Influence Of Air Flow Rate Research Articles

Exergy analysis of packed and fluidized bed thermal energy storage systems

This work presents a detailed exergy analysis that compares two different thermal energy storage (TES) systems that use particles as energy storage media and air as the heat transfer fluid: packed and fluidized beds. The study permits the optimization of both TES systems in terms of exergy storage capacity and quantifies the irreversibilities that appear in both cases. In addition, the influence of air flow rate and particle size has been quantified.The results indicate that when focusing solely on the storage process, there is an optimal charging time that minimizes the exergy destruction in both cases: topt∼mscp,s/ṁacp,a. Although the exergy destruction of the fluidized bed during the beginning of the charging process is higher than that in the packed bed, at the end of the process, the total exergy destruction in both beds is similar. However, in the full storage–recovery process the total exergy destruction is doubled in the fluidized case, with an entropy generation number of approximately 0.6 in comparison with a value of 0.3 for the packed bed. Besides, a sensitivity analysis varying the particle size and the air flow rate indicates that the particle size has a much higher influence on the fluidized bed case due to the change in the minimum fluidization velocity and its influence on the heat transfer rate. Finally, a case study is presented using the storage bed for building heating, and an exergy analysis concludes that the fluidized bed generates 534W/K of entropy, more than three times the entropy generated in the packed bed (161W/K), due to the higher pressure drop needed to fluidize the particles.

Investigation of the behavior of plasma jet in the presence of water under different grounded conditions

AbstractPrevious researches have demonstrated that the ground electrode would influence the performance of the plasma jet. In this study, the characteristics of plasma jets underwater for different grounded conditions are investigated. The influence of airflow rate, and electrode length underwater are experimental studies. When the water is grounded, it would provide another charge channel for the discharge, much more ions would be transferred to the water. The length and discharge intensity would be enhanced. Besides, the length of electrode underwater would also influence the performance of the plasma jet. It is found that the shorter the electrode length, the larger the ratio of plasma jet length to electrode length. Furthermore, an electric diagram is promoted to explain the corresponding mechanism, by analyzing the resistance and capacitance under different working conditions, the theoretical explanation under different experimental working conditions is given, and further analysis demonstrated that the accumulation of charges in water during the discharge process would be the main reason to influence the propagation of plasma jet under water.

Thermodynamic Analysis of Air Conditioning System for a Passenger Vehicle with Suction Line Heat Exchanger Using HFO-1234yf

In this study, the experimental thermodynamic performance and environmental impacts of a vehicle air conditioner using HFO-1234yf with a suction line heat exchanger are studied and compared with HFC-134a results. The influences of air flow rate and air temperature at the evaporator inlet, condenser side air face velocity, and the compressor speeds on the thermodynamic performance of the system are investigated. The results showed that HFO-1234yf has a 12% improved coefficient of performance with 8% higher exergy efficiency than HFC-134a. However, HFO-1234yf has marginally poor performance at higher compressor speeds due to more irreversibilities occurred in the compressor and evaporator. The average SLHX effectiveness was observed to be 45% for HFC-134a, while it was 41% for HFO-1234yf. The HFO-1234yf has a 33.9% and 29.4% and 45.1% lower total equivalent warming impact than HFC-134a for petrol, diesel, and liquefied petroleum gas vehicles, respectively. This study paves a way to promote the use of HFO-1234yf instead of HFC-134a without major modifications in the vehicle air conditioner unit.

Performance simulation of plate-and-tube evaporative cooling frost-free heat pump heat exchanger

To verify the operational feasibility of the plate-and-tube evaporative cooling frost-free heat pump heat exchanger and its influence factors, a single plate-and-tube was selected as the simulation object, and the VOF model, RNG k-ε model, and self-programmed UDF program were used to control the water vapor transfer mass to verify the influence of air flow rate on the internal flow and heat and mass transfer law of the model. The results show that as the air velocity increases, the percentage of turbulent flow inside the model increases, and the solution coverage on the surface of the plate and tube decreases slightly; the heat and mass transfer increases with the increase of the flow velocity, and the latent heat, sensible heat, and total heat exchange increase with increase the of the flow velocity.

The Influence of Airflow Rate on the Thermal Runaway Propagation Characteristics of Lithium-Ion Batteries in a Low-Pressure Environment

The Influence of Airflow Rate on the Thermal Runaway Propagation Characteristics of Lithium-Ion Batteries in a Low-Pressure Environment

Theoretical evaluation on performance of a novel bubbling humidification–dehumidification desalination system directly heated by concentrating sunlight

This work aims to analyze the heat and mass exchange of complex bubbling. First, an empirical correlation for estimating bubbling heat transfer coefficient in different superficial air velocities is obtained based on previous works. Then, a modified theoretical model is set up and used to discuss the performance of the bubbling HDH system. Results show that higher input power enhances water productivity and thermal efficiency, but a maximum exists. When input power is constant, the influence of air flow rate on water productivity is remarkable when air velocity is not large. More importantly, the system has optimal cooling water flow rate and temperature. The optimal cooling water flow rate increases with input power, whereas the optimal cooling water temperature decreases with input power. When input power is 1000 W, the optimal cooling water flow rate and temperature are 60 L/h and 59 ℃, respectively. In addition, ambient temperature variations show a very small effect on system productivity and thermal efficiency. The results of this paper can provide theoretical reference for the design of a bubbling HDH desalination system.

A case study on thermo-hydraulic performance of jet plate solar air heater using response surface methodology

In this present work, the multi-hole jet impingement approach is used to augment the performance of the jet plate solar air heater by improving the rate of heat transfer coefficient between absorber plate and impinging air. The system's usefulness is analytically analyzed, and the influence of airflow rate, length of the collector, jet diameter, pitch distances at a stream, and span-wise directions on thermo-hydraulic efficiency is investigated by adopting Response Surface Methodology (RSM). A quadratic equation is generated by using the RSM technique, which is used to predict the thermohydraulic efficiency. The results show that the optimized results of the design parameters are at the airflow rate of 0.01386 kg/s, 1.5108 m of length, 0.0046 m of jet diameter with a stream-wise pitch distance of 0.05108 span-wise pitch distance of 0 0.03414 m. The comparison results show that the RSM model evaluated values have a deviation within a range of ±1.78% compared with the analytical values developed by the model.

Numerical simulation of air injection in part load operating point

The operation hydro turbines in the off-design operating points is often accompanied by pressure pulsations with a large amplitude. One way to deal with such pulsations is to inject the air into hydro turbine flow passage. The aim of this work is to simulate this process. Previously we carried out calculations in frames of homogeneous incompressible three-phase «liquid – vapor – non-condensable gas» mixture model. The computational domain consisted of wicket gate, runner and draft tube. The wicket gate and runner were considered in the periodic stage approach. The results obtained were in good agreement with experimental data at full load operating point. It was shown that the calculations on the previous model failed to accurately simulate influence of air flow rate on the amplitude and frequency of pressure pulsations in part load. Therefore the part load regime is studied carefully in this work: different computational domains are considered, different solvers are used, including ANSYS CFX and CADRUN, developed at the Institute of Computational Technologies. Different models of «liquid – gas» mixture are used in the calculations, compressibility is also taken into account. The flow rate of the injected air ranged from 0.5 to 2 percent of the water flow rate. The influence of the injected air on the flow pattern, including the vortex rope, is investigated. The results obtained are compared with experimental data.

Experimental investigation of imbert downdraft gasifier using rice straw briquettes

ABSTRACT The mechanized harvesting of rice crop has led to open-field burning of rice straw that liberates a large amount of greenhouse gases (GHGs), which have a negative effect on the environment. Gasification is an efficient technology for the conversion of biomass to producer gas with minimal greenhouse gas emissions. The present study was planned to convert the abundantly available rice straw into briquettes and its thermochemical conversion into producer gas for thermal energy utilization. The performance of imbert type gasifier was investigated using rice straw briquettes as fuel by studying the influence of airflow rate on fuel consumption rate and temperature profile inside the combustion zone. The augmentation of airflow rate from 0.0022 to 0.0042 m3/s led to a significant increase in feedstock consumption rate (63.3%). The time taken for boiling of water also increased with an increase in airflow rate which may be attributed to the corresponding decrease in calorific value of producer gas. Rice straw briquettes with cotton stalks as a binder (90:10) can act as a clean alternative fuel for gasification and the producer gas generated can be used for various thermal applications.

Roughness effects of gas diffusion layers on droplet dynamics in PEMFC flow channels

Water management remains one of the major challenges in optimising the performance of PEMFCs, in which liquid accumulation and removal in gas diffusion layers (GDLs) and flow channels should be addressed. Here, effects of GDL surface roughness on the water droplet removal inside a PEMFC flow channel have been investigated using the Volume of Fluid method. Rough surfaces are generated according to realistic GDL properties by incorporating RMS roughness and roughness wavelength as the main characteristic parameters. Droplet dynamics including emergence, growth, detachment, and removal in flow channels with various airflow rates are simulated on rough substrates. The influences of airflow rate on droplet dynamics are also discussed by comparing the detachment time and droplet morphology. The liquid removal efficiency subject to different surface roughness parameters is evaluated by droplet detachment time and elongation, and regimes of detachment modes are identified based on the droplet breakup location and detachment ratio. The results suggest that rough surfaces with higher RMS roughness can facilitate the removal of liquid inside flow channel. Whilst surface roughness wavelength is found less significant to the liquid removal efficiency. The results here provide qualitative assessments on identifying the key surface characteristics controlling droplet motion in PEMFC channels.

Influence of photobioreactor configuration on microalgal biomass production.

Biodiesel production from microalgae depends on the biomass concentration and lipid content in microalgal cells. Photobioreactors (PBRs) facilitates cultivation of microalgae and renders better process control than open systems. However, reactor configuration and consequential hydrodynamics considerably influence biomass and lipid production from microalgae. Here, four different configurations of PBRs, viz. airlift and bubble column with orifice sparger and newly designed ring sparger, were investigated. Resulting volumetric mass transfer coefficient, mixing time, and shear stress were analyzed at different air flow rates to realize their influence on biomass and lipid production from Neochloris oleoabundans UTEX 1185. Bubble column reactor with ring sparger was observed to exhibit superior performance, which was subsequently simulated using a two-phase Eulerian model to comprehend the influence of air flow rates on mixing time. The developed computational model corroborates well with the experimental findings of optimum air flow rate for maximum biomass yield in bubble column configuration.

Energy-saving potential of separated two-phase thermosiphon loops for data center cooling

This study aims to experimentally examine the energy-saving potential by using R-134a filled separated two-phase thermosiphon loop (STPTL) for data center applications. A parametric study had been made to compare the energy consumption of two data center racks. Two fin-and-tube heat exchangers were attached to one of the racks to form two individual thermosiphon loops. The experiments were carried out subject to different operating conditions, including three ambient temperatures (20 °C, 23 °C, and 27 °C) and filling ratios ranging from 30 to 90% in association with heating loads ranging between 1.5 kW and 6 kW. Parametric influences regarding concentrated heat loading or uniform heat loading are studied. It was found that an appreciable energy-savings can be obtained at high filling ratios and a maximum of 49% energy-saving with the assistance of thermosiphon is observed. Accordingly, the rising of system pressure will result in noticeable savings. Relative to the uniform heat loading of the data rack, the thermosiphon shows even more energy-saving potential in concentrated heat loading. This phenomenon is more pronounced at a lower ambient temperature like 20 °C. On the other hand, there is no appreciable energy-saving for the thermosiphon between concentrated and uniform heating loads when the ambient temperature is high (27 °C). Furthermore, the influence of airflow rate was also investigated under various ambient temperatures with a 90% filling ratio and a heating load of 6 kW. The results revealed that the lower airflow rate in the thermosiphon yields comparatively better energy-saving than the higher flow rate. The study on the influence of using two STPTLs indicated that 15–23% energy-saving can be achieved at a 90% filling ratio and 6 kW heating load for all the studied ambient conditions if compared with testing each loop separately. Lower thermal resistance is seen at the higher filling ratios, ambient temperatures, and heating loads.

Improved measurements of thoron (220Rn) in natural waters

Thoron (220Rn) in water measurements can be useful for prospecting for points of submarine groundwater discharge into surface waters. With a 56 s half-life any detection of thoron must mean that one is close to a source. To improve measurement sensitivity, the influence of airflow rates on both radon and thoron measurements have been investigated using a RAD7 detector. Based on lab experiments, 2.5 L min−1 represents an optimum airflow rate for measuring both radon and thoron. Field data from a coastal zone demonstrates that use of an external air pump produced a thoron response 65% higher than a standard setup.

Remediation of Sulfidic Wastewater by Aeration in the Presence of Ultrasonic Vibration

In the current study, the aerial oxidation of sodium sulfide in the presence of ultrasonic vibration is investigated. Sulfide analysis was carried out by the methylene blue method. Sodium sulfide is oxidized to elemental sulfur in the presence of ultrasonic vibration. The influence of air flow rate, initial sodium sulfide concentration and ultrasonic vibration intensity on the oxidation of sodium sulfide was investigated. The rate law equation regarding the oxidation of sulfide was determined from the experimental data. The order of reaction with respect to sulfide and oxygen was found to be 0.36 and 0.67 respectively. The overall reaction followed nearly first order kinetics.

ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ПО ОПРЕДЕЛЕНИЮ ВЛИЯНИЯ СКОРОСТИ ВОЗДУШНОГО ПОТОКА НА ПРОЦЕСС ИЗМЕЛЬЧЕНИЯ В ЦЕНТРОБЕЖНОЙ СТУПЕНЧАТОЙ МЕЛЬНИЦЕ

ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ПО ОПРЕДЕЛЕНИЮ ВЛИЯНИЯ СКОРОСТИ ВОЗДУШНОГО ПОТОКА НА ПРОЦЕСС ИЗМЕЛЬЧЕНИЯ В ЦЕНТРОБЕЖНОЙ СТУПЕНЧАТОЙ МЕЛЬНИЦЕ

Preliminary measurements on microwave plasma flame for gasification

In this paper, the effects of plasma power and plasma gas flow rate on the geometrical dimensions, the shape of plasma flame and temperature distribution in gasification reactor have been investigated. The effects of plasma power and plasma gas flow rate on the geometrical dimensions, shape of plasma flame and temperature distribution in gasification reactor are presented. The plasma pictures at a variety of plasma power ranging from 300 to 4200 W with the range of plasma gas which is air from 50 to 100 L/min are presented. As expected, an increase in power causes the generation of intensive plasma with enhancement of the plasma flame volume. On the other hand, air flow rate is inversely proportional to the volume of the plasma flame. It is observed that both power and air flow rate has a significant effect on plasma flame shape. The spreading shape of plasma flame is observed at low powers. However, the shape of flame is pointed toward its end with an increase in plasma power. Meanwhile, reducing air flow rate causes a change in shape at lower power levels. The interactive influence of air flow rate and plasma power is confirmation of different plasma flow regimes. The temperature measurements confirm the effects of air flow rate and power on plasma flame regime from 1800 to 6000 W power. Increasing power level causes increment in the reactor temperature. The average temperature in the reactor is increased from 480 °C at 1800 W power to 1018 °C at 6000 W power. The flow rate has a reverse effect on magnitude of the temperature. The average temperature in the reactor is reduced from 480 to 348 °C at 1800 W power and 1018 to 918 °C at 6000 W power when the flow rate is increased from 50 to 100 L/min. However, the temperature distribution is more uniform in higher flow rates. It is also related with the shape of plasma. While the magnitude of temperature and its gradient is high in pointed end plasma, the effects are reversed in spreading shape plasma.

Investigation of Zircaloy-2 oxidation model for SFP accident analysis

The authors previously conducted thermogravimetric analyses on Zircaloy-2 in air. By using the thermogravimetric data, an oxidation model was constructed in this study so that it can be applied for the modeling of cladding degradation in spent fuel pool (SFP) severe accident condition. For its validation, oxidation tests of long cladding tube were conducted, and computational fluid dynamics analyses using the constructed oxidation model were proceeded to simulate the experiments. In the oxidation tests, high temperature thermal gradient along the cladding axis was applied and air flow rates in testing chamber were controlled to simulate hypothetical SFP accidents. The analytical outputs successfully reproduced the growth of oxide film and porous oxide layer on the claddings in oxidation tests, and validity of the oxidation model was proved. Influence of air flow rate for the oxidation behavior was thought negligible in the conditions investigated in this study.

A frosting limit model of air-to-air quasi-counter-flow membrane energy exchanger for use in cold climates

Membrane energy exchangers (MEEs) can reduce or avoid frosting in cold climates since the moisture transfer lowers the dew point of the exhaust air and as a result, the exchanger can be frost-free at lower outdoor air temperatures or higher indoor humidities. A frosting limit is necessary to predict at which conditions the onset of frost occurs for a given membrane energy exchanger. The frosting limit model provides criteria for energy exchanger selection and frost control methods to avoid frosting.A theoretical frosting limit model is developed in this study for a quasi-counter-flow MEE. The frosting limit model uses analytical relationship between the onset of frosting at the coldest location of the exchange and the inlet air conditions. The model is validated with experimental data and consistent agreements are obtained between the theoretical and experimental data. Parametric studies are conducted using the validated model. The influence of airflow rates, exhaust air temperature and channel spacing on the frosting limit is rather limited compared to the diffusive resistance of moisture transfer. A membrane with improved moisture transfer properties is crucial to implement frost-free operation at normal indoor relative humidities.

The Effects of Air Flow Rates, Secondary Air Inlet Geometry, Fuel Type, and Operating Mode on the Performance of Gasifier Cookstoves.

Development of biomass cookstoves that reduce emissions of CO and PM2.5 by more than 50% and 95%, respectively, compared to a three-stone fire has been promoted as part of efforts to reduce exposure to household air pollution (HAP) among people that cook with solid fuels. Gasifier cookstoves have attracted interest because some have been shown to emit less CO and PM2.5 than other designs. A laboratory test bed and new test procedure were used to investigate the influence of air flow rates, stove geometry, fuel type, and operating mode on gasifier cookstove performance. Power output, CO emissions, PM2.5 emissions, fuel consumption rates, producer gas composition, and fuel bed temperatures were measured. The test bed emitted <41 mg·MJd–1 PM2.5 and <8 g·MJd–1 CO when operating normally with certain prepared fuels, but order of magnitude increases in emission factors were observed for other fuels and during refueling. Changes in operating mode and fuel type also affected the composition of the producer gas entering the secondary combustion zone. Overall, the results suggest that the effects of fuel type and operator behavior on emissions need to be considered, in addition to cookstove design, as part of efforts to reduce exposure to HAP.

Influence of Air Flow Rate and Immersion Depth of Designed Flotation Cell on Barite Beneficiation

This study aims to investigate the effect of flotation operating parameters such as immersion depth of downcomer and air flow rate on performance of barite minerals separation. The barite minerals utilized in this experiment mainly consist of barite and gangue minerals such as quartz, kaolinite, illite and microcline having the chemical compositions of 63.12% BaSO4, 18.22% SiO2, 13.49%Al2O3, 1.02% K2O, 0.69% Fe2O3 and 3.46% others and the particle size (d80) of about 37 microns. In the flotation cell, the air bubbles were generated using designed porous materials. The flotation of barite minerals were carried out in an alkaline condition at pH 9 with sodium oleate collector and terpineol frother. It was found that concentrate grades of barite for the air flow rates of 20, 30 and 40 L/min were nearly constant about 70% BaSO4 at the immersion depths of 5 and 10 cm but it increased at the depth of 15 cm. The immersion depth of 5 and 10 cm seems to have no effect on grade of concentrate while the depth of 15 to have such effect. The air flow rate had an effect on concentrate grade when 15 cm immersion depth was used. The optimum air flow rate of 30 L/min gave concentrate grade of 85% BaSO4 with the recovery and enrichment ratio of 73% and 1.3, respectively.