Bubble Generation Rate Research Articles

Two-phase closed thermosiphon with grooved the evaporator section applied for low-grade energy recovery: Thermo-hydrodynamic performance and potentials

High thermal conductivity and simple structure of two-phase closed thermosyphons (TPCTs) facilitate it extensively applied in low-grade thermal recovery, such like geothermal and solar energy exploitation. In present work, by incorporating threaded grooves into the evaporator section of the TPCTs, heat transfer performance could be significantly enhanced. Thermal transport mechanism of thermosyphons with various threaded groove structures was comprehensively investigated, and corresponding thermo-hydrodynamic performance was modelled through CFD/VOF simulations. Numerical procedures were validated well after comparison with experimental ones felled within 5.0 %. Under various heating power levels and filling ratios, heat transfer performance of thermosyphons with threaded grooves evidently surpassed that of smooth thermosyphons. Depending on delicate numerical results, critical point at 33 % filling ratio and 90 W heating power were confirmed that total thermal resistance of the grooved thermosyphon decreased almost close to 4.6 %. Furthermore, deviating from that critical point, higher heating power and lower filling ratio instead confined heat transfer performance of the threaded TPCT, which was primarily due to the rate of bubble generation and growth being significantly was slower than its detachment rate from the wall. In addition, heat and mass transfer performance of thermosyphons with threaded grooves of various pitches and apex angles were further analyzed under various conditions. Our results indicated that, when the groove apex angle turned to 90°, overall thermal transportation capability of the TPCT achieved optimal, with a decline in thermal resistance of up to 6.5 % compared to thermosyphons with smaller apex angles. Apex angle primarily affected the number of nucleation sites and the bubble detachment rate. Additionally, as the screw pitch decreased, boiling heat transfer enhancement, leading to more robust boiling heat transfer of TPCTs. Under high heating power, thermosyphons with larger screw pitch exhibited superior heat transfer performance. Overall, this innovative TPCTs with threaded grooves could be well applied in low-grade energy exploitation, particularly like as geothermal and solar energy fields.

Visualized study and performance evaluation on a micro-grooved vapor chamber

The evaporation resistance and capillary flow both dominates the heat transfer performance of aluminum vapor chamber (VC) with micro-grooved wicks (MGW). This study presents the visualization experiments for three MGW VC samples with different cross-sectional shapes, including semicircular (MGW-S), V-shaped (MGW-V) and trapezoidal (MGW-T). The characterization of capillary rise dynamics is evaluated and compared by depicting the transient liquid front in vertical installation while the thermal spreading capability is examined horizontally at the quasi-steady state. Results show that the MGW-T exhibits the highest capillary pressure, and higher capillary rise rate can be obtained when applying acetone as working medium. As the groove shape impacting on the rate of bubble generation and detachment during evaporation process, the MGW-S obtains the lowest average thermal resistance. However, compared to the uniformly generated bubbles of acetone, it is revealed that ethanol might result in the slug or puddle at the evaporation area, which shortens the flow length of vapor and increases the average thermal resistance. When conducting under incremental heat loads, the boiling phenomenon of the working liquid becomes increasingly turbulent, and the average thermal resistance can be minimized from 2.6 K/W to the level lower than 1 K/W. As the result, when using acetone with filling ratio of 30%, the average thermal resistance of the MGW-T reaches 0.92 K/W under heat load of 60 W.

Effect of foam quality on foam three phase displacement characteristics in porous media-A mechanistic numerical study

Foam technology has shown great potential in enhancing oil recovery as well as fulfilling carbon geological storage practices in mature and low permeability reservoirs. To reveal the mechanism of the foam quality effect on foam displacement behavior in underground formations, numerical studies on three-phase foam flow characteristics in porous media have been carried out based on the Stochastic Bubble Population Balance (SBPB) model. Through modifying the injection gas and liquid rate ratio, various foam qualities between 40% and 90% have been set, and the effect of foam quality was taken into account with higher foam quality corresponding to the larger maximum bubble density parameter in the SBPB model. Comprehensive numerical results, including the dynamic distribution curves of the oil, water, and foam phase saturation, oil phase pressure, and the foam bubble density along the flow direction, were obtained under different foam quality cases. Parameter investigations on the bubble generation rate and the oil viscosity were carried out as well. It is observed the pressure drop and water recovery rate of the foam flooding process increases monotonously with the increasing foam quality, while the ultimate oil recovery rate shows the highest value at the intermediate foam quality of 70%. The numerical results on the foam quality effect agree well with reported experimental observations, indicating the SBPB model could characterize in mechanism the three phase foam displacement behavior in porous media.

INVESTIGATION OF WATERJET EFFLUX NOISE WITH NUMERICAL TECHNIQUES

The URN resulting from a waterjet propulsion (WJP) is to be accurately estimated for stealth considerations. Such WJP systems are designed to operate either with a submerged jet (wet transom) or with a free surface jet (dry transom). The URN due to the operation of WJP system can be broadly categorized as pump noise and nozzle efflux noise. Pump noise includes mainly the cavitation noise and the tonal mechanical/hydrodynamic noise, whereas the nozzle efflux noise is due to jet impact and bubble entrainment. The present study attempts to implement advanced numerical techniques to estimate URN due to the nozzle efflux of a WJP in both wet and dry transom modes. Large Eddy simulations (LES) are carried out to simulate the hydrodynamics of turbulent multiphase flow behind both submerged and free surface water jets. The impact of water jet on free surface and subsequent bubble generation rate is captured using multiphase volume of fluids (VOF) technique. The impact noise is estimated by directly recording the fluctuating acoustic pressure at certain field points during the simulation. A blob detection algorithm is implemented to compute the bubble generation rate. A mathematical model to compute the bubble pulsation noise from bubble generation rate is validated and implemented. The estimated URN levels in wet and dry mode are presented and compared. Key inferences are presented which could be useful in further investigation of URN from water jet of stealth vessels, as well as to investigate bubble noise from propeller cavitation, air lubrication etc.

Effect of gas injection rate on bubble generation characteristics and coal flotation

Using a high-speed motion acquisition system, the effect of gas injection rate on dynamic bubble characteristics in the presence of flotation reagents was investigated, and the force analysis during the bubble generation was performed. The corresponding coal flotation tests were conducted to discuss the relationship of the bubble characteristics and the coal recovery. According to a partition criterion of contact angle as 90° between the bubble and the capillary, the bubble generation process was divided into formation, expansion and contraction stages, and the generation time was majorly allocated to the expansion stage. As the gas injection rate increased, the bubble aspect ratio decreased, the bubble size increased and the bubble generation time decreased. The surface tension was analyzed as the main force for adhering the bubble on the capillary, and the buoyancy was deemed as the main force detaching the bubble from the capillary. Furthermore, the increase in net force was analyzed as the essential factor for the increase in bubble generation rate during the expansion stage. The combustible matter recovery increased as the gas injection rate increased, and the flotation rate constant was analyzed closely related to the bubble deformation. The results can provide valuable insights into the development of technology for mineral flotation.

Joint formation mechanism of different laser transmission welding paths

Abstract In this study, the rectilinear, sine, and spiral paths of polymer transmission welding were used to perform welding comparative experiments, and the influence of various parameters in the polymer transmission welding of different laser paths on the joint performance and the formation of molten pool was discussed. The spiral path exhibited the highest joint strength, that increased by more than 50% compared with conventional rectilinear welding. The molten pool formed by spiral welding had a high depth-to-width ratio. Microscope observations revealed that the glass fiber flow signs in the molten pool were obvious, the glass fiber in the molten pool was abundant, and the bubble generation rate in the molten pool was lower. In this paper, Fortran language was used to construct Gaussian body heat source movement model with different paths. Results show that the spiral welding had higher welding stability than traditional rectilinear welding, welding defects caused by the lack of heat in the previous period can be properly compensated by selecting the appropriate welding period, Therefore, good joint performance can be achieved. In addition, amplitude and period are two important process parameters of spiral welding, and their sizes have important effects on joint strength and molten pool formation

Numerical modeling of adjacent bubble interactions under the influence of induced vibrations in liquid pool using lattice Boltzmann method (LBM)

This paper reports our numerical investigation on the bubble dynamics of two adjacent bubbles formed on the heated surface as the liquid pool is subjected to induced vibrations caused by oscillating solid bodies in periodic motion. The modeling involves 2D simulations of the entire ebullition cycle comprising of bubble nucleation, growth, coalescence, and departure by employing a combination of multiple relaxation time based lattice Boltzmann method with the finite difference method based thermal model. The numerical results throw insight into the different processes pertaining to bubble growth in the two systems, viz., the quiescent system (QS) and the system with oscillating solid bodies (OSBS). These include the bubble growth rate, vapor bridge formation, subsequent coalescence, and movement of three-phase contact lines. It is observed that the induced vibrations in the liquid pool leads to earlier nucleation and growth of the bubbles, and higher bubble departure frequency (f∗) due to additional forces acting on the bubble, which at one instance helps the two adjacent bubbles to coalesce and at the following instance pulls the coalesced bubble off the solid surface. A force balance analysis is presented to explain the evolution of the adjacent bubbles and their interactions. A sensitivity study is conducted to investigate the effects of unequal sizes of nucleation sites, unequal surface superheat (Ja), and distance between the nucleation sites. In all these cases, multiple bubbles are seen to form on the heated elements, which subsequently coalesce with each other and depart in a single ebullition cycle in OSBS, whereas only two initially formed bubbles are seen to merge and depart in a single ebullition cycle in QS. Subsequently, a sensitivity study is conducted to investigate the effects of surface wettability, and it is found that for a given surface superheat (Ja) and configuration of nucleation sites, f* reduces after a threshold value of wetting angle (θ∗) in QS while it reaches a maximum in OSBS before coming down. It is further observed that if the hydrophobicity of the surface is increased from θ* = 1.0 to 1.1 in OSBS, f∗ remains high until a threshold Ja, beyond which it reduces drastically due to a higher rate of bubble generation compared to detachment.

Complete suppression of flow boing instability in microchannel heat sinks using a combination of inlet restrictor and flexible dampener

Flow boiling suffers from the issue of instability due to the high rate of bubble generation in confined spaces within microchannel heat sinks. The cyclic changes in flow regimes lead to prolonged periods of dry out due to the backflow of vapour at high heat fluxes. Poor management of excess vapour and the resulting crowding at the outlet plenum drastically deteriorates the thermal and hydraulic performance of microchannel heat sinks. This study incorporates the simple design of a flexible membrane type pulsation dampener at the outlet port to address the aforementioned issues. The flexible dampener expands to accommodate the excess vapour, thereby minimising backflow and dryout within the channels. The heat sink design with the flexible dampener drastically reduces the fluctuations with lower surface temperature and pressure drop in compassion to the baseline case. Next, we combine the flexible dampener design with the inlet restrictor and compared the performance with and without the flexible dampener. The fluctuations/backflow are completely mitigated in this case, however, at the cost of a slight increase in pressure drop. Nonetheless, a quantitative comparison in terms of performance evaluation criteria suggests that the pulsation dampener can largely minimise the pressure drop penalty due to inlet restrictors while ensuring complete suppression of instability.

Effects of Gravity on Foam Behavior in Roughened Model Fractures

Summary In this study, to investigate how gravity affects foam in open vertical fractures, we report foam experiments in three 1-m-long, 15-cm-wide glass-model fractures. Each fracture has a smooth wall and a roughened wall. Between the two walls is a slit-like channel representing a single geological fracture. Three model fractures (Models A, B, and C) share the same roughness and have different hydraulic apertures of 78, 98, and 128 µm, respectively. We conduct foam experiments by horizontal injection in the three model fractures placed horizontally and sideways (i.e., with the model fractures turned on their long side), and in Model A placed vertically with injection upward or downward. Direct imaging of the foam inside the model fracture is facilitated using a high-speed camera. We find that foam reaches local equilibrium (LE; where the rate of bubble generation equals that of bubble destruction) in horizontal-flow experiments in all three model fractures and in vertical-flow experiments in Model A. In fractures with a larger hydraulic aperture, foam is coarser because of less in-situ foam generation. In the vertical-flow experiments in Model A, we find that the properties of the foam are different in upward and downward flow. Compared with downward flooding, upward flooding creates a finer-texture foam, as sections near the inlet of this experiment are in a wetter state, which benefits in-situ foam generation. Moreover, less gas is trapped during upward flooding, as gravitational potential helps overcome the capillarity and moves bubbles upward. In the sideways-flow experiments, gravity segregation takes place. As a result, drier foam propagates along the top of the fractures and wetter foam along the bottom. The segregation is more significant in fractures with a larger hydraulic aperture. At foam quality 0.8, gas saturation is 27.7% greater at the top than the bottom for Model C, and 19.3% and 10.8% for Models B and A, respectively. Despite the gravity segregation in all three model fractures, water and gas are not completely segregated. All three model fractures thus represent a capillary transition zone, with greater segregation with increasing aperture. Our results suggest that the propagation of foam in vertical natural fractures meters tall and tens of meters long, with an aperture of hundreds of microns or greater, is problematic. Gravity segregation in foam would weaken its capacity in the field to maintain uniform flow and divert gas in a tall fracture over large distances.

Hydrogen bubble-assisted growth of Pt3Te4 for electrochemical catalysts

Novel materials and structures with abundant active sites have been in continuous demand for electrochemical catalytic applications. In this study, we synthesized platinum telluride (Pt3Te4) nanocrystals on two-dimensional metallic molybdenum ditelluride (MoTe2) using a dynamic hydrogen bubble template method in the hydrogen evolution reaction (HER). The local crystal structure and chemical state of the Pt3Te4 nanocrystals were investigated using X-ray nano-diffraction and X-ray nano-absorption spectroscopy. In our electrochemical deposition method, the morphology, and HER performance of the Pt3Te4 nanocrystals could be manipulated through the hydrogen bubble generation rate. Thus, the nanorod-shaped Pt3Te4 nanocrystals, fabricated by a high rate of hydrogen bubble generation, exhibited outstanding HER performance, which is in contrast with the HER performance of hemisphere-shaped Pt3Te4. Our study provides a facile and systematic way of synthesizing high-performance electrochemical catalysts using the hydrogen bubble-assisted growth method.

Effects of Gas Trapping on Foam Mobility in a Model Fracture

In enhanced oil recovery, foam can effectively mitigate conformance problems and maintain a stable displacement front, by trapping gas and reducing its relative permeability in situ. In this study, to understand gas trapping in fractures and how it affects foam behavior, we report foam experiments in a 1-m-long glass model fracture with a hydraulic aperture of 80 upmu m. One wall of the fracture is rough, and the other is smooth. Between the two is a 2D porous medium representing the aperture in a fracture. The fracture model allows direct visualization of foam inside the fracture using a high-speed camera. This study is part of a continuing program to determine how foam behaves as a function of the geometry of the fracture pore space (AlQuaimi and Rossen in Energy & Fuels 33: 68-80, 2018a). We find that local equilibrium of foam (where the rate of bubble generation equals that of bubble destruction) has been achieved within the 1-m model fracture. Foam texture becomes finer, and less gas is trapped as interstitial velocity, and pressure gradient increase. Shear-thinning rheology of foam has also been observed. The fraction of trapped gas is significantly lower in our model (less than 7%) than in 3D geological pore networks. At the extreme, when velocity increases to 7 mm/s, there is no gas trapped inside the fracture. Our experimental results of trapped-gas fraction correlate well with the correlation of AlQuaimi and Rossen (SPE J 23: 788-802, 2018b) for fracture-like porous media. This suggests that the correlation can also be applied to gas trapping in fractures with other geometries.Article HighlightsWe have made a lab-scale 1-meter-long transparent glass model representing a geological fracture with roughened surface, and we have implemented a direct method of image analysis to quantify the texture of bubbles in the fracture and to link the texture with the strength of the foam;We have successfully created surfactant-stabilized foam flow inside the fracture and examined its stability along the 1-meter-long fracture;We explain the mechanism of gas trapping in fractures and how it affects foam behavior. We also discuss how viscous force and capillary force affect gas trapping in fractures at our experimental conditions.Graphic

Experimental investigation on pool boiling for downward facing heating with different concentrations of Al2O3 nanofluids

Abstract An experimental study has been conducted to examine the effect of different concentrations of α-Al2O3 nanofluids on boiling heat transfer for downward facing heating. The experimental results indicated that the surface heat transfer was enhanced with the rise of the nanofluids concentration, due to the bubble generation rate and disturbance increased. For downward facing heating, bubbles were not able to escape since the bouncy force influenced, and the vapor film appeared earlier as the increase of bubble generation rate. However, the heat transfer coefficient remains at a relatively high value in the early stage of film boiling, which suppresses the deterioration of heat transfer, due to the influences of nanofluids. As the various concentrations of nanofluids increased from 0 g/L to 0.012 g/L, it was found that the enhancement of the CHF (critical heat flux) up to 20.5%. After the nanofluids boiling, the surface roughness decreased and the wettability became worse. From the experimental phenomena, under the influence of these two factors, the bubble activity was enhanced.

Parameter calibration of the stochastic bubble population balance model for predicting NP-stabilized foam flow characteristics in porous media

Stochastic Bubble Population (SBP) balance model has been widely applied on investigation of surfactant foam flow characteristics in porous media, while its application on predict nanoparticle (NP)-stabilized foam behavior has not been well refined. There are two empirical parameters in the SBP model, namely, the bubble generation rate Kg and the maximum bubble density nmax. To qualify the SBP model on prediction of the transient NP-stabilized foam propagation behavior, we make the efforts to calibrate the parameters of Kg and nmax based on the literature reported systematic experimental results. Through five sets of simulations in correspondence to the experimental works, it is found Kg has little effect on the pressure drop along the core, while the nmax increases from 200 mm−3 to 8000 mm−3 with the addition of NPs and the increment of NP concentration. Larger nmax values at higher NP concentrations indicates the foam stabilized by NPs has stronger foam structure and therefore leads to a better displacement result. It is concluded that based on the simple but carefully calibrated parameters, SBP model could provide accurate predictions of NP-stabilized foam flow characteristic in porous media.

High-Pressure Pool-Boiling Heat Transfer Enhancement Mechanism on Sintered-Particle Wick Surface

We experimentally study high-pressure pool-boiling heat transfer enhancement using a copper sintered-particle wick structure in water. The wicks are fabricated using the multi-step sintering process using 200 μm sintered copper powder. Thermophysical properties of water change at elevated pressure, therefore changing the bubble dynamics. For the monolayer wick, the Critical Heat Flux (CHF) 179.63 W/cm2, 182.42 W/cm2, and 198.16 W/cm2 are found at 0, 103.4, and 206.8 kPa, respectively. The maximum CHF is found at 206.8 kPa with the wick superheat of 9.89 K. A 110% enhancement is found in the CHF for 206.8 kPa, compared to 0 kPa. While we observe the CHF is 1.8 times higher as compared to the plain copper surface at 0 kPa. The maximum heat transfer coefficient, 252.46 W/cm2 K is found at heat flux 100 W/cm2 for 206.8 kPa. The high-pressure boiling result for the monolayer wick shows that the heat transfer coefficient is enhanced by 100% compared to 0 kPa. We suggest the reasons of enhancements in the pool-boiling performance are primarily due to high rate of bubble generation, high bubble release frequency and reduced thermal-hydraulic length modulation, and enhanced thermal conductivity due to the sintered wick layer. Our analysis suggests that the Rayleigh-critical wavelength decreases by 4.67 % with varying pressure, which may cause the bubble pinning between the gaps of sintered particles preventing bubble coalescence. Similarly, the dominant role of pressure over the wicking layer is also analyzed and found that the critical flow length, λu reduces by three orders of magnitude with 200 μm particles. We suggest that the porous wick layer provides a capillary-assist to liquid flow effect, and delays the surface dry out. The surface modification and the pressure amplify the boiling heat transfer performance. All these reasons may contribute to the CHF, and HTC enhancement in the wicking layer at high pressure.

The numerical modeling of the vapor bubble growth on the silicon substrate inside the flat plate heat pipe

Inside the flat plate heat pipes for the microelectronics packages, the micro scale boiling is a common phenomenon under the suddenly high heat flux. The internal vast vapor bubble nucleation and growth become a challenge for the stable operations. Due to the lack of the direct observations, the vapor bubble growth in early stage is still unclear. In order to study the initial bubble growth, the molecular dynamics models of water-silicon interfaces which have different sizes of simulation boxes were examined. The vapor bubble diameter growth rates (0.18 ± 0.02 × 106 mm/s) were calculated among the different sizes of simulation boxes. Since the lack of extra energy input, the initial vapor bubble can only expand to 45 nm diameter large (under 100 W/cm2 heat flux at 350 K initial temperature). The growth phenomena of 0.1 μm to 0.3 mm scale bubbles could be further modeled by the Mixture models. The observed bubble (bubble diameter between 10 μm and 0.3 mm) had a diameter growth of 0.71 ± 0.19 mm/s that was close to the Mixture model simulated one (0.75 mm/s). In addition, the ratio of the bubble volume growth rate to the bubble covered bottom area was about 7 ± 0.2 mm/s. By calculating the ratio between the growth rate of observed bubbles and volume of the simulated stable nucleation bubble, the bubble generation rate (3 × 1014 bubble/s mm2) under certain conditions might be estimated. Therefore, the whole process of bubbles growth could be deduced.

Statistical and experimental investigation on flow boiling heat transfer to carbon nanotube-therminol nanofluid

In the present work, statistical, regression and experimental studies were conducted to assess the plausible application of an oil-based carbon nanotube nanofluid for high-temperature applications such as solar thermal receivers. Nanofluid was prepared at wt. %=0.1 and wt. %=3 using two-step procedure and was stabilized using ultrasonic together with the addition of surfactant. As a criterion for the stability of nanofluid, the zeta potential value was measured. Results showed that during flow boiling heat transfer, two distinguished heat transfer regions were identified namely forced convective and nucleate boiling heat transfer domains. Likewise, the presence of carbon nanotube within the oil increased the convective heat transfer coefficient (HTC) together with a significant increase in the nucleate boiling HTC. An increase in the heat and mass fluxes were found to enhance the flow boiling HTC both in convective and nucleate boiling regions. The sub-cooling temperature was also found to increase the HTC in convective and nucleate boiling regions due to the enhancement in thermo-physical properties of nanofluid. With an increase in the mass flux, the pressure drop of the system was increased. Heat flux was also enhanced the pressure drop within the system due to the increase in the rate of bubble generation and vapor blanket formation. Likewise, with an increase in the mass concentration of nanoparticles, higher pressure drop was registered in convective and nucleate boiling regions. Thermal performance index of the system showed that carbon nanotube can increase the thermo-hydraulic performance of the system by 56% in comparison with pure therminol 66. Equations were developed to predict the ONB points at various temperatures with A. A. D.% of ±0.9% to ±4.2% obtained with non-linear regression.

Numerical investigations on the inlet and outlet behavior of foam flow process in porous media using stochastic bubble population balance model

Numerical investigations were carried out with special attentions on the inlet and outlet behaviors of foam flow process in a homogeneous porous media with confined entrance and exit boundaries. The Stochastic Bubble Population (SBP) balance model, which usually involves two parameters of the bubble generation rate Kg and the maximum bubble density n∞ for bubble number prediction, was employed to study the dynamic foam generation and development process in porous media. With introduction the Kfp parameter to take into account the foam phase relative permeability reduction effect, the control equations of the two-phase flow process in a two-dimensional computational domain were solved with the IMPES algorithm and the inlet and outlet behavior of the foam displacement process were scrutinized based on detailed analysis of the bubble density, water phase pressure and water phase saturation distributions in porous medium. Numerical results showed a clear entrance effect of higher water saturation, lower pressure gradient and developing bubble density in the inlet region of the porous media in the transient foam displacement process, whereas the confined exit results in elevating water saturation and decreasing pressure gradient towards the outlet of the core. Parametric studies on Kg,n∞, Kfp and inlet & outlet sizes D indicate higher bubble generation rate could remarkably suppress the entrance region in the foam seepage process, while the higher maximum bubble number did not lead to obvious change of the foam flow behavior in the inlet and outlet region, although it could produce higher absolute values of bubble density and pressure drop along the core. With lower Kfp values, the strong foam flooding behavior could be properly predicted with much higher pressure drop and lower water saturation. Two dimensional numerical results at various inlet and outlet sizes clearly show the confined geometry effect on foam flow characteristics with smaller sizes corresponding to longer inlet and outlet regions. Computational domain and numerical results were validated through comparisons with corresponding experimental setup and CT measurement results. It is observed that, the numerical simulation could reproduce not only qualitatively but also quantitatively the experimentally obtained water saturation distribution and pressure drop result. It is concluded that the mechanistic stochastic bubble population model could be reasonably employed on prediction of the inlet and outlet behavior in the transient foam flow process in the homogeneous porous media.

Properties of Thermal Conductivity According to Replacement Ratio of Paper Ash of Lightweight Composite Panel Core

Background/Objectives: Korea, which is mostly composed of multi-family houses, is paying attention to the importance of sound insulation, insulation, and fireproofing in the environment of multi-family housing.Methods/Statistical analysis: This study is a study on the production of lightweight composite panel core using inorganic by-product, blast furnace slag, paper ash, polysilicon sludge and vermiculite. When the paste is lightweight due to the foamability of the paper ash, the applicability of the paste as a building dry panel is examined.Findings:As a result of the analysis of the experimental results, the fluidity shows a tendency to decrease as the replacement rate of the paper ash is increased. The compressive strength shows a tendency to decrease as the substitution rate of paper ash increases and the compressive strength shows a constant tendency with a substitution rate of more than 15%. As the substitution rate of paper ash increases, the size of bubbles on the surface of the cured product increases and the rate of bubble generation increases.Improvements/Applications: As a result of this study, the thermal conductivity decreases as the substitution rate of paper ash increases, and further study is required for the fire resistance test.

Numerical simulations and experimental validation on passive acoustic emissions during bubble formation

In this paper, the volume of fluid (VOF) model in conjunction with continuum surface force (CSF) model is applied to numerically investigate the single bubble formation process in the bubble columns. Meanwhile, the hybrid method (large-eddy simulation (LES) and acoustic analogy method) is used for bubble acoustic prediction. Experimental results provide a reliable validation of the numerical results. Adaptive filtering technique and time–frequency analyses are adapted for the numerical acoustic data at the gas velocity of 0.1m/s. The spectrum and spectrogram approaches indicate that the numerical acoustic data covers two principal frequency components, in which, one is the bubble generation rate and the other is the natural frequency of volumetric bubble oscillation. By combining the studies of flow field and acoustic signals, volumetric bubble oscillation is found to be excited by an axial water jet up into the bubble, immediately following the bubble detachment. The results of this study lead to the proposition that numerical simulation method could be applied to well understanding of the physics behind the passive acoustic emission.

Prediction of Bubble Generation Based on Acoustic Emission

The noise associated with gas discharged from a submerged nozzle is of great interest to many industries because of its important applications. For example, it can be used to size bubbles and to detect gas flow rate. However, the physics associated with the acoustic emission due to bubble formation is complex, particularly when a large number of bubbles are involved, and has not been fully understood. In this study, the dynamics of the bubble formation from a submerged nozzle has been studied experimentally using the Particle Droplet Image Analysis technique. An improved model for prediction of the bubble generation rate and size distribution based on acoustic emission is presented. The experimental study is carried out in a large water tank, of dimensions 10 m \(\times \) 10 m \(\times \) 6 m, using multiple hydrophones. The water tank is carefully calibrated in order to provide free-field measurements. The predicted bubble generation rate and size distribution have been compared with the experimental data. It has been found that the predicted results are in good agreement with the experimental measurement, implying that an accurate prediction of acoustic emission associated with a bubbling plume from a submerged nozzle can be achieved by using the model.