Wet Bulb Temperature Depression Research Articles

A fuzzy knowledge-based model for assessing risk of pesticides into the air in cropping systems

Pesticide use in current cropping systems has become a key input to improve productivity. However, their potential risk to nature demands tools for designing a sustainable use. In this work, a fuzzy knowledge-based model was developed for assessing risk of pesticides into the air. The model was based on fuzzy logic theory which provides a means for representing uncertainty by including knowledge about different processes related to pesticide dynamics using functions, control rules and logical inference systems. All these elements were built through a literature review. Results from the sensitivity analysis on the final model structure showed that the Henry's law constant was the most influential input variable related to the active ingredient identity, while the most influential management and environmental input variables on the pesticide air risk values were the droplet size together with the application method and the current wet bulb temperature depression value, respectively. Results from an independent model validation showed a significant goodness-of-fit between the simulated risk of drift and volatilization and the observed values under experimental conditions. Long-term simulations in a real soybean production system in Argentina showed results of drift reduction in post-emergence conditions of the crop under aerial application condition, and a significant effect of the identity of the active ingredient in the risk values. Simulated risk values from the developed model allow to identify ex ante the combination of agronomic decisions, together with environmental conditions that can reduce the risk of pesticides in the air in real production systems. Further combination with ecotoxicological classification tools should improve pesticide use assessment in agricultural systems.

Theoretical and experimental study on heat and mass transfer of a porous ceramic tube type indirect evaporative cooler

The wettability characteristic of wet channels plays an important role in cooling performance of an indirect evaporative cooler (IEC). To improve its wettability, porous ceramic is used as a novel material for IEC. The porous structure provides hydrophilic feature and water storage capacity. Therefore, the wet-bulb efficiency of the cooler can be improved because of higher wettability and larger specific surface area. This paper presents a theoretical and experimental study on a tubular porous ceramic IEC. The mathematical model of heat and mass transfer was established and numerically solved to evaluate its cooling performance. The influence of various structural parameters and operational parameters of porous ceramic IEC are analyzed, including the tube length, tube spacing, wall thickness, wet-bulb temperature depression and working/output air volume ratio. The experimental study is also carried out, on one hand, to validate the numerical model; and on the other hand, to optimize the working air/product air flow ratio. The results indicate the optimal tube spacing is 40 mm. The tube length plays a significant effect on the cooling performance of IEC when it is less than 1.5 m. Experimental study shows the optimal performance of porous ceramic IEC prototype is achieved under the product air velocity of 3.4 m/s, working air velocity of 4.0 m/s and the working air/product air volume ratio of 0.9.

Climatic applicability of downdraught evaporative cooling in the United States of America

The potential for application of downdraught cooling in the United States of America (U.S.) depends on its climatic characteristics. However, due to the large geographic span of the country, it varies due to differences in latitude, and a range of geographic features influencing climate, including altitude, topography and terrain. This study describes the development of climatic applicability maps of downdraught cooling in the U.S., which can aid designers in the initial identification of the correct cooling strategy for the geographic area of interest. The proposed approach is based on a set of maps, which are derived from two related climatic indexes: dry bulb temperature to wet bulb temperature depression (DBT−WBT), representing the climatic opportunity, and 26 °C minus wet bulb temperature (26 °C−WBT), representing the climatic opportunity against the theoretical cooling requirement for each location. The downdraught cooling strategy and degree of applicability is classified in the map, based on the aforementioned climatic and cooling parameters. Finally, four representative buildings in four different regions with different climatic conditions were selected for climatic analysis. This resulted in the identification of some climate zones for downdraught cooling application in the U.S. and the suggestion of appropriate design strategies for each of them.

Laboratory Measurements on the Sensitivity of Evaporation Rate of Droplets Inside a Spray Cloud

<abstract> <b><sc>Abstract.</sc></b> This article summarizes additional experimental data collected regarding the evaporation rate of water droplets stacked on several threads, positioned downwind of one another, and strengthens previously published results regarding droplet evaporation rates inside a spray cloud. Here, the effect of evaporating water droplets upwind of other droplets is examined, along with changes in tunnel speed, temperature, and relative humidity on droplets positioned on single threads. These results further quantify the wet bulb temperature depression felt by droplets within a spray cloud, along with the effect of the Sherwood number, and are used to enhance the ability of AGDISP to make accurate model predictions for droplets released from spray nozzles.

Initial Laboratory Measurements of the Evaporation Rate of Droplets inside a Spray Cloud

This article calculates the evaporation rate of water droplets stacked on several threads, positioned downwind of one another. The measurement approach was used previously to determine the evaporation rate of isolated suspended droplets, on a single thread, for development of the Spray Drift Task Force (SDTF) droplet evaporation data base. Here, the effect of evaporating droplets upwind of other droplets is examined, recovering the effective evaporation rate of individual water droplets surrounded by other water droplets in a spray cloud. The results quantify the modified wet bulb temperature depression felt by the droplets within the cloud and are used to compare AGDISP model predictions with SDTF aerial deposition data.

ECCENTRIC Buildings: Evaporative Cooling in Constructed ENvelopes by Transmission and Retention Inside Casings of Buildings

New research on evaporative cooling and breathable walls has demonstrated the potential for smart designs where conductive, convective, and radiative heat fluxes are matched or supplemented through low-energy natural phenomena such as wet-bulb temperature depression associated with evaporation. This research seeks to examine the operational and theoretical performance of novel vapor permeable evaporative cooling membrane layers. Latent heat is removed through the evaporation of water through the membrane, where contaminants remain in solution as the hydrophobic membrane allows for passage of only water vapor. Through steady-state analysis of a proposed cooling system for building exterior walls, cooling capacity was shown to exceed cooling loads for large indoor areas. Candidate materials produced from recycled glass were examined through sintering, hydrophobing, and other processes to create materials with the requisite properties specified by simulations. Real data acquired for Princeton, NJ from July 2011 was inputted to the simulations to quantify behavior of the system under real conditions. Even in the humid climate of New Jersey in July, the system can supplement a conventional cooling system, acting as a buffer between interior and external environments. Additionally, the novel mathematical model developed to simulate this evaporative process is in 0.04 ± 0.28°C agreement to measured data.

Evaluating the potential of an indirect evaporative passive cooling system for Brazilian dwellings

The purpose of this study is to assess the applicability of an indirect evaporative passive cooling system (IEPCS) in prototypical dwelling modeled for locations across the Brazilian territory. The thermal performance of the IEPCS is analyzed, originally developed for a dwelling located in hot-humid Maracaibo, Venezuela (Vivienda Bioclimática Prototipo – VPB-1). Diverse configuration modes were tested as part of the experimental field study, from which predictive formulas were generated and validated. The paper shows results of the expected thermal performance of the IEPCS for 411 Brazilian cities, which were obtained from the application of predictive formulas to a database consisting of TMY (Typical Meteorological Year) climate files. The efficiency of the passive cooling system was evaluated for each city with regard to its capability in reducing indoor temperatures relative to outdoors as well as Degree-Day percentages above the upper limit of the adaptive comfort zone. Detailed results for four Brazilian locations are also discussed. Results suggest that the system is capable of ensuring thermal comfort conditions for most of the cities evaluated. Average indoor temperatures reached reductions up to 2.5 °C below outdoor conditions; such reductions depend fundamentally on the wet bulb temperature depression. From such results, it is suggested that the IEPCS could have a great applicability in Brazil with a strong potential for improving indoor comfort conditions and, in the case of air-conditioned buildings, also promote a reduction of the energy demand on HVAC.

Modeling the Heat Transfer during Log Heating

As one of the most commonly planted species in China, Masson pine (Pinus massoniana) logs are potentially used for structural poles and piles. Because phytosanitary regulations require that logs be heat-treated before delivery to customers (log core temperature of 56°C for 30 min), interest has recently arisen in the determination of the time required to reach this criterion. In this study, 12 logs were heat-treated in a laboratory drying kiln with two types of schedules. Using partial differential energy and mass conservation equations with gradient boundary conditions, the temperature increase in a log during heating was simulated. The boundary value problem of heat and mass transfer was solved using a numerical method, namely, a control volume approach. Results from the comparison between the observed and calculated temperatures indicated that the heat transfer performance during log heating can be described with this heating model. This model might therefore serve as a guideline for estimating the log heating times, assisting mill personnel in production planning. In addition, based on the experimental and calculated findings, it was well established that the log diameter, initial moisture content, wood density, and wet bulb temperature depression played significant roles in the heating rate during the heat treatment of logs.

The Psychrometric Constant Is Not Constant: A Novel Approach to Enhance the Accuracy and Precision of Latent Energy Fluxes through Automated Water Vapor Calibrations

Abstract Numerous agencies, programs, and national networks are focused on improving understanding of water and energy fluxes across temporal and spatial scales and on enhancing confidence to synthesize data across multiple sites. Enhancing the accuracy and precision in the surface energy balance and the latent energy (λE) flux lies, in part, with being able to uniformly calibrate water vapor measurements at and among sites to traceable standards. This paper examines (i) the traceable physical controls on field applications of chilled-mirror hygrometers and (ii) an automated means to accurately and precisely calibrate infrared gas analyzers for water vapor concentrations and eddy covariance (λE) data. The environmental physics and gas handling were examined in a theoretical and applied manner that found that chilled-mirror technologies can be a robust measure of dewpoint temperatures and ambient water vapor only if the unit conversions are accounted for between inlet and body temperatures. Psychrometers were also examined and a functional relationship (exponential) was developed for the psychrometric constant against the wet-bulb temperature depression (Tdb − Twb), across a wider range of temperature depressions than previously reported. These empirical estimates of the psychrometer constant for small temperature depressions are much lower than other reported values—that is, ∼0.000 52 K−1 for a wet-bulb temperature depression (Tdb − Twb) of 4.3 K.

Influence of micrometeorological factors on pesticide loss to the air during vine spraying: Data analysis with statistical and fuzzy inference models

Upward spray losses over vines were assessed during a typical air-assisted application using a fluorescent tracer dye and PVC lines as samplers. Linear multiple regression and fuzzy logic inference models were used to evaluate the effects of micrometeorological conditions on pesticide application for two spray qualities (fine and very fine). For the fine spray application (volume median diameter [VMD] 134 μm), the significant variables for the multiple regression were wind speed, air temperature and wet bulb temperature depression, with a coefficient of determination of 0.70. For the very fine spray application (VMD 65 μm), atmospheric stability was also significant, with a coefficient of determination of 0.82. Spray losses were also predicted using fuzzy inference systems, and high coefficients of determination were obtained (R2=0.72 for the fine spray and 0.66 for the very fine spray). Interpretable rules were established for the characterisation of micrometeorological parameters using the two sprays. Both analysis tools can be combined with mathematical modelling in order to evaluate air pollution and spray drift from simplified field tests.

Refining the use of evaporation in an experimental down-draft cool tower

Direct evaporative cooling has long been recognized as an energy-efficient and cost-effective means for space conditioning in hot dry areas. In order to extend the use of evaporative cooling to include exterior or semi-enclosed spaces, a down-draft evaporative ‘cool tower’ was integrated in the project of a 500 m 2 glazed courtyard located at the heart of a building complex in the arid Negev Highlands of southern Israel, designed by the authors. The present article describes the development of the cooling tower system, undertaken in three phases: (i) Prototype analysis. Performance of a small-scale tower was monitored, and comparisons were drawn between varying rates and mechanisms of water and air supply. The results indicated a potential for substantial temperature reduction in the order of 10 °C under summer daytime conditions, but a meager cooling output when using a natural draft system. Mechanical-forced air flow was thus utilized in the actual tower. (ii) Field monitoring. The cool tower, approximately 10 m in height and 10 m 2 in cross-sectional area, was operated and monitored during a summer season; its performance was analyzed using a series of water supply mechanisms and operating modes. The system produced a peak cooling output of just over 100 kW, with a wet bulb temperature depression of close to 85–95% during all hours of operation, and a water consumption rate of approximately 1–2 m 3/day. (iii) Refinement. Potential improvement in the system's operation was investigated through the development of a wind capture mechanism for increasing inlet pressure and air flow to the space. Both fixed and dynamic capture units were investigated, with wind speed and direction as well as internal air speeds measured in the small-scale prototype tower. The wind capture unit with the simplest configuration and best performance is recommended for future integration in the full-scale tower.

Establishment of performance charts of an air conditioner with one certified test point

This paper demonstrates, in terms of both experiments and theory, that the wet bulb temperature depression of a given air conditioner at a given air rate is approximately constant and that the relation between the relative humidity of the inlet and outlet air can be determined by drawing a family of curves through a particular point in the saturated curve on the psychometric chart. Thus it is possible to establish the complete performance charts for a particular air conditioner from one test point.

Measuring Water Potential (Activity) from Free Water to Oven Dryness

Water activities (potentials) in plant materials were measured over the range from free water to oven dryness with a Spanner thermocouple psychrometer. In a two-step procedure, water was first condensed on the thermocouple junction for several minutes. The sample was then inserted under the wet thermocouple and the maximum psychrometric cooling was measured in about 10 seconds. Calibration was with saturated salt slurries of known water activities. Psychrometric cooling was a nearly linear function of the water activity and of the negative log of the water potential. The psychrometric cooling to water activity relationship agreed with wetbulb temperature depression to relative humidity relationships given in tables. Water activities of wheat grains and leaves decreased sharply in a curvilinear fashion as their water contents decreased. Some problems of the procedure are discussed.

Precision of evaporation measurements using the Bowen ratio

Energy balance/Bowen ratio estimation of evapotranspiration is examined to determine the effects of different sources of error. General usage of the approximate psychrometric equation which neglects terms of order 1/p (p atmospheric pressure) can lead to large bias errors if the wet-bulb temperature depression is large. Temperature and pressure corrections on the ‘psychrometric constant’ cannot be neglected without the risk of a bias error in excess of precision limits placed on a result. Aspiration to an isothermal block for wet-bulb temperature measurement compared with measurement at the air stream source does not necessarily lead to a more precise estimate of the Bowen ratio.

The distribution of wet bulb temperature depression

Climatological series of humidity data are defined. It is shown how such series are required for valid climatological analysis. Theoretical normal frequency distributions are proposed for dry bulb and wet bulb temperatures. From these, by theoretical considerations, the distribution of wet bulb depression is found to be a truncated normal distribution. Statistical estimates for the theoretical parameters are given and the fits of the theoretical wet bulb distributions verified on climatological series for three widely different climatic conditions. The effects of variation in the parameters of the wet and dry bulb distributions on the wet bulb depression distribution are discussed.

A Simple Thermocouple Psychrometer for Determining Tissue 6

An apparatus for determining water potential of leaves (ψ) is described. It is a modification of one previously developed by van Andel for determining osmotic potentials of sap (π), for which purpose it may still be employed. A constantan—minalpha thermocouple is used for direct determination of wet-bulb temperature depression of air in moisture equilibrium with leaves. The system has advantages over others in simplicity of manufacture and electrical circuitry, and in adaptability to a range of signal reading and recording methods. It is capable of handling relatively large samples, e.g. 20 cereal leaves of total area (single side) of 300 cm2. Tests of leaf maturity and position effects in two potato crops are described. Differences between corresponding values of ψ and π, considered indicative of cell wall pressures, were less in lower leaves. In one crop, ψ was lower in relation to leaf relative water content with lower than with upper leaves and, in the other crop, with leaves from the more mature stages of growth. These findings are in accord with a higher rigidity of cell walls in lower and more mature leaves. Mean differences of ψ and π involved in the above conclusions were small, usually less than 2 bar, indicating the potential usefulness of the apparatus.

ON FORECASTING CEILING LOWERING DURING CONTINUOUS RAIN

Abstract During steady rain, the ceiling lowers in a discontinuous fashion. The ceiling heights may be predicted with sufficient accuracy by using a set of empirically determined rules. To obtain a relation for the time of occurrence of these ceilings, the factors which influence cloud formation are considered. An expression is derived for the rate of moisture increase due to evaporation from falling raindrops. The rate of moisture change, given by this expression, is combined with the effect of the other factors in order to obtain a formula which may be applied to find the time a ceiling of given height will occur. The variables in the forecast formula are (1) the wet-bulb temperature depression measured before the start of rain and (2) Fz, the effective rate of moisture increase caused by factors other than evaporation. Values for Fz are found empirically. An approximate method, based on the surface value of the depression, is used for finding the time of occurrence of the 800-, 500-, and 300-foot ceili...