Air Flow Humidity Research Articles

Indoor Airflow Distribution in Repository Design: Experimental and Numerical Microclimate Analysis of an Archive

The majority of cultural heritage is stored in archives, libraries and museum storage spaces. To reduce degradation risks, many archives adopt the use of archival boxes, among other means, to provide the necessary climate control and comply with strict legislation requirements regarding temperature and relative air humidity. A strict ambient indoor climate is assumed to provide adequate environmental conditions near objects. Guidelines and legislation provide requirements for ambient indoor climate parameters, but often do not consider other factors that influence the near-object environment, such as the use of archival boxes, airflow distribution and archival rack placement. This study aimed to provide more insight into the relation between the ambient indoor conditions in repositories and the hygrothermal conditions surrounding the collection. Comprehensive measurements were performed in a case study archive to collect ambient, local and near-object conditions. Both measurements and computational fluid dynamics (CFD) modeling were used to research temperature/relative humidity gradients and airflow distribution with a changing rack orientation, climate control strategy and supply as well as exhaust set-up in a repository. The following conclusions are presented: (i) supplying air from one air handling unit to multiple repositories on different floors leads to small temperature differences between them. Differences in ambient and local climates are noticed; (ii) archival boxes mute and delay variations in ambient conditions as expected—however, thermal radiation from the building envelope may have a large influence on the climate conditions in a box; (iii) adopting night reduction for energy conservation results in an increased influence of the external climate, with adequate insulation, this effect should be mitigated; and (iv) the specific locations of the supply air and extraction of air resulted in a vertical gradient of temperature and insufficient mixing of air, and adequate ventilation strategies should enhance sufficient air mixing in combination with the insulation of external walls, and gradient forming should be reduced.

Design, construction, and testing of an accurate low-cost humidistat for laboratory-scale applications

Stable and precise control of humidity is imperative for a wide variety of experiments. However, commercially available humidistats (devices that maintain a constant humidity) are often prohibitively expensive. Here, we present a simple yet effective humidistat for laboratory-scale applications that can be easily and affordably (<€250) constructed based on an Arduino Uno as microcontroller, a set of proportional miniature solenoid valves, a gas washing bottle, and a humidity sensor. The microcontroller implements a PID controller that regulates the ratio of a dry and humid airflow. The design and implementation of the device, including a custom driver circuit for the solenoids, are described in detail, and the firmware is freely available online. Finally, we demonstrate its proper operation and performance through step response and long-term stability tests, which shows settling times of approx. 30 s and an attainable relative humidity range of 10–95%

Compressible pressure-based Lattice-Boltzmann applied to humid air with phase change

A new compressible pressure-based Lattice Boltzmann Method is proposed to simulate humid air flows with phase change. The variable density and compressible effects are fully resolved, effectively lifting the Boussinesq approximation commonly used, e.g. for meteorological flows. Previous studies indicate that the Boussinesq assumption can lead to errors up to 25%, but the model remains common, for compressible models often suffer from a lack of stability. In order to overcome this issue, a new pressure-based solver is proposed, exhibiting excellent stability properties. Mass and momentum conservation equations are solved by a hybrid recursive regularized Lattice-Boltzmann approach, whereas the enthalpy and species conservation equations are solved using a finite volume method. The solver is based on a pressure-based method coupled with a predictor–corrector algorithm, and incorporates a humid equation of state, as well as a specific boundary condition treatment for phase change. In particular, boundary conditions that handle mass leakage are also proposed and validated. Three test cases are investigated in order to validate this new approach: the Rayleigh–Bénard instability applied to humid air, the atmospheric rising of a condensing moist bubble, and finally the evaporation of a thin liquid film in a vertical channel. Results indicate that the proposed pressure-based Lattice-Boltzmann model is stable and accurate on all cases. • New compressible pressure-based Lattice Boltzmann Method with modified equation of state for humid air and phase change. • New boundary conditions for mass conservation in Lattice-Boltzmann method. • Compressibility effects fully taken into account (no Boussinesq approximation).

Performance Assessment of an Open Thermochemical Heat Storage (TCHS) System Using Composite Salt Hydrates

Heat storage performance of an open thermochemical heat storage (TCHS) system using composite salt hydrates of Wakkanai siliceous shale (WSS) - 9.6 wt.% LiCl was investigated numerically. A two-dimensional model considering the combined heat and mass transfer was developed. The calculation results were validated by the experimental results obtained in our previous study. The inlet air temperature, inlet air relative humidity, humid air flow rate, the ratio of the thickness of air channel and the thickness of composite solid wall, and length of the TCHS unit were evaluated to evaluate the heat storage performance. When the ratio of the thickness of air channel and the thickness of composite solid wall is 5 and the length of the heat storage unit is 0.1 m, the volumetric heat storage density of the open TCHS system can reach 510 MJ/m3.

The effect of magnetic field on the performance improvement of a conventional solar still: a numerical study.

Due to growing demand for potable water, the improvement of fresh water production systems such as conventional solar stills is a crucial issue. Conventional solar stills are one of the simplest methods of the production of fresh water from saline water; however, they are fairly low-performance devices. Since oxygen is a paramagnetic gas, the humid airflow in a conventional solar still can be controlled by an externally imposed magnetic field. Therefore, this paper presents the effect of magnetic field on the performance improvement of a conventional solar still as a novel technique. The governing equations of the problem are discretized by the finite volume method. The impacts of the applied magnetic field arising from a multilayer solenoid on the streamlines patterns, temperature and mass fraction contours, the production rate of water ([Formula: see text]), and the average heat transfer rate (Nu) are presented at five specified times (cases). The influences of important factors such as intensity (0≤NI≤100000) and location of the magnetic field (Xc=0.15, 0.49, and 0.83) on the heat and mass transfer rates are explored. It is found that the production rate of water and heat transfer rate are increasing functions of magnetic field intensity. For the applied magnetic field with NI = 105and Xc = 0.83m, water productivity and convective heat transfer rate can be increased by about 43%, 38%, 41%, 40%, and 48% for cases 1, 2, 3, 4, and 5, respectively.

The interaction of the complex transfer processes in the phase transformations regimes of a water droplets

In this article the phase transformations of the water droplets in humid air flow are numerically modelled. The air temperature varies from 20°C to 1000°C, and the volume fraction of water vapor reaches up to 0.4. The droplet surface temperature dynamics defined by a numerical scheme which is based on by the fastest descent method. The interaction of complex heat and mass transfer processes has been investigated in the consistently changing water droplets condensation, transit and equilibrium evaporation regimes. Determination of droplets instantaneous temperatures in the iteration cycles is controlled by calculated heat fluxes balance condition, flowing toward and from the droplet surface, which must correspond to 99.95%. The reliability of the numerical method was confirmed when comparing the calculated water droplets equilibrium evaporation temperature in humid air with the wet bulb thermometer temperature, and with the experiments data. In the case of combined heating a calculated water droplets equilibrium evaporation vapor flux correlates well with other author's experimental data and modeling results. The numerical researches are emphasized specially for cases of water vapor condensate spraying in biofuel combustion technologies. The water droplet heat transfer as well as phase transformations transit and equilibrium evaporation processes were modelled in cases of convective and combined convective-radiative heating. In semi-transparent liquid the impact of absorbed radiation flux for water droplet complex transfer processes interaction was evaluated.

Experimental comparison analysis of two heat transfer enhancement methods on a thermochemical reactor

Abstract This paper experimentally investigates the performance of a thermochemical reactor for space heating using two heat enhancement methods, copper fins and copper plates. It is evaluated under laboratory conditions with the varying inlet air relative humidity and inlet air flow rate. The evaluated parameters are the reactor air pressure drop, outlet air temperature and outlet water temperature. While improving the reactor performance, the study presents comparative reactor performance of the two methods. The study shows that the copper plate reactor achieves a better desorption performance than the copper fin reactor. In charging, the copper plate reactor can reach the maximum outlet air temperature lifts at 95.1°C in 0.35 h, which is 12.3°C higher than copper fin reactor under the same conditions. In discharging, the peak reactor outlet air temperatures for the two reactors are found under different inlet air flow rate for the different internal air flow characteristics resulted from the copper fins and plates. Also, the copper fin reactor presents higher pressure drop than the copper plate reactor. Additionally, the copper fin reactor presents a slightly higher outlet water temperature in discharging than the plate reactor for the relatively larger thermal contact area between the copper fins and water pipe. Further research should be conducted in improving the reactor performance including reducing the heat loss, reactor optimisation and identifying suitable operating conditions.

Spatial-Temporal Distribution of Summer Extreme Precipitation in South China and Response of Tropical Ocean

In the study, the summer extreme precipitation in South China is divided into early rainy season (MJ) and late rainy season (JA). The percentile method (95%) is used to define the extreme precipitation threshold. Based on the international general definition method of extreme precipitation threshold: percentile method (95%), the extreme precipitation thresholds in flood season before and after South China are defined respectively. The total amount and frequency of extreme precipitation in flood season before and after 1979-2014 are calculated in this paper. The change trend of the two indicators is basically the same, and the two indicators have obvious interannual variation and an upward trend. According to the results of wavelet analysis of extreme precipitation frequency, the frequency of extreme precipitation in the first flood season mainly has a period of 3 - 5 years, while the frequency of extreme precipitation in the later flood season has a significant period of 6 - 8 years. The spatial distribution of extreme precipitation before and after the flood season shows that the extreme precipitation in the former flood season is mainly distributed in the central part of Guangdong, the northeast of Guangxi and the western part of Fujian, and the extreme precipitation in the latter flood season mainly occurs in the southern coastal area. The results show that there are different tropical SST regions affecting the extreme precipitation in South China. The former flood season is mainly the tropical Indian Ocean warm SST, and the latter flood season is mainly the tropical Pacific warm SST. The tropical Indian Ocean SST stimulates the anticyclonic anomaly over the South China Sea, which brings the southwest warm and humid air flow into South China, resulting in the increase of extreme precipitation in the first flood season of South China; the tropical Pacific SST stimulates the cyclonic anomaly over the South China Sea, which reduces the water vapor outflow caused by the seasonal northward jump of the subtropical high in South China, resulting in the increase of extreme precipitation in the later flood season of South China.

Методика расчета длины участка течения ненасыщенного влажного воздуха в канале оросителя вентиляторной градирни

In the channels of mechanical-draft cooling tower sprinklers, a saturated air flow section may appear under certain initial conditions, the mass transfer intensity in which is limited by the steam content in the saturated air. For correctly calculating the heat and mass transfer processes in the cooling tower channel, it is necessary to have a method for determining the unsaturated air flow section length. Publications devoted to studying water cooling processes in the channels of mechanical-draft cooling tower sprinklers do not contain an assessment of the unsaturated air flow section length. A method for determining the unsaturated humid air flow section length in the mechanical-draft cooling tower sprinkler channels is proposed, which is based on the well-known criterion equations for calculating the heat transfer and mass transfer coefficients. The effect the initial air parameters have on the unsaturated air section length is studied, and graphic dependences of the unsaturated air section length are drawn up for each of the analyzed parameters. It is shown that the unsaturated humid air flow section length increases with increasing the initial air temperature. It is also found that the unsaturated air flow section length decreases with a growth in the relative air humidity. An increase in the air flow rate with a constant water flow rate leads to an increase in the unsaturated air flow section length. For the considered sprinkler channel, the saturated air region exists at an air temperature of 15°C and below, and for air temperatures above 25°C there is no saturated air flow section. It is shown that the conclusions drawn about the effect the initial air parameters have on the relative change in the unsaturated air flow section length are valid for channels of various shapes and geometric sizes. The proposed methodology and the results obtained can be used in designing mechanical-draft cooling towers and estimating their efficiency.

Features and Possible Causes of the Extreme Precipitation Anomaly in China During Winter 2019/2020

In this paper, the features and possible causes of extreme precipitation in the winter of 2019/2020 in China are investigated based on the observational station daily dataset provided by the China Meteorological Administration and the ECMWF ERA5 reanalysis dataset. Record-breaking precipitations are found in most areas of China in the winter of 2019/2020, particularly for the north of China. The magnitude of precipitation in south (north) of China in 2019/2020 increase 0.39mm/day (0.15mm/day), about 39.0% (105.5%) compared with the climatological mean. Moisture budget analysis shows that contributions of atmospheric circulation anomaly on horizontal moisture advection and total moisture flux convergence are primarily responsible for the positive anomalies of precipitation in China. Further analysis suggests that the weakened East Asian Trough and the anti-cyclone circulation anomaly over the Sea of Japan favor the transportation of low-level warm and humid airflow from the Northwest Pacific and the East China Sea to the north of China. Meanwhile, the westward movement of the Subtropical High and the Southern Branch Trough anomalies transport low-level warm and humid air from the Bay of Bengal and the South China Sea to south of China. The warm moist air flows northeastward from the East China Sea, Bay of Bengal and the South China Sea while the climatological cold wind flows southeastward, which causes the increase of local precipitation in the winter of 2019/2020. In consideration of the fact that stratospheric polar vortex anomaly has a process of downward propagation to the troposphere, it is of great significance to study the changes of the stratosphere and the relationships between stratosphere and troposphere.

Influence of the environmental relative humidity on the inflammatory response of skin model after exposure to various environmental pollutants

The skin is an essential barrier, protecting the body against the environment and its numerous pollutants. Several environmental pollutants are known to affect the skin, inducing premature aging through mechanisms including oxidative stress, inflammation, and impairment of skin functions. Even climate conditions can impact the skin. Therefore, using a Reconstructed Human Epidermis (RHE), we tested the effect of two samples of fine particulate matters (PM0.3-2.5 – one metals-rich sample and the other organic compounds-rich), two Volatile Organic Compounds mixtures (VOCs – from a solvent-based paint and a water-based paint) and Tobacco Smoke (TS). All pollutants affected cellular functionality, but to a lesser extent for the water-based paint VOC. This effect was enhanced when RHE were preconditioned for 2 h by a semi-dry airflow (45% relative humidity) before pollutants application, compared to preconditioning by a humid airflow (90% relative humidity). In the absence of preconditioning, IL-1α, IL-6, IL-8, and RANTES were almost systematically induced by pollutants. When RHE were preconditioned by a semi-dry or humid airflow before being subjected to pollutants, the increase of IL-1α, IL-8, and RANTES falls into two groups. Similarly to RHE not treated with pollutants, RHE treated with VOCs after preconditioning by a semi-dry airflow showed increased IL-1α, IL-8, and RANTES release. On the contrary, RHE treated with PM or TS after preconditioning by a semi-dry airflow show a lower increase in IL-1α, IL-8, and RANTES compared to preconditioning by a humid airflow. The effect of real environmental relative humidity conditions of the air, combined with acute exposure to various environmental pollutants, seemed to relate mainly to structural changes of the skin, determining the outcome of the inflammatory response depending on the physicochemical characteristics of pollutants.

Characterizing thermal tolerance in the invasive yellow-legged hornet (Vespa velutina nigrithorax): The first step toward a green control method.

The yellow-legged hornet, Vespa velutina nigrithorax (Hymenoptera: Vespidae, Lepeletier 1836), is native to Southeast Asia and has been unintentionally introduced in France. The species is spreading in many areas of the world. The European Union has classified V. velutina as a species of concern because the hornet significantly affects beekeeping activities, mostly by preying honeybees (Apis mellifera) at beehive entrances. No current control method is simultaneously eco-friendly and effective. Here, we aimed to develop a greener technique for destroying V. velutina nests, inspired by a defense behavior used by the eastern honeybee (Apis cerana), the “heat ball”. In the laboratory, we tested how V. velutina of different sexes, castes, and developmental stages responded to different heat exposure systems employing a range of temperature levels. Overall, the time of death decreased as temperature increased. Hornets died faster when the temperature was gradually increased than when it was instantaneously increased; larvae seemed to be more thermally tolerant. The most promising and potential technique for quickly destroying hornet nests may be steam injection, as the humid airflow system killed all hornets within 13 seconds, and therefore could be a good candidate for a green nest control method.

Technology proposal and experimental study on an indirect evaporative cooling technology based on ultrasonic atomization

To improve the ventilation and air-conditioning energy efficiency of buildings in hot and dry climates, this paper proposed and experimentally investigated an indirect flash evaporative cooling (IFEC) technology combining plate heat exchanger with ultrasonic atomizer. Compared with traditional indirect evaporative cooling (IEC) technology, working air is humidified to be over-saturated by ultrasonic atomizer in the IFEC technology which enhances water evaporation efficiency and reduces thermal resistance between working air/water and product air. The prototype and experimental setup units of the IFEC were developed to investigate its wet-bulb effectiveness, dry-bulb effectiveness, cooling capacity and thermal resistance under hot/dry and warm/dry climates. Results show the IFEC prototype could supply product air with temperatures of 3–7 °C lower than indoor air, which indicated the IFEC could not only fulfill the incoming outdoor air cooling load, but also provide additional cooling capacity for indoor environment. The wet-bulb effectiveness and dry-bulb effectiveness were measured to be 0.80–0.92, 117%–254% respectively. The wet-bulb effectiveness is higher than existing single stage IEC technology. Sensitivity analysis show the outlet product air temperature is dominantly affected by working air humidity ratio, and the cooling capacity is affected by both working air humidity ratio and airflow rates.

Tropical Cyclones and Possible Winter Thunderstorms on Kamchatka

The influence of tropical cyclones on the thunderstorm activity on the Kamchatka peninsula for winter thunderstorms in the 2008–2018 period is studied. The temporal variations of the quasi-static electric field and meteorological values at the Paratunka Observatory of the Institute of Cosmophysical Research and Radio Wave Propagation (IKIR) of the Far Eastern Branch of the Russian Academy of Sciences (φ = 52.97° N; λ = 158.25° E) and data on the solar, seismic, and cyclonic activities available on the INTERNET are used as an indicator of thunderstorm activity. It is shown that, in addition to from solar flares, which are accompanied by increased radiation in the visible and infrared spectra, the infrared radiation from a series of closely located epicenters of average-intensity earthquakes, as well as distant tropical cyclones in the Pacific Ocean, can be a source of powerful flows of warm and humid air for the formation of thunderstorm activity.

Water Molecule-Triggered Anisotropic Deformation of Carbon Nitride Nanoribbons Enabling Contactless Respiratory Inspection

The exploitation of the interaction between nanostructured matter and small molecules, such as H2O at interfaces via dynamic hydrogen bonding, is essentially the key for smart, responsive nanodevic...

Heat and mass transfer during ethanol evaporation on the walls of a flat channel at forced convection of humid air

• The process of joint heat and mass transfer during the flow of moist air in a flat channel at ethanol evaporation on the walls was studied. A similarity in distributions of velocity, temperature, and component concentration profiles has been found. • The contribution of the heat flux components to the total energy exchange on an adiabatic wall has been determined. It was found that with an increase in the moisture content, the contribution of the convective component decreases. • Condensation of steam intensifies the process of ethanol evaporation, as a result of which the mass flows of water and ethanol vapors increase with increasing inlet air humidity. • The use of ethanol as an evaporative agent allows obtaining of the high values of the air cooling parameter, including those at high humidityφ in → 100%. The results of numerical investigation of heat and mass transfer in the laminar flow of humid air in a plane-parallel channel with adiabatic walls from the surface of which ethanol is evaporated are presented. The main attention is paid to studying the influence of air humidity at the inlet in the entire range of its change from absolutely dry to fully saturated state ( φ = 0 ÷ 100 % ) on the heat and mass transfer intensity and cooling efficiency. It has been established that ethanol evaporation and steam condensation occur simultaneously on the channel walls. The relationship between the components of the heat and diffusion flows on the wall is determined depending on the initial air humidity. An increase in the humidity of steam at the channel inlet is accompanied by an increase in the gas temperature at the outlet of the evaporation cell and, accordingly, deterioration in the cooling efficiency. Nevertheless, even when a steam-air mixture in the saturation state ( φ = 100 % ) with ethanol as an evaporation agent is fed to the cell inlet, the efficiency of such a cell remains high and approximately equal to the theoretical limit of water evaporation into dry air.

Dropwise condensation of humid air - Experimental investigation and modelling of the convective heat transfer

In this investigation dropwise-condensation heat transfer of out of a turbulent flow of humid air is experimentally investigated. The test section consists of a horizontal channel, sized 12 × 32 × 750 mm. The condensation takes placed on a 9 × 6 mm sized section of the vertical channel wall. A model based on the analogy of heat and mass transfer - previously used in the context of filmwise condensation - is adopted in order to describe the data obtained for varying bulk Reynolds numbers (3000–22000), temperatures (36∘C–55∘C) and relative humidities (36%–55%). Modifications are made in order to capture the effect of fog formation within the mixture and the enhancement of the area available for heat transfer induced by the droplets on the substrate. The formulation of the model is intended to be easily adoptable to other geometries, boundary conditions, types and orientations of the substrates. Previous investigations of this group were focused on the thermal resistance of the condensate. Based thereon, the present modelling completes the former approach, resulting in a model capable of predicting the total heat transfer coefficients of dropwise condensation from humid air. The predictions are validated using own experimental data as well as external data.

Experimental study of moist air flow in the gap between the aircraft\u2019s fuselage and its cabin wall

We carried out an experimental study on the moisture transfer and the heat transport in warm and humid air flows between the cabin lining and the fuselage skin. The measurements were performed in a rectangular gap channel, representing the space between fuselage and cabin wall. Long-term measurements were performed for three configurations: without insulation, with fibreglass blanket and with melamine resin foam blanket. To simulate realistic flight conditions in a laboratory setup, we applied a concept of scaling. This concept is intended to guarantee similitude between the real flight conditions and the laboratory experiment. The results reveal that without insulation, the moisture transfer rate is much higher compared to the configurations with insulation blankets. With insulation, most of the water evaporates during ground conditions and just a small amount is entrapped in the insulation. Without insulation, just a small part of the frozen water evaporates on the ground. When comparing the two insulation blankets, it is found that they both have a similar heat transmittance coefficient. However, the condensation rate of the water and the resulting accumulation of water are significant, higher for the fibreglass blanket.

Experimental and modeling investigations of dropwise condensation out of convective humid air flow

In this work, experimental and modeling investigations of convective dropwise condensation from moist air are carried out for the mechanistic understanding of the influence of non-condensable gas. For modeling, different droplet growth models in the presence of non-condensable gas are firstly developed by treating the droplet as an isolated form. During dropwise condensation, the presence of non-condensable gas brings some specific condensation characteristics, including the interaction effect between droplets and convection mass transfer. However, those characteristics cannot be reasonably captured by the droplet growth model. In this work, the distributed point sink method and the droplet Sherwood number are used to evaluate the inter-droplet interaction and convection mass transfer, respectively. Combining those progresses, the droplet growth rate is predicted and the prediction is evaluated by the measurements. Based on the accurate prediction for the droplet condensation rate, a semi-analytical modeling method is released to predict convective dropwise condensation of moist air. It considers the latent heat by condensation and the sensible heat by forced convection. Finally, this work presents the direct comparisons of the overall heat flux measured in experiments and the prediction. Furthermore, mechanistic understanding is discussed simultaneously and conclusively. Throughout this work, we highlight the reduction (the diffusion resistance of water vapor and the inter-droplet interaction) and enhancement (convection mass transfer) factors for dropwise condensation in the presence of non-condensable gas. In addition, in the case of this work, large droplets are more beneficial for heat transfer of dropwise condensation.

Humidity measurement of high temperature and high humidity air flow by TDLAS

Humidity measurement of high temperature and high humidity air flow by TDLAS