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Standard Methods for Examination of Water & Wastewater_8

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Chuyển khối lượng giữa các giai đoạn được gọi là khối lượng chuyển. Ví dụ về các hoạt động đơn vị thể hiện các khái niệm về chuyển khối lượng là chưng cất, hấp thụ, ẩm, khai thác chất lỏng, lọc, và kết tinh. Chưng cất là một hoạt động đơn vị tách ra bởi hỗn hợp chất lỏng bay hơi của các chất dễ bay hơi và thể trộn lẫn vào các thành phần cá nhân hoặc các nhóm của các thành phần. . | 9 Aeration Absorption and Stripping Aeration absorption and stripping are unit operations that rely on flow of masses between phases. When a difference in concentration exists between two points in a body of mass a flow of mass occurs between the points. When the flow occurs between two phases of masses a transfer of mass between the phases is said to occur. This transfer of mass between phases is called mass transfer. Examples of unit operations that embody the concept of mass transfer are distillation absorption dehumidification liquid extraction leaching and crystallization. Distillation is a unit operation that separates by vaporization liquid mixtures of miscible and volatile substances into individual components or groups of components. The separation of water and alcohol into the respective components of liquid air into nitrogen oxygen and argon and the separation of crude petroleum into gasoline oil and kerosene are examples of the distillation unit operation. Absorption is a unit operation that removes a solute mass or masses from a gas phase into a liquid phase. Aeration of water dissolves air into it thus aeration is absorption. Another example of absorption is the washing of ammonia from an ammonia-polluted air. In this operation ammonia is removed from the air by its dissolution into the water. The reverse flow of masses from the liquid phase into the gas phase is called stripping. In stripping the solute molecule is removed from its solution with the liquid into the gas phase. Dehumidification is the removal of a solute liquid vapor from a gas phase by the solute condensing into its liquid phase. The removal of water vapor in air by condensation on a cold surface is dehumidification. The reverse of dehumidification is humidification. In this unit operation the flow of the solute is from the liquid phase evaporating into the gas phase. The end result of this movement is saturation of the gas. For example during heavy rains the atmosphere may become .