Mass Flow Distribution Research Articles

CFD simulation of a four-loop PWR at asymmetric operation conditions

The pressurized water reactor (PWR) with multiple loops may have abnormal working conditions with coolant pumps out of running in some loops. In this paper, a computational fluid dynamics (CFD) numerical study of the four-loop VVER-1000 PWR pressure vessel model was presented. Numerical simulations of the thermohydrodynamic characteristics in the pressure vessel were carried out at different inlet conditions with four and three loops running, respectively. At normal stead-state condition (four-loop running), different parameters were obtained for the full fluid domain, including pressure losses across different parts, pressure, velocity and temperature distributions in the reactor pressure vessel (RPV) and mass flow distribution of the coolant at the inlet of reactor core. The obtained results for pressure losses matched with the experimental reference values of the VVER-1000 PWR at Tianwan nuclear power plant (NPP). For most fuel assemblies (FAs), the inlet flow rates presented a symmetrical distribution about the center under full-loop operation conditions, which accorded with the practical distribution. These results indicate that it is now possible to study the dynamic transition process between different asymmetric operation conditions in a multi-loop PWR using the established CFD method.

Conceptual design of a small modular natural circulation lead cooled fast reactor SNCLFR-100

SNCLFR-100, a 100 MWth lead-cooled small modular reactor with a passive cooling feature to both normal and abnormal operations, was proposed by University of Science and Technology of China (USTC). The reactor is well suited as a remote power source because of its compact size, as well as because it has a refueling interval of 10 years without assembly reconfiguration. The reactor is a typical pool-type fast reactor with an array of heterogeneous square fuel assemblies loaded with MOX fuels. In this paper, the overall design and neutronics features were illustrated and evaluated. The steady state thermal-hydraulic performance, mass flow distribution characteristics and sub-channel T/H features were analyzed and discussed. Two major accident scenarios including unprotected overpower transient (UTOP) and unprotected loss of heat sink transient (ULOHS) were selected for a first evaluation of its dynamic behavior. The results show that the safety criteria are satisfied and reactor is tolerant to the UTOP and ULOHS transients. This implies that the conceptual design of SNCLFR-100 is acceptable and the reactor has excellent inherent safety characteristics.

A Steady-State Thermal-Hydraulic Analysis Method for Prismatic High-Temperature Gas-Cooled Reactors

A new methodology for the accurate and efficient determination of steady-state thermal-hydraulic parameters for prismatic high-temperature gas reactors is developed. Whole-core steady-state temperature, pressure, and mass flow distributions are determined for the conceptual MHTGR-350 [Modular High Temperature Gas Reactor] reactor design and also for a range of values of the important parameters. Full-core three-dimensional heat conduction calculations are performed at the individual fuel pin and lattice assembly block levels. A simplified one-dimensional fluid model is developed to predict convective heat removal rates from solid core nodes. Downstream fluid properties are determined by performing a channel energy balance along the axial node length. To establish flow distribution, channel exit pressures are compared, and inlet mass flows are adjusted until a uniform outlet pressure is reached. Bypass gaps between assembly blocks as well as coolant channels are modeled. Finite volume discretization of energy and momentum conservation equations are formulated and explicitly integrated in time. Iterations are performed until all local core temperatures stabilize and global convective heat removal matches heat generation.Whole-core steady-state, thermal-hydraulic results are presented for various axial power and uniform radial power configurations. For all cases, peak temperatures were below expected normal operational limits for TRISO fuels. Bottom-peaked axial power shapes had the highest peak temperatures but the lowest average temperatures. Different reactor designs with increased core inlet temperatures, reduced flow rates, or higher-power-density fuels could however challenge temperature limits. Partial assembly hydrodynamic and temperature results compared favorably with those available in the literature for similar analyses.

Development of thermal-hydraulic analysis methodology for multiple modules of water-cooled breeder blanket in fusion DEMO reactor

According to the conceptual design of the fusion DEMO reactor proposed by the National Fusion Research Institute of Korea, the water-cooled breeding blanket system incorporates a total of 736 blanket modules. The heat flux and neutron wall loading to each blanket module vary along their poloidal direction, and hence, thermal analysis for at least one blanket sector is required to confirm that the temperature limitations of the materials are satisfied in all the blanket modules. The present paper proposes a methodology of thermal analysis for multiple modules of the blanket system using a nuclear reactor thermal-hydraulic analysis code, MARS-KS. In order to overcome the limitations of the code, caused by the restriction on the number of computational nodes, a supervisor program was devised, which handles each blanket module separately at first, and then corrects the flow rate, considering pressure drops that occur in each module. For a feasibility test of the proposed methodology, 46 blankets in a single sector were simulated; the calculation results of the parameters, such as mass flow, pressure drops, and temperature distribution in the multiple blanket modules showed that the multi-module analysis method can be used for efficient thermal-hydraulic analysis of the fusion DEMO reactor.

Mass Flux Distribution Measurements and Visualizations of a Fluid Sheet Generated by a Partially Immersed Dip-Lubricated Gear

A simplified model of gearbox lubrication flow is investigated. A metric gear with module size 4 mm, tooth number 38, tip radius 80.25 mm and width 40 mm, is partially immersed and rotated between 0–12 1/s frequencies in room temperature distilled water. Flash and laser sheet visualizations of the global flow field and the boundary layer are presented. Resolved mass flow distributions in the fluid sheet above the water surface are obtained with in-situ liquid trapping (bucketing). The relation between the circumferential velocity and integrated mass flux of the fluid sheet is found to be linear above a critical speed, for which an analytical formula is given. Using dimensional analysis, we show that the relation between the mass flux and gear speed signifies a Reynolds-number independent behavior of the boundary layer around the immersed part of the gear.

The Characterization of Pulverized-Coal Pneumatic Transport Using an Array of Intrusive Electrostatic Sensors

Fan/impact mills are commonly applied in the grinding and dilute–pneumatic transportation of lignite or brown coals with high moisture contents to the furnaces in large steam boilers. Each of the two to eight mills feeds pulverized coal into two or more burner nozzles. An online detection of the pulverized-coal mass flow distribution among the burners is vital for the control of the combustion process. Knowing the distribution, measures for the redistribution of the coal or, alternatively, for the adjustment of the combustion air flow according to the actual distribution can be employed. Determining the characteristics of a gas–solid two-phase flow using an electrostatic principle is a promising online method of measurement because it is robust and inexpensive. Furthermore, due to their better spatial sensitivity, rod sensors are more suitable for large rectangular ducts related to fan/impact mills than ring-, pin-, or arc-shaped sensors. Sets of 1-D and 2-D electrostatic sensor arrays with a corresponding data acquisition system were employed to determine the mass flow distribution in the cross section of the duct that feeds the pulverized lignite to the four burner nozzles. Various operating regimes for the fan/impact mill were tested. The time series of the signals from the electrostatic sensors were analyzed statistically. It was shown that the skewness, kurtosis, and autocorrelation time delay at the characteristic value can indicate different grinding qualities of the coal.

Design requirements and performance optimization of waste heat recovery systems for rotary kilns

Heat loss from the shell of a rotary kiln accounts for a certain proportion of total energy consumption. In order to reduce heat loss, a practical heat recovery system with nine heat exchangers is proposed to preheat water in this paper. We first propose a mathematic model to analyze the shell temperatures and heat loss rates of several regions on rotary kilns. Integration of theoretical analyses and experimental measurements yields the temperatures and heat transfer rates of heat exchangers, i.e. the design requirements of the nine heat exchangers in the practical system. Secondly, an optimization model is formed to describe the relation between design parameters, i.e. heat transfer area and mass flow rate of each heat exchanger, and system requirements without introducing any intermediate temperatures. With the aid of the Lagrange multiplier method, the optimal design parameters are obtained. Finally, an optimization case of the practical system is studied. The results show that the heat recovery system should meet the requirements of chemical reactions in rotary kilns and mechanical characteristic of shell. The required total heat transfer area of the system after optimization is reduced by 15.6% compared to the value before optimization. As the total mass flow rate increase and inlet temperature decreases, the required heat transfer area decreases while the mass flow distribution ratios remains unchanged.

Numerical Study on Heat Distribution and Transfer Characteristics of a Manifold in a Coal Mine VAM TFRR Oxidation Bed

A thermal flow-reversal reactor is candidate for utilizing low concentration ventilation air methane. In this paper, a numerical study is performed by using the FLUENT software to explore the details of the transient preheating and starting process of the thermal flow-reversal reactor oxidation bed. The bed was heated by hot gas, which was transported and distributed through the holes of manifolds to the middle of the bed. The homogeneous porous media and coupled heat transfer models were chosen; and the mass and heat flow distributions passing through the holes, the heat transfer on the outer surface of the manifold and the temperature distribution of the bed were calculated. The results indicate that the heat of the hot gas passing through the holes decreases gradually along the direction of the hot gas flowing in the manifold, causing the temperature of the bed decrease accordingly. The calculated temperatures of the oxidation bed are compared with the tested results. The maximum error between the calculation and the test was 8.9%.

The Effect of Mass Flow Distribution Inaccuracies in a Hydraulic Network Model for OD Zig-Zag Cooled Power Transformer Windings

In this paper the mass flow distribution in zig-zag cooled power transformer windings is shown to play a crucial factor to accurately predict the winding temperature. In order to enable thermo-hydraulic network models for transformer design, new correlations are derived for combining and dividing T-junctions and elbow configurations. Good correspondence is achieved in comparison with CFD simulation results for a zig-zag cooled power transformer winding.

Numerical Investigation of Mass Flow Distribution in Wavy Microchannel Heat Sink

In order to cope with ever increasing demands from the electronic, automotive and aerospace industries, cooling devices have to be small in size, light-weight and of high performance.The search for a more efficient cooling technology becomes one of the bottle neck problems of the further development of the electronic and automotive industry. Microchannel liquid cooling is one of the candidates for this purpose. The most important parameter in the microchannel is the distribution of the coolant inside the channel. A uniform flow in the microchannel leads to uniform heat transfer.A numerical simulation is carried out to minimize the flow maldistribution inside the microchannel. The microchannel was made as wavy shaped channel. There are six channels with hydraulic diameter of 1mm each. Header is the major part in the microchannel which supplies fluid into different channels. In this work, five different shapes of the header were considered namely circular, frustum conical, rectangular, triangular and trapezoidal. From the simulation results it was found that the mal-distribution is significantly affected by flow rate and shape of the header.

Synthesis and thermoluminescence properties of SrAl 2 O 4 (EU) phosphor irradiated with cobalt-60, 6 MV and 16 MV photon beams

Abstract Powder samples of SrAl 2 O 4 (Eu) were synthesized by the combustion method using urea as a fuel. The combustion products were calcined at 700 °C for 1 h. X-ray diffraction (XRD) patterns of the prepared sample exhibit sharp diffraction peaks and absence of any amorphous phase. The average crystalline size was found to be ~33.04 nm, calculated by using Debye Scherer's formula. The scanning electron microscope (SEM) images reveal that the crystallites have no uniform shape and the presence of several micro- and nano-particles within the grain. This may be due to the non-uniform distribution of temperature and mass flow in the combustion flame which results in the non-uniform shape of crystallites. The thermogravimetric analysis (TGA) indicates that the prepared sample is thermally stable up to 900 °C. Thermoluminescence (TL) behavior of prepared samples was studied after irradiation with Co-60gamma rays, 6 mega voltage (MV) and 16 MV photon beams at various doses. Glow curve of the prepared SrAl 2 O 4 (Eu:1%) sample was similar in shape irrespective of incident energy and radiation type. The dominant peak in each glow curve appeared around at 312 °C. No shifts in peak positions have been observed. All the glow curves of sample doped with Eu(3%) have relatively higher intensity as compared to the sample doped with Eu(1%). Energy dependence has been observed in the present phosphor. This could be because of increase in the probability of Compton's interaction at this energy range due to transmission of primary as well as scattered radiation and decrease in mass attenuation coefficient with the increase in energy. The trapping parameters namely activation energy ( E ), order of kinetics ( b ) and frequency factor ( s ) have been determined using the glow curve shape (Chen's) method. These phosphors could be utilized for display applications, dating, temperature sensor, low as well as high energy radiation detection and dosimetry especially where tissue equivalency is not much desirable like gamma irradiator, environmental and retrospective dose assessment.

Numerical investigation and modeling of two-phase flow sweeping in rod bundles with mixing vane grid spacers

Grid spacers with mixing vanes are used in nuclear fuel assemblies in order to increase the lateral cross-flows between sub-channels that homogenize the temperature distribution within the fuel rod bundle. For the thermal-hydraulic design of such fuel bundles, sub-channel analysis codes are used in order to predict the mass and temperature distribution. These analysis codes compute sub-channel averaged values and contain empirical correlations that account for the effects of microscopic flow phenomena, such as wall friction, turbulent mixing or heat transfer. Experimental investigations show a strong swirling flow in the vicinity of a mixing vane grid spacer. No model was found in literature that accounts for the swirling flow effect on the lateral cross-exchange of mass, momentum or energy. Systematic CFD investigations of the flow in a 5×5 rod bundle containing a single grid spacer with split-type mixing vanes were performed with single-phase and two-phase flow conditions with void fractions ranging between αg=0%and15%. A cubic non-linear k–ε model was used to simulate the typical rod bundle flow effects, such as secondary flow and non-isotropic turbulence. A detailed analysis of the forces and flows in the gap showed that mixing vane induced swirling flow in the sub-channels strongly affects the inter-sub-channel cross-flow. A new model was developed, based on the CFD simulation results, that predicts the flow sweeping between the sub-channels. This model was implemented into the sub-channel analysis code COBRA-FLX™ that was developed and is used by AREVA GmbH. The new model significantly improves the predictions for the cross-flow and mass flow distribution within the rod bundle in the vicinity of the mixing vane grid spacer.

Investigation of spray pattern in shotcrete applications

Impact kinetic energy is well known to play a central and key role on rebound and consolidation mechanisms controlling the shotcrete placement process. While the impact velocity of the traveling particles at their exit of the nozzle has received some attention recently, the mass flow distribution of the sprayed material as it impacts the receiving surface remains unexplored despite its obvious importance on rebound. In this context, a novel apparatus that collects the sprayed material traveling out of the nozzle was developed; material spatial distribution and composition are brought forward. The incident mass flow of material was found to be denser in the central region around the spray axis and decrease toward the peripheral regions following a Gaussian-type function. Additionally, a cement-rich layer formed in the spray’s peripheral zones is also revealed and its origins are discussed. In light of this work, an innovative and unique analytical characterization tool is proposed to further investigate the spraying process and to improve the understanding of shotcrete, and especially material losses through rebound.

Investigation on a three-cold-finger pulse tube cryocooler

This paper introduces a new type of pulse tube cryocooler, three-cold-finger pulse tube cryocooler (TCFPTC), which consists of one linear compressor and three cold fingers, i.e., CFA, CFB and CFC. Those three cold fingers are driven by the linear compressor simultaneously. This paper investigates two aspects. First, it studies the mass flow distribution among the three cold fingers by varying the input electrical power. The cooling powers of the three cold fingers at constant cooling temperatures and the cooling temperatures of the three cold fingers at constant cooling powers with various input electrical powers are investigated. Secondly, the interaction among the three cold fingers is investigated by varying the heating power of any one cold finger. Generally, if the heating power applied on one cold finger increases, with its cold head temperature rising up, the cold head temperatures of the others will decrease. But, when the cooling power of CFC has been 4W, the cold head temperature of whichever cold finger increases, the cold head temperature of CFA or CFB will seldom change if its heating power keeps constant.

Assessment of a hydraulic network model for zig–zag cooled power transformer windings

The prediction of mass flow distribution is a first, though crucial, step in the thermal design of zig–zag cooled power transformer windings. Typically this prediction is based on thermo-hydraulic network models, which critically depend on the applied correlations. In this paper new correlations for flow through elbows and for dividing/merging flow in T-junctions are numerically extracted from dedicated CFD studies and applied to a case study. It is shown that the new correlations are superior for the prediction of the mass flow distribution for this test case in comparison to correlations thus far available in literature.

A method for the simulation and optimization of district heating systems with meshed networks

There are two main methods nowadays for modeling district heating systems, but a key disadvantage of both is that a real network containing loops cannot be described without artificial simplifications in order to eliminate those distinguishing features. However, loops are very common in mature networks that have developed a meshed structure, and make the distribution of mass and heat flows quite characteristic. For this reason, a new process integration method for modeling complex district heating systems containing loops is described in this paper. This method makes it possible to analyze how loops and bottlenecks affect the behavior of the network, as well as the distribution path of the thermal energy in it. The district heating system in the town of Kiruna (located in the north of Sweden) has a complex design with several loops and part of it is used in the paper as an example of application.

Organic Rankine cycle for power recovery of exhaust flue gas

To study the effects of different working fluids on the performance of organic Rankine cycle (ORC), three working fluids, a mixture that matches with heat source, a mixture that matches with heat sink and a pure working fluid, are selected in this paper. Thermodynamic models were built in Matlab together with REFPROP, with which, the physical properties of the selected working fluids can be acquired. Heat source of the ORC system is the exhaust flue gas of boiler in a 240 MW pulverized coal-fired power plant. Some indicators such as thermal efficiency, inlet temperature of expander, superheat degree, mass flow, volumetric flow, and exergy destruction distribution, as well as the influence of recuperator are studied. The analytical results show that the mixture that matches with heat sink has the greatest efficiency and the mixture that matches with heat source has the lowest superheat degree. The rate of heat exchanged in recuperator to that in evaporator has a maximum value with evaporating pressure. There exists no optimal working fluid for all indicators (thermal efficiency, heat exchanger area, mass flow and volumetric flow etc.). An appropriate working fluid should be chosen by taking both investment cost and power generating benefits into account. The cost-benefit ratio of the proposed ORC plant was evaluated either.

Sensitivity of hydrodynamic parameters' distributions in VVER-1000 reactor pressure vessel (RPV) with respect to uncertainty of the local hydraulic resistance coefficients

Abstract The paper presents an uncertainty and sensitivity (U&S) study of the VVER-1000 reactor hydraulic properties. It is based on the OECD/NEA coolant transient Benchmark (K-3) on measured data at Kalinin-3 Nuclear Power Plant (NPP) [1]. The novelty of the work consists of taking into consideration all hydraulic uncertainty parameters used in the modeling of the reactor pressure vessel (RPV) internals. A detailed parallel channel ATHLET model of the RPV is developed. It consists of ca. 26 600 control volumes most of them connected with junctions for cross flows. The specific geometry of the gap between upper part of the baffle and upper part of fuel assembly and also a fuel assembly head is taken explicitly into account The influence of the input parameters on the sensitivity and uncertainty of the RPV outlet and inlet temperatures and mass flows as well assembly-wise mass flow and coolant temperature axial distributions is shown.

Applications of CFD Techniques in the Design of Fabric Filters

Analyzing the gas flow inside a bag filter experimentally is a difficult challenge to overcome, since the complexity of the highly three-dimensional flow hinders any form of directly measuring the flow. In recent years, the increasing availability of computational resources together with the increasing accuracy of numerical methods built up techniques that describe the flow of fluids in industrial equipments through mathematical modelling and numerical simulations. Among these techniques, Computational Fluid Dynamics (CFD) is noteworthy regarding the design of new equipment, since it uses experimental data in their simulations. In this work, the CFD techniques are applied to investigate the best position for feeding the dirty gas in a filter bag, in order to support the search for a more efficient and durable equipment design. To evaluate the filter bag performance, two different inlet positions were simulated. The first, called “conventional”, with gas jet reaching the bags in the centre and the second with concentric triple feed (called “triple”), in which the same gas flow rate is fed by in three regions roughly in the top, center, and bottom of the filter medium. The aim was to determine which design has improved uniformity of mass flow distribution between the bags and lower the equipment pressure drop, in order to increase the filter lifetime. For this purpose, it was used the isothermal and incompressible single phase flow model with turbulence being treated by realizable k-e model. It was concluded that the “triple” showed a better gas distribution to be filtered among the bags system, thus representing a more advantageous layout option when compared to “conventional”.

Non-ideal Stirling engine thermodynamic model suitable for the integration into overall energy systems

The reliability of modelling and simulation of energy systems strongly depends on the prediction accuracy of each system component. This is the case of Stirling engine-based systems, where an accurate modelling of the engine performance is very important to understand the overall system behaviour. In this sense, many Stirling engine analyses with different approaches have been already developed. However, there is a lack of Stirling engine models suitable for the integration into overall system simulations. In this context, this paper aims to develop a rigorous Stirling engine model that could be easily integrated into combined heat and power schemes for the overall techno-economic analysis of these systems. The model developed considers a Stirling engine with adiabatic working spaces, isothermal heat exchangers, dead volumes, and imperfect regeneration. Additionally, it considers mechanical pumping losses due to friction, limited heat transfer and thermal losses on the heat exchangers. The model is suitable for different engine configurations (alpha beta and gamma engines). It was developed using Aspen Custom Modeller® (ACM®) as modelling software. The set of equations were solved using ACM® equation solver for steady-state operation. However, due to the dynamic behaviour of the cycle, a C++ code was integrated to solve iteratively a set of differential equations. This resulted in a cyclic steady-state model that calculates the power output and thermal requirements of the system. The predicted efficiency and power output were compared with the numerical model and the experimental work reported by the NASA Lewis Research Centre for the GPU-3 Stirling engine. This showed average absolute errors around ±4% for the brake power, and ±5% for the brake efficiency at different frequencies. However, the model also showed large errors (±15%) for these calculations at higher frequencies and low pressures. Additional results include the calculation of the cyclic expansion and compression work; the pressure drop and heat flow through the heat exchangers; the conductive, shuttle effect and regenerator thermal losses; the temperature and mass flow distribution along the system; and the power output and efficiency of the engine. These results show that the model allows an extensive study of different parameters of the engine and thus it is suitable for design optimization studies. In addition, it also presents the capability for the integration into overall Stirling engine combined heat and power systems and therefore will allow the performance evaluation of the engine integrated on these systems.