• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.1-8
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• 2010

Natural convection heat transfer rates in a vertical pipe were measured for $Gr_H$ number from 2.1x$10^6$ to 1.2x$10^9$. Using the analogy concept, heat transfer experiments were replaced by mass transfer experiments. A cupric acid - copper sulfate ($H_2SO_4-CuSO_4$) electroplating system was adopted as the mass transfer system and the mass transfer rates were measured. Comparison of the results with the existing laminar and turbulent natural convection heat transfer correlations on a vertical plate showed very good agreements except for the high $Gr_H$ case, where the boundary layer inside the vertical pipe interferes. The agreements showed the usefulness of the analogy experiment method. Using 3 different anode size and 6 different geometrical configurations, the effects of the anode size and position were explored. As expected, the anode size and position do not affect the limiting currents for most cases. These results will be used as the experimental background for the positioning and sizing of the anodes for a more complex experiment.

• Applied Chemistry for Engineering
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• v.30 no.1
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• pp.62-67
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• 2019

This study was focused on the design and the performance analysis of integral Hot BoP for recovering waste heat from high-temperature exhaust gas in 2 kW class solid oxide fuel cell (SOFC). The hot BoP system was consisted of a catalytic combustor, air preheater and steam generator for burning the stack exhaust gas and for recovering waste heat. In the design of the system, the maximum possible heat transfer was calculated to analyze the heat distribution processes. The detail design of the air preheater and steam generator was carried out by solving the heat transfer equation. The hot BoP was fabricated as a single unit to reduce the heat loss. The simulated stack exhaust gas which considered SOFC operation was used to the performance test. In the hot BoP performance test, the heat transfer rate and system efficiency were measured under various heat loads. The combustibility with the equivalent ratio was analyzed by measuring CO emission of the exhaust gas. As a result, the thermal efficiency of the hot BoP was about 60% based on the standard heat load of 2 kW SOFC. CO emission of the exhaust gas rapidly decreased at an equivalent ratio of 0.25 or more.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.8
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• pp.733-741
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• 2013

This is the first paper on the combustion characteristics of landfill gas in a constant volume combustion chamber for a large displacement volume commercial engine, and it discusses the fundamental characteristics of fuel from the viewpoint of thermochemistry and thermodynamics and compares these results with experimental ones. The results show that the final pressures obtained from theoretical analysis vary under the same heating value owing to the change in the constant volume specific heat owing to the difference in the burned gas composition according to the fuel gas compositions; furthermore, the stoichiometric ratios and trends of analytical and experimental pressures coincide very well, although some minor differences are observed between the two. The root cause of the difference is the heat transfer, which changes the specific heat and lowers the temperature considerably, in the real combustion process. In addition, the large chamber volume and ignition position promote the heat transfer to the wall. Finally, the fuel conversion efficiency increases as the methane mol fraction decreases, and it is maximum when the stoichiometric ratio ranges from 0.8 to 0.9. These increases due to the composition and stoichiometric ratio could sufficiently compensate the decrease due to the specific heat ratio drop, LFG might be more advantageous than pure methane in a real engine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.270-276
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• 2020

3D printing is an additive manufacturing technology that can produce complex shapes in a single process for a range of materials, such as polymers, ceramics, and metals. Recent 3D printing technology has developed to a level that enables the mass-production through an improvement of the printing speed and the continuous development of applicable materials. In this study, 3D printing technology using a laser was applied to manufacture a heat exchanger for an air compressor in a railway vehicle. First, the optimal design of the heat exchanger was carried out by focusing on weight reduction and compactness as a shape suitable for 3D printing. Based on the design derived, heat exchanger prototypes were made of AlSi10Mg alloy material by applying the SLM technique. Moreover, the manufactured prototypes were attached to an existing air compressor, and the heat exchange performance of the compressed air was tested. The test results of the 3D printed prototypes showed a heat exchange performance of approximately 80% and 85% at low and high-pressure, respectively, compared to the existing heat exchanger. From the 𝓔-NTU method results with an external cooling air condition similar to that of the existing heat exchanger, the calculated heat transfer amount of 3D printed parts showed similar performance compared to the existing heat exchanger. As a result, the 3D printed heat exchanger is lightweight with good performance.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.69-74
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• 2015

The study investigated numerically the heat transfer and chemical reaction characteristics of a methane-steam reforming by using a 3-dimensional computational fluid dynamics (CFD) code (Fluent ver. 16.1). The fuel temperature and its species mole fractions were estimated for various Reynolds number in the reformer tube at different burner temperatures. The catalysts were modeled as the porous medium of nicrome in the reformer tube. We considered radiation effect as well as conduction and convective heat transfer because the methane-steam was reformed at very high temperature condition above 1000 K. For two different Reynolds numbers of 49,000 and 88,000 and the burner temperatures were in the range from 1,100 K to 1,300 K. At a low Reynolds number, the fuel temperature increased, leading to increase in hydrogen reforming. However, fuel temperature and hydrogen reforming decreased because of higher convective heat transfer from relatively low fuel temperature. Moreover, the hydrogen reforming also increased with burner temperature.