• Applied Chemistry for Engineering
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• v.32 no.2
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• pp.149-156
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• 2021

A kraft recovery boiler produces steam for power generation by the combustion of black liquor from the kraft pulping process. Since saturated steam became superheated in a superheater above the furnace, it is important to increase the heat exchange efficiency for the superheated steam production and power generation. A nose arch at the bottom of the superheater is important for blocking radiation from the furnace which causes corrosion of the superheater. But the nose arch is the main reason for creating a recirculation region and then decreasing the heat exchange efficiency by holding cold flue gas after the heat transfer to saturated steam. In this study, the size of recirculation region and the temperature of flue gas at the outlet were analyzed by the nose arch structure using computational fluid dynamics (CFD). As a result, when the nose arch angle changed from 106.5° (case 1) to 150° (case4), the recirculation region of flue gas decreased and the heat exchange efficiency between the flue gas and the steam increased by 10.3%.

• Journal of the Korean Society of Combustion
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• v.16 no.1
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• pp.36-45
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• 2011

The heat-flow characteristics and reforming efficiency of steam reformer with combustor are numerically investigated at various operating conditions. SCR(Steam to Carbon Ratio) and GHSV(Gas Hourly Space Velocity) are adopted as important operating conditions. User-Defined-Function(UDF) was used to simultaneously calculate reforming and combustion reaction. Numerical results show that hot burned gas rise by a buoyant force and heat exchange between reforming reactors and cocurrent flow occurs in the combustion region. The results also indicate that an increase of SCR leads to decrease the mole fraction of hydrogen at the reactor outlet. As GHSV increases, conversion rate decreases.

• Journal of Internet of Things and Convergence
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• v.7 no.3
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• pp.63-68
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• 2021

Domestic electric heater manufacturers are focusing on technology development to improve the efficiency of existing products. The electric heater for ship fuel is large in size and has high difficulty in miniaturization/high efficiency, so there are not many companies that try to develop technology yet. The existing electric heater has a structure of low heating efficiency because the contact time with the heat exchange tube of the heating medium is very short because the flow path of the ship engine fuel is monotonous. Since it is manufactured in a tubular shape, the volume is very large regardless of the heating efficiency. As a result, the tubular electric heater device applied by overseas advanced companies has difficulty in maintaining and repairing because it is necessary to decompose all tubular heaters when a specific part of the inside is damaged and if the heat exchange tube is damaged, all the heat exchange tubes must be decomposed. In this study, a basic study on plate type electric heaters capable of heating 10 tons of ship engine fuel per hour and setting a maximum temperature of up to 150℃ was conducted through a 250kW capacity plate type electric heater.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.291-298
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• 2010

A conventional EGR cooler, which is used in an EGR system of an automobile diesel engine, has a low heat-exchange efficiency. To maximize the heat transfer between the exhaust gas and coolant, dimples are formed on the surface of heat exchange tubes. When designing the dimpled EGR cooler, the net heat transfer areas in the conventional and dimpled tube-type EGR coolers are compared. Structural integrity evaluations are also performed by combining finite element analysis with a homogenization method. Subsequently, the process of manufacturing the dimpled tube, i.e., the formation of dimples, edge bending, center v-notch bending, compression, and plasma welding, is established and carried out. Thus, the dimpled EGR cooler is developed, and its performance is verified.

• Transactions of the Korean hydrogen and new energy society
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• v.35 no.2
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• pp.205-215
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• 2024

This study introduced a direct contact heat exchanger to enhance the efficiency of polymer electrolyte membrane fuel cells (PEMFCs) systems. According to previous research, 28% of the operating costs of fuel cell systems are attributed to heat exchanger devices, prompting the design of a direct contact heat exchanger to address this issue. Optimal configurations were determined through computational fluid dynamics analysis and experimental device fabrication, and the enhanced heat exchange performance of the heat exchanger was experimentally confirmed. Through this, the contribution of the direct contact heat exchanger to the heat management and efficiency enhancement of PEMFC systems was established.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1726-1735
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• 2008

Seoulmetro has operated the air cooling equipment for 57 stations to improve services focused on our customers who use Seoulmetro during the summer season and has established every year. However, a new set of problems has arisen with the cooling tower to support a heat exchange of cooling water. The most important matter is loss of efficiency in the cooling tower. The leading cause of this problem is that we use an indoor type. As the cooling tower room is located in the underground of the city because of the residents near the station. Therefore It is difficult to establish the cooling tower on the ground. But it is unsuitable for the location requirements of the underground type because it has a limited space to set up the air cooling equipment, for example, the cooling tower and a ventilating opening. As a result of such an unfavorable condition, the cooling tower doesn't work efficiently and the warmth of cooling water because of insufficiency of a heat exchange and a refrigerator's technical obstacle such as a high-temperature and a high-pressure has arisen. To prevent this situation, the operator tend to reduce refrigerant. Accordingly, the efficiency of the air conditioning is getting lower and lower. Study wishes to analyze the matter to improve indoor cooling tower efficiency and recommend a best practice for a person who manage the establishment.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1161-1166
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• 2008

The objective of this research was to investigate the enhancement of heat transfer by mesh in water/air direct contact air conditioning system. Mesh is inserted as a turbulent promoter in front of the water injection nozzle. The heat transfer characteristics with and without mesh and the effect of the number of inserted mesh and mesh porosity size have been studied experimentally. Inserted mesh improves heat transfer efficiency compared to non-inserted mesh system and heat transfer efficiency increased as the number of mesh is increased. Meanwhile, heat transfer efficiency decreased as the porosity of the mesh is increased. With inserted mesh, inlet and outlet temperature difference of air increased more than 50%. Heat exchange time of water/air to reach the 100% humidity decreased less than 30%. This result shows inserted mesh can enhance the performance of the water/air direct contact air conditioning system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.1
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• pp.75-80
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• 2008

The objective of this research was to investigate the enhancement of heat transfer by mesh in water/air direct contact air conditioning system. Mesh is inserted as a turbulent promoter in front of the water injection nozzle. The heat transfer characteristics with and without mesh and the effect of the number of inserted mesh and mesh porosity size have been studied experimentally. Inserted mesh improves heat transfer efficiency compared to non~inserted mesh system and heat transfer efficiency increased as the number of mesh is increased. Meanwhile, heat transfer efficiency decreased as the porosity of the mesh is increased. With inserted mesh, inlet and outlet temperature difference of air increased more than 50%. Heat exchange time of water/air to reach the 100% humidity decreased less than 30%. This result shows inserted mesh can enhance the performance of the water/air direct contact air conditioning system.

• The Journal of Engineering Geology
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• v.28 no.3
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• pp.475-488
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• 2018

This study evaluates geothermal system efficiency in terms of input power and heat exchange volume on the heat-source and load sides, by applying a combined open-closed type loop system comprising a geothermal system and a groundwater well to a cultivation site. In addition, this study analyzes the effects of heating and cooling for a complex geothermal system, by evaluating the temperatures of an external site and a cultivation site during operation. During cooling operations the heat exchange volume on the heat source side, average 90.0kW/h for an open type system with an input of 235L/minute groundwater, and 40.1kW/h for a closed type system with an input of 85L/minute circulating water, for a total average heat exchange volume of 130.1kW/h. The actual heat exchange volume delivered on the load side averages 110.4kW/h. The average EER by analysis of the geothermal system's cooling efficiency is 5.63. During heating operation analysis, the heat exchange volume on the heat source side, average 60.4kW/h in an open type system with an input of 266L/minute groundwater, and 22.4kW/h in closed type system with an input of 86L/minute circulating water, for a total average heat exchange volume of 82.9kW/h. The actual heat exchange volume delivered on the load side averages 112.0kW/h in our analysis. The average COP determined by analysis of the geothermal system's heating efficiency is 3.92. Aa a result of the tradeoff between the outside temperature and the inside temperature of the production facility and comparing the facility design with a combined well and open-closed loops geothermal(CWG) system, we determine that the 30RT-volume CWG system temperature are lower by $3.4^{\circ}C$, $6.8^{\circ}C$, $10.1^{\circ}C$ and $13.4^{\circ}C$ for ouside temperature is of $20^{\circ}C$, $25^{\circ}C$, $30^{\circ}C$ and $35^{\circ}C$, respectively. Based on these results, a summer cooling effect of about $10^{\circ}C$ is expected relative to a facility without a CWG system as the outside temperature is generally ${\geq}30^{\circ}C$. Our results suggest that a complex geothermal system provides improvement under a variety of conditions even when heating conditions in winter are considered. Thus It is expected that the heating-cooling tradeoffs of complex geothermal system are improved by using water screen.

• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.31-41
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• 2013

The use of energy pile foundation has increased for economic utilization of geothermal energy. In particular, coil-shaped ground heat exchanger (GHE) is preferred to the conventional U-shaped exchanger to ensure better efficiency of heat exchange rate. This paper presents a numerical and experimental study on the heat transfer behavior of PHC energy piles. Field thermal performance tests (TPTs) were conducted for the PHC energy piles installed in a partially saturated weathered granite soil deposit, in which two types of GHEs were considered: W and coil shaped GHEs. Besides, three-dimensional finite element analyses were also conducted, and the results were compared with the experimental results. According to the results of TPT and numerical analyses, the coil shaped GHE showed 10~15% higher heat exchange rate than the W type GHE in the PHC energy piles.