The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Sangkwon Jeong - One of the best experts on this subject based on the ideXlab platform.
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Concept of Cold Energy Storage for Superconducting Flywheel Energy Storage System
IEEE Transactions on Applied Superconductivity, 2011Co-Authors: Jisung Lee, Young Hee Han, Sangkwon Jeong, Byung Jun ParkAbstract:A superconducting flywheel energy storage (SFES) system is an energy storage device with unprecedented small kinetic energy loss by utilizing diamagnetic levitation property of superconductor. The system, therefore, is expected to be one of the most promising candidates in the application of renewable energy field such as PV (photovoltaic) or wind energy development where the power generation is intermittent. An innovative concept to store cold thermal energy as well as kinetic energy in the SFES system is proposed in this paper to decrease required cooling energy during the energy storage period. We have found that the cooling energy can be considerably decreased by the suggested cooling concept. The methodology of cold thermal energy storage is introduced, and the experimental validation is carried out. A specially designed thermosiphon is adopted as a thermal bridge between the high temperature superconductor (HTS) bulks and the cold head of cryocooler, and the working fluid of the thermosiphon is utilized as the thermal energy storage material. Solid nitrogen is generated in the thermosiphon by surplus electricity, and then the mock up HTS bulks are successfully cooled around 64 K by the existence of solid nitrogen even though the implemented cryocooler is turned off.
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Transient thermodynamic behavior of cryogenic mixed fluid thermosiphon and its cool-down time estimation
Cryogenics, 2010Co-Authors: Sangkwon JeongAbstract:Abstract Thermosiphon is an efficient heat transfer device by utilizing latent heat of fluid at liquid–vapor phase change. One of the disadvantages of thermosiphon, however, is that the operational temperature range is fundamentally limited from the critical point to the triple point of the working fluid to maintain two phase state. Nitrogen (N 2 ) and tetrafluoromethane (CF 4 ) were selected as the mixed working fluid to widen their original operational temperature range. Thermodynamic behavior of mixture and its effect on the cool-down time were investigated. A simple calculation model was proposed to estimate the cool-down time of the thermosiphon evaporator prior to experiments. The calculated results agreed well with the experimental results within 5% error. The cool-down time reduction was not achieved by mixing two components at once due to the separation of mixture. One idea to avoid this problem was suggested in this paper where the estimated cool-down time was reduced 17.8% compared to pure N 2 .
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Experimental study on the double-evaporator thermosiphon for cooling HTS (high temperature superconductor) system
Cryogenics, 2009Co-Authors: Junseok Ko, Sangkwon Jeong, Tae Hyun Sung, Se-yong JungAbstract:A cryogenic Thermosiphons is an efficient heat transfer device between a cryocooler and a thermal load that is to be cooled. This paper presents an idea of thermosiphon which contains two vertically-separated evaporators. This unique configuration of the thermosiphon is suitable for the purpose of cooling simultaneously two superconducting bearings of the HTS (high temperature superconducting) flywheel system at the same temperature. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure condition. The interior thermal condition of the double-evaporator thermosiphon was examined in detail during its cool-down process according to the internal thermal states. The double-evaporator thermosiphon has operated successfully at steady-state operation under sub-atmospheric pressure. At the heat flow of 10.6 W, the total temperature difference of the thermosiphon was only 1.59 K and the temperature difference between the evaporators was 0.64 K. The temperature difference of two evaporators is attributed to the conductive thermal resistance of the adiabatic section between the evaporators. The method to reduce this temperature difference has been investigated and presented in this paper. The proper area selection of condenser, evaporator 1, and evaporator 2 was studied by using thermal resistance model to optimize the performance of a thermosiphon. The superior heat transfer characteristic of the double-evaporator thermosiphon without involving any cryogenic pump can be a great potential advantage for cooling HTS bulk modules that are separated vertically.
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Double-Evaporator Thermosiphon for Cooling 100 kWh Class Superconductor Flywheel Energy Storage System Bearings
IEEE Transactions on Applied Superconductivity, 2009Co-Authors: Se-yong Jung, Byung Jun Park, Sangkwon Jeong, Junseok Ko, Byungchul ParkAbstract:This paper presents an idea for a thermosiphon that uniquely implements two integrated evaporators to cool two HTS (High Temperature Superconductor) bulk sets in different locations, simultaneously. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure conditions. The operating target temperature was approximately 65 K. To confirm the feasibility of the double-evaporator thermosiphon, experiments during the cool down process and steady state operation were extensively conducted on the double-evaporator thermosiphon (Ltot = 1075 mm, do = 160 mm). The double-evaporator thermosiphon worked successfully at steady state operation. The results showed that it had a maximum total temperature difference between the condenser and the evaporator of 1.3 K and a temperature difference between the two evaporators of 0.6 K at a heat flow of 87 W. This thermosiphon was designed for actual application to a 100 kWh SFES (Superconducting Flywheel Energy Storage) system. The potential impact of superior heat transfer characteristics of the double-evaporator thermosiphon is discussed in the paper.
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Experimental Study on the Double-Evaporat or Thermosiphon for Cooling Hts (high Temperature Superconductor) System
AIP Conference Proceedings, 2008Co-Authors: Sangkwon JeongAbstract:Cryogenic Thermosiphons are highly efficient heat transfer elements between a cryocooler and the thermal load that is to be cooled. This paper presents an idea of thermosiphon that peculiarly utilizes two evaporators to overcome spatial restriction. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen under sub-atmospheric pressure condition. This thermosiphon is specifically aimed for cooling HTS bulk system. In this paper, the invisible interior condition of the double-evaporator themosiphon is described in detail during the cool-down process according to the internal thermal states. Although the double-evaporator thermosiphon worked successfully under sub-atmospheric pressure condition, there was a little temperature difference between two evaporators at steady-state operation. The cause of this problem is considered as the orientation effect of boiling heat transfer coefficient. An additional experiment was also conducted to examine the orientation effect of boiling heat transfer coefficient of nitrogen under sub-atmospheric pressure condition.
Chi-chuan Wang - One of the best experts on this subject based on the ideXlab platform.
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Energy-saving potential of separated two-phase thermosiphon loops for data center cooling
Journal of Thermal Analysis and Calorimetry, 2020Co-Authors: Mohammed W. Sulaiman, Hafiz M. Daraghmeh, Chi-chuan WangAbstract:This study aims to experimentally examine the energy-saving potential by using R-134a filled separated two-phase thermosiphon loop (STPTL) for data center applications. A parametric study had been made to compare the energy consumption of two data center racks. Two fin-and-tube heat exchangers were attached to one of the racks to form two individual thermosiphon loops. The experiments were carried out subject to different operating conditions, including three ambient temperatures (20 °C, 23 °C, and 27 °C) and filling ratios ranging from 30 to 90% in association with heating loads ranging between 1.5 kW and 6 kW. Parametric influences regarding concentrated heat loading or uniform heat loading are studied. It was found that an appreciable energy-savings can be obtained at high filling ratios and a maximum of 49% energy-saving with the assistance of thermosiphon is observed. Accordingly, the rising of system pressure will result in noticeable savings. Relative to the uniform heat loading of the data rack, the thermosiphon shows even more energy-saving potential in concentrated heat loading. This phenomenon is more pronounced at a lower ambient temperature like 20 °C. On the other hand, there is no appreciable energy-saving for the thermosiphon between concentrated and uniform heating loads when the ambient temperature is high (27 °C). Furthermore, the influence of airflow rate was also investigated under various ambient temperatures with a 90% filling ratio and a heating load of 6 kW. The results revealed that the lower airflow rate in the thermosiphon yields comparatively better energy-saving than the higher flow rate. The study on the influence of using two STPTLs indicated that 15–23% energy-saving can be achieved at a 90% filling ratio and 6 kW heating load for all the studied ambient conditions if compared with testing each loop separately. Lower thermal resistance is seen at the higher filling ratios, ambient temperatures, and heating loads.
Stephan Scholl - One of the best experts on this subject based on the ideXlab platform.
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Modelling and simulation of a pillow plate thermosiphon reboiler
Heat and Mass Transfer, 2019Co-Authors: Robert Goedecke, Stephan SchollAbstract:Thermosiphon reboilers are the most widely used evaporators in the process industry. Experimental studies suggested a superior performance of pillow plate thermosiphon reboilers over conventionally used tubular designs. This contribution presents a comprehensive model to simulate fluid dynamic as well as thermal performance of pillow plate thermosiphon reboilers. Experimental heat transfer coefficients are extracted from measurements at a thermosiphon reboiler test rig. With this information, correlations for the single phase heat transfer coefficient and the heat transfer coefficient with nucleate boiling as well as convective boiling are presented. A correlation for the heat transfer coefficient for film condensation inside the pillow plate and the two-phase pressure drop between the pillow plates is presented. These correlations are implemented in a modular structured simulation program. Good agreements were shown for the heat transfer with water experiments. The fluid dynamic could be described satisfactory with larger uncertainties at small circulation rates.
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Pillow Plate Heat Exchangers as Falling Film Evaporator or Thermosiphon Reboiler
Innovative Heat Exchangers, 2017Co-Authors: Stephan SchollAbstract:This chapter discusses the application of pillow-plate heat exchangers (PPHE) as falling film evaporators or thermosiphon reboilers. In falling film evaporators a thin liquid film driven by gravity flows down at the outside of a vertical pillow plate. To ensure proper functionality and avoid thermal stress to the product, complete wetting of the surface is mandatory. Minimum wetting rates are presented showing a pronounced hysteresis in wetting and dewetting operation. Thermosiphon reboilers are most widely used in the process industry. Their operating principle builds on the density difference of the single phase liquid feed and the two phase vapor/liquid mixture in the reboiler. For PPHE evaporation takes place in the ducts between the pillow plates while the hot service medium, condensing water steam or heating oil, flows inside the pillow plates. Pillow plate thermosiphon reboilers show a broad operating window and very stable operation. They may be applied down to a total pressure of 100 mbar abs and an overall driving temperature difference of 5 K. For both evaporator types thermal design is based on the established concept of dimensionless numbers.
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Enlarged operation ranges for thermosiphon reboilers using pillow plates
Chemical Engineering Research & Design, 2015Co-Authors: Robert Goedecke, Stephan SchollAbstract:Abstract Thermosiphon reboilers are widely used as reboilers in distillation columns and as evaporators in the chemical and petrochemical industry. The main reasons are the low investment and operating costs. Heat transfer and fluid dynamics are strongly linked in thermosiphon reboilers. Therefore the operation range of these evaporators is limited. Pillow plates offer a very good heat transfer with a low pressure drop. Therefore great potential is expected for their use in thermosiphon reboilers. Evaporation experiments with a pillow plate thermosiphon reboiler were carried out with water and a water–glycerol mixture. The total pressure, the submergence and the temperature difference between heating and evaporation side were varied. Circulation rate and heat transfer were measured. Stable natural circulation was seen over a wide range of influence parameters. Even at low total pressures and at low submergences the natural circulation was stable. Compared to literature data for tubular thermosiphon reboilers the operating limits for pillow plate thermosiphon reboilers can be increased, especially at low total pressures, low submergences and low temperature differences. The measured heat transfer is increased compared to tubular stainless steel thermosiphon reboilers.
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Intensification of fluiddynamic and thermal performance of thermosiphon reboilers
Applied Thermal Engineering, 2005Co-Authors: Stephan Scholl, Fahmi BrahimAbstract:The potential benefit of hiTRAN® tube inserts for fluiddynamic as well as heat transfer intensification of thermosiphon reboilers was investigated experimentally. Circulating flow expressed as single phase tube inlet velocity is regarded as primary criterion for fluiddynamic behaviour while product side heat transfer coefficient represents heat transfer performance. Pure water and a 29 mol% glycerol/water mixture were used as test fluids. Fluiddynamic as well as thermal performance of the bare tube vs. five inserts with different loop volume fractions were determined in a single tube lab-scale thermosiphon reboiler. It was found that most beneficial use appears for the glycerol/water system at low driving temperature difference between service and product side employing inserts with a loop volume fraction around 3%. In best cases a more than 50% increase of the product side heat transfer coefficient was obtained.
Byung Jun Park - One of the best experts on this subject based on the ideXlab platform.
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Concept of Cold Energy Storage for Superconducting Flywheel Energy Storage System
IEEE Transactions on Applied Superconductivity, 2011Co-Authors: Jisung Lee, Young Hee Han, Sangkwon Jeong, Byung Jun ParkAbstract:A superconducting flywheel energy storage (SFES) system is an energy storage device with unprecedented small kinetic energy loss by utilizing diamagnetic levitation property of superconductor. The system, therefore, is expected to be one of the most promising candidates in the application of renewable energy field such as PV (photovoltaic) or wind energy development where the power generation is intermittent. An innovative concept to store cold thermal energy as well as kinetic energy in the SFES system is proposed in this paper to decrease required cooling energy during the energy storage period. We have found that the cooling energy can be considerably decreased by the suggested cooling concept. The methodology of cold thermal energy storage is introduced, and the experimental validation is carried out. A specially designed thermosiphon is adopted as a thermal bridge between the high temperature superconductor (HTS) bulks and the cold head of cryocooler, and the working fluid of the thermosiphon is utilized as the thermal energy storage material. Solid nitrogen is generated in the thermosiphon by surplus electricity, and then the mock up HTS bulks are successfully cooled around 64 K by the existence of solid nitrogen even though the implemented cryocooler is turned off.
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Double-Evaporator Thermosiphon for Cooling 100 kWh Class Superconductor Flywheel Energy Storage System Bearings
IEEE Transactions on Applied Superconductivity, 2009Co-Authors: Se-yong Jung, Byung Jun Park, Sangkwon Jeong, Junseok Ko, Byungchul ParkAbstract:This paper presents an idea for a thermosiphon that uniquely implements two integrated evaporators to cool two HTS (High Temperature Superconductor) bulk sets in different locations, simultaneously. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure conditions. The operating target temperature was approximately 65 K. To confirm the feasibility of the double-evaporator thermosiphon, experiments during the cool down process and steady state operation were extensively conducted on the double-evaporator thermosiphon (Ltot = 1075 mm, do = 160 mm). The double-evaporator thermosiphon worked successfully at steady state operation. The results showed that it had a maximum total temperature difference between the condenser and the evaporator of 1.3 K and a temperature difference between the two evaporators of 0.6 K at a heat flow of 87 W. This thermosiphon was designed for actual application to a 100 kWh SFES (Superconducting Flywheel Energy Storage) system. The potential impact of superior heat transfer characteristics of the double-evaporator thermosiphon is discussed in the paper.
B V Kosoi - One of the best experts on this subject based on the ideXlab platform.
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optimizing heat exchange apparatuses with heat pipes and Thermosiphons
Thermal Engineering, 1993Co-Authors: G F Smirnov, O K Biryukov, B V KosoiAbstract:This paper presents a general approach to the problem of optimizing heat-transfer apparatus with heat pipes and thermosyphons. An algorithm and the software realization of the proposed method are given