Papers by Christopher Baker
Drying Technology, 1992
ABSTRACT This paper describes the results of theoretical and experimental studies on the effect o... more ABSTRACT This paper describes the results of theoretical and experimental studies on the effect of air flow on particle transport through cascading rotary dryers. Two possible models are formulated. In the first, the drag coefficient between the air and the solids is calculated on the assumption that the particles can be regarded as isolated spheres. This approach has been employed widely in the literature to estimate particle residence times in rotary dryers. The results yielded coefficients which were 1–2 orders of magntiude greater than those measured experimentally; this demonstrates the inadequacy of this approach. In the second model, the curtains are treated as flat. two-sided plates and the drag coefficient calculated accordingly. The predictions of this model are in much closer accord with the
Powder Technology, 1978
The slugging characteristics of four relatively large sized solids were investigated in smooth an... more The slugging characteristics of four relatively large sized solids were investigated in smooth and rough-walled columns, 0.15 m in diameter. Maximum slug heights were normally distributed, the mean values increasing with initial bed height and gas velocity. Slug rising velocities computed from these measurements generally exceeded the theoretical value, particularly in the rough-walled column. Slug frequencies decreased with bed height and gas velocity and increased with walI roughness. A continued increase in the bed pressure drop above the point of incipient fluidization was attributed to additional losses resulting from particle acceleration and friction between the bed and column wall. J_iS EXPERLMEiSTXL superficial air velocities in the rough-walled column_ Four solids, nameIy moIochite, ballotini, sand and PVC beads, were employed in this investigation_ Their properties are summarized in Table I_ A Jenike shear cell was used to measure the angles of internal friction and wall friction_ In the latter case, the angle characterizes the friction between the solids and a glass plate_ Three bed heights, nominally O-32, 0.55 and O-75 m, were investigated-The actual bed heights in each case are given in Table 1. Thus, the bed height to diameter ratios, Ho/D,
Scientific and Engineering Principles, 1981
ABSTRACT In the last five years or so there has been a significant increase in the number of appl... more ABSTRACT In the last five years or so there has been a significant increase in the number of applications of fluidization principles in many biochemical processes. Biofluidization applications so far have yielded very encouraging results and the trend towards more applications will undoubtedly continue. This paper reviews briefly some of the basic principles of fluidization in liquid-solid and liquid-solid-gas systems and examines the results from applications in immobilized enzyme systems, immobilized whole cells, and waste water treatment processes.
Chemical Engineering Science, 1977
Bubble size and nsmg velocity m freely bubblmg hqmd%as and three phase fhudrzed beds have been me... more Bubble size and nsmg velocity m freely bubblmg hqmd%as and three phase fhudrzed beds have been measured by means of movie photography Three sohds (l-6 mm), a variety of hqtuds, and au were employed as the three phases Both bubble Size and rlsmg velocity were found to Increase with gas velocity but were relatively InsensItIve to the hqtud velocity, vacoslty, and surface tensIon At the high gas rates employed, the bubble charactenstlcs were independent of parkle size Correlations are presented for calculatmg bubble size and nsmg velocity
Food and Bioproducts Processing, 2005
This paper describes the result of a process study undertaken to determine the performance of the... more This paper describes the result of a process study undertaken to determine the performance of the break- and reduction-rolls and plansifters in a commercial flour mill. The parameters measured included the flow rates of selected streams, their ash and moisture contents, and their particle size distributions. The percentage errors in the overall, ash and moisture balances across the plansifters ranged from −17.8 to +1.2, −10.1 to +15.5, and −0.4 to −3.1, respectively. The cumulative size distributions of the first, second and third break-roll outlet streams were found to normalize with respect to roll gap setting using only a single fitting parameter. Similar results were obtained for the first, third and fifth reduction rolls. The procedure was also partially successful in normalizing previously published break-milling data. The measured separation in the six plansifters studied was compared with an ideal separation on the basis of size, assuming that there was no breakdown or aggregation of individual particles within the plansifter. The results suggested that there were significant deviations from ideality.
AIChE Journal, 1983
Wall-to-bed heat transfer coefficients in three-phase fluidized beds with glass beads and cylindr... more Wall-to-bed heat transfer coefficients in three-phase fluidized beds with glass beads and cylindrical 7-alumina particles were determined experimentally. In the present study, the relative increase in heat transfer coefficient was found equal to the relative decrease in liquid holdup in three-phase fluidized beds. Modified Stanton number has been correlated with modified Reynolds number.
Chemical Engineering Science, 1980
The mass transfer of oxygen between an and water has been studled m a bubble column over wide ran... more The mass transfer of oxygen between an and water has been studled m a bubble column over wide ranges of hquld and gas velocity An oxygen probe was used to map the steady-state hqmd phase concentration of oxygen throughout the column At any given pomt m the column, the oxygen concentration mcreased with gas veloety Mmlma were observed m plots of concentration against hqmd velocity Two distinct absorption resons were observed Close to the distributor the concentration decreased rapidly with height and volumetric mass transfer coefficients ranged from about 0 2 to 2 1 s-l These high values were attnbuted to enhanced mass transfer due to turbulence induced by the hquld and gas Jets m the grid regon In the bulk of the column, axial concentration gradients were much smaller and the mass transfer coefficients were up to two orders of magmtude lower than in the grid regon
Drying Technology, 2000
The selection of dryers is an art in which knowledge, experience and science all play important r... more The selection of dryers is an art in which knowledge, experience and science all play important roles. Historically, dryer selection has been made by experts on the basis of their extensive knowledge. However, in recent years, computer-based techniques have been developed, which have the potential of at least partially deskilling this process. Of the various possibilities, fuzzy expert systems, in
Drying Technology, 2005
ABSTRACT Recent European legislation designed to limit carbon emissions and to reward the efficie... more ABSTRACT Recent European legislation designed to limit carbon emissions and to reward the efficient use of energy will undoubtedly encourage dryer operators to reduce their fuel consumption. This article first describes such legislation, which includes the climate change levy, enhanced capital allowances for energy-efficient plant, emissions trading, and the integrated pollution prevention and control regulations. Techniques for measuring dryer performance, benchmarking the results, and analyzing different energy-saving options are then discussed. It is concluded that more stringent legislation coupled with technical improvements, and social, political and economic pressures will result in a cycle of continuous improvement in operating performance.
Computers & Chemical Engineering, 2003
This paper describes an integrated web-based fuzzy expert system for food dryer selection. A modu... more This paper describes an integrated web-based fuzzy expert system for food dryer selection. A modular approach to designing the system was employed. It consists of a number of knowledge sources controlled by a scheduler, which communicate through a common blackboard. The system has been fully implemented to run on the web and provides an excellent example of how a number of heterogeneous tools and applications can be integrated on the www. Java was used as the main programming language, and a new server-side technology, Java servlets, was utilised and found to be very effective in integrating different applications on the web. Rule-based knowledge sources and the inference mechanisms were implemented using ReSolver. The system, which also includes 'foreign' programs coded in Fortran, clearly demonstrated the integration of the various tools in a seamless user-friendly environment. The structure of the developed system is presented together with example runs to demonstrate its main functionality.
The Canadian Journal of Chemical Engineering, 1978
Cryogenic recovery of tar from Athabasca tar sand could be an attractive alternative to the conve... more Cryogenic recovery of tar from Athabasca tar sand could be an attractive alternative to the conventional hot water separation process. It is based on the fact that when frozen tar sand is ground, distinct particles of tar and sand are obtained and can be separated by elutriation. A specially designed fluidized bed grinder was developed for operation at temperatures in the range −30 to −130°C. Preliminary experiments have shown that 88% of the tar can be removed from the sand. Improved results can be expected after further optimization of the unit. La recuperation cryogenique du goudron du sable bitumineux de l'Athabasca pourrait s'averer une methode attrayante pour remplacer le procede classique de separation a l'eau chaude. Ladite methode est basee sur le fait que, lorsqu'on broie un sable bitumineux congele, on obtient des particules distinctes qu'on peut separer par elutriation. On a mis au point un broyeur a lit fluidise et specialement concu pour fonctionner a des temperatures comprises entre -30 et −130°C. On a trouve dans des experiences preliminaires qu'on pouvait separer du sable 88% du goudron; on peut s'attendre a de meilleurs resultats lorsqu'on aura optimise davantage l'equipement en question.
The Canadian Journal of Chemical Engineering, 1973
The partition of solids between stages in baffled fluidized beds bas been studied. The bed, 9 ft ... more The partition of solids between stages in baffled fluidized beds bas been studied. The bed, 9 ft tall and 11 in I.D., was divided into two or three stages by horizontal perforated plate baffles having open areas ranging from 11.5 to 34%. The spacing between baffles was varied from 1.5 to 3.5 ft. Four fluidized solids were studied and the velocity of the fluidizing air was varied between 0.2 and 2.5 ft/sec. A correlation was developed which enabled the solids holdup in each stage to be predicted.
Multiphase Chemical Reactors, 1981
Stewart Postharvest Review, 2005
Purpose of the review: In recent months, the cost of fuel has increased dramatically. As dryers a... more Purpose of the review: In recent months, the cost of fuel has increased dramatically. As dryers are major consumers of energy, it is an opportune time to revisit techniques that may be of value in containing the escalating cost of postharvest drying. This paper therefore focuses on methods that can be used to reduce the energy expended in removing moisture from agricultural crops. Main findings: A range of techniques that have the potential, either now or in the future, for reducing the energy consumption of agricultural dryers were identified. Low-cost measures, such as good housekeeping, effective control systems, and good operating practice are of prime importance as they can be applied to good effect immediately. Greater efforts, perhaps, need to be made to “educate” the diverse users of crop-drying equipment as to the potential benefits of these well-established methods. Computer simulations of dryers, which can often improve their performance, are also discussed. A number of potentially more efficient technologies are available that in theory can replace or be used in conjunction with conventional convective dryers are then described. However, many of these are likely to find only limited application or prove to be impractical or uneconomic. Directions for future research: Most of the technologies discussed in this review would benefit from further study; specific suggestions are made in the “Conclusions and Directions for Future Research” section. Particular emphasis should be placed on the less developed technologies such as high electric field drying and electroosmotic dewatering in order to provide a better understanding of the underlying physics and to assess their ultimate industrial potential. In addition, a comprehensive techno-economic evaluation of the techniques that have been identified in this review as having the potential for reducing the energy consumption of agricultural drying would be of value in focusing research priorities.
Transactions of the Faraday Society
ABSTRACT
Measurements of adsorption isotherms for three VOCs (toluene, 1,2 dichlorobenzene and 1,1,1 trich... more Measurements of adsorption isotherms for three VOCs (toluene, 1,2 dichlorobenzene and 1,1,1 trichloroethane) on three adsorbents, polyacrylonitrile carpet fibers, silica alumina and silica alumina impregnated with KMn04 over the temperature range 2545°C were carried out in a thermogravimetric analyzer. Linear isotherms were observed in all cases with values of the Henry coefficient ranging from 0.01 19 to 0.9407 mm. Silica alumina impregnated with KMn04 showed higher adsorption rates compared to silica alumina and polyacrylonitrile fibers. The results of additional experiments carried out in a simple test chamber containing a single source of VOC showed that the adsorbents acted as a significant sink causing a prolonged elevation of VOC concentration in the air within the chamber. There was good agreement between the equilibrium and kinetic constants obtained in the TGA and test-chamber experiments.
Trans. Faraday Soc.
ABSTRACT
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Papers by Christopher Baker