• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1995.05a
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• pp.78-81
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• 1995

In the present study, the spray column type of direct contact heat exchangers are studied experimentally to analyze heat transfer characteristics for solar energy utilization. These experiments are carried out in the line of solar heating system, major results are as follows ; 1) the flow and aspect of working fluid drop for maxium heat transfer 2) efficiency and volumetric heat transfer coefficient of D. C. H. X. with a heavier working fluid are higher than those of D. C. H. X. with a lighter working fluid

• Journal of the Korean Society of Combustion
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• v.19 no.4
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• pp.49-55
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• 2014

Design criterion for the size of micro Pt-catalytic combustor is investigated in terms of heat release rate. One-dimensional plug flow model is applied to determine the surface reaction constants using the experimental data at stoichiometric butane-air mixture. With these reaction constants, the mass fraction of butane and heat release rate predicted by the plug flow model are in good agreement with the experimental data at the combustor exit. The relationship between the size of micro catalytic combustor and mixture flowrate is introduced in the form of product of two terms-the effect of fuel conversion efficiency, and the effect of chemical reaction rate and mass transfer rate.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.1
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• pp.17-22
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• 2007

The heat flow characteristics of the Gudle (traditional Ondol) used a lot at farm houses have been performed with variations of Bunengki (Fireridge) by numerical analysis and field experiment. The Doedon-Gorae (Return-Firetunnel) Gudle is analyzed among the structure of Gudle. The distribution of heat flow in Gorse (Firetunnel) and the temperature distribution in floor of 3 Buneomgi (Fire ridge) was more uniform than that of 1 Buneomgi. The heat efficiency of 3 Buneomgi was higher than that of 1 Bunengki. That is, the 3 Bunengk is more efficient and more uniform temperature.

• Transactions on Electrical and Electronic Materials
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• v.6 no.2
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• pp.39-45
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• 2005

Numerical and visualization procedures are used in a finite difference grid to analyze and better understand the heat transfer in the MEMS based air micro-jet array (MIA) impingement cooling device. The Navier-Stokes (NS) equations with incompressible flow are solved using an implicit procedure. The temperature contour and velocity vector visualization diagrams are used for illustration. The computed temperature distribution at the bottom of the MIA is in good agreement with the experimental measurement data. The parameters are investigated to improve the efficiency of heat transfer in the MIA. The optimum configuration of the MIA is suggested. The present modeling explains the flow phenomenon and yields valuable information to understand the flow and heat transfer in MIA.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.2
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• pp.163-170
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• 2015

Recently LED fish-attracting lamps have been more widely used in fisheries as low-cost and high-efficiency fishing gear, and development of long-life high-efficiency lamps is required through the design of LED packages to optimize heat resistance. This study developed an improved LED fish-attracting lamp with excellent heat performance, which was verified using a numerical model. Heat-resistance design factors such as the heat-radiation fin shape, PCB type, and LED chip count were investigated and optimized. Comparison with a commercial 180-W LED fishing lamp showed that the increase in initial temperature was 40% higher than that of the surrounding LED chip because of design errors in contact thermal resistance. The 250-W LED lamp developed in this study has a characteristic with thermal rising in linearly stable according to the heat source. In addition, luminance efficiency was improved by 20-65% by using flow-visualization simulation. A decrease of 45% in total power consumption with a fuel-cost reduction of over 55% can be expected when using these optimized heat release design factors.

• Journal of Industrial Technology
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• v.43 no.1
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• pp.33-41
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• 2023

This paper provides a general overview of surface catalytic recombination in hypersonic flow. The surface catalytic recombination phenomena is elaborated in terms of its general overview and numerical modeling associated with it. The general overview of the surface catalytic recombination phenomena describes the elementary surface reactions for the surface catalytic and the role of the surface catalytic recombination efficiency in the heat transfer determination. In the numerical modeling, the surface catalytic recombination is described based on the stagnation-point boundary layer analysis, and finite-rate surface reaction modeling. Throughout this overview manuscript, a general understanding of this phenomena is obtained and can be used as foundation for deeper application with the numerical computational fluid dynamics (CFD) flow solver to estimate the surface heat transfer in the hypersonic vehicles.

• Journal of Biosystems Engineering
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• v.43 no.1
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• pp.21-29
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• 2018

Purpose: The objective of this study is to evaluate the performance of the conical solar concentrator (CSC) system, whose design is focused on increasing its collecting efficiency by determining the optimal conical angle through a theoretical study. Methods: The design and thermal performance analysis of a solar concentrator system based on a $45^{\circ}$ conical concentrator were conducted utilizing different mass flow rates. For an accurate comparison of these flow rates, three equivalent systems were tested under the same operating conditions, such as the incident direct solar radiation, and ambient and inlet temperatures. In order to minimize heat loss, the optimal double tube absorber length was selected by considering the law of reflection. A series of experiments utilizing water as operating fluid and two-axis solar tracking systems were performed under a clear or cloudless sky. Results: The analysis results of the CSC system according to varying mass flow rates showed that the collecting efficiency tended to increase as the flow rate increased. However, the collecting efficiency decreased as the flow rate increased beyond the optimal value. In order to optimize the collecting efficiency, the conical angle, which is a design factor of CSC, was selected to be $45^{\circ}$ because its use theoretically yielded a low heat loss. The collecting efficiency was observed to be lowest at 0.03 kg/s and highest at 0.06 kg/s. All efficiencies were reduced over time because of variations in ambient and inlet temperatures throughout the day. The maximum efficiency calculated at an optimum flow rate of 0.06 kg/s was 85%, which is higher than those of the other flow rates. Conclusions: It was reasonable to set the conical angle and mass flow rate to achieve the maximum CSC system efficiency in this study at $45^{\circ}$ and 0.06 kg/s, respectively.

• Journal of the Korean Solar Energy Society
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• v.39 no.6
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• pp.83-91
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• 2019

Photovoltaic thermal (PVT) collectors are devices that simultaneously produce electricity and heat. Research on conventional air-type PVT collector focuses on installing baffles to enhance the collector's thermal performance. However, the baffles have pressure drop inside the collector which degrades the thermal performance. Thus, it is necessary to design baffles to smoothen the flow inside the air-type PVT collector. Alternatively, installing perforated baffles in air-type PVT collectors can reduce the collector weight, but parameters such as the diameter of the perforated holes and the height of the perforated plates should be considered. Therefore, the main aim of this study was to analyze thermal characteristics of each variable of perforated baffles installed inside air-type PVT collector. For this purpose, the uniformity of air flow in the collector was compared through NX program, and the resultant heat gain and thermal efficiency of the air-type PVT collector were compared and analyzed. Therefore, the main aim of this study was to analyze thermal characteristics of each variable (Baffle angle, length, height, pitch, perforated ratio) of perforated baffles installed inside air-type PVT collector. For this purpose, the uniformity of air flow in the collector was compared through CFD program, and the resultant heat gain and thermal efficiency of the air-type PVT collector were compared and analyzed. As a result, the maximum outlet temperature was increased by 1.45 times and the heat gain was increased by 193.8 Wth, depending on the perforated baffle plate, compared to the collector without the baffle. The heat transfer performance showed that the maximum internal velocity was 1.61 times higher and the Reynolds number was 1.06 times higher depending on the parameters of the baffle plate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1276-1293
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• 1993

A numerical and experimental flow visualization study of the louvered fin array, commonly used in a compact heat exchanger was performed. The flow structure which was obtained by using a finite difference method, was compared with an experimental result. The experimental flow visualization was performed by using a dye injection technique with 13:1 scale model. The effects of Reynolds number and fin geometries on flow structure and heat transfer were examined.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.4
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• pp.368-373
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• 2004

A flow field in a passage with periodically converging-diverging cross-section is investigated experimentally by PIV measurement. A tube with a sinusoidally wavy cross section is one of several devices employed for enhancing the heat and mass transfer efficiency due to turbulence promotion and unsteady vortical motion. While the numerical flow visualization results have been limited to the fully developed cases, existing experimental results of this flow were simple qualitative ones by smoke or dye streak test. Therefore, the main purpose of this study is to produce quantitative flow data for fully developed and transient flow regime by the Correlation Based Correction PIV (CBC PIV) and to conjecture the analogy between flow characteristics and heat transfer enhancement with low pumping power. Another purpose of this paper is to examine the onset position of the transition and the global mixing, which results in transfer enhancement. At Re=2000, evidences of the global mixing are captured at 2.5 wavy module through the variation of RMS values and instantaneous velocity plot.