Heat Transfer Enhancement Techniques. With Special Attention to Passive Methods of Heat Transfer Enhancement

Heat exchangers are widely used in the industrial sector, e.g. in the refrigeration, air conditioning, petrochemical, and agricultural food industry. The high cost of energy and material has resulted in an increased effort aimed at producing high performance heat exchanger equipment. Passive methods of heat transfer enhancement do not need external power for enhancement. One of these kinds of passive technique is twisted tape inserts that enhance the performance of heat exchangers. Using multiple twisted tape inserts gives better enhancement than a single twisted tape insert. Using nanofluid gives also better thermal performance than water. Therefore, nanofluid along with twisted tape inserts was used in this study. For this study, different combinations of multiple twisted tape inserts were designed and fabricated. These different combinations contain dual, triple, and quadruple twisted tapes. Directions of twists are also varied which enables to study the effect of different swirl flow generators. Nanofluid is used with various volume concentrations of 0.07%, 0.14% and 0.21% in order to investigate the effect of nanoparticle concentration on heat transfer enhancement. Experimental investigation was carried out by having a constant heat flux condition and by varying the volume flow rate of flow from 2 to 10 lpm.