• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.780-788
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• 2004

This paper reports the fluid flow and heat transfer around a module cooled by forced air flow generated by a piezoelectric(PZT) cooling fan. The fluids are locally accelerated by a flexible PZT fan which deflects inside a fluid transport system of comparatively simple structure mounted on a PCB in a parallel-plate channel(450${\times}$80${\times}$700㎣). Input voltages of 20-100V and a resonance frequency of 23㎐ were used to vibrate the cooling fan. Input power to the module was 4W. The fluid flow around the module was visualized by using PIV system. The temperature distributions around a heated module were visualized by using liquid crystal film(LCF). The cooling effect using a PZT fan was independent of the vent area ratios at the channel inlet and was similar to the forced convection cooling. We found that the flow type was Y-shape and the cooling effect was increased by the wake generated by a piezoelectric cooling fan.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.1-10
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• 1999

In this study, a numerical analysis is made on the ice-formation for laminar water flow inside a stenotic tube. The study takes into account the interaction between the laminar flow and the stenotic port in the circular tube. The purpose of the present numerical investigation is to assess the effect of a stenotic shape on the instantaneous shape of the flow passage during freezing upstream/downstream of the stenotic channel. In the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the solid and liquid regions are resolved. In a channel flow between parallel plates, the agreement between the of predictions and the available experimental data is very good. Numerical analyses are performed for parametric variations of the position and heights of stenotic shape and flow rate. The results show that the stenotic shape has the great effect on the thickness of the solidification layer inside the tube. As the height of a stenosis grows and the length of a stenosis decreases, the ice layer thickness near the stenotic port is thinner, due to backward flow caused by the sudden expansion of a water tunnel. It is found that the flow passage has a slight uniform taper up to the stenotic channel, at which a sudden expansion is observed. It is also shown that the ice layer becomes more fat in accordance with its Reynolds number.

• Journal of Advanced Marine Engineering and Technology
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• v.4 no.1
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• pp.23-31
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• 1980

The fluid static pressure has been generally measured by means of a small hole leading to a measuring instrument. In case of viscoelastic fluids, however, it has been shown experimentally that a systematic error exists in measuring the static pressure by means of the small hole becuase viscoelasitc fluids have many properties that can not be observed in Newtonian fluids. In this paper, in order to examine the mechanism of the errors in measuring the static pressure of viscoelasitc fluids, flow patterns in the vicinity of static pressure measuring hole were photographically taken and observed graphically. The experiments to take photographs of flow patterns were performed by a parallel plate channel with the steady two-dimensional shear flow of viscoelastic fluids. Results of the experiment are classified as following three regions; (1) Arched symmetrical flow pattern region. (2) Asymmetrical flow pattern region. (3) Rectilinear symmetricl flow pattern region.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.272-277
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• 2003

This paper reports the fluid flow and heat transfer around a module cooled by forced air flow generated by a piezoelectric(PZT) cooling fan. A flexible PZT fan with distortion in a fluid transport system of comparatively simple structure which was mounted on a PCB in a parallel-plate channel($450{\times}80{\times}700mm^3$) accelerates surrounding fluid locally. Input voltages of 20-100V and a resonance frequency of 23Hz were used to vibrate the cooling fan. Input power to the module was 4W. The cooling effect using a PZT fan was larger than that of free convection. Fluid flow around the module were visualized by using PIV system. The temperature distribution around heated module were visualized by using liquid crystal film(LCF). We found that the flow type was y-shaped and the cooling effect was increased by the wake generated by a piezoelectric cooling fan.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.51-58
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• 2008

Many researches for effects of different flow configurations on performance of Proton Exchange Membrane Fuel Cell have extensively been done but the effects of flow direction at the same flow channel shape should be considered for optimal operation of fuel cell as well. In this paper a numerical computational methode for simulating entire reactive flow fields including anode and cathode flow has been developed and the effects of different flow direction at parallel flow was studied. Pressure drop along the flow channel and density distribution of reactant and products and water transport, ion conductivity across the membrane and I-V performance are compared in terms of flow directions(co-flow or counter-flow) using above numerical simulation method. The results show that the performance under counter-flow condition is superior to that under co-flow condition due to higher reactant and water transport resulting to higher ion conductivity of membrane.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1418-1425
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• 1999

Flow over a protruding surface is investigated using numerical simulation. We consider flow between two parallel plates with a cube mounted on one side of the channel. As the flow approaches the cube, the adverse pressure gradient produces three-dimensional boundary-layer separation, resulting In the formation of horseshoe vortices. The objective of our study is to clarify both the steady and the unsteady characteristics of the vortex system. As the Reynolds number increases, the structure of the vortices near the cube becomes complex and the number of vortices increases. The distribution of skin friction on the cube-mounted wall reflects the effect of the horseshoe vortices. All these results are consistent with the experimental findings currently available.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.195-200
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• 2015

The thermal performance in the channels with two-wall rectangular convergent/divergent cross-sectional areas along the axial distance was investigated experimentally. The ribbed rectangular convergent/divergent channels were manufactured with a fixed rib height (e) = 10 mm and the ratio of rib spacing (p) to height (e) = 10. Three different parallel angled ribs (a = $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$) were each placed on the channel's one sided wall only. The convergent channel of $D_{ho}/D_{hi}=0.67$ and the divergent channel of $D_{ho}/D_{hi}=1.49$ were considered. The ribbed divergent channel produced better thermal performance than the ribbed convergent channel in three different restrictions; identical flow rate, identical pumping power, and identical pressure loss.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.6
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• pp.646-652
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• 2002

The influence of reciprocating frequency and radius on heat transfer in the roughened rectangular channel is experimentally investigated. The aspect ratio (width/height) of the duct is 2.33 and the rib height is one fifteenth of the duct height. And the ratio of rib-to-rib distance to rib height is 10. The discrete ribs were periodically attached to the button wall of the duct with a parallel orientation. The parametric test matrix involves Reynolds number, reciprocating, and reciprocating radius, in the ranges, 1,000∼6,000, 1.7∼2.5 HB and 7∼15cm, respectively. The combined effects of reciprocating frequency and reciprocating radius have considerable influence on the heat transfer due to the modified vortex flow structure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.6
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• pp.421-429
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• 2011

Experimental and theoretical studies on cooling performance of two-channel thermoelectric air-cooling system in parallel flow are conducted. The effects of operating temperature to physical properties of thermoelectric module (TEM) are experimentally examined and used in the analysis of an air-cooling system considering thermal network and energy balance. The theoretical predicted temperature variation and cooling capacity are in good agreement with measured data, thereby validating analytic model. The heat absorbed rate increases with increasing the voltage input and decreasing thermal resistance of the system. The power consumption of TEM is linearly proportional to mean temperature differences due to variations of the physical properties on operation temperature of TEM. Furthermore thermal resistance of hot side has greater effects on cooling performance than that of cold side.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3114-3119
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• 2008

Relatively high convective flow exists in the under-rib regions of a gas diffusion layer (GDL) when serpentine flow fields are employed in a PEMFC. This under-rib convection is believed to be favorable for the performance of PEMFCs, by enabling more effective use of catalysts in the under-rib regions. From the fact that the under-rib convection in a GDL is directly proportional to the permeability of the GDL, computational fluid dynamics (CFD) simulations were performed to discover the relationship between the GDL permeability and the PEMFC performance. Single-, triple-, and quintuple-path parallel serpentine flow fields for $9\;cm^2$ active cell area were considered while changing the GDL permeability from $1{\times}10^{-12}$ to $5{\times}10^{-11}m^2$. The results showed that higher GDL permeability generally resulted in better performance of PEMFCs, but the degree of performance enhancement became smaller as the parallel path number increased. The effects of the permeability on the local variables were also discussed.