Abstract

Effluent transport is an important issue in ocean engineering and impact from effluent greatly affects the ocean environment. This study discusses two situations: thermal effluent discharged from pipes with and without diffusers. With different diffusers, the process of dispersion is observed to analyze the relation between discharging jet and diffusers.

A three-dimensional computational fluid dynamics model, FLOW-3D, is used, which solves Navier-Stokes type equations embedded with turbulence closure models. RNG model is utilized to solve turbulence calculation. Heat transfer is also used for the spreading of thermal plume. Distribution of temperatures, which is difficult to measure in the field, has been calculated and investigated clearly in this study.

The interactions among effluents, sea water, and diffusers are discussed, investigated, and summarized. These effects are vital for further prediction and applications in the engineering field. Diffuser with a 45° incline is the best choice for cooling the thermal jet under the same distance and the pipes are expected to discharge directly without any diffuser attached for the lowest excess temperatures at sea surface. With proper prediction of the dispersion of thermal plume, the conservancy of the environment is expected to be improved.

INTRODUCTION

Most coal-fired power plants are sited in coastal regions and their heated waters are discharged into coastal waters. Water used in the power plant for cooling purposes is released as thermal effluent at a slightly elevated temperature level to the nearby environment. The impact of warm water emission from these power plants is an issue of concern for environmental protection. The heated waters from the power plants have caused many environmental problems due to the increase of surrounding water temperatures in coastal waters.

Consequently, it is very important to predict the behavior of thermal plume and analyze its impacts on the environment. According to previous studies, the effects of thermal water on sea water corresponds with many factors. Tang et al. (2003) found that thermal discharge had the greatest impact on sea surface temperature in summer and the smallest impact during winter. Zhu (2014) believed that the vertical temperature difference of seawater during the neap tide period was higher than that of spring tide period. Faming Huang et al. (2019) summarized the dispersion of thermal plume under tidal current, finding that thermal discharge influenced areas within 3 km from the outlet and the thermocline caused by thermal discharge mostly occurred in areas between the sea surface to 7 meters in depth.

This content is only available via PDF.
You can access this article if you purchase or spend a download.