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This paper investigates numerically a two-dimensional turbulent flow in a solar chimney due to free convection heat transfer. For evaluation of the fluid flow and heat transfer in the system, the basic equations including conservation of mass and momentum in the x, y directions and energy in the Cartesian coordinate are converted to the algebraic form using the finite volume method. This simulation (use the commercial CFD code) provides the profile of temperature, velocity, and mass flow rate variations in the solar chimney in different conditions. These results can be used to evaluate the effective parameters and optimize the performance of the system for natural evaporative cooling and ventilating the buildings. Based on climate conditions in Yazd, the optimum dimension of the width of the chimney is 0.3-0.4 m, inlet height is 0.3 m, and the flow rate created in the system and at the outlet is at 0.18 m3/s. The mean cooling rate resulted from the solar chimney is about 800 W/m2. Considering the long hot and sunny days of summer (about 12 h in Yazd), the use of this system in warm and dry region is recommended. We can save a considerable amount of energy sources such as natural gas or oil and lower CO2 emissions. [ABSTRACT FROM AUTHOR]

The efficiency of the fuel cell system nonlinearly depends on operating conditions and the air flow supplied to the fuel cell system is one of the most significant factors in determining the efficiency. The conventional method of controlling the air flow is to stabilize the oxygen supply at a predetermined constant rate for the optimal efficiency. However, in practice, the optimal point can deviate from the pre-set value due to the varying operating conditions, such as the uncontrollable load. Therefore, the maximum efficiency point tracking (MEPT) controller is necessary to maintain the optimal efficiency over a broad range of operating conditions. In this paper, the MEPT controller is designed based on the extremum seeking control algorithm for searching the optimal oxygen excess ratio in real time to maximize the efficiency of the fuel cell system. Simulation was conducted in the matlab/simulink environment and the results demonstrate that the proposed control method is able to track the maximum efficiency point when variations in operating conditions occur. [ABSTRACT FROM AUTHOR]