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This paper aims to study the minimizing of energy consumption in air cooled-heat exchanger through a convenient control system. Thus, the performance of a given air cooler has been considered in different weather conditions for both ideal and non ideal operations.

The minimum number of fans in service has been calculated and used for the study and assessment of a proper controlling system with the purpose of energy saving in air coolers. On-Off controlling has been compared to variable speed drivers controlling to determine a feasible method for the process control of this cooling equipment.

Economical parameters show that installing variable speed drivers could be rational, as the payback period, the net present values of investment and the internal rate of return are completely persuading. The internal rate of return (IRR) for installation of variable speed driver (VSD) controls is 69 per cent. According to the results, there is a possibility of 0.45 and 0.33 MWh energy consumption reduction for VSD control under ideal and non-ideal conditions and consequently reduces annually 318 and 237 ton equivalent CO₂.

Air cooled heat exchangers are used as one of the energy consumption equipment in most plants, but before the emergence of serious problems, not enough attention was given to their operation.

Due to the extensive industrial applications of stagnation flow problems, the present work aims to investigate the magnetohydrodynamics (MHD) flow and heat transfer of a magnetite nanofluid (here Fe₃O₄–water nanofluid) impinging a flat porous plate under the effects of a non-uniform magnetic field and chemical reaction with variable reaction rate.

Similarity transformations are applied to reduce the governing partial differential equations with boundary conditions into a system of ordinary differential equations over a semi-infinite domain. The modified fourth-order Runge–Kutta method with the shooting technique which is developed for unbounded domains is conducted to give approximate solutions of the problem, which are then verified by results of other researchers, showing very good agreements.

The effects of the volume fraction of nanoparticles, permeability, magnetic field, chemical reaction and Schmidt number on velocity, temperature and concentration fields are examined and graphically illustrated. It was found that fluid velocity and temperature fields are affected strongly by the types of nanoparticles. Moreover, magnetic field and radiation have strong effects on velocity and temperature fields, fluid velocity increases and thickness of the velocity boundary layer decreases as magnetic parameter M increases. The results also showed that the thickness of the concentration boundary layer decreases with an increase in the Schmidt number, as well as an increase in the chemical reaction coefficient.

The thermophysical properties of the magnetite nanofluid (Fe₃O₄–water nanofluid) in different conditions should be checked.

Stagnation flow of viscous fluid is important due to its vast industrial applications, such as the flows over the tips of rockets, aircrafts, submarines and oil ships. Moreover, nanofluid, a liquid containing a dispersion of sub-micronic solid particles (nanoparticles) with typical length of the order of 1-50 nm, showed abnormal convective heat transfer enhancement, which is remarkable.

The major novelty of the present work corresponds to utilization of a magnetite nanofluid (Fe₃O₄–water nanofluid) in a stagnation flow influenced by chemical reaction and magnetic field. It should be noted that in addition to a variable chemical reaction, the permeability is non-uniform, while the imposed magnetic field also varies along the sheet. These, all, make the present work rather original.

This study aims to introduce a new modified method for estimating steam turbine high pressure (HP)-intermediate pressure (IP) leakage flow based on the experimental data extracted from a 250 MW re-heat steam turbine.

Effects of measurement uncertainties on the test results are investigated and key parameters are specified via a new modified method to diminish the test uncertainties. The recommended method is based on a constant IP turbine pressure ratio at the same loads. Considering this assumption, it was found that the turbine pressure ratio can be achieved in the second and the third tests with a much longer duration.

The results showed that the cross-over temperature is a major parameter in the leakage flow estimation tests, whereas hot reheat and cross-over pressures are the next priorities. It was also observed that as the cross-over temperature varies by 1°C, the estimated leakage flow error significantly differs by up to 72.6 per cent.

It is concluded that the present modified HP-IP leakage flow estimation method seems to be more accurate in comparison with previously proposed methods in literature.