Research of Sets of Solid Oxide Fuel Cells in Packed Version

The stressed state of fuel cells in a package is considered. It was found that for αi=1.2×10−5k−1, the rational geometric characteristic for a planar SOFC in a batch design is γi=6×10−2. It is concluded that if the relative thickness of the edge element of the SOFC stack is of planar design γi>6×10−2, then the resulting deformation complication will be characterized by the loss of stability of the structure. Otherwise, i. e. at γi<6×10−2, stacked SOFC elements can lose stability until plasticity appears in their materials. Consequently, only at γi=6×10−2, the use of the potentials of structures can be achieved both in terms of the stability of its elements and the strength of their materials.

Numerical study of thermal stress of a silicon mirror forming a beam of synchrotron radiation

Numerical simulation of heat transfer in a mirror for focusing a synchrotron radiation beam and its thermally stressed state has been carried out. The choice of the method for cooling the mirror through contact with the water-cooled plates, which provides the specified limitations on thermal deformation, has been substantiated. The modes of heat transfer, implemented under different conditions of heat transfer at the boundary of the mirror with water-cooled plates, are compared.

Comparison of influence of surfactants on thermokinetic characteristics of alkali-activated slag cement

Increasing the durability of concrete and reinforced concrete structures according to the criterion of crack resistance is a relevant task of construction materials science. To solve this task, this paper proposes effective solutions for adjusting thermofinite characteristics of alkali-activated slag cement (ASC) by using surfactants of various chemical nature in order to control the thermally-stressed state of concrete based on it (ASC concrete). The method of calorimetry was applied to show that the problematic issue is to adjust the structure formation of ASC by anion-active surface-active substances based on complex polyesters. This is predetermined by the instability of the molecular structure of surfactants in the hydration environment of ASC due to the destruction of complex ester bonds as a result of alkaline hydrolysis. Thermokinetic analysis has demonstrated the effectiveness of using anion-active surfactants, which do not contain ester bonds, as regulators of crack resistance of ASC concrete. Simple polyesters and multi-atom alcohols provide the ability to adjust the duration of the induction period while ensuring the required completeness of ASC hydration within a time frame. The effectiveness of cation-active surface-active substances has been shown, which are characterized by the stability of the molecular structure in the hydration environment of ASC and an increased level of adsorbing capacity. The decrease in the effectiveness of surface-active substances has been shown, in terms of the effect on the heat release of ASC, in the following series: alkaline salt of carboxylic acid>salt of the quaternary ammonium compound>simple polyester> polyalcohol>complex polyester. The reported results are important in view of the possibility of effective adjustment of ASC heat release by influencing the structure formation of surfactant with a certain molecular arrangement in order to predictably reduce crack formation in a thermally-stressed state and a corresponding increase in the durability of structures

The thermal stress state arising in the contact area of mass concreteduring construction

Introduction. The contact area of concrete gravity dams is of vital importance. Substantial temperature gradients and tensile stresses can arise in the process of concrete casting and thermal regime creation; they can cause thermal cracking. The practice of monitoring the construction and operation of concrete gravity dams has identified frequent vertical cracking along and across the dam axis, which can have an adverse impact on structural behaviour. Despite the large number of research works, some of which are mentioned in the work, the extent of influence of the modulus of elasticity in the bed on the thermally stressed state of mass concrete has yet to be fully resolved. The purpose of the research is to enhance the insight into the stress-strain state arising in the contact area of mass concrete and the bed, depending on its rigidity. Materials and methods. The research was conducted using the numerical finite element method and the MIDAS software package. Results. The influence of bed rigidity on the thermally stressed state arising in the contact area of mass concrete in the process of construction has been analyzed. Several options featuring different ratios between the modulus elasticity of the bed and mass concrete were considered in respect of a mass concrete structure made of vibrated and rolled concretes. Emerging stresses are compared. Mathematical expressions are obtained to project maximum tensile stresses occurring in the contact area. Conclusions. A more rigid bed rises maximum tensile temperature stresses, which increase the risk of thermal cracking. Research results can be used to predict maximum tensile stresses near the contact section of the mass concrete, whose dimensions are close to those of the structure under research.