Integrated analysis of cooling water systems: Modeling and experimental validation

Cooling towers are widely used in many industrial and utility plants as a cooling medium, whose thermal performance is of vital importance. Despite the wide interest in cooling tower design, rating and its importance in energy conservation, there are few investigations concerning the integrated analysis of cooling systems. This work presents an approach for the systemic performance analysis of a cooling water system. The approach combines experimental design with mathematical modeling. An experimental investigation was carried out to characterize the mass transfer in the packing of the cooling tower as a function of the liquid and gas flow rates, whose results were within the range of the measurement accuracy. Then, an integrated model was developed that relies on the mass and heat transfer of the cooling tower, as well as on the hydraulic and thermal interactions with a heat exchanger network. The integrated model for the cooling water system was simulated and the temperature results agree with the experimental data of the real operation of the pilot plant. A case study illustrates the interaction in the system and the need for a systemic analysis of cooling water system. The proposed mathematical and experimental analysis should be useful for performance analysis of real-world cooling water systems. (C) 2009 Elsevier Ltd. All rights reserved.

Photosynthesis and water relations of well-watered orange plants as affected by winter and summer conditions

The aim of this study was to evaluate how the summer and winter conditions affect the photosynthesis and water relations of well-watered orange trees, considering the diurnal changes in leaf gas exchange, chlorophyll (Chl) fluorescence, and leaf water potential (I) of potted-plants growing in a subtropical climate. The diurnal pattern of photosynthesis in young citrus trees was not significantly affected by the environmental changes when compared the summer and winter seasons. However, citrus plants showed higher photosynthetic performance in summer, when plants fixed 2.9 times more CO(2) during the diurnal period than in the winter season. Curiously, the winter conditions were more favorable to photosynthesis of citrus plants, when considering the air temperature (< 29 A degrees C), leaf-to-air vapor pressure difference (< 2.4 kPa) and photon flux density (maximum values near light saturation) during the diurnal period. Therefore, low night temperature was the main environmental element changing the photosynthetic performance and water relations of well-watered plants during winter. Lower whole-plant hydraulic conductance, lower shoot hydration and lower stomatal conductance were noticed during winter when compared to the summer season. In winter, higher ratio between the apparent electron transport rate and leaf CO(2) assimilation was verified in afternoon, indicating reduction in electron use efficiency by photosynthesis. The high radiation loading in the summer season did not impair the citrus photochemistry, being photoprotective mechanisms active. Such mechanisms were related to increases in the heat dissipation of excessive light energy at the PSII level and to other metabolic processes consuming electrons, which impede the citrus photoinhibition under high light conditions.

Macroscopic root water uptake distribution using a matric flux potential approach

Hydrological models featuring root water uptake usually do not include compensation mechanisms such that reductions in uptake from dry layers are compensated by an increase in uptake from wetter layers. We developed a physically based root water uptake model with an implicit compensation mechanism. Based on an expression for the matric flux potential (M) as a function of the distance to the root, and assuming a depth-independent value of M at the root surface, uptake per layer is shown to be a function of layer bulk M, root surface M, and a weighting factor that depends on root length density and root radius. Actual transpiration can be calculated from the sum of layer uptake rates. The proposed reduction function (PRF) was built into the SWAP model, and predictions were compared to those made with the Feddes reduction function (FRF). Simulation results were tested against data from Canada (continuous spring wheat [(Triticum aestivum L.]) and Germany (spring wheat, winter barley [Hordeum vulgare L.], sugarbeet [Beta vulgaris L.], winter wheat rotation). For the Canadian data, the root mean square error of prediction (RMSEP) for water content in the upper soil layers was very similar for FRF and PRF; for the deeper layers, RMSEP was smaller for PRF. For the German data, RMSEP was lower for PRF in the upper layers and was similar for both models in the deeper layers. In conclusion, but dependent on the properties of the data sets available for testing,the incorporation of the new reduction function into SWAP was successful, providing new capabilities for simulating compensated root water uptake without increasing the number of input parameters or degrading model performance.

Ecophysiological responses of water hyacinth exposed to Cr(3+) and Cr(6+)

Due to its wide industrial use, chromium (Cr) is considered a serious environmental pollutant of aquatic bodies. in order to investigate the ecophysiological responses of water hyacinth [Eichhornia crassipes (Mart.) Solms] to Cr treatment, plants were exposed to 1 and 10 mM Cr(2)O(3) (Cr(3+)) and K(2)Cr(2)O(7) (Cr(6+)) concentrations for two or 4 days in a hydroponic system. Plants exposed to the higher concentration of Cr(6+) for 4 days did not survive, whereas a 2 days treatment with 1 mM Cr(3+) apparently stimulated growth. Analysis of Cr uptake indicated that most of the Cr accumulated in the roots, but some was also translocated and accumulated in the leaves. However, in plants exposed to Cr(6+) (1 mM), a higher translocation of Cr from roots to shoots was observed. it is possible that the conversion from Cr(6+) to Cr(3+), which immobilizes Cr in roots, was not total due to the presence of Cr(6+), causing deleterious effects on gas exchange, chlorophyll a fluorescence and photosynthetic pigment contents. Chlorophyll a was more sensitive to Cr than chlorophyll b. Cr(3+) was shown to be less toxic than Cr(6+) and, in some cases even increased photosynthesis and chlorophyll content. This result indicated that the F(v)/F(0) ratio was more effective than the F(v)/F(m) ratio in monitoring the development of stress by Cr(6+). There was a linear relationship between qP and F(v)/F(m). No statistical differences were observed in NPQ and chlorophyll a/b ratio, but there was a tendency to decrease these values with Cr exposure. This suggests that there were alterations in thylakoid stacking, which might explain the data obtained for gas exchanges and other chlorophyll a fluorescence parameters. (C) 2008 Elsevier B.V. All rights reserved.

Dosage-dependent shift in the spore community of arbuscular mycorrhizal fungi following application of tannery sludge

The controlled disposal of tannery sludge in agricultural soils is a viable alternative for recycling such waste; however, the impact of this practice on the arbuscular mycorrhizal fungi (AMF) communities is not well understood. We studied the effects of low-chromium tannery sludge amendment in soils on AMF spore density, species richness and diversity, and root colonization levels. Sludge was applied at four doses to an agricultural field in Rolandia, Parana state, Brazil. The sludge was left undisturbed on the soil surface and then the area was harrowed and planted with corn. The soil was sampled at four intervals and corn roots once within a year (2007/2008). AMF spore density was low (1 to 49 spores per 50 cm(3) of soil) and decreased as doses of tannery sludge increased. AMF root colonization was high (64%) and unaffected by tannery sludge. Eighteen AMF species belonging to six genera (Acaulospora, Glomus, Gigaspora, Scutellospora, Paraglomus, and Ambispora) were recorded. At the sludge doses of 9.0 and 22.6 Mg ha(-1), we observed a decrease in AMF species richness and diversity, and changes in their relative frequencies. Hierarchical grouping analysis showed that adding tannery waste to the soil altered AMF spore community in relation to the control, modifying the mycorrhizal status of soil and selectively favoring the sporulation of certain species.

Hydrothermal Stability of Modified Silica Membranes for Gas Separation

A new class of hybrid molecular sieve silica (MSS) membranes is developed and tested against standard and organic templated membranes. The hybrid membrane is synthesized by the standard sol-gel process, integrating a template (methyltriethoxysilane - MTES) and a C6 surfactant (triethylhexylammonium bromide) into the silica film matrix. After hydro treatment under a relative humidity of 96% for 50h, the hybrid membrane shows no changes in its gas separation capabilities or energy of mobility. The structural characteristics and integrity of the hybrid membrane are retained due to a high concentration of organophilic functional groups and alkoxides observed using 29 Si NMR. In contrast, the structural integrity of the membranes prepared with non-templated films deteriorated during the hydro treatment due to a large percentage of silanol groups (Si-OH) which react with water. The hybrid membranes underwent a decrease in the H2/CO2 selectivity of only 1% whereas for the non-templated membrane a 21% decrease was observed. The transport mechanism of the hybrid membranes is activated as permeation increased with temperature. The activation energy for the permeation of H2 is positive while negative for CO2. The H2 permeation obtained was 3x 10 -8 mol.m -2 .s -1 .Pa -1 and permselectivities for H2/CO2 and H2/N2 varied between 1-7 and 31-34, respectively.

Model for gas-liquid flow through wet porous medium

A method involving bubbling of air through a fibrous filter immersed in water has recently been investigated (Agranovski et al. [1]). Experimental results showed that the removal efficiency for ultra-fine aerosols by such filters was greatly increased compared to dry filters. Nuclear Magnetic Resonance (NMR) imaging was used to examine the wet filter and to determine the nature of the gas flow inside the filter (Agranovski et al. [2]). It was found that tortuous preferential pathways (or flow tubes) develop within the filter through which the air flows and the distribution of air and water inside the porous medium has been investigated. The aim of this paper is to investigate the geometry of the pathways and to make estimates of the flow velocities and particle removal efficiency in such pathways. A mathematical model of the flow of air along the preferred pathways has been developed and verified experimentally. Even for the highest realistic gas velocity the flow field was essentially laminar (Re approximate to 250). We solved Laplace's equation for stream function to map trajectories of particles and gas molecules to investigate the possibility of their removal from the carrier.

A study of the oxidation of two aromatic polyimide fluoropolymers containing phenylphosphine oxide by a water plasma and gamma-radiolysis in air

The oxidation of two fluorinated polyimides containing phenylphosphine oxide units, TOR-RC and TOR-RC ODPA, have been studied at 300 K for treatment by a water plasma and gamma -radiolysis in air. The changes in the O 1s/C 1s ratios obtained from x-ray photoelectron spectroscopy (XPS) analysis showed that for exposure to the water plasma the ratio increases at short exposure times and then levels to a constant value. Evidence for the formation of phosphate species was also obtained from the XPS analyses. Similar observations were made for gamma -radiolysis of the polymers in air. The polymers containing phenylphosphine oxide were found to be more resistant to oxidation in the water plasma than Kapton(R). Radiolysis of the polymers in air to high doses were also accompanied by a red shift in the visible absorption spectra.

Gas permeation in silicon-oxide/polymer (SiOx/PET) barrier films: role of the oxide lattice, nano-defects and macro-defects

We propose a model for permeation in oxide coated gas barrier films. The model accounts for diffusion through the amorphous oxide lattice, nano-defects within the lattice, and macro-defects. The presence of nano-defects indicate the oxide layer is more similar to a nano-porous solid (such as zeolite) than silica glass with respect to permeation properties. This explains why the permeability of oxide coated polymers is much greater, and the activation energy of permeation much lower, than values expected for polymers coated with glass. We have used the model to interpret permeability and activation energies measured for the inert gases (He, Ne and Ar) in evaporated SiOx films of varying thickness (13-70 nm) coated on a polymer substrate. Atomic force and scanning electron microscopy were used to study the structure of the oxide layer. Although no defects could be detected by microscopy, the permeation data indicate that macro-defects (>1 nm), nano-defects (0.3-0.4 nm) and the lattice interstices (<0.3 nm) all contribute to the total permeation. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of water temperature and oxygen levels on the diving behavior of two freshwater turtles: Rheodytes leukops and Emydura macquarii

Rheodytes leukops is a bimodally respiring turtle that extracts oxygen from the water chiefly via two enlarged cloacal bursae that are lined with multi-branching papillae. The diving performance of R. leukops was compared to that of Emydura macquarii, a turtle with a limited ability to acquire aquatic oxygen. The diving performance of the turtles was compared under aquatic anoxia (0 mmHg), hypoxia (80 mmHg) and normoxia (155 mmHg) at 15, 23, and 30degreesC. When averaged across all temperatures the dive duration of R. leukops more than doubled from 22.4 +/- 7.65 min under anoxia to 49.8 +/- 19.29 min under normoxic conditions. In contrast, aquatic oxygen level had no effect on the dive duration of E. macquarii. Dive times for both species were significantly longer at the cooler temperature, and the longest dive recorded for each species was 538 min and 166 min for R. leukops and E. macquarii, respectively. Both species displayed a pattern of many short dives punctuated by occasional long dives irrespective of temperature or oxygen regime. Rheodytes leukops, on average, spent significantly less time (42 +/- 2 sec) at the surface per surfacing event than did E. macquarii (106 +/- 20 sec); however, surface times for both species were not related to either water temperature or oxygen level.

Dry matter production and allocation in Eucalyptus cloeziana and Eucalyptus argophloia seedlings in response to soil water deficits

Effects of soil water availability on seedling growth, dry matter production and allocation were determined for Gympie ( humid coastal) and Hungry Hills ( dry inland) provenances of Eucalyptus cloeziana F. Muell. and for E. argophloia Blakely ( dry inland) species. Seven-month-old seedlings were subjected to well-watered (100% field capacity, FC), moderate (70% FC) and severe (50% FC) soil water regimes in a glasshouse environment for 14 wk. There were significant differences in seedling growth, biomass production and allocation patterns between species. E. argophloia produced twice as much biomass at 100% FC, and more than three times as much at 70% and 50% FC than did either E. cloeziana provenance. Although the humid provenance of E. cloeziana had a greater leaf area at 100% FC conditions than did the dry provenance, total biomass production did not differ significantly. Both E. cloeziana provenances were highly sensitive to water deficits. E. argophloia allocated 10% more biomass to roots than did E. cloeziana. Allometric analyses indicated that relative biomass allocation patterns were significantly affected by genotype but not by soil water availability. These results have implications for taxon selection for cultivation in humid and subhumid regions.

Online titrimetric and off-gas analysis for examining nitrification processes in wastewater treatment

The two steps of nitrification, namely the oxidation of ammonia to nitrite and nitrite to nitrate, often need to be considered separately in process studies. For a detailed examination, it is desirable to monitor the two-step sequence using online measurements. In this paper, the use of online titrimetric and off-gas analysis (TOGA) methods for the examination of the process is presented. Using the known reaction stoichiometry, combination of the measured signals (rates of hydrogen ion production, oxygen uptake and carbon dioxide transfer) allows the determination of the three key process rates, namely the ammonia consumption rate, the nitrite accumulation rate and the nitrate production rate. Individual reaction rates determined with the TOGA sensor under a number of operation conditions are presented. The rates calculated directly from the measured signals are compared with those obtained from offline liquid sample analysis. Statistical analysis confirms that the results from the two approaches match well. This result could not have been guaranteed using alternative online methods. As a case study, the influences of pH and dissolved oxygen (DO) on nitrite accumulation are tested using the proposed method. It is shown that nitrite accumulation decreased with increasing DO and pH. Possible reasons for these observations are discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.

Effects of soil water availability on water use efficiency of Eucalyptus cloeziana and Eucalyptus argophloia plants

Effects of soil water availability on transpiration efficiency (WUET), instantaneous water use efficiency (WUEi) and carbon isotope composition (delta(13)C) were investigated in 7-month-old plants of humid coastal (Gympie) and dry inland ( Hungry Hills) provenances of Eucalyptus cloeziana F. Muell. and in a dry inland provenance of E. argophloia Blakely (Chinchilla), supplied with 100 (W-100), 70 (W-70) and 50% (W-50) of their water requirements. At W-100, WUET of the three provenances were not significantly different but as available soil moisture decreased, E. argophloia produced greater biomass and demonstrated significantly higher WUET than either E. cloeziana provenance. Midday WUEi was not significantly affected by watering regime within each provenance but was lowest in E. argophloia. A decrease in soil water availability caused a consistent increase in delta(13)C values in all three provenances; however, delta(13)C values of E. argophloia in all three water regimes were significantly lower than those of E. cloeziana provenances, which did not differ significantly from each other. For all three provenances, delta(13)C was not correlated with WUEi but height and root collar diameter were negatively correlated to delta(13)C. There was little evidence of differences in delta(13)C, WUET and WUEi between E. cloeziana provenances but clear differences between E. cloeziana and E. argophloia. The high WUET, low WUEi and low delta(13)C for E. argophloia may have implications in the selection of Eucalyptus provenances for commercial forestry in low-rainfall regions.

Solubility of Ethene in Water and in a Medium for the Cultivation of a Bacterial Strain

The solubility of ethene in water and in the fermentation medium of Xanthobacter Py(2) was determined with a Ben-Naim-Baer type apparatus. The solubility measurements were carried out in the temperature range of (293.15 to 323.15) K and at atmospheric pressure with a precision of about +/- 0.3 %. The Ostwald coefficients, the mole fractions of the dissolved ethene, at the gas partial pressure of 101.325 kPa, and the Henry coefficients, at the water vapor pressure, were calculated using accurate thermodynamic relations. A comparison between the solubility of ethene in water and in the cultivation medium has shown that this gas is about 2.4 % more soluble in pure water. On the other hand, from the solubility temperature dependence, the Gibbs energy, enthalpy, and entropy changes for the process of transferring the solute from the gaseous phase to the liquid solutions were also determined. Moreover, the perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS) model was used for the prediction of the solubility of ethene in water. New parameters, k(ij), are proposed for this system, and it was found that using a ky temperature-dependent PC-SAFT EOS describes more accurately the behavior solubilities of ethene in water at 101.325 kPa, improving the deviations to 1 %.