Fouling is formed on the wall of the heat exchanger, it deteriorates heat transfer. Solid particles could be used for removal of the fouling. Novel concept to mitigate fouling of heat exchangers has been developed to make use of the highly specialized equipment like fluidized bed heat exchangers. A ...
Fouling is formed on the wall of the heat exchanger, it deteriorates heat transfer. Solid particles could be used for removal of the fouling. Novel concept to mitigate fouling of heat exchangers has been developed to make use of the highly specialized equipment like fluidized bed heat exchangers. A fluidized bed heat exchanger can remove severe fouling on the surface of tube by circulated particles in the heat exchanger and increase the heat transfer owing to disturbing the thermal boundary layer. The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. Generally, the economic concept of optimized design and operating conditions can hardly be realized, since the lack of both fundamental knowledge and of scale-up rules leads to the situation that information from laboratory fouling investigations cannot directly be applied to industrial situations. The present experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with the smooth and corrugated tube, at which a variety of solid particles such as glass(bead, 3 ㎜ø), Al(cylinder, 2 ㎜ø, 4.5 ㎜L), Al(cylinder, 3 ㎜ø, 2 ㎜L), steel(cylinder, 2 ㎜ø, 4.5 ㎜L), steel(cylinder, 2.5 ㎜ø, 2.88 ㎜L), Cu(cylinder, 2.5 ㎜ø, 2.88 ㎜L), and sand(grain, 2~4 ㎜ø) were used in the fluidized bed with a smooth and two different corrugated tubes. Seven different solid particles have the same volume. The effects of various parameters such as water flow rates, particle geometries, materials, smooth and corrugated tube geometries were investigated. The movement of spherical particles in a tube was visualized and heat transfer enhancement and scale reduction mechanism by particles were investigated. The Numerical analysis of commercial Computational Fluid Dynamics(CFD) program was also performed to predict the fluid flow in a variety of applications. The CFX code was used with mesh type of tetra-prism mesh and about 480,000 nodes in this study. The fundamental basis of the CFD problem was the Navier-Stokes equations, which defined any single-phase fluid flow. Listed below are major findings; 1) The heat transfer enhancement was done by the fact that the circulating solid particles had not only a heat capacity larger than a gas or a liquid because of larger density, but also a cleaning function. 2) The drag force coefficients of particles in the internal flow were higher than in the external flow in the smooth tubes, in addition, they were lower with the shapes of particles being closer to the spherical geometries. 3) The particles augmented the heat transfer at the flow velocities lower than 1.0 ㎧. However above 1.0 ㎧, the heat transfer coefficients were essentially the same as or lower than those of pure water. 4) The higher densities of particles had the higher drag force coefficients, and the increases in heat transfer were in order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000. 5) The drag force coefficients of particles in the corrugated tubes were usually lower than in the smooth tubes, meanwhile the relative velocities between particles and water in the corrugated tubes were little higher than in the smooth tubes except the glass. In addition, the solid particle periodically hitting the tube wall broke the thermal boundary layer, and increased the rate of heat transfer. 6) The higher thermal capacities of materials and the geometries closer to the spherical one had higher heat transfer performances, in addition, heat transfer coefficients in the corrugated tubes were a little higher than those in the smooth tubes. Particularly when the flow velocity was low, the effect was more pronounced.
Fouling is formed on the wall of the heat exchanger, it deteriorates heat transfer. Solid particles could be used for removal of the fouling. Novel concept to mitigate fouling of heat exchangers has been developed to make use of the highly specialized equipment like fluidized bed heat exchangers. A fluidized bed heat exchanger can remove severe fouling on the surface of tube by circulated particles in the heat exchanger and increase the heat transfer owing to disturbing the thermal boundary layer. The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. Generally, the economic concept of optimized design and operating conditions can hardly be realized, since the lack of both fundamental knowledge and of scale-up rules leads to the situation that information from laboratory fouling investigations cannot directly be applied to industrial situations. The present experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with the smooth and corrugated tube, at which a variety of solid particles such as glass(bead, 3 ㎜ø), Al(cylinder, 2 ㎜ø, 4.5 ㎜L), Al(cylinder, 3 ㎜ø, 2 ㎜L), steel(cylinder, 2 ㎜ø, 4.5 ㎜L), steel(cylinder, 2.5 ㎜ø, 2.88 ㎜L), Cu(cylinder, 2.5 ㎜ø, 2.88 ㎜L), and sand(grain, 2~4 ㎜ø) were used in the fluidized bed with a smooth and two different corrugated tubes. Seven different solid particles have the same volume. The effects of various parameters such as water flow rates, particle geometries, materials, smooth and corrugated tube geometries were investigated. The movement of spherical particles in a tube was visualized and heat transfer enhancement and scale reduction mechanism by particles were investigated. The Numerical analysis of commercial Computational Fluid Dynamics(CFD) program was also performed to predict the fluid flow in a variety of applications. The CFX code was used with mesh type of tetra-prism mesh and about 480,000 nodes in this study. The fundamental basis of the CFD problem was the Navier-Stokes equations, which defined any single-phase fluid flow. Listed below are major findings; 1) The heat transfer enhancement was done by the fact that the circulating solid particles had not only a heat capacity larger than a gas or a liquid because of larger density, but also a cleaning function. 2) The drag force coefficients of particles in the internal flow were higher than in the external flow in the smooth tubes, in addition, they were lower with the shapes of particles being closer to the spherical geometries. 3) The particles augmented the heat transfer at the flow velocities lower than 1.0 ㎧. However above 1.0 ㎧, the heat transfer coefficients were essentially the same as or lower than those of pure water. 4) The higher densities of particles had the higher drag force coefficients, and the increases in heat transfer were in order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000. 5) The drag force coefficients of particles in the corrugated tubes were usually lower than in the smooth tubes, meanwhile the relative velocities between particles and water in the corrugated tubes were little higher than in the smooth tubes except the glass. In addition, the solid particle periodically hitting the tube wall broke the thermal boundary layer, and increased the rate of heat transfer. 6) The higher thermal capacities of materials and the geometries closer to the spherical one had higher heat transfer performances, in addition, heat transfer coefficients in the corrugated tubes were a little higher than those in the smooth tubes. Particularly when the flow velocity was low, the effect was more pronounced.
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