Ph.D. Tezi Görüntüleme | |||||||||||||||||||||
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| Summary: Present study considered here within the division of passive heat transfer augmentation technique. Semi circle forms of flat baffles normal to flow direction were inserted in cylindrical tubes with various angles and distances to one another. Baffles were placed inside the nine various tubes having same characteristics with the arrangement angles of 3.14, 1.57, 0.78 radians and with the ratio of distance between the buffles to diameter of 1, 2, 3. Thermal performance of nine kinds of heat transfer augmentation techniques were calculated, using the first and second laws of thermodynamics and also dissipation energy evaluation methods. Thermal performance were evaluated by the first law of thermodynamics, conservation of energy statement, is used for; 1) Constant Reynolds number, 2) Constant pressure loss, 3) Constant pumping power conditions. Assesting by using the second law of thermodynamics; three evaluation methods were used. These are entropy generation rate, ratio of entropy generation rate and irriversibility minimization. In addition to these six methods, dissipation energy method was also used for performance evaluation in this work. The heat transfer characteristics of these techniques were compared each other. Same type of optimum augmentation technique was observed according to the results of evaluation methods mentioned above. For laminer flow 4562 type, for turbulent flow 9093 type augmentation technique was found as the most effective ones. Performance of optimum enhancement techniques were compared with the other types of augmentation devices given in literature. Statistical ampiric correlations for the augmented Nusselt number and friction factor are also presented. Ampiric equations of enhanced Nusselt number and enhanced friction factor using Statistica software for laminer and turbulent flows covers all possible parameters as well. Correlations of the experimental datas within the range of %87 for Nusselt number and %74 for friction factor for laminer flow. These evaluation values for turbulent flow are %76 and %64 respectively. Optimum enhancement techniques improve heat transfer by a factor 8,75 and 6,09 compared with a smooth tube for laminar and turbulent flow respectively.
Key Words: Heat transfer enhancement, Thermodynamic laws, Forced convection
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