Constant Mass Flow Research Articles

Effect of pressure in the autothermal catalytic partial oxidation of CH4 and C3H8: Spatially resolved temperature and composition profiles

Operation under pressure is a major requirement for the intensification of the catalytic partial oxidation (CPO) of light hydrocarbons. Related issues are the increase of the thermal loads experienced by the catalyst and the promotion of gas phase chemistry, which can lead to the formation of coke precursors. In this work, we analyze the autothermal CPO of C3H8 and CH4, carried out between 1 and 4bar at constant mass flow rate over a Rh-coated honeycomb catalyst. Spatially resolved temperature and concentration profiles are presented and analyzed with a mathematical model of the reactor, which includes appropriate mass and heat transfer correlations and detailed kinetic schemes for the homogeneous and the heterogeneous chemistry. The results show that pressure affects the heterogeneous process thermodynamically but not kinetically. In fact, in the final part of the catalyst, where the reaction approaches the equilibrium, higher pressures cause an increase of the outlet temperatures and a decrease of the selectivity to syngas. In the first part of the catalyst, where the progress of the reaction is controlled by kinetics, pressure has no effect on both temperature and concentration profiles due to the dominant role of mass transfer on the consumption of O2 and fuel. In the case of CH4 CPO, there is no evidence of homogenous reactions, whereas, in C3H8 CPO pressure promotes gas phase cracking, which leads to the formation of methane and intermediate C2+ species. Experiments performed on a thin catalyst slice confirm that heterogeneous steam reforming reactions have a key role in cleaning the gas phase from these C2+ species, preventing the catalyst from coking.

Horizontal centrifuge with screw conveyor (decanter): Optimization of oil/water levels and differential speed during olive oil extraction

Olive oil extraction using a horizontal centrifuge with a screw conveyor is an essential operation to reduce production costs. However, proper control of the plant is required to maintain a high level of extraction yield and olive oil quality. Rheological characteristics of the olive paste, which change in relation to water content, fruit variety, maturity level and seasonal temperature variations, greatly affect the efficiency of centrifugal extraction. If olive paste is fed to a decanter without automatic control, then non-optimal extraction is performed.After successfully testing a suitable flow mass sensor in order to set up an automatic system to control the olive paste mass flow rate fed to a decanter centrifuge during olive oil extraction, a feedback control system was tested in the laboratory and built in-line in an industrial processing plant. This allowed trials to be carried out at constant mass flow rate for both the paste and the added water, on a decanter centrifuge with variable differential speed between bowl and screw conveyor (i.e. variable DN) and with regulation capability of oil–water ring levels. Constant quality olives (cv. Coratina) were used for the trials; the correlation was evaluated between oil/water ring levels and DN with respect to the extraction yield, husk fat content and vegetable water fat content.The “oil recovery efficiency” (ηo) and “separation coefficient” S peaked with maximum residence time, using DN=13.3 and RING=284.8, while ηo minimum was achieved at higher DN. More specifically, for DN values higher than about 18 or lesser than 12, ηo becomes independent of RING. Furthermore, ηo and S values are strictly related to the geometry of the decanter centrifuge, whereas the paste dilution ratio determines the preservation quality of the oil extracted, and the maximum oil recovery efficiency represents the remaining objective related to the quantity of extracted oil.From experimental data some interesting relations were found linking decanter centrifuge parameters; their relationship depends on a complete quadratic interaction model constituted by the input variables that leads to highly correlated polynomials between DN vs. Uopdb (“mass fraction of oil in the fed olive paste” (dry basis)) and ηo optimal vs. Uopdb. These relations allow optimization of DN and RING values such that maximum oil recovery efficiency is achieved. Indeed, knowledge of Uopdb by an on-line method allows the decanter DN and RING operating parameters, to be calculated and modified at once, obtaining optimal maximum oil recovery efficiency.

Modeling of a combined ion transport and porous membrane reactor for oxy-combustion

Ion transport membranes (ITMs) offer promising technology for high purity oxygen production (up to 99%) without adversely affecting the efficiency of the oxy-fired plants. The permeation rate of such ITMs can be increased by replacing the conventional inert sweep gas with a reactant/diluent mixture (e.g. CO2, CH4) as this reduces the permeate partial pressure on the permeate side of the membrane, which, along with the temperature, governs the permeation flux. The significant limitation of this approach is that an uncontrolled, exothermic consumption of the permeated specie, can lead to membrane damage, and thus limits the potential of ITMs using reactive sweep gases (i.e. ITM reactors). By using a multichannel ITM reactor (isothermal reactor), it is proposed to operate the ITM reactor at, or near to isothermal conditions (i.e. a spatially uniform temperature). This may be achieved by introducing a reactant into the permeate stream uniformly across the entire ITM reactor length from an adjacent channel with porous walls. The present work is aimed at modeling a nearly isothermal reactor using an ITM and a porous membrane to achieve uniform stoichiometric ratio of fuel/O2 in order to have a uniform combustion all along the length of the membrane. A two-dimensional, computational fluid dynamics (CFD) model is solved to study the characteristics. The simulations are based on the numerical solution of the conservation of mass, momentum, energy and species transport equations of two dimensional flows. For the CFD calculations, the commercial solver FLUENT has been used. The models used have been validated against the experimental results found in the literature and are found to be in good agreement. The influence on the performance of oxygen separation through the ITM has been studied by varying the flow conditions at the permeate side. Results show that an approximate uniform combustion can be achieved along with effective thermal management of the ITM using the present isothermal reactor. It is also observed that for a constant mass flow rate of fuel mixture, the permeation rate of oxygen through ITM increases with the increase in CH4/CO2 ratio. The results indicate that the oxygen permeation flux increases by approximately 3 times for reactive case compared to separation only case. Moreover it is shown that using the present reactor model the reaction zone can be controlled.

Comprehensive performance evaluation and parametric studies of single pass solar air heater with fins and baffles attached over the absorber plate

This study investigates the influence of fins and baffles attached over the absorber plate on the performance of the upward type single pass solar air heater. A steady-state mathematical model is presented and solved theoretically. The performance evaluation is studied in terms of different performance indicators, such as outlet air temperature, efficiency and effective efficiency. It is found that attaching fins and baffles effectively increases the outlet air temperature and efficiency in comparison to a simple conventional device. However, it is observed that increasing the number of fins and baffles parameters can reduce effective efficiency even less than a simple conventional device in some cases due to the high required pump work. It is found that there is no chance of introducing unique optimum number of fins and baffle parameters in all mass flow rates to achieve the highest performance in terms of effective efficiency, but it can be obtained in constant mass flow rate. The results reveal that the baffle width is a crucial parameter when the Reynolds number increases and the flow regime is turbulent. Increasing the solar intensity leads to achieve higher outlet air temperature and efficiency as well as lower difference between efficiency and effective efficiency.

变厚度轧制时质量守恒的表述方式

The law of mass conservation, when applied to the normal rolling processes, can be expressed as the constant mass flow principle (CMFP). Variable gauge rolling (VGR) processes must obey the law of mass conservation, but whether these processes also satisfy the CMFP requires verification. This paper reports the effect of roll rigid displacement speed in vertical direction in rolling on the element deforment of the work piece, by analyzing the geometric relationship, metal flow, and slab element movement during VGR progress. Using both Lagrange and Euler configurations, the CMFP is demonstrated to not be suitable for VGR processes. The flow difference is related to the vertical speed of the roll. When the roll rotational speed ω is constant, the flow amount of materials in the rolling direction increases during upward rolling but decreases during downward rolling. Rather than the CMFP being applied in VGR processes, the law of mass conservation can be expressed as material volume remains constant at any time for each element during plastic deformation.

Experimental analysis of a paraffin-based cold storage tank

The aim of this study is to characterize a paraffin-based cold storage tank. Novel experimental results are presented for this system which combines a significant amount of paraffin (1450 kg) immersed around 18 spiral-shaped coils disposed in counter-current flow. The paraffin has a phase-change temperature in the range 4–8 °C as measured by a 3-layer calorimeter. Different tests have been carried out with a constant mass flow rate and supply temperature. Around 31% of the paraffin has hardly any contact with the coils and hereby acts as a dead mass. The results show the importance of natural convection within the phase-change-material, particularly during the melting process. The highest efficiency has been achieved for the lowest supply temperatures and mass flow rates of the heat transfer fluid.

Novel three-phase steam–air plasma torch for gasification of high-caloric waste

Research results are presented for an AC electric arc that burns a mixture of steam and air in a three-phase high-voltage plasma torch and can be implemented to produce plasma for plastic waste gasification. The dependences of electric parameters on the ratio of the steam to air mass flows (H2O/air ∼1–6) at an approximately constant total mass flow of the plasma-forming gas are obtained during several experiments. During the experiments, the arc parameters were as follows: voltage drop of 1.0–1.8kV, current of ∼28.5A and power of ∼52–86kW. The thermal efficiency of the plasma torch was ∼94–95%. CCD cameras operating at 4000fps were used to determine the average discharge length of ∼798mm. Photography with a high shutter speed (1/8000s) was used to determine the average arc diameter (∼4.47mm). Arc temperatures were calculated (10,000–11,500K) using the thermodynamic equilibrium approach. Experimental results indicate that increases in the steam content of the steam–air plasma lead to a reduction of the arc’s temperature and electrical conductivity. Using an equilibrium approach, the main parameters of plasma gasification were estimated: syngas yield (3.62–3.48m3/kg), composition (H2 – 55.5–62.5, CO – 32.8–34.1vol.%) and energy consumption (11.0–12.3MJ/kg).

Overall Effectiveness for a Film Cooled Turbine Blade Leading Edge With Varying Hole Pitch

Overall effectiveness, φ, for a simulated turbine blade leading edge was experimentally measured using a model constructed with a relatively high conductivity material selected so that the Biot number of the model matched engine conditions. The model incorporated three rows of cylindrical holes with the center row positioned on the stagnation line. Internally the model used an impingement cooling configuration. Overall effectiveness was measured for pitch variation from 7.6d to 11.6d for blowing ratios ranging from 0.5 to 3.0, and angle of attack from −7.7 deg to + 7.7 deg. Performance was evaluated for operation with a constant overall mass flow rate of coolant. Consequently when increasing the pitch, the blowing ratio was increased proportionally. The increased blowing ratio resulted in increased impingement cooling internally and increased convective cooling through the holes. The increased internal and convective cooling compensated, to a degree, for the decreased coolant coverage with increased pitch. Performance was evaluated in terms of laterally averaged φ, but also in terms of the minimum φ. The minimum φ evaluation revealed localized hot spots which are arguably more critical to turbine blade durability than the laterally averaged results. For small increases in pitch (from p/d = 7.6 to 9.6) there was only a small decrease in performance, but at p/d = 11.6 a significant reduction was observed.

Interpretation of dynamic frontal analysis data in solid/supercritical fluid adsorption systems. I: Theory

A theory is proposed to relate the elution times of the adsorption front shocks of breakthrough curves recorded during classical dynamic frontal analysis (FA) experiments with selected compounds and their adsorption isotherms in solid/supercritical fluid adsorption systems. The actual density and viscosity of binary mixtures of CO2 and methanol were obtained from the NIST REPPROP software. Diluted solutions of S-naproxen were considered (<2% in mass) but the possible effects of the analyte concentration on the viscosity and the density of the eluent percolating through the column were neglected. This allows the determination of the excess adsorption isotherm (or Gibbs excess isotherm) of the adsorbed analyte in the whole column at constant mass and volumetric flow rate of pure CO2 and of the modifier solution. A local Langmuir adsorption isotherm and a constant saturation capacity were assumed in the calculations. The variation of the adsorption–desorption constant with the eluent density was taken from the experimental variation of the retention factor of S-naproxen on a chiral column packed with Whelk-O1 particles. The results show that the isotherm parameters obtained from the best adjustment of the Langmuir model to the SFC excess adsorption data deviates by less than 7% from the assumed saturation capacity and from the average of the equilibrium constant along the chromatographic column. In practice, this conclusion holds true provided that the precision of the measurement of elution times of front shocks of breakthrough curves is better than 1% and that the maximum surface coverage qexp,max/qS is at least equal to 20%.

Numerical study of conjugate heat transfer of cryogenic methane in rectangular engine cooling channels at supercritical pressures

Three-dimensional conjugate heat transfer of cryogenic methane in rectangular engine cooling channels at supercritical pressures with asymmetric heating imposed on the top channel surface is numerically investigated, focusing mainly on effects of the thermal conductivity of the solid channel material and the geometric aspect ratio of the channel on fluid flow and heat transfer. Results indicate that variations of the thermal conductivity in the solid fin produce significant impact on conjugate heat transfer owing to heat flux redistribution in solid region and convective heat transfer variation in fluid phase. The latter factor is dictated by strong variations of fluid thermophysical properties at a supercritical pressure. At a constant inlet mass flow rate, variations of the geometric aspect ratio of the channel exert strong influence on both heat transfer and pressure loss due mainly to fluid velocity variations. Results indicate that convective heat transfer plays a more dominating role than thermal conduction in the solid fin. A thermal performance factor can be used for the combined evaluation of heat transfer and pressure loss. The modified Jackson & Hall empirical heat transfer expression is tested to be applicable for heat transfer prediction of cryogenic methane at supercritical pressures.

A High By-Pass Ratio Turbofan Model Based on CMF Method

In this paper, a detailed research about a high by-pass ratio turbofan engine transient performance model has been carried out, and the relevant solver equations have been deduced by employing constant mass flow (CMF) method. A high by-pass ratio turbofan engine transient model was established by means of employing the solver equations and Matlab programming language. On the basis of comparison, the calculation results of the model have quite remarkable consistency with those results calculated by GSP 11, with maximum error within 3.0%.The simulation results show that the solver equations of aero-engine deduced in this paper are of high validity and applicability.

Numerical Simulation of PRHR System Based on CFD

In this paper numerical simulation of PRHR HX and IRWST is demonstrated using FLUENT, and different numbers of C-type heat transfer tubes and coolant inlet temperature’s effects for the residual heat removal capacity of PRHR HX, IRWST thermal stratification and natural circulation have been researched. It’s found that at a constant flow area when heat transfer tubes’ number increased outlet temperature of PRHR HX is lower, the whole water temperature of IRWST is higher, thermal stratification and natural circulation are more oblivious. At a constant mass flow when inlet temperature of PRHR HX increased, inlet flow velocity increases and outlet temperature is higher. But on the other hand the cooling rate increases at the same time, the average temperature of IRWST is higher, the range of thermal stratification expands and the velocity of natural circulation increases.

The CFD Analysis of Turbulence Characteristics in Combustion Chamber with Non Circular Co-Axial Jets

Co-Axial jets have applications in areas where the mixing of two fluid jets are necessary, the two fluid jets can be effectively mixed by producing the turbulence flow. Turbulence is a chaotic behavior of the fluid particles that comes in to picture when the inertia force of the flow dominates the viscous force and it is characterized by the Reynolds Number. Co-axial jets are effective in producing the turbulence. In the present study the free compressible turbulent coaxial jet problem will be computed using CFD, and compare with different non circular coaxial jets based on constant hydraulic diameter and mass flow rate. Turbulence characteristics of combustion chamber with circular coaxial and non circular coaxial jets are determined and

Experimental Study on Air Cooling Via a Multiport Mesochannel Cross-Flow Heat Exchanger

The air-side heat transfer and flow characteristics of cross-flow multiport slab mesochannel heat exchanger are investigated experimentally in this article. The multiport slab mesochannel heat exchanger consists of 15 finned aluminum slabs; each slab contains 68 flow channels of 1 mm circular diameter. The cold deionized water at a constant mass flow rate was forced to flow through the mesochannels, whereas the hot air at different velocities was allowed to pass through the finned passages of the heat exchanger core in cross-flow orientation. The heat transfer and fluid flow key parameters were examined in the region of the air-side Reynolds number in the range of 972–2758, with a constant water-side Reynolds number of 135. The effect of air-side Reynolds number on air-side Nusselt number was examined and a general correlation of Nusselt number with Reynolds number was obtained. The Nusselt number value was found to be higher in comparison with other research works for the corresponding Reynolds number range. The multiport mesochannel flat slab geometry has offered uniform temperature distribution into the core. This uniform temperature distribution leads to higher heat transfer over stand-alone inline flow tube bank.

Permeability studies of artificial and natural cancellous bone structures

In the development of artificial cancellous bones, two major factors need to be considered: the integrity of the overall structure and its permeability. Whilst there have been many studies analysing the mechanical properties of artificial and natural cancellous bones, permeability studies, especially those using numerical simulation, are scarce. In this study, idealised cancellous bones were simulated from the morphological indices of natural cancellous bone. Three different orientations were also simulated to compare the anisotropic nature of the structure. Computational fluid dynamics methods were used to analyse fluid flow through the cancellous structures. A constant mass flow rate was used to determine the intrinsic permeability of the virtual specimens. The results showed similar permeability of the prismatic plate-and-rod model to the natural cancellous bone. The tetrakaidecahedral rod model had the highest permeability under simulated blood flow conditions, but the plate counterpart had the lowest. Analyses on the anisotropy of the virtual specimens showed the highest permeability for the horizontal orientation. Linear relationships were found between permeability and the two physical properties, porosity and bone surface area.

Experimental and Numerical Study of Recuperative Heat Recirculation

In many power-generating systems heat recirculation is needed in order to increase their thermal efficiency and ensure sufficiently high temperatures required in fuel processing. The current article investigates experimentally and numerically a heat recirculation phenomenon by using gas–gas recuperation. The systematized description of practicalities of heat recirculation is reported. The experimental characteristics of a heat recirculator are presented in terms of the effect of power of the heater at constant mass flow rate, effect of mass flow rate at constant power of the heater, and effect of mass flow rate at constant ratio power of the heater/mass flow rate on heat transferred, heat lost to the surroundings, and processing temperatures. The results show that heat recirculation is maximized at moderate mass flow rate, at large power, and in miniaturized channels. Further, a numerical model is used in order to interpret and extend the experimental data set. The simulations are focused on heat recirculation under conductive, dispersive, and convective regimes of heat transfer. Finally, the principles of thermal integration of power-generating systems by using heat recirculation are expounded.

Parametric investigation of the pintle-perturbed conical nozzle flows

Thrust variation, flow structures and geometric factors of pintle-perturbed conical nozzle are studied experimentally and numerically under the condition of constant mass flow rate. Regulators and choking orifice are installed for constant mass flow rate and static pressure distributions along the nozzle wall, chamber pressure and thrust are measured. In order to prevent transfer of non-linear load to the load cell by the flexible tubes, the load cell for thrust measurement is calibrated. Roeʼs flux-difference splitting scheme is applied to resolve the flow discontinuities such as the lip shock, trailing shock and oblique shock typical in the pintle-perturbed nozzle flows. Three different turbulent models of k–ε, k–ω SST and Spalart–Allmaras are examined to assess their validity for resolving the turbulence. The predicted thrust by empirical method, which includes influence of deliverable thrust coefficient by flow separation, showed good agreement with measured thrust at the minimum and maximum throat area. Spalart–Allmaras model and k–ω SST model showed good agreement with experiment on predicting the thrust especially in the case that the flow separation occurs in the nozzle diverging section, and the Spalart–Allmaras model predicted wall separation point more accurately than the other models. Shock impinging point and the flow separation point induced by shock wave separation occur and move in the nozzle flow as the pintle inserted into the nozzle throat. Because, the dominant factor which determines thrust is chamber pressure, the pintle shape must be considered essentially in view of minimizing the force acting on the pintle.

TRANSFLOW: An experimental facility for vacuum gas flows

The TRANSFLOW experimental facility represents a reliable tool for measuring the conductance of 1:1 scale components as typically used in vacuum systems in a wide range of the Knudsen number (e.g. 10−4≤Kn≤103). The main principle of this facility is the dynamic measurement of the pressure difference upstream and downstream of the duct by setting a constant mass flow rate through the test channel. Many experiments on fully developed and developing flows, based on long and short channels respectively, have been already completed and comparisons with corresponding numerical results have been successfully performed. It has been clearly proven that the TRANSFLOW experimental setup provides conductance results with overall uncertainty between 1 to 10% and it could be used as a benchmark facility for any new proposed scientific numerical method in rarefied gas dynamics and in the whole range of gas rarefaction.

Money versus time: evaluation of flow control in terms of energy consumption and convenience

AbstractFlow control with the goal of reducing the skin-friction drag on the fluid–solid interface is an active fundamental research area, motivated by its potential for significant energy savings and reduced emissions in the transport sector. Customarily, the performance of drag reduction techniques in internal flows is evaluated under two alternative flow conditions, i.e. at constant mass flow rate or constant pressure gradient. Successful control leads to reduction of drag and pumping power within the former approach, whereas the latter leads to an increase of the mass flow rate and pumping power. In practical applications, however, money and time define the flow control challenge: a compromise between the energy expenditure (money) and the corresponding convenience (flow rate) achieved with that amount of energy has to be reached so as to accomplish a goal which in general depends on the specific application. Based on this idea, we derive two dimensionless parameters which quantify the total energy consumption and the required time (convenience) for transporting a given volume of fluid through a given duct. Performances of existing drag-reduction strategies as well as the influence of wall roughness are re-evaluated within the present framework; how to achieve the (application-dependent) optimum balance between energy consumption and convenience is addressed. It is also shown that these considerations can be extended to external flows.

Use of the isopycnic plots in designing operations of supercritical fluid chromatography: IV. Pressure and density drops along columns

The pressure- and the density-drops along a chromatographic column eluted with supercritical fluid carbon dioxide were mapped as a function of the outlet column pressure and the temperature on the P–T diagram of neat CO2. At low densities, the viscosity of CO2 is low, which is expected to result into a low pressure drop along the column. However, at these low densities, the volumetric flow rates of the mobile phase at constant mass flow rates are high, which might result into a high pressure drop along the column. These conflicting effects of an adjustment in the mobile phase density on the pressure drop of the mobile phase along the column makes it nearly impossible to develop a simple intuitive understanding of the relationships between the net pressure drops and the operating temperatures and pressures. The development of a similar understanding of their relationships with the density drop along the column is even more complex, because this density drop depends also on the compressibility of the mobile phase, itself a function of the operating pressures and temperatures. Numerical calculations of the pressure and density drops along columns packed with particles of different sizes, under different operating conditions (temperature, outlet pressure, and flow rate), provide important insights regarding the extent of the pressure and density drops under these operating conditions.