Application of magnified digital in-line holography (MDIH) to the measurement of the evaporation process of desulfurization wastewater droplets in a high-temperature gas flow

Abstract A magnified digital in-line holography was applied to measure the evaporation process of deionized water droplets and desulfurization wastewater droplets in the temperature range of 298–423 K. A quartz-glass evaporation chamber was designed to conduct experiments. The total length in the measurement zone was 450 mm. The droplets were generated by a piezoelectric jetting device (Microfab Inc., Plano, Texas, USA). The nozzle (MJ-AT-01-50) consisted of lead zirconate titanate piezoelectric ceramic (PZT) material and a glass capillary with a 50 μm orifice diameter. The relationships between the evaporation process and operating conditions, such as temperature, the concentration of desulfurization wastewater, added solutes, and velocity of carrier gas, were discussed. The evaporation rates of deionized water at 298 K, 323 K, 373 K, and 423 K were 0.1156 µm2/ms, 0.3398 m2/ms, 0.5204 m2/ms, 0.6381 µm2/ms, respectively. The evaporation rates of desulfurization wastewater at 298 K, 323 K, 373 K, and 423 K were 0.05201 µm2/ms, 0.1673 µm2/ms, 0.2912 µm2/ms, 0.3606 µm2/ms, respectively. The evaporation rate of deionized water is approximately twice that of desulfurization wastewater. The progress hereby presented enables us to study the evaporation of droplets in three aspects: First, the evaporation process of a monodisperse droplet stream injected into a high-temperature gas flow can be investigated. Second, the equivalent pixel was calculated to be 2.4299 µm/pixel and the magnification factor was 5.76. Third, factors affecting the evaporation rate of desulfurization wastewater are investigated. The data are valuable for achieving zero discharge of wastewater and optimizing operating conditions.