共查询到20条相似文献,搜索用时 15 毫秒
1.
Few green roof studies cover intensive and tropical types and specific canopy microclimate. We examined the ecological energetics of a sky woodland in humid-tropical Hong Kong. Environmental sensors monitored the microclimatic and soil parameters for 14 months. Key biophysical variables of transpiration, wind, light, and through-canopy energy flux are modeled to investigate seasonal and weather effects. The woodland forms a cloistered subcanopy environment with rather stable microclimate. Transpiration and latent heat loss are enhanced by solar radiation and low relative humidity, but less by wind. On sunny days, about 20% of incident solar radiation can reach the soil surface. The canopy reflected more near-infrared radiation (NIR) than photosynthetically active radiation (PAR), highlighting a hitherto neglected passive-cooling mechanism. The highest transpiration rate occurs in autumn rather than summer due to dry-mild weather. The woodland canopy could reduce 300 W m−2 energy flux into the substrate. The canopy warmed by solar energy transmits heat to subcanopy air. Latent and sensible heat loss in the subcanopy domain is suppressed, thus dampening the passive-cooling effect. The capability of the tropical intensive green roof to reduce temperature is relatively inefficient comparing with temperate region counterparts. The findings could inform design and choice of green roofs. 相似文献
2.
The Great Salt Lake has a salinity near 150 g/L and is habitat for over 200 species of migratory birds. The diet of many of these birds is dependent on the food web of carbonaceous biostromes (stromatolites) that cover 260 km2 of the lake's littoral zone. We investigated the biostrome community to understand their production processes and to assess whether they are a potential vector for bioconcentration of high mercury and selenium levels in the lake. The periphyton community of the biostromes was > 99% colonial cyanobacteria. Periphyton chlorophyll levels averaged 900 mg m−2 or nine times that of the lake's phytoplankton. Lake-wide estimates of chlorophyll suggest that their production is about 30% of that of the phytoplankton. Brine fly (Ephydra gracilis) larval densities on the biostromes increased from 7000 m−2 in June to 20000 m−2 in December. Pupation and adult emergence halted in October and larvae of various instars overwintered at temperatures < 5 °C. Mean total dissolved and dissolved methyl mercury concentrations in water were 5.0 and 1.2 ηg L−1. Total mercury concentrations in the periphyton, fly larvae, pupae, and adults were, respectively, 152, 189, 379 and 659 ηg g−1 dry weight, suggesting that bioconcentration is only moderate in the short food web and through fly developmental stages. However, common goldeneye ducks (Bucephala clangula) that feed primarily on brine fly larvae at the Great Salt Lake had concentrations near 8000 ηg Hg g−1 dry weight in muscle tissue. Data from a previous study indicated that selenium concentrations in periphyton, brine fly larvae and goldeneye liver tissue were high (1700, 1200 and 24,000 ηg g−1, respectively) and Hg:Se molar ratios were < 1.0 in all tissues, suggesting that the high mercury concentration in the ducks may be partially detoxified by combining with selenium. The study demonstrated that the high mercury levels in the Great Salt Lake are routed through the biostrome community resulting in invertebrate prey that may provide health risks for birds and humans that consume them. 相似文献
3.
Sarah Nahon Viviana A. Castro Porras François Charles 《The Science of the total environment》2009,407(6):1892-1900
The sea urchin Sphaerechinus granularis was used to investigate the impact of relevant levels of UV-B radiation on the early life stages of a common Mediterranean free spawning benthic species. Sperm, eggs and embryos were exposed to a range of UV radiation doses. The resulting endpoints were evaluated in terms of fertilisation success, development and survival rates. Above a weighted UV radiation dose of 0.0029 kJ m− 2, fertilisation capability of irradiated sperm decreased rapidly. The exposure of the eggs to 0.0175 kJ m− 2 and more led to delayed and inhibited development with ensuing embryonic morphological abnormalities. One-day old larvae remained strongly sensitive to UV radiation as shown by the 50% decrease of the larval survival rate for a dose of 0.025 kJ m− 2 UVR. The elevated sensitivity of embryos to experimental UVR went along with a lack of significant amount of sunscreen compounds (e.g., mycosporine-like amino acids) in the eggs. The present results demonstrated that gamete viability and embryonic development may be significantly impaired by solar UV radiation in S. granularis, compromising in this way the reproduction of the species. Unless adaptive behavioural reproductive strategies exist, the influence of ambient UV radiation appears as a selective force for population dynamics of broadcast spawners in the shallow benthic Mediterranean environment. 相似文献
4.
Solar radiation-driven inactivation of bacteria, virus and protozoan pathogen models was quantified in simulated drinking water at a temperate latitude (34°S). The water was seeded with Enterococcus faecalis, Clostridium sporogenes spores, and P22 bacteriophage, each at ca 1 × 105 m L−1, and exposed to natural sunlight in 30-L reaction vessels. Water temperature ranged from 17 to 39 °C during the experiments lasting up to 6 h. Dark controls showed little inactivation and so it was concluded that the inactivation observed was primarily driven by non-thermal processes. The optimised reactor design achieved S90 values (cumulative exposure required for 90% reduction) for the test microorganisms in the range 0.63-1.82 MJ m−2 of Global Solar Exposure (GSX) without the need for TiO2 as a catalyst. High turbidity (840-920 NTU) only reduced the S90 value by <40%. Further, when all S90 means were compared this decrease was not statistically significant (prob. > 0.05). However, inactivation was significantly reduced for E. faecalis and P22 when the transmittance of UV wavelengths was attenuated by water with high colour (140 PtCo units) or a suboptimally transparent reactor lid (prob. < 0.05). S90 values were consistent with those measured by other researchers (ca 1-10 MJ m−2) for a range of waters and microorganisms. Although temperatures required for SODIS type pasteurization were not produced, non-thermal inactivation alone appeared to offer a viable means for reliably disinfecting low colour source waters by greater than 4 orders of magnitude on sunny days at 34°S latitude. 相似文献
5.
Treatment of fresh air in ventilation systems for air-conditioned offices consumes a significant amount of energy and affects the indoor air quality (IAQ). In this study, energy impact on the ventilation systems was examined against certain IAQ objectives for indoor airborne bacteria exposure risk in air-conditioned offices of Hong Kong. The relationship between thermal energy consumptions and indoor airborne bacteria exposure levels based on regional surveys was investigated. The thermal energy consumptions of ventilation systems operating for carbon dioxide (CO2) exposure concentrations between 800 and 1200 ppmv for typical office buildings and the corresponding failure probability against some target bacteria exposure levels were evaluated. The results showed that, for a reference indoor environment at a CO2 exposure concentration of 1000 ppmv, the predicted average thermal energy saving of ventilation system for a unit increment of the expected risk of unsatisfactory IAQ of 1% was 55 MJ m−2 yr−1 and for a unit decrement of 1%, the predicted additional thermal energy consumption was 58 MJ m−2 yr−1 respectively. This study would be a useful source of reference in evaluation of the energy performance of ventilation strategies in air-conditioned offices at a quantified exposure risk of airborne bacteria. 相似文献
6.
Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining 总被引:2,自引:0,他引:2
Alyssa E. Shiel Dominique Weis Kristin J. Orians 《The Science of the total environment》2010,408(11):2357-9224
To evaluate metallurgical processing as a source of Zn and Cd isotopic fractionation and to potentially trace their distribution in the environment, high-precision MC-ICP-MS Zn, Cd and Pb isotope ratio measurements were made for samples from the integrated Zn-Pb smelting and refining complex in Trail, B.C., Canada. Significant fractionation of Zn and Cd isotopes during processing of ZnS and PbS ore concentrates is demonstrated by the total variation in δ66/64Zn and δ114/110Cd values of 0.42‰ and 1.04‰, respectively, among all smelter samples.No significant difference is observed between the isotopic compositions of the Zn ore concentrates (δ66/64Zn = 0.09 to 0.17‰; δ114/110Cd = − 0.13 to 0.18‰) and the roasting product, calcine (δ66/64Zn = 0.17‰; δ114/110Cd = 0.05‰), due to ∼ 100% recovery from roasting. The overall Zn recovery from metallurgical processing is ∼ 98%, thus the refined Zn metal (δ66/64Zn = 0.22‰) is not significantly fractionated relative to the starting materials despite significantly fractionated fume (δ66/64Zn = 0.43‰) and effluent (δ66/64Zn = 0.41 to 0.51‰). Calculated Cd recovery from metallurgical processing is 72-92%, with the majority of the unrecovered Cd lost during Pb operations (δ114/110Cd = − 0.38‰). The refined Cd metal is heavy (δ114/110Cd = 0.39 to 0.52‰) relative to the starting materials. In addition, significant fractionation of Cd isotopes is evidenced by the relatively light and heavy isotopic compositions of the fume (δ114/110Cd = − 0.52‰) and effluent (δ114/110Cd = 0.31 to 0.46‰). In contrast to Zn and Cd, Pb isotopes are homogenized by mixing during processing. The total variation observed in the Pb isotopic compositions of smelter samples is attributed to mixing of ore sources with different radiogenic signatures. 相似文献
7.
Stable isotopes of bulk organic matter to trace carbon and nitrogen dynamics in an estuarine ecosystem in Babitonga Bay (Santa Catarina, Brazil) 总被引:1,自引:0,他引:1
Grace Virgínia Barros Luiz Antonio Martinelli Jean Pierre H.B. Ometto Gian Maria Zuppi 《The Science of the total environment》2010,408(10):2226-1099
The biogeochemical processes affecting the transport and cycling of terrestrial organic carbon in coastal and transition areas are still not fully understood. One means of distinguishing between the sources of organic materials contributing to particulate organic matter (POM) in Babitonga Bay waters and sediments is by the direct measurement of δ13C of dissolved inorganic carbon (DIC) and δ13C and δ15N in the organic constituents. An isotopic survey was taken from samples collected in the Bay in late spring of 2004. The results indicate that the δ13C and δ15N compositions of OM varied from − 21.7‰ to − 26.2‰ and from + 9.2‰ to − 0.1‰, respectively. δ13C from DIC ranges from + 0.04‰ to − 12.7‰. The difference in the isotope compositions enables the determination of three distinct end-members: terrestrial, marine and urban. Moreover, the evaluation of source contribution to the particulate organic matter (POM) in the Bay, enables assessment of the anthropogenic impact. Comparing the depleted values of δ13CDIC and δ13CPOC it is possible to further understand the carbon dynamic within Babitonga Bay. 相似文献
8.
M. Samer C. LoebsinM. Fiedler C. AmmonW. Berg P. SanftlebenR. Brunsch 《Energy and Buildings》2011,43(12):3718-3728
Experiments were performed to study the airflow rates (AFRs) in a naturally ventilated building through four summer seasons and three winter seasons. The AFRs were determined using heat balance (HB), tracer gas technique (TGT) and CO2-balance as averages of the values of all experiments carried out through the different seasons. The statistical analyses were correlation analysis, regression model and t-test. Continuous measurements of gaseous concentrations (NH3, CH4, CO2 and N2O) and temperatures inside and outside the building were performed. The HB showed slightly acceptable results through summer seasons and unsatisfactory results through winter seasons. The CO2-balance showed unexpected high differences to the other methods in some cases. The TGT showed reliable results compared to HB and CO2-balance. The AFRs, subject to TGT, were 0.12 m3 s−1 m−2, 1.15 m3 s−1 cow−1, 0.88 m3 s−1 LU−1, 56 h−1, 395 m3 s−1 and 470 kg s−1 through summer seasons, and 0.08 m3 s−1 m−2, 0.83 m3 s−1 cow−1, 0.64 m3 s−1 LU−1 39 h−1, 275 m3 s−1 and 328 kg s−1 through winter seasons. The AFRs are not independent values, rather they were estimated for specific reference values, which are: area, cow and LU as well as rates. The emission rates through summer seasons, subject to TGT, were 9.4, 40, 3538 and 2.3 g h−1 cow−1; and through winter seasons were 4.8, 19, 2332 and 2.6 g h−1 cow−1, for NH3, CH4, CO2 and N2O, respectively. 相似文献
9.
Minet E Coxon CE Goodhue R Richards KG Kalin RM Meier-Augenstein W 《Water research》2012,46(12):3723-3736
15N and 18O isotope abundance analyses in nitrate (NO3−) (expressed as δ15N-NO3− and δ18O-NO3− values respectively) have often been used in research to help identify NO3− sources in rural groundwater. However, questions have been raised over the limitations as overlaps in δ values may occur between N source types early in the leaching process. The aim of this study was to evaluate the utility of using stable isotopes for nitrate source tracking through the determination of δ15N-NO3− and δ18O-NO3− in the unsaturated zone from varying N source types (artificial fertiliser, dairy wastewater and cow slurry) and rates with contrasting isotopic compositions. Despite NO3− concentrations being often elevated, soil-water nitrate poorly mirrored the 15N content of applied N and therefore, δ15N-NO3− values were of limited assistance in clearly associating nitrate leaching with N inputs. Results suggest that the mineralisation and the nitrification of soil organic N, stimulated by previous and current intensive management, masked the cause of leaching from the isotopic prospective. δ18O-NO3− was of little use, as most values were close to or within the range expected for nitrification regardless of the treatment, which was attributed to the remineralisation of nitrate assimilated by bacteria (mineralisation-immobilisation turnover or MIT) or plants. Only in limited circumstances (low fertiliser application rate in tillage) could direct leaching of synthetic nitrate fertiliser be identified (δ15N-NO3− < 0‰ and δ18O-NO3− > 15‰). Nevertheless, some useful differences emerged between treatments. δ15N-NO3− values were lower where artificial fertiliser was applied compared with the unfertilised controls and organic waste treatments. Importantly, δ15N-NO3− and δ18O-NO3− variables were negatively correlated in the artificial fertiliser treatment (0.001 ≤ p ≤ 0.05, attributed to the varying proportion of fertiliser-derived and synthetic nitrate being leached) while positively correlated in the dairy wastewater plots (p ≤ 0.01, attributed to limited denitrification). These results suggest that it may be possible to distinguish some nitrate sources if analysing correlations between δ variables from the unsaturated zone. In grassland, the above correlations were related to N input rates, which partly controlled nitrate concentrations in the artificial fertiliser plots (high inputs translated into higher NO3− concentrations with an increasing proportion of fertiliser-derived and synthetic nitrate) and denitrification in the dairy wastewater plots (high inputs corresponded to more denitrification). As a consequence, nitrate source identification in grassland was more efficient at higher input rates due to differences in δ values widening between treatments. 相似文献
10.
Atmospheric concentrations and gas-particle partition coefficients were determined for polycyclic aromatic hydrocarbons (PAHs) in the atmosphere of Zonguldak, Turkey between May 2007 and April 2008. Total concentrations of PAHs ranged from 0.52 ng m− 3 to 636 ng m− 3 in the particle phase and from 5.60 ng m− 3 to 725 ng m− 3 in the gas phase. The annual mean concentrations of PAHs in the particle and gas phase were found to be 114 ng m− 3 and 184 ng m− 3, respectively. Significant seasonal variations of particle and gas phase PAH concentrations were observed with higher levels during cold period. The distribution of PAHs between the particle and gas phase was investigated and it was found that three ring PAHs were associated primarily with the gas phase, four ring PAHs were distributed almost equally between the two phases and five and six ring PAHs were mainly associated with the particle phase. Gas-particle partition coefficients (Kp) of PAHs have been calculated and correlated with their subcooled liquid vapor pressures (PLº). The slopes (mr) varied from − 0.63 to − 0.23 were far from the theoretical value (−1) due to the short distance between the sampling point and the emission sources. The relationships between temperature and gas phase partial pressures of PAHs were examined using the Clausius-Clapeyron equation and the obtained positive slopes indicated that PAH concentrations increased with decreasing air temperature as a result of high dominance of local emissions. 相似文献
11.
Photoinitiated oxidation of geosmin and 2-methylisoborneol by irradiation with 254 nm and 185 nm UV light 总被引:1,自引:0,他引:1
The degradation of geosmin and 2-methylisoborneol (2-MIB) by UV irradiation at different wavelengths was investigated under varying boundary conditions. The results showed that conventional UV radiation (254 nm) is ineffective in removing these compounds from water. In contrast to the usual UV radiation UV/VUV radiation (254 + 185 nm) was more effective in the removal of the taste and odour compounds. The degradation could be described by a simple pseudo first-order rate law with rate constants of about 1.2 × 10−3 m2 J−1 for geosmin and 2-MIB in ultrapure water. In natural water used for drinking water abstraction the rate constants decreased to 2.7 × 10−4 m2 J−1 for geosmin and 2.5 × 10−4 m2 J−1 for 2-MIB due to the presence of NOM. Additionally, the formation of the by-product nitrite was studied. In the UV/VUV irradiation process up to 0.6 mg L−1 nitrite was formed during the complete photoinitiated oxidation of the odour compounds. However, the addition of low ozone doses could prevent the formation of nitrite in the UV/VUV irradiation experiments. 相似文献
12.
This paper proposed a new solar assisted air source heat pump system with flexible operational modes to improve the performance of the heating system. A mathematical model was established on the solar assisted air source heat pump system for building heating with a heating capacity of 10 kW, and an air source heat pump unit was developed to validate the model. The effect of the solar collector area on the performance of the system running in Nanjing was studied. The results showed that the COP of the heat pump unit was enhanced with the increase of the solar radiation density during the typical sunny day in the heating season. In addition, the COP also increased in proportion to the solar collector area. Compared with the case when the solar collector area was 0 m2, the COP increase of the heat pump and the energy-saving rate were 11.22% and 24% respectively when the solar collector area was 40 m2. Meanwhile, the solar equivalent generation power efficiency could reach 11.8%. 相似文献
13.
Shanghai is characteristic of subtropical monsoonal climate with the mean annual temperature of 17.6 °C, and receives annual total radiation above 4470 MJ/m2 with approximately 2000 h of sunshine. A solar energy system capable of heating, cooling, natural ventilation and hot water supply has been built in Shanghai Research Institute of Building Science. The system mainly contains 150 m2 solar collector arrays, two adsorption chillers, floor radiation heating pipes, finned tube heat exchangers and a hot water storage tank of 2.5 m3 in volume. It is used for heating in winter, cooling in summer, natural ventilation in spring and autumn, hot water supply in all the year for 460 m2 building area. The whole system is controlled by an industrial control computer and operates automatically. Under typical weather condition of Shanghai, it is found that the average heating capacity is up to 25.04 kW in winter, the average refrigerating output reaches 15.31 kW in summer and the solar-enhanced natural ventilation air flow rate doubles in transitional seasons. The experimental investigation validated the practical effective operation of the adsorption cooling-based air-conditioning system. After 1-year operation, it is confirmed that the solar system contributes 70% total energy of the involved space for the weather conditions of Shanghai. 相似文献
14.
Effect of swine manure dilution on ammonia, hydrogen sulfide, carbon dioxide, and sulfur dioxide releases 总被引:1,自引:0,他引:1
Ji-Qin Ni Albert J. Heber Dan T. Kelly Sun-Tae Kim 《The Science of the total environment》2010,408(23):5917-5923
Animal manure is a significant source of environmental pollution and manure dilution in barn cleaning and slurry storage is a common practice in animal agriculture. The effect of swine manure dilution on releases of four pollutant gases was studied in a 30-day experiment using eight manure reactors divided into two groups. One group was treated with swine manure of 6.71% dry matter and another with manure diluted with water to 3.73% dry matter. Ammonia release from the diluted manure was 3.32 mg min−1 m−2 and was 71.0% of the 4.67 mg min−1 m−2 from the undiluted manure (P < 0.01). Because the ammonia release reduction ratio was lower than the manure dilution ratio, dilution could increase the total ammonia emissions from swine manure, especially in lagoons with large liquid surface areas. Carbon dioxide release of 87.3 mg min−1 m−2 from the diluted manure was 56.4% of the 154.8 mg min−1 m−2 from the undiluted manure (P < 0.01). Manure dry matter was an important factor for carbon dioxide release from manure. No differences were observed between the treatments (P > 0.05) for both hydrogen sulfide and sulfur dioxide releases. Therefore, dilution could also significantly increase the total releases of hydrogen sulfide and sulfur dioxide to the environment because dilution adds to the total manure volume and usually also increases the total gas release surface area. 相似文献
15.
Characteristics of airborne bacteria and fungi were surveyed in the public buildings regulated in Korea, with the six-stage cascade impactor. The total concentrations of airborne bacteria and fungi were averaged to 404 and 382 cfu m−3 in hospital, 931 and 536 cfu m−3 in kindergarten, 294 and 334 cfu m−3 in elderly welfare facility, and 586 and 371 cfu m−3 in postpartum nurse center. Mean respirable concentrations of airborne bacteria and fungi were 194 and 292 cfu m−3 in hospital, 358 and 347 cfu m−3 in kindergarten, 134 and 266 cfu m−3 in elderly welfare facility, and 254 and 289 cfu m−3 in postpartum nurse center, respectively. Based on this results, total and respirable concentrations of airborne bacteria and fungi were significantly highest in kindergarten and lowest in elderly welfare facility (p<0.05). The ratios of indoor and outdoor concentration for airborne bacteria and fungi were below 1.0 in all the investigated public buildings regardless of size distribution. The dominant genera identified in the public buildings were Staphylococcus spp., Micrococcus spp., Corynebacterium spp., and Bacillus spp., for airborne bacteria and Penicillium spp., Cladosporium spp., and Aspergillus spp., for airborne fungi, respectively. Size distributions of airborne bacteria and fungi in terms of the dominant genera were not observed consistently except for Staphylococcus spp., which was detected mainly on the first stage (>7.0 μm) and second stage(4.7–7.0 μm), and Penicillium spp., and Cladosporium spp., showing the highest collection rate at stage 3 (3.3–4.7 μm) regardless of the kind of the public buildings. 相似文献
16.
Year-round bulk air deposition samples were collected at 15 sites in the Pearl River Delta (PRD) on a bimonthly basis from Dec 2003 to Nov 2004, and the particle-phase deposition of BDE-209, PAHs, DDTs and chlordane was measured. The annual deposition fluxes of BDE-209, total PAHs (15 compounds), total DDT (sum of p,p′-DDE, p,p′-DDD, p,p′-DDT, and o,p′-DDT ), and chlordane (sum of trans-chlordane and cis-chlordane) varied from 32.6 to 1970 μg m− 2 yr− 1, 22 to 290 μg m− 2 yr− 1, 0.8 to 11 μg m− 2 yr− 1, and 0.25 to 1.9 μg m− 2 yr− 1, respectively. Spatial variations were higher in the centre of the PRD and lower at the coastal sites for all compounds. The seasonal variations of deposition were found to be compound-dependent, influenced by a number of factors, such as the timing of source input, temperature, and precipitation etc. In particular, source input time affected the deposition fluxes of BDE-209 and high-weight PAHs, while temperature-dependent gas-particle partitioning was a key factor for DDT and light-weight PAH deposition. During the whole sampling period, the atmospheric deposition of BDE-209, ΣPAHs, ΣDDTs, and chlordane onto Hong Kong reached about 93, 86, 2.1 and 2.1 kg yr− 1, respectively, and onto the PRD reached about 13,400, 2950, 82, and 63 kg yr− 1. By comparing the calculated total air deposition with the burden in the soils, the half residual time of BDE-209 in soils was estimated to be 3 years. 相似文献
17.
In the present communication, fifteen different glazing systems ranging from 3 mm single glazed clear glass to double glazed with low-e and solar control coating, have been analysed in terms of their human thermal comfort impact. Thermal comfort is measured in term of PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied). Study encompasses all the six climatic zones of India. By using OPTICS 5.0 and WINDOW 5.0, U-values, solar heat gain coefficient, inside glazing surface temperatures and inside solar radiation have been computed. Depending upon different climatic zones, six sets of different design conditions, in terms of ambient temperatures, solar radiation and wind velocity, have been chosen. Typical values of metabolic rate and clothing insulation taken are 1.2 met and 0.5 clo for summer and 1.0 met and 1.0 clo for winter, respectively. Inside room air velocity is taken as 0.15 m s−1 round the year. Room temperature is taken as 20 °C in winter and 25 °C in summer. It is found that for cold station (e.g. Leh) all glazings except solar control glazings, ensure thermal comfort and total PPD is less than 10% (|PMV|?0.5). For warm and hot climates, solar control glazings are thermally suitable. Results for winter night of Delhi shows that all the 15 glazings are inadequate for thermal comfort and PPD, due to cold feeling, varies between 27% and 33% approximately. 相似文献
18.
The role that surface emissivity plays in the standard furnace test (BS476) is considered for steel sections. Steel samples coated with either a low-emissivity paint or a high-emissivity paint were subjected to furnace tests and cone calorimeter tests in order to quantify the degree to which emissivity affects performance. The cone calorimeter experiments were designed primarily to determine the emissivity of the coatings and to compare with the manufacturer's estimates. However, a welcome additional benefit of this analysis was an estimate of the average convection heat transfer coefficient h for horizontal test specimens in the cone calorimeter. Our measurements suggest that h has been significantly underestimated (in some cases by at least 50%) in the literature to date. Most studies appear to assume a value for h that is close to the value for free convection for a hot plate with hot surface uppermost (something in the region 10–15 W m−2 K−1). Our results suggest that a figure closer to 28 W m−2 K−1 is more appropriate. The furnace tests showed that emissivity has a low-order effect on performance and so we are able to conclude that convective heat transfer is dominant in these situations. 相似文献
19.
Differential scanning calorimetry (DSC) is used to investigate the thermal properties of caprylic acid, 1-dodecanol and their binary system. The experimental results show that the caprylic acid/1-dodecanol binary system presents eutectic point. The eutectic melting temperature (Tem) is 6.52 °C, and the latent heat of melting of eutectic mixture (ΔHem) is 171.06 J g−1. The corresponding mass fraction of 1-dodecanol in eutectic mixture is 30%. The eutectic melting temperature and the latent heat of phase change of eutectic mixture have not obvious variations after 60 and 120 thermal cycles, which proves that the eutectic mixture has good thermal stability. 相似文献
20.
The plants grown in seleniferous soils constitute a major source of toxic selenium levels in the food chain of animals and human beings. Greenhouse and field experiments were conducted to study selenium concentrations of weeds, forages and cereals grown on seleniferous soils located between 31.0417° to 31.2175° N and 76.1363° to 76.4147° E in northwestern India. Eleven winter season (November-April) weed plants were grown in the greenhouse in a soil treated with different levels of selenate-Se. Selenium concentrations of weed plants increased progressively with the levels of selenate-Se in soil. The highest Se concentration was recorded by Silene gallica (246 mg kg− 1) and the lowest by Avena ludoviciana (47 mg kg− 1) at 2.5 mg Se kg− 1 soil. A.ludoviciana and Spergula arvensis proved highly tolerant to the presence of 1.25 and 2.5 mg selenate-Se kg− 1 soil and the remaining weeds were sensitive to Se. Dry matter yield of Se-sensitive weed plants was 25 to 62% of the yield in the no-Se control at 1.25 mg selenate-Se kg− 1 and 6 to 40% at 2.5 mg selenate-Se kg− 1 soil. Other symptoms like change in leaf colour and size, burning of leaf tips and margins, and delayed flowering were also observed due to Se. Dry matter yield of Se-sensitive weed plants expressed as percentage of yield in the no-Se control at both the Se levels was inversely correlated with their Se content (r = − 0.731, p < 0.01, N = 17). Among the weed plants grown in seleniferous soils under field situations, Mentha longifolia accumulated the highest Se (365 mg kg− 1) and Phalaris minor the lowest (34 mg kg− 1). Among agricultural crops grown on a naturally contaminated soil in the greenhouse, Se concentrations were the highest for oilseed crops (19-29 mg kg− 1), followed by legumes (6-13 mg kg− 1) and cereals (2-18 mg kg− 1). Helianthus annuus among the oilseed crops, A.ludoviciana among the winter season weeds, M.longifolia among the summer season (May-October) weeds and Cirsium arvense among the perennial weeds can be used for phytoremediation of seleniferous soils as these accumulate the highest amounts of Se. 相似文献