امیرحسین فرتاش

In this study, the temperature fields in the thermal barrier coating systems (TBC) under various types of thermal loading, including steady and transient thermal loadings, is investigated. Due to the widely use of TBCs on gas turbine blades and the urgent need to increase the temperature of the combustion chamber, thermal barrier coatings are exposed to a variety of harsh thermal loadings, including thermal shock and periodic thermal loads. Therefore, the need to achieve the temperature distribution in different positions in the TBCs, especially in the protective coating is crucial. At first, due to the application of non-uniform temperature distribution on the boundary of the TBC layer, the steady-state temperature distribution inside the coating-substrate is obtained. Using the solution of steady-state temperature distribution as the initial condition, the transient temperature field inside the coating-substrate system is obtained. To investigate the thermal transient response of the TBC system, dual-phase lag (DPL) heat conduction equation is utilized. Fourier and Laplace integral transformations have been used to solve the temperature field equations. The effect of various types of thermal shocks and periodic thermal loading on the TBC is investigated. The results show that the steady-state and transient temperature fields strongly depend on the type of thermal shock, the thickness of the coating and the frequency of thermal loading.

Exposure of the TBCs layers to high temperatures for a long time causes sintering in the ceramic layer, resulting in changes in the porosity. Since the thermal conductivity of air in the porosity of the layers is much lower than the ceramic material in the coating, a decrease or increase in the percentage of porosity will end up with changes in the conductivity of the layer, which subsequently affect the overall efficiency. In this study, a TBC was first applied to the prepared samples from Inconel738 turbine blades. The samples were subjected to an aging process in the furnace for a specified time. The porosity changes in the ceramic layer of the coating during the aging process were investigated using image processing of the SEM images. The porosity of the images obtained from SEM and thermal conductivity in different porosities were determined by OOF2 and ImageJ software, respectively. To validate the numerical results, temperature distribution on the thermal barrier coatings is obtained by the analytical solution of the Fourier equation. According to the analysis performed on the SEM images gathered from the samples during different aging hours, it is observed that by increasing the aging hours during 48 hours, the percentage of porosity of the whole ceramic layer decreased by 8%. According to the results, by decreasing porosity in the ceramic layer, an increase in thermal conductivity has been observed, followed by an increase in the substrate's temperature and a decrease in the overall performance over time.

In order to assess the genetic variability for seed germination parameters under salt stress in sunflower and corresponding QTL locations, an experiment was conducted using a population of 80 recombinant inbred lines obtained from a cross between PAC2 and RHA266. The experiment was arranged under a randomized complete block design with three replications in control and saline conditions. Several germination parameters were measured including time to start germination (TSG), time to 50% germination (T50%G), time to maximum germination (TMG) and percentage of seed germination (PSG). Results showed highly significant variations among genotypes (RILs) for all traits. Salt stress had a negative effect on germination, however the significance of RIL × Condition interaction suggested that the RILs have different responses to salt stress. In this study, “1.T50%G.16.1” and “2.T50%G.17.1” QTLs (controlling T50%G under salt and control conditions, respectively) were introduced as large-effect QTLs. Moreover, “2.TSG.16.1” and “1.TSG.16.1” QTLs (controlling TSG) and also “2.PSG.12.1”, “1.PSG.12.1”, “2.PSG.12.3” and “1.PSG.12.2” QTLs (controlling PSG) were introduced as stable QTLs.