Đang chuẩn bị liên kết để tải về tài liệu:
Heat Transfer Theoretical Analysis Experimental Investigations and Industrial Systems part 9

Tham khảo tài liệu 'heat transfer theoretical analysis experimental investigations and industrial systems part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 310 Heat Transfer - Theoretical Analysis Experimental Investigations and Industrial Systems advantages from ease of installation and operation and efficiency of the process to the variety of products that can be cooled in this type of equipments. The selection of the best cooling method varies according to the desired application and depends on several factors including the cooling rate required subsequent storage conditions and costs of equipment and operation. Systems properly designed may increase efficiency and reduce the cost of operation Talbot Chau 1998 ASHRAE 2002 . Talbot Fletcher 1996 compared the efficiency between an air blast system and a storage chamber. During the cooling process of grapes there was a reduction of 6.7 oC in one hour and 14.6 oC after 2.5 hours compared to a decrease of only 2 C in one hour and 3.5 oC in 2.5 hours in the storage chamber. Experiments carried out using a prototype portable forced-air device offered promising results Barbin et al. 2009 . The system was designed to be used inside cooling and freezing chambers aiming to improve heat flow rates. 2.4 Air flow Cooling time by forced air systems is determined by airflow and product thermal load which affects the amount of energy to move the air around the product and inside the system. The most common industrial applications use direct cold air insufflations inside the system. The airflow varies according to the speed and amount of air flowing through products and its variation results in longer or shorter freezing time. A correct orientation of the air flow inside the equipment and around the product can significantly reduce processing times Cortbaoui et al. 2006 . Surface area of contact between products and cooling air and products arrangement are other parameters that affect forced air cooling Baird et al. 1988 Fraser 1998 Laguerre et al. 2006 . In industrial plants air flow is highly turbulent due to the fans movement and to wakes originated from upstream obstacles. .