• Journal of the Korean Society of Combustion
• /
• v.1 no.1
• /
• pp.19-29
• /
• 1996

This study is to investigate the characteristics of heat transfer of a horizontal tube, with radial fins of various configuration, immersed in a high temperature fluidized bed. The experimental heat transfer variation is compared with that of a smooth tube. The finned tubes and smooth tube, with outside and inside diameter of 48.6mm and 30.6mm, are made of steel tubes. The depth of the fin is 5mm, the rake angles of fin are $25^{\circ},\;35^{\circ},\;45^{\circ}$ and the widthes of fin for each rake angle are 0mm, 1mm, 2mm and 3mm. A bed temperature is fixed at $880\;{\pm}\;10^{\circ}C$. A granular refractory(silica sand) is used as a bed material with mean particle diameters of 1.22mm and 1.54mm. The maximum heat transfer coefficient is achieved with the rake angle of $25^{\circ}$ and the width of 0mm for the mean particle size 1.22mm. The coefficient is 2.14 times larger than that for a smooth tube. The rake angle for the maximum heat transfer coefficient depends on the particle size of bed material. Also the transfer coefficient decreases as the width of fin increases.

• Journal of Environmental Health Sciences
• /
• v.23 no.3
• /
• pp.102-108
• /
• 1997

It has been studied that SO$_2$ removal efficiency of anthracite-bituminous coal blend combustion in a fludized bed coal combustor. The objectives of this study were to investigate SO$_2$ removal characteristics of coal blend combustion with Ca/S, anthracite fraction, bed temperature, and limestone size. The experimental results were presented as follows First, the effect of the desulfurization by the dia size of limestone was great and SO$_2$ removal efficiency was highest in limestone dia 631 $\mu$m. Second, as air velocity increased, the desulfurization rate decreased a little. But the difference of the desulfurization rate according to air velocity was not too large. As the height of fluidized bed combustor increased regardless of air velocity, SO$_2$ concentration tends to increase largely. Third, as Ca/S mole ratio incresed, SO$_2$ desulfurization rate incresed rapidly up to Ca/S mole ratio 3 while the desulfurization rates did not increse too largely in the range of more than the level. Forth, the bed temperature had a great effect on the desulfurization rate and the desulfurization rate tended to increase slightly as anthracite fraction increased.

• Journal of Korea Society of Waste Management
• /
• v.34 no.7
• /
• pp.685-696
• /
• 2017

This study focuses on computational particle fluid dynamics (CPFD) modeling for the fast pyrolysis of biomass in a conical spouted bed reactor. The CPFD simulation was conducted to understand the hydrodynamics, heat transfer, and biomass fast pyrolysis reaction of the conical spouted bed reactor and the multiphase-particle in cell (MP-PIC) model was used to investigate the fast pyrolysis of biomass in a conical spouted bed reactor. A two-stage semi-global kinetics model was applied to model the fast pyrolysis reaction of biomass and the commercial code (Barracuda) was used in simulations. The temperature of solid particles in a conical spouted bed reactor showed a uniform temperature distribution along the reactor height. The yield of fast pyrolysis products from the simulation was compared with the experimental data; the yield of fast pyrolysis products was 74.1wt.% tar, 17.4wt.% gas, and 8.5wt.% char. The comparison of experimental measurements and model predictions shows the model's accuracy. The CPFD simulation results had great potential to aid the future design and optimization of the fast pyrolysis process for biomass.

• Journal of the Korean Society of Combustion
• /
• v.7 no.3
• /
• pp.23-31
• /
• 2002

Processes in an iron ore sintering bed can characterized as a relatively uniform progress of fuel, cokes combustion and complicated physical change of solid particles. The sintering bed was modelled as an unsteady one-dimensional progress of the fuel layer, containing two phases: solid and gas. Coke added to the raw mix, of which the amount is about 3.5% of the total weight, was assumed to form a single particle with other components. Numerical simulations of the condition in the iron ore sintering bed were performed for various parameters: moisture contents, cokes contents and air suction rates, along with the various particle diameters of the solid for sensitivity analysis. Calculation results showed that the influence of these parameters on the bed condition should be carefully evaluated, in order to achieve self-sustaining combustion without high temperature section. The model should be extended to consider the bed structural change and multiple solid phase, which could treat the inerts and fuel particles separately.

• Nuclear Engineering and Technology
• /
• v.56 no.2
• /
• pp.636-643
• /
• 2024

The coolability of the debris bed with a simulant of solidified corium is experimentally studied, focusing on the effects of the structure of the axial stratified debris bed on the dryout heat flux (DHF). DHF was obtained for the four structures with different particle sizes for the axial stratified debris bed under top flooding. The experimental results show that the dryout position of the axial stratified debris bed is formed at the stratified interface indicated by the temperature rise, and the DHF of the axial stratified bed is much lower than that of the homogeneous bed packed with the upper small particles. To predict the dryout heat flux of the stratified debris beds, by considering the properties of the mixed area, a one-dimensional dryout heat flux model of the porous medium is derived from a water and vapor momentum equation for porous medium, two-phase permeability modifications, interfacial drag, and the correlation between capillary pressure and liquid saturation and verified with the experimental data. The modified model can give reasonable results under different structures.

• Nuclear Engineering and Technology
• /
• v.39 no.2
• /
• pp.95-102
• /
• 2007

The conceptual design of the MIT modular pebble bed reactor is described. This reactor plant is a 250 Mwth, 120 Mwe indirect cycle plant that is designed to be deployed in the near term using demonstrated helium system components. The primary system is a conventional pebble bed reactor with a dynamic central column with an outlet temperature of 900 C providing helium to an intermediate helium to helium heat exchanger (IHX). The outlet of the IHX is input to a three shaft horizontal Brayton Cycle power conversion system. The design constraint used in sizing the plant is based on a factory modularity principle which allows the plant to be assembled 'Lego' style instead of constructed piece by piece. This principle employs space frames which contain the power conversion system that permits the Lego-like modules to be shipped by truck or train to sites. This paper also describes the research that has been conducted at MIT since 1998 on fuel modeling, silver leakage from coated fuel particles, dynamic simulation, MCNP reactor physics modeling and air ingress analysis.

• Journal of Energy Engineering
• /
• v.5 no.2
• /
• pp.138-145
• /
• 1996

The particulate collection at high temperature and high pressure (HTHP) is important on the advanced coal power generation system not only to improve the thermal efficiency of the system, but also to prevent the gas turbine from erosion and to meet the emission limits of the effluent gas. The specifications for particulate collection in those systems such as Integrated Coal Gasification Combined Cycle (IGCC) and Pressurized Fluidized Bed Combustion (PFBC) require the absolutely high collection efficiency and reliability. Advanced cyclone, granular bed filter, electrostatic precipitator, and ceramic filter have been developed for particulate collection on the advanced coal power generation system. However, rigid ceramic filters and granular bed filter among them show the best potential. The current technology of these collectors was evaluated in this paper. The experienced problems of these systems on performance, materials, and mechanical design were investigated. Ceramic candle filters has the best potential for IGCC at this moment because it has nearly the highest efficiency comparing with other filtering systems and has accumulated many reliable design data resulted from many field experiences.

• 한국연소학회:학술대회논문집
• /
• 2004.06a
• /
• pp.158-164
• /
• 2004

In the present work, the numerical model was refined to predict the thermal analysis of energy storage in a fixed beds during charging mode. The governing energy equations of both fluid and the solid particles along with their initial and boundary conditions are derived using a two-phase, one dimensional model. The refined model is carried out by taking into account change of (air density , air specific heat) with air temperature and also by taking into considerations heat losses from bed to surrounding. Finite difference method was used to obtain solution of two governing energy equations of both fluid and solid particles through a computer program especially constructed for this purpose. The temperature field for the air and the solid are obtained, also energy stored inside the bed is computed. A comparison between refined model and non refined model is done. Finally using refined model the effect of bed material (Glass, Fine clay ,and aluminum ), and air flow rate per unit area Ga (0.3, 0.4, and 0.5 kg/$m^2$-s) on energy storage characteristics was studied.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.2 no.2
• /
• pp.112-118
• /
• 1990

Characteristics of heat transfer in a smooth and finned tube located vertically in atmospheric fluidized bed combustor which uses low grade anthracite coals was studied. Experiments to investigate the characteristics of heat transfer between smooth and finned tube are carried out and the results depend on particle size, fluidizing air velocity and bed temperature are summarized. It is found that heat transfer coefficient of the smooth and finned tube increases with decrease in particle diameter and increase in bed temperature. Furthermore, it is noted that heat transfer coefficient increase at the first with increase in the velocity of fluidizing air and tends to decrease at a certain fluidizing air velocity. The increase of heat transfer coefficient for the finned tube is appeared to be increased in 30% compared to that for the smooth tube.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.6
• /
• pp.746-752
• /
• 2010

Rib structure has been used to bed and column of machine tool to heighten weight stiffness ratio, cost performance and weight saving. In this paper the bed rib structure was estimated with thermal characteristics. Using superposition principle, machine tool designer can describe every complicated heat generation in the machine tool thermal source. As thermal characteristics, thermal deformation of guide rail and column and Maximum-minimum temperature variation were selected. The size, configuration and direction against the thermal loading surface operated to the thermal characteristics. The DB chart was made following rib structure estimating thermal characteristics. With superposition principle and DB chart, machine tool designer can prognosticate the thermal characteristics without FEM analysis to every bed rib structure.