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931.
932.
933.
934.
Seasonal changes in river water chemistry and in soil atmospheric CO2 concentrations at two depths and drainage water solute composition at two upland peaty podzol sites in north east Scotland were monitored over 12 months. the CO2 concentrations were controlled by changes in soil temperature and moisture status. Highest CO2 concentrations were observed in late summer 1988 when both soil temperatures and the moisture status of the soils were high. Then maximum CO2 concentrations of 4% (v/v) were recorded for one of the sites. No significant correlations between seasonal changes in soil CO2 concentrations and river water solute composition were observed. Nevertheless the field results and laboratory experiments indicated that in upland areas, where soils with acid surface horizons are common, soil CO2 substantially influences river water chemistry at baseflow, increasing the pH and cation concentration of the soil water draining into the river. the results suggest that transfer of carbon as dissolved CO2 in drainage water is a significant pathway for CO2 transfer to the atmosphere. 相似文献
935.
Approximately 37% of forestlands in the conterminous United States are publicly owned; they represent a substantial area of potential carbon sequestration in US forests and in forest products. However, large areas of public forestlands traditionally have been less intensively inventoried than privately owned forests. Thus, less information is available about their role as carbon sinks. We present estimates of carbon budgets on public forestlands of the 48 conterminous states, along with a discussion of the assumptions necessary to make such estimates. The forest carbon budget simulation model, FORCARB2, makes estimates for US forests primarily based on inventory data. We discuss methods to develop consistent carbon budget estimates from inventory data at varying levels of detail. Total carbon stored on public forestlands in the conterminous US increased from 16.3 Gt in 1953 to the present total of 19.5 Gt, while area increased from 87.1 million hactares to 92.1 million hactares. At the same time the proportion of carbon on public forestlands relative to all forests increased from 35% to 37%. Projections for the next 40 years depend on scenarios of management influences on growth and harvest.This article was written and prepared by US Government employees on official time, and it is therefore in the public domain and not subject to copyright. 相似文献
936.
高压往复式压缩机活塞杆断裂分析 总被引:1,自引:0,他引:1
张德华 《中国安全生产科学技术》2005,1(4):86-89
往复式压缩机活塞杆断裂极易造成机组的二次破坏和严重的泄漏、爆炸事故,是化工装置安全生产的重大隐患,本文通过对一起加氢裂化高压压缩机的活塞杆断裂的宏观及微观分析,表明活塞杆断裂失效的主要原因是疲劳断裂和热处理不当;氢腐蚀是促进疲劳裂纹形成和扩展的重要原因,加速了疲劳断裂过程;通过对材料进行光谱分析,表明材料中Si含量严重超标,这对活塞杆的疲劳断裂过程也有一定的影响.并从设计、制造、使用、维护多方面提出相应的改进预防措施. 相似文献
937.
Pamela MacQuarrie Lawrence C. Nkemdirim 《Journal of the American Water Resources Association》1991,27(1):73-82
ABSTRACT: This paper examines the relationship between both potential (E*) and nonpotential evapotranspiration and equilibrium evapotranspiration (EQ) in an irrigated wheat field in southcentral Alberta, Canada. The control exercised by surface wetness and root reservoir moisture content in determining the value of the Priestley-Taylor constant a is explored. Also investigated is the relationship between a and the vapor flux fraction ET/(R-G) where ET is the actual evapotranspiration, R the net radiation, and G the soil heat flux. It is shown that evapotranspiration occurred at the potential rate (E*) when the available soil moisture (ASM) within the root zone was ≥3 percent. a varied from 0.84 for a dry soil to 1.49 for a saturated soil. The mean a for E* was 1.24. Surface wetness sustained evapotranspiration at the potential rate when such wetting exceeded 2mm d?1 following a period of prolonged drawdown of soil moisture, α and ET/(R-G) were positively correlated and this correlation strengthened with increasing soil moisture for constant values of the energy partitioning factor s+γ/s where s is the slope of the saturation humidity-temperature curve and γ is the psychrometric constant. ET=EQ when ETI(R-G) lay within the range of 0.59 to 0.82 corresponding to Bowen ratio (β) values of 0.22 and 0.69, respectively. 相似文献
938.
E. McBean D. Haycock J. Gome 《Journal of the American Water Resources Association》1979,15(3):684-691
ABSTRACT: Increasing energy costs encourage more efficient energy use, including the better use of reject heat from electrical generating stations. Whether it pays to use this heat depends on the price charged. There is to date no relevant market in Canada. This paper estimates lower and upper bounds on the price for reject heat as a first step in determining market feasibility. Price would then be resolved by negotiation. For the case study of Ontario greenhouses, the differential between lower and upper bounds is substantial. An assumed price resolution is consistent with profitable use of this reject heat by this greenhouse industry. 相似文献
939.
ABSTRACT Cold chain industry has a vast potential for waste heat recovery. It is a matter of importance for energy efficiency point of view, as global energy demand is increasing day by day. Ample amount of low-grade energy is either unutilized or underutilized. The heat rejected by a Heat pump or refrigeration system emerged as a promising solution for dehydration by utilizing low-grade waste heat despite higher investment. As compared to solar drying technology, heat pump drying evolved as a reliable method regarding better process control, energy efficiency, and quality of the product to be dried. Energy utilized through the refrigeration system’s waste/exhaust heat recovery in combination with or without renewable energy source enhances the overall efficiency of the system and also reduces the cost. This useful review investigated and compared the research findings of waste heat utilization through heat pump and from condenser of refrigeration system on laboratory, pilot as well as industrial scale for drying of various fruits, vegetables, and agro products. Various drying parameters like drying rate, moisture content, Specific Moisture Extraction Rate (SMER), Coefficient of Performance (COP), Exergy efficiency, and temperature as well as humidity conditions inside the drying chamber were also reviewed to promote the technological advancement of energy utilization by commercial cold storage waste heat recovery. 相似文献
940.
Charles F. Meyer 《Journal of the American Water Resources Association》1976,12(2):237-252
ABSTRACT. The Heat Storage Well concept evolved at TEMPO in 1972. Technical, economic, institutional, and legal aspects of implementing the concept are being studied. Heat Storage Wells offer the possibility of conserving a substantial part of the heat energy now wasted in generating electricity and of reducing thermal pollution caused by the waste heat. Large thermal electric power plants would produce heat at useful temperatures such as 300–400°F. Combined electric- and heat-generating systems will require low-cost, low-loss storage of large amounts of hot water for periods of 90 to 180 days to serve both electric loads and seasonally-varying heat loads. Compared to conventional electricity-only systems, combined electricity-heat systems can save more than 20 percent in energy, reduce the cost of both electricity and heat, and eliminate the need for cooling water or towers. Possibilities for changes in legal and institutional practices are suggested, such as making resource-allocation decisions on the basis of energy units rather than dollars. 相似文献