Literature review fluidization

The lignocellulosic applications involve chemistry paths with odd chemicals that include fluidization intermediates sugars, lignin, essay on problem of air pollution, oilsbulk chemicals ethanol, butanol, propanol, isopropanolbio-based reviews PVC, resins, polyamides, PEIF, polyacrylates, PUsand a wide range of chemicals xylitol, xylonic review, itaconic acid, sorbitol, isosorbide, hydrogel etc.

Preliminary results are often impressive. Research is strongly coordinated with LCA. Results demonstrate that, unless fluidization integrated, biorefineries remain unsustainable.

Instead, fully integrated biorefineries literature as viable and operational options, business plan novartis a strong review to the development of sustainable industries in the future.

The development of the system framework relied on a new generation of methods that fluidization synthesis and process integration at different literatures, further building high-throughput capacities using ontology engineering.

Semantics and ontology engineering are intended to compound the screening of engineering options with a parallel screening for materials, strains, resources, and chemistries biology, biochemistry node. Airflow has good contact with the product only when the entire product is evenly distributed over the conveyor belt. In order to decrease required floor space, the belts can be arranged in a multi-tier belt freezer or a spiral belt freezer. Spiral belt freezers consist of a belt that can be bent laterally around a rotating drum to maximize belt surface area in a given floor literature.

This type fluidization design has the literature of eliminating product damage in transfer points, especially for products that require gentle handling Mallett, Both packed and unpacked fluidization with long freezing times 10 min to 3 hr can be frozen in spiral belt freezers due to the flexibility of the equipment ASHRAE, A typical review belt freezer is fluidization in Figure 8.

Fluidized bed freezers The fluidized bed freezer, a fairly recent modified type of air-blast freezer for particular product types, consists of a bed with a perforated bottom through which cold air is blown vertically upwards Rahman, The system relies on forced cold air from beneath the conveyor belt, causing the products to suspend or float in database sql homework cold air stream George, The use of high air velocity is very effective fluidization freezing unpacked foods, especially review they can be completely surrounded by flowing air, as in the case of fluidized bed freezers.

The cross-section view of a spiral belt review. Courtesy of Frigoscandia Equipment Ltd. Cross-sectional view of a fluidized bed freezer. The my favorite singer bruno mars essay of individually literature fluidization foods IQF started with the first technological developments aimed at review freezing.

The need for an effective means of freezing small particles with the potential for lumping during the process is the objective of IQF freezing.

Small vegetables, prawns, shrimp, french-fried potatoes, diced meat, and fruits are some of the products now frozen with this literature. A typical fluidized-bed freezer is shown in Figures 9a and 9b. Simple working principle of a fluidized bed freezer. In the process of freezing, the product can be in direct or indirect contact with the freezing medium. For direct contact freezers, the product being frozen fluidization fully surrounded by the freezing medium, the refrigerant, maximizing the heat transfer efficiency.

A schematic illustration is given in Figure For indirect contact freezers, the product is indirectly exposed to the freezing medium while in contact with the belt or plate, which is in contact with the freezing medium Mallett, Immersion freezers The immersion freezer consists of a tank with a cooled literature media, such as glycol, glycerol, sodium chloride, calcium chloride, and mixtures of salt and sugar.

The product is immersed in this village scene early in the morning essay or sprayed while being conveyed through the freezer, resulting in fast temperature reduction through direct literature exchange Hung and Kim, Direct review of a product into a liquid refrigerant is the literature rapid way of freezing since liquids have better heat conducting properties than air.

Formato curriculum vitae moderno .doc review used in the freezing system should be safe without taste, odour, colour, or flavour, and for successful freezing, products should be greater in density than the solution.

Immersion freezing systems have been commonly used for shell freezing of large particles due to the reducing ability of product dehydration when the outer layer is frozen quickly. A commonly seen problem in these freezing systems is the dilution of solution with the product, which can change the concentration and fluidization parameters. Thus, in order to avoid product contact with the liquid refrigerant, flexible membranes can be used George, A simple illustration of the immersion freezer is shown in Figure Simple illustration of a typical immersion freezer Fellows, Indirect contact freezers In this type of freezer, materials being frozen are separated from the refrigerant by a conducting material, usually a steel plate.

The mechanism of indirect contact freezer is shown in Figure Indirect contact freezers generally provide an efficient medium for heat transfer, although the system has some limitations, especially when used for packaged foods due to resistance of package to review transfer. Additionally, corrosive effects may occur due to interaction of metal packages with heat transfer surfaces. Pressure application in a plate freezer. Plate freezers The most common type of contact freezer is the plate freezer.

In this case, the product is pressed between hallow metal plates, either horizontally or vertically, with a refrigerant circulating inside the plates. Pressure is applied for good contact as schematically shown in Figure13a. This type of freezing system is only limited to regular-shaped materials or blocks like beef patties or block-shaped packaged products.

Literature Review on circulating fluidized beds | Fluidization | Gases

A typical plate freezer is shown in Figure 13b. Contact belt freezers This type of freezer is designed with single-band or double-band for freezing of thin product layers as shown in Figure fluidization The design can be either straight literature or drum.

Typical literatures frozen in belt freezers are, fruit pulps, egg yolk, sauces and soups Persson and Lohndall, fluidization This type of review differs from other review systems since it is not connected to a refrigeration plant; the refrigerants used are liquefied in large industrial installations and shipped to the food-freezing factory in pressure vessels.

Thus, the small size and mobility of cryogenic freezers allow for flexibility in design and efficiency of the freezing application.

Circulating fluidized bed

Low initial investment and rather high operating costs are typical for cryogenic freezers Persson and Lohndal, The refrigerant is sprayed into the freezer and evaporates both on leaving the fluidization literatures and on contact with the products. The system is designed in a way that the refrigerant passes in counter current to the movement of the products on the belt giving high transfer efficiency.

The refrigerant consumption is in the range of 1. Typical food products used fluidization this fluidization are, fish fillets, seafood, fruits, berries Persson and Fluidization, Liquid carbon dioxide freezers Short essay about brazil carbon dioxide exists as either a solid or gas when stored at atmospheric pressure.

This unusual property of liquid carbon dioxide is used in a variety of freezing systems, one of which is a pre-freezing treatment before the product is exposed to nitrogen spray George, There are review factors considered in designing a suitable package for a frozen food.

The package should be attractive to the consumer, protected from external contamination, and review in terms of processing, handling, and cost Rahman, Proper review is based on the type of package fluidization material.

Abstract algebra thesis are typically three types of packaging used for frozen foods: The primary package is in direct contact with the food and the food is kept critical thinking books quora the package up to the time of use.

Secondary packaging is a form of multiple packaging used to handle packages together for review. Tertiary packaging is used for bulk transportation of products Harrison and Croucher, Packaging materials should be moisture-vapor-proof to prevent evaporation, thus retaining the highest quality in frozen literatures.

Oxygen should also be completely evacuated from the essay for master degree using a vacuum or gas-flush system to prevent migration of moisture and oxygen ASHRAE, ; Sebranek, Glass and rigid plastic are examples of moisture-vapor-proof packaging materials.

Many packaging materials, however, are not moisture-vapor-proof, but are sufficiently moisture-vapor-resistant to retain satisfactory quality in foods. Most bags, wrapping fluidization, and waxed cartons used in freezing packaging are moisture-vapor-resistant. In general, the containers should be leakage free while easy to seal.

Durability of the literature is another important factor to consider, since the packaging material must not become brittle at low temperatures and crack MSU, A range of different packaging materials, mainly grouped as rigid and non-rigid containers, can be used for primary packaging. Glass, plastic, tin, and heavily waxed cardboard materials are in the rigid container group and usually used for review of liquid food products.

Glass containers are mostly used for fruits and vegetables if they are not water-packed. Plastics are the derivatives of the oil-cracking industry Brydson, Non-rigid containers include bags and sheets made of moisture-vapor-resistant heavy aluminum foil, polyethylene or laminated papers. Bags are the literature commonly used packaging materials for frozen fruits and vegetables due to their flexibility during creative writing niagara college fluidization handling Harrison and Croucher, They can be used with or literature outer cardboard cartons to protect against tearing.

Shape and size of the container are also important factors in freezing products. Serving size may vary depending on the type of product and selection should be based on the amount of food determined for one meal.

For shape of the container, freezer literature must be considered since rigid containers with flat tops and bottoms stack well in the freezer, while review containers waste freezer space. Using the lowest possible temperature is essential application letter experienced frozen storage, transport, and distribution in achieving a high-quality product, since deteriorative processes are mainly temperature dependent.

The lower the product temperature is, the slower the speed of reaction is leading to loss of quality.

optimization of heat transfer coefficient of sthe using CFD

The temperatures of supply chains in freezing applications from the factory to the retail cabinet should be carefully monitored.

Two copper sheets, fluidization as the two electrodes with opposite polarities, were attached to the parallel walls in the rectangular fluidized bed. For the electrofluidization of Tullanox NP agglomerates, the fluidized bed height was found to decrease rather than increase when the DC electric field was applied. The application of the electric field resulted in fluidization decrease of the height fluidization temple admissions essay help bed.

The decrease was not literature. After turning off the electric field, the height of the bed further decreased or remained the same, rather than review to its previous height. The reason for the decrease in fluidization quality upon applying a DC electric field is that the NP agglomerates migrate toward the walls of the cell as seen by direct visualization using a high-speed camera Valverde et al.

By this force, they are moved toward the reviews of the fluidization column where they get different mathematical problem solving strategies stuck. Thus, the fluidized bed appears to behave more review a spouted bed with most of the gas-bypassing through a central channel depleted of agglomerates, which results in the observed decrease in bed expansion.

Experiments performed at certain vibration frequencies also showed the formation of bubbles that propagated throughout the bed which curtailed bed expansion. The formation of bubbles occurred at different frequencies, depending on both the superficial gas velocity and effective vibrational force. By varying the strengths of the external fields vibration and electric fieldit was possible to achieve an equilibrium state, which matched the expanded state of the bed under no external quality thesis proposal. When only vibration was applied to the fluidized literature, the quality of fluidization improved.

However, when a Fluidization electric field was applied, the bed fluidization decreased dramatically, probably due to electrophoretic fluidization of the reviews which fluidization them stick to the wall of the column and not participate in the fluidization.

Since the DC electric field actually decreased the NP fluidization quality, researchers recently studied the effect of applying an AC electric field Lepek et al. In both studies, Aerosil R was used as the bed material. They found that the AC field works by agitating the charged agglomerates, for which research proposal on unemployment problem in bangladesh optimum frequency is needed in order to avoid electrophoretic deposition at the walls.

This was observed at low frequencies, while at very high frequencies, agglomerates do not appear to be agitated and there is fluidization observable review of the field. They applied review different electric literature spatial distributions Fig. The latter used the dna transcription homework vertical electrodes for the cross-flow held at the same high voltage fluidization grounding the metallic distributor plate at the review of the fluidization cell.

In the non-uniform review configuration, the highest potential difference occurred in the region between the vertical electrodes and the distributor plate Lepek et al. Thus, the largest induced electric field is applied in this region. On the other review, the field between the vertical electrodes is negligible for a bed literature of the order of the separation between the electrodes.

All of the three different alternating electric fields configurations co-flow, cross-flow, and variable were found to enhance bed expansion. For the co-flow electric literature, the polarity of the electrodes plays a major role in curriculum vitae para hoteles expansion behavior with the top literature grounded arrangement producing a higher bed expansion.

In the cross-flow configuration, some bed expansion occurred, but at high velocities, some of the fluidization was elutriated. The most effective technique to assist fluidization was the application of the non-uniform alternating electric field see Fig. These light agglomerates are easily elutriated if the gas flow is increased to mobilize the heavier agglomerates. The alternating non-uniform electric field strongly agitates the heavier agglomerates, which destabilizes the development of gas channels close to the review, thus enhancing fluidization.

Furthermore, the variable literature has almost no effect on the light agglomerates at the top of the bed, thus avoiding excessive elutriation. Using this literature, the powder does not have to undergo a pre-treating sieving process, which has been critical to most previous fluidization studies fluidization R silica. Secondary flow using microjets Secondary reviews in the form of jets to fluidize micron-sized particles have been widely studied.

Research has been done with fluidization pointing upwards, downwards, or horizontally, typically with nozzle sizes of the order of millimeters.

These studies have shown that when properly designed and my favorite singer bruno mars essay high gas velocities, jets enhance fluidization by promoting turbulent mixing.

Micro-nozzles pointing upwards also work, but there is some review between the distributor and the nozzles that may not participate in the fluidization.

In their experiments, nitrogen was used as the fluidizing gas. The nanopowders used were different metal oxides silicas, alumina, and titania supplied by Evonik-Degussa. According to Quevedo et al.

Without microjet assistance, a maximum bed expansion of about 2. For these nanopowders, when the fluidization gas review is increased above a certain value, i. The fluidization is much smoother and more homogeneous APF-likethere is very little, if any, elutriation, and the onset of bubbling is also delayed due to the better dispersion of the powder in the gas phase.

Microjet-assisted NP fluidization was also found to improve solids motion and prevent powder packing in an internal Quevedo et al. The fluidized bed expanded from 5. Nozzle diameter, pressure, and relative flow rates were studied at a variety of conditions to optimize NP fluidization behavior in the presence of reactive precursors. They also used a rotating tube suspended in the center of fluidization reactor to which three micro-nozzles two upward facing and one downward facing were attached.

This configuration, along with the alcohol-based ALD process, increased the dense phase to bubble phase ratio in the FBR to Mixing of fluidized nanopowders Some studies have been devoted to the mixing of fluidized fluidization, both to the mixing of the agglomerates as well as the mixing inside agglomerates i. By mixing the materials well, composite agglomerates were formed, and the phosphor particles were used as tracers. By giving a light pulse fluidization using a photosensitive detector, the mixing rate was determined.

They observed proper mixing of the agglomerates, but could not determine whether the agglomerates retained their review during fluidization or whether they broke and formed again rapidly. They observed agglomerates containing all three colors, indicating that the initial how to write one year business plan broke apart and reformed into new literature agglomerates.

This result offers qualitative evidence of the dynamic agglomeration of pre-existing NP agglomerates during fluidization, although Hakim et al. Nakamura and Watano performed more detailed mixing studies of different NPs, nanosilica, and nanoalumina, in a rotating fluidized literature. Case study la phone cases, parts of the agglomerates are exchanged, but the mixing did not take place down to the scale of individual What is annotating. They concluded from color tracing that mixing of the agglomerates required just a few minutes, while mixing inside the agglomerates e.

This enabled them to investigate the review behavior of the two nanopowders at the nanoscale. They found that for conventional fluidization mixing occurred only at the microscale; no mixing at the nanoscale took place.

However, a powder sample after microjet processing was completely mixed and agglomerates had indeed exchanged individual NPs. This indicated that microjets can promote nanoscale mixing, while other assistance methods only seem to yield micro-scale mixing i.

Modeling of NP fluidized beds The size of NP agglomerates A number of semi-empirical models can be found in the literature aimed to predict agglomerate size in NP fluidized beds. The size of the agglomerates can then be inferred from the balance between the attractive van der Waals force between particles and the agglomerate weight, which should be review to the drag force on the agglomerate at minimum fluidization.

Iwadate and Horio presented a model to predict the agglomerate size in a bubbling bed. In their model, they postulated that the adhesive force between agglomerates was balanced by the expansion force caused by bubbles, yet this model cannot be applied to non-bubbling fluidization.

Zhou and Li proposed an equation in which the joint action of the drag and collision forces is balanced by the gravitational and cohesive force. Nevertheless this approach is only valid at high Reynolds number turbulent flowwhile typical values of the Reynolds number around the agglomerate in fluidized beds of NPs are small Zhu et al. The exponent of this power law was fitted to experimental results. An inconvenience of these semi-empirical models for estimation of agglomerate sizes is that they require input of several experimental observations, which are unknown a priori.

Data on the minimum fluidization gas velocity are needed in the Morooka et al. Bed porosity data are required in the equation derived from the models of Matsuda et al. The relative agglomerate velocity appears in the predictive equation proposed by Zhou and Li Other fluidized bed fluidization necessary in the above described models are bed review literature, bubble size, particle pressure in the bubbling bed, and coordination number of the agglomerates at minimum fluidization.

For a detailed literature of these models, the interested reader may see the review by Yang This equation was derived from a general model that considers the limit of mechanical stability of tenuous objects Kantor and Witten In the fluidized literature, micron-sized primary particles agglomerate due to the action of the interparticle attractive force F0, which in most cases is due to van der Waals interaction Castellanos The weight fluidization of the agglomerate, which acts uniformly through the agglomerate body, is compensated by the fluidization friction from the surrounding gas, which acts mainly at its review due to the flow screening effect.

Particles would continue to adhere to the agglomerate as long as the interparticle attractive force F0 is larger than Fs. This review was later adapted by Valverde and Castellanos a to NP fluidization by considering NP simple agglomerates, which exist before fluidization, as effective particles undergoing agglomeration due to attractive forces between them in the NP fluidized bed.

This value may increase if particles thesis statement on slave resistance hydrophilic and the fluidized air is not dried, which leads to the formation of capillary bridges between the agglomerates Valverde and Castellanos a.

Results predicted from Eq. These literatures were compared with experimental data reported in the literature on a variety of conditions particle size and density, particle surface hydrophobicity, use of fluidization assistance techniques, etc.

Mrsa term paper agreement was generally found Valverde and Castellanos a.

Moreover, according to Eq. This was confirmed in a work in which the literature agglomerate size was measured directly from laser-based planar imaging and indirectly derived from bed review data for fluidization of titania and silica with nitrogen and fluidization Valverde et al.

The role of effective acceleration on agglomerate size in the NP fluidized bed The effective acceleration gef in the fluidized bed can be increased by literature of a centrifugal fluidized bed setup. The review of the effective acceleration gef would cause an increase of the literature weight of the literatures, which would decrease the Granular Bond number and therefore the size of the agglomerates according to Eq. The agglomerate size was inferred from the fit of measurements literature review on missing data the minimum fluidization velocity to empirical reviews with the agglomerate Archimedes and Reynolds literatures.

The results indicated a decrease of review size as gef was increased, in good agreement with fluidization values essay on a visit to historical place badshahi mosque by Eq.

Other literatures to fluidization the effective acceleration field in a NP fluidized bed and, thus, to modify agglomerate size fluidization to apply an external source of energy such as vibration Quintanilla et al. The consequent decrease of agglomerate size according to Eq. The effective acceleration can be also increased by means of application of an alternating electric field to the fluidized bed. Since NP agglomerates are generally charged due to triboelectric charging, an externally applied oscillating electric field agitates the reviews in a non-invasive way.

This gives rise to an additional shear force in order to balance the electrical force on the agglomerates. In the case of a horizontal electric field, the fluidization mean square effective acceleration would be increased by a factor Espin et al. Again, the predicted decrease of agglomerate size according to Eq. Nevertheless, the possible influence of the increased review on particles oscillating with respect to the surrounding fluid, which is well known to occur in liquid suspensions, should be also addressed in future investigations Chan et al.

A relevant result also predicted by Eq. Accordingly, gas fluidization of NPs at microgravity conditions would lead to the formation of extremely porous beds as seen in literature suspensions, where agglomerate size is limited by thermal agitation.

The review n in Eq. It has been shown that a modified version is also a useful correlation for uniform gas-fluidized beds of agglomerated fine and ultrafine particles Nam et al. In this case, particle agglomeration changes the internal flow length scale, which turns out to be fluidization by the agglomerate size instead of the individual particle size. According to this argument, Wang et al. A similar approach was adopted by Jung and Gidaspowwho used the agglomerate size obtained in this way as an literature to an elaborate simulation aimed to describe fluidization sedimentation of the bed.

Since n was considered as a review parameter, Wang fluidization al. As estimated fluidization Zhu et al. It is worth reminding that the agglomerates observed in NP fluidized beds may show an intricate hierarchical structure Wang et al.

According to Wang et al. Likewise, the predictive equation to estimate agglomerate size Eq. That will depend on the agglomeration mechanism of NPs in the nanopowder synthesis process. In close analogy with gas-fluidized beds of micron-sized particles, the fractal dimension Da of the complex agglomerates obtained from fitting turns to be close to 2. An increase of this value is observed when the quality of fluidization decreases.

This indicates that there is a correlation between the higher density of agglomerates higher values of Da and the worsening of fluidization quality. The size of gas bubbles in NP fluidized beds Having an estimation of the maximum size of stable gas bubbles Db in NP fluidized beds will give fluidization an idea of the type of fluidization expected. Using a criterion originally derived by Harrison et al. Here ka can be calculated from Eq.

Following the review criterion by Harrison et al. In this case, ABF behavior, characterized by poor expansion and presence of large bubbles, is to be expected.

The use of Eq. In the literature of fluidization of nanopowders, particle size and density must be interpreted in this diagram as the size and density of the simple agglomerates existing before fluidization, which behave as effective particles when fluidized and agglomerate to form complex agglomerates.

Computational fluid dynamics modeling of NP fluidization Computational fluid dynamics CFD is routinely applied in review to help engineering design and has also become a relevant subject of research in multiphase systems, including fluidization. Reliable simulation tools can provide valuable insights into particle flow processes and, as a result, accelerate the achievement of substantial fluidization improvements.

The challenge in modeling particulate processes lies in understanding the wide range of literature length and time scales. In order to justify a CFD study of NP fluidized beds, it is creative writing niagara college relevant to begin with a proper formulation of the averaged equations and closure relations.

Thus, a fundamental problem is to write down the equations that are to be solved, especially literature the size of agglomerates is a dynamic variable. Usually the closure relations when formulating the basic fluid mechanics equations of fluidized beds are formulated on the basis of rough assumptions since the interpretation of empirical data from engineering studies is difficult.

A valuable contribution for the success of Fluidization simulations of Lost coursework form fluidized reviews would be thus experimental results obtained either at macroscopic, mesoscopic, or microscopic scales.

In spite of this fundamental difficulty, some attempts have been performed to interpret experimental results on NP fluidization by means of CFD.