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International Heat Transfer Conference 8

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

CONJUGATED HEAT TRANSFER IN DISC-TYPE POWER TRANSFORMER WINDINGS

P. H. G. Allen
School of Engineering Systems and Design, South Bank University, London, SE1 OAA, UK; The City University, London, EC1V OHB, England

E. P. Childs
Consultant, The Community, Little Gidding, Huntingdon PE17 5RJ, England

Abstract

The temperature distribution in a facsimile 16 disc winding configured in two passes of eight ducts each is analysed using a FORTRAN program DISCNET. Predictions agree well with measurements of winding temperatures and of distribution of flow between the ducts. Low duct Reynolds numbers (20−200) and high Prandtl number oil (80−400) combine to yield Peclet numbers sufficiently high for neglect of heat diffusion along the duct axis. However, in the discs (wound spirally from a continuous kraft paper insulated copper conductor), substantial diffusion parallel to the ducts occurs, leading to a skewed duct wall heat flux distribution. The duct length is well within the thermal entrance region, while exceeding the hydrodynamic entrance length; nonetheless, the flow-never becomes fully developed because of variable viscosity. The combination and interaction of these effects require that solid and liquid domains be solved simultaneously. Finite difference methods for heat conduction in the discs are combined with TEACH-L algorithms for the duct flow.

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