Constant Thermal Conditions Research Articles

Numerical Evaluation on Lower Temperature Operation of Blast Furnaces by Charging Carbon Composite Agglomerates

This paper places emphasis on evaluating ironmaking operation at lower temperature. Blast furnace operation with carbon composite agglomerates (CCB) charging and/or lower operation temperature has been numerically examined using a modified multi‐fluid blast furnace model under constant thermal conditions of the raceway. The numerical calculation shows that a lower in‐furnace temperature level is achieved under the operation with the CCB charging. With CCB charging, the location of the cohesive zone shifts downward and the temperature of the thermal reserve zone decreases. The decrease in heat requirements for solution loss, sinter reduction and silicon transfer reactions compensates the increase in heat demands for CCB reduction and direct reduction, and rather improves the efficiency of blast furnaces. Consequently, the productivity improves, the coke rate shows a notable decrease and the total reducing agent rate also tends to decline compared with conventional operation without CCB charging. Therefore, charging carbon composite agglomerates contributes to the enhancement of blast furnace performance. Furthermore, the model predicts that higher operation efficiency is achieved if the melting and/or tapping temperature could be dropped. The innovative technology of lower temperature ironmaking is expected to be applied in industrial blast furnaces after resolving the problems in engineering and economic evaluations.

Circadian rhythms in electric waveform structure and rate in the electric fish Brachyhypopomus pinnicaudatus

Weakly electric fish have long been known to express day–night oscillations in their discharge rates, and in the amplitude and duration of individual electric organ discharges (EODs). Because these oscillations are altered by social environment and neuroendocrine interactions, electric fish are excellent organisms for exploring the social and neuroendocrine regulation of circadian rhythm expression. Previous studies asserting that these oscillations are circadian rhythms have been criticized for failing to control temperature and randomize feeding regimes, or for running the fish under constant conditions for just 2–3 days. Here we show that the day–night oscillations in the EODs of the neotropical gymnotiform fish Brachyhypopomus pinnicaudatus free-run for over a week under constant photic and thermal conditions, and randomized food provisioning. Sex differences were apparent in strength and magnitude of the circadian oscillations; male oscillations were stronger and larger. All three parameters retain a common oscillation period while differing in the persistence of oscillation strength and magnitude, a difference consistent with proposals by others that declines of behavioral circadian rhythms may result from breakdowns downstream of the central oscillator.

Fluidized bed spray granulation: analysis of heat and mass transfers and dynamic particle populations

Abstract - A model was developed taking into consideration the heat and mass transfer processes in liquid-sprayed fluidized beds. Such fluidized beds (FB) are used for granulation, coating and agglomeration. Conclusions are drawn on the relevance of particle dispersion, spraying and drying to temperature and concentrations distributions. In extension, the model was coupled with a population balance model to describe the particle size distribution and the seeds formation for continuous external FBSG (fluidized bed spray granulation) with non-classifying product discharge and a screening and milling unit in the seeds recycle. The effects of seeds formation on the stability of the process is discussed. Keywords : Fluidized bed; Granulation; Population balance. INTRODUCTION The FBSG is a process used for the production of granular high-quality, free-flowing, low-dust and low-attrition solids originating from liquid products, e. g. solutions, suspensions, melts and emulsions. The advantage is the coupling of the wetting, drying, particle enlarging, shaping, homogenisation and separation processes and the the production in a single processing step (Uhlemann and Morl, 1999). Especially for large production units a continuous operation of the FBSG is desirable. The continuous granulation process presents, unlike to the batch-operation, the advantage to operate the plant under stationary condition at high throughputs. The stationary operation point is reached, provided constant granulate spectrum beside constant mass flows and constant thermal conditions, whereby initially fed granulates have to be removed at all. Sometimes this unsteady phase lasting up to a few hours. The aim of the following examinations is to study the stability behaviour of the FB by using of a one-dimensional population balance which is coupled with the heat and mass transfers in such liquid sprayed gas-solid fluidized beds to calculate the time dependent particle size distributions of the fluidized bed and of the product particles and the temperature and humidity progressions. Depending on the seeds formation mechanisms– overspray (non deposited dried drops), attrition, separation – a narrow or wide particle size distribution is obtained. Additionally, this work also introduces a mathematical model for the spatial temperature and humidity distributions, which are evaluated by measurements of the stationary spatial air temperatures at a semi-industrial fluidized bed pilot plant of the institute.

Influence of powder supply on radio-frequency power stability and compositional uniformity in near-stoichiometric LiTaO 3 crystal grown by double-crucible Czochralski method

Near-stoichiometric LiTaO 3 (SLT) crystals were grown from a Li-rich solution by the double-crucible Czochralski (DCCZ) method with and without an automatic powder supply system, to investigate influence of the powder supply system on the stability of radio-frequency (RF) power and the compositional uniformity of the grown crystal. To maintain a constant crystal diameter, the RF power is decreased during crystal growth without the powder supply system, while it is kept almost constant during crystal growth with the powder supply system. The Curie temperature of an SLT crystal grown with the powder supply system was almost constant along both growth and lateral directions, and the [Li]/([Li]+[Ta]) ratio in this crystal was estimated to be 0.4992 by comparing its Curie temperature with those of ceramics of known composition. In contrast, in an SLT crystal grown without the powder supply system, the Curie temperature was observed to increase with increase in distance from the top of the crystal; therefore, the crystal composition was thought to gradually change due to the change of solution composition during crystal growth. In SLT crystal growth, the DCCZ method using the automatic powder supply system provided an almost constant thermal condition during crystal growth as well as compositional uniformity throughout the SLT crystal.

AN INSTRUMENTATION SYSTEM FOR STUDYING FEEDING AND DRINKING BEHAVIOR OF INDIVIDUAL POULTRY

This article describes an instrumentation system that was developed to study the dynamic feeding and drinking behavior of individual birds. The system, consisting of 24 feeding and drinking stations interfaced via an RS 485 communication network to a central PC, provides continuous recording of feeding and drinking events. Each feeding/drinking station includes a precision electronic balance (1210–g capacity and 0.1–g resolution) for the feeder and a temperature–controlled drinking water reservoir (1500–mL capacity and 1000– to 1500–mL operating range) whose height and thus volume was sensed with a differential pressure transducer (0 – 2.5 VDC output). The system was tested using growing broiler chickens subjected to constant or cyclic thermal conditions. Sample data are presented to demonstrate how researchers can use the system to examine and understand the effects of environmental modification on feeding and drinking behavior of individual birds. A series of subsequent studies have been planned that will use the system to investigate the interactive effects of environmental and dietary nutrition manipulations on ingestion behavior and poultry performance.total P.

Influence of Water-Soluble Nonionic Emulsifier on the Rheology of Heat-Set Protein-Stabilized Emulsion Gels

The influence of nonionic emulsifier Tween 20 [polyoxyethylene (20) sorbitan monolaurate] on the small-deformation shear rheological behavior of β-lactoglobulin emulsion gels has been investigated. Measurements are reported for heat-set oil-in-water emulsion gels (5-10 wt % protein, 38 wt % oil, pH 7) containing surfactant added after homogenization but prior to heat treatment (30 min at 90 °C). Storage and loss moduli (frequency 1 Hz) and protein surface coverages of emulsion gels containing 6, 7, and 8 wt % protein have been determined at 30 °C. Comparison with results from the equivalent rheological experiments on pure β-lactoglobulin systems (12-14 wt %, pH 7) shows that the incorporation of fine emulsion droplets greatly reduces the overall concentration of protein required to make a self-supporting gel. For constant oil content and thermal gelation conditions, the emulsion gel strength is very sensitive to protein content and surfactant/protein molar ratio R. In particular, the storage modulus has been shown to increase at low emulsifier contents (R 1), to decrease at intermediate emulsifier contents (R 2), and then at high emulsifier contents (R ≥ 4) either to increase again or to remain low depending on the protein content. This behavior can be explained in terms of the effect of system composition on the balance between the different kinds of interfacial and bulk protein-surfactant interactions.

Effects of growth conditions on thermal profiles during Czochralski silicon crystal growth

An eddy current testing method was used to continuously monitor crystal growth process and investigate the effects of growth conditions on thermal profiles during Czochralski silicon crystal growth. The experimental concept was to monitor the intrinsic electrical conductivities of the growing crystal and deduce temperature values from them. In terms of the experiments, the effects of changes in growth parameters, which include the crystal and crucible rotation rates, crucible position, and pull rate, and hot-zone geometries were investigated. The results show that the crystal thermal profile could shift significantly as a function of crystal length if the closed-loop control fails to maintain a constant thermal condition. As a direct evidence to the effects of the melt flow on heat transfer processes, a thermal gradient minimum was observed when the crystal/crucible rotation combination was 20/-10 rpm cw. The thermal gradients in the crystal near the growth interface were reduced most by decreasing the pull rate or by reducing the radiant heat loss to the environment; a nearly constant axial thermal gradient was achieved when either the pull rate was decreased by half, the height of the exposed crucible wall was doubled, or a radiation shield was placed around the crystal. Under these conditions, the average axial thermal gradient along the surface of the crystal was about 4–5°C/mm. When compared to theoretical results found in literature, the axial profiles correlated well with the results of the models which included radiant interactions. However, the radial gradients estimated from three-frequency data were much higher than what were predicted by known theoretical models. This discrepancy seems to indicate that optical phenomenon within the crystal is significant and should be included in theoretical modeling.

Długość czasu budzenia się z hibernacji trzech gatunków nietoperzy

The time of awakening from winter sleep has been studied in three species of bats: Rhinolophus hipposideros, Myotis myotis and Plecotus auritus under natural conditions. Seasonal changes in the time of awakening have been found in bats R. hipposideros wintering in constant thermal conditions. In autumn (October) and in spring (April) the time was shorter than that observed in the middle of the winter sleep (January).

Physiological adaptation ofMytilus edulis to cyclic temperatures

Mytilus edulis adapted to cyclic temperatures by reducing the amplitude of response of oxygen consumption and filtration rate over a period of approximately two weeks, and thereby increasing their independence of temperature within the range of the fluctuating regime. When acclimated to cyclic temperature regimes within the range from 6 to 20°C, the metabolic and feeding rates, measured at different temperatures in the cycle, were not significantly different from the adapted response to equivalent constant temperatures. Physiological adaptation ofMytilus edulis to different thermal environments was reflected in their metabolic and feeding rate-temperature curves. Animals subjected to marked diel fluctuations in environmental temperature showed an appropriate region of temperature-independence, whereas animals from a population not experiencing large diel temperature fluctuations showed no region of temperature-independence. In a fluctuating thermal environment which extended above the normal environmental maxima, respiratory adaptation occurred at higher temperatures than was possible in a constant thermal environment. The feeding rate was also maintained at higher temperatures in a cyclic regime than was possible under constant thermal conditions. This represented a shortterm extension of the zone of activity in a fluctuating thermal environment. The net result of these physiological responses to high cyclic and constant temperatures has been assessed in terms of ‘scope for growth’. Animals acclimated to cyclic temperatures between 21 and 29°C had a higher scope for growth at 29°C and were less severely stressed than those maintained at the constant temperature of 29°C.