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This research is a continuation of synthetic jet characteristics investigation over convective cooling of impinging jet model. The synthetic jet cooling uses an air flowing in a vertical direction into the heated wall. This model uses an oscilating membrane to push and pull the air from and to the cavity. The purpose of this model of synthetic jet is to create vortices pair to come out from nozzle which will accelerate the heat transfer process occurring at the wall. This heat transfer enhancement principle has became the basis to simulate an alternative cooling system in order to substitute the conventional fan cooling in electronic devices due to its advantage for having a small form factor and low noise. The investigation is conducted in the computational work. In this research, the synthetic jet prototype model was simulated to examine the distribution of heat flow on the walls using a mathematical turbulent model k-ω SST. Meshing order was elements Tet/Hybrid and type Tgrid and the number of grid was more than 233.886 in order to ensure detail discretization and more accurate
calculation results. This simulation used a triangular waveform as it excitation source. The frequencies of excitation were 80 Hz, 120 Hz, 160 Hz and the amplitude was 1 m/s. Using this variation, the main goal is to increase the heat transfer coefficient generated by the synthetic jet blow.

This research investigated the characteristics of convective heat transfer of impinging jet model. The model equipped with synthetic jet of air flowing in a vertical direction into the heated wall. The model used a membrane made of piezo material to move the air with the vibrations that occur in this membrane. The purpose of this model of synthetic jet was to create vortices pair to come out from nozzle which will accelerate the heat transfer process occurring at the wall. This heat transfer enhancement principles became the basis to simulate an alternative cooling system to substitute the conventional fan cooling in electronic devices due to its advantage for having a small form factor and low noise. The investigation combined computational and experimental works. In this research the model was simulated to examine the distribution of heat flow on the walls using a mathematical turbulen model k-ω SST. Meshing order was elements Tet/Hybrid and type Tgrid and the number of grid was more than 233.886 in order to ensure detail discretization and more accurate calculation results. The boundary conditions were inlet velocity of 1.5 m/s, 2 m/s and 1 m/s, the frequency of membrande vibration were 80 Hz, 120 Hz, 160 Hz and the amplitude were 1 mm/s, 2 mm/s, 1.5 mm/s. The movement of the piezo membrane is assumed of sinusoidal motion which moves up and down correspond to the suction and blowing phase respectively.

Geometri kanal aliran yang memiliki pembesaran saluran mendadak di bagian hilir dapat menghasilkan aliran yang terpisah dan bertaut kembali (separated-reattached flow). Model geometri seperti ini salah satunya berbentuk backward facing-step yang merupakan bentuk yang sederhana dan banyak digunakan untuk melakukan simulasi berbagai macam fenomena pada peralatan keteknikan seperti reaktor kimia, sistem kendali aerodinamik kendaraan, sistem pembakaran pada dump combustor dan lain-lain. Pada aplikasinya, dinamika aliran di zona resirkulasi yang terbentuk sangat mempengaruhi kinerja operasional peralatan-peralatan tersebut. Pada penelitian ini dilakukan upaya memodifikasi ukuran zona aliran resirkulasi dengan merubah ketinggian step serta memberikan eksitasi eksternal berupa injeksi slot jet dari fluida panas dengan variasi temperatur 1000 C dan 3000 C. Kajian komprehensif dilakukan dengan pendekatan komputasional dan eksperimental. Model k-ε digunakan dalam kajian komputasi sementara medan aliran resirkulasi divisualisasi dengan menggunakan high speed camera yang kemudian diolah menggunakan image processing software sehingga dapat dianalisis lebih lanjut untuk mendapatkan
informasi mengenai berbagai fitur struktur aliran yang termodifikasi akibat pemberian eksitasi jet pada medan aliran resirkulasi tersebut. Hasil dari eksperimen dan komputasi kemudian digunakan untuk menjelaskan efek dari pengaruh ketinggian step dengan jarak injeksi yang diberikan terhadap bentuk dari zona aliran resirkulasi pada model geometri backward facing step.

Saluran aliran dengan pembesaran mendadak di bagian saluran keluar dapat menghasilkan aliran yang terpisah sehingga menyebabkan timbulnya aliran resirkulasi (separation). Model dari geometri seperti itu merupakan bentuk yang sederhana untuk mensimulasikan fenomena yang sama seperti yang terjadi pada sistem pembakaran (dump combustor),reactor kimia, peralatan elektronik CPU (central processing unit) komputer, proses elektrokimia (electroplating) dan lain-lain. Penelitian ini dilakukan dengan 2 metode yaitu : metode komputasi menggunakan software CFD (Computational Fluid Dynamics) untuk memprediksi medan aliran kecepatan, dan distribusi gas injeksi pada aliran dalam kanal berkontur tangga berupa injeksi jet panas dan metode eksperimental dengan cara melakukan pengukuran secara konvensional menggunakan termokopel.Dalam penelitian ini di fokuskan pada rasio spesifik momentum injeksi I= 0.1 dan I= 0.5 dengan jarak injeksi dari tangga lf = 2H (40mm) dan lf = 4H (80mm) serta variasi temperatur injeksi Tinj=1000C dan Tinj =3000C. Metode komputasi yang digunakan untuk menyelesaikan kondisi tersebut menggunakan metode volume hingga (finite volume method) yang mengganti persamaan-persamaan diferensial parsial dari kontinuitas, momentum, dan energi menjadi persamaan-persamaan aljabar. Model matematika yang dipergunakan untuk memvalidasi dari hasil eksperimental yang telah dilakukan terdahulu menggunakan persamaan aljabar K-epsilon dan RNG untuk kondisi slot jet (2D) dan round jet (3D). Hasil komputasi yang didapat dipergunakan untuk memvalidasi dari hasil eksperimental terdahulu yang ditujukan untuk menjelaskan efek dari geometris injeksi tersebut.

Flow channel with sudden expansion produces a separated flow so that causing a recirculation flow. This investigation is revealing the alteration of the thermal structure within the flow field due to a heated gas penetration. Main focus is placed on the influence of the ratio of specific momentum injection (I=0.1 and I=0.5), the injection location of heated gas (lf= 2H and lf=4H) and the variation of injection temperature (Ti=1000C and Ti=3000C) The investigation was done computationally using finite volume method as well as experimentally in a closed loop flow channel with a
backward-facing step flow configuration. Numerical solution models turbulence used were k-epsilon standard model and RNG k-epsilon. The numerical model was then validated by the experimental results. This model works on 2-D and 3-D Reynolds average Navier-Stokes (RANS) equations. From the results of thermal structure obtained, it can be suggested that increasing the the ratio of specific
momentum injection supports more effective thermal mixing except to the narrow region around area injection. More significant results are obtained in the region of shear layer and area downstream of the injection.