Based on the energy conservation law

an expression formula for calculating the wetness of flowing wet steam measured by heating method for directly heating two concentric sleeve pipes

which are thermally isolated and electrically insulated from each other

an instrument used for measuring wetness of the flowing wet steam has been designed.In this instrument

both inner and outer pipes of the two concentric sleeve pipes are directly used as electrically heating elements.The inner pipe is used to heat the wet steam sample for converting it into superheated steam;the outer pipe is heated for maintaining the inner pipe-wall and the outer pipe-wall at a same temperature

to realize zero dissipation heat loss in heating the wet steam by using the inner pipe.The wetness of flowing wet steam can be accurately calculated by using the expression formula after measuring and substituting the heat quantity used for heating the flowing wet steam sample by the inner pipe

the pressure of flowing wet steam at inlet of the instrument

as well as pressure and temperature of the superheated steam obtained from the flowing wet steam sample heated by the inner pipe

the pressure of flowing wet steam at inlet of the instrument

as well as pressure and temperature of the superheated steam obtained from the flowing wet steam sample heated by the inner pipe

and the flow rate of flowing wet steam.