Navegando por Palavras-chave "Solid State Refrigeration"

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    Estudo do efeito barocalórico em borracha natural, vulcanizada e blendas com pó de pneu
    (Universidade Federal de São Paulo (UNIFESP), 2019-09-06) Usuda, Erik Oda [UNIFESP]; Carvalho, Alexandre Magnus Gomes [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The current refrigeration systems based on vapor compression cycles, also known as conventional refrigeration, have some problems inherent to their technology. One of the problems is the substance used as refrigerant, in most of the cases it is based on hydrocarbons that can contribute to global warming when released to the atmosphere. Furthermore, some refrigerants use chloride in their composition, which contributes to the depletion of the ozone layer. Another problem is related to energy efficiency, which is not high and is reaching their technological limits. Therefore, it is important to search for other alternatives which are more efficient and eco-friendly. A promising technology is the solid-state refrigeration, which is based on materials that present i-caloric effects. In this dissertation, it was studied the barocaloric effect, a class of i-caloric effects, in vulcanized natural rubber (BNV), natural rubber (BN), ground tire rubber (GTR) and blends composed by BNV and GTR (BNV/GTR). In the latter case, it was studied samples with different contents of GTR. In all materials, the results obtained for the barocaloric effect (isothermal entropy change, ΔST, and adiabatic temperature change, ΔTS) reached values above 15 K of ΔTS and surpassed 60 J kg-1 K-1 of ΔST for pressure change up to 390 MPa around room temperature. Such values are comparable or superior to the best i-caloric materials in the literature. Besides, other properties were obtained from these materials, such as the pressure dependence of the glass transition temperature (Tg) and estimated entropy curves under pressure as function of temperature. Also, it was verified that the glass transition reduces the values of ΔST and ΔTS. Among the materials studied here, natural rubber presented the higher values of ΔST and ΔTS, surpassing vulcanized natural rubber. This can be attributed to the greater chain deformation and mobility under pressure. Increasing the GTR content in the blends resulted in a lower effect, still, the results were high. The materials studied in this dissertation presented promising barocaloric effect, envisaging the viability for application in solid-state refrigeration with low environmental impact.