Thermalhydraulic behavior of electrically heated rod during a critical heat flux transient

In nuclear reactors, the occurrence of critical heat flux leads to fuel rod overheating with clad fusion and radioactive products leakage. To predict the effects of such phenomenon, experiments are performed using electrically heated rods to simulate operational and accidental conditions of nuclear fuel rods. In the present work, it is performed a theoretical analysis of the drying and rewetting front propagation during a critical heat flux experiment, starting with the application of an electrical power step from steady state condition. After the occurrence of critical heat flux, the drying front propagation is predicted. After a few seconds, a power cut is considered and the rewetting front behavior is analytically observed. Studies performed with various values of coolant mass flow rate show that this variable has more influence on the drying front velocity than on the rewetting one.

Inverse convection problem of simultaneous estimation of two boundary heat fluxes in parallel plate channels

This paper deals with the use of the conjugate gradient method of function estimation for the simultaneous identification of two unknown boundary heat fluxes in parallel plate channels. The fluid flow is assumed to be laminar and hydrodynamically developed. Temperature measurements taken inside the channel are used in the inverse analysis. The accuracy of the present solution approach is examined by using simulated measurements containing random errors, for strict cases involving functional forms with discontinuities and sharp-corners for the unknown functions. Three different types of inverse problems are addressed in the paper, involving the estimation of: (i) Spatially dependent heat fluxes; (ii) Time-dependent heat fluxes; and (iii) Time and spatially dependent heat fluxes.

Heat Source Estimation with the Conjugate Gradient Method in Inverse Linear Diffusive Problems

In this work, we present the solution of a class of linear inverse heat conduction problems for the estimation of unknown heat source terms, with no prior information of the functional forms of timewise and spatial dependence of the source strength, using the conjugate gradient method with an adjoint problem. After describing the mathematical formulation of a general direct problem and the procedure for the solution of the inverse problem, we show applications to three transient heat transfer problems: a one-dimensional cylindrical problem; a two-dimensional cylindrical problem; and a one-dimensional problem with two plates.

Simulation of Steady-State Nonlinear Heat Transfer Problems Through the Minimization of Quadratic Functionals

In this work it is presented a systematic procedure for constructing the solution of a large class of nonlinear conduction heat transfer problems through the minimization of quadratic functionals like the ones usually employed for linear descriptions. The proposed procedure gives rise to an efficient and easy way for carrying out numerical simulations of nonlinear heat transfer problems by means of finite elements. To illustrate the procedure a particular problem is simulated by means of a finite element approximation.

Effects of condensation in microchannels with a porous boundary: analytical investigation on heat transfer and meniscus shape

In two-phase miniature and microchannel flows, the meniscus shape must be considered due to effects that are affected by condensation and/or evaporation and coupled with the transport phenomena in the thin film on the microchannel wall, when capillary forces drive the working fluid. This investigation presents an analytical model for microchannel condensers with a porous boundary, where capillary forces pump the fluid. Methanol was selected as the working fluid. Very low liquid Reynolds numbers were obtained (Re~6), but very high Nusselt numbers (Nu~150) could be found due to the channel size (1.5 mm) and the presence of the porous boundary. The meniscus calculation provided consistent results for the vapor interface temperature and pressure, as well as the meniscus curvature. The obtained results show that microchannel condensers with a porous boundary can be used for heat dissipation with reduced heat transfer area and very high heat dissipation capabilities.

Some biological aspects of the weed Lesser celandine (Ranunculus ficaria)

Lesser celandine (Ranunculaceae) is a perennial weed with tuberous root. Tubers are the most important means of reproduction and dispersion of this weed. In recent years, it has spread into wheat fields in Western Iran, mainly in the Lorestan province. A series of experiments were conducted to determine cardinal temperatures and to study the effects of pre-chilling, temperature fluctuations, tuber size, freezing and drying on germination of the tubers, as well as the effect of planting depth on sprouting of the tubers. The results obtained showed that the highest percentage of germination occurred when tubers were stored for more than 2 weeks at 4 or 8 ºC. The optimum temperature for germination differed in large and small tubers (8 and 14oC, respectively). Germination was the highest (almost 100%) at temperature fluctuations of 5-10oC. Germination of the finger-like and small tubers was the highest (95%); however, very small, small, and broken tubers showed the lowest germination percentage. In the freezing experiment, decreasing the temperature and increasing the storage duration decreased the germination of tubers. Increasing the osmotic potential and temperature resulted in decreased tuber germination of Lesser celandine. Lesser celandine could sprout down to 20 cm depth but heat demand for tubers from superficial depth was smaller than for tubers planted at greater depth.

Reserve substances and storage of Cyathea delgadii Sternb. spores

The spores used were collected from a population of trees of Cyathea delgadii Sternb. growing in a gallery forest at the Reserva Biológica e Estação Experimental de Moji Guaçu, São Paulo state, Brazil (22°18’S and 47°11’W). The germination of spores of Cyathea delgadii decreases with time when kept in closed bottles under storage at 4°C in darkness. Germination is still very high after storage for one year. Spores stored for three years do not germinate. The results also show a decrease in soluble proteins and an increase in starch after several months storage.

Light and storage on the germination of spores of Dicksonia sellowiana (Presl.) Hook., Dicksoniaceae

Spores of Dicksonia sellowiana are positively photoblastic and reach the maximum percentage of germination at 23 ± 2°C in white light after seven days of imbibition. The pre-induction phase for spores induced by white or red light for 24 hours was 72 hours. Gametophytes grown in white light were plane and bidimensional, while those grown under red light were filamentous. The higher the number of hours of light applied per day during 10 days, the higher the percentage of germination. Germination was higher for long white light treatments applied on a daily basis. The effect of different light intensities on germination was also investigated here. The lower percentages of germination were observed for spores kept under 43% and 2% of full sunlight, while those kept under 26, 19 and 4% presented higher percentages. Spores presented circa 82% of germination after 731 days of storage under refrigeration at aproximately 10°C.

Effect of storage of achenes of Bidens gardneri Baker on light sensitivity during germination

Bidens gardneri is a very common herbaceous species in the cerrados of the state of São Paulo, whose seeds become light sensitive at 25°C only. Achenes of this species were stored in refrigerator at 4°C and in cerrado soil and in forest soil. The field experiments were carried out in the cerrado at the Reserva Biológica e Estação Experimental de Moji Guaçu, in Moji Guaçu and in the forest of the Instituto de Botânica, in São Paulo, Brazil. Achenes of B. gardneri vary in size and achenes from 7 to 12 mm long were used. Achenes stored for up to 6 months at 4°C showed light sensitivity; after 9 months storage, the difference in germination between light and darkness had disappeared for the smallest and the largest achenes used. Seeds of B. gardneri germinated during the period of storage in soil; the number of germinated seeds increased over the storage time, while the number of intact achenes decreased for the same period, no matter if the experiment was being carried out in the cerrado or in the forest. Therefore, the achenes germinated in soil in darkness. Light sensitivity was lost in intact achenes that had been stored in soil for three months.

Storage substances in the androgametogenesis and mature pollen grain of Ilex paraguariensis St. Hil. (Aquifoliaceae)

Storage substances such as starch grains, proteins and lipids were studied during the male gametogenesis and in the mature pollen grain of Ilex paraguariensis St. Hil. (Aquifoliaceae). There are two cycles of amylogenesis and amylolyse. The first cycle lasts until the vacuolated stage when the starch is hydrolyzed and amorphous proteins are stored inside the single vacuole. The next cycle begins after mitosis with the formation of the vegetative and generative cells. At this point, the young vegetative cell stores many starch grains that are bigger than in the first cycle. During the maturation of the male gametophyte, the starch is hydrolyzed and it is absent in the mature pollen grain. Small lipid droplets surround the young generative cell after the mitosis of the androspore and are dispersed in the vegetative cytoplasm during its maturity. The relationship between the pollen storage substances and the ontogeny of the layers in the sporoderm, formation of the generative cell, and the male germ unit were discussed.

Occurrence of xyloglucan containing protuberances in the storage cell walls of cotyledons of Hymenaea courbaril L.

Despite the suggestions of its pectic composition, no clear evidence for this has been presented. Here we show the occurrence of such a structure in walls of cells from cotyledons of Hymenaea courbariI L. These cells are known to accumulate large amounts of storage xyloglucan in the wall and, in this case, the protuberances seem to contain this storage polysaccharide rather than pectin. A hypothetical sequence of events leading from wall strands to protuberances was assembled based on scanning electron microscopy observations. On this basis, a tentative model for how polysaccharides are distributed into the wall, near the regions where protuberances are found, is proposed to explain the presence of storage xyloglucan in their composition.

Effects of moisture content and temperature during storage on germination of the achenes of Bidens gardneri Baker

Bidens gardneri is a herbaceous species of the cerrados, whose seeds are light sensitive at 25 °C, but they become indifferent to light when stored in soil. In this work the effects of moisture content, temperature and light (during storage) upon light sensitivity during germination were studied. Ripe achenes were collected in the cerrados of Itirapina and Moji Guaçu, State of São Paulo, Brazil. The storage conditions of the achenes varied in each experiment. Achenes were stored in darkness or light, in closed bottles, at 4 °C, 20/30 °C or 25 °C. Achenes were imbibed for 24 h at 4 °C, 25 °C or 20/30 °C (in darkness) and then stored for 1, 10, 20, 30 and 40 days (40 days only for 4 °C and 25 °C). Germination tests were conducted at 25 °C and 20/30 °C. The achenes not previously imbibed showed sensitivity to light during germination. High moisture content did not affect light sensitivity of the achenes during germination but high moisture content together with storage temperatures of 25 °C and 20/30 °C had a deleterious effect upon the longevity of the achenes. Alternate temperatures during germination did not change the light sensitivity of newly collected achenes from Itirapina but changed the light sensitivity of the achenes stored imbibed at 4 °C in darkness. Alternate temperatures during storage of achenes with low moisture content did not change their photoblastism when germination was carried out at 25 °C. Alternate temperatures during storage of achenes with high moisture content followed by alternate temperatures during germination changed the light sensitivity of the achenes.

Germination of spores and growth of gametophytes and sporophytes of Rumohra adiantiformis (Forst.) Ching (Dryopteridaceae) after spore cryogenic storage

Rumohra adiantiformis (Forst.) Ching is a fern (Dryopteridaceae) used in floral arrangements. Spores sterilized in 15% (v/v) solution of commercial sodium hypochlorite for 10 minutes and unsterilized spores were plunged in liquid nitrogen and held for 15 minutes and for 90 days. After the cryogenic treatments, spores were taken out of liquid nitrogen and rapidly thawed out in a water bath or slowly at room temperature and were cultured in Mohr's mineral solution as modified by Dyer, kept at 25 ± 2 ºC and a 16-hours photoperiod. Statistical differences were not observed in the germination of unsterilized spores immersed or not immersed in liquid nitrogen, but when the spores were previously sterilized, a severe inhibition of germination was observed in cryopreserved spores. Faster mean germination time was observed for unsterilized spores cryopreserved in liquid nitrogen for 15 minutes. The germination of spores stored in liquid nitrogen for 90 days reached the maximum percentage after 12 days, while control spores reached their maximum percentage after 16 days. Levels of soluble sugars did not vary among treatments in gametophytes cultivated for 10 weeks after spore inoculation. The number of fronds and the length of the longest frond on sporophytes did not differ statistically among treatments. The relative growth rate of sporophytes grown from cryopreserved and control spores were not statistically different among treatments. Spores of R. adiantiformis immersed in liquid nitrogen for 15 minutes apparently produced phenotypically normal plants.

Diurnal changes in storage carbohydrate metabolism in cotyledons of the tropical tree Hymenaea courbaril L. (Leguminosae)

The cotyledons of Hymenaea courbaril store large amounts of xyloglucan, a cell wall polysaccharide that is believed to serve as storage for the period of seedling establishment. During storage mobilisation, xyloglucan seems to be degraded by a continuous process that starts right after radicle protrusion and follows up to the establishment of photosynthesis. Here we show evidence that events related to the hydrolases activities and production (α-xylosidase, β-galactosidase, β-glucosidase and xyloglucan endo-β-transglucosilase) as well as auxin, showed changes that follow the diurnal cycle. The period of higher hydrolases activities was between 6pm and 6am, which is out of phase with photosynthesis. Among the enzymes, α-xilosidase seems to be more important than β-glucosidase and β-galactosidase in the xyloglucan disassembling mechanism. Likewise, the sugars related with sucrose metabolism followed the rhythm of the hydrolases, but starch levels were shown to be practically constant. A high level of auxin was observed during the night, what is compatible with the hypothesis that this hormone would be one of the regulators of the whole process. The probable biological meaning of the existence of such a complex control mechanism during storage mobilisation is likely to be related to a remarkably high level of efficiency of carbon usage by the growing seedling of Hymenaea courbaril, allowing the establishment of very vigorous seedlings in the tropical forest.

Effect of collection, transport, processing and storage of blood specimens on the activity of lysosomal enzymes in plasma and leukocytes

This study was designed to evaluate the effect of different conditions of collection, transport and storage on the quality of blood samples from normal individuals in terms of the activity of the enzymes ß-glucuronidase, total hexosaminidase, hexosaminidase A, arylsulfatase A and ß-galactosidase. The enzyme activities were not affected by the different materials used for collection (plastic syringes or vacuum glass tubes). In the evaluation of different heparin concentrations (10% heparin, 5% heparin, and heparinized syringe) in the syringes, it was observed that higher doses resulted in an increase of at least 1-fold in the activities of ß-galactosidase, total hexosaminidase and hexosaminidase A in leukocytes, and ß-glucuronidase in plasma. When the effects of time and means of transportation were studied, samples that had been kept at room temperature showed higher deterioration with time (72 and 96 h) before processing, and in this case it was impossible to isolate leukocytes from most samples. Comparison of heparin and acid citrate-dextrose (ACD) as anticoagulants revealed that ß-glucuronidase and hexosaminidase activities in plasma reached levels near the lower normal limits when ACD was used. In conclusion, we observed that heparin should be used as the preferable anticoagulant when measuring these lysosomal enzyme activities, and we recommend that, when transport time is more than 24 h, samples should be shipped by air in a styrofoam box containing wet ice.