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Experimental Investigation of Two-Phase Flow Boiling Heat Transfer in Small Diameter Tubes
Bediako, Ernest Gyan; Vít Tomáš, prof. Ing. Ph.D. :55449
In recent years, there has been growing interest in exploring two-phase flow boiling heat transfer characteristics in small diameter tubes, as they offer potential improvement in heat transfer performance and design of compact systems. Despite extensive research in this area, the heat transfer processes and the dominant mechanisms controlling the heat transfer still remain unclear. This research therefore aims to experimentally investigate two-phase flow boiling heat transfer phenomenon in small diameter tubes, with a focus on understanding the underlying mechanisms, identifying critical parameters and testing predictive models for improved thermal performance. An experimental setup from the Thermal Two-Phase Lab in Norwegian University of Science and Technology was modified to investigate the heat transfer characteristics under varying operating conditions, including but not limited to mass flux, heat flux, and saturation conditions. The study was performed in a horizontal 5 mm internal diameter and 8 mm external diameter smooth stainless-steel tube with 1,1,1,2-tetrafluoroethane (R134a) as the working fluid. The main findings reveal that at low and moderate flow boiling conditions, distinct phenomena were observed. A notable peak of heat transfer coefficient near vapor quality of zero, a local minimum and heat transfer deterioration were observed in the low vapor quality region. These distinct observations were sensitive to heat flux but mildly sensitive to mass flux. The main flow patterns recorded with high speed camera were bubble, slug and intermittent flow in the low vapor quality region, annular, dry-out and mist flow in the high vapor quality region. Similar flow patterns were predicted by well-known flow pattern maps in literature. Varying saturation pressure varies the vapor quality at which the flow pattern transitions from intermittent flow to annular flow. Generally, mass flux and vapor quality favor convective boiling heat transfer whiles heat flux and saturation conditions favor nucleate boiling heat transfer. However, their interplay is very significant for clear observation. Pressure drop is observed to decrease with increasing saturation pressure. Overall, this research contributes to the fundamental understanding of two-phase flow boiling heat transfer in small diameter tubes. The insights gained from this study provide valuable guidelines for designing and improving heat exchangers and other thermal system design.
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Cestovní zpráva CitaKon 2024
(2024) Jágrová Trykarová, Markéta
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AI do škol
(2024) Zizienová, Marta; UKN
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Utilization of time-driven activity-based costing and process simulation in cost management of organization
(2024-04-10) Halaska, Michal; Sperka, Roman
The deployment of information and communication technologies in organizations is on the rise. Many organizations consider the application of technologies to be a crucial key to improve their processes. However, traditional costing systems are not suitable for cost estimation of business processes due to the use of volume-based cost drivers, which are often not adequate for the structure of today’s organizations. In this research, we present an overview of how the TDABC (time-driven activity-based costing) model can be combined with process mining and business process simulation for cost estimation of such processes. The objective of this paper is to use the cost dimension as a major attribute for the potential implementation of robotic process automation (RPA) in companies. However, information and communication technologies could be considered in general. We demonstrate our approach in a case study that takes advantage of a real-life event log containing transactional data representing the loan application process in an insurance company. The event log is analyzed and processed using process mining techniques. Based on the preprocessing, a simulation model representing the original loan application process is designed. The designed simulation model is then used for simulation of partial and full implementation of RPA through separate scenarios. Then, we add the cost dimension to the simulation by enriching the event log with cost data based on a formalized cost model. We show that even though partial implementation of RPA might not deliver significant increase in efficiency in the process, it might still represent significant cost savings.