Moist Air Flow Research Articles

Numerical Study of Water Production from Compressible Moist-Air Flow

In this research a numerical study of water production from compressible moist-air flow by condensing of the vapor component of the atmospheric air through a converging-diverging nozzle is performed. The atmospheric air can be sucked by a vacuum compressor. The geographical conditions represent a hot and humid region, for example Bandar Abbas, Iran, with coordinates, 270 11 ’ N and 560 16’ E and summer climate conditions of about 40℃and relative humidity above 80%. Parametric studies are performed for the atmospheric-air temperature between, 40℃ to 50℃, and relative humidity between49.6% to 100.%. For these ranges of operating conditions and a nozzle with the area ratio of 1.17, the liquid mass flow rates falls in the range 0.272 to 0.376 kg/s. The results show that, the energy consumed by the compressor for production 1 kg of water will be 1.279 kWh. The price of 1 kWh is 372 Rials, therefore the price for the production of 1 kg liquid water will be 475.8 Rials, therefore, the scheme is economically suitable.

Modeling moisture condensation in humid air flow in the course of cooling and heat recovery

This article, written as a result of theoretical and practical research, describes a survey of condensate nucleation in heat exchangers utilizing low-potential heat of humid air. The authors conducted a series of studies aimed at developing energy-independent technical solutions to protect heat exchangers from the freezing of the moisture condensing on their exchange surfaces in the course of humid air heat recovery. There was a negative dependence of the thickness of the layer of condensate formed on the heat exchange surface, the condensation rate, and the moisture content of warm air. The article presents the outcomes of the numerical study aimed at building a model of the condensation processes that occur due to a flow of moist air when the air is cooled and heat is utilized. The study provided experimental validation for the consistency of the processes related to water vapor condensation in the flow of cooled moist air. The outcomes presented in the article can apply to both the exchange systems using the low potential heat of the atmospheric air, e.g., for room heating or snow melting, and to the exhaust air energy recovery systems of the building ventilation plant.

Evolution of instability before and during a torrential rainstorm in North China

NCEP-NCAR reanalysis data were used to analyze the characteristics and evolution mechanism of convective and symmetric instability before and during a heavy rainfall event that occurred in Beijing on 21 July 2012. Approximately twelve hours before the rainstorm, the atmosphere was mainly dominated by convective instability in the lower level of 900–800 hPa. The strong southwesterly low-level jet conveyed the moist and warm airflow continuously to the area of torrential rain, maintaining and enhancing the unstable energy. When the precipitation occurred, unstable energy was released and the convective instability weakened. Meanwhile, due to the baroclinicity enhancement in the atmosphere, the symmetric instability strengthened, maintaining and promoting the subsequent torrential rain. Deriving the convective instability tendency equation demonstrated that the barotropic component of potential divergence and the advection term played a major role in enhancing the convective instability before the rainstorm. Analysis of the tendency equation of moist potential vorticity showed that the coupled term of vertical vorticity and the baroclinic component of potential divergence was the primary factor influencing the development of symmetric instability during the precipitation. Comparing the effects of these factors on convective instability and symmetric instability showed some correlation.

Numerical study of non-equilibrium condensation and shock waves in transonic moist-air and steam flows

Transonic condensing/evaporating moist-air flow through converging-diverging nozzles is investigated numerically using non-equilibrium thermodynamic model. In this study, the results of moist-air and pure steam flows through nozzles are compared, in other words, carrier gas effects are investigated numerically. It is observed that, under similar operating conditions for steam, the wetness fraction and droplet nucleation rate along the nozzle in the case of moist-air flow is more than pure steam case. That is due to the internal flow of heat from steam portion towards the air that enhances the wetness fraction and droplet nucleation rate in moist-air case. In this study, the influence of the normal aerodynamic shocks is also studied. It is interestingly observed that, although the entropy of the mixture (steam+air) and steam portion increases along the shock, the entropy of the air portion can be reduced in response to evaporation of the liquid phase. Validation of the results is performed versus the experimental data for pure steam and moist-air flows, which show relatively good agreements.

Effect of non-equilibrium condensation on lift divergence Mach number at transonic speeds

In the present paper, the effects of non-equilibrium condensation on the lift divergence Mach number with the angle of attack in a transonic 2-D moist air flow of NACA0012 are investigated using a numerical analysis with a total variation diminishing scheme. In the case of T0 = 298 K and α = 3°, the lift divergence Mach number Mld decreases with increasing Ф0 up to 40%, whereas beyond Ф0 = 40%, the lift divergence Mach number is nearly constant at Mld = 0.75. On the other hand, for the case of α = 6°, Mld increases with increasing Ф0 up to 47%, and then Mld begins to decrease with an increase in Ф0. Because of the attenuating effect of non-equilibrium condensation on the shock stall, for the case of α = 3°, CL generally decreases with an increase in Ф0, whereas for M∞ = 0.85, which is appreciably larger than the lift divergence Mach number, CL increases with an increase in Ф0. In the case of M∞ = 0.85, regardless of Ф0, it is shown that the location of the maximum Mach number at the upper wall side is nearly constant at x/c = 0.4. It is found that the Mach number for the minimum CL decreases with an increase in Ф0.

Characteristics of transonic moist air flows around butterfly valves with spontaneous condensation

Effects of spontaneous condensation of moist air on the shock wave dynamics around butterfly valves in transonic flows are investigated by experimental and numerical simulations. Two symmetric valve disk shapes namely- a flat rectangular plate and a mid-plane cross-section of a prototype butterfly valve have been studied in the present research. Results showed that in case with spontaneous condensation, the root mean square of pressure oscillation (induced by shock dynamics) is reduced significantly with those without condensation for both shapes of the valves. Moreover, local aerodynamic moments were reduced in case with condensation which is considered to be beneficial in torque requirement in case of on/off applications of valves as flow control devices. However, total pressure loss was increased with spontaneous condensation in both the valves. Furthermore, the disk shape of a prototype butterfly valve showed better aerodynamic performances compared to flat rectangular plate profile in respect of total pressure loss and vortex shedding frequency in the wake region.

Experimental and numerical studies on self-excited periodic oscillation of vapor condensation in a sonic nozzle

The unsteady nozzle flow induced by vapor condensation has many different self-excited periodic oscillation modes and affects flow field and mass flow-rate of sonic nozzle. A detailed discussion of thermal choking and oscillation frequencies of this unsteady flow was carried out. To investigate these different oscillation modes, an experimental sensor for measuring inlet humidity/temperature, and monitoring pressure oscillation was built. A numerical model for condensation process in sonic nozzle was established and validated by experimental data of moist nitrogen reported by Wyslouzil and Lamanna. The output of measurement sensor for nozzle flow of moist air agreed with the results of this numerical model. At last, four different oscillation modes caused by vapor condensation were explored. The rules of frequencies and amplitudes of pressure signals for these oscillation modes were discussed in detail. All results can promote the study on the effect of vapor condensation on accurate metering of sonic nozzle.

Self-Assembly of Conjugated Polymers Into Ring Structures by Breath Figures

A simple method to fabricate rings of conjugated polymers is presented based on the breath figure technique. In humid atmosphere, the rapid evaporation of solvent induces the cooling of the solution surface of conjugated polymers. Water droplets condense onto the solution surface and undergo coalescence to form larger ones. After the solvent and water droplets evaporate completely, isolated rings are formed. Our results show that it is a general method to produce ring structure in different conjugated polymer systems. The influences of solvent properties, solution concentrations, etc. on the pattern formation are investigated. Compared with the conventional honeycomb structure obtained by breath figures, the key to the formation of ring structure is discussed. Furthermore, ring structure can be tuned from circular to elliptic by applying moist air flow with controlled direction onto the surface of the polymer solution. This approach offers a complimentary way to pattern conjugated polymers in a simple, cost-effective, and one-step matter.

Extraordinary heat during the 1930s US Dust Bowl and associated large-scale conditions

Unusually hot summer conditions occurred during the 1930s over the central United States and undoubtedly contributed to the severity of the Dust Bowl drought. We investigate local and large-scale conditions in association with the extraordinary heat and drought events, making use of novel datasets of observed climate extremes and climate reanalysis covering the past century. We show that the unprecedented summer heat during the Dust Bowl years was likely exacerbated by land-surface feedbacks associated with springtime precipitation deficits. The reanalysis results indicate that these deficits were associated with the coincidence of anomalously warm North Atlantic and Northeast Pacific surface waters and a shift in atmospheric pressure patterns leading to reduced flow of moist air into the central US. Thus, the combination of springtime ocean temperatures and atmospheric flow anomalies, leading to reduced precipitation, also holds potential for enhanced predictability of summer heat events. The results suggest that hot drought, more severe than experienced during the most recent 2011 and 2012 heat waves, is to be expected when ocean temperature anomalies like those observed in the 1930s occur in a world that has seen significant mean warming.

Quasi One-Dimensional Model of Natural Draft Wet-Cooling Tower Flow, Heat and Mass Transfer

The article deals with the development of CFD (Computational Fluid Dynamics) model of natural draft wet-cooling tower flow, heat and mass transfer. The moist air flow is described by the system of conservation laws along with additional equations. Moist air is assumed to be homogeneous mixture of dry air and water vapour. Liquid phase in the fill zone is described by the system of ordinary differential equations. Boundary value problem for the system of conservation laws is discretized in space using Kurganov-Tadmor central scheme and in time using strong stability preserving Runge-Kutta scheme. Initial value problems in the fill zone is solved by using standard fourth order Runge-Kutta scheme. The interaction between liquid water and moist air is done by source terms in governing equations.

A CASE STUDY OF USING ENHANCED INTERCONNECT CHANNEL GEOMETRIES ON HEAT AND MASS TRANSFER CHARACTERISTICS OF ANODE-SUPPORTED PLANAR SOFC

The role of enhanced heat transfer inside interconnect channels for improved convective cooling and thermal management of planar solid oxide fuel cells (SOFCs) is investigated. A case study of two different geometries (sinusoidal wavy or corrugated walls and offset-and- interrupted walls) is presented for a uniform electrochemical reaction rate with constant flow of moist hydrogen and air. The coupled heat and mass transfer is modeled by three-dimensional, steady-state equations for mass, momentum, energy, species transfer, and electrochemical kinetics, in which the porous-layer flow is in thermal equilibrium with the solid matrix and is coupled with the electrochemical reaction rate. The heat and mass transfer rates through the interconnect ducts as well as the electrodes on both the anode and cathode sides are computationally obtained. The temperature field and species mass distributions, along with variations in the friction factor and heat transfer coefficients describe the performance of the two flow-channel geometries. The relative thermal and hydrodynamic behavior is compared with that in plain rectangular-duct interconnects to evaluate their convective-cooling performance. The results demonstrate that the offset interrupted-wall geometry yields better cooling of the SOFC module.

Dominant Large-Scale Atmospheric Circulation Systems for the Extreme Precipitation over the Western Sichuan Basin in Summer 2013

The western Sichuan Basin (WSB) is a rainstorm center influenced by complicated factors such as topography and circulation. Based on multivariable empirical orthogonal function technique for extreme precipitation processes (EPP) in WSB in 2013, this study reveals the dominant circulation patterns. Results indicate that the leading modes are characterized by “Saddle” and “Sandwich” structures, respectively. In one mode, a TC from the South China Sea (SCS) converts into the inverted trough and steers warm moist airflow northward into the WSB. At the same time, WPSH extends westward over the Yangtze River and conveys a southeasterly warm humid flow. In the other case, WPSH is pushed westward by TC in the Western Pacific and then merges with an anomalous anticyclone over SCS. The anomalous anticyclone and WPSH form a conjunction belt and convey the warm moist southwesterly airflow to meet with the cold flow over the WSB. The configurations of WPSH and TC in the tropic and the blocking and trough in the midhigh latitudes play important roles during the EPPs over the WSB. The persistence of EPPs depends on the long-lived large-scale circulation configuration steady over the suitable positions.

Impact Assessment of Orography on the Extreme Precipitation Event of July 2010 over Pakistan: A Numerical Study

The topography influences monsoon precipitation and gives rise to significant rainfall events in South Asia. The physical mechanism involved in such events includes mechanical uplifting, thermodynamics, small scale cloud processes, and large scale atmospheric circulations. The investigation into orographic precipitation is pursued by synoptic and model analysis. Deep convection occurs as warm moist airflow is channeling over steep mountains. WRF model coupled with Morrison double moment scheme is used to assess the relative impact of topography on extreme rainfall event of 26–30 July 2010 in Pakistan. Two sensitivity tests with full topography (CTL) and reduced topography by 50% (LOW) are carried out. Two distinct precipitation zones over Hindukush and Himalaya mountains are identified. The topographic changes significantly affect moisture divergence and spatial and temporal distribution of precipitation. A low level jet is created on windward side of big mountains, yielding enhanced moisture flux and instability. Eddy kinetic energy significantly changes with orographic height. Energy flux created further unstabilized atmosphere and deep convection, producing wide spread heavy rainfall in the area in Himalaya foothills. Under the set synoptic conditions, orographic orientation enhanced the moisture accumulation and deep convection, resulting in occurrence of this extreme event.

Large-Scale Atmospheric and Oceanic Conditions for Extensive and Persistent Icing Events in China

AbstractBased on the observational datasets of rime and glaze from 743 stations in China and the atmospheric circulation data from the NCEP–NCAR reanalysis during 1954–2009, large-scale atmospheric and oceanic conditions for extensive and persistent rime and glaze events were examined with a composite analysis. Results show that rime events mostly occur in northern China while glaze events are mainly observed in southern China. The icing events are accompanied by low temperature and high humidity but not necessarily by above-normal precipitation. The Asian low, blocking highs, strong moisture transport, and an inversion layer related to major abnormal circulation systems contribute to the occurrence and persistence of icing events in China. The Ural blocking high plays a major role in the glaze events, and the Okhotsk blocking high is closely related to the rime events. For glaze events, extratropical circulation anomalies and the southward outbreak of cold air play a dominant role. In contrast, the strong northward transport of warm and moist airflows plays a leading role and the blocking high and the southward outbreak of extratropical cold air take a supporting role for rime events. There is nearly an equal chance for occurrences of rime events under La Niña and El Niño backgrounds. However, glaze events more likely occur under the background of La Niña. Additionally, the sea surface temperatures from the tropical Indian Ocean to the tropical northwestern Pacific Ocean also contribute to the occurrence and maintenance of icing events in China.

Long-term erosion rate measurements in gypsum caves of Sorbas (SE Spain) by the Micro-Erosion Meter method

The present work deals with the results of long-term micro-erosion measurements in the most important gypsum cave of Spain, the Cueva del Agua (Sorbas, Almeria, SE Spain). Nineteen MEM stations were positioned in 1992 in a wide range of morphological and environmental settings (gypsum floors and walls, carbonate speleothems, dry conduits and vadose passages) inside and outside the cave, on gypsum and carbonate bedrocks and exposed to variable degree of humidity, different air flow and hydrodynamic conditions. Four different sets of stations have been investigated: (1) the main cave entrance (Las Viñicas spring); (2) the main river passage; (3) the abandoned Laboratory tunnel; and (4) the external gypsum surface. Data over a period of about 18years are available. The average lowering rates vary from 0.014 to 0.016mmyr−1 near the main entrance and in the Laboratory tunnel, to 0.022mm−1 on gypsum floors and 0.028mmyr−1 on carbonate flowstones. The denudation data from the external gypsum stations are quite regular with a rate of 0.170mmyr−1. The observations allowed the collecting of important information concerning the feeding of the karst aquifer not only by infiltrating rainwater, but under present climate conditions also by water condensation of moist air flow. This contribution to the overall karst processes in the Cueva del Agua basin represents over 20% of the total chemical dissolution of the karst area and more than 50% of the speleogenetically removed gypsum in the cave system, thus representing all but a secondary role in speleogenesis. Condensation–corrosion is most active along the medium walls, being slower at the roof and almost absent close to the floor. This creates typical corrosion morphologies such as cupola, while gypsum flowers develop where evaporation dominates. This approach also shows quantitatively the morphological implications of condensation–corrosion processes in gypsum karst systems in arid zones, responsible for an average surface lowering of 0.047mmyr−1, while mechanical erosion produces a lowering of 0.123mmyr−1.

Analysis of a Destructive Wind Storm on 16 November 2008 in Brisbane, Australia

AbstractDuring the late afternoon on 16 November 2008 the Brisbane (Queensland, Australia) suburb of “The Gap” experienced extensive wind damage caused by an intense local thunderstorm. The CP2 research radar nearby detected near-surface radial velocities exceeding 43 m s−1 above The Gap while hail size reports did not exceed golf ball size, and no tornadoes were reported. The storm environment was characterized by a layer of very moist near-surface air and strong storm-relative low-level flow, whereas the storm-relative winds aloft were weak. While the thermodynamic storm environment contained a range of downdraft-promoting ingredients such as a ~4-km-high melting level above a ~2-km-deep layer with nearly dry-adiabatic lapse rates mostly collocated with dry ambient air, a ~1-km-deep stable layer near the ground would generally lower expectations of destructive surface winds based on the downburst mechanism. Once observed reflectivities exceed 70 dBZ, downdraft cooling due to hail melting and downdraft acceleration based on hail loading are found to likely become nonnegligible forcing mechanisms. The event featured the close proximity of a hydrostatically and dynamically driven mesohigh at the base of the downdraft to a dynamically driven mesolow associated with a low-level circulation. This proximity was instrumental in the anisotropic horizontal acceleration of the near-ground outflow and the ultimate strength of the Gap storm surface winds. Weak storm-relative midlevel winds are speculated to have allowed the downdraft to descend close to the low-level circulation, which set up this strong horizontal perturbation pressure gradient.

Thermodynamic characteristics and responses to ENSO of dominant intraseasonal modes in the East Asian summer monsoon

The moisture supply and El Niño Southern Oscillation (ENSO) characteristics are investigated for different intraseasonal modes of the East Asian summer monsoon (EASM) identified as the Meiyu–Baiu, Changma, post-Changma, and dry-spell modes. The investigation is conducted with a type of artificial neural network known as self-organizing map analysis. The major modes tend to be dominated by the moisture convergence of the moisture budget equation along the rain-band. The Meiyu–Baiu mode is strongly linked to both the anomalous low-level convergence and vertical wind shear, which is related to baroclinic instability with warm air rising and cold air sinking. The Changma mode has a strengthened tropic–subtropics connection along the western north Pacific subtropical high, which induces vertical destabilization and strong convective instability by the low-level warm advection of moisture-laden air and upper-level cold advection of dry air. In late summer, the post-Changma and dry-spell modes are characterized by anomalous southeasterly flow of warm and moist air from western north Pacific monsoon, and low-level easterly flow, respectively. In response to the preceding El Niño, the Meiyu–Baiu and Changma modes occur more frequently, while the post-Changma and dry-spell modes show the opposite. The response to the La Niña exhibits a relatively weak connection, indicating asymmetric response on the preceding ENSO. This prominent difference in response to the ENSO leads to different behaviors of the Indian Ocean and western Pacific thermal state, and consequently, the distinct moisture supply and instability variations for the EASM intraseasonal modes.

Characterising the relationship between weather extremes in Europe and synoptic circulation features

Abstract. Extreme weather events in Europe are closely linked to anomalies of the atmospheric circulation and in particular to circulation features like cyclones and atmospheric blocking. In this study, this linkage is systematically characterised with the help of conditional cyclone and blocking frequencies during precipitation, wind gust and temperature extremes at various locations in Europe. Such conditional frequency fields can serve as a dynamical fingerprint of the extreme events and yield insights into their most important physical driving mechanisms. Precipitation extremes over the ocean and over flat terrain are shown to be closely related to cyclones in the vicinity and the associated dynamical lifting. For extreme precipitation over complex terrain, cyclone anomalies are found at more remote locations, favouring the flow of moist air towards the topography. Wind gust extremes are associated with cyclone and blocking anomalies in opposite directions, with the cyclones occurring mostly over the North and Baltic seas for extreme events in central Europe. This setting is associated with pronounced surface pressure gradients and thus high near-surface wind velocities. Hot temperature extremes in northern and central Europe typically occur in the vicinity of a blocking anticyclone, where subsidence and radiative forcing are strong. Over southern Europe, blocking anomalies are shifted more to the north or northeast, indicating a more important role of warm air advection. Large-scale flow conditions for cold extremes are similar at many locations in Europe, with blocking anomalies over the North Atlantic and northern Europe and cyclone anomalies southeast of the cold extreme, both contributing to the advection of cold air masses. This characterisation of synoptic-scale forcing mechanisms can be helpful for better understanding and anticipating weather extremes and their long-term changes.

Overview of the problem of moist air flow in turbo-expanders

The article contains results the analysis of the effect of humidity on the work of the turbo expander

Influence of microphysical schemes on atmospheric water in the Weather Research and Forecasting model

Abstract. This study examines how different microphysical parameterization schemes influence orographically induced precipitation and the distributions of hydrometeors and water vapour for midlatitude summer conditions in the Weather Research and Forecasting (WRF) model. A high-resolution two-dimensional idealized simulation is used to assess the differences between the schemes in which a moist air flow is interacting with a bell-shaped 2 km high mountain. Periodic lateral boundary conditions are chosen to recirculate atmospheric water in the domain. It is found that the 13 selected microphysical schemes conserve the water in the model domain. The gain or loss of water is less than 0.81% over a simulation time interval of 61 days. The differences of the microphysical schemes in terms of the distributions of water vapour, hydrometeors and accumulated precipitation are presented and discussed. The Kessler scheme, the only scheme without ice-phase processes, shows final values of cloud liquid water 14 times greater than the other schemes. The differences among the other schemes are not as extreme, but still they differ up to 79% in water vapour, up to 10 times in hydrometeors and up to 64% in accumulated precipitation at the end of the simulation. The microphysical schemes also differ in the surface evaporation rate. The WRF single-moment 3-class scheme has the highest surface evaporation rate compensated by the highest precipitation rate. The different distributions of hydrometeors and water vapour of the microphysical schemes induce differences up to 49 W m−2 in the downwelling shortwave radiation and up to 33 W m−2 in the downwelling longwave radiation.