Experimental determination of the eutectic temperature in air of the CuO-TiO2 pseudobinary system

Eutectic temperature and composition in the CuO–TiO2 pseudobinary system have been experimentally determined in air by means differential thermal analysis (DTA), thermogravimetry (TG) and hot-stage microscopy (HSM). Samples of the new eutectic composition treated at different temperatures have been characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structural spectroscopy (XANES) to identify phases and to determine the Cu valence state, respectively. The results show that the eutectic temperature in air is higher by 100 °C (∼1000 °C) for a Ti-richer composition (XTiO2=25 mol%) than the one calculated in the literature. The reduction of Cu2+ to Cu+ takes places at about 1030 °C. The existence of Cu2TiO3 and Cu3TiO4 has been confirmed by XRD in the temperature range between 1045 and 1200 °C.

Experimental analysis of energy savings and hygrothermal conditions improvement by means of air curtaines in stores with intensive pedestrian traffic

Current worldwide building legislation requirements aim to the design and construction of technical services that reduce energy consumption and improve indoor hygrothermal conditions. The retail sector in Spain, with a lot of outdated technical systems, demands energy conservation measures in order to reduce the increasingly electrical consumption for cooling. Climatic separation with modern air curtains and advanced hygrothermal control systems enables energy savings and can keep suitable indoor air temperature and humidity of stores with intense pedestrian traffic, especially when located in hot humid climates. As stated in the article, the energy savings in commercial buildings with these systems exceeds 30%

Potenciación de la respuesta productiva en rumiantes mediante el empleo de proteínas protegidas

El principal objetivo de esta tesis fue incrementar la eficiencia proteica en las dietas de rumiantes mediante el uso de proteínas protegidas (harina de girasol y guisante de primavera), así como mejorar la predicción de los aportes de proteína microbiana. Una partida de harinas comerciales de girasol (HG) y de guisante de primavera (GP) fueron tratadas con soluciones 4 N de ácido málico (268,2 g/L) o ácido ortofosfórico (130,6 g/L). Para cada harina, ácido y día de tratamiento, dos fracciones de 12,5 kg fueron pulverizadas sucesivamente en una hormigonera con la solución de ácido correspondiente mediante un pulverizador de campo. Las dos fracciones fueron mezcladas posteriormente y se dejaron reposar durante 1 h a temperatura ambiente. La mezcla fue luego secada en una estufa de aire forzado a 120 ºC durante 1 h. La estufa fue apagada inmediatamente después y el material tratado se mantuvo dentro de ésta hasta la mañana siguiente. El material fue removido durante el proceso de secado cada 30 min durante las primeras 2 h y cada 60 min durante las 5 h posteriores. Este proceso se repitió hasta conseguir las cantidades de harinas tratadas necesarias en los distintos ensayos. En el primer experimento (capitulo 3) se llevaron a cabo estudios de digestión ruminal e intestinal para evaluar los efectos de la aplicación de las soluciones ácidas indicadas y calor a fin de proteger las proteínas de HG y GP contra la degradación ruminal. Estos estudios se realizaron con tres corderos canulados en el rumen y en el duodeno. El estudio de digestión ruminal fue realizado en tres periodos experimentales en los que los corderos fueron alimentados sucesivamente con tres dietas isoproteicas que incluían HG y GP, sin tratar o tratadas con ácidos málico u ortofosfórico. Cada periodo experimental de 21 días incluyó sucesivamente: 10 días de adaptación a las dietas, un estudio del tránsito ruminal de las partículas de HG y GP (días 11 a 14), y la incubación de las muestras de ambos alimentos en bolsas de nailon (días 15–21). Las harinas incubadas en cada periodo experimental correspondieron a las que fueron incluidas en las dietas. Las bacterias ruminales fueron marcadas desde el día 11 hasta el día 21 del periodo experimental mediante infusión intra-ruminal continua con una fuente de 15N. Tras finalizar las incubaciones in situ el día 21 el rumen fue vaciado en cada periodo para aislar las bacterias asociadas a la fase sólida y liquida del rumen. El estudio de digestión intestinal fue realizado veinte días después del final del estudio ruminal a fin de eliminar el enriquecimiento en 15N de la digesta. En este estudio se incubaron muestras compuestas obtenidas mediante la combinación de los diferentes residuos no degradados en el rumen de forma que fuesen representativas de la composición química de la fracción no degradada en el rumen (RU). En esta fase los corderos fueron alimentados con la dieta sin tratar para determinar la digestibilidad de las harinas tanto tratadas como sin tratar mediante la técnica de las bolsas móviles. Además, las proteínas contenidas en las harinas tratadas y sin tratar, así como en las muestras correspondientes a los residuos a 0 h, las muestras compuestas anteriormente indicadas y las muestras no digeridas intestinalmente fueron extraídas y sometidas a electroforesis para determinar el sitio de digestión de las diferentes fracciones proteicas. Las estimaciones de la RU y la digestibilidad intestinal de la materia seca, la materia orgánica (solamente para RU), la proteína bruta (PB) y el almidón (solamente en GP) fueron obtenidos considerando la contaminación microbiana y las tasas de conminución y salida de partículas. Las estimaciones de RU y de la digestibilidad intestinal disminuyeron en todas las fracciones evaluadas de ambos alimentos al corregir por la contaminación microbiana acaecida en el rumen. Todas las estimaciones de RU aumentaron con los tratamientos de protección, incrementándose también la digestibilidad intestinal de la materia seca en la HG. Los bajos valores de la digestibilidad de la proteína de GP tratado y sin tratar sugieren la presencia de algún factor antitripsico no termolábil es esta harina. Los tratamientos de protección incrementaron consistentemente la fracción de materia seca y PB digerida intestinalmente en los dos alimentos, mientras que la fracción de almidón en la muestra de GP solamente aumentó numéricamente (60,5% de media). Sin embargo, los tratamientos también redujeron la fermentación de la materia orgánica, lo cual podría disminuir la síntesis de proteína microbiana. Los estudios de electroforesis muestran la práctica desaparición de la albumina por la degradación ruminal en ambos alimentos, así como que los cambios en otras proteínas de la muestra RU fueron más pronunciados en GP que en HG. La composición de las bacterias asociadas con las fases de digesta ruminal sólida (BAS) y líquida (BAL) fue estudiada para revisar la precisión de un sistema de predicción previo que determinaba la infravaloración del aporte de nutrientes correspondiente a las BAS cuando de usa 15N como marcador y las BAL como referencia microbiana (capitulo 4). Al comparar con BAS, BAL mostraron menores contenidos en materia orgánica, polisacáridos de glucosa y lípidos totales y un mayor contenido en PB, así como un mayor enriquecimiento en 15N. Los datos obtenidos en el estudio actual se ajustan bien a la ecuación previa que predice el enriquecimiento en 15N de las BAS a partir del mismo valor en BAL. Esta nueva ecuación permite establecer que se produce una infravaloración de un 22% en el aporte de PB al animal a partir de las BAS sintetizadas si las BAL son usadas como muestras de referencia. Una segunda relación calculada utilizando los valores medios por dieta expuestos en numerosos trabajos encontrados en la literatura confirma la magnitud de este error. Esta infravaloración asociada al uso de BAL como referencia fue mayor para el aporte de glucosa (43,1%) y todavía mayor para el aporte de lípidos (59,9%), como consecuencia de los menores contenidos de ambas fracciones en BAL frente a SAB. Estos errores deberían ser considerados para obtener mayor precisión en la estimación del aporte de nutrientes microbianos y mejorar la nutrición de los rumiantes. En el experimento 2 se realizó un estudio de producción (capitulo 5) para evaluar los efectos del tratamiento de las harinas HG y GP con soluciones de ácido málico o ácido ortofosfórico sobre el crecimiento, el consumo de concentrado y el rendimiento y engrasamiento de las canales de corderos de engorde. Noventa corderos machos de cruce entrefino procedentes de tres granjas comerciales (peso inicial medio = 14,6, 15,3 y 13,3 kg, respectivamente) fueron asignados aleatoriamente a cinco dietas con diferentes niveles de proteína y diferentes tratamientos con ácidos y engordados hasta un peso medio al sacrificio de 25 kg. Las fuentes de proteína en el pienso control (C; PB=18,0%) fueron harina de soja, HG y GP sin tratar. En tres de los piensos experimentales, las harinas tratadas con ácido ortofosfórico sustituyeron a las de HG y GP sin tratar (Control Ortofosfórico, PC; PB=18,0% sobre materia seca), sustituyéndose, además, la harina de soja parcialmente (Sustitución Media Ortofosfórico, MSP; PB=16,7%) o totalmente (Sustitución Total Ortofosfórico, TSP; PB=15,6%). Finalmente, en uno de los piensos el ácido ortofosfórico fue reemplazo por acido málico para proteger ambas harinas (Sustitución Media Málico, MSM; PB= 16,7%). La paja de trigo (fuente de forraje) y el concentrado fueron ofrecidos ad libitum. Dieciocho corderos fueron distribuidos en seis cubículos con tres animales para cada dieta. Los datos fueron analizados según un análisis factorial considerando el peso inicial como covariable y la granja de procedencia como bloque. Los datos de consumo de concentrado y eficiencia de conversión fueron analizados usando el cubículo como unidad experimental, mientras que los datos sobre ganancia media diaria, rendimiento a la canal, grasa dorsal y grasa pélvico renal fueron analizados usando el cordero como unidad experimental. No se encontró ningún efecto asociado con el nivel de PB sobre ninguna variable estudiada. Esto sugiere que usando proteínas protegidas es posible utilizar concentrados con 15,6% de PB (sobre materia seca) disminuyendo así la cantidad de concentrados de proteína vegetal a incluir en los piensos y la calidad de los concentrados proteicos. Los corderos alimentados con la dieta MSM tuvieron mayores ganancias medias diarias (15,2%; P= 0,042), y mejores rendimiento a la canal en caliente (1,3 unidades porcentuales; P= 0,037) que los corderos alimentados con el concentrado MSP. Esto podría ser explicado por los efectos benéficos ruminales del malato o por el mayor efecto de protección conseguido con el ácido málico. ABSTRACT The main objective of this thesis project was to increase the protein efficiency in ruminant diets by using protected protein (sunflower meal and spring pea), and improving the prediction of microbial protein supply. Commercial sunflower meal (SFM) and spring pea (SP) were treated with 4 N solutions (200 mL/kg) of malic acid (268.2 g/L) or orthophosphoric acid (130.6 g/L). Daily, two fractions of 12.5 kg of one of these meals were successively sprayed with the tested acid solution in a concrete mixer using a sprayer. Both fractions were then mixed and allowed to rest for 1 h at room temperature. The blend was then dried in a forced air oven at 120 ºC for 1 h. Then the oven was turned off and the treated material was left in the oven overnight. During the drying process, the material was stirred every 30 min during the first 2 h and then every 60 min for the subsequent 5 h. This process was repeated until the amounts of treated flour needed for the different trials performed. In the first experiment (chapter 3), ruminal and intestinal digestion trials were conducted to study the effects of the application of these acid solutions and heat to protect proteins of SFM and SP against ruminal degradation using three wethers fitted with rumen and duodenum cannulae. The ruminal digestion study was carried out in three experimental periods in which the wethers were successively fed three isoproteic diets including SFM and SP, untreated or treated with malic or orthophosphoric acids. The experimental periods of 21 days included successively: 10 days of diet adaptation, SFM and SP particle ruminal transit study (days 11–14) and ruminal nylon-bag incubations (days 15–21). The meals incubated in each experimental period were those corresponding to the associated diet. Rumen bacteria were labelled from days 11 to 21 by continuous intra-ruminal infusion of a 15N source and the rumen was emptied at the end of in situ incubations in each period to isolate solid adherent bacteria and liquid associate bacteria. The intestinal digestion trial was conducted twenty days after the end of the ruminal studies to eliminate the 15N enrichment in the digesta. The tested samples were composite samples obtained pooling the different ruminally undegraded residues to be representative of the chemical composition of the ruminally undegraded fraction (RU). Wethers were fed the untreated diet to determine the intestinal digestibility of untreated and treated meals using the mobile nylon bag technique. In addition, protein in untreated and treated meals and their 0 h, composite and intestinally undigested samples were extracted and subjected to electrophoresis to determine the digestion site of the different protein fractions. Estimates of the RU and its intestinal digestibility of dry matter, organic matter (only for RU), crude protein (CP) and starch (only in SP) were obtained considering ruminal microbial contamination and particle comminution and outflow rates. When corrected for the microbial contamination taking place in the rumen, estimates of RU and intestinal digestibility decreased in all tested fractions for both feeds. All RU estimates increased with the protective treatments, whereas intestinal digestibility-dry matter also increased in SFM. Low intestinal digestibility-CP values in untreated and treated samples suggested the presence of non-heat labile antitrypsin factors in SP. Protective treatments of both feeds led to consistent increases in the intestinal digested fraction of dry matter and CP, being only numerically different for SP-starch (60.5% as average). However, treatments also reduced the organic matter fermentation, which may decrease ruminal microbial protein synthesis. Electrophoretic studies showed albumin disappearance in both SFM and SP, whereas changes in other RU proteins were more pronounced in SP than SFM. The chemical composition of bacteria associated with solid (SAB) and liquid (LAB) rumen-digesta phases was studied to examine the accuracy of a previous regression system determining the underevaluation of SAB-nutrient supply using 15N as marker and LAB as microbial reference (chapter 4). Compared with SAB, LAB showed lower contents of organic matter, polysaccharide-glucose and total lipids and the opposite for the CP content and the 15N enrichment. Present data fitted well to the previous relationship predicting the 15N enrichment of SAB from the same value in LAB. This new equation allows establishing an underevaluation in the supply of CP from the synthesized SAB in 22.0% if LAB is used as reference. Another relationship calculated using mean diet values from the literature confirmed the magnitude of this error. This underevaluation was higher for the supply of glucose (43.1%) and still higher for the lipid supply (59.9%) as a consequence of the lower contents of these both fractions in LAB than in SAB. These errors should be considered to obtain more accurate estimates of the microbial nutrient supply and to improve ruminant nutrition. A production study was performed in experiment 2 (chapter 5) to examine the effects of treating SFM and SP meals with orthophosphoric or malic acid solutions on growth performance, concentrate intake, and carcass yield and fatness of growing-fattening lambs. Ninety "Entrefino" cross male lambs from three commercial farms (average initial body weights (BW) = 14.6, 15.3 and 13.3 kg) were randomly assigned to five diets with different acid treatment and protein levels, and fattened to an average slaughter weight of 25 kg. Protein sources in the control concentrate (C; CP=18%) were soybean meal and untreated SFM and SP. In three of the experimental concentrates, orthophosphoric acid-treated meals substituted untreated SFM and SP (Orthophosphoric Control, PC; CP=18% dry matter basis), and soybean meal was partially (Medium Substitution Orthophosphoric, MSP; CP=16.7%) or totally removed (Total Substitution Orthophosphoric, TSP; CP=15.6%). In addition, in one concentrate orthophosphoric acid was replaced by malic acid to protect these meals (Medium Substitution Malic, MSM; CP= 16.7%). Wheat straw (roughage source) and concentrate were offered ad libitum. Eighteen lambs were allocated to six pens of three animals on each diet. Data were analyzed using a factorial analysis with initial body weight BW as covariate and farm of origin as block. Data on concentrate intake and feed conversion efficiency were analyzed using pen as experimental unit, while data on average daily gain, carcass yield, dorsal fat, and kidney-pelvic-fat were analyzed with lamb as experimental unit. No effect associated with the CP level was observed on any parameter. This suggests that with protected proteins it is possible to feed concentrates with 15.6% CP (dry matter basis) reducing the quantity of vegetable protein meals to include in the concentrate as well as the quality of the protein concentrates. Lambs feed MSM had higher average daily gains (15.2%; P= 0.042), and better hot carcass yields (1.3 percentage points; P= 0.037) than lambs feed MSP. This probably can be explained by ruminal malate actions and by greater protection effects obtained with malic acid.

Mathematical modeling of drying process of unripe banana slices

Unripe banana flour (UBF) production employs bananas not submitted to maturation process, is an interesting alternative to minimize the fruit loss reduction related to inappropriate handling or fast ripening. The UBF is considered as a functional ingredient improving glycemic and plasma insulin levels in blood, have also shown efficacy on the control of satiety, insulin resistance. The aim of this work was to study the drying process of unripe banana slabs (Musa cavendishii, Nanicão) developing a transient drying model through mathematical modeling with simultaneous moisture and heat transfer. The raw material characterization was performed and afterwards the drying process was conducted at 40 ºC, 50 ºC e 60 ºC, the product temperature was recorded using thermocouples, the air velocity inside the chamber was 4 m·s-1. With the experimental data was possible to validate the diffusion model based on the Fick\'s second law and Fourier. For this purpose, the sorption isotherms were measured and fitted to the GAB model estimating the equilibrium moisture content (Xe), 1.76 [g H2O/100g d.b.] at 60 ºC and 10 % of relative humidity (RH), the thermophysical properties (k, Cp, ?) were also measured to be used in the model. Five cases were contemplated: i) Constant thermophysical properties; ii) Variable properties; iii) Mass (hm), heat transfer (h) coefficient and effective diffusivity (De) estimation 134 W·m-2·K-1, 4.91x10-5 m-2·s-1 and 3.278?10-10 m·s-2 at 60 ºC, respectively; iv) Variable De, it presented a third order polynomial behavior as function of moisture content; v) The shrinkage had an effect on the mathematical model, especially in the 3 first hours of process, the thickness experienced a contraction of about (30.34 ± 1.29) % out of the initial thickness, finding two decreasing drying rate periods (DDR I and DDR II), 3.28x10-10 m·s-2 and 1.77x10-10 m·s-2, respectively. COMSOL Multiphysics simulations were possible to perform through the heat and mass transfer coefficient estimated by the mathematical modeling.

An investigation of the relationship of hot-hardness to the elevated temperature extrusion behavior of selected arc-cast molybdenum base alloys.

"Project no. 7351."

Optimization of co-current spray drying process of sugar-rich foods. Part I - Moisture and glass transition temperature profile during drying

A steady state mathematical model for co-current spray drying was developed for sugar-rich foods with the application of the glass transition temperature concept. Maltodextrin-sucrose solution was used as a sugar-rich food model. The model included mass, heat and momentum balances for a single droplet drying as well as temperature and humidity profile of the drying medium. A log-normal volume distribution of the droplets was generated at the exit of the rotary atomizer. This generation created a certain number of bins to form a system of non-linear first-order differential equations as a function of the axial distance of the drying chamber. The model was used to calculate the changes of droplet diameter, density, temperature, moisture content and velocity in association with the change of air properties along the axial distance. The difference between the outlet air temperature and the glass transition temperature of the final products (AT) was considered as an indicator of stickiness of the particles in spray drying process. The calculated and experimental AT values were close, indicating successful validation of the model. (c) 2004 Elsevier Ltd. All rights reserved.

Effect of harvest time and drying on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was grown under field conditions in South-East Queensland to study the effects of harvest time and drying conditions on seed quality. Cobs were harvested at different times to obtain seed with two moisture percentage ranges (20-30% and 40-50%) and dried to 12% moisture under different combinations of drying temperatures (30 degrees C, 40 degrees C and 50 degrees C) and air velocities (1.25 m/s, 2.75 m/s and 4.30 m/s). Dried seed was stored at 30 degrees C with bimonthly monitoring of seed quality for 12 months. For standard as well as cold test germinations, statistical analysis yielded significant main effects for temperature, air velocity and harvest moisture content and significant interactions for drying temperature by harvest moisture and drying temperature by air velocity. Germination at the beginning of storage was unaffected by drying temperatures up to 40 degrees C regardless of harvest moisture but was lower at 50 degrees C for higher moisture. However, germination at the end of the storage period of 12 months was greatest for seed harvested at higher moisture and dried at temperatures up to 40 degrees C. Germination was not affected by air velocity for drying temperatures up to 40 degrees C but at 50 degrees C it generally decreased with increase in air velocity. To slow down seed deterioration during storage, it is recommended that sweet corn seed should be harvested at a higher moisture range (40-50%) and dried at 40 degrees C and 4.30 m/s air velocity. The drying temperature can be raised to 50 degrees C for seed harvested at a low moisture range (20-30%) provided the air velocity is kept low (1.25 m/s).

Life Cycle Assessment (LCA) Applied to the Design of an Innovative Drying Process for Sewage Sludge

Most adverse environmental impacts result from design decisions made long before manufacturing or usage. In order to prevent this situation, several authors have proposed the application of life cycle assessment (LCA) at the very first phases of the design of a process, a product or a service. The study in this paper presents an innovative thermal drying process for sewage sludge called fry-drying, in which dewatered sludge is directly contacted in the dryer with hot recycled cooking oils (RCO) as the heat medium. Considering the practical difficulties for the disposal of these two wastes, fry-drying presents a potentially convenient method for their combined elimination by incineration of the final fry-dried sludge. An analytical comparison between a conventional drying process and the new proposed fry-drying process is reported, with reference to some environmental impact categories. The results of this study, applied at the earliest stages of the design of the process, assist evaluation of the feasibility of such system compared to a current disposal process for the drying and incineration of sewage sludge.

Heat and mass transfer during fry-drying of sewage sludge

Deep-frying, which consists of immersing a wet material in a large volume of hot oil, presents a process easily adaptable to dry rather than cook materials. A suitable material for drying is sewage sludge, which may be dried using recycled cooking oils (RCO) as frying oil. One advantage is that this prepares both materials for convenient disposal by incineration. This study examines fry-drying of municipal sewage sludge using recycled cooking oil. The transport processes occurring during fry-drying were monitored through sample weight, temperature, and image analysis. Due to the thicker and wetter samples than the common fried foods, high residual moisture is observed in the sludge when the boiling front has reached the geometric center of the sample, suggesting that the operation is heat transfer controlled only during the first half of the process followed by the addition of other mechanisms that allow complete drying of the sample. A series of mechanisms comprising four stages (i.e., initial heating accompanied by a surface boiling onset, film vapor regime, transitional nucleate boiling, and bound water removal) is proposed. In order to study the effect of the operating conditions on the fry-drying kinetics, different oil temperatures (from 120 to 180 degrees C), diameter (D = 15 to 25 mm), and initial moisture content of the sample (4.8 and 5.6 kg water(.)kg(-1) total dry solids) were investigated.

Effect of drying conditions on pyrethrins content

Windrowed pyrethrum stems were air dried under a range of storage conditions to examine whether the current commercial practice of drying crop material is conducive to pyrethrins' degradation. Crop material was stored for up to 12 days in a commercial windrow, a shed receiving indirect light or a dark, 5 degrees C cool-room. Analysis of pyrethrins extracted from flowers of all treatments demonstrated that pyrethrins were not degrading in windrowed crops, plant material stored in the shed or in the 5 degrees C cool-room. The small differences obtained in pyrethrins content among the treatments can be explained by the natural variation in pyrethrins content of pyrethrum crops. The observation that the achenes were unchanged during this drying period supported the pyrethrins analysis. These results demonstrate that pyrethrins in planta do not degrade as rapidly as extracted pyrethrins. (C) 2005 Elsevier B.V. All rights reserved.

Factors affecting hot spot development in bulk coal and associated gas evolution

There are many physical factors that can affect the self-heating rate of coal. The presence of seam gas has often been referred to as inhibiting coal self-heating due to the limited access of oxidation sites created by the presence of the gas adsorbed on the coal pores. Similarly, the presence of bed moisture in the coal also acts as an inhibitor of oxidation by blocking access of air into the pores. Gas drainage of a coal seam prior to mining removes both gas and moisture from the seam. Bulk coal self-heating tests in a two-metre column on both gassy, as-mined and gas-drained, dried high volatile bituminous coal show that removal of gas and moisture from the coal accelerates the rate of self-heating to thermal runaway from 8.5 days to 4.25 days, from a start temperature of 30°C, with an airflow of 0.25 L/min. The corresponding gas evolution pattern for each of these situations is different. Therefore, it is necessary to take this change in coal condition into consideration when developing a spontaneous combustion management plan.

Mechanisms of convective drying in thick beds of solids

The literature on heat and mass transfer mechanisms in the convective drying of thick beds of solids has been critically reviewed. Related mathematical models of heat transfer are also considered. Experimental and theoretical studies were made of the temperature distribution within beds, and of drying rates, with various materials undergoing convective drying. The experimental work covered thick beds of hygroscopic and non-hygroscopic materials (glass beads of different diameters, polystyrene pellets, activated alumina and wood powder) at air temperatures of 54°C to 84°C. Tests were carried out in a laboratory drying apparatus comprising a wind tunnel through which the air, of controlled temperature and humidity, was passed over a sample suspended from a balance. Thermocouples were inserted at different depths within the sample bed. The temperature distribution profiles for both hygroscopic and non-hygroscopic beds exhibited a clear difference between the temperatures at the surface and bottom during the constant rate period. An effective method was introduced for predicting the critical moisture content. During the falling rate the profiles showed the existence of a receding evaporation plane; this divided the system into a hotter dry zone in the upper section and a wet zone near the bottom. A graphical procedure was established to predict accurately the position of the receding evaporation front at any time. A new mathematical model, based on the receding evaporation front phenomenon, was proposed to predict temperature distributions throughout a bed during drying. Good agreement was obtained when the model was validated by comparing its predictions with experimental data. The model was also able to predict the duration of each drying stage. In experiments using sample trays of different diameters, the drying rate was found to increase with a decrease in the effective length of the bed surface. During the constant rate period with trays of a small effective length, i.e. less than 0.08 m, an 'inversion' in temperature distribution occurred in the bed; the bottom temperature increased and became greater than that of the surface. Experimental measurements were verified in several ways to ensure this phenomenon was real. Theoretical explanations are given for both the effective length and temperature inversion phenomena.

The Single drop drying of heat-sensitive materials

The literature relating to the principles and practice of drying of materials, particularly those susceptible to thermal degradation or undesirable loss of volatile components, has been reviewed. Single droplets of heat-sensitive materials were dried whilst suspended in a horizontal wind tunnel from a specially-designed, rotating thermocouple which enabled direct observation of drying behaviour and continuous measurement of droplet temperature as drying progressed. The effects of drying air temperature and initial solids concentration on the potency of various antibiotics, viz. ampicillin, chloramphenicol, oxytetracycline, streptomycin and tetracycline, were assessed using a modified Drug Sensitivity Testing technique. Only ampicillin was heat-sensitive at temperatures above 100°C, e.g. at an air temperature of 115°C its zone diameter was reduced from 100% to 45%. Selected enzymes, viz. dextran sucrase and invertase, were also dried and their residual activities determined by High Performance Liquid Chromatography. The residual activity of dextran sucrase was rapidly reduced at temperatures above 65°C, and the residual activity of invertase reduced rapidly at temperatures above 65°C; but drying with short residence times will retain most of its activity. The performance of various skin-forming encapsulants, viz. rice and wheat starch, dextrin, coffee, skim milk, fructose, gelatine 60 and 150 Bloom, and gum arabic, was evaluated to determine their capabilities for retention of ethanol as a model volatile, under different operating conditions. The effects of initial solids concentration, air velocity and temperature were monitored for each material tested. Ethanol content was analysed by Gas Liquid Chromatography and in some cases dried crusts were removed for examination. Volatiles retention was concluded to depend in all cases upon the rate and nature of the skin formation and selective diffusion phenomena. The results provided further insight into the inter-relationship between temperature, residence time and thermal degradation of heat-sensitive materials. They should also assist in selection of the preferred dryer for such materials, and of the operating parameter to enable maximum retention of the required physico-chemical characteristics in the dried materials.

Spray drier simulation and air flow pattern studies

The literature pertaining to the key stages of spray drying has been reviewed in the context of the mathematical modelling of drier performance. A critical review is also presented of previous spray drying models. A new mathematical model has been developed for prediction of spray drier performance. This is applicable to slurries of rigid, porous crust-forming materials to predict trajectories and drying profiles for droplets with a distribution of sizes sprayed from a centrifugal pressure nozzle. The model has been validated by comparing model predictions to experimental data from a pilot-scale counter-current drier and from a full-scale co-current drier. For the latter, the computed product moisture content was within 2%, and the computed air exit temperature within 10oC of experimental data. Air flow patterns have been investigated in a 1.2m diameter transparent countercurrent spray tower by flow visualisation. Smoke was introduced into various zones within the tower to trace the direction, and gauge the intensity, of the air flow. By means of a set of variable-angle air inlet nozzles, a variety of air entry configurations was investigated. The existence of a core of high rotational and axial velocity channelling up the axis of the tower was confirmed. The stability of flow within the core was found to be strongly dependent upon the air entry arrangement. A probe was developed for the measurement of air temperature and humidity profiles. This was employed for studying evaporation of pure water drops in a 1.2m diameter pilot-scale counter-current drier. A rapid approach to the exit air properties was detected within a 1m distance from the air entry ports. Measured radial profiles were found to be virtually flat but, from the axial profiles, the existence of plug-flow, well-mixed-flow and some degree of air short-circuiting can be inferred. The model and conclusions should assist in the improved design and optimum operation of industrial spray driers.

Mass transfer coefficient for drying of moist particulate in a bubbling fluidized bed

Experiments on drying of moist particles by ambient air were carried out to measure the mass transfer coefficient in a bubbling fluidized bed. Fine glass beads of mean diameter 125?µm were used as the bed material. Throughout the drying process, the dynamic material distribution was recorded by electrical capacitance tomography (ECT) and the exit air condition was recorded by a temperature/humidity probe. The ECT data were used to obtain qualitative and quantitative information on the bubble characteristics. The exit air moisture content was used to determine the water content in the bed. The measured overall mass transfer coefficient was in the range of 0.0145–0.021?m/s. A simple model based on the available correlations for bubble-cloud and cloud-dense interchange (two-region model) was used to predict the overall mass transfer coefficient. Comparison between the measured and predicted mass transfer coefficient have shown reasonable agreement. The results were also used to determine the relative importance of the two transfer regions.