Analysis of the deposition rate in cooled and uncooled turbine cascades indicates that the temperature difference between the cooled wall and the hot working gas significantly increases the deposited fraction of the solid material, i.e., the “catch efficiency.” Data from residual oil-burning turbines show that a 300°C (572°F) temperature difference between gas and wall can cause a fifteenfold increase in deposition rate as compared with the case of the adiabatic cascade. It is proposed that the increase is due to the phenomenon called thermophoresis: Small particles moving toward colder regions under the influence of a thermal gradient in the continuum surrounding them. An approximate method of calculation is presented which is based on the Einstein/Epstein formula for thermophoresis and simplified cascade considerations; results are compared with laboratory and field data.

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