• Journal of Internet of Things and Convergence
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• v.10 no.3
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• pp.19-24
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• 2024

Recent advances in large-scale data processing technologies such as big data, cloud computing, and artificial intelligence have increased the demand for high-performance storage devices in data centers and enterprise environments. In particular, the fast data response speed of storage devices is a key factor that determines the overall system performance. Solid state drives (SSDs) based on the Non-Volatile Memory Express (NVMe) interface are gaining traction, but new bottlenecks are emerging in the process of handling large data input and output requests from multiple hosts simultaneously. SSDs typically process host requests by sequentially stacking them in an internal queue. When long transfer length requests are processed first, shorter requests wait longer, increasing the average response time. To solve this problem, data transfer timeout and data partitioning methods have been proposed, but they do not provide a fundamental solution. In this paper, we propose a dual queue based scheduling scheme (DQBS), which manages the data transfer order based on the request order in one queue and the transfer length in the other queue. Then, the request time and transmission length are comprehensively considered to determine the efficient data transmission order. This enables the balanced processing of long and short requests, thus reducing the overall average response time. The simulation results show that the proposed method outperforms the existing sequential processing method. This study presents a scheduling technique that maximizes data transfer efficiency in a high-performance SSD environment, which is expected to contribute to the development of next-generation high-performance storage systems

• Journal of Industrial Technology
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• v.25 no.A
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• pp.75-80
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• 2005

A trapezoidal fin is analyzed by using one-dimensional analytic method. For two boundary conditions, the heat transfer rate is given instead of specified temperature at the fin base and heat conduction into the fin tip is equal to heat convection from the tip. Temperatures at three different points within the trapezoidal fin are measured by using experimental apparatus. A comparison of the temperature between one-dimensional analytic method and experimentation is made as a function of dimensionless fin length under both free convection and forced convection conditions. The ratio of heat loss from the fin tip surface to that through the fin base is presented as a function of dimensionless fin length and Biot number. One of results shows that the relative error increases as the air velocity increases for forced convection conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.6
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• pp.530-537
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• 2004

In recent years, carbon dioxide among natural refrigerants has gained consider-able attention as an alternative refrigerant due to its excellent thermophysical properties. However, few investigations have been performed to develop useful correlations of heat trans-fer coefficients and pressure drop during evaporation of carbon dioxide. This study is aiming at providing the characteristics of heat transfer and pressure drop during the evaporation process of carbon dioxide. Heat is provided by a direct heating method to the test section, which was made of a seamless stainless steel tube with an inner diameter of 7.53 mm, and a length of 5.0 m. Experiments were conducted at saturation temperatures of -4 to 2$0^{\circ}C$, heat fluxes of 12 to 20 ㎾/$m^2$ and mass fluxes of 200 to 530 kg/$m^2$s. A comparison of different heat transfer correlations applicable to evaporation of carbon dioxide has been made. Based on the experiments for evaporation heat transfer and pressure drop, new correlations were developed. The newly developed empirical correlations for the heat transfer and pressure drop show average absolute deviations of 15.3% and 16.2%, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.164-170
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• 2001

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.7
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• pp.864-870
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• 1999

An experimental study Is conducted in a four-vane linear cascade in order to examine the influence of the wake behind rectangular bars on the flow and heat transfer characteristics. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress are measured using a hot-wire anemometer, and to measure the convective heat transfer coefficients on the blade surface liquid crystal/gold film Intrex technique is used. Each of experimental cases is characterized by the unsteadiness measured at the entrance of the cascade. The wake behind the rectangular bars enhances the turbulent motion of the flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the blade surface increase with increasing unsteadiness.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.262-268
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• 2008

The present paper dealt with flow heat transfer characteristics of R-410A vaporization in horizontal smooth microchannel. The test sections were made of stainless steel tube with inner diameters of 300 mm and length of 300 mm. The refrigerant was supplied with mass flux range of 260-600 kg/$m^2s$ and applied under operating heat flux range of 5-20 kW/$m^2$ using a direct electric current heating method. The in let saturation temperature was set at $10^{\circ}C$ and vapor quality up to 1.0. The influences of mass flux, heat flux and inner tube diameter on local heat transfer coefficients were presented. Comparison with existing heat transfer coefficient correlations was performed. An improved heat transfer coefficient correlation for refrigerant vaporization in microchannel based on superposition model was developed with a mean deviation of 14.01%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5317-5322
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• 2013

This study presents a prediction method for heat transfer performance of a gas cooler of $CO_2$ heat pump using ${\epsilon}$-NTU method, and compared the results with the experimental data from the open literature. The heat transfer rate, refrigerant side outlet temperature and water side outlet temperature were calculated by using EES(Engineering Equation Solver)program in multi-tube-in-tube type $CO_2$ heat pump gas cooler. Analysis was performed in two methods : The first method performed without dividing into the test section by applying an analysis of the mean properties(mean analysis). The second method, tube length divided into 50 sections, was applied to the local properties(local analysis). From the present study, a good agreement at the local analysis was obtained between the analytical and experimental results by 0.3~1.1%, 1.31~1.88% and 3.12~5.18% for heat transfer rate, water and refrigerant side outlet temperatures, respectively.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.261-264
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• 1998

Controlled transfer (CT) capability, a new ATM transfer capability (ATC) for high-speed data applications which using credit-based flow control, has recently been proposed and studied in ITU-T. In this paper, we review the existing dyanmic buffer allocation schemes and propose an improved scheme. Also, we compare the performances of the existing buffer allocation methods such as static allocation, flow controlled virtual channels (FCVC), and zero queueing flow control (ZQFC) with the proposed method through simulation. Simulation results show that the proposed scheme exhibits a better performance than the existing schemes in terms of throughput, fairness, queue length and link utilization.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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• pp.1001-1012
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• 1998

This paper reports the analysis of dynamic characteristics of air-cooled condenser. At first, there is an assumption that the superheated vapor flows into the condenser inlet. And in order to consider the effect of pressure change in the dynamic characteristics of the condenser the combined system of condenser and compressor was used. By using the equation of energy balance and the equation of mass balance, the basic equation for describing the dynamic characteristics of condenser can be derived. The transfer function for describing dynamic response of the condenser to flow rate change outlet can be obtained from using linearizations and Laplace transformations of the equation. From this transfer function, analytical investigation which affects the frequency responses of condenser has been made. Through this study, it became possible that the information about the dynamic characteristics of air-cooled condenser is offered. While the average heat transfer coefficient of the refrigerant side necessary for the theoretical calculation of the dynamic characteristics is given by calculation method for the tube length and pressure drop of air-cooled condenser.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.231-235
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• 1999

Cooling characteristics of cooling jacket for spindle system with built-in motor are studied. for the analysis, three dimensional model for the cooling jacket is built by using finite volume method. The three dimensional model includes the estimation on the amount of heat generation of bearing and built-in motor and the thermal characteristic values such as heat transfer coefficients on the boundary. The temperature distributions and the cooling characteristics are analyzed by using the commercial software FLUENT. Numerical results show that stream-wise cross section area and flow rate are important factors for cooling characteristics of cooling jacket. Cooling performance of cooling jacket is good in condition that stream-wise cross section's horizontal length is close to its vertical one and flow rate is high. This results show that heat transfer is dominated by velocity profile and heat transfer area.