化学 化工专业 毕业设计论文 冷却塔 外文 英文 文献 翻译.docx

1、外文资料Cooling TowersIf a chiller is used to provide chilled water for building air conditioning, then the heat energy that is absorbed through that process must be rejected. The two most common ways to reject thermal energy from the vapor compression process are either directly to the air or through a

2、 cooling tower. In a cooling tower, water is recirculated and evaporatively cooled through direct contact heat transfer with the ambient air. This cooled water can then be used to absorb and reject the thermal energy from the condenser of the chiller. The most common cooling tower used for HVAC appl

3、ications is the mechanical draft cooling tower (Figure 4.2.13). The mechanical draft tower uses one or more fans to force air through the tower, a heat transfer media or fill that brings the recirculated water into contact with the air, a water basin (sump) to collect the recirculated water, and a w

4、ater distribution system to ensure even dispersal of the water into the tower fill.Figure 4.2.14 shows the relationship between the recirculating water and air as they interact in a counterflow cooling tower. The evaporative cooling process involves simultaneous heat and mass transfer as the water c

5、omes into contact with the atmospheric air. Ideally, the water distribution system causes the water to splash or atomize into smaller droplets, increasing the surface area of water available for heat transfer. The approach to the wet-bulb is a commonly used indicator of tower size and performance. I

6、t is defined as the temperature difference between the cooling water leaving the tower and the wet-bulb of the air entering the tower. Theoretically, the water being recirculated in a tower could reach the wetbulb temperature, but this does not occur in actual tower operations.山东 XX 大学外文文献及译文FIGURE

7、4.2.14 Air/water temperature relationship in a counterflow cooling tower.The range for a chiller/tower combination is determined by the condenser thermal load and the cooling water flow rate, not by the capacity of the cooling tower. The range is defined as the temperature difference between the wat

8、er entering the cooling tower and that leaving. The driver of tower performance is the ambient wet-bulb temperature. The lower the average wet-bulb temperature, the “easier” it is for the tower to attain the desired range, typically 6C (10F) for HVAC applications. Thus, in a hot, dry climate towers

9、can be sized smaller than those in a hot and humid area for a given heat load.Cooling towers are widely used because they allow designers to avoid some common problems with rejection of heat from different processes. The primary advantage of the mechanical draft cooling tower is its ability to cool

10、water to within 36C (510F) of the ambient wet-bulb temperature. This means more efficient operation of the connected chilling equipment because of improved (lower) head pressure operation which is a result of the lower condensing water temperatures supplied from the tower.Cooling Tower DesignsThe AS

11、HRAE Systems and Equipment Handbook (1996) describes over 10 types of cooling tower designs.Three basic cooling tower designs are used for most common HVAC applications. Based upon air and water flow direction and location of the fans, these towers can be classified as counterflow induced draft, cro

12、ssflow induced draft, and counterflow forced draft.One component common to all cooling towers is the heat transfer packing material, or fill, installed below the water distribution system and in the air path. The two most common fills are splash and film.Splash fill tends to maximize the surface are

13、a of water available for heat transfer- 31 -by forcing water to break apart into smaller droplets and remain entrained in the air stream for a longer time. Successive layers of staggered splash bars are arranged through which the water is directed. Film fill achieves this effect byforcing water to f

14、low in thin layers over densely packed fill sheets that are arranged for vertical flow. Towers using film type fill are usually more compact for a given thermal load, an advantage if space for the tower site is limited. Splash fill is not as sensitive to air or water distribution problems and perfor

15、ms better where water quality is so poor that excessive deposits in the fill material are a problem.Counterflow Induced DraftAir in a counterflow induced draft cooling tower is drawn through the tower by a fan or fans located at the top of the tower. The air enters the tower at louvers in the base a

16、nd then comes into contact with water that is distributed from basins at the top of the tower. Thus, the relative directions are counter (down for the water, up for the air) in this configuration. This arrangement is shown in Figure 4.2.15. In this configuration, the temperature of the water decreases as it falls down through the counterflowing air, and the air is heated and humidified. Droplets of water that might have been entrained in the