A flash boiler has a water jacket and a vertically oriented interior passage which includes water tubes or superheating tubes, or both. The interior passage is a hyperboloid surface to induce draft. Water tubes and superheating tubes can be staggered so as to create a helical path for flue gas passing through the boiler. Water tubes and superheating tubes may include, internally or externally or both, heat transfer aids such as pins, fins or vanes, which may also be helicies.

An evaporator with integrated heat recovery incorporates a vapor tube in a combustion chamber surrounded by a water jacket. The water jacket is in fluid communication with an exhaust gas heat exchanger. Coolant circulates through the exhaust gas heat exchanger to recover heat from exhaust gasses leaving the combustion chamber and then circulates through the water jacket surrounding the combustion chamber to recover heat not delivered to the operating fluid. The evaporator may incorporate a condenser within the housing and in fluid communication with the exhaust gas heat exchanger and water jacket. Coolant may enter the evaporator housing at the condenser before circulating through the exhaust gas heat exchanger and water jacket.

The present invention provides a portable battery steam cleaner comprising in combination of a hollow main body, in which a water tank, peristaltic pump, control system and lithium battery; the water tank in connection with the input of the peristaltic pump; the output of the peristaltic pump in connection with one end of silicone hose; and the other end of silicone hose in connection with the steam generator. The present invention can continuously transport liquid from the water tank, through the silicone hose, into the steam generator, and thus eject steam continuously for cleaning purposes.