The numerical evaluation of jet impingement effectiveness in a bottom of confined cavity

There are many studies released about small air jet impingement in today's world and the number of studies and usage areas have been increasing in this direction day by day. Because the size of design of applications are becoming smaller due to ergonomic requirements. There are widely small jet usage area available in the industry in connection with their mass and heat transfer capability and being package friendly. To mention about where they are used; they can be collected under three title. They are drying, cooling and heating. The most common area is the area which is using cooling ability of jet nozzle. In this direction, cooling ability can be divided into two topics as protection and production skill. For example, internal combustion engines, jet engines and some applications in heavy industry (CNC turning, milling etc.), electronic systems require efficient cooling systems to reach better performance and prevent hardware failure. These usage areas use protection skills of jet nozzle. To give an example, obtaining tempered glass method is populer in using production method of jet nozzle. Because, the procedure of production of tempered glass need quick cooling after it gets its melting temperature. The jet nozzle is used due to its heating ability as well. Some products are desired high temperature to stay healthy. However, the storage areas of the products may not have the necessities about temperature. For this reason, jet nozzle heating method is finding a solution to avoid it. Associated with ever growing usage areas of jet nozzle, the design of jet nozzle is becoming important role to get higher effectiveness. The unconscious applications can cause cost and efficiency reduction. In this study, the best design schematic is being tried to find to prevent it. This study is related to time dependance heat transfer characteristics of small jet impingement under variety condition of flow type, the distance between the jet and the bottom wall, the inclination of bottom wall and the blockage effect on the way of flow line on the bottom cavity (293°K). To mention in details with pointing out using air as refrigerant, the first factor is flow characteristic related different Reynolds number (Re) changes in two values of 3,300 to 6,600 which are affected directly from diameter, inlet velocity of circular jet nozzle and kinematic viscosity of air in this inlet temperature (283°K). The second one is to see effect of distance between circular jet and the bottom wall (H) and constant nozzle diameter with 10 mm (D) (H/D) as three different ratio of 1, 5, 10. The third one is the tilt angle of bottom wall which is nearly the first contact with the jet flow with variance of 0, 10 and 20 degrees. The last one is using circular blockage over flow area. Unstructured and structured mesh type are used by looking inclination availability. If the geometry has zero inclination, structured and quadriteral mesh is used. Otherwise, unstructured and triangle mesh is applied at inclined zones. Standart wall function k-e turbulent model is performed all of the simulations. For the validation, standart wall function k-e, realizable k-e and SST k-w turbulent model are compared with one simulation. It is seen that the results are close to each other so it is not problem to continue with standart wall function k-e turbulent model. Lastly, the solution is run by using 2-D and transient method. Totally there are about twenty configurations simulated in the study by changing inputs which have mentioned before. As a consequence of these tests, the first deduction is to impinge the air with as fast as possible to the taget surface since the heat transfer on the surface has directly relationship with Reynolds number namely inlet velocity. Another method of getting increased Reynolds number might be widen diameter of jet nozzle. It also causes efficient heat transfer. The second deduction is to pull the jet nozzle over the surface which is desired to cool, in another saying reduce the distance between the jet nozzle and the effected plate since the effect of air has improved in this case. The third inference is applying inclination has poor effect on the heat transfer between air exit from jet nozzle and the target plate due to nonuniform flow distribution. All these inputs lead quick cooling as well besides increased cooling profile. The last inference is setting blockage on the flow line can be used for increasing head transfer capability but it does not work for increasing cooling acceleration. In conclusion, the lower distance between target plate and jet nozzle, the more Reynolds number, the less inclination and using blockage on the flow line is the best configuration to increase cooling and heat transfer capacity on the confined cavity.