Heat exchanger

摘要

In making a carbon heat-exchanger block such as that described in the parent Specification by assembling grooved carbon plates in a pile, impregnating them with a liquid synthetic or natural resin, and curing the resin, the plates during curing are held together between opposed clamping plates at a pressure sufficient to overcome the tensile stress which would otherwise be set up in the carbon by the pressure of the heat-exchange fluid in the passages in the block when the heat exchanger is in use and to maintain the cemented joints between the plates tight and free from leaks. The assembled carbon plates, lightly clamped between the clamping plates, are first subjected to a vacuum for an hour and then immersed in the liquid resin, to which air pressure of 100 lb. per square inch is applied for 2 hours. The air pressure is released gradually, the body removed and allowed to drain, and the pressure applied by the clamping plates raised to 400-500 lb. per square inch. The resin may be cashew-nut shell resin containing 10 per cent diethyl sulphate as a polymerization catalyst. To reduce its viscosity and facilitate impregnation, it is heated to 70 DEG C. just before use. It is cured by heating the impregnated block in an oven at 80 DEG C. for 24 hours, with cooling at 120 DEG C. for a further 24 hours, and finally heating at 150 DEG C. for another 24 hours. Alternatively, the resin may be made by heating a mixture of equal parts by weight of furfural and furfuryl alcohol with between 0.1 and 0.2 per cent by weight of normal solution of sulphuric acid, neutralizing the mixture with normal caustic-soda solution, cooling it, heating it under reduced pressure to remove water of condensation, and acidifying it with between 0.1 and 0.2 per cent of normal solution of sulphuric acid. It is cured by heating in an oven for 9 hours at 80 DEG C. and for a further three hours at 150 DEG C. Specifications 595,759 and 595,760, [both in Group V], are referred to in the Provisional Specification.