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The present work aims at investigating, numerically, the heat transfer characteristics of transformer cooling system under forced circulation for three different winding configurations. The purpose of a transformer cooling system is to keep the hot spot temperature within the critical value for a long life of transformer, which increases with enhanced cooling of transformer windings. Thus, two different winding configurations are modeled by providing space within the windings (an intra-space model) and in between the windings (an inter-space model) to improve the fluid-solid interaction. A conventional winding, without spacing, is also modeled for comparative study. A 315 kVA, 3-phase core type transformer is taken as the base model from which the winding and core specifications are obtained analytically. Parameters chosen to measure the influence of winding configuration are local temperature distribution in the windings and core and maximum transformer temperature. Results are obtained for all three models with varying space for various cooling mediums like naphthenic oil, silicon oil, and synthetic ester oil at flow velocities ranging from 0.72 m/s to 2.16 m/s. It is observed that the gap between the windings, interspacing, decreases the secondary winding temperatures, while it increases the core and primary winding temperatures. However, the intra spacing configuration finds a drop in local temperatures at all locations of the transformer windings and core. The enhanced heat dissipation to the cooling agent, with intra spacing winding configuration, reduces the maximum transformer temperature. Contrasting to the above, the inter-space model has an adverse effect on maximum temperature at all widths of space considered. Quantitatively, the space within the transformer reduces the maximum temperature by 5% in comparison with the space between the windings. The increased velocity of the cooling medium, Naphthenic oil, from 0.72 m/s to 2.16 m/s reduces the maximum temperature by 4.5 units. The study made to know the role of cooling medium discloses that the synthetic ester oil shows better performance for reducing temperature values due to its highly viscous nature. [ABSTRACT FROM AUTHOR]

A heat sink is a thermal management system for electrical and electronic appliances whose performance is a function of fin geometry, arrangement, and flow field. Earlier research addressed the enhancement in the heat dissipation capacity of the sink with a change in the geometry of the fin. However, the change should increase the heat transfer rate per unit weight and per unit volume. One such attempt is made in the present work, which deals with numerical forced convection heat transfer simulation over a pin fin with three different surface modifications, namely, threads, equilateral triangular perforation, and threads with perforations. A numerical investigation is performed for 0.5773–2.5574 mm pitch of threads, 3–4.8 mm size of perforation, and 2–8 m/s velocities of air. To describe the flow pattern around the fin and its variation with surface modification, streamline profiles are drawn which reveals that the fluid–solid interaction is improved either with threaded or perforated surface and is maximum for threaded–perforated fin. The enhanced convection rates bring down the local fin temperature and the maximum fin temperature, where the drop is more for the threaded surface than that of the perforated surface because of turbulence. A 10° drop in maximum fin temperature is achieved by replacing a plain pin fin with a threaded–perforated pin fin, and the drop is 8° with threads alone and 6° only with perforations. The increased fineness of threads and size of perforation further bring down the maximum fin temperature. [ABSTRACT FROM AUTHOR]