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A differential thermal model for simulation of Stirling engines was presented. In the new model polytropic expansion/compression processes were substituted to traditional isothermal or adiabatic models of previous studies. In addition, the developed polytropic model was corrected for various loss mechanisms of real engines. In this regard, the effect of non-ideal operation as well as heat recovery in the regenerator was considered. In addition, non-ideal heat transfer of heater and cooler were implemented into the model. In pressure analysis and evaluating work produced or consumed in cylinders, the effect of finite speed motion of piston was considered based the concept of finite speed thermodynamics. Moreover, the effects of heat leakage in regenerator, leakage effect and shuttle effect were evaluated. Finally, new differential polytropic model were employed on a benchmark Stirling engine so-called GPU-3 and accuracy of models was validated through comparing with experimental results as well as previous models. As thermal performance of Stirling engines are significantly affected by thermohydraulic performance of regenerator in one hand and there are various thermohydraulic models for regenerator, three famous thermohydraulic models of regenerator was integrated into models and through comparison with experimental performance of GPU-3 engine, a more accurate thermohydraulic model was introduced.

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In this paper, a thermodynamic based constitutive model used to model the behavior of magnetic shape memory alloy (MSMA) during applying strain in an energy harvester. In this type of energy harvester, applying strain changes the internal magnetization of MSMA and as a result changes the flux density around it. Using a coil the flux change can be converted to voltage. In order to study the effect of changing MSMA dimensions on the amount of harvested energy, the demagnetization factor for different dimensions derived from an analytic expression for ferromagnetic prisms and the results are validated by reference data. Increasing MSMA thickness results in increasing longitudinal demagnetization factor and decreasing transversal demagnetization factor. The constitutive model of MSMA is used in modeling an energy harvester using two different configurations; one a pickup coil turned around MSMA and second a system with ferromagnetic core to conduct magnetic flux and the pickup coil around core. Simulation of two models at different thicknesses shows that increasing thickness in system with coil around MSMA results in linear increase of voltage while this parameter in second configuration leads to a nonlinear increase of voltage. Furthermore, simulations show that increase of MSMA width, results in linear increase of output voltage in both configurations but with steepest rate for system with ferromagnetic core. Finally, increasing the length of MSMA specimen shows no changes in voltage for the system with coil around MSMA, while linear increase in voltage for the system with core is recorded.

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This paper presented a numerical modeling of dew-point counter-flow indirect evaporative coolers as a potential alternative to the conventional cooling systems. Unlike the conventional method of assuming constant surface heat (mass) flux or constant surface temperature boundary condition on the separating wall, the present article calculated real boundary conditions. Real boundary conditions were obtained by simultaneous solving of momentum, energy and mass transfer equations of the two flows coupled on the wall. Calculating real boundary conditions lead to a real distribution of humidity ratio and temperature on the separating wall where at each point, the summation of heat fluxes from air streams in adjacent channels is equal to the latent heat of evaporation at that point. Moreover, the model accuracy was increased through considering hydrodynamic and thermal developing flows of two air streams. The model predicted supply air temperature under different conditions, and the results were compared against experimental data as well as previous numerical models. It was shown that the maximum deviation of the supply air temperature was under ±3.3%. Then, a parametric analysis was conducted, which studies the effects of the inlet air velocity, channel gap, channel length and returned air ratio on the supply air temperature, dew-point effectiveness, cooling capacity and pressure drop. The results indicated that increasing channel length and returned air ratio, and reducing channel gap and inlet air velocity improved the dew-point effectiveness but increased the initial cost and pressure drop and decreased the cooling capacity.

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Since dye-sensitized solar cells (DSSCs) have good efficiency in the visible region, they offer a promising way to generate sustainable energy, especially in indoor environments and building applications. Investigating the effect of dye specifications and photoanode thickness changes on cell performance is very important for improving DSSCs. This research focuses on the sensitivity analysis of the impact of important parameters to increase DSSC efficiency using a new numerical model considering factors such as radiation intensity and spectral composition, from conventional indoor light sources such as LED and fluorescent lights. These parameters include dye types, trapping parameters, diffusion coefficients, and photoanode thickness. This model examines steady and transient currents under internal radiation conditions, incorporates time/space-dependent relationships to increase accuracy, and examines electron, iodide, and triiodide interactions under different environmental conditions. The results showed that N749 and 20µm thickness of photoanode have the best effect on cell performance. This study presents a sensitivity analysis to find optimal parameters to improve DSSC performance in real indoor conditions opening avenues for further research in optimizing DSSC technology for indoor energy harvesting applications, thereby advancing the field of renewable energy and sustainable technology integration.