NOVELTY - Fuel cell system (300) comprises: first airflow generator (310) and fuel cell module (320) having air inlets and outlets for airflow from generator to fuel cell module; second airflow generator (330) and fuel cell module (340) having air inlets and outlets for airflow from generator to fuel cell module; and two heat exchanges between first airflow departing from first fuel cell module and second airflow prior to entering second fuel cell module, and between second airflow departing from second fuel cell module and first airflow prior to entering first fuel cell module, respectively.    USE - As a fuel cell system (claimed), useful as a battery.    ADVANTAGE - In fuel cell system, heat exchange is proceeded between first airflow departing from first fuel cell module and second airflow prior to entering second fuel cell module i.e. heat is transferred from first airflow with higher temperature departing from first fuel cell module to second airflow with lower temperature prior to entering second fuel cell module to achieve heat recovery; and another heat exchange is proceeded between second airflow departing from second fuel cell module and first airflow prior to entering the first fuel cell module i.e. heat is transferred from second airflow with higher temperature departing from second fuel cell module to first airflow with lower temperature prior to entering the first fuel cell module to achieve heat recovery. Thus, temperature of first airflow prior to entering first fuel cell module and temperature of second airflow prior to entering second fuel cell module can be promoted. Hence, when first and second airflows respectively flow through first fuel cell module and second fuel cell module, reaction rates of the first and second fuel cell modules are effectively increased; as compared to prior art fuel cell system, in which first airflow and second airflow respectively lower temperatures of reactions in first and second fuel cell modules, such that reaction rates of first fuel cell module and second fuel cell module are reduced. Also in fuel cell, due to presence of heat exchanges, a part of moisture in first airflow departing from first fuel cell module and a part of moisture in second airflow departing from second fuel cell module condense into liquid water, and results in water recovery.    DETAILED DESCRIPTION - A fuel cell system (300) comprises: a first airflow generator (310) that provides first airflow (312) and has first air inlet (314) and first air outlet (316); a first fuel cell module (320) having second air inlet (322) and second air outlet (324), where first airflow sequentially flows through first air inlet, inside of first airflow generator, first air outlet, second air inlet, inside of first fuel cell module and second air outlet; a second airflow generator (330) that provides second airflow (332) and has third air inlet (334) and third air outlet (336); and a second fuel cell module (340) having fourth air inlet (342) and fourth air outlet (344), where second airflow sequentially flows through third air inlet, inside of second airflow generator, third air outlet, fourth air inlet, inside of second fuel cell module and fourth air outlet; and a heat exchange proceeded between first airflow departing from first fuel cell module and second airflow prior to entering second fuel cell module, and another heat exchange proceeded between second airflow departing from second fuel cell module and first airflow prior to entering first fuel cell module. The fuel cell system further comprises a first air duct, where two ends of first air duct are respectively adjacent to first air outlet and second air inlet, and first airflow prior to entering first fuel cell module flows through first air duct; a second air duct adjacent to second air outlet, where first airflow departing from first fuel cell module flows through second air duct; a third air duct, where two ends of third air duct are respectively adjacent to third air outlet and fourth air inlet, and second airflow prior to entering second fuel cell module flows through third air duct; and a fourth air duct, adjacent to the fourth air outlet, where second airflow departing from second fuel cell module flows through fourth air duct. The first air duct connects first air outlet and second air inlet, second air duct connects second air outlet, third air duct connects third air outlet and fourth air inlet, and fourth air duct connects fourth air outlet. The second air duct is thermally coupled to third air duct and first air duct is thermally coupled to fourth air duct. The fuel cell system further comprises at least a first heat conduction element, thermally coupled to first air duct and fourth air duct, and at least a second heat conduction element, thermally coupled to second air duct and third air duct. An end of first heat conduction element passes through pipe wall of first air duct and extends into first air duct, another end of first heat conduction element passes through pipe wall of fourth air duct and extends into fourth air duct; and an end of the second heat conduction element passes through pipe wall of second air duct and extends into second air duct, and another end of second heat conduction element passes through pipe wall of third air duct and extends into third air duct. The heat exchange is present between first airflow prior to entering first airflow generator and fourth air duct; and other heat exchange is present between second airflow prior to entering second airflow generator and second air duct. The fuel cell system further comprises a first air-guiding casing, adjacent to second air inlet and fourth air outlet and comprises first heat conduction baffle, where first heat conduction baffle partitions off first flow way and second flow way in first air-guiding casing, in which first airflow passes through first flow way and enters first fuel cell module, and second airflow departing from second fuel cell module passes through second flow way; and a second air-guiding casing, adjacent to fourth air inlet and second air outlet and having second heat conduction baffle, where second heat conduction baffle partitions off third flow way and fourth flow way in second air-guiding casing, in which second airflow passes through third flow way and enters second fuel cell module, and first airflow departing from first fuel cell module passes through fourth flow way.    DESCRIPTION OF DRAWING(S) - The figure shows top view of fuel cell system.    Fuel cell system (300)    First airflow generator (310)    First airflow (312)    First air inlet (314)    First air outlet (316)    First fuel cell module (320)    Second air inlet (322)    Second air outlet (324)    Second airflow generator (330)    Second airflow (332)    Third air inlet (334)    Third air outlet (336)    Second fuel cell module (340)    Fourth air inlet (342)    Fourth air outlet (344)