Water-Air Aerosol Cooling of Cylindrical Element Rows in a Rectangular Channel

The development of both thermal and nuclear energy in the 21st century has led to a significant increase in water resources demand for removal of low-grade heat into the environment from power plants operating on the Rankine thermodynamic cycle. The evaporative systems (cooling towers, spray basins) form the basis of modern technologies for cooling condensers of steam turbines. Water that evaporates in a significant volume requires constant replenishment from water sources available on the territory, and water vapor forms in the zone where the power plants are located, increased atmospheric humidity and creates an additional condition for the occurrence of a “greenhouse effect”. The development of cooling technologies with low water consumption is one of the important tasks of modern energy.

The paper performs the experimental investigations of heat transfer from cylindrical elements in a staggered arrangement inside a rectangular channel with a fine water aerosol. We have obtained the heat transfer coefficients depending on the Reynolds number and the degree of flow moistening for each row of cylinders. A physical model is proposed for the flow around the surface of cylindrical elements that contains water aerosol particles. This model makes it possible to evaluate their deposition on a heated surface. We have estimated the relative mass of droplet moisture deposited on the cylinder's surface depending on the irrigation density for rows 1, 2 and 3 and obtained a criterion equation that generalizes the experimental data in the form of Nusselt number, operating parameters (Reynolds and Weber numbers), and the position of the elements in the channel. Micro-droplet humidification of the airflow is shown to make it possible to increase the heat transfer efficiency by 1.5–3.5 times. The greatest increase in efficiency occurs in the first two rows of cylindrical elements, which requires the construction of a heat exchanger with a low number of rows, or an additional micro-droplet intermediate water inlet in front of subsequent rows in the direction of airflow.

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