Set Of Inlet Conditions Research Articles

Catalyst optimization in a catalytic flow reversal reactor for lean methane combustion

This paper describes a detailed catalyst configuration study for a catalytic flow reversal reactor for lean methane combustion using computational modelling. The design is based on the use of a platinum group metals catalyst in the form of a washcoated monolith. A small-scale pilot plant reactor is used as the basis for the study. The computational model is based on the fundamental conservation equations of mass and energy that are solved using the finite element method with commercial software. Extensive model validation is performed using experimental data previously obtained on the pilot plant system. It is found that catalyst activity and length of the reaction section play key roles in the stable operation and performance of the system. For methane feed concentrations above about 0.5% by volume, the catalyst activity plays a relatively small role. For concentrations down to about 0.2% both the catalyst activity and reactor length become increasingly important. The complete transient history of the reactor also plays an important role in determining whether or not a stable stationary state can be achieved for a given set of inlet conditions. Computational modelling is shown to be an extremely valuable tool for the design of the reactor system.

Investigation of compressor correction quantities for automotive applications

Turbo performance is represented using maps, measured for one set of inlet conditions. Corrections are then applied to scale the performance to other inlet conditions. A turbo compressor for automotive applications experiences large variations in inlet conditions, and the use of two-stage charging increases these variations. The variations are the motivation for analysing the correction quantities and their validity. A novel surge-avoidance strategy is found in the correction equations, where the result is that a reduction in inlet pressure can increase the surge margin of eight studied maps. The method for investigating the applicability of the strategy is general. An experimental analysis of the applicability of the commonly used correction factors, used when estimating compressor performance for varying inlet conditions, is presented. A set of experimental measurements from an engine test cell and from a gas stand shows a small but clearly measurable trend, with decreasing compressor pressure ratio for decreasing compressor inlet pressure. A method is developed, enabling measurements to be analysed with modified corrections. An adjusted shaft speed correction quantity is proposed, also incorporating the inlet pressure in the shaft speed correction. The resulting decrease in high-altitude engine performance, due to compressor limitations, is quantified and shows a reduction in altitude of 200–600 m, for when engine torque has to be reduced due to limited compressor operation.

Effect of operating and design parameters on the gasification/combustion process of waste biomass in fixed bed downdraft reactors: An experimental study

The main objective of this paper is to study the effect of operating and design parameters, mainly reactor geometry, air superficial velocity, biomass moisture content, particle size and biomass type (pine bark and sewage sludge), on the performance of the gasification/combustion process of waste biomass in fixed bed downdraft reactors. This experimental approach allows optimizing the dynamic behavior of the thermochemical process. Emphasis was put on interactions between the mentioned parameters with output or response variables, such as biomass consumption rate, fuel/air equivalence ratio, producer gas heating value and composition, tars concentration, and flame front velocity. The effect of the operating and design parameters on response variables was studied by means of multifactorial experimental designs. The statistical R2 obtained through the data fitting of the multifactorial experimental designs indicated that the factors taken into account explained between 80.8% and 98.8% of the variability of the response variables. For the particular experiments carried out, the optimal gasification conditions were obtained with the following set of inlet conditions: air superficial velocity of 0.06m/s, biomass particle size between 2 and 6mm, and biomass moisture content of 10.62%. The corresponding response variables were: flame front velocity=11mm/min, fuel air equivalence ratio=3.2, biomass consumption rate=125kg/h/m2, lower heating value of the producer gas=2965.6kJ/Nm3, tar concentration=7.73g/Nm3, and an average composition of the producer gas of 8.0% H2, 13.0% CO, 1.4% CH4, 14.9% CO2, and 62.7% N2.

Internal Condensing Flows inside a Vertical Pipe: Experimental/Computational Investigations of the Effects of Specified and Unspecified (Free) Conditions at Exit

Reported experimental and computational results confirm that both the flow features and heat-transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. The results show that the commonly occurring condensing flows’ special sensitivity to changes in exit conditions (i.e., changes in exit pressure) arises from the ease with which these changes alter the vapor flow field in the interior. When, at a fixed steady mass flow rate, the exit pressure is changed from one steady value to another, the changes required of the interior vapor flow toward achieving a new steady duct flow are such that they do not demand a removal of the new exit pressure imposition back to the original steady value—as is the case for incompressible single phase duct flows with an original and “required” exit pressure. Instead, new steady flows may be achieved through appropriate changes in the vapor/liquid interfacial configurations and associated changes in interfacial mass, heat-transfer rates (both local and overall), and other flow variables. This special feature of these flows has been investigated here for the commonly occurring large heat sink situations, for which the condensing surface temperature (not heat flux) remains approximately the same for any given set of inlet conditions while the exit-condition changes. In this paper’s context of flows of a pure vapor that experience film condensation on the inside walls of a vertical tube, the reported results provide an important quantitative and qualitative understanding and support an exit-condition-based categorization of the flows. Experimental results and selected relevant computational results that are presented here reinforce the fact that there exist multiple steady solutions (with different heat-transfer rates) for multiple steady prescriptions of the exit condition—even though the other boundary conditions do not change. However, for some situations that do not fix any specific value for the exit condition (say, exit pressure) but allow the flow the freedom to choose any exit pressure value within a certain range, experiments confirm the computational results that, given enough time, there typically exists, under normal gravity conditions, a self-selected “natural” steady flow with a natural exit condition. This happens if the vapor flow is seeking (or is attracted to) a specific exit condition and the conditions downstream of the condenser allow the vapor flow a range of exit conditions that includes the specific natural exit condition of choice. However, for some unspecified exit-condition cases involving partial condensation, even if computations predict that a natural exit-condition choice exists, the experimental arrangement employed here does not allow the flow to approach its steady natural exit-condition value. Instead, it only allows oscillatory exit conditions leading to an oscillatory flow. For the reported experiments, these oscillatory pressures are induced and imposed by the instabilities in the system components downstream of the condenser.

Safety implications of an integrated boiling curve model for water-cooled divertor channels

The international fusion community is actively researching advanced heat transfer methods for removal of high thermal loads from next-generation divertor assemblies. Such advanced techniques may indeed optimize the operational and economical performance of future divertor designs. However, with its extensive operational database, water-cooling remains as one of the optimum choices for near-term divertor designs. Critical heat flux (CHF) is the maximum heat flux that water, at a given set of inlet conditions, can remove via fully developed nucleate boiling. Accordingly, an accurate CHF calculation is of the utmost importance for maintaining adequate safety margins in divertor operation. This paper uses the integrated boiling curve model developed at Sandia National Laboratories to examine the safety implications of calculating the CHF. In particular, this paper focuses on the influence of the finite element peaking factor (FEPF) that converts the heat flux predicted by CHF correlations into a plasma heat flux that can be measured. The analyses illustrate that the FEPF is proportional to the plasma heat flux and thus accurate calculation of the CHF requires the use of the appropriate FEPF for the given water conditions and plasma heat flux. It is shown that using a geometric peaking factor is inadequate since the true peak factor is dependent upon the plasma heat flux. The conclusion is that a finite element analysis incorporating an integrated boiling curve is required for accurate calculation of the CHF.

On-site calibration of a phase fraction meter by an inverse technique

The formal calibration procedure of a phase fraction meter is based on registering the outputs resulting from imposed phase fractions at known flow regimes. This can be straightforwardly done in laboratory conditions, but is rarely the case in industrial conditions, and particularly for on-site applications. Thus, there is a clear need for less restrictive calibration methods regarding to the prior knowledge of the complete set of inlet conditions. A new procedure is proposed in this work for the on-site construction of the calibration curve from total flown mass values of the homogeneous dispersed phase. The solution is obtained by minimizing a convenient error functional, assembled with data from redundant tests to handle the intrinsic ill-conditioned nature of the problem. Numerical simulations performed for increasing error levels demonstrate that acceptable calibration curves can be reconstructed, even from total mass measured within a precision of up to 2%. Consequently, the method can readily be applied, especially in on-site calibration problems in which classical procedures fail due to the impossibility of having a strict control of all the input/output parameters.

A model of a frictionless double–diffusive gravity current on a horizontal surface

Abstract A simple model is developed of a double-diffusive gravity current flowing without friction on a horizontal surface. This model captures the effect of the increase in density difference between the gravity current and the environment which is caused by the double-diffusive convection. The double-diffusive flux of buoyancy into the flowing current decreases with time (i.e. with distance from the source) and eventually approaches zero. Steady solutions can then be found which are a function only of distance down-stream from the source. Conservation of momentum shows that entrainment of fluid into the density current is necessary in order to match the imposed condition of a fixed Richardson number at the nose to the arbitrary boundary conditions at the source. When double-diffusive convection and entrainment are both parameterized a priori, the model is overconstrained in the sense that the downstream Richardson number condition at the nose can be satisfied only by a particular set of inlet conditions. This leads us to the conclusion that entrainment and double-diffusive convection must not act independently of each other, but that the presence of the entrainment process must reduce the effectiveness of double-diffusive convection.

Occurrence of Multiple Steady States in the Catalytic Combustion of Propane

Abstract This paper reports experimental results on the existence of multiple steady states in a catalytic combustor for various inlet temperatures (Tin), velocities (Vin), and equivalence ratios (φin). The catalyst was comprised of binary transition metal oxides (CO3O4, Cr2O3) supported on alumina wash-coated ceramic honeycomb substrates. Only oxidation of lean propane-air mixtures (equivalence ratios ⩽0.2) were studied. Multiple steady states were detected only over a narrow range of inlet temperatures (600-670°K). For temperatures outside this range only one steady state exists, while for temperatures in this range at least two steady states, corresponding to heating up and cooling down, exist. In a few cases, when these two steady states were widely separated, one and sometimes two additional steady states (intermediate steady states) were detected. These intermediate steady states, in general, lie close to the heating up or cooling down steady states. For a fixed set of inlet conditions, different st...

The Effect of Irreversibility on the Capacity of a Turbine Blade Row

If the assumption is made that the process followed by the expansion of a gas in a converging blade row is isentropic, thermodynamic analysis leads to the result that the attainment of maximum mass flow, for a given flow area and predetermined inlet pressure and temperature, occurs when sonic velocity is reached at the throat. If, however, as in practice, the expansion proceeds with internal frictional losses, and if certain common assumptions are made regarding these losses, then, assuming adiabatic flow, thermodynamic analysis shows that the maximum flow will occur at a Mach number less than unity. If this paradox is not noticed, it may lead to an appreciable underestimate of the mass flow passed by a blade row for a given set of inlet conditions. This paper examines the relationship between blade row losses and boundary layer characteristics in an attempt to rationalize the calculation of the capacity of a turbine as modified by irreversibility.

The Theory of Pulsating Flow in Conical Nozzles

A knowledge of the dynamic characteristics of nozzles and orifices is important in many control and stability analyses of engineering devices. It is usual to assume that the instantaneous flowrate, for a given set of inlet conditions and outlet pressure, is the same as the nontransient value for the same operating conditions. Recently, in connection with the stability analysis of an externally pressurized thrust bearing, the validity of this assumption was questioned. The analysis presented in this paper was undertaken to provide an answer. The present analysis applies to any fluid, liquid, or gas flowing into a simple conical nozzle. The amplitude and phase of the mass-flux response to a sinusoidally time-varying pressure fluctuation at the nozzle exit are determined. An approximate formula is given for these quantities in terms of the nozzle throat area, the solid angle subtended by the cone, the velocity of the fluid at the nozzle throat, the acoustic velocity at the throat, and the frequency of the pressure fluctuation.