Determination of Refrigerant Path Number for Fin-tube Condenser Considering Heat Transfer Performance and Pumping Power

Fin-tube heat exchangers are widely used in air-conditioners and heat pumps, which are constructed with a lot of tubes. Refrigerant circuit of heat exchanger with numerous pipe can be constructed by many methods. Refrigerant circuit design is usually determined designer’s experience and case by case test without guides. The number of path affects largely on heat exchanger performance. In this paper, design methodology for optimum number of path is suggested by relating convective thermal resistance and pumping power. Suggested methodology is described through an example and verified by various refrigerant circuit simulation results

Guidelines Aimed at Reducing the Risks of User Acceptance Delay in the Context of an IT Service Project Management Plan

Delays in the user acceptance of information technology (IT) service projects in Korea have occurred frequently due to various risk factors. User acceptance delays may hinder the achievement of the client’s project objectives and cause schedule delays or cost overruns. Furthermore, the client may impose a delay charge and claim for additional damages, causing serious disputes between buyer and supplier. The main causes of user acceptance delays are unclear user requirements, changes in user requirements, poor-quality development outputs, excessive functional and non-functional errors, lack of user involvement, unclear user roles and responsibilities, and unclear criteria of user acceptance test.We help foster the timely completion of user acceptance by proposing a method of identifying the risk factors in user acceptance delay and creating a project management plan to weed out the identified risks. We propose a guideline for an IT service management plan that weeds out or lowers the risk factors well in advance. To validate the guideline’s utility, we apply it to IT service projects. The results show that the guideline is effective in identifying and removing risk factors affecting delays in the user acceptance of IT service projects

Observation of R600a flow at subcooled temperature conditions in a vapor compression refrigeration system

Vapor compression refrigeration system is usually designed such that refrigerant exits a condenser at subcooled liquid state in order not to cause possible damage to expansion devices. Even in small refrigeration systems incorporating capillary tube as an expansion device, the refrigerant is supposed to be subcooled before entering the expansion device. In this study, experimental apparatus equipped with several thermocouples, pressure transducers and visualization device was constructed in order to observe the behavior of refrigerant flow at condenser outlet of a vapor compression refrigeration system. Visual observation as well as temperature and pressure readings indicate the presence of two-phase flow at highly subcooled temperature. An alternative equation was suggested to calculate the enthalpy of the two-phase refrigerant in subcooled region and verification test was conducted

NANOTECHNOLOGY FOR ADVANCED NUCLEAR THERMAL-HYDRAULICS AND SAFETY: BOILING AND CONDENSATION

A variety of Generation III/III+ water-cooled reactor designs featuring enhanced safety and improved economics are being proposed by nuclear power industries around the world in efforts to solve the future energy supply shortfall. Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. Phase change by boiling and condensation in the reverse process is a highly efficient heat transport mechanism that accommodates large heat fluxes with relatively small driving temperature differences. This mode of heat transfer is encountered in a wide spectrum of nuclear systems,and thus it is necessary to determine the thermal limit of water-cooled nuclear energy conversion in terms of economic and safety. Such applications are being advanced with the introduction of new technologies such as nanotechnology. Here, we investigated newly-introduced nanotechnologies relevant to boiling and condensation in general engineering applications. We also evaluated the potential linkage between such new advancements and nuclear applications in terms of advanced nuclear thermal-hydraulics.close1

Radiofrequency Ablation of Thyroid Nodules: Basic Principles and Clinical Application

Radiofrequency (RF) ablation has been gaining popularity as a minimally invasive treatment for benign thyroid nodules regardless of the extent of the solid component. RF ablation of benign nodules demonstrated volume reductions of 33–58% after one month and 51–85% after six months, while solving nodule-related clinical problems. RF ablation has recently shown positive short-term results for locoregional control as well as symptom improvement in patients with recurrent thyroid cancers. This paper reviews the basic physics, indications, patient preparation, devices, procedures, clinical results, and complications of RF ablation

Surface modification through oxide ALD to improve oxygen exchange rate on perovskite surface

Segregation and phase separation on perovskite oxide (ABO3) surface have been considered as a key detrimental factor to the performance of energy conversion devices such as solid oxide/electrolysis cells. Recently, the overcoat of less reducible cations has been suggested as a way to suppress the surface Sr segregation on Sr-containing perovskite oxides. However, the detailed requirements of the coating layer to sufficiently stabilize the perovskite surface hasn’t been systematically investigated yet. In this wok, we fabricate La0.6Sr0.4CoO3 (LSC) thin-film model electrode via pulse layer deposition and observe how the degree of Sr segregation varies with the type and thickness of the overcoat layer. Al2O3 and HfO2 with different thickness are coated on LSC via ALD, and the oxygen exchange rate of both bare and ALD-coated samples is measured via electrical conductivity relaxation. It is found that both Al2O3 and HfO2 layers suppress the Sr segregation only within a narrow thickness range, i.e., 1-2 nm for Al2O3 and 0.2 – 0.4 nm for HfO2, respectively. These observations are discussed with solubility and diffusivity of Al and Hf in the host oxide lattice, providing a critical guideline of a new surface modification method to stabilize the perovskite surface at high temperatures. Please click Additional Files below to see the full abstract

The discovery and characterization of tungsten insertase in tungsten cofactor biosynthesis

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Passivity, task segmentation, and relational capital: a study of interpersonal relationship formation among freshman medical students in team-based activities

Purpose Team-based learning in medical education facilitates the formation of interpersonal relationships, enhances academic achievement, and establishes future clinical connections. Despite medical schools’ distinct educational environments and curricula, research investigating students’ learning and behavioral characteristics within this context remains limited. This study aimed to investigate the specific characteristics of interpersonal relationship formation among freshmen medical students in team-based learning activities. Methods Focus group interviews were conducted with 11 students who participated in a team-based class held during the first semester of the premedical year. Results Medical students passively expressed their thoughts and feelings, such as active sympathy for the team’s opinions and self-censorship of SNS (social networking service) conversations. When performing team activities, students were excessively conscious of others and focused on evenly dividing their work, minimizing their opinions, and fulfilling their share to prevent potential interpersonal conflicts. Interpersonal activities were only superficial, as students intentionally maintained a certain distance from team members or used team activities as an opportunity to accumulate relational capital. Conclusion The results of this study are expected to provide a useful basis for designing and conducting team activity classes to enhance interpersonal relationship formation