Multiphase flows frequently occur in many important engineering and scientific applications, but modeling of such flows is a rather challenging task due to complex interfacial dynamics between different phases, let alone if the flow is oscillating in the porous media. Using humid air as the working fluid in the thermoacoustic refrigerator is one of the research focus to improve the thermoacoustic performance, but the corresponding effect is the condensation of humid air in the thermal stack. Due to the small sized spacing of thermal stack and the need to explore the detailed condensation process in oscillating flow, a mesoscale numerical approach need to be developed. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, the Shan-Chen model, the nonideal pressure tensor model and the HSD model. In the current study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the incompressible oscillating flow and condensation in parallel plates. In the initial stage of condensation, the oscillating flow benefits to accumulate the saturated vapor at the exit regions, and the velocity vector of saturated vapor clearly showed the flow over the droplets. It was also concluded that if the condensate can be removed out from the parallel plates, the oscillating flow and condensation will continuously feed the cold surface to form more water droplets. The effect of wettability to the condensation was discussed, and it turned out that by increasing the wettability, the saturated water vapor was easier to condense on the cold walls, and the distance between each pair of droplets was also strongly affected by the wettability. It’s expected that this study can be used to optimize and redesign the structure of thermal stack in order to produce more condensed water, also this multiphase approach can be extended to more complicated 3D structures.

The ash deposition on low-temperature heat transfer surface is a key factor that deteriorates the heat transfer performance and leads to corrosion in the low pressure economizer. In the low temperature flue gas, ash deposition is closely related with acid condensation. The sulfuric acid vapor and water vapor contained in the flue gas will condense on heat transfer surface under low flue temperature, which will aggravate ash deposition. In order to evaluate the influence factors of ash deposition on low-temperature heat transfer surface, a laboratory experiment is carried out in this paper. The acid concentration of flue gas, the ash content, the ash component, the flue temperature and the temperature of heat transfer surface are considered to be the most important influence factors on ash deposition characteristics. The viscosity of ash deposition samples on the outer wall of the double-pipe is measured to describe ash deposition characteristics. The fouling factor is calculated. Meanwhile, the scanning electron microscope SEM is used to the analysis of ash samples obtained from the outer wall of the double-pipe. As conclusion, the changing regulation of viscosity of ash deposition on low-temperature heat transfer surface is obtained. (CSPE)

The Claus reactors is widely used to recover elementary sulfur from hydrogen sulfide that is contained in fresh natural gas. It involves thermal oxidation of hydrogen sulfide and its reaction with sulfur dioxide to form sulfur and water vapor. To improve the efficiency of the process, we built two kinds of 3-dimensional Claus reactor models to explore the key factors that affect the combustion reactions. The two-channel Claus reactor consisted of an air channel and an acid gas channel (60% H 2 S, 33% CO 2 , 7%H 2 O) while the three-channel Claus reactor consisted of two air channels and an acid gas channel (60% H 2 S, 33% CO 2 , 7%H 2 O). The two-channel model was built according to the devices used in the factory while the three-channel model was improved by us from the two-channel model. In both the two models, air and acid gas turned into swirling flow in their channels respectively before their mixture. Then air and acid gas mixed and burned at the throat of the models. The most remarkable difference between the two kinds of Claus reactors was that the three-channel reactor had an additional inner air channel inside the acid gas channel that can be helpful to the mix of the acid gas and air. The second difference was that the two kinds of reactors had different deflectors to swirl in the flow fields. In this study, we compared the flow fields and concentration fields of the two kinds of Claus reactors by using a computational fluid dynamics (CFD) tool. The simulation results indicated that the swirling intensity and the mix intensity played an important role in the combustion reactions. The efficiency of sulfur recovery in Claus reactors increased with an increase of the swirling intensity or the mix intensity. The stronger the swirling intensity or the mix intensity was, the sooner the mixture of air and acid gas reached to the best stoichiometric ratio. The three-channel reactor had a better performance than that of the two-channel reactor due to the additional inner air channel which can strengthen the mix of the acid gas and air from the inside of the acid gas. Moreover, the helix deflectors in the three-channel reactor had a better swirling performance than that of the vane deflectors in the two-channel reactor. From the comparison of the two models, we can obtain a way to improve the process of elementary sulfur recovery in the industry, which can be helpful to reduce pollution emissions and improve economic performance.

Photovoltaic utility-scale grid-connected power generation facilities have performance guarantee bases that often include a reference solar spectrum. EPC contractors are obligated to correct tested performance for solar spectrum, as is done for irradiance and cell temperature, to judge whether contractual performance guarantees have been satisfied. Air mass correlated with solar spectral irradiance offers a convenient way of accomplishing this. This paper offers an improvement in the versatility and accuracy of accounting for spectral effects in this manner. The effects on the spectral composition by atmospheric constituents, like aerosols and water vapor, are investigated. Spectral mismatch curves are derived that characterize the responses of the PV modules and the irradiance measurement device to both the estimated test and the reference solar spectra. Comparison of several supplier performance curves and spectral mismatch curves reveals significant discrepancies. An improvement in accuracy is proposed by the use of supplier spectral response data and estimated solar spectral profiles. Correcting for spectral effects has minimal impact at air mass values near the 1.5 reference value, but grows in significance with increasing air mass. Greater precision in accounting for solar spectral effects on PV plant performance is expected as this segment of the power generation industry matures. This paper proposes a methodology that addresses this expectation.

In order to establish a safety evaluation method of a steam generator of sodium-cooled fast reactors, a computer program called SERAPHIM calculating compressible multicomponent multiphase flow with sodium-water chemical reaction under tube failure accident has been developed. In this study, a numerical model for liquid droplet entrainment from an interface of the gaseous jet and its transport was newly constructed to evaluate the environment of the liquid droplet impingement erosion. The applicability of the SERAPHIM program which incorporates the droplet entrainment / transport model was investigated through the analysis of vertical discharging of water vapor in the liquid sodium pool under the actual condition of the steam generator. The analysis reproduced appearance of the underexpanded vapor jet. The calculated peak temperature agreed with the experimental results well. Also, appearance of the dispersed phase of droplets in the reacting jet and its acceleration by the supersonic gaseous flow were represented successfully.

In a sodium-cooled fast reactor (SFR), if a heat transfer tube in the steam generator (SG) is failed, high pressurized water vapor blows into the liquid sodium and sodium-water reaction (SWR) takes place. SWR may cause damage to the surface of the neighboring heat transfer tubes by thermal and chemical effects. Therefore, it is important to clearly understand the SWR for safety assessment of the SG. From recent study, sodium (Na)–sodium hydroxide (NaOH) reaction as secondary surface reaction of the SWR phenomena in a SFR was identified by ab initio method [1]. However, kinetics of this reaction is a still open question. It is important to obtain quantitative rate constant of sodium monoxide (Na 2 O) generation by Na-NaOH reaction because Na 2 O may accelerate the corrosive and erosive effects. Differential thermal analysis (DTA) provides us with the valuable information on the kinetic parameters, including activation energy, pre-exponential factor (frequency factor) and reaction rate constant. Thus, kinetic study of Na–NaOH reaction has been carried out by using DTA technique. The parameters, including melting points of Na and NaOH, phase transition temperature of NaOH, Na-NaOH reaction temperature and the decomposition temperature of sodium hydride (NaH) were identified from DTA curves. Na, NaOH, and Na 2 O as major chemical species were observed from the X-ray diffraction (XRD) analysis of the residues after the DTA experiment. It was inferred that Na 2 O could be generated as a reaction product. Based on the measured reaction temperature, the first-order rate constant of Na 2 O generation was obtained by the application of the laws of chemical kinetics. From the estimated rate constant, it was found that Na 2 O generation should be considered during SWR. The results can be the basis for developing a chemical reaction model used in a multi-dimensional sodium-water reaction code, SERAPHIM, being developed by the Japan Atomic Energy Agency (JAEA) toward the safety assessment of the SG in a SFR.

For Boiling Water Reactors (BWR) and steam generators, the water level is a safety-relevant process variable. The most commonly applied measuring method is based on the calculation of the liquid level from geodetic pressure differences to a reference column of defined height and density. However, transition processes occurring under operational and accident conditions may lead to dynamic changes in the reference level and therefore to fluctuations in the differential pressure signal. This paper presents experiments and numerical simulations on the steady-state and transient behavior of gas/liquid phase boundaries in “Zero Chamber Level Vessels” (ZCLV). In these slightly inclined miniature tubes, the constant reference level is provided by surface tension forces and the capillary effect, respectively. To investigate the basic topology of gas/liquid interfaces under simplified conditions (environmental parameters, no heat transfer), a test facility with optical access was developed. The construction allows for variations of the inner tube diameter, inclination angle and liquid mass flow rate, respectively. By this means, experiments on phase boundaries were carried out for ethanol/air and water/air. The results provide information about the impact of geometry parameters and their interactions on the interface topology. In addition, the dynamic draining of excess liquid mass at the free end of the tube and at artificial weld seams, which is supposed to be the reason for temperature fluctuations observed in ZCLV during power operation of BWR, was experimentally analyzed. The measurements represent the basis for an experimental validation and optimizations of the numerical flow code ANSYS CFX 12.0. In the next step, water/vapor phase boundaries at 286 °C and 70 bar will be investigated by applying x-ray radiography to a scale model. The results will be discussed in context with the hydrostatic level measurement in BWR.

Coal-fired power plants have traditionally operated with stack temperatures in the 300°F range to minimize fouling and corrosion problems due to sulfuric acid condensation and to provide a buoyancy force to assist in the transport of flue gas up the stack. However, as an alternative, there would be benefits to cooling the flue gas to temperatures below the water vapor and acid dew points, while capturing the condensed water vapor. This paper describes experimental results from a DOE and industry-funded project to develop condensing heat exchangers for application to coal-fired power plants. A system of condensing heat exchangers was designed, fabricated and tested using slip streams of boiler flue gas and experiments were performed to measure the effects of process parameters on rates of heat transfer and water vapor condensation. In addition, measurements were made to characterize the acid concentrations in the condensed water which collected on the heat exchanger tubes and to quantify the effects of the heat exchangers on flue gas mercury concentrations.

This work presents the results of canonical test cases that highlight the importance of nucleation bulk surface tension factor (NBTF) on CFD predictions for condensing flows in steam turbines. Numerical simulations are carried out on nozzle and cascade geometries to explore modeling effects on the condensation of water vapor. The recent Euler-Euler approach [10] for modeling homogeneous condensation provides better results than the equilibrium assumption. Modeling of the nucleation rate plays a significant role in the non-equilibrium approach and it depends on the free surface energy of each droplet. NBTF is introduced in the classical homogeneous condensation nucleation rate expression to control the intensity of the homogeneous condensation event [3, 10]. It is observed that the NBTF controls the location of the condensation front, degree of super cooling, wetness fraction and droplet size. In addition, no unique value of NBTF is found in the range of simulations to match the experimental observations. Finally, by increasing the value of NBTF from 0.7 to 1.0 for a particular nozzle case, the location of condensation front is shown to be delayed by 60 mm and super cooling increased by 20%. This in turn will affect quantities such as the flow angle, pressure at the blade row exit and the thermodynamic loss which are relevant for the turbine designer.

Moist air conversion to water and power by a system that uses atmospheric water vapor as its fuel is described. Water vapor is separated from moist air using a vapor separation barrier system. This system has atmospheric pressure on one side of the barrier and the opposite side has a low pressure maintained by the inlet of a vacuum pump/compressor system. The pressure difference across the barrier promotes water-vapor transport through the barrier into the vacuum-pump inlet. Additional compression is necessary to raise the water-vapor pressure and temperature to values appropriate for efficient energy transfer and condensation. The magnitude of compression depends on the ambient water-vapor concentration that varies with location and season. Intercooling between compressors and the magnitude of compression are issues. In this paper the use of a two-compressor system without intercooling is developed and applied to Miami, FL, during the summer. Output power calculations are modeled as an improved Rankine-cycle with reheaters, regenerators, and feedwater heating to improve overall cycle efficiency. The net power output for a water-vapor throughput of 1 kg/s (2.204 lbm/s) is +151.1 kW (+515.5 kBtu/hr) with the water discharged from the system as a liquid. A turbine-based power extraction system is described that uses the warmed cooling fluid flowing from the steam condenser following the main turbine for power production. This system converts approximately 1% of the heat from the condenser into power. System calculations are specific to humid coastal areas, such as Miami, FL.

A method to process moist air into dry air and water results in a surplus of energy for the process. The sun evaporates water everywhere on earth and expends 2.26 MJ/kg (429.9 Btu/lbm) for each kg (2.204 lbm) of water evaporated. A mass of 1 kg (2.204 lbm) of water with a mixing ratio of 0.3% in dry air represents 2.26 MJ (199 Btu) of latent heat energy distributed in a volume of approximately 333 cubic meters (11,759 cubic feet). A system is described by which ambient water vapor is enriched, condensed with the release of latent heat in a heat-exchange boiler, which vaporizes a working fluid used in a Rankine-cycle turbine generator system. Water vapor enrichment is achieved with a vapor-separation barrier. Fans draw moist air through an air-intake system which brings the air into contact with a large surface-area vapor-separation barrier. The intake of a compressor imposes a vacuum on the extraction side of the barrier at a pressure that is lower than the ambient water-vapor pressure. This pressure difference drives water vapor across the barrier into the compressor. A two-stage compressor is used to maintain the low pressure and convey water vapor at high temperature and near atmospheric pressure to a heat-exchange boiler. Two processes occur in the heat-exchange boiler: 1) water vapor condenses and is pumped out of the boiler, and 2) heat is transferred to a working fluid that vaporizes. The vaporized working fluid drives a turbine in a Rankine cycle with condenser. Exhaust heat from the turbine is dissipated with a water-cooled condenser. An air-cooled rock-bed system is suggested as an alternative, when water cooling is not possible. Current advances in materials, the efficiency of turbomachinery, and the effectiveness of heat exchangers suggest that a system can be conceived that is completely fueled by moist air and produces water and excess shaft horsepower that can be converted into electricity. The analysis treats turbomachinery and heat exchangers as ideal components constrained by the Carnot and isentropic efficiencies. Pumps and fans are treated as components with state-of-the-art efficiency. System computations for an ideal 100% efficient system indicate that approximately 25% of the latent heat can be converted to electricity. For a system made with contemporary state-of-the art components a yield of a few percent is predicted. Principles of operation and engineering details are quantified.

How well a condenser is performing is shown to be difficult to determine. The result obtained by using defined measurements in this determination is sometimes biased by shell side conditions that are often not well understood, leading to gross error in calculated condenser performance parameters. This paper describes some of these conditions, identified through recent research findings, and introduces methods to minimize the extent of the error. The discussion addresses how these condenser operating conditions have impact on calculated condenser performance parameters and how they may be properly understood by making use of relatively new measurements or through the application of comprehensive knowledge of the water vapor and noncondensable gas mixture dynamics. Such conditions as measured air in-leakage, and knowledge of no or very low tube fouling based on recent cleaning, are important for the purpose of quantifying the impact of design deficiencies on calculated condenser performance parameters. With proper condenser monitoring, telltale indicators of these deficiencies are clearly observed and will be presented. An investigation program that identifies the amount of performance loss, and the recoverable portion through condenser modifications, is discussed.