Heat transfer enhancement using nanofluids in the compression exchanger in a solar Stirling engine

In this paper a improvement in the heat exchange of a solar Stirling engine during the compression phase was studied. The viability of using nanoparticles as ceramic oxide (Al2O3 in water) at different concentrations instead of conventional refrigerants (water or air) was evaluated. Since these systems could behave as non- Newtonian fluids the dynamic viscosity was measured, as well as other thermophysical properties. The results showed that the convective heat transfer coefficient could raise one order of magnitude respect to the conventional heat transfer fluids at moderately volume fractions (over 0.15).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Characterization and thermophysical properties of rutile and alumina nanofluids

The characterization in relation to shape and particle size of alumina and rutile suspensions was performed. The intrinsic viscosity exhibited the presence of nonspherical aggregates in both suspensions although TEM images showed non monodisperse spherical shape of alumina particles. DLS indicated the existence of particle aggregates for both systems. In all cases, the increase in thermal conductivity with respect to the base fluid is verified. The thermal conductivities obtained experimentally were compared with three mathematical models, which yielded lower values than those measured. From rheological measurements and by means of the Peclet number defined in colloidal suspensions, values of thermal conductivity were also proposed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Rheological study of the aggregation state of alumina nanofluids

Se adjunta una comunicación, aunque se han publicado tres comunicaciones más.The presence of alumina solid particles in aqueous phase induces a change in the viscosity of the suspension from Newtonian to non- Newtonian flow. Besides, the presence of solid particles is adequate for the use as a heat exchanger fluid. The effect of nanoparticle size on thermal properties of nanofluids is still today a question, which is far from being answered. In this respect, the results reported in the literature are contradictory [1], probably due to the formation of aggregates when particles are dispersed in the liquid phase. Regarding to the nanoparticle shape influence in thermal conductivity, cylinders and spheres have been considered as the more effective in heat transfer. Spherical nanoparticles of alumina, which is one of the most investigated nanofluid, dispersed in water were used in this study. TEM images showed a mean average diameter of 50 nm. However, DLS measurements showed monodispersed particles of 260 nm. Very recently [2], the relationship between shear rheology and aggregation state of suspensions has been reviewed. Mechanical and physical properties of the resultant materials depend on shape, size and size distribution, which are considered determining parameters in the formation of particle aggregates. The steady shear flow (figure 1) has shown that these clusters, when they are at rest, are formed by highly branched aggregates that erode when shear rate increases, until a suspension of individual particles is achieved. These results are in good agreement with the intrinsic viscosity obtained by Money and Krieger-Dougherty models. In both cases, these values are far from the 2.5 corresponding to spherical particles. The temperature effects were also taken into account.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Liderazgo pedagógico directivo y la calidad de la gestión educativa de una IE rural- Tacna, 2022

El objetivo de la investigación fue: Determinar qué relación existe entre el Liderazgo pedagógico directivo y la calidad de la Gestión Educativa de una IE rural- Tacna, 2022, la investigación, corresponde al enfoque cuantitativo, del paradigma positivista, asimismo, el tipo de investigación es básica, de diseño no experimental, transversal, también asumen el nivel descriptivo correlacional. La muestra la conformó 17 docentes del nivel primario de una institución educativa rural, se aplicó dos encuestas validadas, por tres expertos, asimismo con niveles aceptables de confiabilidad, los resultados de la investigación según el nivel de significancia α (p<0.05), indica que existe una correlación positiva con una intensidad perfecta (r=0.925), entre el liderazgo pedagógico directivo con la calidad de la Gestión Educativa de una IE rural- Tacna, 2022

Thermophysical and flow properties of coconut oil with silica fumed nanoparticles

This work is concerned with the rheological and thermal study of silica fumed dispersed in coconut oil. The dispersed phase behave as a non newtonian fluid during the phase change. The addition of nanoparticles complicates considerably the flow behaviour of the system. Therefore, a very thoughtful study of the flow and thermal properties with temperature when silica particles are added must be carried out.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

A comparative rheological study of amaranth, wheat and chickpea doughs

Legume flours due to their nutritional benefits (e.g., high levels of proteins, fiber, complex carbohydrates, micronutrients and vitamins) are ideal ingredients for improving the nutritional value of bread and bakery products. Although proteins has a major role in the quality breads, however, few studies related to the evaluation of doughs containing chickpea flour(or other legume flour) alone or blended with other ingredients have been published. This work performs a comparative study of the flow properties of three different flours: wheat, amaranth and chickpea, at two temperatures. The flow curves showed shear-thinning behaviour although amaranth flour presented the higher values of viscosity and wheat flour de lower values. The influence of the protein content in the three doughs was evaluated by means of step- up-stepdown tests and frequency sweeps (Fig. 1). Amaranth flour presented the higher elastic modulus and the wheat flour the lower. This can explain the compactation observed in gluten-free bread. The results of the flow studies are prone to the combination of cereal and legume flours in order to improve the taste and quality of gluten-free breads.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Self-limited autoimmune disease related to transient donor B cell activation in mice neonatally injected with semi-allogeneic F1 cells

BALB/c mice injected at birth with 108 semi-allogeneic (C57BL/6 x BALB.IgHb)F1 spleen cells develop a lupus-like syndrome in which autoantibodles bear exclusively the donor allotype. We have analyzed the evolution of donor B cell chimerism and the autoimmune manifestations during the first year of life in these mice. Anti-DNA, -histone, and -cardiolipln IgG antibodies as well as circulating immune complexes appeared in the second week of life, reached the highest values around the sixth week, and then progressively dropped to normal values after the sixth month in most mice. The kinetics of the evolution of the autoimmune manifestations, as well as the kinetics of serum donor Ig allotype, were parallel to the kinetics of donor B cell chimerism, which was particularly prominent in the spleens in early weeks of life, and progressively decreased after remission of the autoimmune syndrome. Membrane-proliferative glomerulonephritls, which was followed as the more representative histological abnormality in this model, was particularly evident after 10 weeks of life, but disappeared by the end of the follow-up. Interestingly, when mice with a self-limited disease were re-injected with 108 F1 spleen cells i.v., a flare in the serologlcal manifestations was observed. In these re-injected mice a predominance of anti-DNA, lgG1 antibodies bearing exclusively the donor allotype was also observed, as in the early weeks of life. These results emphasize the central role of donor B cell chimerism in the development and in the self-limitation of the autoimmune disease in parental mice neonatally injected with F1 cells and Indicate that the capacity to react with F1 cells, to generate a renewed burst of symptoms, persists in these mice after the disappearance of autoimmune finding

Living with zombie companies: do we know where the threat lies?

This paper shows the existence of extreme types of zombie firm, i.e. companies with negative equity that continue to do business despite having lost their entire equity. We explain how these firms are measured and how the riskier ones are defined with different determinants. Using a Spanish sample from 2010 to 2014 an index called the EZIndex is developed that includes four dimensions of the extreme zombie problem: extension, contagion, recovery signs and immediacy. The paper contributes to zombie theory on the one hand by developing a method for ranking zombie firms based on risks and changes over time, and on the other hand by using a log-linear model to detect the riskiest corporate profiles out of all these risky firms. It demonstrates significant implications that need to be considered by the competent authorities not only in terms of their impact as a whole but also in regard to the particular profile of extreme zombie firms: they are less regulated, large and located in regions with large business fabrics

Influence of recycled aggregate quality from precast rejection on mechanical properties of self-compacting concrete

The use of coarse aggregates from crushing pre-existing concrete in the manufacturing of new concrete needs experimental results to validate its influence in the properties of the new concrete elements. In the present study we assessed the impact of using different proportions of replacement up to 100% of natural aggregates with recycled aggregates in the concrete properties; moreover, the effect of pre-treatments of pre-saturation, washing and the aggregates’ source (from precast concrete rejected pieces and construction and demolition waste) was analysed. The best results were obtained with dry and washed recycled aggregates, the compressive strength increment was between the 8 and 17% compared to conventional concrete. Results also pointed out that recycled aggregate that exclusively comes from precast concrete pieces lead to a better concrete mechanical characteristic than the aggregates which origin is construction and demolition waste. In addition, a clear relationship between the percentage of recycled aggregate substitution and the workability and mechanical performance of self-compacting concrete is observed. The results presented in this paper allow to state that precast concrete factories can recycle their rejected elements into recycled coarse aggregates for manufacturing new products, this will allow to protect the environment by reducing the need of raw material consumption and the C&DW landfill