Hydrogen-air heat exchanger (HEX) and condensor in the engines with air precooling amount to, by various estimations, (in different schemes) 20-40% of total engine mass. The influence of some heat transfer increase methods on cooler mass and size is discussed.Atmospheric air cooling may result in frost formation on cooled surfaces and heat exchanger characteristics deterioration. The location of probable frost formation zones in different conditions may be determined by using two- dimensional mathematical model of heat exchanger.The model experimental study of frost formation was carried out. The quantitative parameters of this process are discussed. It was found that both reduction and increase of heat transfer may be obtained according to flow regime.Significant instability of flow with air condensation accompanied by large pressure pulsations was obtained. Methods to prevent the phenomenon are under study. The influence of two-phase flow structure on heat transfer characteristics is discussed.