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CHT-08: MODELLING OF THE ELECTRO-THERMAL BEHAVIOUR OF CURRENT PASSAGE TUBES IN CONDUCTIVE POLYMER COMPOSITE

DOI: 10.1615/ICHMT.2008.CHT.830
12 pages

Jean Pierre Ploteau
GE44 - LRTI / CRTT - BP 406 - 44602 Saint-Nazaire cedex - France

Patrick Glouannec
LET2E, Université de Bretagne Sud, Lorient, France

Herve Noel
LET2E, Université de Bretagne Sud, Lorient, France

Philippe Chauvelon
LET2E, Université de Bretagne Sud, Lorient, France

Jean Francois Feller
LET2E, Université de Bretagne Sud, Lorient, France

Abstract

This paper aims at presenting the conception of Current Passage tubes "CPT" in Conductive Polymer Composites. These materials (CPC) result from the association of an insulating polymer matrix with electrical conductive fillers (carbon black, carbon fibres and metal particles). For heating applications, the optimisation of electrical properties is only one part of the problem. The crossing of direct electric current through the charged polymer induces internal power dissipation by Joule effect, which may result in important temperature gradients in the material.
To help optimise the design of tube heaters (geometry, exchange with water and/or air) two different axis-symmetric, T(r,z) finite element models are developed with COMSOL®.
To look at the induced phenomena, a first model, which represents the electro-thermal behaviour of a current passage tube with only inside water flow is developed. The external surface exchanges by natural convection with the ambient air and by radiation with its environment. An electrical potential difference is applied at the ends of the tube by copper electrodes. The simulations make it possible to visualize, in steady state mode, the temperature and current density fields. They show the incidence of electrical and thermal conductivities. As soon as the density of dissipated power reaches 10 kW.m−2 the temperature gradients in the thickness of the wall are highlighted.
A second model is, then also developed in 2D axis-symmetric, with a water circulation inside and outside the heating tube. The tube in CPC is placed inside a PVC tube and water circulates as in a co current flow exchanger in the 2 tubes. In this new model, the Navier-Stokes equations are coupled with the heat diffusion equation in the annular space between the 2 tubes and in the inner tube. The electrical and thermal equations are still solved in the CPC.
The measurements taken on two different prototypes developed at the laboratory make it possible to validate simulations.

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