COMPARAÇÃO DAS PROPRIEDADES REOLÓGICAS DA MASSA DE CACAU TORRADA CONVENCIONALMENTE E POR MICROONDAS

Two kinds of roasting cocoa system: conventional batch method in electrical oven, and by microwaves, in a continuous microwave rotary applicator (2450MHz), were compared with respect to viscosity. Cocoa was roasted in whole beans and in nibs. The variable used in the microwave treatment was the power density applied to the whole beans (254,45 to 290,80 Wh/kg) and to the nibs (227,27 to 262,23 Wh/kg), with a constant holding time of 10 minutes. The variable used in the conventional roasting process was the roasting time of the beans (40 to 44 min) and the nibs (34 to 38 min), with constant temperature in the jacket of electric oven (150°C). Viscosity was measured in a Brookfield rheometer (mod RV-DVIII) at 40°C. In general, the plastic viscosity of the microwaved samples was lower than that of the conventional roasted samples. Also the nibs showed lower viscosities than the whole beans when roasted in the electric oven. The viscosity of the samples roasted in the microwave oven was lower in the whole beans than in the nibs. The product was sensorially evaluated by three experts in cocoa flavour, and it was shown that the flavour of the microwave roasted products was similar to that of the conventionally roasted products, with the advantage of a reduction in process time.

FLOW PROPERTIES AND TUBE FRICTION FACTOR OF MILK CREAM: INFLUENCE OF TEMPERATURE AND FAT CONTENT

The rheological behavior of milk cream was studied for different fat contents (0.10 to 0.31) and for a wide temperature range (2 and 87C) using a rotational rheometer. Newtonian behavior was observed, except for fat content between 0.20 and 0.31 and temperature between 2 and 33C, where viscoplastic behavior was remarkable. The rheological parameters (Newtonian viscosity, plastic viscosity and yield stress) and density were well correlated to temperature and fat content. Tube friction factor during flow of cream was experimentally obtained at various flow rates, temperatures and tube diameters (86 < Re < 2.3 x 104, 38 < Re(B) < 8.8 x 103, 1.1 x 103 < He < 6.7 x 103). The proposed correlations for density and rheological parameters were applied for the prediction of friction factor for laminar and turbulent flow of cream using well-known equations for Newtonian and viscoplastic flow. The good agreement between experimental and predicted values confirms the reliability of the proposed correlations for describing the flow behavior of cream. PRACTICAL APPLICATIONS This paper presents correlations for the calculation of density and rheological parameters (Newtonian viscosity, Bingham plastic viscosity and yield stress) of milk cream as functions of temperature (2-87C) and fat content (0.10-0.31). Because of the large temperature range, the proposed correlations are useful for process design and optimization in dairy processing. An example of practical application is presented in the text, where the correlations were applied for the prediction of friction factor for laminar and turbulent tube flow of cream using well-known equations for Newtonian and viscoplastic flow, which are summarized in the text. The comparison with experimental data obtained at various flow rates, temperatures and tube diameters showed a good agreement, which confirms the reliability of the proposed correlations.

Development of an injectable grout for concrete repair and strengthening

This paper deals with the coupled effect of temperature and silica fume addition on rheological, mechanical behaviour and porosity of grouts based on CEMI 42.5R, proportioned with a polycarboxylate-based high range water reducer. Preliminary tests were conducted to focus on the grout best able to fill a fibrous network since the goal of this study was to develop an optimized grout able to be injected in a mat of steel fibers for concrete strengthening. The grout composition was developed based on criteria for fresh state and hardened state properties. For a CEMI 42.5R based grout different high range water reducer dosages (0%, 0.2%, 0.4%, 0.5%, 0.7%) and silica fume (SF) dosages (0%, 2%, 4%) were tested (as replacement of cement by mass). Rheological measurements were used to investigate the effect of polycarboxylates (PCEs) and SF dosage on grout properties, particularly its workability loss, as the mix was to be injected in a matrix of steel fibers for concrete jacketing. The workability behaviour was characterized by the rheological parameters yield stress and plastic viscosity (for different grout temperatures and resting times), as well as the procedures of mini slump cone and funnel flow time. Then, further development focused only on the best grout compositions. The cement substitution by 2% of SF exhibited the best overall behaviour and was considered as the most promising compared to the others compositions tested. Concerning the fresh state analysis, a significant workability loss was detected if grout temperature increased above 35 degrees C. Below this temperature the grout presented a self-levelling behaviour and a life time equal to 45 min. In the hardened state, silica fumes increased not only the grout's porosity but also the grout's compressive strength at later ages, since the pozzolanic contribution to the compressive strength does not occur until 28 d and beyond. (C) 2012 Elsevier Ltd. All rights reserved.

Study of the rheology of self-compacting concrete with fine recycled concrete aggregates

This work studies the effect of incorporating fine recycled aggregates on the rheology of self-compacting concrete over time (at 15,45 and 90 min). The fine fraction of the natural aggregates was replaced at 0%, 20%, 50% and 100% with recycled sand. The fresh-state properties were studied by empirical tests (slump-flow, J-Ring, L-Box) and fundamental ones in an ICAR rheometer. The mixes with 50% and 100% recycled sand lost their SCC characteristics at 90 min. Contrarily the mix with 20% replacement maintained suitable passing and filling ability. The causes of this trend were an initial increase of plastic viscosity and afterwards an increase of yield stress. The compressive strength of the 50% and 100% replacement mixes decreased significantly and that of the 20% replacement mix less than 10%. (C) 2015 Elsevier Ltd. All rights reserved.

Flows of Bingham Materials Through Ideal Porous Media: an Experimental and Theoretical Study

The flow of Bingham liquids through porous media has been studied. Experiments have been performed to determine the flow rate / pressure drop relationship for the flow of a grease of Binghamian rheological behavior through an array of rods of circular cross section. The yield stress and plastic viscosity of the grease have been determined with the aid of a controlled stress rotational rheometer. To investigate a wider range of the flow parameters, the mass and momentum conservation equations have been solved numerically, in conjunction with the generalized Newtonian constitutive law and the bi-viscosity model. The finite volume method has been employed to obtain the numerical solution. These numerical results also yielded a flow rate / pressure drop relationship, which is in very good agreement with the experimental results. A capillaric theory has been developed to determine an analytical relationship between the flow rate and pressure drop for flows of Bingham liquids through porous media. It is shown that the predictions of this theory are in good agreement with the experimental and numerical results.

Thermophysical and rheological properties of dulce de leche with and without coconut flakes as a function of temperature

Dulce de leche (DL), a dairy dessert highly appreciated in Brazil, is a concentrated product containing about 70% m/m of total solids. Thermophysical and rheological properties of two industrial Brazilian Dulce de leche formulations (classic Dulce de leche and Dulce de leche added with coconut flakes 1.5% m/m) were determined at temperatures comprised between 28.4 and 76.4 °C. In general, no significant differences (p < 0.05) were observed in the presence of coconut flakes in the two formulations. Heat capacity varied from 2633.2 to 3101.8 J/kg.°C; thermal conductivity from 0.383 to 0.452 W/m.°C; specific mass from 1350.7 to 1310.7 kg/m³; and, thermal diffusivity from (1.082 × 10-7 to 1.130 × 10-7) m²/s. The Bingham model was used to properly describe the non-Newtonian behavior of both formulations, with yielding stress values varying from 27.3 to 17.6 Pa and plastic viscosity from 19.9 to 5.9 Pa.s.

Avaliação do comportamento reológico de pastas de cimento para poços de petróleo com adição de plastificantes

The isolation of adjacent zones encountered during oilwell drilling is carried out by Portland-based cement slurries. The slurries are pumped into the annular positions between the well and the casing. Their rheological behavior is a very important component for the cementing process. Nowadays, several alternative materials are used in oilwell cementing, with goal the modification and the improvement of their properties, mainly the increase of the fluidity. And this can be reached by using plasticizers additives able to account for different oilwell conditions, yielding compatible cement slurries and allowing enough time for the complete cementing operation. If the rheological properties of the slurry are properly characterized, the load loss and flow regime can be correctly predicted. However, this experimental characterization is difficult. Rheological models capable of describing the cement slurry behavior must be capable of predicting the slurry cement deformation within reasonable accuracy. The aim of this study was to characterize rheologically the slurries prepared with a especial class of Portland cement, water and plasticizers based on lignosulfonate, melamine and polycarboxylate at temperatures varying from 27°C to 72°C. The tests were carried out according to the practical recommendations of the API RP 10B guidelines. The results revealed a great efficiency and the dispersive power of the polycarboxylate, for all temperatures tested. This additive promoted high fluidity of the slurries, with no sedimentation. High lignosulfonate and melamine concentrations did not reduce the rheological parameters (plastic viscosity and yield stress) of the slurries. It was verified that these additives were not compatible with the type of cement used. The evaluated rheological models were capable of describing the behavior of the slurries only within concentration and temperature ranges specific for each type of additive

Pastas compósitas cimento/sílica/polímero para cimentação de poços de baixa profundidade sujeitas à injeção de vapor

The production of heavy oil fields, typical in the Northeastern region, is commonly stimulated by steam injection. High bottom hole temperatures are responsible not only for the development of deleterious stresses of the cement sheath but also for cement strength retrogression. To overcome this unfavorable scenario, polymeric admixtures can be added to cement slurries to improve its fracture energy and silica flour to prevent strength retrogression. Therefore, the objective of the present study was to investigate the effect of the addition of different concentrations of polyurethane (5-25%) to cement slurries containing 40% BWOC silica flour. The resulting slurries were characterized using standard API (American Petroleum Institute) laboratory tests. In addition to them, the mechanical properties of the slurries, including elastic modulus and microhardness were also evaluated. The results revealed that density, free water and stability of the composite cement/silica/polyurethane slurries were within acceptable limits. The rheological behavior of the slurries, including plastic viscosity, yield strength and gel strength increased with the addition of 10% BWOC polyurethane. The presence of polyurethane reduced the fluid loss of the slurries as well as their elastic modulus. Composite slurries also depicted longer setting times due to the presence of the polymer. As expected, both the mechanical strength and microhardness of the slurries decreased with the addition of polyurethane. However, at high bottom hole temperatures, the strength of the slurries containing silica and polyurethane was far superior than that of plain cement slurries. In summary, the use of polyurethane combined with silica is an interesting solution to better adequate the mechanical behavior of cement slurries to heavy oil fields subjected to steam injection

Formulação e caracterização de pastas espumadas por incorporação de ar e estabilizantes minerais

Cementing operations may occur at various stages of the life cycle of an oil well since its construction until its definitive abandonment. There are some situations in which the interest zones are depleted or have low fracture pressure. In such cases, the adoption of lowdensity cement slurries is an efficient solution. To this end, there are basically three ways to reduce the density of cement slurries: using microspheres, water extending additives or foamed cement. The objective of this study is to formulate, to study and to characterize lowdensity foamed cement, using an air entrainment surfactant with vermiculite or diatomite as water extenders and stabilizers. The methodology consists on preparation and evaluation of the slurries under the American Petroleum Institute (API) and the Brazilian Association of Technical Standards (ABNT) guidelines. Based on calculated densities between 13 and 15 ppg (1.559 and 1.799 g/cm3), the slurries were prepared with fixed surfactant concentration, varying the concentrations of vermiculite and diatomite and were compared with the base slurries. The results of plastic viscosity, yield point and gel strength and the compressive strength for 24 h showed that the slurries presented suitable rheology and mechanical strength for cementing operations in oil wells, and had their densities reduced between 8.40 and 11.89 ppg (1.007 and 1.426 g/cm3). The conclusion is that is possible, under atmospheric conditions, to obtain light weighted foamed cement slurries with satisfactory rheological and mechanical properties by means of air entrainment and mineral additions with extenders and stabilizers effects. The slurries have great potential for cementing operations; applicability in deep wells, in low fracture gradient formations and in depleted zones and bring cost savings by reducing the cementing consumption

Efeito da adição de microfibras de lã de vidro na tenacidade à ruptura de pastas de cimento para poços de petróleo

Although there are a wide variety of additives that act in fresh state, to adjust the properties of cement, there is also a search by additions that improve the tenacity of the cement in the hardened state. This, in turn, can often be increased by inserting fibers, which act on the deflection of microcracks. This study aimed to use a microfiber glass wool (silica-based) as an additive reinforcing the cement matrix, improving the rupture tenacity, in order to prevent the propagation of microcracks in the cement sheath commonly found in oil wells submitted to high temperatures. The fibers were added at different concentrations, 2 to 5% (BWOC) and varied average sizes, grinding for 90 s, 180 s, 300 s, 600 s. The cement slurries were made with a density of 1,90 g/ cm3 (15,6 lb/gal), using Portland cement CPP- Special Class as the hydraulic binder and 40% silica flour. The characterization of the fiber was made by scanning electron microscopy (SEM), particle size by sieving, X-ray fluorescence (XRF), X-ray diffraction (XRD) and thermogravimetry (TG / DTG). Were performed technological tests set by the API (American Petroleum Institute) by rheology, stability, free water, compressive strength, as well as testing rupture energy, elastic modulus and permeability. The characterization results showed good thermal stability of the microfiber glass wool for application in oil wells submitted to steam injection and, also, that from the particle size data, it was possible to suggest that microfibers milled up to 300 s, are ideal to act as reinforcement to the cement slurries. The rheological parameters, there was committal of plastic viscosity when larger lengths were inserted of microfiber (F90). The values obtained by free water and stability were presented according to API. The mechanical properties, the incorporation of microfiber to the cement slurries gave better rupture tenacity, as compared to reference cement slurries. The values of compressive strength, elastic modulus and permeability have been maintained with respect to the reference cement slurries. Thus, cement slurries reinforced with microfiber glass wool can ensure good application for cementing oil wells submitted to steam injection, which requires control of microcracks, due to the thermal gradients

Constribuição técnica de um sistema de emulsão inversa a base de óleos vegetais para fluidos de perfuração

The developments in formulating drilling fluids to apply in petroleum fields are based on new technologies and environmental challenges, where the technical performance of a developed drilling fluid is used to produce a minimum environmental impact, showing great economy in costs. It is well known that the potential use of oil-based drilling fluids is limited because these fluids when discharged in the sea do not disperse as much as water-based ones and may form waterproof films in the seabed, having a profound effect on plants and animals living in this environment. The current works have been made in investigating fluids called pseudofluids, which are synthetic ester-based, n-paraffin-based and other fluids formed from inverse emulsion. In this research the principal parameters involved in inverse emulsion process were studied, in laboratory scale, using esters as main component. Others commercial drilling fluids were used as comparative samples, as well as samples from laboratory and field where these drilling fluids are being applied. Concentrations of emulsifier and organophilic clay, which are viscosity donor, were varied to verify the influence of these parameters, in different oil/water ratios (55/45, 60/40, 65/35, 70/30, and 75/25). The salt concentration (NaCl) is an indicative parameter of stability and activity of an esterbased fluid. In this research the salt concentration was varied in 10,000, 20,000, and 50,000 ppm of NaCl. Some rheological properties of the produced fluids were studied, such as: initial gel, plastic viscosity, yield point, and apparent viscosity. Through the obtained rheological measures, the existence of two systems could be verified: fluid and flocculated. It could be noticed that the systems were influenced, directly, by the oil/water ratio and emulsifier, organophilic clay and NaCl concentrations. This study showed the viability to use an ester obtained from a regional vegetable product babaçu coconut oil to obtain an efficient and environmental safe drilling fluid

FLOW PROPERTIES and TUBE FRICTION FACTOR of MILK CREAM: INFLUENCE of TEMPERATURE and FAT CONTENT

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermophysical and rheological properties of dulce de leche with and without coconut flakes as a function of temperature

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determinação de parâmetros reológicos de concretos através do ensaio de abatimento de tronco de cone modificado: estudo de caso

Pós-graduação em Engenharia Mecânica - FEIS

Estudo do comportamento reológico de sucos combinados de frutas vermelhas

The aim of this work was to evaluate the rheological behavior of combined juices of strawberry, blackberry and raspberry in two different temperatures of interest in industrial processes in the food industry, using rheological analyses on non-oscillatory regime and the Response Surface Methodology (RSM). The rheological data were fitted by the Casson model. All samples of combined juices of ref fruits showed a Newtonian behavior and the rheological parameters yield stress (Kc) and plastic viscosity of Casson (Koc) had a decrease in its values with the temperature increase. By the analysis of the ternary diagrams it is evident that the raspberry juice effectively contributed to the higher values of yield stress and plastic viscosity of Casson in both temperatures studied.