tailieunhanh - Evaporation Condensation and Heat transfer Part 6

Tham khảo tài liệu 'evaporation condensation and heat transfer part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 190 Evaporation Condensation and Heat Transfer coolers. Over design in all of these components is a common practice in industrial applications such practice guarantees that the cooling utility is always available regardless of the expenditure of power. Under such circumstances it is common to find that the operation of the cooling system remains unaltered even when plant throughput changes however one consequence of this mode of operation is the rise in operating costs due to pumping. The way to keep pumping power consumption at a minimum is by means of a flexible cooling system. A flexible cooling system is one that is ableto adapt to the process heat removal demands as the plant throughput varies such a systems is depicted in Figure 1 in this diagram the cooling duty is represented by the length of the rectangles. Three different situations are shown a cooling duty for 100 throughput b cooling duty for for reduced throughput and c cooling duty for for increased throughput. Increased throughput Reduced Throughput Fig. 1. Flexible cooling water system designed to supply the required heat load for changed plant throughput. Heat Load 100 Throughput A cooling tower is one of the main thermal co mponents of a cooling system since in the operation of these types of units atmospheric air is used to cool down hot water its thermal performance is strongly affected by the ambient conditions such as wet bulb temperature and air relative humidity Castro et al. 2000 . The need then arises for a model that allows a quick and reliable determination of the therma I performance of cooling systems when they are subject to changed operating conditions. The experimental and theoretical investigation of the thermal performance of cooling towers has drawn the attention of many researchers either experimentally or theoretically Bernier 1994 Jameel-Ur-Rehman et al. 2004 Gharagte et al. 2007 Chengqin 2006 Nenad 2001 . Expressions to apply the thermal effeciveness method directly to .