Mechanism of the rapid generation of superheated and saturated steam using a water-containing porous material

Superheated steam (SHS) is employed in various fields for everyday activities and industrial production, e.g., drying, cleaning, and reaction engineering. Although a facile method for realizing rapid SHS and saturated steam generation from water-containing porous materials has been proposed, with a second order start-up/cut-off response time and high energy utilization efficiency, the mechanism of this rapid SHS generation has not been clarified despite the proposition of a two-step process, including heating-based evaporation beneath the wire heater and reheating in the flow path. In this study, further experiments were conducted to separately consider both heating processes. The steam temperature directly beneath the wire heater correlated well with the film temperature, which is equal to the average temperature of the wire heater and the saturation temperature of the surface of the porous material. The measurement results of the temperature distribution inside the porous material block as well as the results of the electrical resistance directly beneath the wire heater revealed that no dry-out area was formed directly beneath the wire heater during SHS generation. Further, the three-dimensional laser scanning results revealed significant roughness on the surface of the porous material. The narrow gap, which was formed between the wire heater and the surface of the porous material, was critical to SHS generation, and the detailed mechanism was presented.