Low Dew Point Research Articles

Selective oxidation and segregation during annealing of steels at low oxygen partial pressures

Industrial annealing of automotive steel grades is carried out in order to improve the mechanical properties and to adjust the grain size. However, the surface chemistry changes drastically due to selective oxidation and segregation phenomena, which significantly influence the further surface treatment, i.e. hot dip galvanizing.The paper discusses results of laboratory experiments on selective oxidation and segregation of minor alloying elements Mn, Al, Cr and Si and non-metallic elements B, P and S during annealing of steel sheets in an N2–5%H2 atmosphere as a function of dew point. It will be shown that at lower dew points mostly external oxidation of Al and Mn occurs, where B shows a high tendency to segregate to the free surface and to form a BN film, especially observed on ferritic/austenitic steel. With increasing dew point, the oxidation of Al becomes internal and Mn, Si and Cr are oxidized externally. Boron also segregates to the surface by forming mixed Mn–B oxides and in the case of ferritic steels suppresses Si segregation and oxidation. The formation of phosphates by segregation of P becomes important at a D.P. of 0°C.

The Role of Airmass Types and Surface Energy Fluxes in Snow Cover Ablation in the Central Appalachians

Abstract A one-dimensional snowpack model, a unique airmass identification scheme, and surface weather observations are used to investigate large ablation events in the central Appalachian Mountains of North America. Data from cooperative observing stations are used to identify large ablation events within a 1° latitude × 1° longitude grid box that covers the majority of the Lycoming Creek basin in northern Pennsylvania. All 1-day ablation events greater than or equal to 7.6 cm (3 in.) are identified for the period of 1950 through 2001. Seventy-one events are identified, and these days are matched with a daily airmass type derived using the Spatial Synoptic Classification technique. Average meteorological characteristics on ablation days of each airmass type are calculated in an effort to understand the diverse meteorological influences that led to the large ablation events. A one-dimensional mass and energy balance snowpack model (“SNTHERM”) is used to calculate surface/atmosphere energy fluxes responsible for ablation under each airmass type. Results indicate that large ablation events take place under diverse airmass/synoptic conditions in the central Appalachians. Five airmass types account for the 71 large ablation events over the 52-yr period. Forty-three of the events occurred under “moist” airmass types and 28 under “dry” airmass conditions. Large ablation events under dry airmass types are driven primarily by daytime net radiation receipt, especially net solar radiation. These events tend to occur early and late in the snow cover season when solar radiation receipt is highest and are characterized by relatively clear skies, warm daytime temperatures, and low dewpoint temperatures. Moist airmass types are characterized by cloudy, windy conditions with higher dewpoint temperatures and often with liquid precipitation. During these events sensible heat flux is most often the dominant energy flux to the snowpack during ablation episodes. However, in many cases there is also a significant input of energy to the snowpack associated with condensation. Combinations of high sensible and latent heat fluxes often result in extreme ablation episodes, similar to those witnessed in this area in January 1996.

Advanced equation of state method for modeling TEG–water for glycol gas dehydration

An advanced equation of state has been developed for modeling triethylene glycol (TEG)–water system for glycol gas dehydration process. The dehydration of natural gas is very important in the gas processing industry. It is necessary to remove water vapor present in a gas stream that may cause hydrate formation at low-temperature conditions that may plug the valves and fittings in gas pipelines. In addition, water vapor may cause corrosion difficulties when it reacts with hydrogen sulfide or carbon dioxide commonly present in gas streams. The most effective practice to remove water from natural gas streams is to use TEG in the gas dehydration process. In modeling such a process, it is crucial that the phase behavior of the TEG–water–natural gas system is correctly modeled, with methane being the predominant component in natural gas. Of the three binaries, methane–water, methane–TEG and TEG–water, the methane binaries can be adequately modeled by an equation of state, e.g. [J.R. Cunningham, J.E. Coon, C.H. Twu, Estimation of aromatic hydrocarbon emissions from glycol dehydration units using process simulation, in: Proceedings of the 72nd Annual Gas Processors Association Convention, San Antonio, TX, March 15–17, 1993]. For the TEG–water binary, the Parrish's empirical hyperbolic correlation [W.R. Parrish, K.W. Won, M.E. Baltatu, Phase behavior of the triethylene glycol–water system and dehydration/regeneration design for extremely low dew point requirements, in: Proceedings of the 65th Annual GPA Convention, San Antonio, TX, March 10–12, 1986] is recommended by GPSA [GPSA Engineering Data Book, 10th ed., First Revision, Gas Processors Suppliers Association, Tulsa, OK, 1994] and is currently widely used in the industry. In this work, we applied the TST (Twu–Sim–Tassone) equation of state to model this binary system. A methodology was also developed to determine the water dew point and calculate water content for this system. The TST equation of state is shown to accurately represent the activity coefficients of TEG–water solutions as well as water dew point temperatures and water content of gas over the entire application range of temperature, pressure and concentration encountered in a typical TEG dehydration unit.

Galvanizability of Complex Phase High Strength Steel

Complex phase (CP) steels have very high ultimate tensile strengths, resulting from the use of specific alloying elements, which improve the hardenability but cause difficulties when applying a zinc coating by means of continuous hot‐dip galvanizing. The galvanizability of a cold rolled 1000MPa complex phase steel was investigated by monitoring the surface chemistry before dipping and evaluating the quality of the zinc coatings applied by a laboratory hot‐dipping simulator. Two steel compositions with different Cr levels were used. The influence of the most important production parameters, the annealing temperature and the dew point of the annealing atmosphere, was investigated. Both steel compositions were galvanizable, but both the surface appearance and zinc coating adhesion were improved when low Cr contents were used. At a low dew point of ‐30°C, Cr, Mn and Si segregated to the surface and the presence of Mn2SiO4 could be demonstrated. At high dew point of +10°C, less oxides were present at the steel surface. There was no effect of the annealing temperature on the coatability.

Galvanisability of silicon free CMnAl TRIP steels

Transformation induced plasticity (TRIP) steels are a promising solution for the production of cars with low body mass because of the combination of high strength and large uniform elongation that they offer. However, conventional CMnSi TRIP steels with more than 1 wt-%Si have the drawback of poor Zn coating quality after continuous galvanising. This problem is due to the presence of complex Si–Mn oxides on the strip surface. The present research work therefore focused on the full substitution of Si by Al in TRIP steels and the detailed analysis of the galvanising behaviours of these Si free CMnAl TRIP steels. If the hot dipping is done after a combination of intercritical annealing and isothermal bainitic transformation in a furnace atmosphere with a high dewpoint, the wetting of the strip by the liquid Zn is improved significantly. However, the improvement is limited and not enough to avoid bare spots and coating defects cannot be avoided on conventional CMnSi TRIP steel. In contrast, the Si free CMnAl TRIP steel has a much better wettability when annealed at a low dewpoint. The surface segregation of the elements, which have a high affinity for oxygen, i.e. Si, Al, and Mn, was studied in detail and this revealed that Si was much more readily enriched on the surface than Al during the annealing in the low dewpoint atmosphere. The difference in the surface segregation between Si and Al resulted in a clear difference in the galvanisability. The limited presence of Al on the strip surface is due to the fact that Al can be oxidised internally during hot rolling. As a result, an Al depleted surface region is formed owing to selective internal oxidation of Al before the continuous galvanising.

Mechanisms of the hydrogen reduction of molybdenum oxides

The two stages of the hydrogen reduction of MoO 3 to Mo were investigated in a thermal balance under well defined reaction conditions. Starting with different grain and agglomerate sizes for both stages, the influence of a set of parameters (temperature, local partial pressure of H 2O, gas flow, etc.) on the reaction progress and the final result were studied in detail. Depending on the set of parameters used, different reaction mechanisms like pseudomorphic transformation or chemical vapour transport (CVT) were observed. Taking into account that grains and agglomerates deviate from a spherical shape and a definite grain size, the extent of reaction is well described by standard theoretical gas–solid reaction models such as the shrinking core model or the crackling core model (CCM). Thermo-gravimetric analysis, X-ray diffraction, scanning electron microscopy, surface area measurements (BET method) and laser diffraction were used for these studies. Under all conditions, the first stage shows a reaction path MoO 3→Mo 4O 11→MoO 2 via CVT. The reaction extent follows the CCM. Depending on the local partial pressure of H 2O during reduction, the formed Mo 4O 11 and MoO 2 exhibit different size distributions and shapes of the grains. The extent of reaction of the second stage develops according to the shrinking core model. Depending on the local dew point, two different reaction paths can occur: Pseudomorphic transformation at low dew points and transformation via CVT at high dew points. This paper is an extract from the Ph.D. thesis of W.V. Schulmeyer “Mechanismen der Wasserstoffreduktion von Molybdänoxiden”, 1998, Darmstadt University of Technology, Institute of Material Science, Department of Chemical Analytics, FRG. It focuses on a phenomenological description of the most important results.

Air–sea exchange in the Black Sea estimated from atmospheric analysis for the period 1979–1993

The air–sea exchange in the Black Sea is revisited in the paper on the base of data provided from the ECMWF atmospheric re-analysis for the period 1979–1993. Climatological characteristics of analysis data are compared against available climatic data, demonstrating quite a good consistency. Several drawbacks are found: too low temperatures in the easternmost part of the sea, too low dew point temperature and slight underestimation of precipitation. However, the seasonal and inter-annual oscillations are resolved correctly, as well as the horizontal patterns of air–sea exchange. The shallow penetration of thermal signal in the Black Sea is well detected by the very small heat transports inferred from the ECMWF data. Thus, the conclusion is that the analysis ‘sees’ quite well the major thermal peculiarity of the Black Sea associated with its extremely small thermal inertia caused by the specific stratification.

Dehydration of natural gas using solid desiccants

Natural gas is an important source of primary energy that, under normal production conditions, is saturated with water vapor. Water vapor increases natural gases' corrosivity, especially when acid gases are present. Several methods can be used to dry natural gas and, in this paper, a solid desiccant dehydrator using silica gel is considered due to its ability to provide extremely low dew points. The design analysis of a two-tower, silica gel dehydration unit to dry one million standard m 3 of natural gas per day is presented in this paper and the effects of various operating parameters on the design of the unit are discussed. The study also covers the analysis of energy requirements for the regeneration of the weak desiccant bed based on some simplified assumptions and it is found that the higher the regeneration temperature, the smaller are the required quantities of regeneration gas.

Sintering, microstructure, and mechanical properties of PM manganese–molybdenum steels

The effects of 0·5 wt-%Mo addition on the processing, microstructure, and strength of PM Fe–3·5Mn–0·7C steel are described. Water atomised and sponge irons, Astaloy 1·5Mo, milled ferromanganese, and graphite were the starting powders. During sintering in 75H2 /25N2 or pure hydrogen the dewpoint was controlled and monitored; in particular the effects of improving it from -35 to -60°C were investigated. Faster heating rates (≥20 K min-1), sufficient gas flowrates, milling the ferro alloy under nitrogen, a low dewpoint (<-60°C), and a getter powder can all contribute to the reduction or prevention of oxidation of the manganese, in particular formation of oxide networks in the sintered steels. For 600 MPa compaction pressure densities up to 7·1 g cm-3 were obtained; these were not significantly affected by sintering at temperatures up to 1180°C. The sintered microstructures were sensitively dependent on the cooling rate. Irrespective of the presence of Mo, slow furnace cooling at ∼4 K min-1 resulted in mainly pearlitic structures with some ferrite and coarse bainite, whereas fast cooling at ∼40 K min-1 produced martensite and some retained austenite, very fine pearlite, bainite, and some ferrite. Young's modulus, determined by tensile and ultrasonic tests, was in the range 110–155 GPa. Sintering with -60°C dewpoint resulted in tensile and transverse rupture strengths of420 and 860 MPa for the Mn steel, rising to 530 and1130 MPa as a result of the Mo addition. This contrasts with strength decreases observed when processing included use of high oxygen containing ferromanganese and sintering with -35°C dewpoint.

In situ analysis of ash deposits from black liquor combustion

Aerosols formed during combustion of black liquor cause a significant fire-side fouling problem in pulp mill recovery boilers. (Black liquor is a recycled by-product formed during the pulping of wood in the paper-making industry). The ash deposits reduce heat transfer effectiveness, plug gas passages, and contribute to corrosion. Both vapors and condensation aerosols lead to the formation of such deposits. The high ash content of the fuel and the low dew point of the condensate salts lead to a high aerosol and vapor concentration in most boilers. In situ measurements of the chemical composition of these deposits is an important step in gaining a fundamental understanding of the deposition process. Infrared emission spectroscopy is used to characterize the composition of thin film deposits resulting from the combustion of black liquor and the deposition of submicron aerosols and vapors. New reference spectra of Na 2SO 4, K 2SO 4, Na 2CO 3 and K 2CO 3 pure component films were recorded and compared with the spectra of the black liquor deposit. All of the black liquor emission bands were identified using our new reference spectra as well as literature data and ab initio calculations. The ab initio calculations predict the locations and intensities of infrared bands for the alkali-containing vapors of interest.

Pipeline drying using dehumidified air with low dew point temperature

The presence of humidity may be detrimental to the operation of pipelines transporting natural gas or other petroleum products. In particular conditions water solidifies or reacts chemically with hydrocarbons, forming hydrates. Such crystalline substances may cause obstruction of the lines and damage the equipment of the relevant facilities. A procedure for predicting the performance of drying a pipeline using dehumidified air with low dew point is described in this paper. The mathematical model estimates the time required for the complete removal of moisture in the pipeline for the given operating conditions with simplified assumptions. The governing equations are solved analytically as well as numerically and the results are briefly discussed in the paper.

Radiation damages in TRISTAN vacuum systems

The TRISTAN e+e− collider, the all aluminum (Al) alloy vacuum system, has been operated for 4 years at a beam energy between 27.5 and 32 GeV, with a characteristic energy of the synchrotron radiation between 187 and 295 keV. The radiation in the TRISTAN tunnel was measured using thermoluminescence dosimeters. Radiation damage in the aluminum vacuum system is mainly from HNO3 produced from NOx. N2 and SO2 in atmosphere are oxidized, combined with H2O, and turned to HNO3 and H2SO4 in TRISTAN tunnel. Freon also turned to HCl and HF. Corroded materials on aluminum surface is amorphous Al(NO3)3⋅9H2O. To decrease corrosion due to the radiation, one or two of the components in the atmosphere must be removed. This can be realized by pumping with a rotary pump (RP) or a RP together with a turbomolecular pump, or supplying N2 or He with low dew point, to protect beryllium (Be) windows for internal targets and beam injection and extraction, and race track type bellows. SiO2 coating superior to almite coating is applied to protect bellows from radiation damage. Most organic materials are decomposed with the radiation. Halogens in the materials are decomposed and turned to acids combining with H2O. Connectors of distributed ion pumps and cables of beam position monitors were damaged by fluorine gas, resulting from the decomposition of Teflon insulators in cables and connectors. Polyimide and polystyrene are durable under radiation of about 1010 rad. They however turned fragile and caused insulation failure in connectors. Rubbers and oils also received radiation damage. Organic materials must be exchanged to inorganic or metallic materials to avoid radiation damage. Mineral insulation cable is developed and is under test.

Bright-annealing of stainless steels.

This review describes a recent advanced knowledge of the thermodynamics of Fe-Cr-O system in such low oxygen potential atmospheres as that in bright annealing. More attention is paid to the redox reactions of Fe-Cr-O system, especially the reaction of chromiun in a ferrous alloy with the water vapor in BA atmospheres having low dew points to form Cr2O3 and FeCr2O4. An outline of the surface characteristics of Fe-Cr alloy as bright annealed is given together with a discussion of the crystal structure of oxide films and their effect on the behavior of corrosion.

Demonstration of a problem in estimating sensible heat loss from the respiratory tract by thermometry.

We have investigated sensible respiratory loss, which is usually taken as the product of expired volume and the temperature difference between inspired and expired air (VE X delta T). Air temperature was measured with a 0.122 mm copper-constantan thermocouple mounted in the mouthpiece of a T-piece breathing system, and expired volume with a pneumotachograph. Changing air temperature (delta T) at the mouth and expired air volume (VE) were recorded simultaneously while the subject voluntarily breathed at different tidal volumes and rates. Inspired temperatures were controlled at 12.05 degrees C, 21.80 degrees C and 25.74 degrees C at a low dewpoint temperature of 4-5 degrees C. Temperature volume "loops" were constructed using an x-y plotter. The areas of each "loop" and enclosing rectangle (VE X delta T) were measured. The difference was divided by the weight of the rectangle to give the percentage of overestimation of sensible heat loss, which ranged from 5.5 to 17.2 per cent. The error increased significantly with decreasing tidal volume and increasing respiratory rate.

A Model for Predicting Synoptic Weather Types Based on Model Output Statistics

An objective classification model was developed that can automatically predict synoptic weather types in southern California. Stepwise discriminant analysis was used to match the National Meteorological Center's Limited-area Fine Mesh (LFM) Model Output Statistics to subjectively classified weather types or patterns. The five classified weather types range from hot, dry, windy Santa Ana days to cool, rainy, cloudy days caused by a synoptic low. Discriminant function equations were developed for predicting each weather type 12 and 24 h in advance by screening 80 potential predictors consisting of forecasts at 500, 700 and 850 mb from the LFM model. Model output at nine grid points was used because that information adequately describes the meteorological patterns over southern California. Using independent LFM model forecasts valid 12 and 24 h in advance, the objective classification model predicted the probability of the days being in each of the five weather types, then the type with the highest probability was selected. Eighty-eight of 107 24 h periods (days) centered 12 h in advance (81%) were correctly predicted. Of 99 independent days centered 24 h in advance, 71 (72%) were correctly predicted. Hourly means and standard deviations of surface temperature and dew points at eight research sites in the San Bernardino Mountains computed by month for the five weather types had distinct diurnal variations corresponding with weather types. Summarizing hourly temperatures in August at the eight sites by weather type reduced their standard deviation by almost one-half. Measurements of mean daily maximum ozone at a San Bernardino Mountain crest site, where chronic ozone injury to ponderosa pine has occurred, showed significant differences between the weather types. The mean surface wind, temperature and dew-point patterns at 2100 GMT over southern California for type 1 (Santa Ana) days show strong offshore winds, high temperatures and very low dew points, whereas type 5 (synoptic low) days show strong onshore winds, low temperatures and high dew points.

The Mesoscale Temperature and Dew Point Fields of a Very Cold Airflow Across the Great Lakes

Abstract The mesoscale air temperature and dew point fields in a synoptic situation where air with a temperature at least 25°C colder than lake water temperature passed over the western Great Lakes is investigated. The airflow experienced an average temperature rise of 8°C and a dew point rise of 15°C from one shore of Lake Michigan to the other. Leeward of Lake Michigan the surface air temperature and dew point of the airflow decreased approximately 2°C and 4°C, respectively, as the air moved inland. Strong temperature gradients, referred to as lake–end pseudofronts, were found perpendicular to the flow downwind from the end of the lakes. The lake-end pseudofront at the southern end of Lake Michigan was 25–50 km wide, extended over 100 km downstream, and had an average magnitude of 0.5°C (5 km)−1. A band of heavy snow was associated with it. Ice on the lakes, coupled with a transitory wind shift, allowed unmodified cold air to penetrate into lower Michigan for several hours. Low dew points accompanied th...

International aspects of air conditioning with movable insulation

Natural air conditioning, involving heating with solar energy and summer cooling to the night sky, is accomplished with ceiling ponds and movable insulation. Pertinent international aspects of climate, economies, mores and needs are related to industrialized and to developing countries. Tested throughout 15 months, in Phoenix, Arizona, when temperatures varied from below freezing to 115°F days, extensive data were obtained for very hot-dry and hot-humid climates. The Sky Therm system met these weather types with six means for modulating ambient conditions: solar heating, heat capacity, nocturnal radiation, water evaporation; radiation, evaporation and fan-coil operation; and evaporation, fan-coil and pond-blower use. Typical results are presented with a chart indicating that average daily room temperatures between 70° and 80°F can be maintained throughout a normal year, in Phoenix, without supplementary heating or cooling. During low dewpoint periods, water evaporation is not required until maximum temperatures exceed 100°; until 105° is exceeded, no electricity is needed. With dewpoints above 50° and dry-bulb maxima over 100°, both evaporation and electricity were used. In most developing countries nearer the equator, ample heating with horizontal pond collectors can be expected at normal altitudes. Acclimatization of people to somewhat higher summer temperatures may make the use of electricity and water evaporation unnecessary. The required plastics are being increasingly produced in industrializing countries, but cost may restrict use of the new method to buildings of higher priority than those to which the system would be applied in industrialized countries. Dual effects obtainable simultaneously with the same movable insulation include keeping one building or room warm and another one cold. The efficiency of a solar water-heater (or a solar still) can be improved by covering it at night with insulation moved from over a container in which water is cooled (or frozen) by nocturnal radiation; this water is maintained cold throughout the day when the insulation is positioned over it.

The effect of temperature on extensibility of isolated corneum and its relation to skin chapping.

SUMMARY.— As part of a study on the effect of water on the extensibility of isolated corneum we have investigated the effect of temperature on extensibility under conditions where the corneum water content was kept as constant as possible. The results showed that corneum extensibility was decreased at lower temperatures. These results may be of significance in the appearance of skin chapping in winter. The incidence of chapping has been related to low dewpoints and the hypothesis was that a low dewpoint leads to a low corneum water content. Our results suggest that low temperatures play an equally important part and that chapping is not related purely to a low corneum water content.

低合金鋼の内部酸化

Fe-Al, Fe-Cr and Fe-Si alloys were internally oxidized at 800°∼1050°C in a H2/H2O mixture which was adjusted not to oxidize Fe into FeO. The character and the depth of the subscale formed were investigated with an optical microscope, and the distribution of alloying elements with E.P.M.A.The results are summarized as follows:(1) The character of the subscale can be classified into 5 types. The types depend on the heating temperatures, kinds and concentrations of alloying elements, and not on the surface oxygen partial pressure.(2) Generally, the depth of the subscale is proportional to the biquadratic root of the surface oxygen partial pressure and is inversely proportional to the square root of the concentration of alloying element.(3) Alloying elements are enriched in the subscale formed at low oxygen partial pressure.(4) No subscale was found in Fe-Si alloys heated at 850°C in H2 of a fairly low dew point. That is probably because, as a result of the enrichment, the precipitated oxide particles have become a compact layer to hinder the diffusion of oxygen.(5) The diffusion coefficient of oxygen through internally oxidized iron at 850°C was found to be 2∼3×10−8 cm2 sec−1.

Fractionation during condensation of vapor mixtures

AbstractPartial condensers of the reflux type are capable of producing substantial fractionation of vapor mixtures. For vapor products having low dew points they may be preferred to conventional equipment for adiabatic distillation plus total condensation.Experimental studies of a condenser used to fractionate mixtures of ethylene dichloride and toluene show that observed mass transfer effects are in agreement with the Colburn‐Drew film theory, which accounts for the influence of the net mass exchange on the relative mass transfer rates of the components. In an adaptation of the transfer‐unit concept to partial condensation, new equations are derived relating the number of transfer units to liquid‐ and gas‐phase resistances, surface area, and amount of condensation. Observed resistances to mass transfer agree qualitatively with values independently measured; the diffusional resistance of the liquid phase has a pronounced effect on the fractionation, which does not conform to the Rayleigh theory of equilibrium differential condensation.Partial condensers appear, to require more interracial area than adiabatic distillation equipment in order to produce the same fractionation at the same heat load; for the same interfacial area condensers require more heat removal.Although only the system ethylene dichloride‐toluene was investigated here, the results of this work are believed pertinent binary liquid mixtures also. Knowledge of the vapor‐liquid equilibrium relationship of the new system and of the liquid and vapor‐phase transfer coefficients is required in order to employ the calculation methods introduced here.