Initial Gas Temperature Research Articles

Multiphase flash calculation for system containing TBAB semiclathrate: Application to semiclathrate-based post-combustion CO2 capture

A algorithm coupled with modified Patel-Teja equation of state and Chen-Guo hydrate model is developed to conduct vapor-liquid-semiclathrate multiphase flash calculation for TBAB containing systems. To quantitatively describe the gas consumption ability of semiclathrate slurry, a new concept, i.e., the apparent liquid phase, is introduced. The Patel-Teja equation of state (PT EOS) combined with a Debye-Hückel electrostatic term is chosen to describe the fugacity of TBAB in aqueous solution and calculated gas solubility in aqueous phase. The Chen-Guo hydrate model is extended to calculate the fugacity of TBAB in semiclathrate phase. Several parameters in Chen-Guo model for TBAB are retuned by correlating phase equilibrium data. A mathematical approach based on the secant iteration is successfully applied to solve flash calculation. Results from flash calculations are in satisfactory agreement with experimental data reported in other literature. This new algorithm provides an extended range of calculations for semiclathrate phases, such as amounts of semiclathrate formed, and then, the contributions of absorption and hydration upon separation performance can be quantitatively described. In addition, multistage separation are simulated using this flash algorithm. The effects of TBAB concentration of solution, initial gas liquid volume ratio, temperature, and pressure on separation efficiency are systematically discussed from the perspective of thermodynamics and mass balance.

Large Eddy Simulation on the Flame Structure for Split Injections of n-dodecane at Different Temperatures and Densities

ABSTRACTLarge eddy simulation coupled with linear eddy model is applied for the simulation of n-dodecane spray flames with multiple injections (0.5 ms injection/0.5 ms dwell/0.5 ms injection). The numerical model is validated by comparing the vapour penetration length at inner condition and the predicted ignition delay times at reacting conditions with the experimental results. Good agreement between the predicted and measured data is observed. The effects of initial conditions, including the initial temperature and ambient gas density on the development of double injections are analyzed. By decreasing the ambient gas density or initial temperature, the appearance of high-temperature kernels is delayed. The tip penetration travels faster both for the first and second injections when the initial gas density is reduced from 22.8 to 15.2 kg/m3 at an initial temperature of 900 K. By decreasing the initial gas temperature from 900 to 800 K, the tip penetration travels much slower. This is because that the high-temperature combustion appears very early at 900 K. The combustion of the first injection leads to the increase in local velocity and this effect becomes more obvious as the ignition delay (ID) is shortened. At latter times, the penetration velocity is almost the same for the second injection. Moreover, as the second spray is injected into hotter environment containing different key intermediate species, ID is reduced for the second injection. The reduction in ID is also related to the time when the second spray catches up with the first one. The inhibited mixing between fuel and air leads to richer ignition in the second injection compared with the first injection. For fuel-rich cells with the mixture fraction greater than 0.1, formaldehyde (CH2O) is quickly formed. Moreover, CH2O mass fractions in all of these cells have higher values compared with the first injection.

Sensitivity analysis and optimization for occupant safety in automotive frontal crash test

Abstract Nowadays, safety is a competitive advantage for automotive products and therefore receives considerable attention by automotive research centers. In this paper, a frontal crash test of sedan product of an under development platform is simulated and occupant head injuries are investigated based on ECE R94 regulation. First, an initial evaluation of the crash behavior of the sedan car is carried out and then airbag, dummy and seat belt are added to the model to study occupant head injuries under crash test. In this study, peak head acceleration and head injury criteria (HIC36) are considered as two output parameters based on ECE R94 regulation. Considering these two output parameters, sensitivity analysis and optimization are performed using Taguchi and analysis of variance (ANOVA) methods. In this way, airbag distance to dummy, trigger time, initial inflator gas temperature and tank pressure are considered as input parameters. Obtained results show that in all computer experiments designed by Taguchi responses values satisfy the requirements of ECE R94. Two different out-of-position conditions are considered by reducing the distance between dummy and airbag relative to the optimum design obtained by Taguchi. The worst case of design and its response values are also predicted using Taguchi. Finally, re-evaluating finite element analyses are performed based on the optimum and the worst cases. The results of these simulations show the validity of approach of this paper.

Particle scale study on heat transfer of gas–solid spout fluidized bed with hot gas injection

ABSTRACTIn this paper, the heat transfer characteristics of a 2D gas–solid spout fluidized bed with a hot gas jet are investigated using computational fluid dynamics-discrete element method. The initial temperature of the background gas and particles in the spouted bed was set to 300 K. The particle temperature distribution after injection of 500 K gas from the bottom, center of the bed, is presented. The simulation results indicate well heat transfer behavior in the bed. Then, statistical analysis is conducted to investigate the influence of inlet gas velocity and particle thermal conductivity on the heat transfer at particle scale in detail. The results indicate that the particle mean temperature and convective heat transfer coefficient (HTC) linearly increase with the increase in inlet gas velocity, while the conductive HTC and the uniformity of particle temperature distribution are dominated by the particle thermal conductivity. The conductive and convective heat transfer play different roles in the spout fluidized bed. These results should be useful for the further research in such flow pattern and the optimization of operating such spouted fluidized beds.

Improving the removal of fine particulate matter based on heterogeneous condensation in desulfurized flue gas

To reduce the emission of fine particulate matter (PM) in coal-fired power plants, a new method aimed to improve the removal of fine particulate matter based on heterogeneous vapor condensation was investigated. The ideal supersaturation environment, necessary to the occurrence of heterogeneous vapor condensation, was achieved by reducing the initial temperature of limestone-gypsum desulfurization flue gas with a fluorine plastic heat exchanger. The temperature drop, initial relative humidity and initial temperature of desulfurized flue gas have an important influence on the establishment of ideal supersaturation environment and the reduction efficiency of fine particulate matter. Numerical calculation indicates that a higher temperature drop and initial relative humidity of the desulfurized flue gas is beneficial to the establishment of ideal supersaturation environment, while the influence of initial temperature of desulfurized flue gas is unobvious. It has been also experimentally proved that the increase of temperature drop and initial relative humidity have a positive effect to the improvement of the reduction efficiency. However, it can be also found that the reduction efficiency changes slightly with the variation of the initial temperature of desulfurized flue gas. Therefore, this method is suitable for different initial temperatures of desulfurized flue gas and is more applicable for practical industrial applications. Most commonly, the optimal value of temperature drop of desulfurized flue gas is in the range of 4 to 6 °C and the corresponding number concentration of fine particulate matter emission can be reduced as high as about 43%.

Determination of the gas hydrate formation limits to isenthalpic Joule–Thomson expansions

Due to the perennial problems associated with the gas hydrate phenomenon in natural gas and oil industries, it is crucial to avoid hydrate formation. If a natural gas passes through a throttling process, hydrate formation may occur. In this study, novel methodologies were developed to determine the hydrate formation limits to isenthalpic Joule–Thomson (JT) expansions for the first time. First, a new empirical correlation is introduced for predicting the required minimum initial temperature of a natural gas passing through a JT expansion without the risk of hydrate formation. Next, state-of-the-art algorithms including adaptive neuro-fuzzy inference system (ANFIS), least squares support vector machine (LSSVM), and radial basis function artificial neural network (RBF-ANN) were utilized for presenting the models capable of predicting the gas initial temperature. According to the results of the performed error analysis, it is found that the proposed methods provide excellent estimations. The proposed models show R2 to be more than 0.99 and AARD% to be less than 0.5. However, the most accurate estimations are obtained from the presented RBF_ANN model.

Measurements and Experimental Database Review for Laminar Flame Speed Premixed Ch4/Air Flames

Laminar flame speed (SL) of CH4 was determined at atmospheric pressure and initial gas temperatures in range from 298 to 358 K. The heat flux method was employed to measure the flame speed in non-stretched flames. The kinetic mechanism GRI 3.0 [1] were used to simulate SL. The measurements were compared with available literature results. The data determined with the heat flux method agree with some previous burner measurements and disagree with the data from some vessel closed method and counterflow method. The GRI 3.0 mechanism was able to reproduce the present experiments. Laminar flame speed was determined at pressures range from of 1 to 20 atmospheres through mechanism GRI 3.0. Based on experimental data and calculations was obtained SL dependence on pressure and temperature. The resulting of dependence recommended use during the numerical simulation of methane combustion.

Parameter optimization and performance comparison of several power cycles for waste heat recovery from moderate temperature flue gas

Focus on waste heat power recovery from flue gas of initial temperature of 350-550ºC, comparative assessment was carried out on the net power outputs of organic Rankine cycle(ORC), organic trans-critical cycle(OTC), single pressure steam cycle, dual-pressure steam cycle, flash steam cycle and ethanol/water-RC based on parameter and configuration optimization. The results show that ethanol/water-RC gives the highest net power output among all the cycles within the whole initial temperature range considered. ORC’s and OTC’s net power outputs are greater than the steam cycles’ until the initial temperature of flue gas exceeds 500ºC.

X3 expansion tube driver gas spectroscopy and temperature measurements

The University of Queensland’s X3 facility is a large, free-piston driven expansion tube used for super-orbital and high Mach number scramjet aerothermodynamic studies. During recent development of new scramjet test flow conditions, experimentally measured shock speeds were found to be significantly lower than that predicted by initial driver performance calculations. These calculations were based on ideal, isentropic compression of the driver gas and indicated that loss mechanisms, not accounted for in the preliminary analysis, were significant. The critical determinant of shock speed is peak driver gas sound speed, which for a given gas composition depends on the peak driver gas temperature. This temperature may be inaccurately estimated if an incorrect fill temperature is assumed, or if heat losses during driver gas compression are significant but not accounted for. For this study, the ideal predicted peak temperature was 3750 K, without accounting for losses. However, a much lower driver temperature of 2400 K is suggested based on measured experimental shock speeds. This study aimed to measure initial and peak driver gas temperatures for a representative X3 operating condition. Examination of the transient temperatures of the driver gas and compression tube steel wall during the initial fill process showed that once the filling process was complete, the steady-state driver gas temperature closely matched the tube wall temperature. Therefore, while assuming the gas is initially at the ambient laboratory temperature is not a significant source of error, it can be entirely mitigated by simply monitoring tube wall temperature. Optical emission spectroscopy was used to determine the driver gas spectra after diaphragm rupture; the driver gas emission spectrum exhibited a significant continuum radiation component, with prominent spectral lines attributed to contamination of the gas. A graybody approximation of the continuum suggested a peak driver gas temperature of 3200 K; uncertainty associated with the blackbody curve fit is ±100 K. However, work is required to quantify additional sources of uncertainty due to the graybody assumption and the presence of contaminant particles in the driver gas; these are potentially significant. The estimate of the driver gas temperature suggests that driver heat losses are not the dominant contributor to the lower-than-expected shock speeds for X3. Since both the driver temperature and pressure have been measured, investigation of total pressure losses during driver gas expansion across the diaphragm and driver-to-driven tube area change (currently not accounted for) is recommended for future studies as the likely mechanism for the observed performance gap.

Modeling of downdraft gasification process: Studies on particle geometries in thermally thick regime

In this study, a downdraft gasifier model is coupled with a single-particle model to analyze the effects of particle geometries such as slab, cylindrical, and spherical on different parameters. Simulations were performed using particles in a thermally thick regime with larger particle sizes of 0.003–0.05 m, which are generally used in commercial gasifiers. This combination of the downdraft gasifier model and single particle model was implemented using Comsol Multiphysics software program. The results obtained are in good agreement with those of obtained in previous studies. The low thermal conductivity of biomass (kB), small particle size (dp), high gas temperature (Tg), higher molar fraction of oxygen in primary air (XO2), and high mass-transfer coefficient (km) favor the formation of carbon monoxide (CO), hydrogen (H2), high tar conversion, and higher lower heating value. To maximize the CO composition and tar conversion, the initial gas temperature (Tg) is more crucial. The least sensitive parameter is the thermal conductivity of biomass (kB) in relation to product composition of CO, carbon dioxide (CO2), H2, and methane (CH4). The sensitivity for all the parameters is found to be the highest for the spherical geometry and is least for the slab geometry.

Reducing the flue gases temperature by individual droplets, aerosol, and large water batches

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950K). The temperature of a gas-vapor mixture in the area of droplet traces is measured using low-inertia thermocouples (thermal lag is less than 0.1s). The paper considers aerosol flows with droplet size of 0.04–0.4mm and concentration of 3.8·10−5–10.3·10−5m3 of droplets/m3 of gas, as well as individual droplets (sized 1.5–2.5mm), and relatively large water massifs (sized 22–30mm). The typical gas temperature reduction in the trace of a moving liquid ranges from 15K to 140K. The times of keeping the low temperature of the gas-vapor mixture in the droplet trace are from 3s to 30s relative to the initial gas temperature. The study indicates how such factors as initial droplet size, velocities of the high-temperature gas flows, volume concentration of droplets, combustion products temperature and initial water temperature influence the integral characteristics of temperature traces of droplets. For the experiments with single drops, large masses and aerosol drops, the comparative analysis takes place for conditions, at which the convective heat transfer between liquid and combustion products dominates over an evaporation. The experimental data substantiate the hypothesis which suggests that the temperature traces of water droplets are kept during quite a long time even for small droplets. The experimental data are a key basis for the development of the drip systems of controlled gas temperature reduction via the intensification of phase transitions.

Presepsin for Early Infection Diagnosis during Acute Necrotizing Pancreatitis

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950 K). The temperature of a gas-vapor mixture in the area of droplet traces is measured using low-inertia thermocouples (thermal lag is less than 0.1 s). The paper considers aerosol flows with droplet size of 0.04–0.4 mm and concentration of 3.8·10−5–10.3·10−5 m3 of droplets/m3 of gas, as well as individual droplets (sized 1.5–2.5 mm), and relatively large water massifs (sized 22–30 mm). The typical gas temperature reduction in the trace of a moving liquid ranges from 15 K to 140 K. The times of keeping the low temperature of the gas-vapor mixture in the droplet trace are from 3 s to 30 s relative to the initial gas temperature. The study indicates how such factors as initial droplet size, velocities of the high-temperature gas flows, volume concentration of droplets, combustion products temperature and initial water temperature influence the integral characteristics of temperature traces of droplets. For the experiments with single drops, large masses and aerosol drops, the comparative analysis takes place for conditions, at which the convective heat transfer between liquid and combustion products dominates over an evaporation. The experimental data substantiate the hypothesis which suggests that the temperature traces of water droplets are kept during quite a long time even for small droplets. The experimental data are a key basis for the development of the drip systems of controlled gas temperature reduction via the intensification of phase transitions.

Thermo-hydro-mechanical coupled mathematical model for controlling the pre-mining coal seam gas extraction with slotted boreholes

Drainage influence radius is the basic parameter for borehole arrangement, while the effect of high pressure water jet slotting technology on borehole drainage influence radius has not been studied systematically. In this paper, a fully thermo-hydro-mechanical (THM) coupled model which represents the non-linear responses of gas extraction was implemented to demonstrate the reliability of this model through history data matching. Based on this model, the susceptibilities of gas extraction with single slotted borehole, including the permeability, the gas pressure, the temperature, the coal adsorption characteristics and the radius of slot, were quantified through a series of simulations. The simulation results revealed that increasing the permeability, initial gas pressure and temperature could develop the influence radius of single slotted borehole. This finite element model and its simulation results can improve the understanding of the coal-gas interactions of underground gas drainage and provide a scientific basis for the optimization of drainage systems.

MODELLING OF HEAT AND MASS TRANSFER PROCESSES IN PHASE TRANSFORMATION CYCLE OF SPRAYED WATER INTO GAS 5. NUMERICAL MODELLING OPTIMIZATION OF PHASE TRANSFORMATION CYCLE FOR DROPLETS SLIPPING IN GAS FLOW

Condensing and transit evaporation regimes for phase transformation cycle were modelled for slipping droplets in humid gas. By concluded results of droplet thermal, energetic, dynamics and phase transformation parameters P it is based on that according to unit initial Reynolds number grouped droplet cloud, universality of dimensionless transfer parameters PFo functions graphs is valid in aspect of droplet dispersity for cases defined by water and gas initial temperature and humidity. According to phase transformation cycle modelling results for intensively slipping droplet by conditions 0 Re  50 it was received that by "c" heat transfer model calculated droplet moment mass mean temperature m,"c" T can exceed up to 2.5 K temperature m,"k " T calculated according to "k" heat transfer model. An applied droplet mass mean temperature model can lead to ± 0.05 percent imbalance for calculated droplet surface area.DOI: http://dx.doi.org/10.5755/j01.mech.23.1.13689

Studying gas temperature variation upon aerosol injection

Variation of the temperature of gaseous combustion products upon pulsed injection of aqueous aerosols (water, NaCl solution, clay suspension) with droplet sizes within 40–400 μm has been experimentally studied at initial gas temperatures from 520 to 910 K. The motion of aerosol droplets in the counterflow of combustion products was visualized by panoramic optical techniques. It is established that the process of gas cooling depends on the degree of aerosol dispersion, NaCl concentration in solution, clay content in suspension, and the conditions of liquid phase injection.

Laminar burning velocity of diacetyl + air flames. Further assessment of combustion chemistry of ketene

Ketene is important intermediate in high-temperature chemistry of several oxygenates, such as acetone, acetic acid, and diacetyl. Ketene reactions appear in the sensitivity spectra of calculated burning velocities of the first two species. To provide independent experimental data for validation of the ketene sub-mechanism, the laminar burning velocities of diacetyl + air flames at 1 atm and initial gas temperatures of 298 K, 318 K, and 338 K were determined for the first time. Measurements were performed using the heat flux method in non-stretched flames, stabilised on a perforated plate burner at adiabatic conditions. Recently developed detailed kinetic mechanism for acetic acid flames with updated ketene sub-mechanism has been extended by reactions of diacetyl and includes revised rate constants for reactions of acetaldehyde and acetyl radical. The model was first compared with available experimental data on ketene pyrolysis and oxidation. Its performance in prediction of C2 species formation was improved by significant reduction of the previously estimated rate constants of ketene reactions with CH3 and CH2 radicals. The updated mechanism was then compared with the new measurements for diacetyl and earlier data for acetaldehyde, acetone and acetic acid flames. The model closely reproduces burning velocity of diacetyl + air in lean and rich mixtures while underpredicts in stoichiometric and slightly rich flames. Performance of the model for acetaldehyde + air flames was much improved as compared to the Konnov mechanism version 0.6. Good agreement of the modelling with experimental data for acetone + air flames was also demonstrated. The disparity between predicted burning velocities of acetic acid and recent measurements did not change. The model was further examined using sensitivity analysis for these flames to elucidate common reactions affecting its performance. It was concluded that the mechanism performance in prediction of the burning velocities of acetic acid flames could be improved by revision of reactions between CH2CO and OH radicals, while keeping its agreement with other flames studied. Remaining uncertainties in the ketene sub-mechanism are outlined.

Effect of Chemical Reactions of H2/O2 Combustion Gas on Wall Heat Flux in a Turbulent Channel Flow

The effect of chemical reactions of burnt gas on heat transfer on a cooled wall in a turbulent channel flow is investigated by direct numerical simulations. Burnt gas from a H2/O2 mixture is used as a fluid and a detailed chemical reaction mechanism that considers eight chemical species and 19 elemental reactions is used in the reaction calculation. The initial gas temperature and pressure are 3173 K and 2.0 MPa, respectively. The Reynolds number based on the channel width and mean streamwise velocity is approximately 6400 and that based on the channel half width and friction velocity is approximately 200. The results show that heat release because of consumption of radicals such as OH and H near the wall increases the heat flux on the wall and that the heat flux is enhanced by the significant increase in the local heat flux at high-speed streaks where radicals are supplied by sweep events constituting bursting motions in the turbulent boundary layer.

Decreasing the mass indices of gas turbine engines regenerators by means of choosing rational parameters

The purpose of the conducted research was to develop a method for determining parameters of GTE regenerator, which would ensure at the initial stages of designing a minimum mass of the heat exchanger with the assigned values of efficiency. We obtained dependences that establish relationships between the regenerator and the GTE, which allow analyzing the influence of effectiveness and pressure losses in regenerator on the efficiency of GTE and the mass of the regenerator. Relationship between parameters of the regenerator and performance efficiency of regenerative GTE was described by functional dependence, where energy parameters of the regenerator are collected in a single complex. It was established that the magnitude of effectiveness of the regenerator is associated with efficiency by inversely proportional function, and pressure losses – by linear function. Effectiveness of the regenerator is associated with the mass of the heat exchanger and the geometry of heat exchange surface by exponential dependence, and relative pressure losses – by algebraic irrational function. Based on these dependences, the algorithm for selecting rational energy and geometrical parameters of regenerators of GTE was developed. It was found that by selecting rational values of effectiveness of regenerator and pressure losses, it is possible to provide for a significant decrease in mass of the regenerator with a constant value of performance efficiency of GTE. The obtained results of calculations of regenerators of GTE with different structural solutions allow a designer engineer to choose rational values of effectiveness of the regenerator, pressure losses, and initial gas temperature. Comparison of complex regenerative GTE by the mass of regenerator at constant values of performance efficiency was conducted. Based on the analysis of results of calculations, the stage dependence of specific mass of regenerator on the assigned increase in performance efficiency of regenerative GTE was obtained, which gives the possibility to estimate the mass of tubular regenerator at the initial stages of designing. Implementation of the obtained results into the practice of designing regenerative GTE will make it possible to ensure the choice of their rational parameters and to decrease the time of designing.

On electron–proton energy exchange in strong magnetic field

Heating of protons in cold electron gas in strong magnetic field is studied. Calculations of heating process are preformed using molecular dynamics method. Estimations of heating rate depending on initial proton energies and electron gas temperatures are made.

Modeling, simulation and optimization of downdraft gasifier: Studies on chemical kinetics and operating conditions on the performance of the biomass gasification process

The cracking of tar from rice husk pyrolysis is examined using tar reaction conditions similar to gasification and combustion because of the practical importance of tar cracking in the modeling of biomass gasification processes. Experiments have been performed in a two-stage gasifier to determine the kinetics of the tar cracking reaction. A new kinetic scheme is proposed for secondary tar cracking of biomass. The model is developed for downdraft biomass gasification and incorporates crucial effects of the pyrolysis fraction and char reactivity factor in its simulations. The model equations are solved using COMSOL Multiphysics. This model provides better agreement with experimental data than the model proposed by other researcher. This model is used to examine the influence of operating conditions in the gasifier, such as the length of the gasification zone, initial gas temperature, air flowrate, and mole fraction of oxygen in primary air, on product compositions (CO, CO2, H2, CH4, and tar). The result concludes that the increase in temperature leads to higher composition of carbon monoxide and lower composition of tar, and consequently higher low heating value (LHV). In addition, sensitivity analysis has been conducted to determine the influence of these parameters on product compositions.