External Heat Transfer in Moist Air and Superheated Steam for Softwood Drying

In kiln drying of softwood timber, external heat and moisture mass transfercoefficients are important in defining boundary temperature and moisture content at the woodsurface. In addition, superheated steam drying of wood is a promising technology but this has notbeen widely accepted commercially, partially due to the lack of understanding of the dryingphenomena occurred during drying. In this work, experimental investigation was performed to quantifythe heat transfer between wood surface and surrounding moist air or superheated steam. In theexperiment, saturated radiata pine sapwood samples were dried using dry-bulb/wet-bulb temperaturesof 60℃/50℃, 90℃/60℃, 120℃/70℃, 140℃/90℃, 160℃/90℃, 140℃/100℃ and 160℃/100℃. The lasttwo schedules were for superheated steam drying as the wet-bulb temperature was set at 100℃. Thecirculation velocity over the board surface was controlled at 4.2m·s^(-1). Two additional runs(90℃/60℃) using air velocities of 2.4 m·s^(-1) and 4.8 m·s^(-1) were performed to check theeffect of the circulation velocity. During drying, sample weight and temperatures at wood surfaceand different depths were continuously measured. Prom these measurements, changes in woodtemperature and moisture content were calculated and external heat-transfer coefficient wasdetermined for both the moist air and the superheated steam drying.

Water Losses in Arid and Semi-Arid Zone:Evaporation, Evapotranspiration and Seepage

The primary purpose of this study was to assess water losses by evapotranspiration, evaporation and seepage in arid zone.Normally, evaporation and seepage are the main causes of water losses.For modeling water losses,a combination of Genetic Programming(GP),Penman-Monteith(PM) and Penman combination model for measurement of evapotranspiration,evaporation and seepage has been developed.The results were found to be varying depending on how the evaporation and seepage phenomena are modeled.These results show that that there is an improvement in reducing evapotranspiration,evaporation and seepage losses in arid and semi-arid region.

RESEARCH ON THE LOCAL CORRECTION MODEL OF ATMOSPHERIC DRY DELAY IN GPS REMOTE SENSING WATER VAPOR

The precision of atmospheric dry delay model is closely correlated with the accuracy of GPS water vapor in the process of GPS (Global Position System) remote sensing. Radiosonde data (from 1996 to 2001) at Qingyuan are used to calculate the exact values of the atmospheric dry delay. Base on these calculations and the surface meteorological parameters, the local year and month correction models of dry delay at the zenith angle of 0° are established by statistical methods. The analysis result shows that the local model works better and is slight more sensitive to altitude angle than universal models and that it is not necessary to build models for each month due to the slight difference between year model and month model. Furthermore, when the altitude angle is less than 75°, the difference between curve path and straight path increases rapidly with altitude angle’s decrease.

Effect of Sustained Deficit Irrigation on Stem Water Potential of Navel Oranges in Jordan Valley

Research was conducted to find the relationship between deficit irrigation treatments （DIT） and stems water potential. The study was conducted on 14 years old navel orange trees grafted on sour oranges for the growing season 2006/2007 at a private farm in the Northern part of Jordan Valley （latitude： 32° 50′ N, longitude： 32° 50′ E, altitude： -254 m）. Three levels of irrigation treatments （IT） were applied; namely 100%, 75% and 50% of reference evapotranspiration, representing over irrigation （OIT）, full irrigation （FIT）, and deficit irrigation （DIT）, respectively. A drip irrigation using one irrigation source line with drippers spaced 0.5 m having average discharge of 2.3 L/hr at pressure 1.5 bar, was used. Stem water potential （SWP） at 100% over irrigation treatment （OIT） of navel orange trees had less negative value during the irrigation seasons （-1.57 MPa）, whereas the highest negative value （-2.17 MPa） occurred at 50% deficit irrigation treatment （DIT）.

Physical Properties in Drying of Food Products with Combined Sublimation and Evaporation

Drying is an important unit operation in processing of biological resources. The drying process may influence the product properties and quality, which may shrink, break or undergo rheological, physical and biochemical changes. The important parameters responsible for such changes are drying conditions, type of drying technology and residence drying time. Thermal conductivity, thermal-mass diffusivity, enthalpy, porosity and density are the main material property and heat-mass transfer parameters, which are essential for understanding the changes in product quality and for designing and dimensioning the drying processes. In this paper physical properties of food products undergoing a combined sublimation and evaporation were studied. Pieces of vegetables and potatoes were dried in a heat pump fluidized bed dryer at combined modes with temperatures below the freezing point in the beginning and a final drying step at temperatures above the freezing point. Samples of products were tested at different moisture contents with respect to physical properties. Physical properties of leek and potato samples were measured and mass diffusivities were determined from drying kinetic data. Based on bulk density and rehydration measurements it was clearly observed that drying temperature and modes influenced the final product physical properties. The potato cube run dried with initial atmospheric freeze-drying step had rehydration ability 430%above a run dried only above the freezing point. The average effective mass diffusivity for 5 mm slabs of leek was 0.5 x 10-11m2·s-1 for the sublimation stage and 2.2 x 10-11m2·s-1 for the evaporation stage.

Changes in spatial variations of sap flow in Korean pine trees due to environmental factors and their effects on estimates of stand transpiration

It is difficult to scale up measurements of the sap flux density(J_S) for the characterization of tree or stand transpiration(E) due to spatial variations in J_S and their temporal changes.To assess spatial variations in the sap flux density of Korean pine(Pinus koraiensis) and their effects on E estimates,we measured the J_S using Granier-type sensors.Within trees,the J_S decreased exponentially with the radial depth,and the J_S of the east aspects were higher than those of the west aspects.Among trees,there was a positive relationship between J_S and the tree diameter at breast height,and this positive relationship became stronger as the transpiration demand increased.The spatial variations that caused large errors in E estimates(i.e.,up to 110.8 % when radial variation was ignored) had varied systematically with environmental factors systematic characteristics in relation to environmental factors.However,changes in these variations did not generate substantial errors in the E estimates.For our study periods,the differences in the daily E(E_D) calculated by ignoring radial,azimuthal and tree-to-tree variations and the measured E_D were fairly constant,especially when the daily vapor pressure deficit(D_D)was higher than 0.6 k Pa.These results imply that the effect of spatial variations changes on sap flow can be a minor source of error compared with spatial variations(radial,azimuthal and tree-to-tree variations) when considering E estimates.

Effect of Steaming, Steam-Drying and Frying on the Provitamins A and Ascorbic Acid Contents of Squash （ Cucurbita Spp.）

Vitamin A deficiency still remains a nutritional concern in Cameroon. Squashes pulp is rich in provitamins A and could help to reduce this deficiency. Unfortunately, in Cameroon, squash pulp is more often reserved for the nutrition of sick people and domestic animals. This study aimed at encouraging the consumption of squash pulp to contribute to vitamin A needs. The contents of a-carotene, all-trans-β-carotene and ascorbic acid were determined respectively by HPLC and titration with 2.6 dichlorophenol-indophenol in five landraces of raw, steamed, steam-dried and fried squash pulp from Cameroon. Moisture and total lipid content were also determined. Peeled pulp squash of 5 cm slice was steamed at 90℃ for 30 min or at 85℃ for 30 min, sliced again at 5 mm thickness and dried at 80℃ during 4 h to obtained steamed or steam-dried squashes. To have fried squashes, 40 g of 1 mm thickness slices pulp were fried in boiling refined palm oil （free of carotenoids） bath at 150℃ during 7 and 10 min. The results obtained showed that steam-drying and frying of squashes leaded to water losses （89%-95%）. As a consequence of this, the a-carotene, all-trans-β-carotene and ascorbic acid contents （expressed in g （100 g）-1 fresh portion） of steam-dried and fried squashes were significantly higher （P 〈 0.05） than those of steamed and raw pulp. However, the retention rate of provitamins A and ascorbic acid was more elevated in steamed than in steam-dried and fried squashes. These results suggest that steam-dried and fried squashes could contribute to fight against vitamin A deficiency while increasing availability of squashes.

Spray Evaporation of Different Liquids in a Drying Chamber--Effect on Flow, Heat and Mass Transfer Performances

Almost without exception literature data and modeling effort are understandably devoted to water as the sprayed liquid since it constitutes the most common liquid used in spray drying applications. In selected applications, however, the liquid making up the solution or suspension may not be water. The objective of this work is to examine the differences in flow patterns, thermal behavior and drying rates caused by different liquids having different thermo-physical properties spray into a spray dryer using a computational fluid dynamic model.Numerical experiments were carried out for water (base case), ethyl alcohol and isopropyl alcohol-the latter two as model non-aqueous liquids. The chamber geometry was cylinder type with a co-current axial pressure nozzle and also an axial central exit so that the configuration is two dimensional and axi-symmetric. It is shown that the liquid properties can have major influence on the thermal field, droplet trajectories, residence times and overall evaporation capacity when all parameters of the problem are held fixed. Deviations from the single phase turbulent airflow in the same chamber without spray are different for the three liquids examined.

Evaporation from Bare Soil in Extremely Arid Environment in Southern Israel

Microlysimeters of different sizes(5 cm 10 cm and 15 cm in length)were used extensively in the present study for the measurements of soil evapondion in site in an extremely arid area in southern Israel.All of the data obtained from the microlysimeters were used to evaluate two conventional eVaporation models developed by Black et al.and Ritchie,respectively.Our results indicated that the models could overestimate total cumulative evaporation by about 30% in the extremely arid environment.Reducing the power factor of the conventional model by a faCtor of 0.1 produced good agreement between the measured and simulated cumulative evaporation.Microlysimeter method proved to be a simple and accurate approach for the evaluation of soil evaporstion.

Developments in Humidity Standards and the Psychrometer Equation

Determination of the wet-bulb temperature at the surface of a material is the basis of one class ofhumidity measuring instruments, and is important in industrial applications such as dryer modelling and simula-tion. The psychrometer equation is a frequently used method of estimating wet-bulb temperature, and contains apsychrometer 'constant'. Analysis shows that this is in fact a variable coefficient affected by temperature, pressure,radiation and conduction effects, and the identity of the gas and vapour. Radiation and conduction affect the dif-ference between adiabatic saturation temperature and indicated wet-bulb temperature. Inconsistencies in currentlyrecommended values for the psychrometer coefficient, including published international standards, are identifiedand explained. Particular problems arise when the enhancement factor is applied to vapour pressure to accountfor non-ideality of gases. Special considerations are also needed for wet-bulb temperatures approaching the boilingpoint, where the psychrometer coefficient tends to zero. Self-consistent recommendations recently published in thenew British Standard BS1339 are given, which cover both the air-water system and a general vapour-gas system.

Drought and Spatiotemporal Variability of Forest Fires Across Mexico

Understanding the spatiotemporal links between drought and forest fire occurrence is crucial for improving decision-making in fire management under current and future climatic conditions. We quantified forest fire activity in Mexico using georeferenced fire records for the period of 2005–2015 and examined its spatial and temporal relationships with a multiscalar drought index, the Standardized Precipitation-Evapotranspiration Index(SPEI). A total of 47975 fire counts were recorded in the 11-year long study period, with the peak in fire frequency occurring in 2011. We identified four fire clusters, i.e., regions where there is a high density of fire records in Mexico using the Getis-Ord G spatial statistic. Then, we examined fire frequency data in the clustered regions and assessed how fire activity related to the SPEI for the entire study period and also for the year 2011. Associations between the SPEI and fire frequency varied across Mexico and fire-SPEI relationships also varied across the months of major fire occurrence and related SPEI temporal scales. In particular, in the two fire clusters located in northern Mexico(Chihuahua, northern Baja California), drier conditions over the previous 5 months triggered fire occurrence. In contrast, we did not observe a significant relationship between drought severity and fire frequency in the central Mexico cluster, which exhibited the highest fire frequency. We also found moderate fire-drought associations in the cluster situated in the tropical southern Chiapas where agriculture activities are the main causes of forest fire occurrence. These results are useful for improving our understanding of the spatiotemporal patterns of fire occurrence as related to drought severity in megadiverse countries hosting many forest types as Mexico.

Daily SPEI Reveals Long-term Change in Drought Characteristics in Southwest China

Drought is the most widespread and insidious natural hazard, presenting serious challenges to ecosystems and human society. The daily Standardized Precipitation Evapotranspiration Index(SPEI) has been developed to identify the regional spatiotemporal characteristics of drought conditions from 1960 to 2016, revealing the variability in drought characteristics across Southwest China. Daily data from142 meteorological stations across the region were used to calculate the daily SPEI at the annual and seasonal time scale. The Mann-Kendall test and the trend statistics were then applied to quantify the significance of drought trends, with the following results. 1) The regionally averaged intensity and duration of all-drought and severe drought showed increasing trends, while the intensity and duration of extreme drought exhibited decreasing trends. 2) Mixed(increasing/decreasing) trends were detected, in terms of intensity and duration, in the three types of drought events. In general, no evidence of significant trends(P < 0.05) was detected in the drought intensity and duration over the last 55 years at the annual timescale. Seasonally, spring was characterized by a severe drought trend for all drought and severe drought conditions, while extreme drought events in spring and summer were very severe. All drought intensities and durations showed an increasing trend across most regions, except in the northwestern parts of Sichuan Province. However, the areal extent of regions suffering increasing trends in severe and extreme drought became relatively smaller. 3) We identified the following drought hotspots: Guangxi Zhuang Autonomous Region from the 1960 s to the 1990 s, respectively. Guangxi Zhuang Autonomous Region and Guizhou Province in the 1970 s and 1980 s, and Yunnan Province in the 2000 s. Finally, this paper can benefit operational drought characterization with a day-to-day drought monitoring index, enabling a more risk-based drought management strategy in the context of global warming.

Energy and Exergy Analysis of a Novel Efficient Combined Process by Hydrothermal Degradation and Superheated Steam Drying of Degradable Organic Wastes

This paper considers the combination of hydrothermal degradation （HTD） and superheated steam （SHS） drying in disposal and processing of degradable organic wastes in municipal solid wastes （MSW）. In SHS drying, a fraction of dryer thermal energy input can be recovered and used to satisfy the heat requirement in maintaining the HTD operating temperature. Both energy and exergy analysis are applied to the combined process. The analysis covers ranges of dryer inlet temperatures of 202.38-234.19~C and feed water content of 32.5-65%. Thermal energy analysis shows that the combination of HTD and SHS drying can achieve thermal energy self-sufficiency （TES） by manipulating process variables. The exergy analysis indicates the location, type, and magnitude of the exergy losses during the whole process by applying the second law of thermodynamics.

Spatio-temporal variation of the wet-dry conditions from 1961 to 2015 in China

As an important part of the regional environment, the wet-dry climate condition is determined by precipitation and potential evapotranspiration （expressed as ETo）. Based on weather station data, this study first calculated ETo by using the FAO56 Penrnan-Monteith model. Then, the dryness index K （ratio of ETo to precipitation） was used to study the spatio-temporal variation of the wet-dry condition in China from 1961 to 2015; moreover, dominant climatic factors of the wet-dry condition change were discussed. The annual precipitation and ETo of the Qinling-Huaihe line were close to a balance （K≈1.0）. The annual precipitation in most areas exceeded the ETo in the south of this line and the east of Hengduan Mountains （K〈0.0）, where the climate is wet. Furthermore, the precipitation in the northwest inland areas of China, where the climate is dry, was markedly lower than ETo （K≥4.0）. The overall annual K of China fluctuated around the 55-year mean and its linear trend was not significant. However, a relatively wet period of about 10 yr （1987-1996） was recorded. The overall annual K of China showed strong cyclicality on the time scale of 3, 7-8, 11 and 26-28 yr, and regional differences of the annual K trends and cyclicality were large. The degrees of wetness in the Northwest China and western Qinghai-Tibet Plateau were substantially increased, whereas the degrees of dryness in the Yunnan-Guizhou Plateau, Sichuan Basin, and Loess Plateau were markedly increased. The linear trend of the annual K in most regions of China was not significant, and the annual K of most areas in China showed strong cyclicality on the 8-14 yr time scale. Precipitation was the dominant factor of wet-dry condition change in most areas, especially in North China, where the annual K change was highly correlated with precipitation.

Formation of wavy-ring crack in drying droplet of protein solutions

The formations of desiccation cracks and their pattems in drying droplets of protein solutions are studied experimentally. The solvent evaporation causes the dehydration self-organization phenomenon in colloidal droplets, followed by the formations of desiccation cracks. Two categories of highly ordered crack patterns, which we name ＂daisy＂ and ＂wavy-ring＂, are identified in the drying droplets. We explore the shifting of crack patterns from the ＂daisy＂ to the ＂wavy-ring＂ by varying the concentration of protein droplets. The results show that the concentration correlates with the pattern of deposition film directly, and modulates the periodicity of the crack pattern. We investigate the formations and periodicities of these two kinds of crack patterns, and obtain the scaling law of periodicity of the ＂wavy-ring＂ crack pattern. The relationship between the deposition pattern and the highly ordered crack patterns is also examined. This study will help in understanding the formation mechanisms of crack patterns in drying droplets of protein solutions and assist the future design of crack patterns in practical applications.

Responses of Different Physiological Indices for Maize(Zea mays) to Soil Water Availability

Knowledge of plant responses to soil water availability is essential for the development of effcient irrigation strategies.However,notably different results have been obtained in the past on the responses of various physiological indices for different plants to soil water availability.In this study,the responses of various plant processes to soil water availability were compared with data from pot and field plot experiments conducted on maize(Zea mays L.).Consistent results were obtained between pot and field plot experiments for the responses of various relative plant indices to changes in the fraction of available soil water(FASW).A threshold value,where the relative plant indices began to decrease with soil drying,and a lower water limit,where the decline of relative plant indices changed to a very slow rate,were found.Evaporative demand not only influenced the transpiration rate over a daily scale but also determined the difference in transpirational response to soil water availability among the transient,daily and seasonal time scales.At the seasonal scale,cumulative transpiration decreased linearly with soil drying,but the decrease of transpiration from FASW = 1 in response to water deficits did not affect dry weight until FASW = 0.75.On the other hand,the decrease in dry weight was comparable with plant height and leaf area.Therefore,the plant responses to soil water availability were notably different among various plant indices of maize and were influenced by the weather conditions.

Influence factors and variation characteristics of water vapor absorption by soil in semi-arid region

The adsorption of water vapor by soil is one of the crucial contributors to non-rainfall water on land surface, particularly over semi-arid regions where its contribution can be equivalent to precipitation and can have a major impact on dry agriculture and the ecological environment in these regions. However, due to difficulties in the observation of the adsorption of water vapor,research in this area is limited. This study focused on establishing a method for estimating the quantitative observation of soil water vapor adsorption(WVA), and exploring the effects of meteorological elements(e.g., wind, temperature, and humidity) and soil environmental elements(e.g., soil temperature, soil moisture, and the available energy of soil) on WVA by soil over the semi-arid region, Dingxi, by combining use of the L-G large-scale weighing lysimeter and meteorological observation. In addition, this study also analyzed the diurnal and annual variations of WVA amount, frequency, and intensity by soil, how they changed with weather conditions, and the contribution of WVA by soil to the land surface water budget. Results showed that WVA by soil was co-affected by various meteorological and soil environmental elements, which were more likely to occur under conditions of relative humidity of 6.50% and the diurnal variation of relative humidity was large, inversion humidity, wind velocity of 3.4 m/s,lower soil water content, low surface temperature and slightly unstable atmospheric conditions. There was a negative feedback loop between soil moisture and the adsorption of water vapor, and, moreover, the diurnal and annual variations of WVA amount and frequency were evident—WVA by soil mainly occurred in the afternoon, and the annual peak appeared in December and the valley in June, with obvious regional characteristics. Furthermore, the contribution of WVA by soil to the land surface water budget obviously exceeded that of precipitation in the dry season.

Spatiotemporal variations of aridity in China during 1961–2015: decomposition and attribution

Changes in global climate intensify the hydrological cycle, directly influence precipitation, evaporation, runoff, and cause the re-distribution of water resources in time and space. The aridity index （AI）, defined as the ratio of annual precipitation to annual potential evapotranspiration, is a widely used numerical indicator to quantify the degree of dryness at a given location. This study examined the effects of climate change on Al in China during 1961-2015. The results showed that the nationally averaged AI experienced a notable interdecadal transition in 1993, characterized by increasing AI （wetter） between 1961 and 1993, and decreasing AI （drier） after 1993. Overall, the decreased solar radiation （solar dimming） was the main factor affected the nationally averaged AI during 1961-1993, while the relative humidity dominated the variations of nationally averaged AI during 1993-2015. However, the roles of individual factors on the changes in AI vary in different subregions. Precipitation is one of the important contributing factors for the changes orAl in almost all subregions, except the Mid-Lower Yangtze and Huaihe basins. Solar radiation has been significantly decreased during 1961-1993 in South China, Southwest China, Mid-Lower Yangtze and Huaihe basins, and the Tibetan Plateau. Therefore, it dominated the trends of AI in these subregions. The relative humidity mainly affected the Mid-Lower Yangtze and Huaihe basins, Southwest China, and the Tibetan Plateau during 1993-2015, hence dominated the trends of Al in these subregions. The changes of temperature and wind speed, however, played a relatively weak role in the variations of AI.