Gas Mass Flow Rate Research Articles

EFFECT OF NON-AXISYMMETRIC INLET PORTS AND OPERATING CONDITIONS ON DROP DYNAMICS OF AN INTERNAL MIXING ATOMIZER

The effect of a non-axisymmetric inlet ports configuration of an internal-mixing twin-fluid atomizer on the spray characteristics is experimentally investigated. Inside the atomizer, two water jets are impinged on each other and are further disrupted by a central gas stream coming from the top. The operating conditions consider the variation of the gas mass flow rate at Reynolds and Weber numbers in the order of 10<sup>4</sup>-10<sup>5</sup>. Phase Doppler anemometry (PDA) measurements at four radial, four axial, and two perpendicular azimuthal positions are combined with a patternator device to obtain droplet size, axial velocity, and mass flux distributions. An approach for evaluating the overall spray asymmetry based on the mass flux distributions is proposed, which enabled the detection of slight asymmetries throughout the azimuthal direction, where especially differences in droplet sizes and velocities measured between the two azimuthal positions are observed. Higher Sauter mean diameters (SMDs) and lower velocities in regions of the spray with higher liquid mass flux are observed when compared to the azimuthal position perpendicular to it. In general, the liquid is considerably faster in the spray center than at the boundaries, where the fluctuating component of the velocity is higher due to the interaction of small droplets with the surrounding air. Overall, an increase in the gas flow rate reduces the droplet sizes and increases the velocity across the spray.

Numerical Investigation of the Initial Charging Process of the Liquid Hydrogen Tank for Vehicles

Liquid hydrogen has been studied for use in vehicles. However, during the charging process, liquid hydrogen is lost as gas. Therefore, it is necessary to estimate and reduce this loss and simulate the charging process. In this study, the initial charging process of a vehicle liquid hydrogen tank under room temperature and atmospheric pressure conditions was numerically investigated. A transient thermal-fluid simulation with a phase-change model was performed to analyze variations in the volume, pressure, mass flow rate, and temperature. The results showed that the process could be divided into three stages. In the first stage, liquid hydrogen was actively vaporized at the inner wall surface of the storage tank. The pressure increased rapidly, and liquid droplets were discharged into the vent pipe during the second stage. In the third stage, the mass flow rates of liquid and hydrogen gas at the outlet showed significant fluctuations, owing to complex momentum generated by the evaporation and charging flow. The temperatures of the inner and outer walls, and insulation layer, decreased significantly slower than that of the gas region because of its high heat capacity and insulation effect. The optimal structure should be further studied because the vortex, stagnation, and non-uniform cooling of the wall occurred near the inlet and outlet pipes.

A Numerical Study of Turbulent Combustion of a Lignocellulosic Gas Mixture in an Updraft Fixed Bed Reactor

Lignocellulosic biomass is an established source of energy with various applications. Yet, its diversity renders the proper combustion of its thermochemical degradation vapors challenging. In this work, the combustion of syngas obtained from biomass thermochemical conversion was numerically investigated to limit pollutant emission. The Computational Fluid Dynamics (CFD) simulation was performed using the open-source OpenFOAM. The reactor was considered in an axisymmetric configuration. The gas mixture resulting from the pyro-gasification devolatilization was composed of seven species: CO, CO2, H2O, N2, O2, light, and heavy hydrocarbon, represented by methane (CH4) and benzene (C6H6), respectively. The evolutions of mass, momentum, energy, and species’ concentrations were tracked. The flow was modeled using the RANS formulation. For the chemistry, reduced kinetic schemes of three and four steps were tested. Moreover, the Eddy Dissipation Concept (EDC) model was used to account for the turbulence–chemistry interaction. The numerical prediction enabled us to describe the temperature and the species. Results show that all transported variables were closely dependent on the mass flow rate of the inflow gas, the primary and the secondary air injections. Finally, from a process perspective, the importance of the secondary air inlet to limit pollutants emissions can be concluded.

Optimal tuning of model predictive controllers for organic Rankine cycle systems recovering waste heat from heavy-duty vehicles

The organic Rankine cycle power system is an emerging technology, which is able to recover the waste heat from the diesel engine of heavy-duty trucks and thus increase the overall engine efficiency. One of the major technical challenges for the integration of the organic Rankine cycle unit on-board trucks are the broad and rapid fluctuations of the available waste heat, caused by the unsteady driving conditions of the truck. Model predictive control has shown to be a powerful tool to ensure safe operation and optimal performance of the organic Rankine cycle unit on-board trucks. This paper presents a novel systematic method for the tuning of model predictive controllers based on a multi-objective optimization routine using a fourth-order reduced linear model. The objectives of the optimization are the settling time due to a step change of the exhaust gas mass flow rate and the cumulative controller effort due to measurement noise. The results suggest that a trade-off exists between the two objectives. Among the controller design parameters, the input rate weight has the largest influence on the controller performance. Interestingly, the simplified optimization procedure based on the reduced-order linear model of the organic Rankine cycle unit can provide key information about the controller performance based on a more complex nonlinear model of the organic Rankine cycle unit when subjected to a realistic waste heat profile. The results indicate that the settling time due to a step change of the exhaust gas mass flow rate is a good indicator of the absolute mean square tracking error over the profile, and it should not exceed 15 s for an absolute mean square tracking error below 2 K. On the other hand, the cumulative controller effort due to measurement noise is strongly correlated to the cumulative controller effort over the profile, and it should stay below 0.5 %/s for a cumulative controller effort over the whole profile below 2 %/s. The presented method is a powerful tool to help the control designer to find the optimal design parameters of model predictive controllers in a systematic way, in contrast to the time-consuming, experience-based trial and error methods.

Power-heat conversion coordinated control of combined-cycle gas turbine with thermal energy storage in district heating network

Thermal energy storage, with its low energy storage cost and wide distribution in industrial processes, is an effective way to improve the operational flexibility of power plants. Due to colossal energy storage capacity and small deployment costs, this article proposes connecting district heating networks to combined cycle gas turbine (CCGT) plants as a thermal energy storage capacity, improving the flexibility of CCGTs. The main focus here is on developing an appropriate control strategy to effectively control the power-heat conversion, meet the heat and power demands of the connected network, and the operational flexibility of the plant. The major problem is that the intrinsic static and dynamic conversion relationship of power and heat in the CCGT and district heating network and the buildings are multi-factor interactive and unknown. Therefore, the CCGT bottom cycle and district heating network, and building models were built to obtain the power-heat conversion parameters and the dynamic model for control design. Then, the energy storage coefficient of 0.105 MW/kg/s is obtained through the model simulation instead of a complex thermodynamic calculation, corresponding to the 113.22 GJ energy storage capacity of the district heating network. Based on the obtained conversion rules, a new control strategy called ‘conversion coordinated control’ is designed and applied, using load signal decomposition and synergistic load response of flue gas mass flow rate and steam extraction valve. The simulation results show that the proposed method can promote a ramping load rate of 8.6 MW/min in the first 30 s with only 0.3 °C building temperature variation. The control strategy can effectively reduce the gap between the grid demand and CCGT power and ensure grid stability without compromising thermal users’ comfort.

Evaluation of fire smoke and heat exhaust performance of shafts by natural venting in tunnels

Theoretical analysis and numerical simulations are performed to study the smoke and heat exhaust performance of natural venting system with different shaft forms. Based on the mass conservation for the gas flow in the shaft, equations for estimating the total gas mass flow rate are derived. The methods for determining the smoke and heat exhaust efficiencies are also proposed. A numerical model is built for series of CFD simulations considering different shaft forms (length–width ratio of shaft vent and shape). The results clearly present the details of the natural venting process by displaying the temperature and velocity fields. The boundary layer separation and plug-holing phenomena are also observed. The effects of the shaft shapes on the smoke and heat exhaust efficiencies have been discussed quantitatively. It is highlighted that when the cross-sectional area of shaft is constant, a smaller length–width ratio of the shaft vent leads to higher smoke and heat exhaust efficiencies. Moreover, the smoke and heat exhaust efficiencies of cylindrical shafts are higher than those of cubic ones. The findings of this paper could provide some principles for the design of natural ventilation shaft in urban tunnels. For example, the length–width ratio of shaft vent less than 1:3 is recommended for the design of natural venting system in tunnels.

Flow measurement based on the combination of swirler and differential pressure under slug flow

The alternating appearance of elongated bubbles and liquid slugs of slug flow in the pipe causes severe pressure fluctuation. As a result, measuring the flow rate of the slug flow with the throttling unit based differential pressure method is difficult. This paper investigates a new swirler-based flow measurement method in slug flow. The swirler converts the slug flow into a swirling annular flow, and the differential pressure method is used to measure the flow rate. The influences of gas and liquid flow rates on the differential pressure ΔPX across the swirler as well as its downstream axial differential pressure ΔPZ are investigated. ΔPX0.5 increases linearly as the liquid mass flow rate increases, and the slope of the curve increases as the gas mass flow rate increases. The influence of gas mass flow rate on ΔPX0.5 is comparable to that of liquid mass flow rate on ΔPX0.5. ΔPZ0.5 increases linearly with increasing gas/liquid mass flow rate, and the slope of the curve of ΔPZ0.5 with ml differs slightly from the slope of the curve in single-phase water conditions. Based on the research presented above, new empirical correlations of mass flow rate based on ΔPX and ΔPZ are established respectively. The superficial liquid velocity ranges from 0.6 to 2 m per second, while the superficial gas velocity ranges from 2 to 6 m per second. If the gas mass flow rate and ΔPX are known, the relative error of liquid mass flow is less than 3%. The relative error of the gas mass flow rate is less than 10% if the liquid mass flow rate and ΔPX are given. The calculation accuracy of the flow measurement model using ΔPX is better than the calculation accuracy of the flow measurement model using ΔPZ.

A new correlation to determine the Lockhart-Martinelli parameter from vertical differential pressure for horizontal venturi tube over-reading correction

Venturi tubes are widely used to measure the gas flow rate in a wet-gas stream. To calculate the gas flow rate, wet-gas Venturi tubes require the liquid loading (i.e. Lockhart-Martinelli parameter) to be known as an input to a so-called over-reading correction correlation. It is challenging to derive the Lockhart-Martinelli parameter without installing additional devices in series to the Venturi tube thus adding significant cost and complexity. A relatively low cost and easy to implement method is to derive the Lockhart-Martinelli parameter by measuring the pressure drop across the Venturi tube or along a pipe section. A correlation that predicts the Lockhart-Martinelli parameter by measuring the pressure drop along a vertical pipe section downstream of the Venturi tube is presented. The correlation was obtained by fitting experimental results from TUV-SUD National Engineering Laboratory's wet-gas test facility with nitrogen-water in a 4″ vertical pipe, Lockhart-Martinelli from 0.04 to 0.29, and gas Froude number from 1 to 2.7. Further experiments were conducted at Spirax Sarco Engineering plc to evaluate the performance of the proposed correlation under steam-water conditions. Tests were conducted with steam-water in a vertical 2″ pipe, Lockhart-Martinelli from 0.005 to 0.064, and gas Froude number from 0.55 to 1.35. The Lockhart-Martinelli parameter is predicted within ±0.035 absolute value with the proposed new correlation for both the National Engineering Laboratory and Spirax Sarco datasets. Gas flow rate values within approximately ±5% error are obtained with the proposed correlation together with ISO/TR 11583 over-reading correlation for the NEL dataset. Although further improvements to the proposed method are required, this work demonstrates the efficacy of an agile, simple, and low-cost differential pressure method to aid the Venturi meter to determine the gas mass flow rate in wet-gas flow.

Analysis of the flow through the blowhole of twin-screw machines with different rotor profiles using dimensionless numbers

To ensure safe operation, gaps in a screw machine are essential. Some are relatively easy to adjust, like front and housing gaps, while it is more difficult, if they depend directly on the selected rotor profile shape, such as the inter-lobe clearance and the blowhole. Consideration of mass flow rates through those clearances is crucial to predict operation conditions or design screw machines. When using chamber model simulations, it is common to calculate idealized, theoretical mass flow rates and to combine them with a flow coefficient which represents the effect of e.g. friction losses. This paper deals with the flow coefficient of the blowhole, which is formed by the two rotors and the housing cusp. Therefore, a set of dimensionless numbers is used, including physical and geometrical influences on the flow coefficient. The real mass flow rate of an ideal gas (e.g. air) through the blowhole is calculated by CFD-simulations. The dimensionless numbers are systematically varied to identify their specific influences on the gained mass flow rates.

Calculation of Nuclear Reactor Cooling Tower Performance With Limited Data Streams

AbstractMonitoring of cooling tower performance in a nuclear reactor facility is necessary to ensure safe operation; however, instrumentation for measuring performance characteristics can be difficult to install and may malfunction or break down over long duration experiments. This paper describes employing a thermodynamic approach to quantify cooling tower performance, the Merkel model, which requires only five parameters, namely, inlet water temperature, outlet water temperature, liquid mass flowrate, gas mass flowrate, and wet bulb temperature. Using this model, a general method to determine cooling tower operation for a nuclear reactor was developed in situations when neither the outlet water temperature nor gas mass flowrate are available, the former being a critical piece of information to bound the Merkel integral. Furthermore, when multiple cooling tower cells are used in parallel (as would be in the case of large-scale cooling operations), only the average outlet temperature of the cooling system is used as feedback for fan speed control, increasing the difficulty of obtaining the outlet water temperature for each cell. To address these shortcomings, this paper describes a method to obtain individual cell outlet water temperatures for mechanical forced-air cooling towers via parametric analysis and optimization. In this method, the outlet water temperature for an individual cooling tower cell is acquired as a function of the liquid-to-gas ratio (L/G). Leveraging the tight tolerance on the average outlet water temperature, an error function is generated to describe the deviation of the parameterized L/G to the highly controlled average outlet temperature. The method was able to determine the gas flowrate at rated conditions to be within 3.9% from that obtained from the manufacturer’s specification, while the average error for the four individual cooling cell outlet water temperatures were 1.6 °C, −0.5 °C, −1.0 °C, and 0.3 °C.

Development and optimization on separated structure steam generator based on a new thermal design model

• A new thermal design model with the micro-element superposition was proposed. • The effect of operation on the thermal performance of the SS-SG was discussed. • The optimization design has been conducted using a hybrid intelligent algorithm. • The total cost can be greatly reduced with precise structural design for the SS-SG. Adopting the traditional LMTD method to design the SS-SG (Separated Structure Steam Generator) usually leads to a larger deviation due to drastically change in physical properties of flue gas with changing temperature. This makes the consumption of steel tubes and power energy during both the manufacturing and operation processes increase. As an exploratory investigation, a novel thermal design model was developed with the idea of micro-element superposition and validated against the experiment herein. It revealed that the maximum absolute deviation between prediction and experiment was less than 2.5%, which outperformed a lot compared to the traditional method. As an application case, this model was used to design an actual steam generator in this study. The design results showed that the steel tube consumption can be reduced by 27.19%, while the power energy consumption can be saved by 11.45% for long-term operation. Using the proposed model, the effect of operating conditions on thermal performance of the steam generator was discussed. It indicated that the increase in the inlet temperature and mass flow rate of flue gas, as well as the operating pressure, generally weakens the comprehensive thermal performance indexes PE A and PE B . Besides, this novel model can also be combined with an intelligent algorithm to perform structure optimization. For this case, compared to the original structure, the total cost can be further decreased by 17.57% with the obtained optimal structure from an economic point of view. It is of great significance to improve the economics of recovering flue gas waste heat.

An Experimental and Modeling Study on the Effect of Wall Opening Location on the Under-Ventilated Compartment Fire

An experimental and modeling study was carried out to investigate the effect of wall opening location on the mass flow rates of gases through the opening and the associated fire phenomena, such as compartment temperature, projected flame height through the opening, and the heat release rates inside and outside the compartment. A 0.3 m by 0.3 m opening was placed at three different elevations—bottom, middle, and top—of a narrow end wall of a 0.8 m by 1.2 m by 0.8 m (H) compartment. A propane gas burner was used to provide four different fire sizes in the compartment: 90, 110, 130, and 150 kW. The existing correlations for mass flow rates and heat release rates generally do not include the wall opening location as a variable and are functions of only the opening area and height. Based on the experimental and modeling analysis, it is found that the wall opening location affects the internal and external fire phenomena. Two fundamental factors, K and O, are introduced to explain the effect quantitatively. Factor K is the ratio of the air inflow predicted by Fire Dynamics Simulator (FDS) to the existing correlation (0.5AoHo), and Factor O is the ratio of the oxygen consumption rate in the compartment to the oxygen flow rate into the compartment, indicating combustion efficiency. Factor K ranges from 0.78 to 0.94, and O ranges from 0.67 to 0.85 for different opening locations, which suggests that the existing correlations may overestimate the amount of airflow to and the combustion efficiency within the compartment.

Thermoeconomic analysis of a waste heat recovery system with fluctuating flue gas scenario

The performance and economy of a waste heat recovery system featuring a fin tube heat exchanger (FTHE) and an organic Rankine cycle system with a fluctuating flue gas were investigated. The output power of this system increased with the temperature and mass flow rate of the flue gas (m˙f), which had positive and negative effects, respectively, on the effectiveness (εFT) of the FTHE. Furthermore, εFT increased with the evaporation temperature (Teva). The system performance and economy can be increased and decreased, respectively, through an increase in Teva, especially for as the m˙f less than the design conditions. A method in which the flow rate of the working fluid is restricted through adjustment of the rotation speed of the expander is proposed to reduce the heat absorbed by the evaporator when the evaporation temperature increases. At a low evaporation heat transfer rate, when the rotation speed of the expander decreased from 1350 to 900 rpm, the evaporation pressure increased from 1.36 to 1.77 MPa, and system efficiency and output power increased by 1.0% and 204.7 W, respectively. Finally, results of the experiment confirmed that increasing evaporation pressure can increase system performance under low heat transfer rate.

Energy Recovery from Exhaust Gas of Diesel and Petrol Engine by Turbo-electric Generator

A turbo-electric generator has been placed on the exhaust port of the petrol and diesel engines to investigate the possibility of recovering energy from the exhaust gas. Turbo-electric generator is a combination of a turbocharger and a generator. The aim of the study is to find the possibility and effectiveness of the turbo-electric generator for recovering the energy from the exhaust gas of an engine. The test has been conducted on the two engines, i.e. first one is TD 202 small test engine bed (diesel engine) and another one is Honda CG125 cc (petrol engine) motorcycle. Two types of motor i.e. DC motor and AC motor have been used as generators by altering the way a motor works. Firstly, a DC motor is used as a generator in the turbo-electric generator for both test engines. The results show that turbo-electric generator recover less than 1% energy of the exhaust gas for both engines when a DC motor is used as a generator (TD 202 and Honda CG125 cc motorcycle). But in case of Honda CG125 cc motorcycle, the percentage of recovering energy is comparatively higher than the TD 202 test engine. The experiment is further extended by using an AC motor as a generator only for the Honda CG125 cc motorcycle. The results show better energy recovering from exhaust gas through turbo-electric generator, which is more than 1% of exhaust gas. The results reveal that the engine speed and the mass flow rate of the exhaust gas play a major role in harvesting the energy from the exhaust gas. Moreover, it is found that the turbo-electric generator module provides good efficiency when an AC motor is used as a generator in the module. The experimental results have been compared with available literature.

Simulation and validation of the gas flow in close-coupled gas atomisation process: Influence of the inlet gas pressure and the throat width of the supersonic gas nozzle

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29∙Lo, 0.5∙Lo, 0.77∙Lo and 2∙Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

Assessment of an Exhaust Thermoelectric Generator Incorporating Thermal Control Applied to a Heavy Duty Vehicle

The road transport industry faces the need to develop its fleet for lower energy consumption, pollutants and CO2 emissions. Waste heat recovery systems with Thermoelectric Generators (TEGs) can directly convert the exhaust heat into electric energy, aiding the electrical needs of the vehicle, thus reducing its dependency on fuel energy. The present work assesses the optimisation and evaluation of a temperature-controlled thermoelectric generator (TCTG) concept to be used in a commercial heavy-duty vehicle (HDV). The system consists of a heat exchanger with wavy fins (WFs) embedded in an aluminium matrix along with vapour chambers (VCs), machined directly into the matrix, that grant the thermal control based on the spreading of local excess heat by phase change, as proposed by the authors in previous publications and patents. The TCTG concept behaviour was analysed under realistic driving conditions. An HDV with a 16 L Diesel engine was simulated in AVL Cruise to obtain the exhaust gas temperature and mass flow rate for each point of two cycle runs. A model proposed in previous publications was adapted to the new fin geometry and vapour chamber configuration and used the AVL Cruise data as input. It was possible to predict the thermal and thermoelectric performance of the TCTG along the corresponding driving cycles. The developed system proved to have a good capacity for applications with highly variable thermal loads since it was able to uncouple the maximisation of heat absorption from the regulation of the thermal level at the hot face of the TEG modules, avoiding both thermal dilution and overheating. This was achieved by the controlled phase change temperature of the heat spreader, that would ensure the spreading of the excess heat from overheated to underheated areas of the generator instead of wasting excess heat. A maximum average electrical production of 2.4 kW was predicted, which resulted in fuel savings of about 2% and CO2 emissions reduction of around 37 g/km.

Experimental and numerical investigation of change in boil-off gas and thermodynamic characteristics according to filling ratio in a C-type cryogenic liquid fuel tank

This paper covers the experimental and numerical investigation of the changes in boil-off gas and thermodynamic characteristics due to filling ratio (FR) in a cryogenic liquid fuel tank. An experiment on a vertically oriented C-type fuel tank with an insulation system was carried out using LN2 to allow validation of the simulation results. The data for temperature inside the tank and mass flow rate of boil-off gas were acquired with respect to the different FRs. It was observed that the amount of BOG tends to increase in the form of a quadratic function based on the trend line, as FR increases. The simulation seemed to well express the complex physical phenomenon associated with heat transfer, heat flow, and vaporization occurring in the entire system of the tank. Especially the flow visualization of the simulated physical quantities helped to understand physical phenomena more easily, such as a mechanism of BOG caused by vaporization, which are not easy to approach in experiments. On the other hand, the BOR according to the FR showed a very slight difference of less than 3% on average compared to the experiment, which made it possible to confirm the validity of the multi-physics simulation technique.

A novel negative carbon-emission, cooling, and power generation system based on combined LNG regasification and waste heat recovery: Energy, exergy, economic, environmental (4E) evaluations

In this paper, a novel negative carbon-emission, cooling, and power generation (NCCP) system was proposed to improve the energy efficiency of the liquid natural gas (LNG)-powered hydrogen production plant. With LNG cold energy and waste heat recovery, the NCCP system integrated organic Rankine cycle (ORC) power generation, data center cooling, and CO2 capture. The NCCP system could operate under seven scenarios and the system performance evaluations were performed via energy, exergy, economic and environmental (4 E) analysis. It was found that the NCCP system showed the best performance when all subsystems were running simultaneously. The system could produce 31.67 MW of power, 24.92 MW of cooling capacity, and 29.97 t/h of CO2 capture. The levelized energy cost and the payback period of the NCCP system were 0.071 $/kWh and 7.9 years, respectively. LNG cold energy utilization efficiency, system energy efficiency, and exergy efficiency were 43.20%, 19.08%, and 29.28%, respectively. The environmental profits are validated with the negative carbon index of 29.47 t/h. Moreover, the effects of the LNG pressure, flue gas mass flow rate, and the temperature of the medium temperature shift gas on the NCCP system performances were investigated. The results show that the proposed system is a polygeneration system with the advantages of high efficiency, diversified energy output, fast return on investment, and CO2 capture. It is expected to be an energy conversion technology that could be used for reference in practical applications.

Investigations on Spray Characteristics and Self-Pulsation of a Gas-Centered Shear Coaxial Injector

The spray characteristics of a gas-centered shear coaxial injector under different conditions and recess ratios (RR) were studied through experiments and numerical simulations. The numerical study was carried out based on the coupled level set and volume-of-fluid (CLSVOF) method and the adaptive mesh refinement (AMR) method. The results indicated that without recess, the spray angle first stayed almost constant and then dropped linearly with an increase in the gas mass flow rate (m˙g) when holding the liquid mass flow rate (m˙l) constant. In contrast, with recess, the spray angle was found to increase with m˙g, which could be attributed to the secondary expansion of the central gas flow. Under specific conditions, self-pulsation occurred and was accompanied by a loud scream. The frequency of the self-pulsation increased with both m˙g and m˙l. Moreover, the self-pulsation frequency decreased with RR. Meanwhile, the mechanism of self-pulsation was initially explored through numerical simulation. It was concluded that self-pulsation was caused by the surface tension and the pressure difference between the inside and outside of the liquid sheet, together with the central airflow impact extrusion.

Topological and hydrodynamic analyses of solar thermochemical reactors for aerodynamic-aided window protection

ABSTRACT Particles and condensing vapors contribute to the contamination of optical components of solar thermochemical reactors including windows and secondary concentrators and result in severe reactor performance deterioration. We propose an impinging-jet solar reactor in a distinctive topology to enhance aerodynamic-aided window protection. The vector fields on the two-dimensional inner surfaces of the impinging-jet reactor and four conventional reactors are analyzed for the first time using differential topology. The topological analysis demonstrates that the application of an impinging jet in the reactor leads to the prevention of the stagnation point in the vicinity of the window, which is inevitable in any axisymmetric flow field of the conventional reactors. The transient two-dimensional flow fields of all reactors are numerically investigated using the finite volume method to understand the effects of the reactor geometry, aspect ratio, and sweep gas mass flow rate on the window protection performance characterized by the contaminant residence time and peak volumetric concentration near the window. The impinging-jet reactors with aspect ratios of one and two are found to be the most effective designs in aerodynamic-aided window protection among all investigated configurations.