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The circumferential film thickness distribution in an air-water horizontal annular two-phase flow was investigated in 26 mm pipe diameter by using the conductance probe. The superficial gas and liquid velocities were 10–40 m/s and 0.025–0.4 m/s, respectively. In general, the film thickness decreases as the liquid velocity decreases and the gas velocity increases. For low superficial gas velocity, high asymmetry of liquid film thickness distribution is generally found. In addition, the liquid film at the upper half of the pipe mostly consists of surge of waves with frequency lower than that of the bottom. At the lowest superficial liquid velocity of the present experimental range, the mean film thickness at the bottom ranges from 0.24 mm to 1.3 mm. Meanwhile, at the highest superficial liquid velocity, it ranges from 1.0 to 4.29 mm, depending on the superficial gas velocity. At the higher superficial gas velocity, a more uniform of liquid film thickness distribution is commonly found. Under this flow condition, the wave at the upper has a similar frequency to that of the lower half and a coherent liquid wave is normally found. To predict the film thickness at any circumferential position, an empirical correlation is proposed on the basis of the physics of the phenomena. In comparison to the available experimental data, the correlation has a good capability to predict the circumferential liquid film thickness distribution. [ABSTRACT FROM AUTHOR]

Potential of hydroelectric plants depend on the availability of discharge and head flow. The steep slope of rivers and the abundant of water flow in rural areas are as potential locations of hydroelectric power plant site (HPPS). The lack of discharge data measurements on the tributaries are the main obstacles to determining the potential sites. This paper proposed a method to identify the potential sites for HPPS. The method based on two main information: (1) location of the steepest slope, and (2) discharge generation of tributaries. In this case, ASTER GDEM 2 was used to: delineate watershed boundary, determine river network, and derive slope. Then, long section of the selected tributaries was analyzed to obtain the location the steepest slope potentially to HPPS. Furthermore, generated discharges for selected sites were calculated using Clark UH running under HEC-HMS program. The model was calibrated using daily discharge data observed at the watershed outlet. The time series period used for calibration process is range from 2002 to 2014. Simulation model of rainfall-runoff at a variety of outlets were selected to obtain the dependable discharge assisted with hydro-office program. This result show that total potential of hydroelectric plants can reach up to 653 kW. [ABSTRACT FROM AUTHOR]

The idea of using microalgae as a bio-source of biodiesel is being taken seriously because of the escalating price of fossil fuel. As the tropical country, which gets the sun a year round, Indonesia has big potential for cultivating microalgae in large scale, as biodiesel feedstock. This study examines the algal oil extraction of selected monoculture microalgae species of Botryococcus braunii , Nannochloropsis sp. , Arthrospira platensis and mixed cultures microalgae from South Coast of Yogyakarta, Indonesia. Among all species of microalgae studied, Nannochloropsis sp. was found to have the highest algal oil yield (0.0346 g dry algal oil/g dry microalgae) and theoretical calorific value (187.69 kcal/kg dry microalgae). [ABSTRACT FROM AUTHOR]

Chlorella zofingiensis Dönz is popular as food sources and as potential source for biofuel. In order to determine the potential of Chlorella zofingiensis Dönz as a source for biofuel, it is necessary to enhance its growth and to identify the carbohydrate and lipid content using red, blue, and white light as well as various salinities for the cultivation. Among the process conditions tried, cultivation using blue light at salinity 19 ppm was considered as the optimum one which resulted in greater dry weight of biomass as well as greater lipid content. However, the other process conditions, with lower dry weight of biomass, had carbohydrate as the major component so that actually the process condition selection depended on what kind of biofuel will be produced. Based on the optimum condition in interest of biodiesel production, kinetic study was ran using blue light with salinity 19 ppm. The suitable model to describe the growth kinetic of microalgae was Contois model. [ABSTRACT FROM AUTHOR]

This research aims to determine the range of parameter value, baseflow index and the appropriate method for base flow separation . Seven (7) recursive-digital-filters (RDF) and two (2) graphical methods are used for this study. Discharge data from 8 watersheds in the administrative area of UPT PSDA Bondowoso in East Java were used to test the methods. Firstly, each method was calibrated using daily discharge data for each year (annually) to separate baseflow. Then, optimal parameter values are obtained by averaging the annual values. Calibration process produced optimal parameters value for each watershed. Furthermore, validation was performed using optimal parameter values from watershed having complete discharge data to other watersheds. The results show that optimal parameter values from calibrated watershed can be used to separate base flow in other watersheds. Principally, all methods can be used to separate base flow on this region, however three methods (EWMA, Line-Hollick and Local Minimum) perform better than others 6 methods. [ABSTRACT FROM AUTHOR]

The effects of fluid properties on the wave velocity and frequency of gas–liquid annular two-phase flow were investigated in 26 and 16-mm inner pipe diameters. The liquid viscosity was varied from 1.02 to 6.57 mPa s using water and glycerol solution and the surface tension was varied from 34.0 to 71.7 mN/m using water and butanol solution. The range of superficial liquid and gas velocities were set to 0.05–0.2 m/s and 12–40 m/s, respectively. In general, the wave frequency decreases with increasing liquid viscosity and decreasing surface tension. The wave velocity decreases with increasing liquid viscosity for all range of superficial gas and liquid velocities. The lower surface tension gives the lower wave velocity for low superficial liquid velocity. For high superficial liquid velocity, however, the wave velocity increases with decreasing surface tension. The wave frequency decreases with the increase of liquid viscosity and the decrease of surface tension, with more significant effects are found at the higher superficial gas and liquid velocities. Comparisons of experimental data with the existing correlations for wave velocity and wave frequency have been carried out and new correlations have been developed with a considerably good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to propose an image processing technique in order to study the interfacial behavior of air-water slug two-phase flow in horizontal pipes. Here, the experiments were performed in two sets of transparent acrylic pipes with inner pipe diameters of 16 mm and 50 mm. To observe the interfacial behavior of slug flow, the liquid and gas superficial velocities were set to 0.2–0.77 m/s and 0.7–2.83 m/s, respectively. Visualization studies by using high speed video camera combined with image processing techniques were since it offered numerous advantages. Moreover, a sequential procedure was implemented for processing of each image. This technique has succeeded to enhance the image contrast and remove the uneven background. Next, a number of steps applied to binary image were also performed in order to remove the dispersed bubble attached on bubble tail which becomes one of the biggest challenges for the visualization studies of slug flow. As a result, the developed image processing technique was able to minimize the errors in order to produce the accurate measurement. Moreover, the processed image have been utilized to gather the quantitative information. It reveals the comprehensive characteristics of slug flow in horizontal pipes. Finally, a good agreement between the present and previous works proves the reliability of the developed technique. [ABSTRACT FROM AUTHOR]

The interfacial dynamics of the micrometric size liquid droplets during impact onto inclined hot surfaces have been experimentally studied. The inclination angles were varied at 15°, 30°, and 45° from horizontal for surface temperatures were decreasing from 500 °C to 100 °C. The droplet diameters tested were 500 μm and 700 μm. The tested material was stainless steel-grade 304 (SUS 304) with varying surface roughness ranging from Ra 0.04 up to Ra 10. The interfacial dynamics during the impact onto inclined hot surfaces were investigated by using a high-speed video camera with the frame speed of 15,000 fps. The objectives of this study are to provide insight into the dynamic behaviors of contact angles and dependence of importance parameters at various surface temperatures. It was found that depending on the surface temperature the droplet evaporation and its bouncing process play an important role on the droplet detachment mechanisms from the inclined surface. Three transient regions of the interfacial evolution during the micrometric droplets impacting onto oblique hot surface were identified. Moreover, the contribution of the important physical parameters, such as, advancing and receding contact angles on the interfacial dynamics are presented. [ABSTRACT FROM AUTHOR]

The study on the interfacial phenomena of flooding during the counter-current flow of gas-liquid in a complex pipe was carried-out experimentally. It consists of a combination of the horizontal pipe, elbow and inclined pipes to simulate the hot leg pipe in a PWR. The inner diameter was 25.4 mm as scale down of real hot leg pipe of German Konvoi type reactor. The visual observations were performed using high-speed video cameras. The measured parameters were the liquid film thickness and the pressure difference between reactor pressure vessel (RPV) simulator and steam generator (SG) simulator. The film thickness inside the test pipe was determined by using the processed image of visual data. As a result, three different mechanisms at the onset of flooding in counter-current were clarified, and are strongly affected by liquid superficial velocity. At low liquid superficial velocity (J L ), the flooding mechanism is triggered by the presence of wavy interface along the horizontal pipes in the form of a liquid blockage on the elbow. At the medium J L , the slug was detected along the horizontal pipe. However, the slug collapses immediately since the water is insufficient to maintain the blockage. At high J L , the slug occurs and travels along the horizontal pipe until the elbow. Moreover, the effect of the length of horizontal pipe on the interfacial behavior of air water counter current flow also can be explained. As the length of the horizontal pipe decreases, the onset of flooding occurs at a higher gas liquid mass flow rate. [ABSTRACT FROM AUTHOR]

Slug flow is the most prevalent problem of two-phase fluid transportation in the petroleum industries. Here, large amplitude waves lead to the pipe blockage that possible to cause the damage of the mechanical structure. The experimental investigation of gas-liquid slug two-phase flow in a horizontal pipe was carried out to investigate the initiation and flow development mechanisms. Air and water were used as the working fluids. The inner pipe diameter was 26 mm. In the present experimental study, the slug initiation mechanisms were explained by visual observation and pressure fluctuations. Moreover, the initiation frequency of slug flow and the evolution of passing slug frequency along the pipeline were also observed by using two high video cameras. As a result, several basic mechanisms of slug flow initiation in a horizontal pipe were clarified. Those were the wave coalescences, the wave growth mechanism, and the large disturbance waves. A flow initiation map was proposed to address those mechanisms. Here, the slug initiation frequency and the passing slug frequency were obtained in relation to the pipe length position. The static pressure measurement was also used to verify the image processing results on the characteristics of slug initiation mechanisms. The obtained qualitative and quantitative results from the investigation can be used to evaluate the recent available models. [ABSTRACT FROM AUTHOR]

In order to improve the understanding of transient behavior of gas-liquid plug two-phase flow in a horizontal pipe, CFD simulations and experimental studies on the relevant phenomena were carried-out. The pipe diameter and pipe length were 26 and 9.5 m respectively. The transient calculations were carried out using a Volume of Fluid (VoF) multiphase flow model of the commercial CFD code of FLUENT 6.3. The corresponding CFD solution has been obtained by using the Best Practice Guidelines of CFD for thermal engineering purposes. In the present works, the series of high quality experimental data was used to validate the CFD calculations in terms of time and space. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicate also a quantitative agreement between calculations and experimental data for the elongated bubble length and the time variation of the liquid hold-up. [ABSTRACT FROM AUTHOR]

The effect of surface roughness on the dynamic behavior and the heat transfer phenomena of multiple successive micrometric water droplets impacting onto inclined heated solid surfaces has been studied experimentally. The inclination angles were 15°, 30°, and 45° from horizontal. The droplet diameters were 500 μm and 700 μm. The solid surface temperatures were decreased from 500 °C to 100 °C. The test material was stainless steel-grade 304 (SUS 304) with different surface roughness ranged from Ra 0.04 up to Ra 10. The droplet dynamics during the impacting onto inclined hot surfaces were investigated by using high-speed video camera. It was found that the surface roughness significantly affects quenching behavior. The higher the surface roughness, the lower the quenching time during the spray cooling. The solid-droplet contact time and the droplet spread diameter increase with the increase of surface roughness. Thus causing the decrease of the quenching time of inclined hot walls. Meanwhile, the critical heat flux and Leidenfrost temperatures are shown to be insensitive to the surface roughness. [ABSTRACT FROM AUTHOR]