tailieunhanh - Environmental Fluid Mechanics - Chapter 10

Các lĩnh vực cơ học chất lỏng môi trường kéo dài một loạt các chủ đề. Mặc dù chủ yếu dựa trên cơ học chất lỏng thủy lực khái niệm, như mô tả trong phần 1 của văn bản này, khu vực đã phát triển trong vài thập kỷ qua bao gồm nhiều ứng dụng trong mô hình chất lượng nước. Một kết nối quan trọng giữa các lĩnh vực này sau và cơ học chất lỏng tinh khiết nằm ở việc xác định điều kiện cần thiết để xác định việc vận chuyển và tỷ lệ pha trộn cho. | 10 Environmental Transport Processes INTRODUCTION The field of environmental fluid mechanics spans a broad range of topics. Though based primarily on fluid mechanics and hydraulics concepts as described in Part 1 of this text the area has grown in the past few decades to encompass many applications in water quality modeling. A major connection between this latter field and pure fluid mechanics lies in the determination of terms needed to specify the transport and mixing rates for a given parameter of interest. This will be seen in the present chapter in which the classic advection-diffusion equation is derived to express a mass balance statement for a dissolved chemical species distributed in a fluid flow field. In later chapters this idea is expanded to include transport of suspended sediment particles and several important classes of environmental flows are discussed. Typical parameters of interest might include concentrations of dissolved gases particularly oxygen nutrients such as phosphorus or nitrogen various chemical contaminants both organic and inorganic salinity suspended solids temperature biological species and others. In order to fully describe the fate and transport of a particular species a knowledge of specific source and sink terms including interactions with other species must be incorporated in the general conservation equation. The present text with several exceptions generally does not deal directly with these terms but rather concentrates on the physical transport mechanisms. Water Heat and Solute Transport Earlier we saw that certain quantities control the rate at which different properties of a flow are transported either by mean motions or by diffusion. For example kinematic viscosity may be thought of as a molecular diffusivity for momentum. Thermal diffusivity represents a similar transport term for heat energy and solute diffusivity represents a corresponding transport mechanism Copyright 2001 by Marcel Dekker Inc. All Rights