The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Ji Hwan Jeong - One of the best experts on this subject based on the ideXlab platform.
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SUCTION PIPE DESIGN CRITERION FOR R-134a REFRIGERATORS TO SECURE OIL RETURN TO COMPRESSOR
International Journal of Air-Conditioning and Refrigeration, 2020Co-Authors: Sangchul Do, Ji Hwan JeongAbstract:Polyol Ester oil–air two-phase counter current flow experiments were performed with small diameter tubes to measure gas velocities for the counter current flow limitation Point and the flow Reversal Point. The test section was made of a Pyrex glass tube to allow visual observation. The geometry of the test section was designed to simulate various shapes of suction lines of refrigerators. The inner diameter of the test tube was 7 mm and the height was 1 m. The inclination of the test tubes varied from vertical to crank type with various horizontal lengths. An empirical oil return criterion was suggested based on the flow Reversal Points. This criterion was also verified using a refrigerator test apparatus and refrigerant.
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Development of suction pipe design criterion to secure oil return to compressor
2020Co-Authors: Jin Yong Jang, Ji Hwan Jeong, Sangchul Do, Bongjun ChoiAbstract:In the present work, phenomena associated with counter current flow limitation (CCFL) were experimentally investigated using small diameter tubes in order to suggest criterion for which the oil return is secured. The test section is made of Pyrex glass tube to allow visual observation. The inner diameter of the test tube is 7mm and the height is 1m. The inclination of test tubes varied from vertical to crank type with various horizontal lengths. Waterair flow and lubricant oil-air flow were examined through a series of experiment at various liquid flow rates. In this experimental study, flow Reversal and flooding phenomena were visually observed and two-phase flow rate were measured. Flow Reversal Point represents the air flow rate when the liquid film begins to flow downwards in the tube below the liquid inlet location. Whole supplied liquid flows upward when the gas flow rate is larger than this value. So the flow Reversal Point can be interpreted as oil return criterion and the flow Reversal Points were measured using various shape of test section in a wide range of liquid flow rate. The gas velocities for the flow Reversal Point appeared to be similar over a certain range of liquid flow rate. Flooding Point was defined as the air flow rate when liquid starts to flow above the liquid inlet part. The air flow rate needed to cause flooding is inversely proportional to the liquid flow rate. Both flow Reversal and flooding velocity also depend on the inclination angle, horizontal length and liquid property.
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Experimental study on flooding and flow Reversal in small diameter tubes with various inclinations and horizontal lengths
International Journal of Refrigeration, 2014Co-Authors: Tiandong Guo, Ji Hwan JeongAbstract:Lubricant oil return to compressor in household refrigerator is controlled by oil-refrigerant two-phase flow behavior in the suction pipe. Conditions of flooding and flow Reversal were considered as a conservative bound for the oil return. Phenomena associated with counter current flow limitation (CCFL or flooding) and flow Reversal were experimentally investigated using small diameter tubes with vertical, inclined and crank-type configurations. Flooding and flow Reversal phenomena were visually observed. Both flooding and flow Reversal Points were measured using various shapes of test section in a wide range of liquid flow rate. The gas velocities for flooding were found to be inversely proportional to the liquid flow rates and independent of the tube configurations. The gas velocities for the flow Reversal Point appeared to be at a similar level over a certain range of liquid flow rate but strongly depend on the inclination angle, horizontal length and kind of liquid. © 2013 Elsevier Ltd and IIR. All rights reserved.
Miaomiao Wang - One of the best experts on this subject based on the ideXlab platform.
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a potential strain indicator for brittle failure prediction of low porosity rock part i experimental studies based on the uniaxial compression test
Rock Mechanics and Rock Engineering, 2015Co-Authors: Meng Qi, Guoliang Li, Pei Li, Miaomiao WangAbstract:In this paper, we have investigated the quantitative relationship between the axial strain threshold at the volumetric strain Reversal Point (e1cd) and the strain threshold at the peak stress (e1ucs) during the uniaxial compression tests. We found that normalized values of e1ucs/e1cd for different rock types are typically ~1.34(±0.24). This is especially true for igneous and metamorphic rocks, or low-porosity sedimentary rocks. To verify this finding, we investigated seven granitic gneiss samples using the uniaxial compression test. Our results were consistent with the above statistics. We inferred that e1ucs/e1cd may be an intrinsic property of low-porosity rocks, and may be a potential indicator for predicting failure strains in laboratory-scale rock samples.
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A Potential Strain Indicator for Brittle Failure Prediction of Low-porosity Rock: Part I—Experimental Studies Based on the Uniaxial Compression Test
Rock Mechanics and Rock Engineering, 2014Co-Authors: Meng Qi, Guoliang Li, Pei Li, Miaomiao WangAbstract:In this paper, we have investigated the quantitative relationship between the axial strain threshold at the volumetric strain Reversal Point (e1cd) and the strain threshold at the peak stress (e1ucs) during the uniaxial compression tests. We found that normalized values of e1ucs/e1cd for different rock types are typically ~1.34(±0.24). This is especially true for igneous and metamorphic rocks, or low-porosity sedimentary rocks. To verify this finding, we investigated seven granitic gneiss samples using the uniaxial compression test. Our results were consistent with the above statistics. We inferred that e1ucs/e1cd may be an intrinsic property of low-porosity rocks, and may be a potential indicator for predicting failure strains in laboratory-scale rock samples.
Pengyu Lu - One of the best experts on this subject based on the ideXlab platform.
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a new lstm based Reversal Point prediction method using upward downward Reversal Point feature sets
Chaos Solitons & Fractals, 2020Co-Authors: U Juhyok, Pengyu LuAbstract:Abstract A novel Long-Short Term Memory (LSTM)-based prediction model of stock price Reversal Point was proposed by using upward/downward Reversal Point feature sets. (1) Based on the combinations of candlestick indicators and technical indicators, 27 sets of feature candidates were constructed, and then the feature sets suitable to each stock in terms of URP/DRP prediction were respectively extracted. (2) LSTM-based URP/DRP predictors were constructed, the results of which are combined to improve the prediction accuracy. Using this model, Reversal Point prediction has been conducted for 10 Chinese stocks and 10 American stocks. In results, the mean prediction accuracy (F1) was 68.6% and 55.2% for the Chinese and the American stock markets, respectively. Results show that the average prediction accuracy has been evaluated to be higher for Chinese market by 13.4% compared to American one. Comparing with Support Vector Machine (SVM), Multilayer Perceptron (MLP) and Convolutional Neural Networks (CNN) model, F1 of proposed model has been increased by 5.9%, 11.7% and 5.3%, respectively.
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A new LSTM based Reversal Point prediction method using upward/downward Reversal Point feature sets
Chaos Solitons & Fractals, 2020Co-Authors: Juhyok U, Pengyu LuAbstract:Abstract A novel Long-Short Term Memory (LSTM)-based prediction model of stock price Reversal Point was proposed by using upward/downward Reversal Point feature sets. (1) Based on the combinations of candlestick indicators and technical indicators, 27 sets of feature candidates were constructed, and then the feature sets suitable to each stock in terms of URP/DRP prediction were respectively extracted. (2) LSTM-based URP/DRP predictors were constructed, the results of which are combined to improve the prediction accuracy. Using this model, Reversal Point prediction has been conducted for 10 Chinese stocks and 10 American stocks. In results, the mean prediction accuracy (F1) was 68.6% and 55.2% for the Chinese and the American stock markets, respectively. Results show that the average prediction accuracy has been evaluated to be higher for Chinese market by 13.4% compared to American one. Comparing with Support Vector Machine (SVM), Multilayer Perceptron (MLP) and Convolutional Neural Networks (CNN) model, F1 of proposed model has been increased by 5.9%, 11.7% and 5.3%, respectively.
Meng Qi - One of the best experts on this subject based on the ideXlab platform.
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a potential strain indicator for brittle failure prediction of low porosity rock part i experimental studies based on the uniaxial compression test
Rock Mechanics and Rock Engineering, 2015Co-Authors: Meng Qi, Guoliang Li, Pei Li, Miaomiao WangAbstract:In this paper, we have investigated the quantitative relationship between the axial strain threshold at the volumetric strain Reversal Point (e1cd) and the strain threshold at the peak stress (e1ucs) during the uniaxial compression tests. We found that normalized values of e1ucs/e1cd for different rock types are typically ~1.34(±0.24). This is especially true for igneous and metamorphic rocks, or low-porosity sedimentary rocks. To verify this finding, we investigated seven granitic gneiss samples using the uniaxial compression test. Our results were consistent with the above statistics. We inferred that e1ucs/e1cd may be an intrinsic property of low-porosity rocks, and may be a potential indicator for predicting failure strains in laboratory-scale rock samples.
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A Potential Strain Indicator for Brittle Failure Prediction of Low-porosity Rock: Part I—Experimental Studies Based on the Uniaxial Compression Test
Rock Mechanics and Rock Engineering, 2014Co-Authors: Meng Qi, Guoliang Li, Pei Li, Miaomiao WangAbstract:In this paper, we have investigated the quantitative relationship between the axial strain threshold at the volumetric strain Reversal Point (e1cd) and the strain threshold at the peak stress (e1ucs) during the uniaxial compression tests. We found that normalized values of e1ucs/e1cd for different rock types are typically ~1.34(±0.24). This is especially true for igneous and metamorphic rocks, or low-porosity sedimentary rocks. To verify this finding, we investigated seven granitic gneiss samples using the uniaxial compression test. Our results were consistent with the above statistics. We inferred that e1ucs/e1cd may be an intrinsic property of low-porosity rocks, and may be a potential indicator for predicting failure strains in laboratory-scale rock samples.
Mathias Fink - One of the best experts on this subject based on the ideXlab platform.
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Relation between time Reversal focusing and coherent backscattering in multiple scattering media: A diagrammatic approach
Physical Review E, 2004Co-Authors: Julien De Rosny, Arnaud Tourin, Arnaud Derode, Bart Van Tiggelen, Mathias FinkAbstract:In this paper, we revisit one-channel time Reversal (TR) experiments through multiple scattering media in the framework of the multiple scattering theory. The hyperresolution and the self-averaging property are retrieved. The developed formalism leads to a deeper understanding of the role of the ladder and most-crossed diagrams in a TR experiment and also establishes the link between TR and coherent backscattering (CBS). Especially, we show that when the initial source and the time Reversal Point are at the same location, the time-reversed amplitude is twice higher. Surprisingly, this enhancement is due to the ladder diagrams and not to the most-crossed ones, contrary to CBS. These theoretical predictions are confirmed by experimental results. The experiments are performed with ultrasonic waves propagating through a random collection of parallel steel rods.
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One-channel time-Reversal in chaotic cavities: Theoretical limits
Journal of the Acoustical Society of America, 1999Co-Authors: Carsten Draeger, Mathias FinkAbstract:One-channel time-Reversal experiments in closed chaotic cavities produce excellent, but not perfect, time-reversed focusing. This paper investigates such experiments by a simple eigenmode analysis of the system. It shows that the process is, even for long reversed signals, subject to an information loss during recording and re-emission which prevents perfect time-Reversal. This fact can be expressed by a simple equation, called the cavity equation, which states that the signal of a one-channel time-Reversal is equal to the signal of a perfect time-Reversal after convolution with the backscattering impulse response of the Reversal Point (i.e., from this Point to this Point). The latter convolution describes the introduction of the loss of information. Furthermore, arguments are presented suggesting that one third of the total energy of the time-reversed wave field is actually contained in the refocusing wavefront. The predictions are verified by numerical finite-difference time-domain simulations.
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One-channel time-Reversal in chaotic cavities: Experimental results
The Journal of the Acoustical Society of America, 1999Co-Authors: Carsten Draeger, Jean-Christian Aime, Mathias FinkAbstract:One-channel time-Reversal experiments in closed chaotic cavities produce excellent, but not perfect, time-reversed focusing. This paper investigates such experiments by a simple eigenmode analysis of the system. It shows that the process is, even for long reversed signals, subject to an information loss during recording and re-emission which prevents perfect time-Reversal. This fact can be expressed by a simple equation, called the cavity equation, which states that the signal of a one-channel time-Reversal is equal to the signal of a perfect time-Reversal after convolution with the backscattering impulse response of the Reversal Point (i.e., from this Point to this Point). The latter convolution describes the introduction of the loss of information. Furthermore, arguments are presented suggesting that one third of the total energy of the time-reversed wave field is actually contained in the refocusing wavefront. The predictions are verified by numerical finite-difference time-domain simulations.