Increasing Air Humidity Research Articles

Airside thermal and hydraulic characteristics of compact bare tube heat exchanger under dry and wet conditions

An experimental study was conducted to investigate the thermal and hydraulic performance of a compact bare tube heat exchanger, under both dry and wet condition. Chilton–Colburn j and f power law correlations were developed for Reynolds number range of 562–1266. Discrepancies between experimental data and new correlations are within ±2%. In wet mode, experimental conditions were varied by two inlet air humidity levels, three air flow rates and three water flow rates. From the experimental results, it was found that the heat transfer performance (j factor) and friction (f factor) decrease as air flow rate increases. Heat transfer performance decreases and friction increases slightly as inlet air humidity increases. But the changes are insensitive. Mass transfer (jm factor) slightly decreases as air humidity increases. The effect of inlet air humidity, air flow rate and water flow rate on total heat transfer capacity, sensible heat, latent heat and pressure drop are discussed. Chilton–Colburn j, jm and f power law correlations were developed for Reynolds number range of 315–1080 under wet condition, with maximum deviation of ±10%, ±7% and ±7%.

Factors determining the surface oil concentration of encapsulated lipid particles—impact of the spray drying conditions

The impact of spray drying conditions on encapsulated rapeseed oil was investigated regarding the encapsulation efficiency (EE). The drying rate was modified by the solid content (25–55% w/w) of atomized feed droplets, the inlet temperature (140–220 °C) and relative humidity (0.12–1.57%) of the drying air. The moisture, aw, bulk and tapped density, particle size, and EE were analyzed. An accelerated drying rate due to a higher solid content and inlet temperature as well as a slower drying induced by an increased air humidity resulted in larger particle and more efficient encapsulation. A higher EE was obtained with increasing particle size which is in accordance with a theoretical EE calculated based on the particle- and oil droplet diameter.

Terrestrial isopods as bioindicators for environmental monitoring in olive groves and natural ecosystems

ABSTRACTTerrestrial isopods (Crustacea: Isopoda: Oniscidea) are an important component of biodiversity as they constitute useful bioindicators for monitoring environmental quality in a variety of natural and agricultural ecosystems. In the present study, the predictive strength of several important components of biodiversity (e.g. herbaceous and woody plants, etc.) and agro-environmental factors for isopod species richness in each management system of olive groves and a natural ecosystem in central Greece was investigated. Our study highlights an increase in isopod species richness with increasing air humidity, woody plant species richness and soil organic matter in organic olive groves. It is noteworthy that woody plant species richness could be utilised as the best candidate for monitoring isopod species richness. In the conventional olive groves, isopod species richness decreases possibly due to herbicide and inorganic fertiliser application. In abandoned olive groves, isopod species richness increases with increasing soil plant litter and pH. Moreover, soil organic matter has been proved to be a positive indicator of isopod species richness in maquis ecosystems. The species Porcellio laevis can be regarded as an indicator for organic olive groves. Conclusively, this paper contributes to the integration of biodiversity conservation with ecologically sustainable agriculture, conservation of agroecosystem and natural ecosystem services and preserving landscape.

Energy efficiency of exhaust air heat recovery while controlling building air humidity: A case study

One modern method of lowering building energy use is heat exchange between outgoing and incoming air. Exhaust air moisture (partly) condenses in the heat exchanger, giving liquid water to be removed. With low absolute humidity of inlet air especially at low outdoor temperatures, a significant drying effect results for the air inside the building. Increasing air humidity by, for example, spraying water or increasing watering of plants will give an energy penalty. This paper presents an analysis of the energy efficiency (recovered versus input exergy) of a modern house equipped an exhaust air heat recovery system and external heating supplied by a geothermal heat pump. Indoor temperature is 22 °C and relative humidity is 50 or 30%. Temperature and humidity of inlet air and ventilation flow rates are variable and the effects on power use by the heat pump are assessed. Results show that without moisture recirculation a water loss up to 1 kg/h from the building may occur. Several kWh of electricity may be consumed daily by a (geothermal) heat pump supplying heat depending on outdoor temperature, and indoor and outdoor air humidity. Besides water consumption, this may imply 10–15% of total electricity use.

Influence of air humidity on 248-nm ultraviolet laser pulse filamentation.

At first glance, the amount of water molecules naturally contained in humid air is negligibly small to affect filamentation of ultrashort laser pulses. However, here we show, both experimentally and numerically, that for ultraviolet laser pulses with 248nm wavelength this is not true. We demonstrate that with increase of air humidity the plasma channels generated by the ultraviolet laser pulses in air become longer and wider, while the corresponding electron density in humid air can be up to one order of magnitude higher compared to dry air.

Leaf structural and hydraulic adjustment with respect to air humidity and canopy position in silver birch (Betula pendula).

Climate change scenarios predict an increase in air temperature and precipitation in northern temperate regions of Europe by the end of the century. Increasing atmospheric humidity inevitably resulting from more frequent rainfall events reduces water flux through vegetation, influencing plants' structure and functioning. We investigated the extent to which artificially elevated air humidity affects the anatomical structure of the vascular system and hydraulic conductance of leaves in Betula pendula. A field experiment was carried out at the Free Air Humidity Manipulation (FAHM) site with a mean increase in relative air humidity (RH) by 7% over the ambient level across the growing period. Leaf hydraulic properties were determined with a high-pressure flow meter; changes in leaf anatomical structure were studied by means of conventional light microscopy and digital image processing techniques. Leaf development under elevated RH reduced leaf-blade hydraulic conductance and petiole conductivity and had a weak effect on leaf vascular traits (vessel diameters decreased), but had no significant influence on stomatal traits or tissue proportions in laminae. Both hydraulic traits and relevant anatomical characteristics demonstrated pronounced trends with respect to leaf location in the canopy-they increased from crown base to top. Stomatal traits were positively correlated with several petiole and leaf midrib vascular traits. The reduction in leaf hydraulic conductance in response to increasing air humidity is primarily attributable to reduced vessel size, while higher hydraulic efficiency of upper-crown foliage is associated with vertical trends in the size of vascular bundles, vessel number and vein density. Although we observed co-ordinated adjustment of vascular and hydraulic traits, the reduced leaf hydraulic efficiency could lead to an imbalance between hydraulic supply and transpiration demand under the extreme environmental conditions likely to become more frequent in light of global climate change.

О ВЛИЯНИИ ПРОЦЕССОВ ИСПАРЕНИЯ ВОДЫ НА ЭФФЕКТИВНОСТЬ ОХЛАЖДЕНИЯ В ГРАДИРНЯХ

Представлены результаты теоретического исследования охлаждения капель воды при их движении в потоке холодного воздуха в условиях, характерных для башенных градирен большой производительности, и результаты численного анализа распределений температуры по радиусу капель. Вследствие больших перепадов температур и значительных скоростей движения в рассматриваемой системе распределение температур внутри капель принято изменяющимся по радиусу. Учтено повышение влажности воздуха в пристеночной области за счет испарения воды. Полученная система нестационарных дифференциальных уравнений в частных производных решена методом конечных разностей с использованием неявной четырехточечной разностной схемы. Решение задачи с подвижной границей проведено методом ловли фронта в узел пространственной сетки. Для решения нелинейных уравнений применялся метод итераций. Цель работы – численная оценка вклада процессов конвективного и испарительного охлаждения в формирование температурного поля капли воды в условиях, типичных для современных градирен. Анализ проведен для двух характерных значений температуры окружающего воздуха, соответствующих летнему и зимнему периодам года. Выполнен анализ влияния охлаждения капель за счет испарения воды и теплопроводности. Получены распределения температуры по радиусу для различных значений характерных размеров капель. Показано, что изменение радиуса для всего диапазона характерных размеров капель за время их полета составляет менее 0,73 % и не оказывает значительного влияния на величину охлаждения воды в градирне. Установлено, что поглощение теплоты испарением играет важную роль в формировании распределения температур в каплях оборотной воды на выходе из градирен. Показано, что при отрицательных температурах наружного воздуха чрезмерное дробление капель является нецелесообразным.

The State of Air Pollution with PM2.5 in the City of Targu Jiu

Atmospheric particle matters which have many negative effects to the environment and human health have raised the public awareness in last years. Urban centers, through their specific activities, generate a new and complex form of pollution that affects all the quality factors, including those of the environment, the population being the main victim. This paper presents the status of PM2.5 in the air of T�rgu-Jiu city for for 2015-2017, and assessment of the effect of meteorological factors to the values of PM2.5 content. The results indicate that from the three years under study, the annual PM2.5 concentration values exceeded the admissible limit value only for 2015. The highest pollution levels occurred during the months of February, March, October and November of the three analyzed years due to a higher fuel consumption for heating. Regarding the effect of meteorological factors such as: rainfall and temperature to the PM2.5 level, it was observed a decrease of the concentration of PM2.5 as air humidity increases and an increase of PM2.5 concentration as air temperature decreases.

Modeling the development of hydrogen vapor cloud considering the presence of air humidity

A three-dimensional CFD model for large-scale liquid hydrogen spills is developed and validated by the experiments carried out by NASA. The effect of humidity on the development of hydrogen vapor cloud is emphasized, with the modified expressions of Lee model accounting for the phase changes of water and hydrogen. The results show that the numerical prediction is more consistent with the experiment considering the presence of air humidity. The condensation of water in the atmosphere increases the buoyancy of the vapor cloud, and promotes the diffusion of the cloud in vertical direction. The dimension of the cloud in streamwise direction changes little under different humidity, due to the balance between the height-dependent wind speed and the induced buoyancy. The scope of visible cloud indicated by the condensed water vapor expands with the increasing air humidity, and still lies within the flammable domain when the relative humidity approaching to 75%. Water vapor condensation induces the cloud temperature rise under the same concentration, and the leeward part is more influenced compared with the upwind part.

The Influence of Air Humidity on Convective Cooling Conditions of Electronic Devices

The aim of this paper is to demonstrate the impact of ambient air humidity on the efficiency of heat sink operation. It was observed that increased air humidity enabled higher power dissipation in a transistor used as a test device, without increasing its junction temperature. The presented simulation results are showing a correlation between air humidity and an estimated heat flux value. The paper also contains a mathematical analysis of humidity impact on the convective heat transfer coefficient. The natural convection phenomena are visualized in different infrared spectral ranges. A multispectral approach revealed that this convective air flow is best viewed in the MWIR spectral range.

Effect of Humidity on Condensation in Vapour Compression Refrigeration System for Fresh Foods Transport Vehicles

In today’s world the developed countries rely on the refrigerated container (reefer) vehicles for the transportation of cold chain products such as fresh foods. In India this technology was introduced in late 1980s but the growth was very slow compared to other countries and failed to match the international trends. However recently, with fast development of roadways, urbanisation and connectivity the reefers get a massive response. The reefers have several advantages but they consume considerable amount of electrical energy to operate. Reefer works based on vapour compression refrigeration cycle in which condenser is an important device. This condenser uses fan-blown atmospheric air over it to remove vaporization heat from refrigerant. The temperature of refrigerant after condensation has effects on Coefficient of performance (COP) of the refrigeration system. This temperature can be altered by the relative humidity of air. The result of our project shows that the increase in air humidity by 18.60% increases the COP by 11.37% and also it reduces the power consumption.

Experimental study of triboelectric charging of polyethylene powders: Effect of humidity, impact velocity and temperature

The manufacturing and handling of polyethylene (PE) powders is associated with undesired charging, resulting in agglomeration of charged particles, wall sheeting and eventually leading to plugging of reactors/conveyors. In this work, we measured the triboelectric charging of PE powders using both sliding and shaking apparatuses in dependence on humidity, impact velocity of colliding particles and temperature of the colliding particles or of the wall. As expected, saturation charge of PE particles is reduced with increasing air humidity. However, in a more detailed study we observed that whenever we change the humidity, the saturation charge rapidly reaches the equilibrium value and no hysteresis in charging that might be caused, for example, by adsorption/desorption thermodynamics is observed. Saturation charge is believed to be independent of impact velocity; however, we show that the saturation charge is proportional to impact velocity in the system of PE particles of non-spherical shape. The charging is more pronounced as the temperature of PE particles increases, however, it is unchanged if only the metal wall in contact with the particles is heated. That is a different trend than observed for spherical metal particles (Greason, 2000).

Response of bryophytes to afforestation, increase of air humidity, and enrichment of soil diaspore bank

The abandonment of agricultural areas is usually accompanied by the stochastic encroachment of shrubs and trees or deliberate afforestation, but this leads as a rule to the decline of grassland plant diversity. Future climate change may increase precipitation and air humidity in temperate and boreal forest zones, and thus change vegetation dynamics.We conducted a five-year experiment on the Free Air Humidity Manipulation experimental facility (FAHM) with planted deciduous trees to examine how both the grassland afforestation with deciduous trees and the increase of air humidity in interaction with forest soil supplementation and cover of herbaceous layer affect the species richness, composition and cover of bryophyte layer. The effects of the same factors on the cover of herbaceous layer were also analysed. The species of bryophytes and cover of herbaceous and bryophyte layer were surveyed in September of 2007–2011.During these early years of forest succession, herbaceous layer cover decreased and bryophyte cover increased, although the direct suppressing effect of tree canopy was observed on both layers. The input of forest soil as diaspore deposit of bryophytes had some positive effect on the cover of bryophytes, while the increased air humidity had quite limited effect. The density of tree canopy (defined in our study through Leaf Area Index) first promoted the species richness of bryophytes, particularly of species with grassland preference. However, together with the herbaceous layer it became suppressing in the last year.The species richness of bryophytes declined during the first years and then stabilised. The decline relied mainly on the disappearance of grassland species. The richness of bryophytes was supported by forest soil supplementation only in the initial year.The bryophyte species composition changed rapidly in first two years mainly due to decline of short-lived grassland species and perennial species started to dominate.Our results show that bryophyte succession during the afforestation is largely driven by natural loss of grassland specialists after tree canopy closure, while diaspore supplementation from forest and improved air moisture level had small effects.

Impact of urban park’s tree, grass and waterbody on microclimate in hot summer days: A case study of Olympic Park in Beijing, China

Urban heat island (UHI) often cause negative impact and has been linked to heart stroke rate, morality, human comfort, energy consumption and air pollution. Fortunately, urban green spaces have been considered as an effective element to mitigate UHI through their cooling effect. However, further empirical research is necessary in order to efficiently guide the design and planning of urban green space. We observed the impacts of urban park's tree, grass and waterbody on microclimate inside the Olympic park of Beijing during summer days. The results indicated that, on average, the park was 0.48–1.12 °C cooler during the day, as well as increased air humidity 2.39–3.74% and reduced human comfort index 1.02–2.43 to generate more comfortable thermal environment. Urban park's cluster trees with short ground vegetation generated higher cooling effect than single trees, grass and waterbodies; proper irrigation regime enhanced the cooling effect of grasses, even the irrigated grass have similar cooling effect with small waterbody on sunny, windless summer days. Therefore, we advise to increase undergrowth coverage and grass irrigation management in order to take advantage of cooling effect of urban parks.

MONITORING KARBON MONOKSIDA (CO) DAN PARAMETER METEOROLOGIS DI TERMINAL TAWANG ALUN KABUPATEN JEMBER

AbstractTawang Alun Terminal Jember Regency is one of the dense areas ofvehicles have potential to experience carbon monoxide gas pollution and very lowrainfall compared to the surrounding neighborhoods. This research has shown thecondition of air and carbon monoxide concentration in terminal area of TawangAlun. Monitoring used a set of sensor-based tools with an Arduino microcontroller.The results of monitoring of carbon monoxide and meteorological parameters,obtained the highest concentration of carbon monoxide occured during the day butgradually decreased in the afternoon until late in the night when the temperaturewas getting down and the air humidity increases. In contrast to the amount of windspeed that showed the linear distribution pattern as time changed. The averageresult of carbon monoxide measurements on holidays is 71,000-158,000 μg / Nm3 onweekdays of 62,000-69,000 μg /Nm3. This value showed that has exceeded theambient air quality standard limit for carbon monoxide gas is 30,000 μg / Nm3. Theamount of carbon monoxide content is influenced by the volume of vehicles with aregression rate of 82.3%..Keywords: Carbon Monoxide, meteorological parameters, the ambient air qualitystandard

Impact of tree shading on the microclimate of a coffee plantation: a case study from the Peruvian Amazon

L’agroforesterie est considérée comme l’une des stratégies agricoles pouvant contribuer à l’adaptation des cultures au changement climatique. La présente étude de cas visait à comparer les conditions microclimatiques d’une parcelle de Coffea arabica cultivée sous ombrage, principalement Inga spp., et celles d’une parcelle de C. arabica menée en monoculture sans ombrage dans la même plantation de café, dans la région de Pasco au Pérou. La température et l’humidité de l’air, la température du sol et la disponibilité en eau du sol ont été mesurées pendant trois ans. Les résultats indiquent que l’ombrage des arbres réduit la température moyenne de l’air de 0,4 ± 0,04 °C et la température du sol de 1,7 ± 0,3 °C, et augmente l’humidité de l’air de 3,9 ± 0,4 % par rapport à la zone sans ombrage. Cependant, la moyenne mensuelle des températures de l’air dans la zone non ombragée, et même la température maximale, ne dépassent pas outre mesure la limite permettant la photosynthèse (seuil 34 °C). De plus, les températures minimales mensuelles diffèrent peu entre les zones ombragées et non ombragées, alors que la fluctuation des températures du sol est plus marquée dans la zone non ombragée. Un des principaux constats de cette étude concerne la sécheresse plus marquée des sols dans la zone ombragée, surtout au début et à la fin de la saison sèche. Ceci s’explique probablement par l’augmentation de la transpiration totale par celle des arbres d’ombrage. L’absorption d’eau plus importante en agroforesterie pourrait ainsi avoir un impact négatif sur la croissance des caféiers dans les situations où la disponibilité en eau est un facteur limitatif.

Future shift of the relative roles of precipitation and temperature in controlling annual runoff in the conterminous United States

Abstract. This study examines the relative roles of climatic variables in altering annual runoff in the conterminous United States (CONUS) in the 21st century, using a monthly ecohydrological model (the Water Supply Stress Index model, WaSSI) driven with historical records and future scenarios constructed from 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models. The results suggest that precipitation has been the primary control of runoff variation during the latest decades, but the role of temperature will outweigh that of precipitation in most regions if future climate change follows the projections of climate models instead of the historical tendencies. Besides these two key factors, increasing air humidity is projected to partially offset the additional evaporative demand caused by warming and consequently enhance runoff. Overall, the projections from 20 climate models suggest a high degree of consistency on the increasing trends in temperature, precipitation, and humidity, which will be the major climatic driving factors accounting for 43–50, 20–24, and 16–23 % of the runoff change, respectively. Spatially, while temperature rise is recognized as the largest contributor that suppresses runoff in most areas, precipitation is expected to be the dominant factor driving runoff to increase across the Pacific coast and the southwest. The combined effects of increasing humidity and precipitation may also surpass the detrimental effects of warming and result in a hydrologically wetter future in the east. However, severe runoff depletion is more likely to occur in the central CONUS as temperature effect prevails.

Experimental studies on frost and defrost of fine tube bundles under coolant temperature between −20 and −58 °C

Experiments are carried out on the frost and defrost characteristics of fine tube bundles under coolant temperature between −20 and −58°C. The diameter of the tube is 2mm. The frost and defrost processes are observed by taking photos and measuring pressure drops. The results indicate that the frost layer thickness on the tube surface increases with decreasing coolant temperature, but decreases with increasing air humidity. A model is given to explain the variation of frost thickness. The experiments verified that spraying ethanol is effective on inhibiting the formation of the frost.

The role of Casuarina equisetifolia on micro climate improvement of sandy beach land at Kebumen

Sandy beach is a marginal land, when it is not managed properly the conditions will be worsened and at the end it cannot be planted. This marginal land is aggravated by unfavorable conditions such as extreme high temperatures, the presence of salt vapor that causes the plants to die, and the lacking of water for plants. With regard to this matter, it is necessary to conduct a research that aims to determine the role of Casuarina equisetifolia in improving the microclimate of sandy beaches. The research was conducted on sandy beaches in Karanggadung, Petanahan Subdistrict, Kebumen since 2005, with climate observations from 2009 to 2014. The climate observation method is by measuring light, air temperature, humidity, air pressure and altitude. Each measurement used three repetitions for each location and measured twice a day: 07.00 and 16.00. The results showed that the existence of C. equisetifolia gave a positive effect on micro climate improvement at Karanggadung Beach, Kebumen which included: 1) decreasing light intencity from 1925 lux to 213 lux, 2) decreasing air temperature from 31 °C to 25 °C, 3) increasing air humidity from 84% to 100%, 4) increasing air pressure from 1007 mb to 1008 mb, and 5) increasing sand dune level from 27 m ASL (Above Sea Level) to 35 m ASL.

Increasing air humidity influences hydraulic efficiency but not functional vulnerability of xylem in hybrid aspen

Climate models predict greater increases in the frequency than in the amount of precipitation and a consequent rise in atmospheric humidity at high latitudes by the end of the century. We investigated the responses of hydraulic and relevant anatomical traits of xylem to elevated relative humidity of air on a 1-yr-old coppice of hybrid aspen (Populus×wettsteinii) growing in the experimental stand at the Free Air Humidity Manipulation site in Eastern Estonia. The hydraulic conductivity of stems was measured with a high pressure flow meter; artificial cavitation in the stem segments was induced by the air injection method. Specific conductivity of xylem decreased from 4.42 in the control to 3.94kgm−1s−1MPa−1 in the humidification treatment, while the trend was well correlated with increasing wood density. Humidified trees exhibited smaller leaf area at the same xylem cross-sectional area, resulting in 34% higher average Huber values compared to the control. Control and humidity-treated trees differed by neither native embolism level nor susceptibility to dehydration-induced cavitation. Increasing atmospheric humidity reduces the hydraulic efficiency of hybrid aspen trees expressed on a xylem area basis and causes substantial changes in resource allocation between photosynthetic and water transport tissues. This climate trend does not influence stem vulnerability to cavitation.