Numerical Study on the Wall to Bed Heat Transfer in a Conical Fluidized Bed Combustor

Hamada Mohamed Abdelmotalib,Mahmoud Abdelftah Youssef,Ali Ahmed Hassan,윤석범,임익태 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.

In this work a numerical investigation of wall to bed heat transfer, and the related flow characteristics, was conducted along a conical fluidized bed combustor with a height of 0.8 m and a cone angle of 30o. A two-fluid Eulerian-Eulerian model was used while applying Kinetic Theory for Granular Flow (KTGF) to a wall-to-bed FB reactor. The heat transfer coefficient and hydrodynamics are discussed for two different drag models, namely the Gidaspow and Syamlal-O’Brien models. Furthermore, computational calculations were carried out for a variety of inlet velocities(1.4Umf~4 Umf) and different particle sizes. The heat transfer coefficient in the bed region was evaluated and compared with that calculated by penetration theory. The bed expansion for the two models was compared with that calculated using correlations from literature in order to validate the numerical calculations. The heat transfer coefficient was found to be increasing with increasing gas velocity and decreasing with increasing particle diameter.

Numerical Study on Heat Transfer According to Different Flow Regimes in Fluidized Bed Reactors

Hamada M. Abdelmotalib,Ik-Tae Im(임익태) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.4

Numerical Modeling of Conical Fluidized Bed Combustors Considering Particle Slip on Wal

Hamada Abdelmotalib,Ik-Tae Im(임익태) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

In this paper, the hydrodynamics and wall to bed heat transfer of a gas?solid flow in a conical fluidized bed were simulated using the Eulerian-Eulerian model. Sand with a particle diameter of 560 μm was used as a bed material, and its properties were calculated by applying the kinetic theory of granular flow (KTGF). Different amounts of slip between the particle and wall were shown by varying the specularity coefficient. The effects of specularity (0, 0.2, 0.5, and 1.0) on hydrodynamic and wall to bed heat transfer at a superficial gas velocity of 2 m/s were investigated. It was found that the wall to bed heat transfer coefficient decreases with increasing specularity coefficient. Different values of the specularity coefficient resulted in almost the same hydrodynamic behavior near the wall and the center of the bed.

Computational study of flow characteristics in a carbon fiber carbonization reactor

Abdelmotalib Hamada M.,고동국,이교우,임익태 한국탄소학회 2022 Carbon Letters Vol.32 No.5

Carbon fibers are commonly used in many specialized, high-performance applications such as race cars and aircraft due to their lightweight and high durability. The most important stage in the production of carbon fibers is the carbonization process. During this process, carbon fibers are subjected to high temperatures in the absence of oxygen to prevent fibers from burning. Labyrinth seals are attached to a carbonization furnace to prevent airflow into the furnace and to assist in the elimination of off-gases. This study investigated flow characteristics inside a carbonization furnace and the effects of different geometric parameters of labyrinth seals such as labyrinth tooth shape, number of teeth, and tooth clearance. Varying carbonization furnace operating conditions were also studied in regard to flow behavior, including fiber movement and outlet vacuum pressure. A high working gas flow rate at the furnace inlet resulted in recirculation zones. Properly regulated gas flow from the main and labyrinth inlets enabled uniform flow around the fibers’ inlet and outlet which prevented air from being trapped in the reactor. Flow behavior was minimally effected by changes to labyrinth seal geometry such as tooth length, tooth clearance, and outlet pressure. However, the movement of fibers had a clear effect on flow characteristics in the furnace.

A study on the particle temperature in a conical fluidized bed using infrared thermography

Hamada Mohamed Abdelmotalib,임익태 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.9

Of the three main modes of heat transfer in fluidized bed reactors, surface-to-bed heat transfer has been more thoroughly studied compared to gas-to-particle or solid-to-solid heat transfer. The difficulty in studying both gas-to-solid and solid-to-solid heat transfer processes is due to a limited ability to measure the temperature of the particles. The traditional method to measure temperature, such as inserting temperature probes into the bed, do not provide accurate results because these measure the temperature of the bed and not the solid particles. The present study introduces a technique using infrared thermography to measure the particle temperature. The particle temperature was measured using an IR camera, and a type-K thermocouple was used to measure the bed temperature. Glass beads with different sizes were used as bed material fluidized by air to study the effect that the inlet gas velocity and particle size had on the particle temperature. An increase in the inlet gas velocity resulted in a decrease in the particle temperature without a noticeable effect on the bed temperature, and an increase in the particle size resulted in an increase in the temperature of both the particles and the bed.

COOLING EFFICIENCY ACCORDING TO SHAPE CHANGES TO THE STRAIGHT VENTILATION HOLE IN CARBON-CERAMIC BRAKE DISKS

고동국,Hamada Mohamed Abdelmotalib,Ik-Tae Im,Dong Won Im,Suck Ju Yoon 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.6

In this study, in order to examine the cooling efficiency of a carbon-ceramic brake disk, the temperature distribution of the disk, depending on the AMS (Auto-Motor-Sport) Fade mode, was analyzed using a numerical method. Two brake disks with different straight ventilation hole shapes were considered. The ventilation holes configuration was changed from base models in order to find a higher cooling efficiency disk design. In the Model A disk, the mean temperatures of the mid-plane and the entire disk, at the AMS Fade mode end time decreased 1.9 oC and 3 oC, hole length respectively. This was done by decreasing the length of the a2 hole from 94 mm to 59 mm. When a2 hole length was increased from 94 mm to 128 mm, the mean temperature of the entire disk and the disk mid-plane increased 3.7 oC and 16.2 oC, respectively. This was due to the increased affined air stagnation in the disk. In the Model B disk, after removing stagnation region of the b2 hole, the hole diameter expanded from 13 mm to 17.6 mm. As a result, the mean temperature of the entre disk and the mid-plane decreased 2.8 oC and 18.7 oC, respectively, (compared to the base model). As a result, increasing the surface area of the ventilation holes gave a higher cooling efficiency.

Computational study on heat transfer and bed flow according to different regimes of fluidized beds

소병문,Hamada Mohamed Abdelmotalib,Mohamed Y. Hashim,임익태 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.12

This work presents a computational study to compare heat transfer processes and flow behavior of the bed among different regimes of fluidized bed reactors with fixed, bubbling, and slugging flow regimes. Sand particles with a mean diameter of 550 μm were used as a bed material fluidized by air. Wall-to-bed heat transfer and fluidization behavior were studied at different inlet velocities to represent different flow regimes. A two-phase model with kinetic theory of granular flow was used to simulate both heat transfer and flow characteristics. Simulation findings were validated by comparing them with available experimental results, in which there was good agreement. The obtained results demonstrated that the gas-solid heat transfer and wall-to-bed heat transfer processes strongly depend on the bed flow structure, especially void and solid volume fractions. Slugging beds related to the highest inlet velocity achieved the best conditions of a heat transfer process, as indicated by the highest gas-solid and wall-to-bed heat transfer coefficients. Simulation results also showed that slugging behavior had no negative effect on the heat transfer process despite problems such as obstruction and entrainment.

원추형 유동층 연소기 내의 열전달에 미치는 복원계수의 영향에 대한 수치해석 연구

강승모,박외철,Hamada Abdelmotalib,고동국,임익태 한국반도체디스플레이기술학회 2015 반도체디스플레이기술학회지 Vol.14 No.4

In this paper, numerical simulations on conical fluidized bed combustors were carried out to estimate the effect of coefficients of restitution between particle and particle and particle to wall on hydrodynamics and heat transfer. The Eulerian–Eulerian two-fluid model was used to simulate the hydrodynamics and heat transfer in a conical fluidized bed combustor. The solid phase properties were calculated by applying the kinetic theory of granular flow. Simulations results show that increasing the restitution coefficient between the particle and particle results in increasing the bed pressure drop. On other hand, the increasing of particle to wall coefficient of restitution results in decreasing the bed pressure drop. It is found that the coefficient of restitution has little effect on heat transfer.

원추형 유동층 연소기의 수력학적 특성 및 열전달에 항력 모델이 미치는 영향에 대한 연구

강승모(Seung Mo Kang),Hamada Abdelmotalib,고동국(Dong Guk Ko),박외철(Woe-Chul Park),임익태(Ik-Tae Im) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.11

본 연구에서는 서로 다른 항력 모델이 원추형 유동층 연소기 내의 수력학적 특성과 열전달 현상에 미치는 영향에 대해, 입자상 유동에 대한 분자운동론을 적용한 오일러-오일러 모델을 사용하여 수치해석적으로 연구하였다. Gidaspow 항력 모델과 Syamlal-O’Brien 항력 모델에 대해 유입 공기의 속도와 입자의 크기를 변화시키면서 연소기 내의 압력강하나 베드 팽창률 및 벽과 베드 사이의 열전달 계수의 변화를 조사하였다. 그 결과 베드의 팽창률은 속도가 증가함에 따라 커졌으며 압력강하는 속도의 증가에 따라 감소하였다. 벽과 베드 사이의 열전달 계수는 유입 속도가 증가하면 증가하고 입자의 크기가 증가하면 감소하는 것으로 나타났다. 베드의 팽창률이나 압력 강하와 같은 수력학적 특성은 항력 모델에 큰 영향을 받지 않았으나 열전달 계수는 항력 모델에 따라 차이가 나타났다. In this study, wall to bed heat transfer and hydrodynamic characteristics in a conical fluidized bed combustor was investigated using computational fluid dynamics method. A two-fluid Eulerian-Eulerian model was used with applying the kinetic theory for granular flow(KTGF). The effects of the two drag models, Gidaspow and the Syamlal-O"Brien model, different inlet velocities(1.4Umf~4Umf) and different particle sizes on the hydrodynamics and heat transfer were studied. The results showed that the hydrodynamic characteristics such as bed expansion ratio and pressure drop were not affected significantly by the drag models. But the heat transfer coefficient was different for the two drag models, especially at lower gas inlet velocities and small particle sizes.

A Study on Heat Transfer in Conical Fluidized Bed Combustor

Ik-Tae Im(임익태),Hamada Abdelmotalib,Dong Guk Ko(고동국),Suk Bum Youn(윤석범) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.열공학 No.-