• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.292-300
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• 2010

This study strives to develop an effective strategy to inhibit cavitation inception on hydrofoils by using local cooling technique. By setting up a temperature boundary condition and cooling a small area on the upper surface of a hydrofoil, the fluid temperature around the cooling surface will be decreased and thereby the corresponding liquid saturation pressure will drop below the lowest absolute pressure within the flow field. Hence, cavitation can never occur. In this paper, a NACA0015 hydrofoil at $4^{\circ}$ angle of attack was numerically investigated to verify the effectiveness of the proposed technique. The CFD results indicate that the cooling temperature and the cooling surface roughness are the critical factors affecting the success of such technique used for cavitation suppression.

• Journal of ILASS-Korea
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• v.15 no.4
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• pp.202-207
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• 2010

Mist cooling is widely employed as a cooling technique of high temperature surfaces, and it has heat transfer characteristics similar to boiling heat transfer which has the convection, nucleate and film boiling regions. In the present study, mist cooling heat transfer was experimentally investigated for the mist flow impacting on the heated surfaces of mico-fins. The mist flow was generated by supersonic vibration. Experiments were conducted under the test conditions of droplet flow rate, $Q=6.02{\times}10^{-9}{\sim}3.47{\times}10^{-8}\;m^3/s$ and liquid temperature, $T_f=30{\sim}35^{\circ}C$. From the experimental results, it is found that an increase in the droplet flow rate improves mist cooling heat transfer in the both case of smooth surface and surfaces of micro-fins. Micro-fins surfaces enhance the mist cooling heat transfer. Besides, the experimental results show that an increase in the droplet flow rate decrease the heat transfer efficiency of mist cooling.

• The KSFM Journal of Fluid Machinery
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• v.12 no.4
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• pp.44-53
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• 2009

Numerical design optimization of a fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness by combining a three-dimensional Reynolds-averaged Navier-Stokes analysis with the radial basis neural network method, a well known surrogate modeling technique for optimization. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. Twenty training points are obtained by Latin Hypercube sampling for three design variables. Sequential quadratic programming is used to search for the optimal point from the constructed surrogate. The film-cooling effectiveness has been successfully improved by the optimization with increased value of all design variables as compared to the reference geometry.

• The KSFM Journal of Fluid Machinery
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• v.19 no.4
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• pp.13-18
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• 2016

The various film cooling hole shapes have been proposed for effective external cooling of gas turbine blade. In this study, the film cooling effectiveness by three different hole shapes (cylindrical hole, $15^{\circ}$ angle anti-vortex hole, 30-7-7 fan-shaped hole) were examined experimentally. Pressure Sensitive Paint (PSP) technique was used to measure the film cooling effectiveness. The coolant to mainstream density ratio was 1.0 and three blowing ratios of 0.5, 1.0, and 2.0 were considered. Results clearly showed that the effect of hole shape on the distribution of film cooling effectiveness. For the cylindrical hole case, the film cooling effectiveness decreased remarkably as the blowing ratio increased due to the jet lift off. Because of large hole exit area and low coolant momentum, the 30-7-7 fan-shaped hole case showed the highest film cooling effectiveness at all blowing ratio, followed by the anti-vortex hole case.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.4
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• pp.78-84
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• 2001

This study deals with the heat-treatment technique of SM45C steel with respect to less of deformation in control. The whole process for the production of landing gear must go through with uniformally controlled heat treatment, where as most deformation usually occur in nonuniform cooling environment. When a heated metal is submerged into a certain quenchant, the rate of cooling rapidity can be measured rather slow during the early stage of the procedure due to an Occurrence of a vapor blanked. As the additional course of cooling action is applied and the vapor from a vapor blanked is destroyed simultaneously, the speed of cooling promptness can be considered rather swift. The object of this study is to control the certain deformations as in the procedure of a heat treatment for landing gear by analyzing and improving the conditions of different substance of quenching liquids. Several noticeable curves indicating the temperature variation on the ap-plied metals during the cooling procedures, along with detectable rates of water verses oil and that of different polymer solutions are illustrated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.10
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• pp.966-978
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• 2011

Transpiration cooling is the most effective cooling technique for the high-performance liquid rockets and air-breathing engines operating in aggressive environments with higher pressures and temperatures. When applying transpiration cooling, combustor liners and turbine blades/vanes are cooled by the coolant(air or fuel) passing through their porous walls and also the exit coolant acting as an insulating film. Practical implementation of the cooling technique has been hampered by the limitations of available porous materials. But advances in metal-joining techniques have led to the development of multi-laminate porous structures such as Lamilloy$^{(R)}$ fabricated from several diffusion-bonded, etched metal thin sheets. And also with the availability of lightweight, ceramic matrix composites(CMC), transpiration cooling now seems to be a promising technique for high-performance engine cooling. This paper reviews recent research activities of transpiration cooling and its applications to gas turbines, liquid rockets, and the engines for hypersonic vehicles.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.425-432
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• 2009

In this study, the improvement of cooling capacity by applying gas injection technique in a two-stage heat pump using R410A was experimentally investigated. A twin rotary type compressor with gas injection was applied to the heat pump system. The optimum refrigerant charge for the injection and the non-injection cycles was selected to achieve the maximum COP at the cooling standard condition. The injection cycle showed less optimum refrigerant charge than that of the non-injection cycle. The cooling performances of the injection and the non-injection cycles were measured and compared by varying compressor frequency from 40 to 90 Hz. The cooling capacity of the gas injection cycle was 1.6% -11.3% higher than that of the non-injection cycle. The COP of the gas injection cycle was 13.7% to 28.9% higher than that of the non-injection cycle at the same cooling capacity. The heat pump system showed stable operation after 30% of the injection valve opening.

• The KSFM Journal of Fluid Machinery
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• v.12 no.2
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• pp.24-30
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• 2009

Flow and noise analyses are conducted for examining a new design concept of impinging jet electronics cooling, and the analysis results are compared with conventional electronics cooling techniques. For the application of impinging jet electronics cooling method, the present study considers the air duct where air is supplied by axial fan and air flow from the duct is impinged vertically onto the electronic component heat source. Applying CFD simulation technique and fan noise model to the present cooling scheme, the cooling performance of the impinging jet as well as the operation condition and the noise characteristics of fan are investigated for various impinging jet nozzle conditions and fan models. Furthermore, the impinging jet electronics cooling analysis results are compared with the conventional parallel-flow cooling scheme to give the design concept and criteria of impinging jet cooling method.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.5
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• pp.67-72
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• 2008

The film cooling effectiveness on a flat plate measured by pressure sensitive paint technique. Six film cooling hole were fabricated on a flat plate with 30 degree angle with respect to the surface and three blowing ratios of 0.5, 1, and 2 were tested. Results showed that PSP technique successfully evaluated the distribution of film cooling effectiveness and showed similar results with references. The film cooling effectiveness near the film cooling holes was higher for lower blowing ratio case. As the blowing ratio was increased, the film cooling effectiveness near the film cooling hole decreased due to the lift off of the coolant. At far downstream, the film cooling effectiveness for higher blowing ratio was higher due to the coolant reattachment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.6
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• pp.59-65
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• 2010

This study deals with the characteristic of refrigerant for heat-treatment deformation control of SCM415 steel. The control of heat-treatment deformation must need the progress of production parts for an industry machine. Most of the deformation is occurred on unequal cooling. The unequal cooling is occurred by a property of quenching refrigeration. When a heated metal is deposited in the refrigeration, the cooling speed is so slow in early period of cooling because of occurring a steam-curtain. After more cooling, the steam-curtain is destroyed. In this progress, the cooling speed is very fast. The object of this study is to control the deformation of heat-treatment for the part of the industry machine by improving the conditions of quenching. The cooling curves and cooling rates of water, oil and polymer solution are obtained and illustrated. From the characteristics of the quenching refrigerant, the effects of heat-treatments on the thermal deformation and fatigue strength are also investigated.