Spray cooling process has many parameters such as extended surface, angle of inclination, effect of gravity, diameter of nozzle, angle of spray, mass flux, geometry of cooled surface, thermal performance and critical heat flux of spray etc. Many effective parameters to carry out the experiments with conventional test methods are both expensive and time consuming. As a solution in these circumstances, Taguchi method, which is one of the modern experimental design and optimization methods and very effective in solving such problems, was used in this study. Taguchi method, as well as being in effective to improve the quality of products, also gives the opportunity to achieve better results with much less experiment. Using Taguchi method, as well as to reach the target value exactly, the sensitivity of the design against uncontrollable factors is reduced to a minimum. Thus, the optimum tolerance range in cost and quality factors is determined. When compared to conventional experimental design methods, Taguchi method has many advantages. One of them is that the test costs are minimized and the deviation around the target is kept to a minimum while in bringing targeted level of the average value of performance. Another advantage is that the obtained results in the laboratory can be obtained in the real production environment and also saved a time of production. Nowadays, the planning of the multi-factorial experiments can be provided with great flexibility and simplicity by Taguchi method. In these experiments with using rectangular pin fin heat sinks, the effects of the longitudinal and lateral distances of the consecutively arranged nozzle or diffuser-like fin pairs, widths of the fins, angle of fins, heights of fins, spraying time, air flow rate, liquid flow rate (ALR, the ratio of air-liquid flow rate) and the ratio of the nozzle-heat sink distance to the nozzle diameter (h/d) on heat and flow characteristics have been investigated by using Taguchi experimental design method. For this reason, characteristics of flow and heat transfer are considered separately. Nusselt number considered as performance statistic, L27(311) orthogonal array has been selected as an experimental design plan for the eleven parameters mentioned above. The Nusselt number was calculated by taking into account the characteristic length of heat sink and the optimized results were found to be fin width of 45 mm, fin angle of 45o, fin height of 15 mm, x direction distance between fins of 20 mm, y direction distance between fins of 20 mm, x direction distance between slices of 15 mm, y direction distances between slices of 20 mm, air flow rate of 10-3 m3/s, liquid flow rate of 5,83*10-6 m3/s, spraying time of 5 s and the ratio of the nozzle-heat sink distance to the nozzle diameter (h/d) of 667.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4596
Flow Characteristics of Churn Flow at Low Liquid Flow Rate.