Numerical simulation of heat and mass transfer in fluidised bed heat treatment furnaces

In this paper, a novel combined theoretical and computational model is developed to simulate the heat and mass transfer between a fluidised bed and a workpiece surface, and within the workpiece by considering the fluidised bed as a medium consisting of a double-particle layer and an even porous layer. The heat and mass-transfer flux from the fluidised bed to the workpiece surface is contributed by dense and bubble phases, respectively. The convective heat and mass transfer is simulated by analysing the gas dynamics in the fluidised bed, while radiative heat transfer is modelled by simulating photon emission in a three-dimensional particle array. The simulation shows that convection is approximately constant, while radiation contributes significantly to the heat transfer. The heat-transfer coefficient on an immersed surface near particles is about 6–10 times that on other areas. The transient heat and mass-transfer coefficient, heat and mass-transfer flux on any surface of the workpiece, transient temperature and carbon distributions at any position of the workpiece during the metal carburising process are studied with the simulation.

Heat and mass transfer in fluidised-bed heat-treatment furnaces

The mechanisms of heat and mass transfers between heat-treatment fluidised beds and immersed workpiece were studied by using computational simulation and experimental validation. A model called Double Particle-layer and Porous Medium was developed to simulate the gas flow and heat transfer between fluidised beds and immersed workpiece.

Coupled modelling of hydrodynamics and mass transfer in membrane filtration

This research produced a novel predictive computational model for the water treatment processes of nanofiltration and reverse osmosis. This model combined commercial computational fluid dynamics codes with numerical mass transfer models developed by the candidate to provide a rigorous description of these processes’ hydrodynamic and pollutant removal behaviour.

Heat and moisture transfer through silkworm cocoon walls.

A silkworm cocoon is a biological porous structure which provides multiple protective functions. The knowledge from this natural protective system could contribute to develop advanced materials and structures with superior performances and meet the human demanding of novel breathable materials for enhanced thermal protection and comfort.

Dynamic characteristics and efficiency of a fluidized bed heat treatment process

The dynamic characteristics of gas bubbles in fluidized beds are important to determine the heat and mass transfer rates at component surfaces and the treated profiles of components. They also have great impact on the components’ structural, mechanical and physical properties. However, it has been very difficult to monitor those characteristics dynamically. In this paper, a specifically designed fluidized bed was introduced to facilitate the capturing of its dynamic characteristics and a new video image processing and analysis algorithm was developed. The algorithm is robust and adaptive in terms of locating both bubbles and components in beds with a single or multiple components. It has many advantages in dynamic characterization of gas bubbles and monitoring component treatment. By using this algorithm, the properties of gas bubbles over any period of time can be accurately obtained. This technology will provide a potential on-line dynamic monitoring and quality control system for the chemical heat treatment processes with fluidized beds.

Advances in membrane distillation for water desalination and purification applications

Membrane distillation is a process that utilizes differences in vapor pressure to permeate water through a macro-porous membrane and reject other non-volatile constituents present in the influent water. This review considers the fundamental heat and mass transfer processes in membrane distillation, recent advances in membrane technology, module configurations, and the applications and economics of membrane distillation, and identifies areas that may lead to technological improvements in membrane distillation as well as the application characteristics required for commercial deployment.

Qualitative assessment of bubble behaviour for central and asymmetric injection in 2D gas-solid fluidized bed using image analysis technique and CFD modelling

Bubble characteristics such as shape, size, and trajectory control the hydrodynamics and therefore heat transfer in fluidized bed reactors. Thus understanding these characteristics is very important for the design and scaleup of fluidized beds. An earlier developed Eulerian-Eulerian two-fluid model for simulating dense gas–solid two-phase flow has been used to compare the experimental data in a pseudo-two-dimensional (2-D) bed. Bubbles are injected asymmetrically by locating the nozzle at proximity to the wall, thus presenting the effect wall has on asymmetrical injection as compared to symmetrical injection. In this work, a digital image analysis technique was developed to study the bubble behaviour in a two-dimensional bubbling bed. The high-speed photography reveals an asymmetric wake formation during detachment indicating an early onset of mixing process. The wall forces acts tangentially on thebubble and has a significant impact on the bubble shape, neck formation during detachment and its trajectory through the bed. Larger bubbles drifting away from the centre with longer paths are observed. This qualitative behaviour is well predicted by CFD modelling. Asymmetric injection can significantly influence the heat and mass transfer characteristics.

Permeability mapping in porous media by magnetization prepared centric-scan SPRITE

The ability of porous media to transmit fluids is commonly referred to as permeability. The concept of permeability is central for hydrocarbon recovery from petroleum reservoirs and for studies of groundwater flow in aquifers. Spatially resolved measurements of permeability are of great significance for fluid dynamics studies. A convenient concept of local Darcy’s law is suggested for parallel flow systems. The product of porosity and mean velocity images in the plane across the average flow direction is directly proportional to permeability. Single Point Ramped Imaging with T 1 Enhancement (SPRITE) permits reliable quantification of local fluid content and flow in porous media. It is particularly advantageous for reservoir rocks characterized by fast magnetic relaxation of a saturating fluid. Velocity encoding using the Cotts pulsed field gradient scheme improves the accuracy of measured flow parameters. The method is illustrated through measurements of 2D permeability maps in a capillary bundle, glass bead packs and composite sandstone samples.

A method and its optimal parameters for the measurement of mass transfer coefficient in heat treatment furnaces

The mass transfer coefficient is an important kinetic factor to control the thermo-chemical treatment processes of metals and alloys. More importantly, the mass transfer coefficient is different at different surface positions of a metallic part treated, which depends on the dynamic characteristics of the atmosphere close to the treated surface. Understanding the local mass transfer coefficient would be significant to approach the expected physical and mechanical properties of treated surfaces. In this paper, a reverse method was proposed to measure the mass transfer coefficient at component surface and the diffusivity in metal during heat treatment. The methodology of the reverses method and the optimal parame-ters are discussed in some detail. This method was successfully used to determine the car-bon transfer coefficient at the surface of a part in a carburizing furnace and carbon diffusiv-ity from the carbon distribution within the diffusion layer.

Influence of the geometry of an immersed steel workpiece on mass transfer coefficient in a chemical heat treatment fluidised bed

The mass transfer during carburising in a fluidised bed and in a steel workpiece has been studied experimentally in this work. This involved carburising experiment in an electrically heated fluidised bed at 900–970°C with natural gas and air as the atmosphere. A steel workpiece was designed to provide a range of carbon transfer surfaces of different geometries in the fluidised bed, and the carbon transfer coefficient was measured at these surfaces. The carbon transfer coefficient was determined from the carbon distribution within the diffusion layer of the sample. An empirical relationship of the carbon potential as a function of carburising atmosphere, bed temperature and fluidising velocity was determined, based on the understanding of the mass transfer mechanism and analysis of the experimental results.

Measurement of the mass transfer coefficient at workpiece surfaces in heat treatment furnaces

The mass (e.g. carbon) transfer coefficient at a workpiece surface is an important kinetic factor to control the heat treatment process of the workpiece and to evaluate heat treatment equipment. The coefficient can be calculated from the carbon concentration at the surface of a sample carburized in a carburizing furnace for a given time. Two common measurement methods which use a thin plate and employ a component as samples respectively are evaluated and compared for sensitivity and uncertainty. The comparison shows that the use of a component produces higher measurement precision and also has the advantage in measuring the carbon transfer coefficients at different treated positions. This method is then extended and discussed methodologically. Also two equations are proposed to calculate the carbon transfer coefficient and its uncertainty, respectively. This method is also applied to measure the carbon transfer coefficient in a fluidized bed heat treatment furnace.

Pd embedded in porous carbon (Pd@CMK-3) as an active catalyst for Suzuki reactions: accelerating mass transfer to enhance the reaction rate

Heterogeneous catalysts are promising candidates for use in organic reactions due to their advantages in separation, recovery, and environment compatibility. In this work, an active porous catalyst denoted as Pd embedded in porous carbon (Pd@CMK-3) has been prepared by a strategy involving immersion, ammoniahydrolysis, and heating procedures. Detailed characterization of the catalyst revealed that Pd(0) and Pd(II) species co-exist and were embedded in the matrix of the porous carbon (CMK-3). The as-prepared catalyst has shown high activity toward Suzuki reactions. Importantly, if the reaction mixture was homogenized by two minutes of ultrasonication rather than magnetic stirring before heating, the resistance to mass transfer in the pore channels was significantly reduced. As a result, the reactions proceeded more rapidly and a four-fold increase in the turnover frequency (TOF) could be obtained. When the ultrasonication was employed throughout the entire reaction process, the conversion could also exceed 90% even without the protection of inert gas, and although the reaction temperature was lowered to 30 °C. This work provides a method for fabricating highly active porous carbon encapsulated Pd catalysts for Suzuki reactions and proves that the problem of mass transfer in porous catalysts can be conveniently resolved by ultrasonication without any chemical modification being necessary.[Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Identification of expressed HSP`s in blacklip abalone (Haliotis rubra Leach) during heat and salinity stresses

Both prokaryotes and eukaryotes express a set of highly conserved proteins in response to external and internal stress. The stressors include tissue trauma,anoxia, heavy metal toxicity, infection, changed salinity, and the mmost characterized, heat shock. The result is an expression of stress proteins or heat shock proteins (HSP's) which lead to protection of protein integrity, and also to tolerance under continued heat stress conditions. The Australian backflip abalone (Haliotis rubra) is found principally in southern coastal water and also in estuarine/bay environments. Esturaine/bay environments have greater fluctuations in environmental conditions, especially those of salinity and water temperature, than they are found along oceanic coasts. Abalone from esturaine/bay and oceanic coastal environments were subjected to either increased temperature (2° C/day for a total of 10°C) or hyposalinity (80% seawater). Esturaine/bay abolone were less affectes than the oceanic animals by temperature increase and also demonstrated the ability to volume regualte 3 h after the initial salinity shock. SDS-PAGE and Western blotting techniques, together with dot blots of total protein, using HSP70 specific antibodies, were used to detect HSP70s in the foot muscle of the animals and indicated an expression of HSP70 in response to heat shock in abalone, but not following hyposalinity shock. RT-PCR yeilded a partial cDNA clone of HSP70 from the foot muscle.

Carburising and carbon transfer coefficient in a fluidised bed furnance

The carburising of a steel workpiece with complex geometry in a fluidised bed hasbeen studied experimentally. This involved carburising experiment in an electrically heated fluidised bed at 900 - 970°C with natural gas and air as the atmosphere. The carbon transfer coefficient at the workpiece surface and diffusivity within the workpiece were determined from the carbon distribution within the diffusion layer of the sample. A reverse method and the Levenberg-Marquardt algorithm were used in the calculations. The methodology of the reverses method to extract the carbon transfer coefficient and diffusivity is also discussed in some detail.