Flow Characteristics of Orifice Plate in Vertical Multistage Flash Evaporator for Waste Heat Recovery

Abstract

A vertical multistage flash device uses orifice plates as pressure isolation devices, so wastewater flows from the upper stage to the next stage by its gravity, which can significantly lower the system’s surface area. To study the resistance characteristics of the flash flow during wastewater flowing through the pressure isolation device, a flow and flash model for the wastewater in an orifice was developed and the corresponding flash process was numerically investigated by FLUENT. The effects of the inlet temperature of wastewater, flash pressure, and orifice thickness on the flash were analyzed. The results show that the closer to the orifice outlet we are, the lower the temperature of wastewater and the larger the vapor volume fraction become. While the temperature is lower, the vapor volume fraction is larger near the orifice wall than it is towards the center. While the temperature reduction of wastewater is not immediately apparent, the vapor volume fraction in the orifice increases as the pressure differential between the orifice’s input and output increases.