Wet-bulb Depression Research Articles

Analysis of modified counter-flow cooling towers

Evaporative air cooling for human comfort and other applications, whenever possible and feasible, is less expensive than conventional air conditioning. A cooling tower is used in the centralised evaporative air cooling system. In the present study, the counter-flow cooling tower is modified to pre-cool the air at the tower inlet, either by the water after the cooling load, or the tower exit air. These two modified cooling towers are modelled and their thermal performances are compared with the conventional counter-flow cooling tower. For generality, the results are presented in terms of number of transfer units ( NTU), a dimensionless number for a cooling tower indicating its size. The modified cooling towers are found to be better than the conventional one in lowering the tower approaches below about 2°C. These cooling towers seem to be distinctly advantageous when operating at low approaches, small ranges and large wet-bulb depressions, thus making them quite useful in evaporative air cooling applications.

Modelling grapevine phenology against weather: Considerations based on a large data set

Phenological data for 11 districts, 12 varieties and four seasons were modelled against averages of daily records of maximum and minimum temperatures and wet bulb depression. Weather data were taken from the nearest government weather station, which was commonly up to 10 km from the vineyard. The use of so-called ‘heat degree day’ methods (e.g. Winkler et al., 1974) were abandoned because the inherent correlation between elapsed time and the value of an accumulation confounds regression procedures and interpretation; averages, rather than accumulations, were used as variates in all regressions. The model of budburst involved small district and year effects, and accounted for 94.5% of the variation in the data. This demonstrated that off-site weather data can provide effective models. Models of flowering and harvest accounted for 89.2% and 92.5% of the variation in the data respectively, but involved large district and year effects. Averages of weather taken from 3 weeks or more prior to all events were significantly associated with the dates of those same events. The wet bulb depression provided significant and useful variates in the model of budburst. In addition to other associations, the date of flowering was significantly associated with the weather conditions prior to budburst. Likewise, the date of harvest was significantly associated with weather conditions prior to both budburst and flowering. Budburst and harvest dates were also associated with averages of weather taken over the 10 days just before the event. The variety of these associations encourages the use of a wider range of variates than is common in phenological studies. The district and year effects in the case of the flowering and harvest models could result from the complicated effect of the canopy on vine microclimate, or the influence of short term weather events such as storms, or, in the case of harvest, they could result from imprecise definitions of maturity. Time series methods are advocated as a means to cope better with short term weather events and also to facilitate physiological interpretation of phenological models.

IMPROVING THE QUALITY OF TIMBER FROM RED BEECH (N. FOSCA) BY INTERMITTENT DRYING

ABSTRACT The effect of cycling the external conditions on the timber quality and drying time during seasoning has been studied for red beech (Nothofagus fusca), a difficult-to-dry New Zealand hardwood, inalaboratorybatchdryer. Intermittent drying at anair temperature of 45°C and a wet-bulb depression of 10°C takes longer to yield a given moisture content than continuous drying under the same conditions, but produces timber without honeycomb or severe case-hardening as observed in continuous drying. The experiments also indicate that the timber can tolerate a higher air temperature (55°C) in intermittent drying at the same wet-bulb depression with less case-hardening and without showing honeycomb compared with continuous drying at 45°C, having a similar total drying time. Intermittent drying at a slightly higher dry-bulb temperature (60°C) and a much higher wet-bulb depression (18°C) gives a similar degree of case-hardening to that found in samples dried continuously at a dry-bulb temperature of 45°C.

Check formation during the drying of Eucalyptus Globulus

The effects of temperature, wet bulb depression and high humidity treatments on the formation and extension of checks during the first two weeks drying Eucalyptus globulus boards from the green were investigated. In 6 runs 33 matched quarter- and backsawn boards of different dimensions and 400 mm in length were predried simultaneously under various drying conditions. The results show that damage caused by checks inside the boards was significantly lower when the initial drying temperature was low and the surface layers were periodically rewetted with high humidity treatments at low temperatures than damage resulting with conventional drying schedules for this species. A further reduction in checks was attained when the boards were steamed before drying was started. Under the above conditions it was possible to dry up to 60 mm thick quarter- and backsawn boards without significant checking.

Control Algorithms for an Aspirated Psychrometer

Relative humidity in agricultural buildings can be computed with readings from an aspirated psychrometer by utilizing an algorithm for selecting the appropriate values of wet and dry bulb temperature observed during each aspiration period. A dataset consisting of observations of wet and dry bulb temperature from four psychrometers during 10-min aspiration periods was analyzed to determine the effect of four different algorithms on the computed relative humidity. Algorithms designed to reduce aspiration time by sensing steady or increasing wet bulb temperature gave inconsistent results. The recommended algorithm uses wet and dry bulb temperature readings corresponding to the occurrence of the maximum wet bulb depression during aspiration, with an aspiration period of 4-6 min being adequate for most purposes using the psychrometer tested.

Drip vs. Wetted-Pad Evaporative Cooling of Farrowing Houses in Oklahoma

A comparison of drip cooling vs. wetted-pad evaporative cooling was performed on 61 sows over three farrowings. There were no significant differences between cooling methods for piglet weight gain, percentage of piglets weaned or sow weight loss. There was a significant difference in respiration rates between cooling methods. Respiration rate was a function of wet-bulb depression.

EFFECTS OF HYBRID AND GRAIN DAMAGE ON ESTIMATED DRY MATTER LOSS FOR HIGH-MOISTURE SHELLED CORN

ABSTRACT NMR imaging was used to nondestructively measure transient moisture profiles during the drying of an ear of sweet com. Two-dimensional proton density images were measured, transient moisture profiles were determined, and shrinkage was measured from the proton densitiesAn interactive computer program was used to examine the effect of physical damage, hybrid, and weather conditions on dry matter loss during drying of 22% m.c. (wet basis) shelled corn with air at ambient conditions. Simulations used official weather data for October and November of 1969, 1975, and 1977 for locations in southwest, central, and northeast Indiana. Multipliers corrected allowable storage time for differences in grain damage and hybrid resistance to storage mold. Regardless of location or physical damage level, dry matter losses (DMLs) of the hybrids resistant to mold growth were con-sistently 30 to 40% lower than DMLs for susceptible hybrids. When 45% of the kernels had damage to the pericarp or were broken, there was 2.0 to 2.3 times the DML in the top layer of com as there was when 15% had damage. The effect of damage was slightly greater in hybrids susceptible to mold invasion. Hybrid storage mold resistance had approximately the same effect as changing the percentage of damaged kernels from 45% to 30%. Allowable storage time was influenced by both corn temperature and drying time. For the location-year combinations studied, average wet bulb depression during the drying period was a good indicator of time required to dry and average wet bulb temperature was a good indicator of potential for DML. These two factors can be used to interpret the influence of weather on differences in damage and hybrid resistance. Minimum deterioration of the top layer occurred when the average wet bulb temperature was relatively low and the average wet bulb depression was large. The increase in DML for a good year versus a bad year was equivalent to changing kernel damage from 30% to 45%..

Sensitivity of Penman estimates of evaporation to errors in input data

A reliable estimate of crop water requirements is one of the key design criteria required for the planning and operation of irrigation schemes. This in turn requires accurate estimation of evaporation for which the Penman form of the combination equation is widely used. This paper examines the sensitivity of evaporation estimates to errors in input data, and to uncertainties in the values of the parameters used in the equation. Results from a wide range of stations over the globe show that estimates are most sensitive to temperature, and that this sensitivity can have a marked seasonal fluctuation. The effects of uncertainty in the equation's parameter values are small and comparable to the sensitivities of the other input variables; wet bulb depression, wind speed and sunshine hours.

On the techniques of forecasting fog/stratus over The Dundigal airfield of Hyderabad

In this paper a new technique named 'Technique of Elimination' has been introduced for the forecasting of fog/stratus which utilizes the criterion of condition necessary to be satisfied by relative humidity during night prior to the formation of fog/stratus. Taylor's technique of ‘fog prediction diagram' has been modified by including the incidence of stratus also and it has been shown that it is feasible to give a forecast of fog/stratus as early as 1730 IST of the previous day in the months of November and December. Tendency of wet bulb depression at midnight has been computed and it has been shown that fog/stratus formed on most of the occasions when the interval of time so guessed fell within the normal hour of minimum temperature; Synoptic situations favourable for the formation of fog/ stratus at Dundigal have also been studied.

Wet-Bulb Temperatures and Wet-Bulb Depressions in the United States and Southern Canada

ABSTRACT MAPS of mean wet-bulb temperature isolines and mean wet-bulb depression isolines (and their standard deviations) for the U.S. and southern Canada were drawn for each month of the year using weather data from 140 observing sites. Map isolines use degrees Celsius units.

9 Biophysical and Physiological Integration of Proper Clothing for Exercise

In this chapter, I have presented a potpourri of examples of proper clothing to wear during various exercise demands in different environments. These examples are not wholly exact for all persons. For example, during the 1984 Olympics in Los Angeles, clothing wear related to the particular environment was totally different. We have already described the aerodynamic necessities of cyclists and runners. At the other extreme, equestrians had to contend with a warm, moderately humid environment, plus a solar load that added to the effective heat stress, while wearing clothing having clo values of nearly 0.8-0.9, plus headgear that limited evaporative heat loss. Obviously, garments with high water vapor permeation and bellows properties were necessary. Runners in the marathon faced equal thermal challenges. In addition, they incurred variable levels of hypovolemia and cardiovascular strain. A. Salazar, for example, was advised to omit shower sprays, and he ran with a prototype high-permeability singlet. The excessive wetting plus time to maneuver to the spray was deemed of no value, since Mr. Salazar chafes easily from wet clothes (L. Armstrong, personnel communication). One interesting response to this advice is to consider the clothed runner as a wet globe thermometer under forced convection. A high-contact fabric, especially one like cotton, does allow evaporative cooling, provided that the skin-ambient vapor pressure gradient is not diminished by high relative humidity. Salts in sweat may reduce the skin's vapor pressure ; however, Woodcock and Breckenridge point out that "secreted sweat (especially with heat acclimation) is so dilute that no appreciable lowering of vapor pressure would occur unless sweat were concentrated many times by evaporation." Thus, the degree of "human" wet bulb depression simulated by a completely wet runner may or may not be an advantage, since all other variables are also constant (i.e., humidity, weight of clothing as in Figure 13, etc.) or the level of hypovolemia is not excessive and the person is fully heat acclimated. Problems such as these may be theoretical, but they serve to show that the thermal biophysics and physiology of exercise follow similar fundamental pathways that can be highly pertinent. As we sought to point out in this chapter, these pathways have merged in the last 30 years with developments such as warmth without bulk for backpackers (which is a welcomed contrast to heavy arctic wear), materials that allow athletes to remain somewhat comfortable while sweating, and other advances that luckily have replaced the less appealing sports apparel such as the old woolen baseball uniform.(ABSTRACT TRUNCATED AT 400 WORDS)

Modifications to A Controlled Environment Cabinet to Gain Proportional Control Over Temperature and Humidity

Modifications to A Controlled Environment Cabinet to Gain Proportional Control Over Temperature and Humidity

Germination of Direct Harvested Peanut Seed

ABSTRACT THE germination of seed from samples of peanuts dried in the laboratory with controlled (constant and cyclic) air temperature, humidity and airflow was determined. The peanuts were direct hravested, i.e., digging and picking in one pass through the field, to eliminate the uncertainties of windrow exposure and its effect on peanut seed germination. A range of entering air conditions (specified in terms of wet bulb (WB) temperature and depression) and airflow rates were studied during several harvest seasons (1971-1979). The study involved 97 harvest dates, 2 cultivars and 914 germination analyses. A sub-set of data (123 samples from near the point of air entry) was selected to establish relationships between seed germination and drying conditions (WB temperature, airflow and WB depression). The three relationships were presented graphically in terms of geometric germination means. The results suggested an optimum drying air WB temperature of 21 C with a 10% germination reduction from the optimum when WB temperatures of 16.2 and 29.4 C were used. A gradual reduction in average germination was reported with increased airflow and increased drying air potential (WB depression). The temperature relationship was extended to lower WB temperatures with data collected during 1978 and 1979. The results of two studies by others on peanut seed germination were shown compatible and supported the temperature relationship. The results provide a basis for germination loss estimates for direct harvested peanuts when dried with different entering air conditions and airflow rates.

A General Theory of Wet Surface Heat Exchangers and its Application to Regenerative Evaporative Cooling

Wet surface heat exchangers such as cooling towers and wet plate heat exchangers are important in air conditioning. A linear approximate model of wet surface heat exchangers is proposed. The equations of the model are rearranged, enabling solutions for wet bulb depression and wet bulb temperature to be obtained independently, by analogy from published solutions for dry bulb temperature in dry surface heat exchangers. Performance predictions by this method for a crossflow cooling tower are found to agree with those from a prevous finite difference solution. Published performance measurements for a crossflow wet plate heat exchanger are lower than predicted by the method possibly due to poor wetting or excessive water flow. Excellent performance is predicted for a proposed regenerative evaporative cooler using such an exchanger.

Rainfall interception in a forest stand estimated from grassland meteorological data

Meteorological data collected over grassland were used in the Rutter and analytical interception models to predict interception losses for a Scots pine stand in Thetford Forest during 84 weeks in 1975 and 1976. Rutter and analytical model estimates using grassland data overestimated the observed losses by 37% and 25%, respectively; estimates using data collected over the forest overestimated by 8% and 5%, respectively. Systematic differences in the meteorological parameters controlling the evaporation rate from wet forest and wet grass are the cause of the overestimation of interception losses when grassland data are used in the models. Mean air temperature over the wet forest was 0.75°C cooler, mean wet-bulb depression was 0.25°C smaller, and mean vapour pressure deficit was 0.4 mbar smaller than the mean values observed over wet grass in 116 hr when ⩾ 0.5 mm of rain fell at both observation sites. No significant differences between sites were found when both the grass and the forest canopy were dry. Regression equations for forest-site parameters on grassed-site parameters were used to adjust the grassed-site data for use in the models. Analytical model estimates using adjusted data were closely comparable to both observed losses and model estimates using above-forest data. Rutter model estimates using adjusted data were significantly different from the observed losses for 1976 and for the combined 1975–1976 data, but were comparable with the observed losses and model estimates using above-forest data in 1975.

Título en español.

Se preparó una harina de guineo verde de una calidad aceptable usando un deshidratador de gabinete. Los guineos verdes se pelaron a vapor, se cortaron en cubos pequeños y se pusieron en bandejas para deshidratarlos. Se probaron seis formas distintas a base del espesor de la camada de cubos y de las temperaturas. Los 3 niveles fueron: una sola camada de cubos (6 1/2 lb.), dos camadas (hasta la mitad, 13 lb.); y cuatro camadas (completamente llenas, 23 1/2 lb.). Las temperaturas fueron: 160°F. (71.1° C).) por la primera hora de deshidratación subiendo luego a 200°F. (93.3° C.) el resto del período; y otras a 200° F. todo el período. El período de deshidratación fue de 6 horas. A los niveles más bajos de llenado la deshidratación fue más rápida. La humedad inicial de los cubos de guineo verde fue más determinante de la rapidez de deshidratación que los niveles de temperatura usados dentro de un mismo nivel de llenado. De la harina se prepararon bizcochitos que tuvieron gran aceptación. Estos se prepararon mezclando cantidades iguales de harina de guineo y harina de trigo.

A Method for the In Situ Measurement of Lichen Moisture Content

Up to the present time a non-destructive method of measuring the moisture contents of individual lichens in situ has not been available. Such a method is described; it operates on the principle of thallus cooling as a function of thallus moisture content. Small thermocouples are used to measure wet and dry lichen temperatures which serve as reference points for a third temperature-the 'ambient' lichen temperature. As the moisture content of the 'ambient' lichen thallus fluctuates, its temperature fluctuates between the two fixed reference temperatures. The proportion of maximum wet-bulb depression shown by the 'ambient' lichen can be made a measure of its moisture content through the use of suitable calibration. Field and laboratory tests indicate that reliable in situ measurements of thallus moisture content are obtainable using this method, provided reasonable precautions are taken to maintain the moisture status of the reference thalli.

Possible Influence of Evaporation Below Cloud Base on Rain Enhancement

Abstract The possibility is discussed that evaporation in the subcloud layer might be a major factor controlling the efficiency of rain enhancement by seeding, under the simplistic assumption that seeded clouds produce larger proportions of small raindrops than unseeded clouds. The concept of an evaporation parameter, E = ∫0HΔTdh, is introduced, and it is shown that this quantity is a measure of the amount of water evaporated from a raindrop falling through an air column of height H and with a wet-bulb depression profile ΔT(h). Based on the evaporation parameter a simple numerical model is constructed, which models the evaporation process as a function of air mass conditions and raindrop-size distributions. This makes it possible to estimate what changes in rainfall at the ground might occur for given changes in rainfall at cloud base. Numerical results are obtained for ambient conditions of the Swiss hail suppression project Grossversuch III. These results establish the potential importance of evaporatio...

On the Measurement of In-Cloud and Wet-Bulb Temperatures from an Aircraft

Measurements of air temperature with an immersion thermometer from an aircraft are invariably affected by the increased temperature of the decelerated air in the vicinity of the element. For dry air and a dry thermometer this effect is well known and usually taken into account. However, the evaporation of water from an element which has been wetted either intentionally (as in a wet-bulb thermometer) or unintentionally (by cloud or rain droplets) reduces this temperature increase. The psychrometric equation generalized for high-speed flow is used to calculate the aerodynamic correction factor for a wet temperature sensor. As an example of the magnitude of the evaporation effect, the temperature difference between a wet and a dry thermometer in a saturated airstream moving at 70 m sec−1>1C. Aircraft measurements in clouds from 3 different temperature sensors are discussed. The temperature differences between an exposed and a protected thermometer are found to be as large as 1C in conditions where the exposed thermometer is wet and the protected thermometer is dry. More importantly, the outputs of the two sensors are well correlated in clear air but are uncorrelated in cloud. Humidity measured with a wet-bulb depression sensor is found to compare very well with the output of a dewpoint hygrometer in clear air. This sensor is also a good cloud indicator since the wet-bulb depression is ∼0 only when the dry-bulb thermometer is completely wet.

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.