Browsing by Author "Lin, Kai-Hsiang"

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A Flash Scheduling Strategy for Current Capping in Multi-Power-Mode SSDs
(2017-01-01)
Chang, Li-Ping
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Cheng, Chia-Hsiang
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Lin, Kai-Hsiang
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資訊工程學系
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Department of Computer Science
Solid state disks (SSDs) employ internal parallelism for high throughput, but concurrent flash operations can draw a high instantaneous current. Due to power budgeting or power-source changing, SSDs could be forced into a new operation mode with a lower current supply limit. This study presents a flash scheduling algorithm to optimize the SSD internal parallelism subject to the current limit. Based on realistic flash current models, our scheduler decides the actual starting times of every flash operation, and it efficiently examines the peak current only at a few time points. Our experiments show that our approach outperformed existing methods, and its feasibility had been verified on the OpenSSD platform.
Experimental investigation of moist air condensation on hydrophilic, hydrophobic, superhydrophilic, and hybrid hydrophobic-hydrophilic surfaces
(2017-12-01)
Yang, Kai-Shing
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Lin, Kai-Hsiang
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Tu, Cheng-Wei
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He, Yu-Zhen
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Wang, Chi-Chuan
This study experimentally investigates the condensation performance amid hydrophobic, hydrophilic, superhydrophilic and hydrophobic-hydrophilic hybrid patterned surfaces with air velocity ranging from 0.5 m/s to 4.0 m/s and relative humidity of 85%, 60% and 40%. The hybrid novel surface employs inverted V shape channels design with alternate hydrophilic and hydrophobic channel to direct condensate, and the accumulated condensate is gathered at vertical hydrophilic channel for further effective condensate removal. It is found that the heat transfer coefficient for hydrophobic surface is higher than that of hydrophilic surface irrespective of the operational velocity and relative humidity. Dropwise condensation prevails for the hydrophobic surface and a twig-like structure of condensate is seen for the hydrophilic surface, and this phenomenon becomes more pronounced when the relative humidity is increased. The superhydrophilic surface shows the worst heat transfer performance due to filmwise condensation. The hybrid surface shows superior heat transfer performance over other surfaces. The heat transfer coefficient obtained is around 3-9% higher than that of hydrophobic surface and is about 6-16% higher than hydrophilic one. The proposed novel design offers a shorter cyclic condensate removal time and better condensate drainage. It is found that the maximum diameter.for the hybrid surface is about 80-90% smaller than the hydrophobic surface and the droplet size before falling off is relatively independent of operational velocity. (C) 2017 Elsevier Ltd. All rights reserved.
KVSSD: Close Integration of LSM Trees and Flash Translation Layer for Write-Efficient KV Store
(2018-01-01)
Wu, Sung-Ming
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Lin, Kai-Hsiang
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Chang, Li-Pin
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資訊工程學系
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Department of Computer Science
Log-Structured-Merge (LSM) trees are a write-optimized data structure for lightweight, high-performance Key-Value (KV) store. Solid State Disks (SSDs) provide acceleration of KV operations on LSM trees. However, this hierarchical design involves multiple software layers, including the LSM tree, host file system, and Flash Translation Layer (FTL), causing cascading write amplifications. We propose KVSSD, a close integration of LSM trees and the FTL, to manage write amplifications from different layers. KVSSD exploits the FTL, mapping mechanism to implement copy-free compaction of LSM trees, and it enables direct data allocation in Hash memory for efficient garbage collection. In our experiments, compared to the hierarchical design, our KVSSD reduced the write amplification by 88% and improved the throughput by 347%.
Modeling and simulation of the transcritical CO2 heat pump system
(2013-12-01)
Lin, Kai-Hsiang
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Kuo, Cheng-Shu
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Hsieh, Wen-Der
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Wang, Chi-Chuan
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機械工程學系
In this study, a CO2 transcritical cycle model without imposing any excessive constraints such as fixed discharge pressure and suction pressure is developed. The detailed geometrical variation of the gas cooler and the evaporator have been taken into account. The model is validated with the experimental measurements. Parametric influences on the CO2 system with regard to the effect of dry bulb temperature, relative humidity, inlet water temperature, compressor speed, and the capillary tube length are reported. The COP increases with the dry bulb temperature or the inlet relative humidity of the evaporator. Despite the refrigerant mass flowrate may be increased with the inlet water temperature, the COP declines considerably with it. Increasing the compressor speed leads to a higher heating capacity and to a much lower COP. Unlike those of the conventional sub-critical refrigerant, the COP of the transcritical CO2 cycle does not reveal a maximum value against the capillary tube length. (C) 2013 Elsevier Ltd and IIR. All rights reserved.
Performance of a tube-in-tube CO2 gas cooler
(2012-11-01)
Yu, Pei-Yu
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Lin, Kai-Hsiang
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Lin, Wei-Keng
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Wang, Chi-Chuan
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機械工程學系
In this study, a tube-in-tube heat exchanger model applicable to supercritical CO2 and water was developed. The developed model is first validated with some existing measurements. Normally, the variation of the heat transfer rate for a constant-property working fluid shows a monotonic decrease from the inlet of minimum heat capacity flow rate (C-min). By contrast, the CO2 may present a local minimum and a local maximum along the length of the heat exchanger, provided CO2 passes through the pseudo-critical temperature, and this phenomenon becomes more and more pronounced when the pressure is close to the critical pressure. In contrast, it is possible for a local maximum heat transfer rate to occur near the inlet of C-min even when the CO2 does not pass through the pseudo-critical point. This happens when C-min is on the water side and the property variation of CO2 is taken into account. The calculation also shows that the effect of the inlet pressure on the variation of the CO2 temperature is not as apparent as the effect of the inlet pressure on the heat transfer rate, even when there is a significant change in the overall heat transfer coefficient, implying that the heat transfer characteristics of CO2 near the pseudo-critical region is similar to normal refrigerants, which show an invariant temperature at the condensation point. Hence, it would be beneficial to extend the influence of the pseudo-critical region when taking the heat transfer augmentation into consideration. (C) 2012 Elsevier Ltd and IIR. All rights reserved.