• 한국유체기계학회 논문집
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• 제10권3호
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• pp.25-32
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• 2007

The present paper deals with the heat/mass transfer characteristics for the rotating impingement/effusion cooling system. By changing the size and number of injection hole, its effects on heat/mass transfer are investigated and three different injection hole cases are considered such as LH, DH and SH, respectively. Reynolds number based on the effusion hole diameter is fixed to 3,330 and two jet orientations are considered. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. The LH case shows that the local heat/mass transfer is significantly varied by the rotation. Moreover, the low and non-uniform Sh distributions occur because the impinging jet is deflected by Coriolis force. Meanwhile, for DH and SH cases, the local heat/mass transfer coefficients are enhanced significantly compared to LH case and the rotation effect decreases with increasing the jet velocity. The averaged Sh value of DH and SH case rises up to 45%, 85% than that of LH case. However, the uniformity of heat/mass transfer deteriorates due to the steep variation of heat/mass transfer.

• Journal of Mechanical Science and Technology
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• 제14권10호
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• pp.1159-1167
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• 2000

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration. The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to $78{\mu}m$. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.271-280
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• 2001

An NAO friction material (low-steel type) containing 15 ingredients was investigated to study the role of transfer film on the friction characteristics. The friction material specimens with extra 100% of each ingredient were tested using a pad-on-disk type tribotester. A non-destructive method of measuring the transfer film was developed by considering the electric resistance of the transfer film. Results showed that solid lubricants and iron powder assisted transfer film formation on the rotor surface. Average friction coefficient was independent of transfer film thickness in this experiment. On the other hand, the thick transfer film on the rotor surface reduced the amplitude of friction oscillation under temperature conditions ( 250$^{\circ}C$) that transfer film forms.

• 대한기계학회논문집B
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• 제25권3호
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• pp.405-413
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a rotating two-pass rectangular duct. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The objective of this study is to determine the effects of turning geometry with rotation for 0.0$\leq$Ro$\leq$0.24. The results reveal that the sharp-turn corner has the larger pressure drop and lower heat transfer in the post-turn region than those of the round-turn corner. The strong secondary flow enhances heat transfer for the round-turn corner. Coriolis force induced by the rotation pushes the high momentum core flow toward the trailing wall in the first passage with radially outward flow and toward the leading wall in the second passage with radially inward flow. Consequently, the high heat transfer rates are generated on the trailing surface and the leading surface in the first and second passage, respectively. However, the strong secondary flow due to the turning dominates the flow pattern in the second passage, thus the heat transfer differences between the leading and trailing surfaces are small with the rotation.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.357-362
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• 2006

This research focused on the multi-pass heat exchanger using the minichannel possessing the spring fin. An air-water was used as working fluid. The characteristics of liquid single phase heat transfer were verified. The compact heat exchanger (heat transfer area density : ${\beta}=2,146 m^2/m^3$), based on the shape of header(Top combining header), 63 minichannels ($D_i$ : 1.4 mm, L : 0.25 m) and the air side adopting the copper wire spring fin, was fabricated. The heat transfer area density of the air side was improved up to 161% when compared with the conventional fin-tube heat exchanger that adopts the heat transfer tube with the inner diameter of 5 mm. With regard to heat transfer performance, heat transfer rate per unit volume increased up to 142% when compared with the fin-tube heat exchanger adopting the heat transfer tube with the inner diameter of 5 mm.

• 한국기계가공학회지
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• 제20권6호
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• pp.82-91
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• 2021

We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.528-533
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• 2001

An experimental study is carried out to investigate the effects of air and water mass flow rates on cooling characteristics of mist impinging jet on a flat plate. Experiments are conducted with air mass flow rates from 0.0 to 3.0 g/s, and water mass flow rates from 5.0 to 20.0 g/s. An air-atomizing nozzle is used for the purpose of controlling air and water mass flow rates. In this study, a new test section is designed to obtain local heat transfer coefficient distributions. Heat transfer characteristics of the mist impinging jet are explained with the aid of flow visualization. Surface temperature and heat transfer coefficient distributions become more uniform as air mass flow rate increases, and that the increases in water flow rate mainly enhance cooling performance. Air mass flow rate weakly influences averaged heat transfer coefficient when water mass flow rate is low, but averaged heat transfer coefficient increases remarkably as air mass flow rate in case of high water mass flow rate.

• Journal of Power Electronics
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• 제18권4호
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• pp.1154-1164
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• 2018

In single-phase magnetically coupled resonant (MCR) wireless power transfer (WPT) systems, the transfer characteristics, including the output power and transfer efficiency, are significantly influenced by the spatial scales of its coils. As a potential alternative, a three-phase MCR WPT system with cylinder-shaped coils that are excited in a voltage-fed manner has been proposed to satisfy the requirements of compact space. This system adopts a phase-shifted angle control scheme to generate a rotating magnetic field and to realize omnidirectional WPT that is immune to spatial scales. The magnetic field model and equivalent circuit models are built to holistically analyze the system characteristics under different angular misalignments. Research results show that the transfer characteristics can be improved by modulating the phase-shifted angle in each phase. Experiments have also been carried out to evaluate the accuracy of the theoretical analysis and to confirm the validity of the system modeling method.

• 대한기계학회논문집B
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• 제32권1호
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• pp.15-22
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• 2008

Recently, ultra-lightweight materials with open, periodic cell structures take much attention owing to its potential for multi-functionality such as load bearing, thermal dissipation, and actuation. This paper presents experimental results on the fluid flow and heat transfer characteristics for the Wire-woven Bulk Kagome (WBK) composed of aluminum 1100 wires. The overall pressure drop and heat transfer of the WBK specimen was experimentally investigated under forced air convection condition. The pressure loss and heat transfer performance of the aluminum WBK were compared with other heat dissipation media. It was shown that heat transfer characteristics depended on relative density and surface area density. Comparison with metal foams and other heat dissipation media such as packed beds, lattice frame materials, louvered fins, and others suggests that the aluminum WBK competes favorably with the best available heat dissipation media in heat transfer performance.

• 설비공학논문집
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• 제10권2호
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• pp.193-201
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• 1998

A heat exchanging system employing the impinging air jet is still widely used In the various fields due to its inherent merits that include the easiness in engineering applications and the high heat and/or mass transfer characteristics. The purpose of this study is to investigate the enhancement of heat transfer and flow characteristics by placing a turbulence promoters in front of heat exchanging surface. In this study, a series of circular rods are placed at the upstream of a flat plate heat exchanger that is located at potential core region(H/W=2) of a two-dimensional impinging air jet. Heat transfer enhancement is achieved by inserting turbulence promoter that results in the flow acceleration and disturbance of boundary layer. The average Nusselt number of the flat plate with the turbulence promoters is found to be around 1.42 times higher than that of the flat plate without the turbulence promoters. Based on the results of flow visualization with a smoke wire, it is confirmed that the heat transfer enhancement is caused by the flow separation and disturbance of boundary layer by inserting the turbulence promoter.