Water Vapor Partial Pressure Research Articles

Minimization of thermal insulation thickness taking into account condensation on external walls

Condensation occurs in the inner layers of construction materials at whatever point the partial pressure of water vapor diffuses and reaches its saturation pressure. Condensation, also called sweating, damages materials, reduces thermal resistance, and by increasing the total heat transfer coefficient, results in unwanted events such as increased heat loss. This study applied minimization of thermal insulation thickness with consideration given to condensation in the external walls. The calculations of heat and mass transfers in the structure elements are expressed in a graphical form. While there was an increase in the required thermal insulation thickness subsequent to an increase in the internal environment’s temperature, relative humidity, and the external environment’s relative humidity, the required thickness decreased with an increase in the external environment’s temperature. The amount of water vapor transferred varied with internal or external conditions and the thickness of the insulation. A change in the vapor diffusion resistance of the insulation material can increase the risk of condensation on the internal or external surfaces of the insulation.

Constraining Data Mining with Physical Models: Voltage- and Oxygen Pressure-Dependent Transport in Multiferroic Nanostructures.

Development of new generation electronic devices necessitates understanding and controlling the electronic transport in ferroic, magnetic, and optical materials, which is hampered by two factors. First, the complications of working at the nanoscale, where interfaces, grain boundaries, defects, and so forth, dictate the macroscopic characteristics. Second, the convolution of the response signals stemming from the fact that several physical processes may be activated simultaneously. Here, we present a method of solving these challenges via a combination of atomic force microscopy and data mining analysis techniques. Rational selection of the latter allows application of physical constraints and enables direct interpretation of the statistically significant behaviors in the framework of the chosen physical model, thus distilling physical meaning out of raw data. We demonstrate our approach with an example of deconvolution of complex transport behavior in a bismuth ferrite-cobalt ferrite nanocomposite in ambient and ultrahigh vacuum environments. Measured signal is apportioned into four electronic transport patterns, showing different dependence on partial oxygen and water vapor pressure. These patterns are described in terms of Ohmic conductance and Schottky emission models in the light of surface electrochemistry. Furthermore, deep data analysis allows extraction of local dopant concentrations and barrier heights empowering our understanding of the underlying dynamic mechanisms of resistive switching.

Broad-Range Detection of Water Vapor using Cavity Ring-down Spectrometer

Quantitative measurement of water vapor is essential in many fields including semiconductor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy. The instrument is high-vacuum compatible, self-calibrated by using the free-spectral-range of the ring-down cavity made of low-thermal-expansion Invar. Using a single tunable diode laser working at 1.39 µm, detection of trace water vapor in vacuum and in high-purity helium gas, and also determination of humidity at ambient conditions, have been demonstrated. It indicates that the instrument can be used to detect the partial pressure of water vapor in a very broad range from 10−7 Pa to 103 Pa. Such an optical hygrometer can be potentially applied as a primary moisture standard to determine the vapor pressures of water (ice) at low temperatures.

Overpotential and Interfacial Conductivity of Ni/YSZ Anode Based on Species Territory Adsorption Model in SOFCs

Introduction Recently, a new anode incorporating a BaCe0.8Y0.2O3-δ (BCY) proton conductor was proposed by the authors to increase a power density of SOFCs, and it was found that the anode overpotential was reduced by incorporating BCY particles to the conventional Ni/GDC cermet anode1. Moreover, it was found that BCY particles might contribute to supply the adsorbed hydrogen to the triple phase boundary (TPB) in anodic reaction2. Based on these results, a modified reaction model around the TPB was proposed to explain the mechanism of overpotential reduction in the anode incorporating the proton conductor, and analytical expression of current density with oxygen activity and anode overpotential with current density were obtained3. In this study, the analytical expression of interfacial conductivity of anode (the inverse of the anode polarization resistance) was obtained based on the reaction model3. In addition, the analytical results of overpotential or interfacial conductivity of conventional Ni/YSZ anode were compared with those obtained from experiments4, and the validity of the reaction model was discussed. Reaction model The details of the reaction model were shown in our previous work3. In this model, some finite areas, which contribute to species adsorption, are assumed around TPB, and hydrogen and oxygen are assumed to be adsorbed mainly on the surface areas of Ni and oxide ion conductor, respectively (We define this idea as “species territory adsorption model”). In addition, it is also assumed that the reaction rate in the anode is controlled by the surface reaction between Had and Oad, while all other reaction takes place under the condition of chemical equilibrium. Based on the model, under the condition that the pure oxygen (P O2=1atm) is used in the cathode side, a simple expression for current density i and anode overpotential ηa could be obtained explicitly as a function of an oxygen activity at the anode a O and a current density i, respectively. Here, a O is expressed as a O=exp(2FE/RT) (E is anode potential). Using the analytical expression of i as a function of a O, the interfacial conductivity (σE ) of anode, which is described as the inverse of the anode polarization resistance, is derived as follows. Eq. [1] Here, θV (1) and θV (2) means the coverage of vacant adsorption site on the surface areas of Ni and oxide ion conductor, respectively. These are described as follows. Eq. [2, 3] Here, P H2 and P H2O are partial pressure of hydrogen and water vapor at the anode side, respectively. Ki , K'i (i = species) and kaj , kcj (a, c = anodic or cathodic reaction for 2Had+Oad → H2Oad+2Vad ) show the equilibrium constant and the rate constant, respectively. A unique combination of fitting parameters, such as equilibrium constants and reaction rate constants were obtained from a comparison between analytical and experimental results4 for the case of Ni/YSZ anode. Analytical results and discussions with experiments Figure 1 shows the analytical and experimental4 results of anode overpotential of Ni/YSZ with current density at 1273K. From Figure 1, it was disclosed that the anode overpotential decreased with increasing humidity from 3% to 20%, while, it increased with increasing humidity from 20% to 40%. These results are in good agreement with those of experiments. Moreover, Figure 2 shows the analytical and experimental4 results of interfacial conductivity of Ni/YSZ as a function of water vapor pressure at 1273K under the open-circuit condition. In this case, the hydrogen partial pressure P H2 was equal to 1-P H2O atm. The analytical results were calculated from Eq. [1]. From Figure 2, it was disclosed that the interfacial conductivity had a local maximum value in the range of P H2O=0.15-0.25 atm in the experiments. These results successfully followed the analytical results. From the analytical results, it was disclosed that the term ∂i/∂a O decreases with increasing P H2O, while ∂a O /∂E increases. As a result, σE has a local maximum value. Conclusions Based on the reaction model of SOFC anode proposed by the authors, the overpotential and interfacial conductivity of conventional Ni/YSZ anode was discussed. The experimental results of humidity dependence of anode overpotential or interfacial conductivity is in good agreement with those obtained by the analytical results based on the proposed model.

Experimental Study of Internal Reforming on Large‐area Anode Supported Solid Oxide Fuel Cells

AbstractThe effect of endothermic internal steam reformation of methane and exothermic fuel cell reaction on the temperature of a planar‐type anode‐supported solid oxide fuel cell was experimentally investigated as a function of current density and fuel utilization. We fabricated a large‐area (22 × 33 cm2) cell and compared temperature profiles along the cell using 30 thermocouples inserted through the cathode end plate at 750 °C under various conditions (Uf ∼50% at 0.4 A cm−2; Uf ∼70% at 0.4 A cm−2; Uf ∼50% at 0.2 A cm−2) with hydrogen fuel and methane‐steam internal reforming. The endothermic effect due to internal reforming mainly occurs at the gas inlet region, so this process is not very effective to cool down the hot spot created by the exothermic fuel cell reaction. This eventually results in a larger temperature difference on the cell. The most moderate condition with regards to thermal gradient on the cell corresponds to high fuel utilization (Uf ∼70%) and low current density (∼0.2 A cm−2). The electrochemical performance was also measured, and it was found that the current–voltage characteristics are comparable for the cell operated under hydrogen fuel and internal steam reforming of methane because of lower polarization resistance with high partial pressure of water vapor.

Estimation of psychrometric parameters of vapor water mixtures in air

ABSTRACTIn the present paper, a Visual Basic program was developed by describing the set of equations required to determine the value of seven different psychrometric properties (partial pressure of water vapor, absolute humidity, percentage humidity, relative humidity, dew point temperature, humid heat, humid volume or adiabatic saturation temperature) for mixtures of water vapor in air given the dry bulb temperature, the total atmospheric pressure and one additional parameter. Eight different cases are studied according to the corresponding input parameters. © 2015 Wiley Periodicals, Inc. Comput. Appl. Eng. Educ. 24:39–43, 2016; View this article online at wileyonlinelibrary.com/journal/cae; DOI 10.1002/cae.21670

Organic-Free Synthesis of CHA-Type Zeolite Catalysts for the Methanol-to-Olefins Reaction

Chabazite (CHA)-type zeolites are prepared from the hydrothermal conversion of faujasite (FAU)-type zeolites, dealuminated by high-temperature steam treatments (500–700 °C), and evaluated as catalysts for the methanol-to-olefins (MTO) reaction. The effects of temperature and partial pressure of water vapor during steaming are investigated. Powder X-ray diffraction (XRD) and Ar physisorption data show that the steam treatments cause partial structural collapse of the zeolite with the extent of degradation increasing with steaming temperature. 27Al MAS NMR spectra of the steamed materials reveal the presence of tetrahedral, pentacoordinate, and octahedral aluminum. NH3 and i-propylamine temperature-programmed desorption (TPD) demonstrate that steaming removes Bronsted acid sites, while simultaneously introducing larger pores into the CHA materials that make the remaining acid sites more accessible. Acid washing the steamed CHA-type zeolites removes a significant portion of the extra-framework aluminum, prod...

Development of a Tritium Monitor Combined with an Electrochemical Tritium Pump Using a Proton Conducting Oxide

To fabricate a tritium monitoring system with electrochemical hydrogen pumping attached, a tritium monitor system was constructed and assembled with a commercial tritium monitor and an electrochemical hydrogen pump using a proton conducting oxide. The hydrogen pump with CaZr0.9In0.1O3−α as the proton conducting oxide was operated at 973 K under electrolysis conditions using tritiated water vapor (HTO). The tritium molecules (HT) were extracted and controlled by the applied current over a range of two orders of magnitude. The tritium molecules have an advantage with respect to the tritium memory effect in the monitor because the tritium contamination is reduced. Next, a system feasibility test was conducted under various water vapor partial pressure conditions. Thus, the measurement of the tritium concentration via this proposed system was successfully demonstrated.

Reaction of soda–lime–silica glass melt with water vapour at melting temperatures

The soda–lime–silica glass melt was exposed to an atmosphere with a high water vapour partial pressure at temperatures of 1400–1500°C and the processes in the melt were observed and monitored using the high temperature observation method. The glass batch containing sulfates with carbon – so that the molar ratio between the carbon and sulfate ions in the batch varied between 0 and 9 – the batch without any fining agent and the batch with the addition of antimony oxide were prepared. The foaming and bubble nucleation on the level of the molten glass were observed in glasses with sulfate additions when the water vapour partial pressure in the atmosphere exceeded 50kPa, but the bubble nucleation in the reduced glass was observed also at a lower partial pressure. The bubble nucleation intensity increased with temperature. No bubble nucleation was observed in the melts with antimony oxide or in the melt without any fining agent. The bubbles nucleated on the glass level in both the oxidized and reduced melts with sulfate additions grew by a growth rate exceeding the bubble growth rate in the volume of glass by almost one order of magnitude. The unstable but rapidly renewed foam subsequently spread over the glass level. The most intensive foaming was observed in the glass melt without carbon and in the slightly reduced glass. The mechanism of the reaction between water vapour and glass is discussed in terms of a controlling process as well as its impact on the glass melting process.

Modeling of electrical conductivity in the proton conductor Ba0.85K0.15ZrO3−δ

The electrical conductivity of Ba0.85K0.15ZrO3−δ (BKZ) has been studied as a function of both oxygen and water vapor partial pressure in the temperature range of 550–700°C, to determine the partial conductivities of protons, holes, and oxygen vacancies from the defect model. It is shown that p-type conduction is dominant in dry oxidative atmospheres, while in wet oxidative atmospheres, a conduction transition from proton to hole conduction is found with increasing temperature. On the contrary, in wet nitrogen atmosphere, proton conduction is dominant over the whole temperature range. The calculated activation energies for oxide-ion, electron-hole and proton conduction are 0.86, 1.36 and 0.59eV, respectively. The standard solution enthalpy for water dissolution is −90kJ/mol, which is lower in absolute terms than that typically reported for doped barium cerates but very close to that reported for BaZr0.85Y0.15O3−δ.

Thermal expansion of materials in the barium cerate-zirconate system

The thermal expansion of proton-conducting materials in the BaCe0.8 − xZrxY0.2O3 − δ system has been investigated in air. The influence of the zirconium concentration and the measurement mode (heating/cooling) on the form of dependences ΔL/L = f(T) has been established and values of the thermal expansion coefficient have been determined. The obtained results have been discussed from the viewpoint of the structure of materials and the influence of the partial water vapor pressure.

Water Vapor Oxidation of Ferritic 441 and Austenitic 316L Stainless Steels at 1100 °C for Short Duration

A ferritic 441 and an austenitic 316L steels have been exposed to wet argon at 1100°C. This study focus on the characterization of the oxide scales formed after different exposure times in the range of 2.5-20min. Raman spectroscopy, XRD, SEM and XPS have been used. For all exposure times, 316L forms a breakaway type thick oxide scale (rupture of the pre-existing passivating film) with iron oxides on its outer part and a mix of spinels with Fe, Cr and Ni for its inner part. For lower water vapor partial pressure, iron oxides are constituted of wüstite. For higher water vapor partial pressure, iron oxides are constituted of a layer of hematite over a layer of magnetite slightly enriched in chromium. Due to strong oxidation condition, oxide scale is not always homogeneous and iron oxides spallation may occur. For 2.5min of oxidation on 441, a very thin layer of protective chromium oxide is formed. For longer exposure time, an almost homogeneous and much thicker layer mainly consisting of Cr2O3 is produced. The thickness varies slightly and gradually from 4 to 20min of oxidation. There are Mn-Cr spinels mixed with the chromium oxide. The most external part is strongly enriched in Mn and Fe in a spinel structure. The diffusivity of chromium is regarded as the main cause of the difference of oxidation behavior. In both cases, the first step is a very thin chromium oxide layer. When the oxidation conditions becomes too strong in terms of exposure time or water vapor partial pressure, this oxide layer breaks. The ferritic steel is able to heal and thicken its protective chromium oxide, preventing the breakaway. The healing would be due to the high diffusivity of chromium. The thickening would be caused by the presence of the Mn-Cr spinels which are a less effective diffusion barrier. The lower diffusivity of chromium in austenite promotes the breakaway.

Multi-observation meteorological and GNSS data comparison with Numerical Weather Prediction model

In this study we have investigated a number of meteorological and GNSS data sources; our long-term plan is to construct an integrated model of neutral atmosphere with high temporal and spatial resolution. The integrated model will be based on a Numerical Weather Prediction (NWP) model with high spatial resolution and vertical information about various meteorological parameters. In the first step (covered by this study) we have compared the NWP model outputs with the reference data consisting of: high-quality ground-based meteorological observations, radiosonde profiles and GNSS products and we have established the accuracy of the provided parameters. The radiosonde and the GNSS observations have been found to be consistent (Zenith Total Delay (ZTD) discrepancy below 10mm), whereas the ground-based observations and soundings detect in NWP data: 1) a negative bias in air pressure, 2) a negative bias in water vapor partial pressure, and 3) a positive bias in temperature. The standard deviation of ZTD residuals of reference data and the NWP model is on order of 20mm. The NWP model COAMPS (Coupled Ocean/Atmosphere Mesoscale System) used in our study does not provide meteorological parameters with acceptable accuracy for positioning.

Theoretical derivation and comparative evaluation of mass transfer coefficient modeling in solar distillation systems – The Bowens ratio approach

In the present investigation a group of mass transfer coefficient expressions was derived based on the definition of Bowen’s ratio as applied on a properly modified diffusive interface model, under specific assumptions which impose the restrictive conditions for application in solar distillation systems. These conditions determine the validity range of the derived expressions that include Dunkle’s mass transfer models, which as it was recently derived by extensive experimental evidence although are sufficiently accurate at ordinary fail at higher operating temperatures. Based on the developed analysis it was found that this is mainly attributed to the full account of partial water vapor pressures and the neglecting of induced flow enhancement phenomena, which decisively influence the mass transfer as the operating temperature increases. It was also derived that the impressive accuracy of the Chilton–Colburn model, which has been experimentally validated at a broad range of operating conditions, is basically attributed to the complete lack of specific restrictive assumptions. These, combined to the proper account of Lewis number for saturated mixtures as well as the appropriate consideration of mass transfer enhancement phenomena at higher operating temperatures, contribute to the development of an accurate mass transfer model of a more universal nature, suitable for application at a broad range of operating conditions.

Electrochemical behaviour of Ni-BZO and Ni-BZY cermet anodes for Protonic Ceramic Fuel Cells (PCFCs) – A comparative study

The matrix phase of protonic ceramic fuel cell (PCFC) cermet anodes potentially plays a vital role in hydrogen oxidation kinetics. The present work aims to investigate such involvement by selecting ceramic-oxide matrices with widely dissimilar levels of proton conduction. The materials chosen were that of the proton conducting phase BaZr0.85Y0.15O3-δ and the nominal composition BaZrO3 of negligible proton conduction. Cermet anodes Ni-BaZrO3 and Ni-BaZr0.85Y0.15O3-δ were synthesized by the acetate-H2O2 combustion method for Ni contents of 40 vol%. The microstructure and electrochemical performance of the cermet anodes were investigated by scanning electron microscopy (SEM) and electrochemical impedance measurements (EIS) respectively. The polarisation behaviour of the two nickel cermet anodes was studied as a function of temperature, hydrogen partial pressure (pH2) and water vapor partial pressure (pH2O). The results confirm that polarisation resistance is highly sensitive to the composition of the ceramic phase of the cermet anode and that the higher frequency electrode response exhibits strong links to levels of proton transport in the ceramic-oxide matrix.

Thermal effect during moisture re-adsorption of dewatered lignite

The adsorption activation energy and heat released from the moisture re-adsorption process of dewatered lignite were calculated and related to the drying and re-adsorption behaviors of Chinese lignite. The re-adsorption type and rate of moisture were discussed based on the surface changes of dewatered lignite determined by nitrogen adsorption and in-situ FTIR techniques. The heat quantities released by 1 g dewatered lignite at 353, 393, and 453 K adsorbing 1 mol moisture were, respectively, 65.0, 68.6, and 70.6 kJ, which were greater than the condensation heat of per gram pure water (44.4 kJ mol−1). It was suggested that the water adsorbed by dewatered lignite existed mainly in the physical and chemical adsorption states, in which the physically adsorbed moisture was dominant. With increasing of drying temperature, the collapsing degree of pore structure intensified, which leads to the decline of the amount of physically adsorbed moisture, but the slight increase of chemically adsorbed moisture. The amount of saturated re-adsorption moisture at different temperatures varied linearly with water vapor partial pressure. The re-adsorption process had two obvious segments corresponding to the two types of adsorbed moisture. And the higher the adsorption temperature, the shorter the transition time of two segments. The activation energies of two segments were, respectively, 7.9 and 17.3 kJ mol−1.

Prioritizing factors associated with thermal stresses imposed on workers in steel and iron casting industries using the Monte Carlo simulation and sensitivity analysis.

The aims of this study were to develop approaches for monitoring and prioritizing factors associated with thermal stresses imposed on workers in iron and steel casting industries, and to eventually purpose effective control strategies. The whole study was completed in the furnace areas of two steel casting and two iron casting plants, where the air temperature (Ta), radiant temperature (Tr), air velocity (Va) and partial water vapor pressure (Pa) were measured continuously during two consecutive work cycles. Simultaneously, the metabolic rates (M) of all workers in the furnace area were also measured. Using the WBGT as an index for screening purposes, our results suggest that all furnace area workers in both types of casting plants might experience severe heat stress. The predicted heat strain (PHS) model proposed by ISO 7933 was further adopted for detailed analysis from the physiological aspect. Through use of the Monte Carlo simulation and sensitivity analysis, both M and Tr were found to be the two most important factors associated with workers' thermal hazard. Therefore, two effective control strategies were suggested, including reducing workloads of workers and reducing radiant heat transmitting from furnaces to workplace environments. The approach developed in the present study would be beneficial to many other industries for initiating strategies to avert the thermal hazard imposed on workers.

Electrochemical properties of dual phase neodymium-doped ceria alkali carbonate composite electrolytes in intermediate temperature

Composite electrolyte materials composed of neodymium-doped ceria (Nd0.2Ce0.8O1.9; NDC) and (Li–0.5Na)2CO3 are investigated to understand the unique behaviors of their multi-ionic conduction. In the intermediate temperature, the NDC-based carbonate composite electrolytes exhibit a much higher conductivity compared to pure NDC. It has been claimed that the oxide ions are transported in the doped-ceria phase via oxygen vacancies and the protons are conducted through the second carbonate phase, thereby resulting in an enhanced ionic conductivity. However, it has not been experimentally demonstrated if the proton conduction within the carbonate phase aided in improving the conductivity of oxygen ions in the composite system. Hence, the primary objective of this work is to cultivate a deeper insight into the conduction property of these composites as an attempt to clarify the ionic transport phenomenon responsible for enhanced conductivity. Electrical conductivities of NDC and NDC/carbonate materials are investigated as a function of oxygen partial pressure and vapor pressure of water to understand transport properties of composite electrolytes. The ionic and electronic transference numbers of composite electrolytes are measured by the oxygen- and hydrogen-concentration cells containing water. The dominant charge carriers are identified quantitatively through the analysis of the partial conductivity of proton, oxygen ions, and electrons (holes). Understanding the transport properties and transference numbers of composite electrolytes can contribute to the development of commercial solid oxide fuel cells, which can be done by reducing the operating temperature using a highly ionic conductive NDC/carbonate composite electrolyte at the intermediate temperature.

Research on regional zenith tropospheric delay based on neural network technology

Tropospheric delay is a primary error source in earth observations and a variety of radio navigation technologies. However, the main problem still present is that not all strategic points around the world will have a GPS receiver. To overcome the shortcoming, a Fusion model was proposed to compensate for errors in prediction of zenith tropospheric delay (ZTD), by incorporating back propagation neural network (BPNN). The input parameters include the surface meteorological data (altitude, atmospheric pressure, absolute temperature and water vapour partial pressure) and Hopfield model predicted ZTD, the output is the difference between the Hopfield predicted and high altitude balloon derived ZTD (also called true ZTD). The datasets covered ∼250 meteorological observation stations within 8∶00 and 20∶00 for May 1st, 10th, 30th, and July 1st, August 1st and September 1st, 2010. Data from 16 uniformly distributed stations were used for training at 8∶00 on May 1st, and the remaining for validation. Modelling results from the Hopfield and current model were compared by reference to the true ZTD. It shows that the current model generates an average RMSE value of 0.0040 m, compared with 0.3445 m for the Hopfield model. In overall, the current model can improve ZTD prediction accuracy by more than 90%. In addition, ZTD predictions from the current model were compared to those obtained directly from GPS data, indicating that our model provides a good alternative for ZTD prediction when the GPS receiver at a specific location is absent.

Structural and electrical properties of strontium substituted Y2BaNiO5

The Y2−xSrxBaNiO5 (x=0, 0.1, 0.2 and 0.3) acceptor substituted system has been synthesized by solid state reaction. Structural and microstructural properties have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Lattice volume is shown to decrease linearly with increasing Sr content until composition x=0.2, highlighting the limit of the solid solution. The electrical response in the temperature range (700–100°C) was assessed by A.C. impedance spectroscopy in wet and dry O2 and N2 atmospheres. Conductivity measurements as a function of oxygen partial pressure (pO2) were also performed. The data reveal that the conductivity Y2BaNiO5 can be increased by one and half orders magnitude by Sr-doping and is independent of both water vapour and oxygen partial pressures (pH2O and pO2). The low activation energy for electrical conduction (0.216–0.240eV) suggests a thermally activated electron hopping mechanism, while the observed pO2 and pH2O independence of conductivity suggests that charge compensation for Sr is predominantly by formation of Ni3+ rather than formation of oxygen vacancies.