A miniature vaporizer for effectively vaporizing a process fluid (e.g., a liquid media) in small energy system applications, such as systems employing chemical reformers and fuel cells. The vaporizer of the present invention can employ a heating medium, such as a hot exhaust generated by a power system, as the heating source for generating steam or for evaporating a fluid (e.g., liquid chemicals or fuels). The vaporizer of the invention can optionally be configured to vaporize water thereby functioning as a miniature steam generator, to evaporate a process fluid thereby functioning as a miniature evaporator or heat exchanger, or to evaporate a process fluid and mix the fluid with another medium. This evaporator/mixer configuration can be used in reformer plants where a liquid chemical or fuel (e.g., gasoline, diesel, methanol, etc.) needs to be first evaporated and mixed with steam prior to the introduction of the resultant mixture to a converter (e.g., reformor or fuel cell).