制冷技术(英文版)Ch.docVIP

Chapter 11 Condensing Equipment 11-1) Function and Classification of Condensers Function of Condensers The heat-transfer process in a condenser occurs in three stages as implicated in Fig.11-1. 1. Desuperheating of the hot vapor. 2. Condensing of the vapor to liquid state and release of the latent heat. 3. Subcooling of the liquid refrigerant. Fig.11-1, The state and temperature variation inside a condenser Classification of Condensers Fig.11-2 Classification of condensers [1] 11-2) Water-Cooled Condensers Types of water-cooled condensers can be classified according to their construction (Fig.11-2). Each has features that make it suitable for certain application. (1) Double-pipe condenser Fig.11-3, Double-pipe water-cooled condenser Fig.11-4 Circular and trombone double-tube condenser [11] Fig.11-5 Double pipe condenser with cleanable tubes (2) Shell-and-coil condenser 壳盘管冷凝器 Fig.11-6 Shell-and-coil condenser (vertical type) [1] (3) Shell-and-tube condenser壳管冷凝器 The shell-and-tube condenser consists of a cylindrical metal shell and a number of straight tubes which are arranged in parallel and held in place at the ends by tube sheets. There are two main types of shell-and-tube condensers: horizontal and vertical. a) Horizontal shell-and-tube condenser Fig.11-7 Two-pass shell and tube condenser b) Vertical shell-and-tube condensers Fig.11-10 Vertical shell-and-tube condenser (4) Heat transfer in water cooled condenser The following equation is used to calculate heat transfer in water cooled condenser. (11-1) where : Heat transfer rate, kW. : overall heat transfer coefficient, kW/m2 K : Heat transfer area, m2 : mean effective temperature difference (METD), K The overall heat transfer coefficient: (11-2) where : thermal resistance in refrigerant side : thermal resistance of tube wall : thermal resistance of water fouling : thermal resistance in water side : rati