Air Injection Rate Research Articles

Viscous fingering and interface splitting instabilities in air-water-oil systems.

Viscous fingering instabilities of air displacing water displacing mineral oil is controlled by the air injection rate. Given the lower viscosity of the water, air would tend to finger through the water and then after it reaches the oil, proceed to finger through the oil. In a radial Hele-Shaw cell, experiments were conducted on air injection into mineral oil and air injection into a volume of water at the center of the cell which in turn is surrounded by mineral oil. The images of the fingers are analyzed to quantify the fingering patterns to compare the behaviours between the two and three phase systems. Significantly different fingering patterns occur between the two and three phase systems. When air fingers penetrate the water layer and reach the oil, the air propagates along the interface between water and oil in an interface splitting instability mode resulting in development of more intricate fingering patterns. It was also observed that air fingers penetrate within water fingers that penetrate the oil. In addition, the fingertip moves faster with the presence of water exhibiting a discontinuity of the fingertip velocities across the water and mineral oil regions.

Enhancing wastewater treatment efficiency through hydrodynamic cavitation and advanced oxidation processes: Experimental insights and comparative analysis

BackgroundThe escalating industrial wastewater production mandates effective treatment methods to mitigate environmental and health risks. Hydrodynamic cavitation (HC) and its combination with advanced oxidation processes (AOPs) offer promising approaches for wastewater pollution reduction. MethodsThis study investigates the enhancement of HC efficiency for Chemical Oxygen Demand (COD) reduction by integrating hydrogen peroxide (H2O2) and air injection. Synthetic wastewater resembling industrial effluent COD levels serves as the experimental medium. Varied inlet pressures, H2O2 concentrations, and air injection rates were examined to gauge their impact on COD reduction. Significant FindingsHigher inlet pressures directly correlate with increased COD reduction, highlighting intensified cavitation effects. Combining HC with H2O2 or air, especially when directly injected into the venturi throat, showcased substantial synergy, significantly reducing COD levels. Notably, the maximum extent of COD reduction, achieved at 51.85 %, was with the combination of (HC+H2O2+Air). The COD reduction percentages for other processes, including HC alone, (HC+Air tank injection), (HC+Air throat injection), (HC+H2O2 tank injection), and (HC+H2O2 throat injection), were 4.21 %, 19.7 %, 20.9 %, 37.8 %, and 39.4 %, respectively.

Optimization of Flotation Efficiency of Micro Bubbles Using Low-Energy Best Available Technique

Global warming caused by urbanization, industrialization, and population growth is leading to climate change and threatening our sustainable lives. As a response to this climate crisis, a best available technique(BAT) that minimizes the emission of existing pollutants and is also economical is required. The purpose of this study is to develop a lowenergy micro bubble generator to reduce energy consumption in water treatment facilities and to evaluate its performance in comparison with dissolved air flotation(DAF) and coagulation-flocculation processes. The low-energy micro bubble generator consists of an air injector, a chamber, and a nozzle. The experimental results showed that the low-energy micro bubble generator generated micro bubbles of similar size to DAF at an air injection rate of 5 ml/min. In addition, the flocculant concentration experiments showed that the low-energy micro bubble generator had 1.3-2.5 times higher turbidity removal efficiency than DAF and coagulation-flocculation processes even with flocculant injection of 8 mg/L or less. These results suggest that the low-energy micro bubble generator is effective in removing suspended solids from water and is an optimal solution for reducing carbon emissions. This study is expected to contribute to the increased utilization of this technology in industrial sites.

Injection Of air control of propeller performance

With the rise of bubble lubrication technology in transport ships, the interaction between propellers and bubble flow has become increasingly important. On the basis of solving the Reynolds averaged equation and the volume fraction equation, a numerical model of the propeller in a water air mixed fluid was established using the sliding mesh technique. Based on verifying the numerical calculation model of the semi-immersed propeller, uncertainty analysis was conducted on the KP505 propeller flow numerical model, and the open water performance of the propeller was calculated to be affected by the injection position and injection volume. A linear model was established to describe the relationship between the open water performance of the propeller at the axis and the injection rate. The performance surface model was used to describe the effect of the air injection position moving towards the blade tip on open water performance at different air injection rates. The strength and dissipation of the tip vortex and hub vortex of propeller are affected by the radial air injection position. Air injection at the axis causes the hub vortex to expand and connects the tip vortex to form a vortex ring in the far field. The air injection position moves towards the blade tip, and the vortex system at the blade tip accelerates and rapidly dissipates.

Correlation between subretinal tissue plasminogen activator and air injection rates with pressure in a retina mimicking model

By investigating the correlation between the injection rate and pressure of subretinal tissue plasminogen activator (tPA) and air using a standard Viscous Fluid Control (VFC) system with a 38-gauge cannula, we aimed to establish guidelines for stable injections. We fabricated a retina mimicking model (RMM) with 0.25% agarose solution and an aluminum plate, and substituted submacular hemorrhage (SMH) and tPA with blood-mimicking fluid (BMF) and balanced salt solution (BSS), respectively. The diameter of the pre-bleb mimicking SMH in RMM was 1.30 ± 0.16 cm, increasing to 1.98 ± 0.24 cm and 1.83 ± 0.22 cm after bleb propagation with BSS and air, respectively. BSS injection rates were 2.86 ± 0.04 µl/sec, 6.74 ± 0.48 µl/sec and 8.55 ± 0.16 µl/sec at 8, 12, and 16 psi, respectively. Air injection rates were 37.98 ± 3.11 µl/sec, 79.01 ± 5.13 µl/sec and 156.06 ± 13.72 µl/sec at 2, 3 and 4 psi, respectively. By experimenting with different pressures in the RMM, we found 12 psi to be the minimum for proper BSS injection and 2 psi for air. These findings provide crucial parameters for safer surgery to prevent irreversible damage.

Cavitating flow control and noise suppression using air injection

The cavitation phenomenon not only reduces hydrodynamic performance but also generates vibrations and noise, significantly compromising the operational stability of the system. In this study, we investigate the efficiency of air injection in controlling cavitation patterns and reducing noise on hydrofoil, both experimentally and numerically. The focus is to assess how the location of air injection on the suction side of the hydrofoil, the rate of air injection, and the cavitation number affect the cavitating flow. The hydrofoil has a span and chord length (C) of 100 mm. The air is injected from a column of multi-holes positioned at x/C = 0.05, 0.10, 0.30, and 0.40 separately and controlled through a flow meter. The cavitation number ranges from 3.65 to 1.62, while the air injection rates are set at 1, 3, and 5 standard liters per minute. The experiments are conducted at Chungnam National University's high-speed cavitating tunnel. Simultaneously, a high-speed camera is used to observe cavitating flow, and a pressure transducer is employed to measure noise levels. The results indicate that injecting air closer to the leading edge has the most significant impact on reducing vapor cavitation and noise. Injecting air at x/C = 0.05 reduces the length of the vapor sheet cavity by 27% compared to cases without air injection. Increasing the air injection rate increased the volume of ventilated cavitation. Noise reduction is primarily noticeable in the high-frequency region (>2 kHz) at a high cavitation number of 2.22. As the cavitation number decreases to 1.62, the noise reduction shifts mainly to the low-frequency region, and the effectiveness of air injection in suppressing noise is reduced.

Bubble linking anterior growth strategy to prepare hydrogel tubes with different range, branch and voyager function

Hydrogel tubes (HTs) represent a significant facet of hydrogel morphology. Nevertheless, the continuous, rapid, and facile fabrication of hydrogel tubes remains a formidable challenge. In this study, we introduce a novel technique named as Anterior Growth (AG) for the continuous preparation of HTs. This innovative approach employs air bubbles as guidance to direct the growth of polyvinyl alcohol (PVA) HTs crosslinked by copper ions in alkaline solution. Various factors that affect the sizes of HTs from micrometers to millimeters have been explored, including gauge of needles, air bubble volumes, injection rates, and concentrations of NaOH, copper nitrate and PVA. Single HT with various sizes can be easily fabricated by simply adjusting injection rates. The reversibility of PVA-Cu2+ crosslinking makes it possible to produce HTs with multiple branches in a convenient way by generating an orifice out of the HT wall and then repeating the growing process. Inspired by plant thigmotropism, HTs can be guided to grow along designed shapes such as different angles and patterns by combination of air bubble and silicone rubble substrates. Remarkably, this method allows HTs to serve as voyagers navigating intricate flow channels with a projected trajectory, indicating the capabilities of patterning and traversing complex channels. To further application, AG allows other materials to prepare HTs such as sodium alginate or more, showcasing excellent practical value.

Insights into temporal and spatial evolutions of air saturation and its effects on nitrobenzene removal during air sparging remediation

Air saturation (Sa) can significantly influence the removal effect during air sparging (AS). However, there have been few studies focused on the temporal and spatial distribution of the Sa, which is adverse to precise remediation of AS technology. In this study, temporal and spatial evolutions of the Sa and its effects on nitrobenzene removal were investigated by the one-dimensional column experiments during AS. Experimental results demonstrated that the variation of Sa at different positions of the aquifer was significantly different with the increase of sparging time under the same air injection rate (Qinj), and the variation of middle and lower position was 0.3%-11.0%, however, the variation of Sa at the upper position was 21.0%-40.0%. When the Qinj was small, the number of airflow channels was little, and the nitrobenzene removal rates at the middle and upper position were low. With the increase of Qinj, the number of airflow channels was many, and the main region of airflow (Trapezium distribution) began to appear at the lower position, and the nitrobenzene removal rate at the upper position was low, which showed that the nitrobenzene removal rate was mainly affected by the spatial and temporal distribution of Sa in AS process. Based on the above, the mathematical model of relationship between nitrobenzene removal rate, sparging time and Sa was established, which was conducive to the accurate design of AS technology in the site application.

Effects of liquid viscosity and air injection rate on air invasion in a highly compacted granular material

Using laboratory experiments on a network scale together with numerical simulations on a granular scale, we investigate the displacement process as air invades a highly compacted granular material. Experiments in a vertically placed Hell-Shaw cell reveal a non-monotonic behavior of branching formation as air injection rate Q increases from 0.1 to 50 ml min–1 when the liquid viscosity is less than 22.5 mPa s. In the low-injection-rate region where Q < 1 ml min–1, fractures grow in random directions, and the number of branches increases as the air injection rate decreases. However, after the transition to the high-injection-rate region where Q≥ 1 ml min–1, the number of branches increases with increasing air injection rate. At a given air injection rate, increasing the liquid viscosity from 1.01 to 219 mPa s leads to an increasingly concentrated air flow. The numerical simulations exhibit good agreement with the experimental results. More importantly, they shed light on the physics underlying the growth of the fractures by capturing the distribution of the magnitude of velocity, as well as computing the inter-grain force chains in the granular material. The simulations suggest that a high liquid viscosity concentrates the velocity field and force chains and reduces the speeds and inter-grain forces of the grains adjacent to fractures, while a higher air injection rate increases the grain speeds and inter-grain forces. In addition, the distribution of the forces chains behaviors non-monotonically as the air injection rate decreases, which explains the non-monotonic behavior of branching formation observed in the experiments.

Scaling up in situ combustion process for enhanced oil recovery in water-flooded light oil reservoirs from laboratory to field implementation

Aiming at low permeability, high water content light reservoir with a recovery rate higher than 20%, an improved air injection enhanced heat flooding technology is applied by combining the combustion reaction flow and flue gas flooding mechanism. The method involves the injection of air into the reservoir, which reacts with the crude oil at temperatures ranging from 220 to 300 °C. This reaction consumes part of the oil, enabling effective evaporation and flow of the remaining oil. This process combines combustion reaction flow with flue gas flooding, using high-temperature oxidation reactions to mobilize residual oil. Experimental results from combustion tube tests demonstrate stable reaction fronts, peak temperatures reaching up to 550 °C, and a significant increase in recovery rates, reaching 73.8% in some cases. Field applications of this technology require maintaining high air flux and burning rates in low-permeability zones to ensure effective heat-driven evaporation. The geological model of the well group shows that the recovery factor of the target block can be increased by more than 20% by air injection based on the water drive recovery factor of 28%–30%. The oil exchange ratio can be less than 4000 sm3/m3 by optimizing the air injection rate and oxygen content. The research results provide technical feasibility for heat flooding to significantly improve oil flow and recovery in low-permeability light oil reservoirs.

Fixation of air nitrogen to ammonia and nitrate using cathodic plasma and anodic plasma in the air plasma electrolysis method

AbstractThe fixation of nitrogen (N2) from the air into ammonia (NH3) and nitrate (NO3−) is usually conducted using the Haber–Bosch process, which requires the raw material of hydrocarbons for hydrogen (H2), which has a large amount of energy but produces high CO2 emissions. An environmentally friendly and energy‐saving alternative is the air plasma electrolysis method, which can be used to synthesize NH3 and NO3− under ambient conditions. In this study, this method was used to inject air into the plasma zone in a K2SO4 electrolyte solution to produce N2 fixation compounds. The results showed that the use of cathodic plasma promoted the formation of NH3 but suppressed NO3− production. The optimal air injection rate was achieved at 0.6 L.min−1 and an electrical power of 452 W, with a total fixed N2 of 51.66 mmol. The highest formation of NO3− in cathodic plasma was obtained in 35 min, with a value of 29.92 mmol, and 2.57 mmol NH3 was achieved at 60 min. The high concentration of H2 gas, which is a by‐product of this process, can contribute to increasing the use of Haber–Bosch green technology in the production of NH3.

Investigation on natural to ventilated cavitation considering the air-vapor interactions by Merging theory with insight on air jet location/rate effect

Cavitation is of significant practical importance since unstable flow characteristics can have noticeable consequences on objects nearby. An essential approach for controlling the cavitation flow field's instability is air injection. This work aims to conduct a numerical and experimental investigation on the natural to ventilated cavitation around a Clark Y hydrofoil. Having three phases: water, vapor, and air, the cavitation model is adjusted based on the Merging theory to consider the impact of dissolved air on cavitation. Furthermore, the Density Corrected-based Method (DCM) is used to alter the turbulence model. The experimental tests are carried out in the water tunnel, which can maintain the constant water flow rate (Qwater=490 m3⁄h) and regulate the pressure level (105–180 kPa). The Clark Y hydrofoil is fixed at an angle of attack of 8° and includes injection and pressure taps. Two holes, called Tap1-injection and Tap5-injection, are alternatively used for air injection purposes.Two cavitation numbers (σ=1.1, 1.6) and three air injection rates (Q = 0, 0.5, 1 l/min) are considered current case studies. The results demonstrate the meaningful impact of location and rate of aeration on the dynamic/average characteristics of cavitation. Increasing the air injection rate results in an increase in the pressure coefficient values, a decrease in the shedding frequency, and an elongation of the cavity with an M-shaped structure. Also, during a cycle of cavity development, air injection may take place in the reversed jet, perpendicular jet, or direct jet configurations. In addition, a close agreement between numerical and experimental results is recorded.

A simulation-optimization integrated framework for subsurface air barrier strategies to mitigate seawater intrusion in a 3D coastal aquifer

Subsurface air barrier, owing to readily accessible and sufficiently clean of injected air, is a more attractive alternative for mitigating seawater intrusion (SWI) in arid and semi-arid coastal regions, compared to hydraulic barrier. Nevertheless, it remains an enormous challenge to recognize the appropriate layout scheme of air barrier system in a 3D coastal aquifer, including the spatial structure of air-injection zone and the adopted injection pressure, simultaneously considering the environmental and economic performances. This study established a simulation–optimization (S-O) integrated framework for determining the optimal air barrier scheme with minimizing total cost while effectively controlling the extent of SWI. Within the proposed S-O framework, the liquid–gas two-phase flow and solute transport (LGST) numerical model was linked with the micro-population genetic algorithm (mGA). Layout parameters of air barriers, salinity at constraint points and air injection rates were continuously exchanged between the LGST model and mGA at each optimization step. A hypothetical 3D confined aquifer was then employed to evaluate the stability of this S-O framework. The total cost of air barriers increasingly declines to a stable minimum value with the evolutionary processes. With the optimal scheme, there forms a complete and continuous air barrier system between adjacent air-boreholes, giving rise to the intrusive seawater decreasing by 69.7 % and the 0.5 isochlor retreating by 43.4 % at 365.0 day. Furthermore, the 3D aquifer system gradually reaches a quasi-steady state with time and the air injection rate cannot indefinitely increase in response to air injection. The proposed S-O framework can therefore provide a decision support system for designing subsurface air barrier with the least cost on the promise of controlling SWI in 3D coastal aquifers.

Experimental study on insertion loss of air bubble layer in freestream flow

Air injection in water has several engineering advantages, such as an air lubrication system, cavitation control, and noise reduction. The present study investigates the effect of air injection rate and stream velocity on bubble layer volume fraction, thickness, and noise mitigation. The air bubble volume fraction is controlled through the injection rate of 2 to 25 SLPM at different stream velocities. The Froude number is in the range of 30.30 to 70.7. The image processing technique quantifies the air bubble projected void fraction and thickness. The air is injected through a multi-hole pipe placed on a modified NACA 0010 hydrofoil with a 100 mm chord length. The acoustic measurement system consists of a sound transmitter that projects sound waves at the frequency range of 7 to 50.5 [kHz], and on the opposite side of the air bubble layer, a hydrophone is placed to receive the transmitter sound wave. The results showed that the air bubble projected void fraction increased as the air injection and Froude number increased. Higher stream velocity promotes air bubble breaking and the formation of diverse air bubble patterns such as mono-dispersion bubbles and clustering bubbles. As the Froude number increases, the size of the bubble decreases. At various air injection rates and stream velocities, the thickness of the air bubble layer is found to be nearly constant. The bubble layer effectively reduces the noise in all frequency ranges of the present study. The sound pressure level (SPL) inhibition rate increases as the air bubble projected void increases. The insertion loss increases with stream velocity as higher flow velocity leads air bubbles to break and form a cluster of air bubbles, which is found to be more effective in reducing noise than a single bubble. Regardless of injection rate, the maximum insertion loss is 44 [dB] in a frequency of 20 [kHz] and Froude number 70.7.

Investigation into the key factors influencing the establishment and propagation of combustion front in ultra-deep high-temperature heavy oil reservoirs

The in-situ combustion technique is currently on the exploratory stage for ultra-deep high-temperature heavy oil reservoirs. In this work, the oxidation experiments of heavy oil were conducted using thermogravimetry, high-pressure differential scanning calorimetry, and combustion tube. Based on these experimental results, a reaction kinetics model was developed, which was then integrated into the Computer Modeling Group (CMG) STARS reservoir simulation software by adjusting stoichiometric numbers, kinetic parameters, and reaction enthalpy to match the experimental data obtained. Furthermore, a corrected reservoir simulation approach was employed, combining the variance analysis and a Pareto chart, to identify the key factors influencing the establishment and propagation of combustion front in the absence of electrical ignition. The results indicate that a reservoir temperature of 148 °C leads to the establishment of combustion front approximately 7 m away from the injection well, with a delay time of around 25.21 days. The Pareto chart reveals that reservoir temperature and water saturation are the primary controlling factors for combustion occurrence. Specifically, a reservoir temperature above 148 °C and water saturation below 60% increase the likelihood of combustion front formation. Among the examined factors, the reservoir temperature has the most significant effect on combustion front propagation. Once the reservoir temperature reaches 208 °C, a stable combustion front is formed, and the average temperature of combustion front remains around 400 °C throughout 8 years of model operation. When the water saturation was 50%, a consistently stable combustion front can be established within the first 6 years of model operation. However, beyond the 6th year, the average front temperature decreases below 400 °C. Therefore, it is recommended to introduce a certain amount of oxidation catalysts into the oil reservoirs after 6 years of air injection to enhance the combustion reactions. Increasing the air injection rate or pre-exponential factor does not have a significant effect on the average front temperature after 8 years of model operation, which remains below 350 °C. This study can provide significant references for future assessments and decision-making processes related to the application of ISC in ultra-deep high-temperature heavy oil reservoirs.

Techno-Economic Analysis and Optimization of a Compressed-Air Energy Storage System Integrated with a Natural Gas Combined-Cycle Plant

To address the rising electricity demand and greenhouse gas concentration in the environment, considerable effort is being carried out across the globe on installing and operating renewable energy sources. However, the renewable energy production is affected by diurnal and seasonal variability. To ensure that the electric grid remains reliable and resilient even for the high penetration of renewables into the grid, various types of energy storage systems are being investigated. In this paper, a compressed-air energy storage (CAES) system integrated with a natural gas combined-cycle (NGCC) power plant is investigated where air is extracted from the gas turbine compressor or injected back into the gas turbine combustor when it is optimal to do so. First-principles dynamic models of the NGCC plant and CAES are developed along with the development of an economic model. The dynamic optimization of the integrated system is undertaken in the Python/Pyomo platform for maximizing the net present value (NPV). NPV optimization is undertaken for 14 regions/cases considering year-long locational marginal price (LMP) data with a 1 h interval. Design variables such as the storage capacity and storage pressure, as well as the operating variables such as the power plant load, air injection rate, and air extraction rate, are optimized. Results show that the integrated CAES system has a higher NPV than the NGCC-only system for all 14 regions, thus indicating the potential deployment of the integrated system under the assumption of the availability of caverns in close proximity to the NGCC plant. The levelized cost of storage is found to be in the range of 136–145 $/MWh. Roundtrip efficiency is found to be between 74.6–82.5%. A sensitivity study with respect to LMP shows that the LMP profile has a significant impact on the extent of air injection/extraction while capital expenditure reduction has a negligible effect.

Numerical Simulation of the Fin Impact on the Cooling of the Shell of a Rotary Kiln

This work consists of a numerical study of a thermally stressed rotary kiln shell part in a cement plant. The numerical simulations are performed by using the finite volume method for the discretization and the simple algorithm for resolution. The velocity air injection, its temperature, and the kiln rotational velocity are the main parameters under investigation. The distribution of temperature, velocity, and pressure, as well as the evolution of the Nusselt number are determined. In the second step of this study, fins are inserted on the shell to examine their effect on cooling. The results analysis shows that the insertion of fins to the shell has a significant influence on the decrease in temperature of the shell’s external surface. The study shows that this decrease in temperature depends significantly on the air injection rate, not on its temperature, and a bit less on the rotating velocity of the kiln. To avoid overloading our equipment (weight of the shell), only four fins distributed around the kiln are added to explore their effect.

Large-scale micro-aerobic digestion studies at municipal water resource recovery facilities for process-integrated biogas desulfurization

Biogas generated from anaerobic digestion processes typically requires gas conditioning including hydrogen sulfide removal before it is used on-site to generate electricity and heat or before upgrading to biomethane for gas pipeline distribution or vehicle fuel. Experiments of process-integrated micro-aeration in three different large-scale sludge digesters (effective volume 2450 m3, 3250 m3 and 3300 m3) were undertaken at municipal wastewater treatment plants and compared with large-scale applications reported in literature. This work discusses critical process parameters, advantages, and potential limitations of micro-aerobic digestion in comparison with other commonly used biogas desulfurization methods. It shows that high H2S reduction in the biogas can be obtained and that the H2S reduction is dependent not only on the air injection rate and location, but also on the digestion activity identified by the volumetric biogas production. Reliability testing of typical micro-aerobic upset scenarios and long-term micro-aerobic digester operation as part of this study provided deeper insights in the MA process that could also provide valuable input to what operational, maintenance and safety measures should be considered when applying micro-aeration in large-scale digesters. The large-scale micro-aerobic digestion trials demonstrated that the hydrogen sulfide concentration in the biogas can be controlled using minimal plant upgrades, contributing to the sustainability and economic efficiency of the energy recovery process of waste sludge digestion at water resource recovery facilities.

Combustion tube experiments on key factors controlling the combustion process of air injection with light oil reservoir

High pressure air injection (HPAI) has unique advantages due to its rich gas source and unique high-energy displacement effect of the thermal front. Thermal effect of air injection after combustion is the key factor affecting the oil displacement effect. Combustion tube experiments are conducted to study the combustion characteristics of light oil and the influence of different factors on combustion process. We find that light oil (content of asphaltene is only 1.13%) can be ignited and combustion front can advance forward stably, which proves that the implement of HPAI in light oil reservoir can achieve good results. High temperature makes combustion more intense and the advancing of combustion front more stable. The experimental results show that when the air injection rate is low, low temperature oxidation of light oil will dominant, or the combustion front cannot successfully advance. But when the injection rate is too high, the combustion front moves forward too fast and gas channeling will occur. With pressure increasing, the solubility of O2 in oil increases, causing a more violent oxidation reaction. Increasing pressure can reduce the air/oil ratio and improve the utilization rate of O2. Thus, HPAI is more ideal for the reservoirs with high temperature and high pressure. And for a specific reservoir, an optimal injection rate exists. The conclusions of the research can provide references for field applications of HPAI in light oil reservoirs.

Air rumbling for online fouling mitigation of calcium carbonate aqueous solution under subcooled flow boiling heat transfer

In this research, increasing the shear stress by injecting air into the working system was implemented to mitigate crystallization fouling of calcium carbonate (CaCO3) aqueous solution. For this purpose, various experiments were conducted under subcooled flow boiling condition for analysing the effect of air injection on reduction of fouling formation inside a vertical annular channel with upward flow. These experiments were conducted at different operating conditions including air injection rate of 2–10 l/min, air injection freqency (f) of 0.5–2 h−1, heat flux of 52–83 kW/m2, fluid flow rate of 2–4 l/min, fluid bulk temperature (Tb) of 30–55 °C, and at a constant CaCO3 concentration of 0.2 g/l. The results showed that by increasing f from 0.5 to 2 h−1, the rate of fouling formation decreased. Also, the air rubmbling was more effective when Tb increased from 30 °C to 55 °C, by decreasing the fouling resistance from 38% to 57% comparing with no-mitigation experiment. When the heat flux was 83 kW/m2, air rumbling could decrease the fouling resistance by 57%. On the other hand, at lower heat flux of 52 kW/m2, air injection not only failed to reduce the fouling resistance, but increased it by about 20%. Also, when the air injection rate increased from 2 to 10 l/min, fouling resistance increased slightly. This environmentally friendly method has not received much attention before. Hopefully, the results presented in this research can pave the way for more research works on the mitigation of crystallization fouling using air injection.