The purpose of this paper is to study the effects of using paint as a protection against corrosion on external surfaces of fin-tubed thermosyphon economizers. The thermosyphons used in the experiment were made of steel tubes with steel fins, aluminium tubes with aluminium fins and copper tubes with aluminium fins. All tubes had an outside diameter of 21.7 mm 19.05 mm and 19.18 mm respectively and were 630 mm in length with 10 mm high fins. The length of the evaporator section was 10 mm and the condenser section was 200 mm. The tubes were grouped into four sets. Each set consisted of uncoated and coated steel thermosyphons, uncoated and coated copper thermosyphons, uncoated and coated aluminium thermosyphons. Three different thicknesses of paint were employed on the evaporator section. The coated sample pieces, made of the same material as the tubes, were attached to both sides of each thermosyphon

the side facing the gas flow and the lee side, in order to test the flow direction. The test was conducted using exhaust gas burned at 225 oC using a mixture of grade A heavy fuel and 20% diesel. The experiment was conducted over 16 hours per day for a total of 1,000 hours. Heat transfer temperatures were analyzed

the temperature of the economizer was taken, along with corrosion and fouling levels on the thermosyphon at 250, 500, 750 and 1,000 hours. All the data on corrosion was obtained from 25 times extended photos taken by an optical microscope. Inorganic and organic compounds in the fouling were analyzed by an X-ray defractometer and an Infrared spectroscope. Fouling thickness was obtained by measuring the surface of the thermosyphon and the average rate of fouling was calculated from the increased weight of the samples. Fouling resistance was calculated from the changes in temperature of the economizer caused by fouling . Economic viability was calculated from the total expenditure of components used. It was found that neither the placement of the facings nor the thickness of paint affected the corrosion, the fouling thickness or the average rate of fouling. At the completion of the experiment, the corrosion of the coated black steel thermosyphon, the coated copper thermosyphon and the coated aluminium thermosyphon was less than the uncoated thermosyphon by 2x, 1.5x and 1.5x respectively. The inorganic compound that was found in the fouling on the thermosyphons surface was CaSO4, which came from fuel combustion. However, no organic compound was found in this investigation. Thus fouling on the thermosyphons surface did not originate from the material used in the tubes production, the coating or the operating time. The corrosion and the average rate of fouling in terms of time was Cr = Atm and RWfouling = Btn where A and B were constants, m the positive slope and n the negative slope which varied according to the material used in the tubes production and coating. The correlation between fouling thickness and time of the steel thermosyphons (with steel fins) , aluminium thermosyphons (with aluminium fins) and copper thermosyphons (with aluminium fins) was Rfouling = 42.2386(1-e-0.0012t), Rfouling = 36.6862(1-e-0.0019t) and Rfouling = 15.873(1-e-0.0063t), respectively. The equation for fouling resistance and time was Zfouling = 1.O38(1-e-0.0034t). It can be concluded that tubes used in thermosyphons at temperatures between 150 and 2500C should be made of 0.3 mm steel.