[en] Highlights: • The study analyzes the performance of generator air coolers for a hydro-power plant. • The study investigates the effects of cooler design, time variation, and locations. • Malfunction of some coolers is equivalent to reduction in the heat transfer area. • The original coolers suffer from permanent fouling due to corrosion and erosion. • Effectiveness for both cooler designs agrees with those obtained empirically. -- Abstract: The present research study was carried out on the performance of generator air coolers for the hydro-power plant of Aswan High Dam at Egypt. The study is carried out under varying operating conditions associated with diurnal variations of the generation from power units and with the place that air-water coolers are located. Air temperatures and cooling water pressures were measured together with recording the generated power so that investigating the performance characteristics of the original and new air coolers. Both coolers were designed with excess surface area enabling the coolers to work well for long periods under dirt conditions. The effectiveness values for both cooler designs were in good agreement with those obtained by the related previous research works at the same flow condition. The maximum and minimum values of the actual fouling factor for both coolers give representative average values for the original cooler twice those representative average values for the new cooler. Also, the malfunction of some original coolers was equivalent to the reduction in the heat transfer area. The hot air temperatures showed good uniformity indicating good flow behaviour of the circulating air so that satisfying the normal design temperature range.

[en] This paper presents a mathematical model for agricultural fires based on a multi-phase formulation. The model includes dehydration and pyrolysis of agricultural fuel and pyrolysis products. The model considers a homogeneous distribution of the agricultural solid fuel particles, interacting with the gas flow via source terms. These terms include: drag forces, production of water vapour and pyrolysis products, radiative and convective heat exchange. A multi-phase radiative transfer equation for absorbing-emitting medium is considered to account for the radiative heat exchange between the gas and solid phases of the fire. The main outputs of the present model are most important to study the influence of agricultural fire occurring beneath high voltage transmission lines. The agricultural fire causes a flashover due to the ambient temperature rise and soot accumulation on the insulator of these transmission lines. Numerical results of the present model are obtained for flat grassland fires to study the effects of wind velocity, solid fuel moisture content and ignition length on some selected fire outputs. These outputs include the temperature, velocity, soot volume fraction fields of the gas phase, together with fire propagation rate and flame geometry. The numerical results are compared to the available experimental work in the literature. -- Research highlights: → The model is sensitive to the initial condition of the ignition length affecting the fire propagation rate and width. → The model predicts the effects of both the wind velocity and the fuel moisture content on fire propagation rate, in agreement with the available experimental work in the literature. → The model shows that both the wind velocity and the fuel moisture content are important factors affecting the fire plume thickness, location, and inclination. → The model is able to visualize the flame geometry through tracing radiative heat rates exceeding a threshold value for flame visibility (60 kW/m³). → The model predicts large volume fractions of soot particles liable to accumulate on structural elements facing the fire.