Validation of computational fluid dynamic analysis of natural convection conditions for a resin dry-type transformer with a cabin

Many industrial products work under different constraints. Examples of these products include transformers and keeping them in certain operating temperatures is an important design constraint. However, since power transformers have different requirements, there are no standard products. For this reason, it is difficult and costly to test each one by considering these constraints and to design them accordingly. Satisfactory thermal analysis using a 3-D finite volume-based CFD model is an important step to understand natural convection and necessary design modifications under the desired conditions. The aim of this study is to verify the performance and reliability of the design by comparing the experimental results with 3-D finite volume analysis results by considering cooling of a dry resin type transformer with a cabin. The effect of the cabin on the product in terms of natural heat convection is also evaluate

Numerical Investigation of Various Approaches to Avoid Natural Convection Instabilities Inside the Channels of Horizontal Plate Fin Heat Sinks

In case of natural heat convection from a horizontal plate fin heat sink, heat transfer rates highly depend on the geometric parameters. It is observed that if the fin height is very low, fresh cooler air may not be able to reach middle parts of the heat sink causing an ineffective use of the extended heat transfer area. Using a validated numerical model of an underperforming heat sink, various ways of improving heat sink geometry has been investigated. The tried approaches include leaving gaps in the length of the fins in different patterns, adding two different shape pin fins in the channels between the plate fins and raising the height of the fins on the edges. The last approach is shown to be effective in improving heat transfer by blocking the side flows over the heat sink. By numerical simulations, causes of the unwanted in-channel longitudinal vortices were also investigated in detail with the help of powerful flow visualization capability of Computational Fluid Dynamics.

Development of a Conjugate Heat Transfer Simulation Methodology for Prediction of Steam Turbine Cool-Down Phenomena and Shell Deflection

Shell deflection during shutdown, cool-down process is a phenomenon well known to the steam turbine community. The main reason for this phenomenon is slower cooling of the top half shell and a relative faster cooling of the bottom half shell. There are multiple reasons for such thermal behavior of the two half casings, including natural heat convection from the bottom half to the top half, asymmetrical distribution of mass, dissimilar behavior of thermal insulation over the top and the bottom halves, etc. Shell deflection poses considerable challenge to the clearance engineer in terms of configuring operating clearance which ensures rub free operations. Understanding the cool-down process for the rotor is also equally important as the allowable steam inlet temperature during the hot or warm restart will depend on prevailing local temperature of the rotor. This paper describes an exemplary physics-based cool-down prediction methodology capable of accurately capturing the rotor cool-down process. The methodology involves development of a full 3D rotor casing thermal model, integrated conjugate heat transfer FE model and validated with measured field data.

Natural Heat Convection Analysis on Cylindrical Al Slug of LED

This paper presents the characterization of a single chip high power LED package through simulation. Ansys version 11 was used for the simulation. The characterization of the LED package with aluminum cylindrical heat slug was carried out under natural convection condition at ambient temperature of 25°C. The junction temperature and the stress of the LED chip was assesed. The LED chip was powered with input power of 0.1 W and 1 W and the heat dissipation was assesed. Results showed that that the junction temperature and the Von Mises Stress of the single chip LED package increases with the increased input power.

OPTIMASI RONGGA TERHADAP VARIASI DERAJAT KEVAKUMAN SEBAGAI ISOLATOR

In the world of industry, insulation materials are often utilized to maintain the temperature,either low or high. However, since the insulation materials often need to be thick, thus,costly, they are frequently deemed impractical. Therefore, in the attempt to replace the insulationmaterials, a cavity with low vacuum pressure is opted for. Yet, to attain a total (100%) airfreecavity is not an easy task. Such, the cavity usually still bears some amount of air pressurewhich results in natural heat convection through the two surfaces making up the cavity. Thetransfer coefficient of natural heat convection (h) is influenced by some factors, such as, the temperaturedifference, geometry of the cavity, cavity orientation, and characteristics of the fluid,for instance, its pressure, temperature, conductivity, specific gravity (density), and viscosity.The purpose of the study is to find answers to the following question: “How do vacuum pressurevariation and cavity ratio affect the rate of natural heat convection through the a cavity?” Pertinentto the question, the study was aimed to find the appropriate value of the vacuum pressurewhich can function well as an insulator. This study is significant in the attempt to lower downthe rate of heat transfer taking place in a system vis-à-vis the surrounding media. The studyfound out that the degree of emptiness of -60 cm Hg and =5.96, results in a lower rate of heattransfer compared with -20 cm Hg and -40 cm Hg. This means that the vacuum pressure of-60cm Hg bears a bigger thermal resistance than the -20 cm Hg and -40 cm Hg do.