Moist Air Stream Research Articles

EFFECTS OF BINARY MIXTURE CONDENSATION ON TURBULENT MIXED CONVECTION HEAT AND MASS TRANSFER IN A VERTICAL CHANNEL

A numerical analysis was carried out to study the detailed heat and mass transfer processes between a condensation liquid film and mixed turbulent moist airflow. Results show that the condensation latent heat transfer is more important for a system with higher inlet relative humidity or lower inlet Reynolds number of a moist airstream. The heat and mass transfer coefficients are higher for a system with higher inlet relative humidity and inlet Reynolds number of moist air. In addition, the aiding-buoyancy forces cause diminution in heat and mass transfer results compared with the corresponding results of forced convection.

Degradation of Octachlorodibenzofuran and Octachlorodibenzo-p-dioxin Spiked on Fly Ash: Kinetics and Mechanism

Octachlorodibenzofuran (OCDF) degradation kinetics in a moist nitrogen stream and those of octachlorodibenzo-p-dioxin (OCDD) in a dry or moist airstream on pretreated fly ash were studied in a laboratory pilot plant with temperature ranging from 200 to 350 °C and reaction times varying from 15 to 240 min. The mathematical treatment of experimental data indicated that two reaction pathways, decomposition and dechlorination, operated independently because of a partition of the reagents in the fly ash according to a physical and a chemical adsorption. The decomposition reaction was of the first order with respect to the reactant adsorbed physically. The dechlorination reaction involved first-order series reactions. Here, the kinetic scheme for the first two dechlorination steps is discussed. Kinetic constants and partition constants at different temperatures as well as Arrhenius and Eyring parameters and the isosteric enthalpy of adsorption are calculated.

Analysis of heat and mass transfer in a countercurrent-flow wet surface heat exchanger

A numerical analysis was carried out to study the detailed heat- and mass-transfer characteristics in a countercurrent-flow wet surface heat exchanger. The coupled conservation equations for hot fluid, liquid film and moist air stream are solved together. The heat-transfer rates in the wet surface heat exchanger are compared with those obtainable in the dry surface heat exchanger. Furthermore great attention is paid to investigating the effects of latent heat transfer associated with liquid-film vaporization on the thermal performance of the exchanger. Results show that the energy transported across the liquid film is mostly absorbed by the process of film vaporization.

Role of O2–, OH–and anion vacancies in the degradation of Y-TZP in moist environments

X-Ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) have been used to study the changes in surface chemistry and crystallography of yttria–tetragonal zirconia polycrystal during exposure to either a moist air stream (200 °C) or an autoclave environment (120 or 170 °C). XPS measurements indicate that there is a significant increase in the O2– and %Zr3+ levels during the transformation of the surface tetragonal phase to the monoclinic phase. No significant levels of zirconium hydroxide species were detected during exposure to moist air or autoclave treatment. Yttrium hydroxide was detected only after severe autoclave treatment at 170 °C. A model is proposed whereby destabilisation of the tetragonal phase is caused by annealing of anion vacancies by O2–.

A Numerical Investigation of the Natural Convection Heat and Mass Transfer From Uniformly Heated Falling Films in Vertical Channels

In the design of solar collector/regenerators for use in open-cycle absorption refrigeration (OCAR), the problem of predicting evaporation rates and solution temperatures is of paramount importance in determining overall cycle performance. This transport of heat and mass is dominated by natural convection with buoyant forces primarily generated as a result of film heating by the solar flux, but aided by the evaporation of water (the lighter species) into the rising moist air stream. In order to better understand the mechanism of these combined buoyant interactions, the governing equations for natural convection flow in a vertical channel bounded by a heated falling film (simulating a glazed collector/regenerator) were solved using several different finite difference techniques. Under the assumptions appropriate to solar collector/regenerator falling films, the gas-side problem may be uncoupled from the falling film side, with the interfacial conditions treated as unknown boundary conditions for the gas-side flow which are iteratively determined from the film mass and energy balances. The numerical results were validated against existing experimental and numerical results for simplified boundary conditions. The appropriate nondimensionalization for the falling film boundary condition was established, ostensibly for the first time, and a parametric study for an air-water vapor mixture was conducted. Curve fits to the numerical results were determined for engineering design applications.

La dynamique des situations météorologiques des 21-22 et 26-27 septembre 1992 dans le sud du couloir rhodanien / The dynamics of the meteorological patterns of 21-22 and 26-27 September 1992 in the southern Rhône corridor

Diluvian rains related to the meteorological patterns of 21 and 22, 26 and 27 September 1992, were the result of the rapid eastward motion of two, early and strong MPHs having a direct meridional path over the Atlantic Ocean. Their power allowed them to move in the form of an airmass over the Iberian relief towards the western Mediterranean, and then to force a strong southerly, warm and moist airstream towards the southern part of France, where highlands amplified the stormy nature of disturbances. The month of September 1992, was characterized by a large number of MPHs with strong meridional paths. These dramatic events are connected with a climatic change governed by a cooling trend over the Arctic Ocean area.

Two-dimensional fin efficiency with combined heat and mass transfer between water-wetted fin surface and moving moist airstream

A two-dimensional model has been developed to analyze the fin performance with combined heat and mass transfer in cooling and dehumidifying processes. The effect of the variations in moist air temperature and humidity on fin performance has been taken into account. The present results vary significantly, especially at low relative humidities, from those of the existing one-dimensional model. This may prove that the assumption of a lumped parameter to model the mass transfer effect is perhaps oversimplified. By means of this model, the fin temperature distribution, fin efficiency, and the properties of air in contact with the fin surface are predicted. The two-dimensional results show that the streamwise variations in moist air properties have a substantial effect on the fin performance and the trend is to further reduce fin efficiency. A nonuniform transverse distribution of outlet air properties is predicted. In other words, the air path line on the psychrometric chart along the fin base is not the same as the along the fin tip, while a simple straight air path line was assumed in the development of conventional one-dimensional fin model. It is also shown that, for a given inlet air dry bulb temperature, partial condensation occurred on the fin surface at low relative humidities, and a totally dry fin surface is formed at certain low relative humidities.

The Recovery of Selenious Acid Aerosols on Glass Fiber Filters

Previous workers have shown that selenium is only partially trapped on a filter during air sampling. In some cases, these losses have been attributed to volatilization of selenium dioxide. Our results demonstrate that selenium dioxide, in the presence of moist air, is completely recovered (apparently as selenious acid aerosols) and that the previous shortfalls must be due to other selenium species as yet unidentified. Selenious acid aerosols in our study were formed by volatilizing selenium dioxide (approximately 3 mg) into a stream of moist ambient air (relative humidity, greater than 50%), and trapped on glass fiber filters using a high-volume air sampler. Selenium(IV) was ultrasonically extracted from the filter with water and analyzed by atomic absorption spectrometry. Selenious acid aerosols were trapped on the filters with high efficiency (105 +/- 5 percent) using a 50 minute sampling period. With an extended sampling period (24 hours) the recovery was 103 +/- 6 percent.

A Numerical Investigation of East Coast Cyclogenesis during the Cold-Air Damming Event of 27–28 February 1982. Part I: Dynamic and Thermodynamic Structure

A cyclogenesis event combined with strong cold-air damming, coastal frontogenesis, and extensive mixed precipitation, which occurred on February 27-28, 1982 at the South Carolina coast is investigated numerically. The prestorm environment and subsequent cyclogenesis was simulated using a nested version of the Penn State/NCAR mesoscale model with 35-km fine-mesh resolution. The model was found to successfully reproduce most principal synoptic and mesoscale features associated with this cyclogenesis case, including the storm path and intensification, the coastal front structure, cold-air damming, circulations induced by a polar jet streak, low-level jets, and precipitation. The results of this study reveal the existence of two moist airstreams fed by an onshore flow from the marine boundary layer east of the coastal front.

Adsorption of water vapor and microporous structures of carbonaceous adsorbents Communication 10. The effect of preliminary preparation conditions and the modification of activated charcoals on their adsorption properties

1. Preliminary desorption under vacuum of activated charcoals at an elevated temperature affects their adsorption capacity for water vapor. The greater the loss of adsorbent sample mass as a result of heating, the more significantly the water-vapor adsorption isotherms change. 2. In the adsorption of water vapor by activated charcoals heated at 673 K, chemisorption of water molecules proceeds simultaneously with physical adsorption. The greater the extent of rehydration of the activated charcoals, the greater the extent to which their capacity for adsorbing water vapor is regenerated. The results obtained indicate that chemisorbed water serves as primary adsorption sites in the physical adsorption of water vapor. 3. Demineralization of the activated charcoals leads to an increase in the total number of primary adsorption sites, basically by increasing the number of labile surface oxygen-containing groups (in particular, chemisorbed water) that are removed from the surface of the activated charcoal even upon moderate heating. 4. Oxidation of the activated charcoals in a stream of moist air at 623 K increases the concentration of relatively thermally stable adsorption sites, the numbers of which correlate with the number of acid surface groups neutralized by Na2CO2, by reducing the number of unstable oxygen-containing groups while leaving practically unchanged the number of primary adsorption sites.

Spontaneous ignition of sodium in dry and moist air streams

The spontaneous ignition behavior of liquid sodium was studied experimentally, using the stagnation region of impinging air streams of various humidity, and a unique technique which kept the sodium from reacting until it was heated to a predetermined temperature. It was found that the spontaneous ignition temperature increased with increasing humidity of the air stream, and also that ignition occurred in two distinct stages of surface reaction, and finally a gas phase reaction. The first stage of the surface reaction, which was affected by humidity, was controlled by the rate of the surface reaction, while the second stage was controlled by the oxygen diffusion rate through the boundary layer formed over the sample surface. The ignition mechanism is discussed, and the effect of moisture on the ignition temperature is explained in terms of the formation of “protective” NaOH in the reaction film produced on the sample surface during the ignition process.

Klinokinetic and klinotactic humidity reactions of the beetles Hylobius abietis and Tenebrio molitor

ABSTRACT. The effects of spatially uniform but temporally changing air humidity stimuli on the orientation behaviour of the large pine weevil (Hylobius abietis L.) and the flour beetle (Tenebrio molitor L.) were studied in a specially constructed vertical air flow chamber. Moist‐acclimatized but hygronegative pine weevils were exposed for 10 s to a moist air stream (c. 85% R.H.) and then for 10 s to a dry air stream (c. 50% R.H.). The Tenebrio were divided into two groups acclimatized to moist and dry air respectively. For each group the humidity during the initial 5 s in the air stream was the same as during acclimatization, and then changed to the alternative level. In Hylobius the change from moist to dry air caused a decrease in spatial displacement brought about by a decrease in walking speed and an increase in the amount of turning per unit time. In Tenebrio the change from dry to moist air caused a decrease of walking speed and a turning‐back reaction based, presumptively, on idiothetic information about the insect's previous walking direction. The average angle turned during 2 s after the humidity change was 165°. In moist‐adapted beetles the dry air stream caused an identical orthokinetic arrestment, but no klinokinetic or klinotactic reaction. Klinokinesis is redefined as a change in the circular variance of turning angles per unit time, which does not change the mean direction (or directions in cases of multimodal distributions) of the circular distribution. Accordingly, klinotaxis consists of a change in the mean directions) of the circular distribution of angular velocities. In both species the turning frequency was more constant than turning per unit distance, suggesting a temporal control in the nervous system of klinokinetic and klinotactic behaviour.

On the two-dimensional, hydrostatic flow of a stream of moist air over a mountain ridge

Abstract The small perturbation of a steady, two-dimensional horizontal stream of a moist inviscid, Boussinesq fluid is treated analytically by use of an asymptotic method when a certain parameter ∊ is small and numerically by use of an iterative method for general values of ∊. This parameter is a measure of the difference between dry and wet adiabats in the model atmosphere, which is absolutely stable and which contains a moist layer near the ground. Vapour condenses (evaporates) where the vertical displacement of a fluid particle exceeds the ascent condensation level and the vertical motion is upward (downward). The condensation of vapour and release of latent heat are nonlinear phenomena which are treated, but otherwise the equations of motion and boundary conditions are linearized. We limit our attention to an airflow of uniform properties over a mountain ridge. The hydrostatic approximation is made. As a result, the horizontal wavelengths must be long compared to the vertical ones and lee waves are a...

The determination of fluorine in rocks and minerals by a pyrohydrolytic method

A rapid pyrohydrolytic method, with simple apparatus, is described for the determination of fluorine in rocks and minerals. The sample is heated with a three-component flux in a stream of moist air, and the liberated hydrogen fluoride is absorbed into an alkaline solution. The recovered fluorine is determined either colorimetrically or by means of a fluoride-specific electrode. The method is suitable for determining fluorine at concentrations down to about 50 p.p.m.

Laboratory studies of insecticides against the coffee leaf-miner Leucoptera Meyricki Ghesq. (Lepidoptera, Lyonetiidae)

The coffee leaf-miners Leucoptera meyricki Ghesq. and L. caffeina Wshbn. are serious pests of arabica coffee in Kenya. At the present time sprays containing parathion, methyl-parathion or diazinon are used extensively for their control.To facilitate preliminary investigations into various aspects of insecticidal control of the larval stages of these pests, a laboratory bioassay technique was developed. Larvae were reared on detached coffee leaves placed on moist filter paper in plastic boxes. When the larvae were in their third instar, the leaves were sprayed in a Potter tower and then kept in a moist air stream for three days before the mines were dissected to enable mortality counts to be made.Of 22 new insecticides screened, only Sumithion (O, O–dimethy1 O–(3–methy1–4–nitrophenyl) phosphorothioate) and fenthion gave mortalities higher than those achieved with diazinon. Parathion gave somewhat higher mortalities than methyl-parathion, and emulsifiable formulations of these insecticides were more effective than wettable powders. The inclusion of additional wetting agents increased the efficiency of commercial formulations of these two insecticides. These results are subject to confirmation in field trials.The mode of action of parathion was investigated. Dosage/mortality lines were constructed for parathion, methyl-parathion and diazinon so that resistance to these insecticides by L. meyricki could be detected should it develop at some future date. L. caffeina was found to be apparently more susceptible to these insecticides than L. meyricki and this was believed to be due to its greater rate of feeding.

On forecasting hailstorms by the method of vectorial wind changes

The conditions leading to the occurrence of a number of hailstorms over northwest India have been investigated, The method of assessment of convergence by using 24-hour vectorial wind changes was found in these situations .be superior to the conventional methods and of definite prognostic value. The border region between cyclonic and anticyclonic wind shear patterns was found suitable for thunderstorm development whenever the cyclonic shear appeared in a moist air stream, notwithstanding the unfavourableness of the winds and of the thermal structure aloft. Strong upper winds and a pronounced vertical shear are found to promote transformation of the thunderstorms so formed into hailstorms. The direction of the associated squall, if any, lies close to that of the isellobaric wind.

Studies on the Responses of the FemaleAëdesMosquito. Part I.—The Search for Attractant Vapours

The question of the attractancy of water-vapour, carbon dioxide and candidate attractant compounds was investigated by the use of an olfactometer emitting freely into a 360-cu. ft. cage filled with female adultAëdes aegypti. Moist air (85 per cent. R.H.) was found to attract 3–5 times as many mosquitos as dry air (15 per cent. R.H.). A moistened billiard-ball was found to attract about seven times as many mosquitos as a dry one, the result being similar whether black or white balls were used. The attractancy was reduced and even reversed at very high room humidities.The addition of 10 per cent. CO2to a dry air stream approximately doubled its ability to bring mosquitos within 0·5 inches of the olfactometer port. Its addition to a moist air-stream did not significantly increase its attractancy. Pure CO2vapour proved to be no more attractive than dry air, and several times less attractive than moist air.A number of chemical compounds found in body exudations, and some housefly attractants, were tested in the olfactometer for their effect onAëdesadults. None were consistently attractive, and many were significantly repellent. However, sweat itself proved significantly attractive at a low vapour concentration, while significantly repellent at a high concentration.

The Deposition of Ice Crystals on Cooling Surfaces in Low Temperature Plant

A study is made of the conditions governing the deposition of ice crystals from a moist air stream on to the inside surface of a cooled tube. The promoting effect of impurities such as oil vapour in the air stream is demonstrated. Series of experiments were made to establish the effect of air velocity, and of the temperature difference between the tube wall and air stream, on the amount of deposition. In the flow range tested (Reynolds' number 11,000 to 27,000) it was observed that increasing the air velocity increased the percentage deposition; at the lower velocities there was no evidence of progressive deposition. The effect of temperature difference on the percentage adhesion in the range 7° to 14° C. was small, but an experiment at a value of 4.6° C. showed a decrease in the amount of condensed snow deposited. In most experiments a glass tube was used but in others use of a brass tube gave similar results.

Precipitation, River Stages and Forecasts in the Ohio River Flood of 1937

The cause of the great flood of 1937 in the Ohio River Valley was the excessive rainfall. This is easily shown. The reason for the unusual distribution of the masses of air, which resulted in the excessive rainfall, is much more difficult to understand and explain. During most of the month of January the semi-permanent area of high pressure over the Atlantic Ocean, was close to and partially over the south Atlantic coast. This resulted in a stagnant bank of high pressure along the south Atlantic coast for long periods of time. A constant stream of warm moist air moved from the Gulf of Mexico to the Ohio valley. Other areas of high pressure, moving down from the Northwest, contained great masses of cold polar air. The northwest winds out of these northern high areas met the warm moist winds from the south over the lower Ohio valley. The of air mass discontinuity, or trough of low pressure, extended from Arkansas northeastward to Indiana or Ohio. For several days this line was over or parallel to the lower stretches of the Ohio river extending from Cairo, 111., to Cincinnati, Ohio, and beyond. As the cold heavy air from the northwest moved in and under the warm moist air from the south, the temperature dropped rapidly, and great quantities of moisture were precipitated. Along this

The Oxidation of Glutathione in Human Erythrocytes--A Reversible Reaction.

The observations here reported have been made while working on an adaptation for human blood of Tunnicliffe's method for the determination of a reduced glutathione. A complete report of these studies will appear later. The general plan of the experiments was as follows: a given specimen of human blood was saturated with CO2, a sample or samples removed for estimation of reduced glutathione; the remaining blood was saturated with air, again sampled and the remainder saturated a second time with CO2 and a portion taken for determination of reduced glutathione. Saturation with CO2 or with air was accomplished by shaking the blood gently in a 250 cc. Erlenmeyer flask in a specially designed motor-driven apparatus as a stream of moist CO2 or air was passed through the flask. Samples were removed with a 10 cc. Oswald-Folin pipette and allowed to run into 10% trichloracetic acid. The samples which were saturated with CO2 were run into the acid contained in flasks in which the air had been replaced by CO2. The trichloracetic acid filtrates were titrated with 0.001 N iodine solution to the starch end point and with 0.001 N thiosulphate to the disappearance of color, as suggested by Perlzweig and Delrue. The excess of potassium iodide they suggest was omitted. The nitroprusside reaction as an outside indicator has been used as a check on the starch indicator in a large number of determinations on human blood. When the nitroprusside end point is used the figures obtained are from 85% to 95% of those obtained with filtrates containing a higher concentration of reduced glutathione and poorer agreement when the concentration is less. It appears that the same substance is being measured by either of the indicators and starch is much more accurate in my hands.