• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.5
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• pp.716-724
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• 1998

The objective of this research was to investigate the enhancement of heat transfer by mesh in impinging air jet system. The technique used in this research is to place mesh as a turbulence promoter in front of the impinging plate. The heat transfer characteristics with and without mesh, the effect of clearances between impinging plate and mesh, the effect of distance between nozzle exit and impinging plate, and the effect of nozzle exit velocity have been studied experimentally. When mesh was installed in front of the impinging plate, heat transer has been increased due to the acceleration between rectangular holes and divided small jets. When clearances are changed, heat transfer comes to a maximum under the condition of C = 1 mm, irrespective of nozzle exit velocity or H/B. Also the average heat transfer enhancement with mesh has been increased about 44% under the condition of U = 18 m/s, H/B = 2 and C = 1 mm, compared to the result of a flat plate without mesh. And the results of this research are compared with existing heat transfer augmentation method by rectangular or circular rod.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.58-66
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• 2019

This study investigated heat transfer and flow characteristics of a sweeping jet issued from a rectangular nozzle with a thin plate. A thin vertical aluminum plate was attached on outlet of fluidic oscillator to increase velocity of central area with Coanda effect and enhance heat transfer performance. From visualization and PIV experiments, sweeping jet with a thin plate has larger velocity distribution in center region than that of the normal sweeping jet while oscillating frequency is similar as the normal one. Thermographic phosphor thermometry method was used to visualize the temperature field and Nu distribution of plate with impinging sweeping jet with thin plate. Four Reynolds numbers and three jet-to-wall distances were selected as parameters. It is found that heat transfer performance in the low jet-to-wall spacing was enhanced as the cooled area was expanded. However, when the jet-to-wall spacing became greater than 8dh, heat transfer performance became similar due to reduced impinging velocity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.42-50
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• 1991

The purpose of this study is an augmentation of heat transfer in the case of upward rectangular impinging water jet system. The variables of this study are nozzle-to-heated surface distance, jet velocity and supplementary water height. Optimum heights of supplementary water which augment the heat transfer rate are S/B=2 for H/B=30 and S/B=I for H/B=40, 50. On the Y-direction of nozzle, there exhibits the secondary peak of heat transfer coefficient when supplementary water is not used, however using the supplementary water, it does not exhibits. In the case of using supplementary water, heat transfer coefficient increases not only in stagnation region but also in wall jet region.

• Journal of Aerospace System Engineering
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• v.12 no.5
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• pp.40-47
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• 2018

The objective of this study is to investigate the turbulence models with compressibility correction for large separation-flow in a supersonic convergent-divergent rectangular nozzle. As turbulence models, Yang and Shih's Low-Re $k-{\varepsilon}$ model, Mener's $k-{\omega}$ SST model and Wilcox's $k-{\omega}$model were evaluated. In order to get a significant compressible effects, Sarkar and Wilcox compressibility correction models were applied to the turbulence models respectively. Also, the simulation results were compared with experimental data. The turbulence model with compressibility correction model improves both of shock position and pressure recovery, but deteriorates the length of Mach disk.

• Solar Energy
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• v.15 no.1
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• pp.53-71
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• 1995

Experiments have been conducted on a planar, free surface jet of water to investigate the effects of aspect ratios(AR=6.67, 15, 26.67), average nozzle velocity($V_0=3.3m/s{\sim}78m/s$) and nozzle-to-plate spacings($Z/W=6{\sim}40$) on the characteristics of heat transfer, when 3 rectangular waterjets impinging on a flat plate which has the uniform heat flux. the scondary peaks which produced by circular jets also produced by rectangular water jets. The position of the scondary peaks depends upon the aspect ratio of nozzle. The heat transfer coefficient was subjected to the influence of aspect ratio. The heat transfer correlations and best position of nozzles which produced maximum heat transfer coefficient at stagnation point are provided.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.324-330
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• 2005

For axial-type turbines which operate at partial admission, a performance prediction model is developed. In this study, losses generated within the turbine are classified to windage loss, expansion loss and mixing loss. The developed loss model is compared with experimental results. Particularly, if a turbine operates at a very low partial admission rate, a circular-type nozzle is more efficient than a rectangular-type nozzle. For this case, a performance prediction model is developed and an experiment is conducted with the circular-type nozzle. The predicted result is compared with the measured performance, and the developed model quite well agrees with the experimental results. So the developed model could be applied to predict the performance of axial-type turbines which operate at various partial admission rates or with different nozzle shape.

• The KSFM Journal of Fluid Machinery
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• v.9 no.4 s.37
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• pp.13-19
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• 2006

For axial-type turbines which operate at partial admission, a performance prediction model is developed. In this study, losses generated within the turbine are classified to windage loss, expansion loss and mixing loss. The developed loss model is compared with experimental results. Particularly, if a turbine operates at a very low partial admission rate, a circular-type nozzle is more efficient than a rectangular-type nozzle. For this case, a performance prediction model is developed and an experiment is conducted with the circular-type nozzle. The predicted result is compared with the measured performance, and the developed model quite well agrees with the experimental results. So the developed model could be applied to predict the performance of axial-type turbines which operate at various partial admission rates or with different nozzle shape.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.849-854
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• 2008

We have been developing a 1500N-thrust Swirling-Oxidizer-Flow-Type hybrid rocket engine. In order to put the engine into practical use, we conducted long duration burning experiments up to 25s to examine the influence of configuration change of fuel grain on the engine performance and designed an LOX vaporization nozzle to supply GOX for the 1500N-thrust engine. The experiment with a small hybrid rocket engine showed that combustion was stable and the engine performance was approximately constant during combustion. There was no essential problem to with increasing combustion time. The LOX vaporization nozzle designed had 30 rectangular channels with a depth of 0.5mm. During passing through the nozzle, the LOX increased in temperature and vaporized sufficiently.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.4
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• pp.12-24
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• 2020

The dual-throat nozzle is an extremely effective method in the thrust vectoring control field, utilizing another convergent section to connect with the divergent part of the conventional convergent-divergent nozzle. In the present research, the numerical simulation is conducted to investigate the effects of the injection angle on thrust vectoring performance in a 3D supersonic nozzle. Five injection angles are discussed and core performance variations are analyzed, including the deflection angle, injected mass flow ratio, system resultant thrust ratio, efficiency, Mach number contour and streamline on the symmetry plane, and Mach number contours at different slices. Meaningful conclusions are offered for fighter jet designers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.34-39
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• 2005

In this study, 3-D nozzle shape and the shape of nozzle at exit plane were adopted as design parameter of 3-D supersonic nozzle and numerical analyses for these parameters have been performed to investigate the flow and performance characteristics for design parameters of the turbine. Firstly, comparing results for nozzle shape, rectangular nozzle had less total pressure loss occurred in axial gap and more power by 1.5% than circular nozzle did. Next, comparing the results for the shape of nozzle at exit plane, it is found that the performance of partial admission turbine was largely depended upon the gap between nozzle wall at exit plane and the hub / tip of rotor blade and the length between nozzles.