Antonio Celso Fonseca de Arruda

Transient behavior of an electrorheological fluid in shear flow mode

Electrorheological (ER) fluids made of starch particles in silicone fluid were studied under different electric field strength, particle concentration, water content, and shear rate. The ER fluids were sheared under constant shear rates during at least 210 min and the shear stress was measured. According to the results, the shear stress increased with time until a maximum was reached, decreased a little, and then stabilized. Some samples did not show a point of maximum, but after increasing with time, they stabilized at a given shear stress. The influence of the shear rate on the shear stress depended on the time the sample was sheared, on the electric field strength, on concentration, and on water content. The results were analyzed in terms of changes of lamellar formations in the direction of shear.

Modeling of the efficiency of fibrous filters through numerical simulation and X-ray tomography

This paper describes modeling of the efficiency of fibrous filters using numerical simulation and X-ray computerized tomography (XCT). Variations in the flow field within the filter due to particle accumulation and structural inhomogeneities are taken into account in the mathematical model. Both the theoretical results and the experimental XCT data (digital images) showed that in the depth filtration process analyzed there is graded particle accumulation. Larger particles form bridges and can improve the collection for smaller particles during the filtration time. It is also found that smaller particles tend to promote a more pronounced pressure drop.

TRANSIENT BEHAVIOR OF THE MICROSTRUCTURE OF ELECTRORHEOLOGICAL FLUIDS IN SHEAR FLOW MODE

It was reported that under the simultaneous stimulus of an electric field and shear, the particles in an ER fluid form lamellar formations in the direction of shear (adhered to one of the electrodes) which may be responsible for the ER activity more than the strength of the chains. In this way, it would be expected that the shear stress should change consistently with the morphology of the formations. In this work we studied the effect of shearing time, electric field strength and shear rate on the shear stress. We suggest that changes on shear stress with time are due to changes of the morphology of the lamellar formations.

Electrorheological Fluids Response under Mechanical Testing

In most research, ER fluids have been studied and characterized as if they were extremely viscous liquids. In this work, electrorheological fluids were characterized as solids and their mechanical properties in tensile, compression and shear tests were determined. Two different fluids were studied: one of them was made of starch in silicone fluid and the other was composed of carboxymethylcelullose (CMC) in silicone fluid. From the results we concluded that fluids made of CMC have a better performance than those made of starch and also that ER materials are more resistant to compression, tensile and shear stress, in this order. More precisely, ER fluids made of CMC have an elasticity modulus similar to that of rubber. They have tensile strength 600 to 104 times lower than that of LDPE (low density polyethylene) and static yield stress 1 O4 times lower than that of ABS (acrylonitrile-butadiene-styrene terpolymer).

Testes in vitro e in vivo com o Coração Artificial Auxiliar (CAA): um novo modelo de coração artificial totalmente implantável e heterotópico

A miniaturized artificial heart is being developed in the authors laboratories, the Auxiliary Total Artificial Heart (ATAH). This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center aluminum piece. This pusher plate type ATAH is controlled based on Frank-Starlings law. The beating frequency is regulated through the change of the left preload, assisting the natural heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical procedure of implantation in the right thoracic cavity performed without removal of the natural heart. The left and right stroke volumes are 35 ml and 32 ml, respectively. In vitro tests were made and the performance curves demonstrated that the ATAH produces 5L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mmHg of left outlet mean pressure). Preliminary acute In vivo tests were performed in two sheeps with 50 ± 5 kg, during 5 hours. The ATAH performance is satisfactory for helping the natural heart to obtain the required blood flow and arterial pressure. With the ATAH and the natural heart working simultaneously the ATAH control system is simpler, also the risks of a fatal misoperation is minor compared to a total artificial heart, for patients that still present some cardiac function.A miniaturized artificial heart is being developed in the authors laboratories, the Auxiliary Total Artificial Heart (ATAH). This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center aluminum piece. This pusher plate type ATAH is controlled based on Frank-Starlings law. The beating frequency is regulated through the change of the left preload, assisting the natural heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical procedure of implantation in the right thoracic cavity performed without removal of the natural heart. The left and right stroke volumes are 35 ml and 32 ml, respectively. In vitro tests were made and the performance curves demonstrated that the ATAH produces 5L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mmHg of left outlet mean pressure). Preliminary acute In vivo tests were performed in two sheeps with 50 ± 5 kg, during 5 hours. The ATAH performance is satisfactory for helping the natural heart to obtain the required blood flow and arterial pressure. With the ATAH and the natural heart working simultaneously the ATAH control system is simpler, also the risks of a fatal misoperation is minor compared to a total artificial heart, for patients that still present some cardiac function.

Characterization of the Mechanical Properties of Electrorheological Fluids Made of Starch and Silicone Fluid

In the majority of published articles on the topic, ER fluids have been studied as if they were viscous liquids. In this work, electrorheological fluids were characterized as solids and their mechanical properties were determined. The results infer that ER materials are controllably resistant to compression, tensile and shear stress, in this order of magnitude. More precisely, fluids made of starch have elasticity modulus similar to that of rubber, they have tensile strength 103 to 5×104 times lower than that of low density polyethylene (LDPE), static yield stress 4×104 to 8×105 times lower than that of acrylonitrile-butadiene-styrene terpolymer (ABS) and fatigue life similar to some polymers like polyethylene(PE) and polypropylene (PP).

Analysis of contaminant distribution in filter cartridges using X-ray computerized tomography

Abstract The purpose of this paper is the application of an internal visualization method for contaminant distribution analysis and quantification in filter cartridges, based on X-Ray Computerized Tomography (XCT). The cartridge filters were contaminated with glass beads and scanned in a medical device. The scanning process was carried out both with and without contaminant in the filter to compare the attenuation coefficient of the clean filter and the contaminated filter. Hundreds of images were collected and the mapping of the particles in each section of the filter were analyzed using the segmentation technique, based on the difference between contaminant (glass beads) and filter (wound polypropylene fibers) attenuation coefficients. The more relevant images were selected and quantitatively analyzed. The shape of the distribution is also presented. Finally, the results show the potential of the technique for the proposed analysis.

Impact Project: Searching for Solution to the Underride Problem

Rear underride crashes kill thousands of people yearly worldwide. Underride guards did not follow the progress achieved by the automotive safety technology. Searching for solutions to this problem, two new guards have been designed and three crash tests carried out. A new articulated, an energy absorbing conceptual guard and a guard constructed according to the European (ECE-R58) regulation were tested. Both the new guards could avoid underride, the ECE-R58 one could not. The tests showed that the new articulated guard could be used after a few modifications and the conceptual one needs further optimization to become commercially feasible. (A) For the covering abstract of the conference see ITRD E203705.

Influence of filtration conditions evaluated by X-ray computerized tomography

This research article investigates the effect of flow rate conditions on particle distribution within cartridge filters using X-Ray computerized tomography. Graphical analysis and an image reconstruction technique show that particle distribution and particle capture efficiency are significantly different for each flow condition.

Using X-ray Computerized Tomography for Characterization of Defects in Cartridge Filters

Cartridge filter manufacturers conventionally use air permeability and bubble point tests for the evaluation of integrity and filtration rating of their filter elements. These tests reveal information only upstream and downstream of the filters. If a region of low density and a region of high density (compared to the mean density of the filter) exist in the interior of the element, these two regions may be superimposed and the results of the test may cause acceptance of an imperfect filter. The present paper shows the use of an X-ray computerized tomography scanner for visualization of internal defects in the cartridge filter elements used in industrial and domestic applications. Tomographic images with good contrast were obtained. The images clearly revealed cracks in the activated carbon filter and regions of high density in the fibrous filter (meltblown type). Finally, the main objective of this paper is to show that X-ray computerized tomography can be used successfully within the filter industries as a potential tool in the evaluation of existing products, and as a support in new product development.