Jet impingement cooling is one of the potential convective cooling techniques and its use extended to various engineering and industrial application. Further, it has the scope to enhance the heat transfer rate according to upcoming customer requirements due to its high heat flux removal rates. It has the opportunity to remove high volumetric dissipation rates that helps not only to enhance the performance but also to obtain a reasonable service life of components using passive augmentation technique. Besides, the jet impingement cooling with passive enhancement
technique is simple in design and less costly compare to other convective cooling methods. In
consideration of this, the present research focuses on the experimental investigation of cooling
performance of jet impingement by providing various types of small surface roughness elements
on the heated surface.

Ahead of design and development of experimental apparatus for the present work, 3D simulation
of jet impingement heat transfer was performed using Ansys Fluent. The solution domain of
numerical simulation was generated using a 3D structured grid in ICEM CFD. The results,
obtained by conjugate heat transfer technique, helps to evaluate average heat transfer characteristic of the heated surface more accurately and to determine the basic dimensions of experimental setup related to jet impingement. An experimental apparatus was designed and fabricated using the results and dimensions of numerical simulation. Experiments are performed for single circular air jet for the diameter of nozzle 7 mm, 9.5 mm and 12 mm. The governing parameters chosen for the experimental investigation is Reynolds number varies from 10000 to 33000 and for different standoff distance 2 to 10 times the diameter of the nozzle.
The present experimental study has been carried out to investigate the influence of single
protrusion, multi-protrusion and V-grooved roughness element on heat transfer enhancement and
compare with that of the plane surface at the similar operating condition. Further, demonstrate the surface element, which is more effective and economical. The impinging plate was heated by a mica heater that is placed at the bottom of the impingement plate to accomplish the objective of
the present research work. The symmetrical air jet flow in the turbulent regime impinges on the
heated plate. The average Nusselt number is reported as a function of jet Reynolds number, nozzleto- plate spacing, roughness type, and nozzle diameter for 60 W and 90 W heat inputs.
The surface roughness elements used for the present work are single protrusion of depth
1 mm, 2 mm and 3 mm, well-separated multi-protrusion and continuous V-grooves. There is no
criterion for the dimensions of the single protrusion. However, the criterion for the size of the other two surface roughness elements is the laminar sublayer thickness. The results show that
enhancement of heat transfer increases with protrusion depth. This enhancement is attributed to
the increase in surface area, disruption of boundary layer and local turbulence on the heated
surface.
Further, the two different types of surface roughness elements such as multi-protrusions and
continuous V-grooves are selected to investigate the influence of local turbulence nearby heated
surface on the enhancement of jet impingement heat transfer. The result demonstrates that the wellseparated
multi-protrusiones enhance the local micro-scale mixing, which in turn augments the
average heat transfer co-efficient. Whereas, the air circulation inside the tiny V-grooves acts as an insulator between the heated surface and air jet. This mechanism limits the enhancement of heat transfer co-efficient though the surface area has increased significantly.
The second objective of the present work is to investigate the effect of different heat input on the
enhancement of jet impingement heat transfer. Hence, the experiments are performed at 60 W and 90 W heat input values on flat and modified surfaces. Further, the influence of the geometry of surface roughnes elements on the augmentation of jet impingement heat transfer is also
investigated. The results reveal that the enhancement of heat transfer decreases with the increase
in heat input values for all the surfaces. The analysis of the results interprets that the natural
convection setup on the heated impingement surface resists the forced jet impingement heat
transfer. The strength of the natural convection increases with the heat input values and surface
area of modified surfaces. The experiments conducted for different nozzle diameter reveals that the average heat transfer characteristics of the heated plate improve with the diameter of the nozzle. The nondimensionalized temperature profile across the impingement surface is plotted using local temperature measured by the thermocouples. The slopes of the curve show that the temperature drop in the impingement zone is relatively higher than that of the wall jet zone.
The regression and correlation analysis is applied to establish the relationship between the average Nussult number and various governing parameters such as Reynolds number, stand-off distance, surface roughness parameters and Rayleigh number which represents the natural convection on heated impingement surface. The plots of predicted values versus experimental values demonstrate that the modelled values have a close match with experimental values.