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Penelitian ini dilakukan untuk mengetahui distribusi ukuran diameter gelembung yang dihasilkan oleh alat pembangkit gelembung udara mikro (microgelembung generator/MBG). Gelembung yang dihasilkan direkam dengan menggunakan kamera berkecepatan tinggi (high speed camera). Metode yang digunakan untuk mengetahui ukuran gelembung yang dihasilkan adalah dengan menggunakan metode digital image processing (MDIP). MDIP ini memiliki keunggulan yaitu dapat mengukur dimensi distribusi gelembung pada aliran yang tidak teratur secara akurat serta pada operasinya tidak mempengaruhi aliran yang terbentuk. Hasil akhir dari ekstraksi data image processing ini adalah distribusi diameter microgelembung yang dinyatakan dalam Probability Distribution Function (PDF) dan digunakan untuk mempresentasikan perbandingan disribusi dimensi gelembung udara yang dihasilkan oleh MBG Kata Kunci: Gelembung Udara Mikro, Digital Image Processing, Highspeed Camera, Probability Distribution Function

The bubble breakup pattern on a swirl-type bubble generator (MBG) with water and air fluids was experimentally studied. The bubble breakup pattern was analyzed visually and characterized using several parameters such as Pressure Drop (∆P), Kolmogorov Entropy, Standard Deviation, and DWT (Discrete Wavelet Transform), which were taken from the extraction of pressure signals at the water inlet and outlet of the bubble generator. The wavelet spectrum of the measured signal was shown to identify the overall bubble breakup pattern, and the wavelet variance vector is proposed as a character vector to identify the bubble breakup pattern. The results show that there were three types of different flow breakup patterns: (1) static breakup, (2) dynamic breakup, and (3) tensile breakup. The observed bubble breakup sub-patterns can be categorized into tensile, moderate tensile, high tensile, dynamic, low dynamic, static, and high static sub-patterns. The static clustered breakup pattern has the highest wavelet energy compared to the tensile and dynamic clustered breakup.

A nuclear power plant operation requires reliability safety systems. Therefore, an accidental scenario such as the LOCA becomes a specific attention. This relates to a countercurrent flow phenomenon which permits the occurrence of a flooding regime. This study aims to investigate the effets of I/D ratios of the riser on the onset of flooding and time-series voltage fluctuations of differential pressure signals of the flooding regime on a complex geometry representing a PWR hot leg. The test section contains a combination of a horizontal, an elbow and an inclined pipes. Three I/D ratios containing 1.9 (R1), 3.9 (R2) and 8.3 (R3) were assesed. The tabulated data are expressed in the term of a flooding curve. Meanwhile, the statistical features of the time-series voltage fluctuations of the signals are presented on both PDF and PSD graphs. The results obtained show that the assesed I/D ratios do not conduct significance effects on the onset of flooding. On the other hand, there are trends which can be obtained from the time-series signals with the increase of the I/D ratio. Those trends can also be observed in the such statistical features; the PDF and PSD graphs, respectively.

Pada peradaban saat ini, telah terjadi peningkatan yang signifikan dalam perkembangan dan penerapan teknologi saluran microchannel dikarenakan keunggulan serta manfaatnya. Salah satu aplikasinya adalah liquid cooling system yang terdapat pada CPU atau GPU komputer dan sistem pendingin reaktor mikro. Seiring berjalannya perkembangan teknologi, kebutuhan sistem pendingin pada ukuran yang lebih kecil seperti pada telepon genggam, tablet, dan laptop menjadi tantangan tersendiri. Studi eksperimental aliran dua fasa pada saluran microchannel dilakukan terhadap karakteristik pola aliran untuk fluida newtonian dan perbandingannya secara spesifik dengan fluida non-newtonian untuk karakteristik pola aliran yang terbentuk. Saluran micro-fluidic chip berpenampang persegi dengan ukuran 0,8 mm x 0,8 mm dilewati oleh fluida kerja cairan newtonian berupa Air dan non-newtonian berupa Carboxymethyl Cellulose (CMC) konsentrasi 0,2% serta 0,4% dengan nitrogen sebagai fluida kerja gas. Kecepatan superfisial cairan yang digunakan adalah pada rentang JL= 0,05 – 1 m/s dan gas JG = 0,07 − 8,594 m/s. Differential pressure transducer dan high speed camera digunakan untuk menganalisis fenomena yang terjadi. Metode image processing digunakan dengan aplikasi MATLAB R2021a. Pola aliran yang teridentifikasi adalah bubbly, slug, slug-churn, churn, wavy-annular, dan slug-annular. Karakteristik slug seperti geometri dan waktu pembentukan dianalisa dengan membandingkan fluida kerja Air, CMC 0,2%, dan CMC 0,4% serta pengaruh variasi JG dan JL.

Tujuan penelitian ini ialah untuk mempelajari pengaruh densitas cairan, viskositas cairan, dan densitas gas terhadap karakteristik counter current flow limitation atau flooding pada pipa horizontal. Analisis numerik dilakukan menggunakan software CFD Ansys Fluent 2020 R2 student version dengan menerapkan model volume of fluid (VOF). Aparatus penelitian yang digunakan ialah geometri pipa hot leg reaktor PWR tipe German Konvoi skala 1/30 yang terdiri dari reactor pressure vessel, pipa hot leg, dan steam generator. Pipa hot leg yang digunakan memiliki diameter dalam D = 25,4 mm dan panjang pipa horizontal L = 635 mm (L/D = 25). Cairan yang digunakan ialah air, kloroform, larutan gliserin 10%, dan propil asetat, sedangkan gas yang digunakan ialah udara dan uap air. Hasil penelitian menunjukkan bahwa peningkatan densitas cairan menyebabkan peningkatan kecepatan superficial flooding gas, serta menyebabkan pergeseran hydraulic jump dan locus of slugging menjauhi belokan. Hasil dari peningkatan viskositas cairan menunjukkan pola yang berkebalikan dibandingkan hasil dari peningkatan densitas cairan. Penurunan densitas gas menyebabkan flooding terjadi pada kecepatan superficial gas yang lebih tinggi, serta menyebabkan pergeseran hydraulic jump dan locus of slugging menjauhi belokan.

The micro-bubble generator (MBG) is a novel aeration technology utilizing the concept of fluid flow through an orifice, where air is sucked into the internal chamber of the MBG by the pressure difference created by the orifice and immediately pushed by the high-velocity flow of the fluid. This mechanism creates micro-size bubbles with a high dissolution rate. This study focused on studying the effect on the oxygen dissolution rate of the two most important operating parameters, i.e. the volumetric flow rate of the liquid (Q L ) and the volumetric flow rate of the air (Q G ). Various combinations of values for Q L and Q G were systematically compared by means of the oxygen mass transfer coefficient (k L a). The experiment was carried out in a transparent container of 2.8 m x 0.6 m x 0.4 m filled with tap water that was aerated using an orifice/porous-pipe type MBG. The dissolved oxygen (DO) values were measured at distances of 60 cm, 120 cm, and 180 cm from the MBG outlet. The experiment was designed with five different values for Q L and Q G respectively. The results showed that the value of k L a, which is proportional to the oxygen dissolution rate, increased asymptotically with increasing Q L value, while the Q G values did not significantly affect the k L a value.

This study was aimed at investigating the phenomena and interactions between water droplets and hot metal surfaces using an experimental method. In this study, the droplet was dropped from 50 mm from the top of the metal surface with a frequency of 8.5 droplets per second. The observed droplet diameter was 3.12 mm. The metal used was copper with a surface temperature between 110-240 ° C. High speed video camera with a speed of 2000 fps was used to record visual data. Then the image processing technique was applied to calculate the change in droplet diameter. The results show that at low temperatures, droplets tend to maintain their initial position of contact with fluctuating deformations. While at high temperatures, a bounce phenomenon occurs which results in collisions between droplets being imperfect. Visualization results can reveal the complete change in the droplet geometry in the form of spreading ratio and complete apex height. The temperature of 140° C is the initial transition area for phenomena that result in droplets has no contact with hot surfaces so that the process of heat transfer between surfaces is inhibited.STUDI EKSPERIMEN PADA FENOMENA SUCCESSIVE DROPLETS MENUMBUK PERMUKAAN TEMBAGA PANASPenelitian ini bertujuan untuk mempelajari fenomena dan interaksi antara tetesan air (droplet) dan permukaan logam panas dengan metode eksperimental. Pada penelitian ini, droplet dijatuhkan dari posisi 50 mm dari atas permukaan logam dengan frekuensi 8,5 droplet per detik. Diameter droplet yang diamati sebesar 3,12 mm. Logam yang digunakan adalah tembaga dengan temperatur permukaan di antara 110-240° C. High speed video camera dengan kecepatan 2000 fps digunakan untuk merekam data visual. Teknik image processing diaplikasikan untuk menghitung perubahan diameter droplet. Hasil penelitian menunjukkan bahwa pertama, pada temperatur rendah, droplet cenderung mempertahankan posisi awal kontak dengan perubahan bentuk yang fluktuatif. Kedua, temperatur tinggi, terjadi fenomena bouncing yang mengakibatkan tumbukan antar droplet menjadi tidak sempurna. Hasil visualisasi dapat mengungkap perubahan geometri droplet berupa spreading ratio dan apex height secara lengkap. Dari penelitian ini juga diketahui bahwa temperatur 140°C menjadi daerah transisi awal terjadinya fenomena yang mengakibatkan droplet tidak bersinggungan dengan permukaan panas sehingga proses perpindahan kalor antar permukaan terhambat.

Microbubble aeration has been recognized as a tool to improve dissolved oxygen and fish culture performance in limited water aquaculture. This research aims to investigate the effect of microbubble aeration on increasing dissolved oxygen, fish culture performance, and stress resistance of red tilapia. The study used 3 treatments of aerations namely microbubble, blower, and without aeration with 3 replicates each. Red tilapia weighing 115.27±3.93 g were stocked in a plastic tank of 800 L water volume at density 50 individual/tank and cultured for 50 days in a recirculating aquaculture system (RAS). Dissolved oxygen, fish culture performance, and stress resistance were evaluated. Dissolved oxygen was monitored daily. In the middle of the research period, a stress test was performed using different salinity at 12 and 24 ppt. Statistical analysis was subjected to water quality, fish culture performance, and stressed resistance. The microbubble aeration was able to stabilize DO level on 4.28 mg/L until the end of the experiment and suppressed the CO2 and ammonia content. Fish biomass was higher in microbubble treatment, with a lower FCR value, lower stress level indicating fish in good health and promoting good culture performance. HIGHLIGHTS The critical parameter of water quality in aquaculture is dissolved oxygen (DO) and to increase its content is by aeration A nobel microbubble aeration was able to increase DO level higher than blower aeration and stabilize DO at requirement level until the end of the fish culture The strong relationship of DO with fish hematology parameters those more stable that indicate a lower stress level Stable physiological conditions and low stress of fish implied that the cultivated fish is in good health and good performance by microbubble aeration GRAPHICAL ABSTRACT

Spray cooling merupakan aplikasi dari droplets yang digunakan sebagai salah satu teknik pendinginan. Pemanfaatan dari multiple droplets ini banyak dikaji sebagai sistem pendinginan pada peralatan elektronik dan pembuatan material quenching . Dinamika tumbukan multiple droplets pada permukaan bidang miring yang dipanaskan akan dikaji pada penelitian ini. Material uji yang digunakan adalah stainless steel 304 . Temperatur permukaan yang diamati adalah 120 oC, 180 oC dan 220 oC pada bilangan Weber medium 70 dengan variasi bidang kemiringan adalah sebesar 10o, 20o dan 30o. Dinamika droplet selama tumbukan diamati menggunakan high-speed camera dengan kecepatan 4000 fps kemudian hasilnya diolah menggunakan image processing . Telah diperoleh hasil bahwa spreading ratio tertinggi terjadi saat temperatur permukaan 180 oC pada sudut kemiringan 30 o dan terendah pada temperatur 220 oC. Fenomena secondary droplet dapat meningkatkan nilai spreading ratio . Adapun fenomena bounching terjadi pada temperatur 220 oC. Kata kunci : Spray cooling, multiple droplets, stainless steel, image processing, spreading ratio ABSTRACT Spray cooling is an application of the use of droplet on a cooling system. Spray cooling is usually used in a cooling system of electronic devices, and material quenching. In this study, the dynamic behavior of multiple droplets impacting into inclined hot surfaces will be investigated. The material used in the present work is stainless steel 304 with the temperature 120 oC,180 oC,dan 220 oC at medium Weber number 70. The inclined surface varied at 10o, 20o dan 30o. The droplet dynamics during the impact have been observed using high-speed camera with the frame rate of 4000 fps then the results were analized by using image processing technique. The result of this study shows that The presence of second droplets and the higher of inclined surfaces can increases value of spreading ratio ,it is noticed that at 180°C, droplet impacting at 30o showed the highest spreading ratio and at 220 oC is the lowest. The presence of secondary droplet can increases value of spreading ratio and bouncing phenomena occurs at 220 oC. Keyword : Spray cooling, multiple droplets, stainless steel, image processing, spreading ratio

Single droplet impingement onto an inclined heated surface was studied experimentally. The droplet was dropped from 70 mm fixed height to the material surface with a 45º impact angle. The experiment used three types of materials; Stainless Steel AISI 304, Aluminum Alloy 2024, and Copper. Each test material has average surface roughness, Ra 0.06 μm. Materials are assumed to have the same surface treatment condition. Droplet behavior observed at surface temperatures of 100 ºC and 140 ºC. Droplet has a 3.0 mm diameter and 28.5 Weber number (low impact category). A high-speed camera 4000 fps (frames per second) with image resolution 1024 x 768 was used to analyze the droplet behavior after impact. MATLAB image processing technique used to determine the spreading ratio and dimensionless height. The results showed that the droplets have different behavior even at the same surface temperature. Boiling regimes influence both spreading and dimensionless height ratios. In the natural convection regime, the oscillation of the spreading droplet ratio influenced by Weber number and gravity. During the nucleate boiling and at Leidenfrost temperature, the spreading ratio influenced by bubble growth and secondary atomization.

The slug flow phenomena are often encountered in various industrial applications such as petroleum, process, and power plant. The presence of slug flow should be avoided as it causes structural damage due to resonance, corrosion and pipes blast. From the view point of multiphase flow, the understanding of the slug initiation mechanism is very important in pipeline design. This research is conducted using horizontal transparent acrylic pipes with diameters of 50 mm with a variation on the superficial velocity of water between 0,1 m/s and 0,77 m/s and superficial velocity of air between 0,31 m/s and 6,2 m/s. In the present experimental study, the slug initiation mechanisms was explained by visual observation by using high speed video cameras. As the results, the slug flow initiation mechanism were clarified. Furthermore, the proposed of flow initiation map was introduced.

Tujuan dari penelitian ini adalah untuk melakukan evaluasi terhadap efek dari perlakuan padat tebar yang berbeda dan penggunaan injektor venture terhadap laju pertumbuhan udang Litopenaeus vannamei yang dipelihara di bak beton. Udang Vannamei (berat awal 0,3 ± 0,07 g) dimasukkan ke dalam 32 bak pemeliharaan dengan ukuran 8x8x1 m dengan padat tebar 300, 400, 500, 600 udang m-2 dan masing-masing padat tebar memiliki delapan pengulangan. Untuk pengamatan injektor venturi, dilakukan di dua kepadatan berbeda yakni 300 dan 600 udang m-2 dengan memasang injektor venturi masing-masing di tiga bak pengamatan dan dibandingkan dengan kontrol. Jumlah pakan yang diberikan ditentukan terlebih dahulu berdasarkan asumsi pertambahan berat udang Vannamei 1 g per minggu, rasio konversi pakan (FCR) 1,4 dan kematian mingguan sebanyak 3 %. Hasil pengamatan menunjukkan bahwa terdapat korelasi negatif antara peningkatan padat tebar dengan laju pertumbuhan udang. Berat akhir udang berada di kisaran 13,0±0,2, 11,6±0,5, 10,3±0,4 dan 9,3±1,0 g untuk padat tebar 300, 400, 500, dan 600 udang m-2. Laju pertambahan berat harian berada di kisaran 0,14±0,02 – 0,17±0,02 g dan semakin membaik ketika pada tebar diturunkan (P

Thermoacoustic refrigeration utilizes the temperature changes that occur due to pressure oscillations within a sound wave to transport heat from one point to another and achieve cooling. As such, it neither requires complicated machinery nor hazardous or environmentally harmful refrigerants. By altering the acoustic field, it is possible to also alter the direction of heat pumping allowing a single device to be capable of functioning as a heater or cooler without addition of complicated machinery. We have constructed a thermoacoustic heat pump employing dual opposing acoustic drivers or speakers connected by a resonator tube and a regenerator formed by layers of steel mesh positioned at the centre of the resonator to investigate the alteration of the acoustic field due to the interaction of opposing travelling waves. The acoustic field was manipulated by changing the phase difference and magnitude difference between the waves generated by the acoustic drivers. Experimental results show that the acoustic power flow on both sides of the regenerator was altered thus resulting in a change in heat pumping direction along the regenerator. In addition, it was also observed that the heat pumping was also influenced by the changes in the standing wave component (SWC) and the travelling wave component (TWC).

An experimental study to examine the capabilities of the microbubble generator (MBG) on aerobic wastewater treatment was carried out under laboratory and industrial conditions. The tested MBG types were porous pipe & orifice and an MBG with a spherical body and drilled holes. In the laboratory-testing condition, an MBG was placed at a depth of 40 cm from the water surface. Three different pressure transducers were installed around the body of the MBG in order to analyze the inlet water pressure, the air-suction pressure, and the pressure at the outlet of the MBG. Next, the bubble diameter was measured by capturing the bubble pictures using a digital camera and analyzed using a developed image-processing technique. In order to simulate the application of the microbubble generator in the industrial field, a feasibility test of the MBG in aerobic wastewater treatment was performed. The results show the increase in MBG quantity with a higher ability to increase the oxygen, and that it is necessary to arrange the placement of each MBG in configuration to minimize bubble coalescence. Furthermore, by using a bio-ball as the porous media for microorganism attachment in aerobic wastewater treatment, the feasibility test showed promising results. Carbon on demand (COD) could be reduced to around 354 mg/l. The value of dissolved Oxygen (DO) was larger than 2 mg/L. The Ph level remained at 6, and temperature remained no more than 35ºC, which meet the requirements of aerobic wastewater treatment.

Survival rate and immunity of white leg shrimp ((Litopenaeus vannamei) postlarvae against acute salinity stress were evaluated in indoor experimental trials. The research was conducted with 2x2 factorial design with two levels of aeration (microbubble and macro bubble) and two levels of diet (with and without probiotics) resulting four treatments in triplicate: application of microbubble with gut probiotics (MiP), without gut probiotics (MiC), and macro bubble with gut probiotics (MaP) and without probiotics (MaC). White leg shrimps measuring 7.6 g were maintained in the tanks for 60 days and fed five times a day at a dose of 5% biomass. Harvested shrimp were tested for low salinity stress (5 ppt) for 3 hours. Glucose level, total protein, bactericidal activity, natural agglutination, phenoloxidase, respiratory burst, and superoxide dismutase activities in the hemolymph and the shrimp survival rate (SR) were analyzed before and after the stress tests. Although all examined parameters remained the same between groups before the stress test, significant differences were found among them after the stress test. Microbubble aeration obtained stabilization of hemolymph glucose level, best survival rate, bactericidal activity, and agglutination activities. No significant effect was resulted by the dietary probiotic treatments, but the interaction with aeration treatments revealed the importance to compensate shrimp survival rate when microbubble aeration is unavailable.

The lid driven cavity problem has been studied numerically. The present work is focused on reviewing the fluid flow patterns for the lid driven cavity problem. The left, right and bottom walls are maintained at no slip boundary condition and the top wall is moved in the right direction with uniform velocity (u = 1.0). The governing equations are processed by the mass and momentum equations and solved by using the radial basis function (RBF) method. The governing equations are expressed using a primitive variable formulation. The method was based on implicit Euler scheme for temporal discretization and RBF method for spatial discretization. The effects of the Reynolds number on the fluid flow in the square cavity are investigated. Stream functions and pressure contours are presented for various Reynolds numbers, such as 102, 4x102 and 103. Comparing the numerical results obtained using the present method with other numerical methods from the literatures shows very good agreement.

Qualified and preserved water is declining due to metal, waste, and hazardous chemicals contamination. Demand on fresh water raises and leads to the efforts on processing waste water with effective and efficient technology. Microbubble generator technology developed lately to result dissolved oxygen for raising microorganisms to decompose waste in waste water. This research used porous-ventury microbubble generator with 30° inlet angle and 20° outlet angle, placed in the center of 280 cm x 60 cm x 40 cm aquarium for experiment. This research aimed to find out bubble distribution and microbubble generator (MBG) performance. Measurement on bubble distribution conducted using Phantom Control Camera. Obtained data analyzed using MATLAB R2016a, while MBG performance measured using pressure transducer. Analysis conducted on variations of gas debit (0,1 lpm; 0,4 lpm., and 1 lpm) and water debit (30- 80 lpm) effects toward performance parameters, such as hydraulic power (Lw) and bubble generating efficiency (ηB). Results show that the greatest microbubbles’ diameter is 150- 500 μm, hydraulic power (Lw) increases with the inclining water debit (QL), effect of gas debit variation exert low effect towards Lw, and declining number of bubble generating efficiency (ηB) parameter with the inclining number of the water debit (QL).

The effect of drop frequencies and surface temperature on the maximum spreading ratio, heat transfer rate and heat transfer coefficient of convection have been studied experimentally. The experiments were carried out by investigating different values of drop frequencies at 250, 400 and 600 drops/minute. The surface material of stainless steel with a temperature range of 120°C to 200°C was used in the study. An image processing technique was used to measure the diameter of droplets that were captured by using a high-speed camera. The results of the study show that by increasing frequency of drops has improved significantly the maximum spreading ratio, heat transfer rate and heat transfer coefficient of convection. The results also shown that by increasing the drop frequency has increased accordingly the droplet contact with the surface. It was found that, at higher surface temperature has contributed to the increase of the heat transfer rate and convection heat transfer coefficient. This study suggest that the peak and wetting limit conditions has occurred at the surface temperature of 180°C.