Humidity Generation Research Articles

The role of petal transpiration in floral humidity generation

Main conclusionUsing petrolatum gel as an antitranspirant on the flowers of California poppy and giant bindweed, we show that transpiration provides a large contribution to floral humidity generation.Floral humidity, an area of elevated humidity in the headspace of flowers, is believed to be produced predominantly through a combination of evaporation of liquid nectar and transpirational water loss from the flower. However, the role of transpiration in floral humidity generation has not been directly tested and is largely inferred by continued humidity production when nectar is removed from flowers. We test whether transpiration contributes to the floral humidity generation of two species previously identified to produce elevated floral humidity, Calystegia silvatica and Eschscholzia californica. Floral humidity production of flowers that underwent an antitranspirant treatment, petrolatum gel which blocks transpiration from treated tissues, is compared to flowers that did not receive such treatments. Gel treatments reduced floral humidity production to approximately a third of that produced by untreated flowers in C. silvatica, and half of that in E. californica. This confirms the previously untested inferences that transpiration has a large contribution to floral humidity generation and that this contribution may vary between species.

Split flow humidity generator equilibration and stability study

Generation and control of humidity in a testing environment is crucial when evaluating a chemical vapor sensor as water vapor in the air can not only interfere with the sensor itself, but also react with a chemical analyte changing its composition. Upon constructing a split-flow humidity generator for chemical vapor sensor development, numerous issues were observed due to instability of the generated relative humidity level and drift of the humidity over time. By first fixing the initial relative humidity output of the system at 50%, we studied the effects of flowrate on stabilization time along with long term stability for extended testing events. It was found that the stabilization time can be upwards of 7 h, but can be maintained for greater than 90 h allowing for extended experiments. Once the stabilization time was known for 50% relative humidity output, additional studies at differing humidity levels and flowrates were performed to better characterize the system. At a relative humidity of 20% there was no time required to stabilize, but when increased to 80% this time increased to over 4 h. With this information we were better able to understand the generation process and characterize the humidity generation system, output stabilization and possible modifications to limit future testing issues.

Calibration of RS41 humidity sensors by using an upper‐air simulator

AbstractThe upper‐air simulator (UAS) was developed at the Korea Research Institute of Standards and Science to test commercial radiosonde sensors under representative conditions. In this framework, humidity generation is performed through a two‐temperature mode in which the temperatures of the saturator and the test chamber are controlled independently. The operation range of the UAS in terms of the temperature, dew/frost‐point temperature, and relative humidity (RH) is −70 to +20°C, −80 to +20°C, and 5%–100%, respectively. The total combined uncertainty of the UAS humidity generation is within 1.1 %RH at a coverage factor k = 2. As a proof of concept, the calibration of Vaisala RS41 humidity sensors is demonstrated. The maximum difference between the humidity measured using the RS41 sensors and UAS reference humidity is approximately 3 %RH at −67°C, which gradually decreases to approximately 1 %RH as the temperature is raised to 21°C. The repeatability of a single RS41 unit and reproducibility of three different units are 0.5 and 0.9 %RH, respectively, in terms of the standard deviation. The uncertainty of an RS41 humidity sensor is 0.9–1.4 %RH (k = 2) at −67°C. Realizing the calibration of commercial radiosondes by using the UAS can enhance the traceability to the International System of Units and emphasize the role of metrology for meteorology and climate research.

Impact of meteorological condition changes on air quality and particulate chemical composition during the COVID-19 lockdown

Stringent quarantine measures during the Coronavirus Disease 2019 (COVID-19) lockdown period (January 23, 2020 to March 15, 2020) have resulted in a distinct decrease in anthropogenic source emissions in North China Plain compared to the paralleled period of 2019. Particularly, 22.7% decrease in NO2 and 3.0% increase of O3 was observed in Tianjin, nonlinear relationship between O3 generation and NO2 implied that synergetic control of NOx and VOCs is needed. Deteriorating meteorological condition during the COVID-19 lockdown obscured the actual PM2.5 reduction. Fireworks transport in 2020 Spring Festival (SF) triggered regional haze pollution. PM2.5 during the COVID-19 lockdown only reduced by 5.6% in Tianjin. Here we used the dispersion coefficient to normalize the measured PM2.5 (DN-PM2.5), aiming to eliminate the adverse meteorological impact and roughly estimate the actual PM2.5 reduction, which reduced by 17.7% during the COVID-19 lockdown. In terms of PM2.5 chemical composition, significant NO3− increase was observed during the COVID-19 lockdown. However, as a tracer of atmospheric oxidation capacity, odd oxygen (Ox = NO2 + O3) was observed to reduce during the COVID-19 lockdown, whereas relative humidity (RH), specific humidity and aerosol liquid water content (ALWC) were observed with noticeable enhancement. Nitrogen oxidation rate (NOR) was observed to increase at higher specific humidity and ALWC, especially in the haze episode occurred during 2020SF, high air humidity and obvious nitrate generation was observed. Anomalously enhanced air humidity may response for the nitrate increase during the COVID-19 lockdown period.

Why Does a High Humidity Level Form in Low-Income Households Despite Low Water Vapor Generation?

This study uses long-term field measurements to quantify the indoor humidity generation rates of low-income households vulnerable to condensation and related problems. We found that the mean internal moisture excess of low-income households in Korea was 4.69 g/m3 higher than those of prior studies. Indoor water vapor generation rates of various activities considering the life style of low-income households were also quantified. The moisture generation rates of the shower and bath were 125.3 g/event and 51.1 g/event, respectively, and showed a similar or lower value compared to the existing results. The moisture generation rate of cooking showed the largest difference due to the residential characteristics of low-income households, such as cooking less frequently due to meal delivery services from the welfare center and the lower number of residents per household. Even though the moisture generation rates of low-income households for certain activities showed lower values compared to the results of prior studies, the indoor conditions were very humid due to the lower ventilation rates and studio-type open floor plan.

Calibration of hygrometers at non-static conditions

The current practice of calibrating humidity sensors at discrete measurement points under static conditions is time-consuming, i.e. expensive, due to the long stabilization times. In order to reduce the calibration time, we introduce a new calibration method based on humidity ramp measurements, i.e. measurements are performed at first while humidity is increased with constant speed and then decreasing with the same speed. A calibration system based on the mixing flow humidity generation principle was developed for generating linear humidity ramps inside a measurement chamber. Two different calibration approaches were investigated. In the first one, high accuracy was targeted with moderate ramp speeds (2 h to 12 h) and a large volume measurement chamber using a chilled mirror hygrometer as a reference. In the second approach, a shorter calibration time was achieved with fast ramp speeds (0.5 h to 2 h) and a small volume chamber using a fast capacitive humidity sensor as a reference. The developed calibration procedure was validated by comparing results of non-static and static calibrations to each other for five different capacitive humidity sensors from two manufacturers. The non-static calibration was found to provide equivalent results compared to the static calibration with a potential of reducing the overall calibration time by up to 50%. Preconditions of the non-static calibration related to the ramp speed and sensors response times are discussed, and an estimation of the calibration uncertainty is given. The main advantage of the developed non-static calibration method is that calibrations can be performed faster and more data on the sensor behaviour is obtained than with the conventional point-wise calibration without any significant increase in uncertainty.

Calibration of a radiosonde humidity sensor at low temperature and low pressure

Relative humidity in upper air is frequently measured using radiosondes at an altitude of up to roughly 35 km. In this study, the calibration of a radiosonde humidity sensor was demonstrated using a humidity generator that can mimic the humidity, temperature, and pressure conditions in upper air. The calibration of the radiosonde humidity sensor was conducted in terms of relative humidity at a temperature range of −70 °C to 20 °C, and at a pressure range of 5 kPa to 101 kPa. Consequently, it was revealed that the radiosonde humidity sensor presents a significant temperature dependency in such a way that indicates lower humidity values than the reference values measured by the generator as temperature is lowered. The deviation from the reference humidity was measured at about 30%rh at −70 °C. However, the effect of low pressure (5 kPa) on the sensor measurement was less than 1%rh. The uncertainty budget on the calibration of the radiosonde humidity sensor, including factors due to humidity generation, correction of temperature effect, pressure effect, and sensor reproducibility, are presented. Consequently, the calibration uncertainty of the humidity sensor was 3.8%rh at the coverage factor k = 2. The calibration capability of the radiosonde humidity sensor demonstrated in this study will provide traceability to the International System of Units (SI) in the humidity measurement in upper air.

Moisture-Driven Power Generation for Multifunctional Flexible Sensing Systems.

Flexible self-powered multifunctional sensing systems provide a promising direction for the development of wearable electronics. Although increased efforts have been devoted to developing self-powered integrated devices, the development of flexible and adaptable sensing systems with miniaturized stable power supplies is highly desirable yet greatly challenging. Herein, an ambient moisture-induced self-powered wearable sensing system was fabricated by integrating a porous polydopamine layer with a hydroxy group gradient (called g-PDA) based moisture-enabled power generator and a flexible pressure sensor. Due to the large amount of gradient-distributed free cations (H+) and locally confined anions produced in wide electrode spaces during hydration of the thin porous g-PDA film, the moisture-induced potential and effective output power density of the g-PDA-based power generator rapidly reaches up to 0.52 V and 0.246 mW cm-2, respectively. Importantly, the voltage output within 120 s only has 6% change, and a continuously open-circuit voltage can be maintained after 1900 s of attenuation, which is a breakthrough for the duration of humidity generation. Finally, a self-powered wearable multifunctional sensing system has been demonstrated to be able to provide real-time monitoring of human physiological signals, without an external power supply, which opens new opportunities for future self-powered multifunctional sensing systems.

THERMAL AND MECHANICAL ANALYSIS OF GRAIN STORAGE SILOS UNDER FORCED AERATION CONDITIONS USING ADVANCED MODELLING METHODS

The most important storage problems in wheat silos are heat and moisture accumulation and there are no early warning systems to know the occurrence of heat and humidity generation. Silo wall and bottom stresses changes are investigated to be suitable indicators for early warning and controlled aeration. Aeration is a popular tool, used to treat and modify the microclimate of grain bulk. A model silo with three horizontal and vertical load cells was constructed for heat and moisture transfer studying under the influence of three different airflow rates and patterns of aerations with three unlike heights of stored wheat during winter season of 2016 in the laboratory of Agricultural Process Engineering, Agricultural Engineering Department, Faculty of Agriculture, Kafrelsheikh University. The three vertical load cells were homogenously distributed to measure the stresses from the three longitudinal prism sections on bottom layer which provides information about mass transfers among longitudinal sections. As by same technique the horizontal load cells afford data about mass transfer among horizontal layers. For heat transfer monitoring, three vertical thermocouples were installed at equal heights. Storage quality indicators are temperature gradient among wheat layers and loads differences among longitudinal and horizontal sections, as the storage system keeps the temperature gradient and vertical loads differences to be at lower levels, and then the system has higher storage efficiency.

Development of a low-temperature low-pressure humidity chamber for calibration of radiosonde humidity sensors

A low-temperature low-pressure humidity chamber has been developed at the Korea Research Institute of Standards and Science for the calibration of radiosonde humidity sensors. The humidity generator operates in a two-temperature and two-pressure mode in which a saturator and a test chamber are separately immersed in two baths. The saturation performance of the saturator is first evaluated at a low temperature (−75 °C) and at atmospheric pressure. In this condition, the uncertainty of the frost-point temperature by the saturator is 53 mK with the coverage factor k = 2. Then, a chilled mirror hygrometer is calibrated for the compensation of low-pressure effects such as a pressure drop along the tubing line inside the hygrometer. Significant differences between the frost-point temperature at the hygrometer inlet and that measured by the hygrometer are observed at a pressure lower than 20 kPa. An empirical formula for compensating the low-pressure effects on the hygrometer is obtained and, subsequently, is used for the validation of the frost-point temperature generated at a low temperature and low pressure in the test chamber. The corresponding uncertainty due to the calibration of the hygrometer including the compensation of low-pressure effects is 306 mK at k = 2. A representative humidity generation and its validation by the hygrometer is demonstrated at a temperature (−70 °C) and two pressures (4.6 kPa and 20 kPa) in the test chamber. Uncertainty budgets on relative humidity in the test chamber are presented from 10 %rh to 40 %rh with a 10 %rh interval at both pressures. Consequently, the combined uncertainty is less than 2%rh (k = 2) which includes uncertainty factors such as the saturation efficiency, the adsorption/desorption hysteresis, the validation by the hygrometer measurement at low pressures, and so on. The newly developed humidity chamber enables the calibration of radiosonde humidity sensors at low temperature and low pressure conditions that mimic upper air environments in a traceable manner to the International System of Units (SI).

Aging and Degradation of Organic Solar Cells Using QUV Accelerated-Weathering Tester

In this paper, we have reported some investigation on the QUV aging of organic solar cells (OSCs). The use of QUV chamber leads to study the effect of cyclic aging on the electrical properties namely PCE, Jsc, FF and Voc under variation of UV irradiation, temperature, humidity and dark. Samples of commercial encapsulated cells supplied by Infinity OPV manufacturer were subjected to 45 cycles (1080 h) of aging. Each cycle of 24 h contains 8 h of illumination with UVA-340 lamp under 50 °C, followed by 4 h of spray (raining) and condensation (humidity generation) at 50 °C, and finished by 12 h of dark. The effect of three different UV irradiation doses (0.83 W/m2, 1.2 W/m2 and 1.3 W/m2) was studied. The degradation process of the OSCs under cyclic aging fits with the earlier finding in the literature and is occurred in two phases with deferent aging rates. The first phase is characterized by the fast decrease of overall electrical properties at the beginning of aging and is due the synergistic effects of rapid variation in the temperature, light and humidity. The second phase is more stable and all the curves reach some saturation. This stabilized phase is the consequence of no bleaching of the semiconductor layer over time. Time constants and constant of degradation were deduced from the first exponential and linear fits of the studied properties. Furthermore, it has been found that the OSCs lose more than 60% of their initial performances, and for some properties like PCE the decrease reaches 80%. This drastic drop of the OSCs performances, associated to the formation of bubbles, indicates that samples undergo very hard bulk degradation.

Humidity generation model by the mixture of air flows

Se presenta el desarrollo de un modelo hibrido para generar humedad que se obtiene con base en el principio de conservacion de masa en un sistema abierto. El modelo tiene dos entradas (aire seco y vapor de agua) que se mezclan en una camara de prueba, y una salida que libera el aire al ambiente. En el modelo general, la humedad se expresa como el cociente de la masa de vapor de agua y la masa de aire seco y mediante relaciones de gases, se obtienen las ecuaciones de humedad relativa y de temperatura de punto de rocio. En estas ecuaciones la humedad depende de seis magnitudes de entrada susceptibles de medirse y controlarse, lo cual hace posible su materializacion. Con el proposito de determinar las mejores condiciones de operacion de un generador de este tipo, se realizo una evaluacion exhaustiva del modelo obtenido mediante variaciones razonables de las magnitudes de entrada. Como resultado de la evaluacion del modelo, se encontro que la variacion simultanea de dos o mas magnitudes permite generar un amplio intervalo de humedad relativa (≈ 0% a 99 %) y de temperatura de punto de rocio (desde trazas de humedad hasta la saturacion), que es superior al cubierto por los metodos de dos presiones, dos temperaturas y de flujo dividido usados de manera individual. El modelo se puede desarrollar sin complicaciones y tiene varias aplicaciones entre las que se encuentran el control de atmosferas de humedad en la industria farmaceutica, aire acondicionado, en la fabricacion de semiconductores, asi como en laboratorios de calibracion y centros de investigacion, entre otros

Correlation Effects in the Uncertainty Estimation of Two-Pressure Humidity Generators

This paper presents an analysis of the correlation effect in the uncertainty estimation of a system for humidity generation based on the two pressures principle. In order to compare the validity of the calculations, two methods for evaluating uncertainty, including the correlation between the input variables, were used. The first one was the classical approximation based on the applicability of the central limit theorem, while the second consisted of the propagation of the input distributions using Monte Carlo simulations. The obtained results show that the usual assumption of negligible correlations between the input variables is valid for uncertainty levels in calibrations of hygrometers.

On-site calibration system for trace humidity sensors

A portable device for calibration of trace humidity sensors and an adopted calibration procedure have been developed. The calibration device is based on humidity generation by permeating water through polymeric membrane tubes. Water vapour transmission rates for various polymers were experimentally determined in order to select the most suitable polymeric material. The developed trace humidity generator consists of a gas-flow polymeric hose immersed in a water reservoir thermostated by a sensor-controlled heater. Mole fractions of water vapour between 1μmolmol−1 and 350μmolmol−1 (equivalent to frost-point temperatures from −76°C to −31°C) were generated by varying either the operating temperature or gas flow. The operating temperature can be varied from 20°C to 60°C and kept stable within 0.1K. Uncertainty analysis indicated that the trace humidity generator produces gas flows of constant humidity amounts with a relative expanded uncertainty less than 3.4% (k=2) of the generated value.

High‐accuracy measurements of the vapor pressure of ice referenced to the triple point

AbstractThe vapor pressure of hexagonal (Ih) water ice was measured over the temperature range 175 K to 253.4 K and referenced to the value at the triple point of water. This experiment combined a highly accurate humidity generation system containing an ice‐coated saturator (millikelvin‐level temperature control) to provide humidified streams of nitrogen to a cavity‐enhanced laser absorption spectrometer. The measured ice vapor pressures had relative standard uncertainties ranging from 0.4% to 0.7% over the entire temperature range. We demonstrate that these measurements validate thermodynamic correlations for ice vapor pressure based on integration of the Clapeyron equation. Moreover, they also indicate that some commonly used vapor pressure correlations are inaccurate and should be avoided.

Design and Performance of the New NIST Hybrid Humidity Generator

Abstract:A new humidity generator has been constructed at the National Institute of Standards and Technology and is now fully operational. The NIST Hybrid Humidity Generator (HHG) has replaced the Two-Pressure (2-P) Humidity Generator Mark II as the NIST primary humidity generation standard for frost/dew points from −70 °C to +25 °C using calibration gas flows up to 150 standard liters per minute. The HHG extends the NIST humidity generation range up to 85 °C, and outperforms the 2-P Generator in terms of accuracy. The HHG combines the two-pressure and divided-flow humidity generation techniques (hence the name “hybrid”). The centerpiece of the HHG is a heat-exchanger/saturator that is immersed in a temperature-controlled bath stable to within 1 mK. A precisely regulated pre-saturation process minimizes sensible and latent heat loading on the final saturator. For dew/frost point temperatures above −15 °C, the two-pressure principle is employed. For frost points at or below −15 °C, the divided-flow method ...

An improved method to validate the relative humidity generation in sorption balances

Sorption balances are instruments in which samples are weighed as they are exposed to a programmed relative humidity (RH). Such instruments are used to measure sorption isotherms and to study solid–vapour interaction. There are different methods to validate the performance of the RH generation in such instruments by charging them with saturated salt solutions and ramping/stepping the RH past the deliquescence RH of the salts. In this paper, an improved approach to perform validation is presented, where the RH is kept stepwise constant at a quasi-randomly chosen set of RH-values above and below the deliquescence RH. From the rates of change of mass as a function of RH, it is possible to calculate the RH at which deliquescence takes place. This alternative method gives similar results as the slow ramp method, but it is less sensitive to disturbances and is less time consuming.

Reducing the Uncertainty of Industrial Trace Humidity Generators through NIST Permeation-Tube Calibration

Permeation-tube moisture generators (PTGs) are commonly used by the semiconductor industry as transfer standards for the calibration of hygrometer systems measuring trace amounts of water vapor in gases (water vapor mole fractions typically below 1 × 10−6). They are relatively simple devices that generate a steady stream of humidified gas by diluting water vapor delivered at a constant rate from a permeable capsule with precisely metered purified gas, usually nitrogen. Here a new calibration service enabling the measurement of PTG permeation rates directly in terms of NIST primary standards of trace humidity generation is described. Rather than using commonly employed gravimetric methods for permeation-tube calibration, the method applied here links the permeation rate of the permeation tube to the thermodynamic properties of ice. Using a hygrometer based on cavity ringdown spectroscopy, we compare the water vapor concentrations produced by the NIST low frost-point generator (LFPG) and a specially constructed PTG containing the permeation tube undergoing calibration. A least squares fit of the data determines the permeation rate of the tube under test. We describe the calibration system, experimental procedure and present sample calibration data. The expanded relative uncertainty of NIST permeation-tube calibrations is 1.8% with a coverage factor k = 2, dominated by the Type A uncertainties.

Low-uncertainty H 2O line intensities for the 930-nm region

We measured room-temperature H 2O spectra of the 3 ν polyad within the wave number range 10 603 cm −1 to 10 852 cm −1 using frequency-stabilized cavity ring-down spectroscopy. More than 70 transitions, divisible into two groups based on their relative intensities (strong and weak) were investigated. For the 23 lines comprising the set of strong transitions, the water vapor sample was prepared as a dilute mixture in a steady flow of N 2 carrier gas, and the measurement of the water vapor sample number density was linked to primary methods of humidity generation. For these strong transitions, the measured line intensities were within 1% of previous measurements. The line intensity measurements of the weaker H 2O transitions, were made on samples of static pure water vapor, and these results were systematically greater than previous measurements by approximately 20%.

Improvement of flow and pressure controls in diffusion-tube humidity generator: Performance evaluation of trace-moisture generation using cavity ring-down spectroscopy

A system of flow and pressure controls for a magnetic suspension balance/diffusion-tube humidity generator (MSB/DTG) has been developed to realize a humidity standard in the trace-moisture region. The system essentially consists of a pressure regulator combined with a piezo valve, and adopts a simple stepwise change in the total flow rate. It has been demonstrated that the uncertainty of evaporation rates is greatly reduced by applying buoyancy correction to mass data measured with the MSB. Using the system and buoyancy-corrected data, the negative effect on the MSB/DTG observed upon changing the total flow rate become negligible. The relative standard uncertainty of total flow rates is evaluated using mass flow meters composed of critical flow Venturi nozzles to be less than or equal to 0.22%. The uncertainty of humidity generation has been significantly reduced by improvements introduced in this work. A comparison between humidity generated with the DTG and humidity measured with a moisture analyzer (MA) based on cavity ring-down spectroscopy is presented in the amount-of-substance fraction range between 10 nmol/mol and 250 nmol/mol. The results of the comparison confirm that the DTG is capable of producing a trace-moisture gas down to approximately 10 nmol/mol, and of easily varying and controlling the amount-of-substance fraction of water using the system. The sources of bias observed in the MA reading are attributable mainly to systematic errors in the temperature of the absorption cell and absorption cross section used to calculate the water concentration with the MA.