryogenic etching have high global warming potential (GWP). This study introduces a −100 °C chiller using a mixed refrigerant (MR) with a GWP of 150 or less, aiming to comply with stricter environmental standards and contribute to environmental preservation. The optimal configuration for the CMRC was determined based on a previously established methodology for selecting the best MR configuration. Comprehensive analyses—energy, exergy, environmental, and exergoeconomic—were conducted on the data obtained using Matlab simulations to evaluate the feasibility of replacing conventional refrigerants. The results reveal that using eco-friendly MRs increases the coefficient of performance by 52%, enabling a reduction in compressor size due to significantly decreased discharge volumes. The exergy analysis indicated a 16.41% improvement in efficiency and a substantial decrease in exergy destruction. The environmental analysis demonstrated that eco-friendly MRs could reduce carbon emissions by 60%. Economically, the evaporator and condenser accounted for over 70% of the total exergy costs in all cases, with a 52.44% reduction in exergy costs when using eco-friendly MRs. This study highlights the potential for eco-friendly refrigerants to be integrated into semiconductor cryogenic etching processes, responding effectively to environmental regulations in the cryogenic sector. [ABSTRACT FROM AUTHOR]

This study analyzes several design cases to identify the optimum geometric structure of the offset fin, determined by two design factors: the number of fins in the flow direction and the number of fins in the vertical direction. Increasing the number of fins in the vertical direction has relatively minor effects on the heat transfer rate and surface area. In contrast, adding more fins in the flow direction results in enhancement of thermal performance. Correlations for the Colburn j factor and the Fanning f factor, incorporating Nfin,v and Nfin,f, are established. The resistance curve of each case is yield based on the f factor correlation, and the heat transfer rate at the actual coolant flow rate is obtained the j factor correlation. A difference in the pressure drop resulted in a different coolant flow rate despite using the same circulation pump, showing a difference of 1.67 times between the minimum and maximum values. Although a different coolant circulates in each case, there was no reversal in the heat transfer rate compared to the situation in which a constant amount flows. The impact of the pump's performance curve on the heat transfer rate becomes relatively pronounced with an increased pressure drop. When Nfin,f was 30, the ratio of maximum to minimum heat transfer rate was 8.73% with a constant coolant flow rate, but this ratio increased to 13.08% when considering the actual coolant flow rate facilitated by a pump. [ABSTRACT FROM AUTHOR]

The demand of river-crossing is steadily increasing, the speedy and safety are two most important factors that decide the success of the applied solutions. This paper partially proposes a method for ribbon bridge installation and self-correction by describing the planar motion for a ribbon bridge, including several experimentally identified over a certain range of speeds. The mathematical modeling and system identification aim to provide a model that is sufficient for allowance of model-based control designs. In order to design the stable yaw control system of auto-correction of positional displacement, the Linear-Quadratic Regulator (LQR) was employed for yaw controller. Accordingly, the numerical study was carried out under a variety of disturbances to verify the system modeling and the efficiency of the designed controller. The simulation results demonstrate that the proposed controller has promising feasibility of the yaw placement automatic correct during operation and further extended results of the whole bridge system.

In these days, many studies on ocean fisheries have been conducted for developing their own industries. Especially, the efforts of using seawater cooling system were actively conducted to keep the caught fisheries fresh, increase the catches, and decrease the manpower. The purpose of this study is to suggest design criteria of seawater cooling system using the flood-type evaporator. In this study, the seawater cooling system using flooded-type evaporator was manufactured as a prototype capacitating 15kW. This study examined performance of the seawater cooling system and then compared the performance with the system capacitating 163kW and 238kW, which is actually being loaded on the fishery boats. In addition, heat transfer characteristics of the flooded-type evaporator used in the equipment are analysed.