Mass Flow Distribution Research Articles

Fluid dynamics of oscillatory flow in three-dimensional branching networks

The present study is aimed at understanding and thoroughly documenting the complex unsteady fluid dynamics in six generations of a model human bronchial tree, comprising 63 straight sections and 31 bifurcation modules, during a complete breathing cycle. The computational task is challenging since the complexity of an elaborate network is augmented with adopted stringent criteria for spatial and temporal accuracy and convergence at each time step (10−8 for each scaled residual). The physical understanding of the fluid dynamics of steady expiratory flow is taken to a similar level of fine details that have been previously established for steady inspiratory flow in earlier publications of the authors. The effects of three-dimensional arrangement of the same branches on the oscillatory flow structure are determined. It is found that the quasisteady assumption is approximately valid in the neighborhood of the peak flow rate, both during inspiration and expiration. Unsteady effects are at their maximum during the changeover from expiration to inspiration and inspiration to expiration. At these time instants, regions of bidirectional flow are observed in all branches with significant secondary motion at various cross sections (none of these features can be predicted by steady state simulations). It is described how the symmetry of the solution with respect to both space and time—found in the oscillating, fully developed flow in a pipe—are destroyed in the unsteady effects that occur in the oscillating flow in a branching network. As the Womersley number is increased, the unsteady effects at all branches increase, and bidirectional flow exists over a greater portion of a cycle. The flow division at a bifurcation module during inspiratory flow generates large asymmetry in the flow field with nonuniform mass flow distribution among the branches of a generation (even in a geometrically symmetric network), whereas flow combination at the same bifurcation module during expiratory flow tends to produce more symmetry in the flow field, displaying essential irreversibility of fluid dynamics.

HYDRODYNAMICS, DISTRIBUTION OF FLOWS AND THERMAL EFFICIENCY OF COIL HEAT EXCHANGERS IN UNITS OF HEAT-USING APPARATUS OF TUBE FURNACES

The theoretical foundations of construction, mathematical description and engineering calculation of heat exchangers of the serpentine type in blocks of heat-using equipment of tube furnaces and other types of reactors designed for carrying out endothermic reactions (in particular, reforming of natural gas with water vapor) are considered. It is shown that the thermal efficiency of heat exchangers of the coil type is significantly affected by the correct choice of parameters ensuring a uniform distribution of energy flows over the surface of heat-resistant heat exchange tubes. This technological problem is solved by compiling the heat balance and selecting the system of the corresponding equations, which allows to calculate the temperature contour of the coil heat exchanger, its hydrodynamic characteristics and the distribution of mass and heat flows through the heat exchange tubes. The use of the tensor form of the Boussinesq hypothesis is considered, with which the Reynolds equation describing a turbulent flow is transformed to a partial differential equation for a single unknown function and its averaged form is obtained. In relation to the problem under consideration, the correctness of the chosen approach was confirmed both theoretically and experimentally. It is shown that in the core of a turbulent flow with an intense suction or injection, the liquid behaves almost as ideal and the well-known Helmholtz – Friedmann theorem holds with the necessary accuracy. From the aforementioned averaged equation, expressions are obtained that are suitable for describing heat fluxes in channels with suction or injection. According to this theoretical model, thermal calculations of coil-type heat exchangers were carried out, a more accurate assessment of the temperature of the heated medium in each coil tube was made, and the temperature gradient of the external heat carrier over the cross section of the gas duct was found. For the first time in the practice of calculations when choosing the parameters of coils, a number of boundary conditions were taken into account, such as the condition of the coil layout, the necessary heat exchange surface, permissible restrictions on hydraulic resistance, etc.

The influence of lateral ejection on the thermal performance of matrix cooling channel

Matrix is applied as an internal cooling scheme for gas turbine blades or vanes. This paper focuses on the Influence of lateral ejection on the cooling performance of matrix channel. The purpose is to improve the internal heat transfer and thermal performance of matrix channel with proper configurations of ejection holes. A validated computational method is used to obtain flow and heat transfer results of a typical matrix channel. The influence of location, dimension and outflow orientation of the ejection holes are discussed in detail. A channel with the absence of straight flow exit is also included for comparison. The result implies that the location of ejection is the most important factor that influences the cooling performance, holes in the downstream part of sidewall turning are better than those in the upstream part. More improvement can be achieved with smaller holes and positive outflow orientation. The blockage of the straight flow exit must be avoided because heat transfer deteriorates due to uneven distribution of coolant mass flow. The effect of reduction of internal coolant mass flow can be compensated by the increased turbulence with well-designed lateral ejection.

Modeling of the Flows of Admixtures in a Random Layered Strip with Probable Arrangement of Inclusions Near the Boundaries of the Body

We study the random flow of admixtures in a two-phase stochastically inhomogeneous strip with the most probable arrangement of inclusions in the vicinity of the surfaces of the body. A mathematical model is formulated for the function of diffusion flow with nonzero constant initial concentration. A random diffusion flow is represented in the form of a Neumann series. The procedure of averaging of the random mass flow over the ensemble of phase configurations with arcsine distribution function is performed. The influence of the characteristics of the medium on the distribution of mass flow is analyzed. It is shown that if the diffusion coefficient of admixtures in the inclusion is higher than for the matrix, then the increase in the characteristic thickness of the layers causes a decrease in the value of the diffusion flow, whereas the mass flow in the entire body increases with the volume fraction of the inclusions.

On-the-field simulation of fertilizer spreading: Part 3 – Control of disk inclination for uniform application on undulating fields

To improve the quality of fertiliser centrifugal spreading, several control devices have already been developed to manage some disruptions occurring on horizontal fields. However, controls which manage disruptions on non-flat fields due to changes in tractor attitude (pitch and roll) have not been developed. In this study, the design of a new control device is developed for a twin-disk spreader by considering two new degrees of freedom for each disk and controlling the longitudinal and lateral tilts of each disk. These tilt corrections are derived from solving a constrained optimization problem. The cost function is the weighted sum of squared differences between the travelled distances of the particles obtained in the considered topography and those that would have been obtained on a horizontal surface. The weighting coefficients are provided by the experimental angular mass flow distribution. In order to reduce the computation time and expect the use of the method for a real-time correction device, a simplified optimization problem is proposed. The method is assessed for three ground surface configurations: longitudinal slope break, side slope break and combined slopes. The simulation demonstrates that using the new control device the application errors are lower than 10% while they reach up to 40% without tilt correction. Moreover the study shows that the problem of optimization uniformity on non-flat fields can be solved computing the travelled distance for only a very few number of particles of mean diameter. This helps in reducing the computational time required to solve the optimization problem and in making possible the development of real-time control devices.

Flow Distribution Characteristics of Supercritical Hydrocarbon Fuel in Parallel Channels with Pyrolysis

Due to the asymmetric geometry of flowpath and combustion organization, the heat flux distribution on RBCC's walls are extremely non-uniform. With a validated numerical model considering the changes of thermophysical properties and chemical components, the present study analyzed the effects of heat flux intensity, non-uniformity of heat flux distribution and inlet manifold on the mass flow distribution of parallel regenerative cooling channels. Results show that the intensity of heat flux enlarges the non-uniformity of parallel channels, however, the non-uniformity is reduced when the outlet temperature is above the completely pyrolysis value; and the non-uniformity heat flux distribution increases the mal-distribution of parallel channels dramatically, the difference of mass flow rate reaches to 33.2% when the heat flux difference is only 0.25 MW/m2; increasing the flow area of inlet manifold would improve the flow distribution of parallel channels with decrease of heat transfer efficiency and increases of pressure drop.

Numerical Investigation on the Influence of Length–Width Ratio of Fire Source on the Smoke Movement and Temperature Distribution in Tunnel Fires

The behaviors hot and toxic smoke in tunnel fires is important to the engineering applications of fire protection systems. The shapes of fire source may affect the characteristics of smoke movement in tunnels. In the current study, a numerical investigation is conducted to explore the effect of fire source shape on the smoke movement and temperature distribution in a full scale road tunnel. The area of fire was fixed with the length–width ratio (n) varying from 1 to 11 and the heat release rate (HRR) of the fire source varying from 5 MW to 15 MW. Results show that with increasing HRR and decreasing n, the impinging flow on the tunnel ceiling transits from buoyancy plume to continuous flame and the smoke becomes more difficultly to be uniform along the longitudinal direction, resulting in further starting position of one-dimensional spread stage (L). Due to the change of entrainment behavior, for a certain HRR, the smoke mass flow rate decreases with decreasing n, which is proportional to the perimeter of the fire source. As n decreases from 11 to 1, the smoke mass flow rate decreases for 23%. Moreover, a correlation of the longitudinal smoke temperature distribution under the tunnel ceiling is developed, with the temperature at the initial position of the one-dimension spread stage as the reference value. This study obtains the variation laws of smoke mass flow and temperature distribution under the effects of fire source shape. It can provide a reference for the smoke control and safe evacuation in straight tunnel without forced flow.

Performance Prediction Based on Effects of Wrapping Angle of a Side Channel Pump

This paper seeks to predict the performance of the side channel pump by considering the influences of different wrapping angles. Firstly, three pump cases 1, 2 and 3 are modeled with wrapping angles 15°, 30° and 45°, respectively. Secondly, different physical parameters comprising exchanged mass flow, pressure and velocity distributions are plotted at the best efficiency point (QBEP) to analyze the internal flow characteristics. Since the flow exchange times depend on the size of the wrapping angle, the size of the wrapping angle has significant effects on the pump head performance. Case 1 with the smallest wrapping angle recorded the largest head improvement at all operating conditions compared to case 2 and case 3. Case 1 at QBEP attained a head coefficient increase of about 9.8% and 38.6% compared to that of case 2 and case 3, respectively. However, the size of the wrapping angle had a slight effect on the pump efficiency; thus, case 1 still predicted a marginal increase in efficiency compared to case 2 and case 3 at all operating conditions. Lastly, the numerical simulations were validated with experimental data after manufacturing pump case 2.

Study on architecture design of electroactive sites on Vanadium Redox Flow Battery (V-RFB)

Numerous researches have been conducted to look for better design of cell architecture of redox flow battery. This effort is to improve the performance of the battery with respect to further improves of mass transport and flow distribution of electroactive electrolytes within the cell. This paper evaluates pressure drop and flow distribution of the electroactive electrolyte in three different electrode configurations of vanadium redox flow battery (V-RFB) cell, namely square-, rhombus- and circular-cell designs. The fluid flow of the above-mentioned three electrode design configurations are evaluated under three different cases i.e. no flow (plain) field, parallel flow field and serpentine flow field using numerically designed three-dimensional model in Computational Fluid Dynamics (CFD) software. The cell exhibits different characteristics under different cases, which the circular cell design shows promising results for test-rig development with low pressure drop and better flow distribution of electroactive electrolytes within the cell. Suggestion for further work is highlighted.

Development of a dynamics model for graphite-moderated channel-type molten salt reactor

A molten salt reactor (MSR) is one of the six advanced reactor concepts selected by the generation IV international forum because of its advantages of inherent safety, and the promising capabilities of Th-U breeding and transuranics transmutation. A dynamics model for the channel-type MSR is developed in this work based on a three-dimensional thermal–hydraulic model (3DTH) and a point reactor model. The 3DTH couples a three-dimensional heat conduction model and a one-dimensional single-phase flow model that can accurately consider the heat conduction between different assemblies. The 3DTH is validated by the RELAP5 code in terms of the temperature and mass flow distribution calculation. A point reactor model considering the drift of delayed neutron precursors is adopted in the dynamics model. To verify the dynamics model, three experiments from the molten salt reactor experiment are simulated. The agreement of the experimental data and simulation results was excellent. With the aid of this model, the unprotected step reactivity addition and unprotected loss of flow of the 2 MWt experimental MSR are modeled, and the reactor power and temperature evolution are analyzed.

Numerical investigation on thermal characteristics and flow distribution of a parallel micro-channel separate heat pipe in data center

This study focuses on the flow distribution and heat transfer characteristics of the evaporation terminal of a micro-channel separate heat pipe (MCSHP) used in data center. A complete CFD model for the parallel tubes with simplified louvered fins of the evaporator structure was established to consider the thermal enhancement while reduce the computing costs. The CFD model was validated by comparing the cooling capacity and outlet temperature of MSCSHP with experiments. The transformation process from bubble flow to slug flow was visualized using VOF model. The simulations reveal that the maximum cooling capacity of the studied MCSHP system could reach 9610 W when the corresponding optimal refrigerant filling ratio is 65.27%. The generation and motion of vapor bubbles influence the height of liquid pool in the evaporation terminal, thus leaded to the change of effective heat transfer area. Moreover, it is found that configurations of inlet and outlet have great impacts on the distribution of mass flow and heat flux under low filling ratios. While under higher filling ratios, the heat flux distribution is not affected by these factors due to the flat tubes filled with two-phase refrigerant.

Heat and mass transfer in confined jet plasma reactor with peripheral vortex flow

A fundamentally new solution for the creation of a peripheral vortex flow is proposed: by the means of rotation of a rotor placed in a reactor. Experimental studies have been performed based on which the distributions of the heat fluxes to the wall of the plasma reactor were obtained by creating a vortex flow by a rotating rotor. It is established that the presence of a vortex flow leads to a significant change in the distribution of heat and mass flow to the reactor wall. The presence of a vortex flow leads to a change in the distribution of the isotherms in the mixing zone of the high-temperature paraxial flow with the gaseous medium of the reactor.

Thermal Analyses of Active-Cooled Strut in RBCC Engine

Fuel-injection strut is an efficient way to increase the depth of fuel penetration and strengthen the mixing process of hot gas in supersonic combustor. With a validated numerical model, this article analyzed the effects of leading edge's radius, wall thickness and mass flow distribution on cooling efficiency of fuel-injection strut and proposed an optimizing strategy for active-cooled strut. Results showed that the larger radius of leading edge not only decreased the heat flux on the leading edge, but also has a negative effect on the aerodynamic performance of strut; and a thinner wall could enhance the cooling efficiency and uniformize the temperature distribution of the wedge; furthermore, the flow distribution of inlet coolant had a significant impact on the heat transfer and flow processes, an optimized way of flow distribution was obtained by comparing three different ways of distribution.

A study of the impact of mixed mode of fuel salt in plenum on steady-state performance of channel-type molten salt reactor

In this study, a coupled neutronics and thermal-hydraulics (THs) code named MOREL2.0, based on multi-group diffusion theory and multi-channel THs model, was employed to analyze a channel-type molten salt reactor TMSR-LF and the impact of different fuel mix mode in plenum on its steady-state performance was also discussed. MOREL2.0 adopts “two-step” calculation scheme, in which few-group homogenized parameters are generated by lattice code PIJ, and diffusion equation considering the drift of delayed neutron precursors is coupled with multi-channel THs model, and the least square method is implemented for cross-section feedback in coupling scheme. The numerical results indicate that TMSR-LF has negative reactivity coefficients in term of inlet fuel temperature and core power level, and the response of keff to mass flow is different for cases of nominal power and zero power, and keff decreases with the rise of time of fuel salt spent in external loop and gradually tends to steady. Different mix mode in plenum have a greater impact on the mass flow distribution and delayed neutron precursors distribution, but less impact on core lumped parameter such as keff and effective delayed neutron fraction.

Numerical investigation of influence of treatment of the coke component on hydrodynamic and catalytic cracking reactions in an industrial riser

A three dimensional gas-solid reactive flow model based on the Eulerian-Eulerian approach was used to simulate the hydrodynamic, heat transfer and catalytic cracking reaction within in a conventional Fluid Catalytic cracking (FCC) riser. A 12-lump kinetic model was used to represent the catalytic cracking reaction network. It was proposed a catalyst deactivation model as a function of the weight percentage of coke amount on the catalyst to replace the deactivation model dependent of the residence time. It was compared the effects of novel treatment for coke component (coke produced in the solid phase) with common treatment (coke produced in the gas phase) on the fluid dynamic and catalytic cracking. The results showed that the treatment for coke component affects radial distribution of coke mass flow. It also showed that the treatment for coke plays an important role in simulation with catalyst deactivation as a function of coke amount on catalyst.

Development of a Coupled Code for Steady-State Analysis of the Graphite-Moderated Channel Type Molten Salt Reactor

The molten salt reactor (MSR) is one of the six advanced reactor concepts selected by Generation IV International Forum (GIF) because of its inherent safety and the promising capabilities of TRU transmutation and Th-U breeding. In this study, a three-dimensional thermal-hydraulic model (3DTH) is developed for evaluating the steady-state performance of the graphite-moderated channel type MSR. The coupled code is developed by exchanging the power distribution, temperature, and fuel density distribution between SCALE and 3DTH. Firstly, the thermal-hydraulic model of the coupled code is validated by RELAP5 code. Then, the mass flow distribution, temperature field, keff, and power density distribution for a conceptual design of the 2MWt experimental molten salt reactor are calculated and analyzed by the coupled code under both normal operating situation and the central fuel assembly partly blocked situation. The simulated results are conductive to facilitate the understanding of the steady behavior of the graphite-moderated channel type MSR.

Modular life cycle assessment of municipal solid waste management

Life cycle assessment (LCA) is commonly applied to examine the environmental performance of waste management systems. The system boundaries are, however, often limited to either one tonne of material or to specific waste treatments and are, therefore, lacking a systems perspective. Here, a framework is proposed to assess complete waste management systems based on actual waste flows, assessed with a detailed material flow analysis (MFA) in a modular MFA/LCA approach. The transformation of the MFA into a product-process-matrix facilitates a direct link between MFA and LCA, therefore allowing for the assessment of variations in flows. To allow for an up-to-date and geographically specific assessment, 190 LCA modules were set up based on primary industrial data and the ecoinvent database. The LCA modules show where there have been improvements in different recycling processes over the past years (e.g. for paper recycling) and highlight that, from an environmental perspective, closed-loop recycling is not always preferable to open-loop recycling. In a case study, the Swiss municipal solid waste management system, of which there is already a detailed MFA, was modeled using the new LCA modules and applying the modular MFA/LCA approach. Five different mass flow distribution scenarios for the Swiss municipal solid waste management system were assessed to show the environmental impact of political measures and to test the sensitivity of the results to key parameters. The results of the case study highlight the importance of the dominant fractions in the overall environmental impacts assessment; while the metal fraction has the highest impact on a per kilogram basis, paper, cardboard, glass and mixed municipal solid waste were found to dominate the environmental impacts of the Swiss waste management system due to their mass. The scenarios also highlight the importance of the energy efficiency of municipal solid waste incineration plants and the credits from material substitution as key variables. In countries with advanced waste management systems such as Switzerland, there is limited improvement potential with further increases in recycling rates. In these cases, the focus of political measures should be laid on (i) the utilization of secondary materials in applications where they replace high-impact primary production, and (ii) an increased recovery of energy in waste-to-energy plants.

Estimation of the solid circulation rate in circulating fluidized bed systems

The results of experiments performed in four different fluidized bed units (two pilot plants and two cold flow models, with a wide range of operating conditions) together with correlations from literature are used to establish methods to estimate the solid circulation rate in a circulating fluidized bed system. The estimation is based on the measured pressure drop in the upper part of the riser as well as particle properties and geometry of the riser exit. Investigations included smooth as well as abrupt riser exit configurations.In case of a smooth riser exit geometry (direct gas solids separation exit), the assumption of a uniformly upflow of solids in the riser is sufficient for the estimation of the solid circulation rate. Further, for an abrupt exit (L-shape exit), two methods were developed. Both methods are based on the assumption that the rate of reflected particles at the top of the riser increases with the so-called exit Froude number. One method is based on a correlation between interstitial gas velocity in the riser, slip velocity, mean particle velocity in the riser, and exit Froude number where it was possible to keep the difference between measured and estimated solid circulation rate in the range of approximately +75% and −40%. Further, this method is not able to consider the local mass flow distribution in the riser. For the other method, the output of a detailed mathematical model, based on information from literature, was used to establish a correlation between, exit Froude number, exit reflecting coefficient and local mass flow to estimate the solid circulation rate. Using this method it was possible to keep the difference between measured and estimated solid circulation rate in the range of ±40%. For both methods, the accuracy of the measurement of the pressure drop in the upper part of the riser is a significant parameter for the prediction of the solid circulation rate.

CFD preliminary assessment of a protrusions based facility

The design of compact heat exchangers and their mass flow distributors is still based on empirical approaches and both numerical analyses and experimentations are needed for designing the best geometries useful to reduce the mass flow rate non uniformities in parallel channels. As known, this is indeed a cause of reduction in both thermal and fluid-dynamic performances.In this paper a series of single-phase CFD simulations on water and water with air injection are carried out in order to estimate the capabilities of the solvers implemented in the OpenFOAM code to reproduce (in comparison with experimental data) such kind of configurations and phenomena. The effects of different turbulence models (both RANS and LES) implemented in OpenFOAM are investigated; additionally some general considerations on the differences and analogies among different Reynolds numbers flow and turbulence model effects applied to the present configuration are discussed. Finally, the capability of the code to reproduce the peculiar behaviour of a protrusions based experimental facility is investigated, with the aim of obtaining an acceptable simulation of the non-uniform mass flow distribution in each protrusion.The present paper is an extended version including the main conclusions and observations emerged in the 2nd AIGE-IIETA International Conference in Genoa.

Numerical and experimental study on the characteristics of 4 K gas-coupled Stirling-type pulse tube cryocooler

A novel gas-coupled Stirling-type pulse tube cryocooler (SPTC), coupling with a colder-stage at the cold head of pre-cooling stage, has been presented, which features extremely compact structure. The gas-coupled characteristics, such as interaction of phase distribution, mass flow distribution and available energy regenerator loss, have been numerical and experimental studied. A negligible phase interaction is found between the two gas-coupled stages, which means the phase of each stage can be optimized individually. The colder-stage regenerator material diameter has a significant effect while its inertance tube size has a weak effect on mass flow distribution. The sphere-type colder-stage regenerator has a different available energy loss mechanism with the mesh-type regenerator of pre-cooling stage. At present, the prototype achieves a no-load temperature of 4.94 K. A cooling power of 12.4 mW/6 K can be achieved with an input power is 270 W and a precooling power of 12.43 W/77 K.