PURPOSE: To achieve a marked improvement in thermal conductivity, good resistance to chemicals, and other useful effects by passing saturated steam, etc., through a tubular vessel consisting of sintered silicon carbide which forms an aggregation of pores of less than a specific size to heat a corrosive liquid through the pores.

CONSTITUTION: Inside a tank 1 which holds a corrosive liquid 4 such as an acid a tubular vessel 2 is placed, which consists of sintered silicon carbide forming an aggregation of numerous pores 5 of less than 10μm and whose surface appears black. By passing a stream of saturated steam or hot air through the inside of the tubular vessel 2 the corrosive liquid 4 inside the tank 1 is heated through the pores 5. Since the whole of the tubular vessel 2 is made up of numerous projections and depressions formed by numerous pores 5, the area for heat exchange is enlarged and the heat load density is multiplied. Therefore, the synergy of this effect with the excellent thermal conductivity of silicon carbide itself enables efficiently heating the corrosive liquid 4 in the tank 1.