The elusive thomson effect in thermoelectric devices. Experimental investigation from 363 k to 213 k on various peltier modules

At steady state, in the governing equation of one-stage thermoelectric cooler, the heat resulting from Fourier conduction is balanced by heat generation due to the Joule and Thomson effects inside semiconductors. Since the heat flux observed at the junction of a semiconductor, r pair includes the Peltier effect and the Fourier heat flux caused by both the aforementioned contributions, the Thomson effect is easily masked by the Joule heat, which makes it elusive. With the aim of highlighting the contribution of the Thomson effect, measurements were carried out in the temperature range from 363 K to 213 K on different Peltier modules. The temperature dependence of the Seebeck and Thomson coefficients was evaluated as well as the electrical resistivity, and thermal conductivity of the Peltier modules examined. The results obtained show that the temperature dependence of the thermoelectric properties can reduce the cooling capacity of the Peltier module compared to what is declared in the technical datasheets of the commercial devices. The analyses allow us to conclude that an increase in the Thomson effect could have a positive effect on the performance of the Peltier only if it were possible to reduce the Joule contribution simultaneously

Preliminary investigation on thermal behavior of vehicles in different climate conditions

The objective of this paper is to provide an initial estimate, albeit rough, about the possible energy savings that can be achieved by reducing the use of the air condition system in cars. A simplified numerical model of the car has been created to predict the cabin temperature in different climatic conditions. In order to reduce the thermal load and so the temperature inside the cabin several different types of glazing have been considered, characterized by different absorbance coefficients and solar factors. Furthermore, two types of coatings with different absorbance coefficients were examined for the envelope. The paper describe

Calorimetric analysis of ice onset temperature during cryoablation: a model approach to identify early predictors of effective applications

Aim of the present study is to analyze thermal events occurring during cryoablation. Different bovine liver samples underwent freezing cycles at different cooling rate (from 0.0075 to 25 K/min). Ice onset temperature and specific latent heat capacity of the ice formation process were measured according to differential scanning calorimetry signals. A computational model of the thermal events occurring during cryoablation was compiled using Neumann’s analytical solution. Latent heat (#1 = 139.8 ± 7.4 J/g, #2 = 147.8 ± 7.9 J/g, #3 = 159.0 ± 4.1 J/g) of all liver samples was independent of the ice onset temperature, but linearly dependent on the water content. Ice onset temperature was proportional to the logarithm of the cooling rate in the range 5 ÷ 25 K/min (#3a = − 12.2 °C, #3b = − 16.2 °C, #3c = − 6.6 °C at 5K/min; #3a = − 16.5 °C, #3b = − 19.3 °C, #3c = − 11.6 °C at 25 K/min). Ice onset temperature was associated with both the way in which the heat involved into the phase transition was delivered and with the thermal gradient inside the tissue. Ice onset temperature should be evaluated in the early phase of the ablation to tailor cryoenergy delivery. In order to obtain low ice trigger temperatures and consequent low ablation temperatures a high cooling rate is necessary

Numerical and experimental analysis of labyrinth seals with rhomboidal cells

The labyrinth seals are devices commonly used in turbomachinery to reduce hot gas leakages through engine clearances, which adversely affect the gas turbine performance. For this reason, in the last decades, many in-depth analyses and optimization studies were carried out on this topic using experimental, analytical and numerical approaches. In this work, an innovative rhomboidal pattern is presented, obtained through Computational Fluid Dynamics (CFD) simulations, which is more dissipative than commonly used honeycomb cells. The experiments, performed using a Test Article that reproduces a stage and the next stator of a real low-pressure turbine suitably scaled, allowed to validate the numerical results in a situation that closely approximates the real one of use. The results obtained show that the leakages flow fraction of the total mass flow rate that bypasses the blade, which is 29.4% using a honeycomb pattern, is reduced to 27% with rhomboidal cells. The experimental results also made it possible to verify that the new pattern also behaves well from a thermal point of view, giving rise to temperature differences with respect to the honeycomb of less than 1%

Effect of preparation method on activity and stability of LaMnO3 and LaCoO3 catalysts for the flameless combustion of methane

A set of LaMnO3 and LaCoO3 catalysts was prepared through different synthesis procedures. The selected techniques included the sol-gel method, flame hydrolysis from aqueous solution, complexation through EDTA and solid-state reaction. The last was accomplished through reactive grinding by ball-milling either in a vibration mill or in a planetary mill. EDTA complexation was applied for LaCoO3 only and did not improve significantly catalyst activity or stability, with respect to other techniques. Ball-milling never allowed obtaining a pure perovskitic phase, at least under the most energetic grinding conditions permitted by our apparatus. The highest activity for the catalytic flameless combustion of methane was obtained with the sol-gel prepared samples, though thermal resistance revealed insufficient for high temperature applications. A bit lower activity, but coupled with good thermal stability was obtained with the samples prepared through flame hydrolysis

The role of antioxidants in the interplay between oxidative stress and senescence

Cellular senescence is an irreversible state of cell cycle arrest occurring in response to stressful stimuli, such as telomere attrition, DNA damage, reactive oxygen species, and oncogenic proteins. Although beneficial and protective in several physiological processes, an excessive senescent cell burden has been involved in various pathological conditions including aging, tissue dysfunction and chronic diseases. Oxidative stress (OS) can drive senescence due to a loss of balance between pro-oxidant stimuli and antioxidant defences. Therefore, the identification and characterization of antioxidant compounds capable of preventing or counteracting the senescent phenotype is of major interest. However, despite the considerable number of studies, a comprehensive overview of the main antioxidant molecules capable of counteracting OS-induced senescence is still lacking. Here, besides a brief description of the molecular mechanisms implicated in OS-mediated aging, we review and discuss the role of enzymes, mitochondria-targeting compounds, vitamins, carotenoids, organosulfur compounds, nitrogen non-protein molecules, minerals, flavonoids, and non-flavonoids as antioxidant compounds with an anti-aging potential, therefore offering insights into innovative lifespan-extending approaches

Fibroblasts from patients with Diamond-Blackfan anaemia show abnormal expression of genes involved in protein synthesis, amino acid metabolism and cancer

Background: Diamond-Blackfan anaemia (DBA) is a rare inherited red cell hypoplasia characterised by a defect in the maturation of erythroid progenitors and in some cases associated with malformations. Patients have an increased risk of solid tumors. Mutations have been found in several ribosomal protein (RP) genes, i.e RPS19, RPS24, RPS17, RPL5, RPL11, RPL35A. Studies in haematopoietic progenitors from patients show that haplo-insufficiency of an RP impairs rRNA processing and ribosome biogenesis. DBA lymphocytes show reduced protein synthesis and fibroblasts display abnormal rRNA processing and impaired proliferation. Results: To evaluate the involvement of non-haematopoietic tissues in DBA, we have analysed global gene expression in fibroblasts from DBA patients compared to healthy controls. Microarray expression profiling using Affymetrix GeneChip Human Genome U133A 2.0 Arrays revealed that 421 genes are differentially expressed in DBA patient fibroblasts. These genes include a large cluster of ribosomal proteins and factors involved in protein synthesis and amino acid metabolism, as well as genes associated to cell death, cancer and tissue development. Conclusion: This analysis reports for the first time an abnormal gene expression profile in a non-haematopoietic cell type in DBA. These data support the hypothesis that DBA may be due to a defect in general or specific protein synthesis. \ua9 2009 Avondo et al; licensee BioMed Central Ltd