2009 Volume 10 Issue 3 Pages 163-173
A heating system using superheated steam (SHS) in combination with a spray of hot water micro droplets (WMD) has been developed to prevent drying of food material during SHS heating. In the SHS＋WMD system, a mixture of SHS (115℃) and WMD is generated by throttling boiling water and steam (120 to 140℃) with a nozzle. If the moisture content of food material can be controlled through regulation of the SHS/WMD ratio, the combination system is expected to provide flexible application of SHS for food processing. In this study, methods for measuring and regulating the ratio of SHS and WMD in the nozzle jet were investigated. It was found that the SHS/WMD ratio could be easily determined from the difference between the water uptake rate of the system and the theoretical steam flow rate through the nozzle (derived from the internal pressure of the nozzle). The WMD ratio increased as the nozzle internal pressure increased; by decreasing the nozzle throat diameter or by increasing the water uptake rate. SHS＋WMD was generated when the nozzle internal pressure was greater than 0.188 MPa and the steam velocity at the nozzle throat was sonic, regardless of the nozzle throat diameter.
