• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1684-1691
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• 2015

For performance improvement and compactness, usage of enhanced tube is inevitable. However, studies on enhanced tubes for generator is very limited. In this study, pool boiling tests were conducted for 7 heat transfer tubes. Test range covered pressure 7.38~101.3 kPa and heat flux $20{\sim}40kW/m^2$. Results show that boiling heat transfer coefficient increases as pressure or heat flux increases. Under atmospheric condition, high heat transfer coefficients were obtained for notched fin and low fin tubes(225% and 202% of the 19.0 mm smooth tube, which yielded the lowest heat transfer coefficient). As pressure decreased, high heat transfer coefficients were obtained for a low fin tube(290% and 288% of the 19.0 mm smooth tube at 12.34 and 7.38 kPa).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1466-1473
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• 2012

Soft icecream is made by scraping an ice formed on the inside of the cylindrical evaporator, where R-404A is evaporating in the annulus. The heat transfer characteristics of the refrigerant evaporation and those during icecream formation were experimentally investigated. Results show that the refrigerant-side heat transfer coefficients are highly dependent on the location in the evaporator due to the complex annulus configuration. The heat transfer coefficient at the inlet is generally lower than those of other locations. The average heat transfer coefficient increases as heat flux increases or saturation temperature decreases. A correlation is developed to predict the refrigerant-side heat transfer coefficient. The icecream-side heat transfer coefficient oscillates continuously due to the periodic removal of ice formed on the surface. The average heat transfer coefficient during icecream formation is approximately 280 W/$m^2K$, and that during single-phase cooling increased from 150 W/$m^2K$ to 250 W/$m^2K$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.399-402
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• 2006

The purpose of this study is to propose a method for protecting injector face for prolonged combustion time and heat flux measurement technique at the injector face. To obtain basic design data and verify the performance of the proposed method, a regenerative cooling injector face was designed and manufactured for the hot firing test. Due to the safety reason, hot fire test were performed 3, 10, 30, 60 and 120 seconds time step. The discrepancy between analytical results adapting to combustion and nozzle and experimental results is believed due to the over estimation of the convection heat transfer calculation. for the injector face, flow velocity is almost negligible, therefore radiation is more important than convection. Consecutive hot firing test during 10, 30, 60 and 120 seconds combustion time shows good repeatability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.275-281
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• 2016

In this study, we investigate the pool boiling enhancement caused by perforated plates on top of a smooth surface. We conduct tests using R-123 at atmospheric pressure. It was shown that perforated plates significantly enhanced the pool boiling of the smooth surface. The reason may be attributed to the increased bubble contact area between the plates. The results showed that the enhancement ratio was dependent on the heat flux. At high heat flux, the enhancement ratio increased as the porosity increased. However, at low heat flux, the enhancement ratio decreased as the porosity increased. For the present investigation, the optimum configuration had a pore diameter of 2.0 mm, pore pitch of $2.5mm{\times}5.0mm$ or $5.0mm{\times}5.0mm$, and a gap width of 0.5 mm, which yielded heat-transfer coefficients that are close to those of GEWA-T. The optimum porosity for R-123 was significantly larger than that of water or ethanol. The reason for this may be the large liquid-to-vapor density ratio along with the small latent heat of vaporization of R-123. The perforated plates yielded smaller boiling hysteresis compared with that of the smooth surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.891-896
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• 2011

In this study, experiments were carried out to investigate the convective heat transfer characteristics of rectangular microchannels. The sample used in the experiments contained 20 rectangular microchannels in parallel. The channels had a hydraulic diameter of 700 ${\mu}m$. Distilled water was used as the working fluid. In the experiments, the Reynolds number ranged from 400 to 800, heat flux ranged from 35 to 85 kW/$m^2$, and the inlet fluid temperature was $20^{\circ}C$. As a result, the convective heat transfer coefficient increased upon increasing the Reynolds number and ranged from 4.6 to 6.4 kW/$m^2/^{\circ}C$ in the thermally fully developed region. Moreover, the higher the Reynolds number, the longer the thermal entry length in the rectangular microchannels. However, it was observed that a variable heat flux did not affect the thermal entry length. In conclusion, a correlation was proposed to indicate the heat transfer characteristics in a thermally fully developed region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.840-848
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• 2009

In the boiling heat transfer mechanism, CHF(critical heat flux) is the significantly important parameter of the system. So, many researchers have been struggling to enhance the CHF of the system in enormous methods. Recently, there were lots of researches about enormous CHF enhancement with the nanofluids. In that, the pool boiling CHF in nanofluids has the significantly increased value compared to that in pure water because of the deposition of the nanoparticle on the heater surface in the nanofluids. The aim of this study is the comparison of the effect of the nanoparticle deposited surface and the modified surface which has the similar morphology and made by MEMS fabrication. The nanoparticle deposited surface has the complex structures in nano-micro scale. Therefore, we fabricated the surfaces which has the similar wettability and coated with the micro size post and nano structure. The experiment is performed in 3 cases : the bare surface with 0.002% water-ZnO nanofluids, the nanoparticle deposited surface with pure water and the new fabricated surface with pure water. The contact angle, a representative parameter of the wettability, of the all 3 cases has the similar value about 0 and the SEM(scanning electron microscope) images of the surfaces show the complex nano-micro structure. From the pool boiling experiment of the each case, the nanoparticle deposited surface with pure water and the fabricated surface with pure water has the almost same CHF value. In other words, the CHF enhancement of the nanoparticle deposited surface is the surface effect. It also shows that the new fabricated surface follows the nanoparticle deposited surface well.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.11
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• pp.768-778
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• 2019

The ability to calculate aerodynamic heating and surface temperature is essential to ensure proper design of aircraft components in high speed flight. In this study, various empirical formulas for efficiently calculating aerodynamic heating of aircraft were first analyzed. A simple computational code based on empirical formulas was developed and then compared with commercial codes; ANSYS FLUENT based on the Navier-Stokes-Fourier equation, and ThermoAnalytics MUSES based on an empirical formula. The code was found to agree well with the results of FLUENT in the wall and stagnation point temperatures. It also showed excellent agreement with MUSES, within 1% and 5% in temperature and heat flux, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1760-1769
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• 1992

An experimental study of thermal transport from a uniformly heated pipe to a pulsating flow has been carried out. Surface of the pipe is imposed with constant heat flux providing by electric heating band. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. Temporal Variatiens of temperature and pressure inside the circular pipe are measured. The dependence of temperature distributions and heat transfer rate on the mean flow rate in the pipe and on the pulsating frequency is investigated in detail. The experimental results indicate that the measured temporal variations of temperature and pressure become nearly sinusoidal The amplitude of temperature variation near the pipe wall is much more substantial than that in core of the pipe. It is also found that the heat transfer rate is increased significantly as the frequency of the pulsating pressure is increased or the mean flow rate in a pipe is increased. The results obtained are also compared with those for non-pulsating flow circumstance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.597-603
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• 2017

In this study, experiments were conducted on the MFB(minimum film boiling) point of highly heated vertical metal rod quenched in aqueous surfactant solution at various temperature conditions. The aqueous Triton X-100 solution(100 wppm) and pure water were used as the liquid pool. Their temperatures ranged from $77^{\circ}C$ to $100^{\circ}C$. A stainless steel vertical rod of initial center temperature of $500^{\circ}C$ was used as a test specimen. In both liquid pools, as the liquid temperature decreased, the time to reach the MFB point decreased with a parallel increase in the temperature and heat flux of the MFB point. However, over the whole present temperature range, in the aqueous Triton X-100 solution, the time to reach the MFB point was longer, while the temperature and heat flux of the MFB point were reduced when compared with pure water. Based on the present experimental data, this study proposed the empirical correlations to predict the MFB temperature of a high temperature vertical metal rod in pure water and in aqueous Triton X-100 solution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1547-1555
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• 1993

An experimental study on convection heat transfer characteristics from a heated tube to an oscillating flow has been carried out, . This problem is of particular interest in the design of heat exchangers in Stirling cycle machines. Experimental system has been developed to measure temporal variations of temperature inside a heater tube during oscillating modes in a Stirling cycle machine. The dependence of temperature distributions and heat transfer rates on the oscillating frequency as well as the swept volume ratio and the mean pressure of a Stirling cycle machine is investigated in detail. The experimental results indicate that the measured temporal variations of temperature become nearly sinusoidal. The amplitude of temperature variation in the core of the tube is much more substantial than that near the tube wall, whereas the reverse is true for pulsating flows. It is also found that the heat transfer rate is increased significantly as the oscillating frequency or oscillating amplitude or the mean pressure in a tube is increased.