Vented Chambers Research Articles

Explosion Load Characteristics of Fuel—Air Mixture in a Vented Chamber: Analysis and New Insights

The advances in research on the explosion load characteristics of the fuel–air mixture in vented chambers are reviewed herein. The vented explosion loads are classified into three typical types based on this comprehensive literature research. These models are the accumulation load model, attenuation load model, and interval jump load model. The characteristics of the three different typical vented explosion load models are analyzed using Fluidy-Ventex. The research results show that overpressure is largely determined by methane concentrations and vented pressure. The turbulent strength increased from the original 0.0001 J/kg to 1.73 J/kg, which was an increase of 17,300 times, after venting in the case of a 10.5 v/v methane concentration and 0.3 kPa vented pressure. When the vented pressure increased to 7.3 kPa, the turbulent strength increased to 62.2 J/kg, and the overpressure peak correspondingly increased from 69 kPa to 125 kPa. In the case of the interval jump load model, the explosion overpressure peak tends to ascend when the intensity of the fluid disturbance rises due to the venting pressure increasing at a constant initial gas concentration. When the venting pressure reaches tens of kPa, the pressure differential increases sharply on both sides of the relief port, and a large amount of combustible gas is released. Therefore, there is an insufficient amount of indoor combustible gas, severe combustion is difficult to maintain, and the explosion load mode becomes the attenuation load model.

Thermal Analysis of Conjugate Convective Flow in a Vented Chamber Featuring Different Heat-Generating Solid Objects

Thermal Analysis of Conjugate Convective Flow in a Vented Chamber Featuring Different Heat-Generating Solid Objects

Effects of Hydrogen Fraction on Explosion Characteristics of Hydrogen/Methane/ Air in a Vented Chamber

Effects of Hydrogen Fraction on Explosion Characteristics of Hydrogen/Methane/ Air in a Vented Chamber

Nitrous oxide emissions from manured, no-till corn systems

Using dairy manure and legumes in crop rotations can reduce inorganic N inputs for corn (Zea mays L.), yet these practices can also contribute to nitrous oxide (N2O) emissions. In two crop rotations we investigated how different (i) organic and inorganic N amendments and (ii) prior legume crops with broadcast manure influenced direct N2O emissions from silt-loam soils planted to no-till corn. We measured N2O fluxes from April to December for two years using closed vented chambers from soils planted to corn with no spring residue to compare inorganic N fertilizer (S-UAN) and two liquid dairy manure application methods: surface broadcasted (S-BM) and injected (S-IM). Emissions were also measured to compare the effect of crop residue of perennial forages, a green manure legume, or soybean (Glycine max L. Merr.) from soils all amended with liquid dairy manure. Nitrous oxide emissions were greatest during the 15–45 days after manure was injected compared to broadcasting, and cumulative N2O emissions were larger from S-IM (2.8–2.5 kg ha−1) than S-BM (1.4–0.7 kg ha−1) and S-UAN (0.3 kg ha−1). Cumulative and yield-scaled N2O emissions did not differ among the prior legume treatments. A ranking approach based on random forests, identified the most important variable contributing to N2O emissions in both comparisons as corn growing degree days, indicative of the asynchrony of spring legume termination and manure application with corn planting and N use; and changing environmental conditions for N mineralization and denitrification.

Soil nitrous oxide emissions associated with conversion of forage grass to annual crop receiving annual application of pig manure

The disruptive land-use change during forage grass conversion to annual crop can be critical for determining nitrous oxide (N2O) emissions, but this is an understudied period. We measured soil N2O fluxes (using closed static vented chambers) together with potential environmental drivers of these fluxes from liquid pig manure (LPM) and solid pig manure (SPM) applied to an annual crop (ANN) and perennial forages (FPP) that was converted to annual crop. Unamended plots were used as a control (CON). The results showed that in 2013, average soil nitrate-N was significantly higher on the recently converted FPP (ranging from 19 to 83 mg N kg−1) than the continuous ANN plots (from 16 to 35 mg N kg−1). The recently converted perennial forage system produced three times greater N2O than the continuous annual system, which is likely a result of accelerated N mineralization from the accumulated soil organic matter (over 4 yr) and grass residues of the recently killed forage grasses. However, during the second year of the study when the FPP plots were reseeded to perennial grasses, the system emitted 30% less N2O than the ANN system. These results suggest that including perennial forage grass in rotation with annual crops can provide N-saving and climate change mitigation benefits; however, some of the N stored in the soil would be lost when the perennial grass plots are cultivated to grow annual crops.

Soil Water Potential Control of the Relationship between Moisture and Greenhouse Gas Fluxes in Corn-Soybean Field

Soil water potential (Ψ) controls the dynamics of water in soils and can therefore affect greenhouse gas fluxes. We examined the relationship between soil moisture content (θ) at five different levels of water potential (Ψ = 0, −0.05, −0.1, −0.33 and −15 bar) and greenhouse gas (carbon dioxide, CO2; nitrous oxide, N2O and methane, CH4) fluxes. The study was conducted in 2011 in a silt loam soil at Freeman farm of Lincoln University. Soil samples were collected at two depths: 0–10 and 10–20 cm and their bulk densities were measured. Samples were later saturated then brought into a pressure plate for measurements of Ψ and θ. Soil air samples for greenhouse gas flux analyses were collected using static and vented chambers, 30 cm in height and 20 cm in diameter. Determination of CO2, CH4 and N2O concentrations from soil air samples were done using a Shimadzu Gas Chromatograph (GC-14). Results showed that there were significant correlations between greenhouse gas fluxes and θ held at various Ψ in the 0–10 cm depth of soil group. For instance, θ at Ψ = 0 positively correlated with measured CO2 (p = 0.0043, r = 0.49), N2O (p = 0.0020, r = 0.64) and negatively correlated with CH4 (p = 0.0125, r = −0.44) fluxes. Regression analysis showed that 24%, 41% and 19% of changes in CO2, N2O and CH4 fluxes, respectively, were due to θ at Ψ = 0 (p < 0.05). This study stresses the need to monitor soil water potential when monitoring greenhouse gas fluxes.

Effect of Soil Air and Water on Greenhouse Gases Emissions in a Corn-Soybean Rotation

Knowledge of the impact of soil and crop management practices on soil processes is important in the study of greenhouse gases emissions from agricultural fields. We assessed the effect of soil air (pore space indices) and water (content, θ; and potential, Ψ) on greenhouse gases emissions in corn/soybean field. The study was conducted in 2011 and 2012 on a silt loam soil at Freeman farm of Lincoln University. Soil samples were collected at four depths: 0-10, 10-20, 20-40 and 40-60cm and they were oven dried at 105oC for 72h for the calculation of air filled porosity (AFP), total pore space (TPS) and other soil physical properties. Pore space indices were computed using diffusivity models based on AFP and TPS. Soil samples were later saturated then brought into a pressure plate for measurements of moisture content (θ) at five different water potentials (Ψ). Soil air samples for the measurements of greenhouse gases emissions were collected using static and vented chambers of 30cm height and 20cm diameter. The concentrations of CO2, CH4 and N2O in soil air samples were determined using a Gas Chromatograph GC-14. Results showed that pore space indices significantly correlated with greenhouse gases fluxes (p<0.05) with correlation coefficient (r) ranged from 0.27 to 0.53. More correlations were found in 2012 than 2011. Similarly, significant correlations were found between greenhouse gases and θ at Ψ = 0 and Ψ = -0.05. Moisture content (θ) held at Ψ = 0 positively correlated with CO2 (r = 0.49), N2O (r = 0.64) and negatively correlated with CH4 (r = - 0.43) at p<0.05. Soil pore space indices and soil water (content and potential) seem to control greenhouse gases emissions in this soil. Inclusion of these controlling factors in models will certainly improve our understanding of the dynamics of greenhouse gases fluxes from soil.

Biochar and Manure Effects on Net Nitrogen Mineralization and Greenhouse Gas Emissions from Calcareous Soil under Corn

Few multiyear field studies have examined the impacts of a one‐time biochar application on net N mineralization and greenhouse gas emissions in an irrigated, calcareous soil; yet this use of biochar is hypothesized as a means of sequestering atmospheric CO2 and improving soil quality. We fall‐applied four treatments: stockpiled dairy manure (42 Mg ha−1 dry wt.), hardwood‐derived biochar (22.4 Mg ha−1), combined biochar and manure, and no amendments (control). Nitrogen fertilizer was applied in all plots and years based on treatment's preseason soil test N and crop requirements and accounting for estimated N mineralized from added manure. From 2009 to 2011, we measured greenhouse gas fluxes using vented chambers, net N mineralization using buried bags, corn (Zea mays L.) yield, and N uptake, and in a succeeding year, root and shoot biomass and biomass C and N concentrations. Both amendments produced persistent soil effects. Manure increased seasonal and 3‐yr cumulative net N mineralization, root biomass, and root/shoot ratio 1.6‐fold, CO2–C gas flux 1.2‐fold, and reduced the soil NH4/NO3 ratio 58% relative to no‐manure treatments. When compared with a class comprising all other treatments, biochar‐only produced 33% less cumulative net N mineralization, 20% less CO2–C, and 50% less N2O‐N gas emissions, and increased the soil NH4/NO3 ratio 1.8‐fold, indicating that biochar impaired nitrification and N immobilization processes. The multi‐year nature of biochar's influence implies that a long‐term driver is involved, possibly related to biochar's enduring porosity and surface chemistry characteristics. While the biochar‐only treatment demonstrated a potential to increase corn yields and minimize CO2–C and N2O‐N gas emissions in these calcareous soils, biochar also caused decreased corn yields under conditions in which NH4–N dominated the soil inorganic N pool. Combining biochar with manure more effectively utilized the two soil amendments, as it eliminated potential yield reductions caused by biochar and maximized manure net N mineralization potential.

Nitrous oxide emissions and herbage accumulation in smooth bromegrass pastures with nitrogen fertilizer and ruminant urine application

Agricultural soils contribute significantly to nitrous oxide (N2O) emissions, but little data is available on N2O emissions from smooth bromegrass (Bromus inermis Leyss.) pastures. This study evaluated soil N2O emissions and herbage accumulation from smooth bromegrass pasture in eastern Nebraska, USA. Nitrous oxide emissions were measured biweekly from March to October in 2011 and 2012 using vented static chambers on smooth bromegrass plots treated with a factorial combination of five urea nitrogen (N) fertilizer rates (0, 45, 90, 135, and 180 kg ha−1) and two ruminant urine treatments (distilled water and urine). Urine input strongly affected daily and cumulative N2O emissions, but responses to N fertilizer rate depended on growing season rainfall. In 2011, when rainfall was normal, cumulative N2O emissions increased exponentially with N fertilizer rate. In 2012, drought reduced daily and cumulative N2O emission responses to N fertilizer rate. Herbage accumulation ranged from 4.46 Mg ha−1 in unfertilized pasture with distilled water to 16.01 Mg ha−1 in pasture with 180 kg N ha−1 and urine in 2011. In 2012, plots treated with urine had 2.2 times more herbage accumulation than plots treated with distilled water but showed no response to N fertilizer rate. Total applied N lost as N2O ranged from 0–0.6 to 0.5–1.7 % across N fertilizer rates in distilled water and urine treatments, respectively, and thus, support the Intergovernmental Panel on Climate Change default direct emission factors of 1.0 % for N fertilizer additions and 2.0 % for urine excreted by cattle on pasture.

Greenhouse gases fluxes and soil thermal properties in a pasture in central Missouri

Fluctuations of greenhouse gases emissions and soil properties occur at short spatial and temporal scales, however, results are often reported for larger scales studies. We monitored CO 2,CH 4, and N 2O fluxes and soil temperature ( T), thermal conductivity ( K), resistivity ( R) and thermal diffusivity ( D) from 2004 to 2006 in a pasture. Soil air samples for determination of CO 2,CH 4 and N 2O concentrations were collected from static and vented chambers and analyzed within two hours of collection with a gas chromatograph. T, K, R and D were measured in-situ using a KD2 probe. Soil samples were also taken for measurements of soil chemical and physical properties. The pasture acted as a sink in 2004, a source in 2005 and again a sink of CH 4 in 2006. CO 2 and CH 4 were highest, but N 2O as well as T, K and D were lowest in 2004. Only K was correlated with CO 2 in 2004 while T correlated with both N 2O( r = 0.76, p = 0.0001) and CO 2 ( r = 0.88, p = 0.0001) in 2005. In 2006, all gases fluxes were significantly correlated with T, K and R when the data for the entire year were considered. However, an in-depth examination of the data revealed the existence of month-to-month shifts, lack of correlation and differing spatial structures. These results stress the need for further studies on the relationship between soil properties and gases fluxes. K and R offer a promise as potential controlling factors for greenhouse gases fluxes in this pasture.

Nitrous Oxide Emissions from a Northern Great Plains Soil as Influenced by Nitrogen Management and Cropping Systems

Field measurements of N2O emissions from soils are limited for cropping systems in the semiarid northern Great Plains (NGP). The objectives were to develop N2O emission-time profiles for cropping systems in the semiarid NGP, define important periods of loss, determine the impact of best management practices on N2O losses, and estimate direct N fertilizer-induced emissions (FIE). No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum), and conventional till (CT) wheat-fallow, all with three N regimes (200 and 100 kg N ha(-1) available N, unfertilized control); plus a perennial grass-alfalfa (Medicago sativa L.) system were sampled over 2 yr using vented chambers. Cumulative 2-yr N2O emissions were modest in contrast to reports from more humid regions. Greatest N2O flux activity occurred following urea-N fertilization (10-wk) and during freeze-thaw cycles. Together these periods comprised up to 84% of the 2-yr total. Nitrification was probably the dominant process responsible for N2O emissions during the post-N fertilization period, while denitrification was more important during freeze-thaw cycles. Cumulative 2-yr N2O-N losses from fertilized regimes were greater for wheat-wheat (1.31 kg N ha(-1)) than wheat-fallow (CT and NT) (0.48 kg N ha(-1)), and wheat-pea (0.71 kg N ha(-1)) due to an additional N fertilization event. Cumulative losses from unfertilized cropping systems were not different from perennial grass-alfalfa (0.28 kg N ha(-1)). Tillage did not affect N2O losses for the wheat-fallow systems. Mean FIE level was equivalent to 0.26% of applied N, and considerably below the Intergovernmental Panel on Climate Change mean default value (1.25%).

Analysis of a new design of a multi-stage flash–mechanical vapor compression desalination process

A new design for a multi-stage flash–mechanical vapor compression (MSF–MVC) desalination process was investigated. The analysis of the proposed MSF–MVC system was performed based on the energy, exergy and thermoeconomic methodologies. The considered system was investigated under different operating conditions using a developed Design and Simulation (VDS) software. To examine the performance of the proposed process, a comparison with the conventional MSF desalination process was performed. Thermoeconomic results show that the best operating suction pressure for the compressor is 8 kPa and the best top brine temperature is 110°C. The effect of the stages number of the heat recovery section was studied, and the results show that the low unit product cost was obtained at 20 stages. The effect of the temperature difference across the vent chamber was measured, and the results show that the lower unit product cost was 6°C. Thermoeconomic analysis shows that the last stage (vent chamber) had the highest value of the sum of capital and operation and maintenance costs in addition to the exergy destruction cost. Also, the last stage had a higher relative cost difference and lower exergetic efficiency. This in turn shows that a reduction in the exergy destruction within the vent chamber reduced the unit product cost. The performance ratio of the proposed MSF–MVC system was 2.4 times the performance ratio of the conventional MSF process. The heat transfer area of the MSF–MVC system was 57% higher than that of conventional MSF. The exergetic efficiency of the MSF–MVC system was 67% higher than that of MSF. The thermoeconomic results show that the unit product cost of MSF–MVC, under the specified conditions, was calculated by 2.0 $/m 3; this value is 25% less than that of the conventional MSF process.

Nitrous Oxide Emissions from Corn–Soybean Systems in the Midwest

Soil N2O emissions from three corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] systems in central Iowa were measured from the spring of 2003 through February 2005. The three managements systems evaluated were full-width tillage (fall chisel plow, spring disk), no-till, and no-till with a rye (Secale cereale L. 'Rymin') winter cover crop. Four replicate plots of each treatment were established within each crop of the rotation and both crops were present in each of the two growing seasons. Nitrous oxide fluxes were measured weekly during the periods of April through October, biweekly during March and November, and monthly in December, January, and February. Two polyvinyl chloride rings (30-cm diameter) were installed in each plot (in and between plant rows) and were used to support soil chambers during the gas flux measurements. Flux measurements were performed by placing vented chambers on the rings and collecting gas samples 0, 15, 30, and 45 min following chamber deployment. Nitrous oxide fluxes were computed from the change in N2O concentration with time, after accounting for diffusional constraints. We observed no significant tillage or cover crop effects on N2O flux in either year. In 2003 mean N2O fluxes were 2.7, 2.2, and 2.3 kg N2O-N ha(-1) yr(-1) from the soybean plots under chisel plow, no-till, and no-till + cover crop, respectively. Emissions from the chisel plow, no-till, and no-till + cover crop plots planted to corn averaged 10.2, 7.9, and 7.6 kg N2O-N ha(-1) yr(-1), respectively. In 2004 fluxes from both crops were higher than in 2003, but fluxes did not differ among the management systems. Fluxes from the corn plots were significantly higher than from the soybean plots in both years. Comparison of our results with estimates calculated using the Intergovernmental Panel on Climate Change default emission factor of 0.0125 indicate that the estimated fluxes underestimate measured emissions by a factor of 3 at our sites.

System for enhancing the sound of an acoustic instrument

A system is disclosed that provides sound control for an acoustic musical instrument. Typical to all acoustic instruments, the instruments have a structure or housing that defines a vented acoustic chamber. An input or sound inducing mechanism (such as strings of a guitar) imparts a vibration to the structure which causes acoustic waves to resonate within the acoustic chamber. The motion of air in and out of the vent causes acoustic waves to emanate from the chamber that combine with the acoustic waves emanating from the structure to form sound/musical notes. In accordance with the invention, a system controls the sound emanating from such an acoustic instrument. In accordance with one embodiment of the invention, at least one integral or smart sensor is disposed adjacent a sensing location of the structure, and the sensor is configured to generate sensed electric signals indicative of the magnitude of structural vibration of the structure at the sensing location. A controller in communication with the sensor, includes a processor for processing the sensed electric signals in accordance with a predetermined method (e.g., computer program). In response, the controller produces output electrical signals. At least one integral or smart actuator is disposed adjacent an actuator location of the structure, and the actuator is in communication with the controller and is configured to receive the output electrical signals and induce structural vibration of the structure at the actuator location. As a result of the foregoing structure and operation the induced vibration of the structure at the actuator location creates acoustics that alter the sound emanating from the acoustic chamber as well as that emanating from the structure. Specifically, signature frequency response characteristics of acoustic instruments like damping and frequency values of structural and acoustic resonances can be altered to alter the sound of the acoustic instruments. The use of integral or smart sensors and actuators put no restrictions on the movement of the acoustic instrument player since they are part of the guitar structure.

Computation of passively controlled transonic wing

A computational investigation has been conducted to examine the effect of passive control on the transonic wing flowfield. The effect of passive control was included through the use of a porous surface over a vent chamber on the upper surface of a wing. The passive control was numerically simulated by the use of a linear form of the Darcy pressure law. The solutions of the three-dimensional Euler equations were generated using the finite volume multistage Runge-Kutta time-stepping scheme. The computational results indicated that the fundamental behavior of passive control is two dimensional in nature, but spanwise variations of the passive control effect exist.

Numerical study of a supersonic open cavity flow and pressure oscillation control

Numerical experiments were performed to study the flow structure and suppression of pressure oscillation in the M.,. = 2.5 supersonic open cavity flow problem. Numerical results show that the large pressure variation within the cavity induced by the shear layer's wavy shape produces new vortices not found in situations where M.,. < 2.5. The proposed suppression device imposes mass transfer on the cavity's aft bulkhead. The proposal is tested by replacing one of the cavity walls with a porous wall and adjoining vent chamber. Constant porosity and uniform vent-chamber pressure are assumed. Replacing the aft bulkhead with a porous wall/vent chamber combination provides the most effective suppression of pressure fluctuation, even with a porosity value as small as 0.1 for vent-chamber pressure ranging from p, to l.5py.. Mass transfer at the cavity floor and forward bulkhead are also examined, but they are found to be less effective.

Navier-Stokes study of supersonic cavity flowfield with passive control

A computational investigation of the supersonic turbulent flow past a two-dimensiona l rectangular cavity with passive venting is described. The effect of passive venting was included through the use of a porous surface over a vent chamber in the floor of the cavity. The passive venting was numerically simulated by the use of a linear form of the Darcy pressure-velocity law. The time-accurate solutions of the two-dimensional, Reynoldsaveraged, Navier-Stokes equations were generated using the explicit MacCormack scheme. The capability Of the numerical scheme is first demonstrated by the computations of an open and closed cavity without passive venting. The results of these computations also provide a reference case for the passive venting computations. The effect of passive venting on the closed cavity is then demonstrated and analyzed. These results show that the passive venting dramatically changes the closed cavity flow to nearly an open cavity flow. The free shear layer formed between the high-speed outer flow and slower inner flow is seen to bridge the cavity completely j resulting in an open cavity flow. The passive venting velocities are determined to be less than 5% of the freestream velocities, and largely confined to the upstream and downstream portions of the cavity floor. The computational results show good agreement with available experimental data.

Passive venting system for modifying cavity flowfields at supersonicspeeds

The drag of airfoils in transonic flow can be reduced through the use of a passive venting system that employs a porous plate for part of the airfoil upper surface with a vent chamber underneath the porous plate Attention is given to the results obtained with a wind tunnel model employing such a porous floor system. This passive venting system has been used to extend the length/height value before the onset of high drag-producing closed cavity flow at supersonic speeds.

New Gas-Lift Concept-Continuous-Flow Production Rates From Deep, Low-Pressure Wells

With this unique chamber system, which involves automatic cycle control and a separate tubing string for venting the formation gas, it is possible to achieve gas-lift production rates of 1,000 BID from 10,000 feet at low flowing bottom-hole pressures. In a field test oil four wells, production increased immediately in three of the wells, and more gradually in the fourth. Introduction The Automatic Vent Chamber (AVC) System was developed to overcome the disadvantages inherent in using deep, high-volume lift systems such as large-beam, hydraulic, or electric submersible pumps. These systems require a large initial capital investment and are often expensive to operate and maintain - especially in wells with high gas/liquid ratios or sandy conditions. The capital investment required for an AVC system is especially attractive when there is gas compression equipment already on the lease. Gas-lift systems have proved to be an extremely flexible and economical means of lifting fluid from deep wells, particularly from those with high flowing bottom-hole pressures. However, means of lifting large volumes of fluid from deep, low-formation pressure wells have been limited, Conventional pressure wells have been limited, Conventional chambers have been used with good results, but these systems also have volume limitations. With the advent of the AVC system, a whole new realm of artificial lift was introduced. It is actually two system in one. The chamber system automatically pumps liquids from the chamber to the producing tubing where the upper standing valve producing tubing where the upper standing valve retains the liquid. It then vents the chamber, allowing it to refill. The gas-lift system above the chamber lifts the liquid from the upper standing valve to the surface. Thus the chamber is refilling while the previous chamber load is being lifted by the gas-lift previous chamber load is being lifted by the gas-lift system. Of course, while the chamber is refilling, formation gas is being Produced through the chamber and up the vent tubing. This eliminates the problems experienced with conventional chambers in gaseous wells. The chamber cycles repeat at a rate equal to the well's producing capability. The tubing cycles repeat with each one or two chamber cycles. In summary, the AVC system provides an automatic chamber that can handle formation gas with case and achieve a lower bottom-hole pressure than was ever before possible with gas lift. As with any chamber application, wells with high productivity indices (PI's) are the best candidates, productivity indices (PI's) are the best candidates, but in offshore fields, in subsea work, or on city lots where gas lift is a practical necessity, the AVC system may be economically applied to wells with high bottom-hole pressures and medium to low Pi's. it is felt that the system is particularly suited to fields undergoing secondary recovery. Production History Production History Four wells have been equipped with AVC systems and each illustrates the effectiveness of the system. Table 1 shows the production history of each well for several months. Each well was equipped with 2 7/8-in. production tubing and 1.900-in. OD vent tubing. JPT P. 13