Oleum (98% concentrated is diluted with water for the production of superphosphate fertilizers. Cooling of the diluted acid is carried out in a heat exchanger made of gra-phite. Experimental models of heat exchangers simulating an industrial one were prepared from metallized graphite by imp-regnating synthetic graphite blocks with molten lead , copper and polytetraflouroethylene (PTFE). The effectiveness of these samples were investigated. Results obtained show that in a cross-flow heat exchanger , the effectiveness increases with the increase in the heat transfer surface area , the density of the graphite material and the flow velocity of the coolant. The properties of the imp-regnants such as the specific gravity , thermal conductivity mass up-take and chemical stability determine the feasibility of the impregnant.