WALL RESISTANCE IN GRAPHITE-BLOCK HEAT-EXCHANGERS

Accurate data have been obtained on the thermal conductivity of sir gr ades of manufactured graphite. In particular, the effect of orientatio n, manufacturing process, and impregnant content on the thermal conduc tivity was investigated Using the thermal conductivity data, a three-d imensional finite-element model has been set up to determine the wall resistance of a particular graphite block. The effect of the anisotrop y of the extruded graphite on the wall resistance was investigated It was found that the anisotropy can be neglected if the wall resistance is calculated by assuming that the blocks have an isotropic thermal co nductivity equal to the thermal conductivity perpendicular to the dire ction of extrusion. Also the phenol formaldehyde film on the surface o f the heat exchanger channels was determined to have a significant the rmal resistance. It was calculated that, for typical operating film co efficients with water on both sides, the overall heat transfer coeffic ient can be expected to increase by more than 50% if the resin layer i s removed.