Increasing Air Flow Rate Research Articles

High mass flux air atomized spray with subcooled water: A novel methodology to enhance the heat transfer rate in film boiling regime

The main challenging tasks in the successful implementation of ultrafast cooling in the manufacturing process are significant reduction of Leidenfrost effect and achievement of unaltered surface morphology. The literature does not reveal any methodology depicting the aforesaid two characteristics and therefore, in the current work, an attempt has been made to develop a cooling process describing the above mentioned characteristics. In the proposed methodology, by using subcooled water as a coolant in case of high mass flux air atomized spray, the heat transfer rate is significantly enhanced without altering the surface morphology. The high mass flux subcooled water atomized spray augments the heat transfer rate by reducing the stability of the vapour film separating the coolant from the hot plate. The cooling ability of the subcooled water atomized spray is compared with the coolants, which depict significant enhancement, and the comparison confirms the suitability of the current process for the fast cooling operation. For the experimental investigation, air atomized spray cooling was conducted at 1000 °C initial surface temperature on a 6 mm thick AISI 304 steel plate by using subcooled water as a coolant. The surface heat flux and surface temperatures are predicted by using the solution of inverse heat conduction problem (IHCP). For the understanding of heat transfer mechanism, the thermal properties, physical properties and spray properties at different conditions of air-atomized spray were analysed. The percentage of enhancement in initial heat flux (qIHF) is found to be almost 60% of water temperature at 15 °C and this shows the appropriateness of the process for the fast cooling operations. The heat transfer analysis illustrates that the cooling rate achieved for water temperature of 15 °C is found to be almost three times of that corresponding to 50 °C. In addition to the above, the comparison of the morphologies between the heat-treated and the untreated substrate corroborates zero deposition of coolant after cooling. The effects of air flow rate and spray impingement density on the cooling rate are investigated. With the increasing airflow rate up to 30 m3/h, the heat transfer rate rises and thereafter, further increment declines the heat transfer rate.

The performance of up-draft gasifier with various of air flow rate in gasification palm starch waste

Conversion of palm starch waste biomass into energy sources through gasification process could be done to meet the energy requirement in palm noodle industry. This research used the Refuse Derived Fuel (RDF-5) based on the palm Starch waste. This is due to the how to overcome the solid waste around the home industry of noodle in Jawa Tengah. This study was conducted to determine the performance of up-draft gasifier with variations of air flow rate, i.e., 72 lpm, 95 lpm, and 123 lpm. The results showed that the variation of air flow rate has affected to the gasification product. The optimum LHV value occurred at 122 l/m air flow rate, where the LHV value increased with the increase of air flow rate, but after passing 122 l/m, the LHV value was continually decreasing.

Experimental studies on the performance of dehumidifier using calcium chloride as a liquid desiccant

The performance of liquid desiccant air conditioning system (LDAS) mainly depends on dehumidifier of the system. In this study, the effects of inlet parameters on the performance of liquid desiccant dehumidifiers were studied with and without indirect evaporative cooler or intercooler (IDEC) between the dehumidifier for single stage and double stage. The results show that: i) the dehumidification effectiveness decreases by 8.6% for the all types considered here, with increase in air flow rate from 0.05 kg/s to 0.11 kg/s; ii) the dehumidifier effectiveness decreases due to decrease of moisture removal rate with increasing desiccant temperature in all stages; iii) the moisture condensation rate and dehumidifier effectiveness increases by 30% and 22.67% respectively with increase in desiccant flow rate; iv) the moisture condensation rate is increased by 13% in increasing desiccant concentration. It is concluded that double stage desiccant dehumidifier with indirect evaporative cooler performs better.

Emission characteristics of aviation kerosene combustion in aero-engine annular combustor with low temperature plasma assistance

A plasma-assisted combustion test platform for annular combustor was developed to validate the feasibility of using plasma-assisted combustion actuation to reduce emission levels. Combustor outlet temperature and emission levels of O2, CO2, H2, CO, and NOx were measured by using a thermocouple and a Testo 350-Pro Flue Gas Analyzer, respectively. Combustor combustion efficiency was also calculated. The effects of duty ratio, feedstock air-flow rate, and actuator position on combustion efficiency and emission performance have been analyzed. The results show that the target of CO and NOx emissions reduction in plasma-assisted combustion could not be fully achieved for kerosene/air mixture with different combustor excessive air coefficients. It is also shown that plasma-assisted combustion with dilution air hole actuation is superior to that of secondary air hole actuation for the combustion of liquid-kerosene fuel. Besides, plasma-assisted combustion effect is more obvious with an increase of duty ratio or feedstock air-flow rate. These results are valuable for the future optimization of kerosene-fueled aero-engine when using plasma-assisted combustion devices to improve emission performance of annular combustor.

Experimental Research on Optimizing Inlet Airflow of Wet Cooling Towers under Crosswind Conditions

A new approach of installing air deflectors around tower inlet circumferentially was proposed to optimize the inlet airflow and reduce the adverse effect of crosswinds on the thermal performance of natural draft wet cooling towers (NDWCT). And inlet airflow uniformity coefficient was defined to analyze the uniformity of circumferential inlet airflow quantitatively. Then the effect of air deflectors on the NDWCT performance was investigated experimentally. By contrast between inlet air flow rate and cooling efficiency, it has been found that crosswinds not only decrease the inlet air flow rate, but also reduce the uniformity of inlet airflow, which reduce NDWCT performance jointly. After installing air deflectors, the inlet air flow rate and uniformity coefficient increase, the uniformity of heat and mass transfer increases correspondingly, which improve the cooling performance. In addition, analysis on Lewis factor demonstrates that the inlet airflow optimization has more enhancement of heat transfer than mass transfer, but leads to more water evaporation loss.

Measurement of scrubbing behaviour of simulated radionuclide in a submerged venturi scrubber

Post Fukushima accident, the societal impact of radiological leakage to the environment necessitated further exploration and robust strategy to safeguard the nuclear reactor containment. In view of this, design of Filtered Containment Venting System (FCVS) plays an important role in depressurizing the reactor and preventing release of radionuclides to the environment. In this context, a venturi scrubber submerged in alkaline solution along with demister pad housed in a scrubber tank is investigated experimentally at prototypic conditions for retention of iodine vapors in the scrubber system. The hydrodynamics and the scrubbing performance of the submerged venturi scrubber is simulated at air flow rates of 1500–3500 lpm at the submergence height of 4 m. The iodine concentration retained in the scrubber tank and its bulk decontamination is measured by ICP-OES and ICP-MS analysis respectively.It is observed that the overall pressure drop in the venturi scrubber increases with an increase in flow rate. The two phase axial pressure drop characteristics reveal an increase in the pressure drop in the converging section with increase in flow rate. The pressure drop also increases after the scrubbing liquid from the hydrostatic pool is suctioned and no recovery is found in the diverging section of the venturi scrubber. The iodine retention in the scrubber tank increases sharply with an air flow rates up to 2200 lpm after that the increase is gradual with the maximum of 95% retention at 3400 lpm. It is seen that in all the experiments the amount of iodine leaving the facility is negligible and the bulk decontamination is high. Further, effect of submergence height on the retention of iodine vapors in the scrubber tank is compared at 3 m and 4 m. It is seen that an increase in submergence height significantly increased the percentage of iodine arrested in the scrubber tank at 1700 lpm air flow but further increase in air flow rate has lesser impact on the iodine retention in the scrubber tank despite the increase in submergence height.

Techno – economic analysis of ventilation driven through solar metallic wall for a hostel building of National Institute of Technology Raipur India

The aim of present work is to investigate theoretically the ventilation flow rate produced using solar metallic wall system. In this effort, the effect of various design parameters on the performance of solar metallic wall system is evaluated under the climatic condition of Raipur (21.2514° N, 81.6296° E), Chhattisgarh. A computer simulation program based on the mathematical model of proposed system has been developed using MATLAB software. The performance of solar metallic wall system is evaluated by predicting the volumetric air flow rate. The effect of air gap, height and different metallic sheets are determined. It has been observed that with increase in air gap and height, volumetric air flow rate increases, about 203 % increase in volumetric air flow rate is observed for increase in air gap from 0.1 m to 0.5 m and 57 % increase in volumetric air flow rate is observed for increase in height from 1 m to 2 m. The best performance of solar metallic wall system is observed on using aluminium as metallic sheet as compared to the other chosen materials. The ratio of volumetric air flow rate obtained for iron, copper, and aluminium is 1, 1.11, 1.45 that shows, volumetric air flow rate for ventilation by metallic wall of aluminium is about 45% more than its competitor. Finally the system is proposed for a hostel of NIT Raipur and it is concluded that 3024 kWh per year of energy is saved if solar metallic wall is used in place of conventional electrical system. The amount of carbon-dioxide emitted to atmosphere is also reduced by 0.02 tonne per year. The payback period of total solar metallic wall units required in place of exhaust fans to completely ventilate the hostel building during day hours is coming out to be 7 years and 8 months.

Analyzing chemical kinetics of coal gasification in mini gasifier reactor

Coal gasification is a chemical reaction that has a purpose to change the original solid coal into gaseous compounds. Converting the coal into gaseous compounds will make the combustion process easier and results in increasing combustion efficiency. The sulfur and nitrogen are also easier to be separated in order to obtain cleaner flue gas. This paper presents kinetic analysis of coal gasification reactions in mini gasifier (or known as GasMin in Bahasa) reactor. The results show that the increase of the air-coal ratio (ACR) affected the maximum temperature of the reactor, which means that an increase of the intake air flow rate will increase the amount of oxygen for combustion reaction. Meanwhile, the increase of the team coal ratio (SCR) will increase flow rate of the mixture of air-steam feed. As a result, the ability of coal gasification has also increased. This will increase gasification efficiency around 3-5% which then will also increase the gas yield. The maximum value of SCR was 0.06, further than that of the yield gas and the q- value will slightly decrease. The simulation result showed that the producer gas was dominated by CO with 26.72% mole fraction; H2 with 14.06% mole fraction, and N2 with 47.88% mole fraction. Meanwhile CO2, CH4 and O2 mole fraction were 5%, 0.24%, and 1.20% respectively

A thermoelectric cooler coupled with a gravity-assisted heat pipe: An analysis from heat pipe perspective

Thermoelectric cooler (TEC) is attractive for cooling electronic devices because of its light, compact size, quiet and vibration free characteristics. However, its cooling performance is restricted by the thermal resistance at TEC hot side. To improve the TEC cooling performance, a gravity-assisted heat pipe (GAHP) was proposed to attach on the TEC hot side. The cooling feasibility of the TEC system coupled with a GAHP was experimentally investigated in a climatic chamber, compared with a TEC system coupled with an air cooled-heat sink on its hot side. It was observed that the cooling capacity of TEC was improved by 64.8% using GAHP. A mathematical model was established to analyze the effect of refrigerant filling ratio, TEC hot side temperature and air flow rate. Optimal parameters of the proposed system were evaluated from the heat pipe perspective. Findings showed that the optimal refrigerant filling ratio was 134%, which resulted in the maximum heat transfer ability. Increasing air flow rate was able to improve the cooling capacity but with a limitation caused by the restriction of TEC.

Towards improved accuracy in modeling aeration efficiency through understanding bubble size distribution dynamics

Aeration is the largest energy consumer in most water and resource recovery facilities, which is why oxygen transfer optimization is fundamental to improve energy efficiency. Although oxygen transfer is strongly influenced by the bubble size distribution dynamics, most aeration efficiency models currently do not include this influence explicitly. In few cases, they assume a single average bubble size. The motivation of this work is to investigate this knowledge gap, i.e. a more accurate calculation of the impact of bubble size distribution dynamics on oxygen transfer. Experiments were performed to study bubble size distribution dynamics along the height of a bubble column at different air flow rates for both tap water and solutions that mimic the viscosity of activated sludge at different sludge concentrations. Results show that bubble size is highly dynamic in space and time since it is affected by hydrodrynamics and the viscosity of the liquid. Consequently, oxygen transfer also has a dynamic character. The concept of a constant overall volumetric oxygen transfer coefficient, KLa, can thus be improved. A new modeling approach to determine the KLa locally based on bubble size distribution dynamics is introduced as an alternative. This way, the KLa for the entire column is calculated and compared to the one measured by a traditional method. Results are in good agreement for tap water. The modeled KLa based on the new approach slightly overestimates the experimental KLa for solutions that mimic the viscosity of activated sludge. The difference appears to be lower when the air flow rate increases. This work can be considered as a first step towards more accurate and rigorous mechanistic aeration efficiency models which are based on in-depth mechanism knowledge. This is key for oxygen transfer optimization and consequently energy savings.

Optimization of aeration conditions in the hybrid process of coagulation-ultrafiltration with air sparging

To optimize the aeration conditions in the hybrid process of coagulation-ultrafiltration with air sparging, a series of air flow rates under continuous and intermittent sparging were investigated. The water quality characteristics that surrounded membranes, bubble characteristics, fouling resistances, and energy consumption under different aeration conditions were analyzed. The results showed that increasing air flow rates generated more bubbles with a wider size distribution (i.e., more favorable hydrodynamic conditions). The turbidity and ultraviolet absorbance at 254 nm (UV 254 ) of the water that surrounded membranes were reduced as the air sparging kept flocs away from membranes. Thus, the membrane fouling was effectively mitigated by increasing air flow rates despite aeration modes. For a given air flow rate, less fouling was obtained under continuous sparging than the intermittent mode. With respect to intermittent sparging, the mode of 40-min aeration per hour more effectively alleviated membrane fouling than the mode of 30-min aeration per hour. Weighing the energy consumption and membrane fouling, optimum air flow rates under continuous mode were between 15 and 30 mL/min, and the optimal aeration condition for intermittent mode was set at the air flow rate of 30 mL/min under the mode of 40-min aeration per hour.

OH and O radicals production in atmospheric pressure air/Ar/H2O gliding arc discharge plasma jet

Atmospheric pressure air/Ar/H2O gliding arc discharge plasma is produced by a pulsed dc power supply. An optical emission spectroscopic (OES) diagnostic technique is used for the characterization of plasmas and for identifications of and radicals along with other species in the plasmas. The OES diagnostic technique reveals the excitation Tx ≈ 5550–9000 K, rotational Tr ≈ 1350–2700 K and gas Tg ≈ 850–1600 K temperatures, and electron density under different experimental conditions. The production and destruction of and radicals are investigated as functions of applied voltage and air flow rate. Relative intensities of and radicals indicate that their production rates are increased with increasing content in the gas mixture and applied voltage. reveals that the higher densities of and radicals are produced in the discharge due to more effective electron impact dissociation of and molecules caused by higher kinetic energies as gained by electrons from the enhanced electric field as well as by enhanced The productions of and are decreasing with increasing air flow rate due to removal of Joule heat from the discharge region but enhanced air flow rate significantly modifies discharge maintenance properties. Besides, significantly reduces with the enhanced air flow rate. This investigation reveals that plays a significant role in the production of and radicals.

ZnO-Photocatalyzed Oxidative Transformation of Diphenylamine. Synergism by TiO2, V2O5, CeO2 and ZnS

Diphenylamine (DPA) undergoes photocatalytic transformation on nanoparticulate ZnO surface yielding N-phenyl-<em>p</em>-benzoquinonimine (PBQ). The reaction rate increases with the increase of (i) DPA-concentration, (ii) ZnO-loading, (iii) airflow rate and (iv) light intensity. The formation of PBQ is larger on using UV-C light instead of UV-A light. The photocatalyst is reusable. The mechanism of the photocatalytic transformation has been discussed with a suitable kinetic law. Nanoparticulate TiO2, V2O5, CeO2 and ZnS enhance the ZnO-photocatalyzed PBQ formation indicating interparticle charge transfer in semiconductor mixtures.

Hypoglossal nerve stimulation therapy for obstructive sleep apnea hypopnea syndrome

Obstructive sleep apnea hypopnea syndrome(OSAHS) is a clinical and critical disease to health, which the accuratly pathogenesis is not very explicit. The mainstream research suggested that dysfunction of upper airway dilator muscles is one of the hazard factors. Genioglossus innervated by the hypoglossal nerve plays crucial roles. It could expand volume of pharyngeal cavity, and increase airflow rate when stimulate it.With the development of anatomy and physiology, hypoglossal nerve stimulation(HGNS) entered into clinical trials, and had made tremendous progress since 2001. Most of clinical trials show that, it could dramatically improve the smooth general peculiarity of the upper respiratory tract in patients with OSAHS in the sleeping state.

A Study of Throat Size Effect on Downdraft Biomass Gasifier Efficiency

The present research article aims to study the throat size effect on downdraft biomass gasifier efficiency. Two type of biomass; eucalyptus and leucaena were used as fuel for producing producer gas by gasification process. The downdraft gasifier has a 30 cm diameter and 250 cm high. For combustion zone, the throat size was varied to 10, 15, 20 and 25 cm respectively. The consumption of biomass was 10 kg with the size of biomass was 5-10 mm thick and moisture content less than 15%. The air flow rate into the combustion chamber was set at 1 – 5 m3/hr. to determine the gasifier efficiency and composition of producer gas. The experimental results showed that the gasifier efficiency increase with the air flow rate increase. The throat size 20 cm and air flow rate at 5 m3/hr showed the highest efficiency. The gasifier efficiency of the downdraft biomass gasifier was calculated as 35.30 % for leucaena and 43.36 % for eucalyptus. A heating value was calculated as 3.84 MJ/Nm3 and 4.87 MJ/Nm3 for eucalyptus and leucaena respectively.

Energy and exergy analysis of a PCM-based solar powered winter air conditioning using desiccant wheel during nocturnal

In this paper, heating and humidification of air for space have been carried out by using a phase change material (PCM)-based solar-powered desiccant wheel air conditioning (SPDWAC) in winter. The analysis of the setup has been done at different air flow rates. At low and high air flow rates, system has mean thermal coefficient of performance of 0.121 and 0.172, respectively, and mean exergy efficiency of 0.0787 and 0.0846, respectively. The mean thermal coefficient of performance of the system at high air flow rate (127.23 kg h-1) is 1.42 times the low air flow rate (63.62 kg h-1) and average exergy efficiency of the system at high air flow rate is 1.07 times the low air flow rate. It is observed that with an increase in air flow rate, efficiency of the evacuated tube solar air collector (ETSAC) increases. The average efficiency of the ETSAC at high air flow rate is 15.60%. The maximum average energy efficiency (17.80%) and exergy efficiency (17.08%) of the PCM storage system have been obtained at high air flow rate. The overall performance of the system showed that the use of PCM storage is feasible to run the system in winter during the hours of darkness.

Study on the performance of celdek packed counter flow liquid desiccant regenerator

Regenerator is major component of liquid desiccant regeneration system. The influence of operating parameters; air flow rate, solution flow rate and concentration of desiccant is investigated experimentaly on the performance parameters; outlet specific humidity, evaporation rate, air outlet temperature, mass transfer coefficient and effectiveness of the regenerator. Air and desiccant solution flow in counter direction with celdek pads as packing material. It is concluded that evaporation rate increases with increasing solution temperature, air flow rate and solution flow rate whereas same decreases with increasing concentration of desiccant. The effectiveness of regenerator is increased by 99 % with increase in air flow rate. A comparison of present finding with those available in the literature is presented in the last. Simulation results have revealed good agreement between the present experimental results.

Performance evaluation of a solar energy assisted hybrid desiccant air conditioner integrated with HDH desalination system

In this study, the performances of a solar energy assisted hybrid desiccant air conditioning system integrated with humidification–dehumidification (HDH) desalination system are numerically investigated. The aim of this study is to benefit from the temperature rise of the regeneration air outside of the desiccant conditioning system as well as the water vapor content in this regeneration air by feeding it to the humidification-dehumidification water desalination unit to produce distillate water. The distillate water productivity, human thermal comfort issues, and energy saving represent the main objective of the present numerical study. The simulated results developed for subsystems are validated with the published experimental results. The effects of regeneration air temperature and flow rate on supply cooled air temperature, distillate water productivity, the cooling coefficient of performance and overall daily coefficient of performance of the proposed system are investigated. The results show that (i) the distillate water productivity increases from 3.175 to 5.011L/h and overall daily coefficient of performance decreases from 4.392 to 3.636 with increasing the regeneration air temperature from 75 to 95 as (ii) the increase in the regeneration air flow rate from 70 to 130 m3/h, increases the distillate water productivity from 2.988 to 4.78L/h and decrease the overall daily coefficient of performance from 4.66 to 3.386. The study demonstrates that the proposed system represents the best options in hot and humid regions.

Formaldehyde removal performance analysis of a liquid desiccant dehumidification system

Liquid desiccant (LD) systems are an efficient method for humidity control. Moreover, LD systems also function to purify the air and remove volatile organic compounds such as formaldehyde. This study aims to analyze the performance of a LD system for formaldehyde removal from indoor air while simultaneously considering air dehumidification requirements. A theoretical model is proposed to predict the formaldehyde removal efficiency (εformaldehyde) of the LD system with various flow mediums, such as an air-LiBr solution, air-LiCl solution, and air-CaCl2 solution. Prior to assessing the LD system performance with the model, Henry's law constants (HLCs) of formaldehyde in the three solutions are tested at the salt concentration range of 30–50 wt% and at the temperature range of 10–50 °C. Based on the results, the correlation equation of the HLC's temperature dependence are given, and then adopted for the simulation model. The effects of the number of mass transfer units of formaldehyde (NTUmf), formaldehyde concentration in the return air, solution flow rate, and airflow rate on system performance are investigated and compared with various flow mediums. The results indicate that NTUmf is a key factor influencing the εformaldehyde. However, the NTUmf do not influence the dehumidification performance of the LD system. Both the εformaldehyde and dehumidification performance remain unchanged with the increase of formaldehyde concentration in the return air. Both the εformaldehyde and dehumidification performances decreased when the solution flow rate increased, and they likewise decreased with increased airflow rates.

Regional analysis of bin aeration as an alternative to insecticidal control for post-harvest management of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.)

The objectives of this study are to 1) develop an integrated aeration and insect pest modeling system and 2) determine the potential of aeration in controlling rice weevil, Sitophilus oryzae (L.), and lesser grain borer, Rhyzopertha dominica (F.), as an alternative to the use of insecticides. Grain temperature, moisture, and pest population dynamics were simulated at each layer and radial position within a storage bin using a two-dimensional aeration model coupled with an age-structured distributed-maturation insect population model. The models were parameterized and validated using data from the literature and controlled experiments. Regional analysis across major U.S. rice states suggests adult populations of both species decrease progressively towards higher latitudes mainly due to lower fall and winter temperatures, with much lower populations for lesser grain borer than for rice weevil. Increasing the target temperature for storage bin aeration from 7.2°C to 15.6°C more than doubled the adult populations in the southern states, but the effect in the more northerly rice states was much less due to ambient air temperatures seldom reaching the target temperature. An increase in aeration airflow rate from 0.69 to 1.38m3/min/MT (metric ton) had a much greater impact in reducing adult populations than a decrease in the aeration target temperature. Weather variation between years within a county greatly impacted pest populations. Even in the southern states, predicted rice weevil populations under aeration exceeded 1000 adults/MT in less than half of the years. These results highlight the site-specific impact of aeration on S. oryzae and R. dominica and the need to develop cost-effective site-specific aeration and insect pest management strategies.